IONIZING RADIATION:
SOURCES AND BIOLOGICALEFFECTS
United Nations Scientific Committee
on the Effects of Atomic Radiation
1982 Report to the General Assembly, with annexes

UNITED NATIONSNew York, 1982

NOTE
The report of the Committee without its annexes appears as Official Records of the General Assembly, Thirtyseventh Session, Supplement No. 45 (A/37/45).
The designations employed and the presentation of material in this publication do not imply the expression of
any opinion whatsoever on the part oft he Secretariat of the United Nations concerning the legal status of any country,
territory. city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries.

UNITED NATIONS PUBLICATION
Sales No. E.82.IX.806300PANNEXI
Genetic effects of radiation

CONTENTSParagraphs

Paragraphs

E.

INTRODUCTION ....................... .

I. HUMAN DATA ........•...........
A. Naturally-occurring
hereditarydiseases and defects ............. .
B. Effects of radiation: Hiroshima andNagasaki studies ............... .
C. Numerical and structural chromosome abnormalities ............. .
1. Surveys of newborn children
2. Clinicalsignificanceofchromosome abnormalities ..
3. Chromosome anomalies inperinatal deaths ........... .
4. Chromosome anomalies inspontaneous abortions ..... .
5. Mutation rates ............ .
6. An overview of the importance of aneuploidy and structural aberrations ........... .
7. Progress in work with Down's
syndrome ................•
8. Satellite associations: their
possible functional significance and relevance for autosomal trisomies ............ .
9. Non-disjunction in the humanmale studied through direct
examination of the germ cellstages .................... .
10. Detection of chromosome
anomalies in human sperm
through direct cytologicalanalysis: interspecific cellfusion studies ............. .
11. Cytogenetic studies in offspring of atomic bomb survivors of Hiroshima andNagasaki: further data ..... .
12. New chromosomal abnormalities and birth defects ...... .
13. Summary and conclusions .. .
D. Genes, chromosomes and cancer ... .
1. Monogenic disorders andneoplasia ................. .
2. Specific chromosomal defects
in cancer ................. .
3. Summary and conclusions .. .

2-258
2-18
19-20
21-120
21-30
31-40
41
42-46
47-48
49-55
56-74

75-82

83-87

F.

Human disorders showing increased
sensitivity to the induction of genetic
damage by physical and chemicalmutagens: the role of DNA repair ..
1. Sensitivity at the individuallevel ..................... .
2. Sensitivity at the cellular level
3. DNA repair .............. .
4. Summary and conclusions .. .
Other relevant data ............. .
1. Chromosome aberrations inlymphocytes of individuals
livi~g i?. an area of highrad1oacuv1ty .............. .
2. Chromosome aberrations inlymphocytes of nuclear dockyard workers .............. .
3. Chromosome aberrations inlymphocytes of nuclear power
plant workers ............. .
4. Chromosome aberrations inlymphocytes of classified radiation workers ............. .
5. Chromosome aberrations inlymphocytes of uranium miners ...................... .
6. Chromosome aberrations inlymphocytes of workers withinternal depositions of plutonium .................... .
7. Chromosome aberrations inatomic bomb survivors ofHiroshima ................ .
8. Summary and conclusions .. .

181-231183-184
185-201202-223224-231232-258

233-235236-238239-240241
242-243244-249
250-251
252-258

88-89

90-91
92-109110-120121-180
121-148
149-172
173-180

JI. EFFECTS
IN
EXPERIMENTAL
MAMMALS AND OTHER SYSTEMS
A. Dominant lethals and reproductive
capacity ...................... .
1. The mouse ................ .
2. Other species ............. .
3. Summary and conclusions .. .
B. Translocations ................. .
1. Introduction .............. .
2. Reciprocal translocations inmale germ cells of the mouse259-517259-308260-287288-292
293-308309-360309-311312-332425

Pamgr.iphs

3.

C.

D.

E.

F.

Heritable reciprocal translocations in female mice .....
4. Chromatid-intcrchangcs andother aberrations in mouse
and Chinese hamster oocytes:
in vitro studies ............ .
5. Reciprocal trnnslocations m
spcrmatogonia of the rhesus
monkey and comparison withresults from other mammalian
species ................... .
6. Summary and conclusions .. .
Loss or addition of chromosomes:
non-disjunction ................. .
1. Introduction .............. .
2. Methods to study ancuploidy
3. Spontaneous incidence ofaneuploidy ............... .
4. The mouse ................ .
5. Other species ............. .
6. Summary and conclusions .. .
Point mutations ................. .
1. Specific-locus mutations inmale mice: effects of JH and2l•pu ..................... .
2. Specific-locus mutations infemale mice ............... .
3. Nature of specific-locus mutations ..................... .
4. Autosomal recessive lethals inmale mice ................ .
5. Sex-linked recessive lethals inmale mice and rats ......... .
6. Autosomal recessive lethals infemale mice ............... .
7. Biochemical mutations detected by electrophoresis .... .
8. Dominant mutations ....... .
9. Histocompatibility mutations
10. Inductionofcongenital
anomalies and tumours by irradiation of mouse germ cells
11. Summary and conclusions ...
Genetic effects of internal emitters
Other rele,·ant data ............. .
1. Biological effects in mice andrabbits kept in an area of highnatural radioactivity ....... .
2. Further data on the relationship between chromosome
arm number and relative
radiosensitivity in different
mammalian species ........ .
3. Molecular mechanisms involved in the production ofchromosome aberrations .....
4. A test of the hypothesis ofwhether there is proportionality between spontaneous andinduced rates of mutations ...
5. Chromosomal evolution m
primates and its possible relevance for inter-specific comparisons and for assessing thechromosomal basis of humanpathology ................ .
6. Summary and conclusions .. .

Ill. EFFECTS OF X-IRRADIATION ON
SURVIVAL KINETICS OF SPERMATOGONIAL CELLS IN MICE AND
RATS ............................. .

333-334

335-343344-347348-360
361-392361
362-364534-542

V. SENSITIVITY OF MAl\fMALIAN FEMALE GERM CELLS TO KILLING
J3Y IRRADIATION ................ .

543-559

VI. SOMATIC CELL GENETICS ....... .

560-625A.

365
366-375376-385386-392
393-4548.
393-397

C.
398-403404-416417
418-419420-422423-424425-433434-438439-442443-454455-458459-517

D.
E.

F.
G.

Mutation induction at the HG-PRT
locus ......................... .
1. Chinese hamster ovary (CHO)
cells ..................... .
2. Chinese hamster V-79 cells .. .
3. Mouse lymphoma (L 5178Y)
cells ..................... .
4. Human diploid fibroblasts .. .
5. Human peripheral blood lymphocytes ................. .
Mutation induction at the thymidine
kinase (TK) locus ............... .
Mutations to ouabain-resistance(OUAR) ...................... .
Resistance to methotrexate (MTXR)
Nature of radiation-induced mutations in somatic cells ............ .
Mutagen-sensitive cell strains ..... .
Summary and conclusions ........ .

VII. EVALUATION OF GENETIC RADIATION HAZARDS IN MAN ........ .

A.
B.

459-463464-475

C.
476-492D.

493-497E.

561-588561-567568-572573-574575-581582-588589-590591-594595
596-604605-611612-625626-783

A summary of the main conclusions
reached by the Committee in its
I 977 report .................... .
Relevant new information that has
become available since the publication of the 1977 report ........... .
1. Confirmatory data ......... .
2. Data that shed light on thevalidity of assumptions, tentative conclusions and controversial view-points ...... .
3. Data that seem relevant in aqualitative sense ........... .
4. Data useful for quantitative
assessment of genetic radiation hazards .............. .
Some relevant recent publications on
quantitative evaluation of genetic radiation hazards in man .......... .
Current risk assessments of theCommittee .................... .
I. Direct method ............ .
2. Doubling dose method ..... .
3. Index of harm, genetic detriment and the impact ofgenetic disease ............ .
Summary and conclusions ........ .

626-639640-669
641-656657-660661-668669

670-709710-772710-729730-734735-772773-783498-506

507-517
VIII. SUGGESTIONSFORFUTURERESEARCH ...................... .

784

References .............................. .

548

Paxe

518-533

Introduction
1. The 1977 UNSCEAR report [Ul] presented adetailed review of the genetic effects of ionizing

426

Pamgraphs

IV. TIMING OF OOCYTE MATURATION IN THE MOUSE AND ITSRELEVANCE TO RADIATION-INDUCED CELLKILLING AND
r,tUTATIONAL SENSITIVITY ...... .

radiation. This Annex is aimed at an updating of the
1977 report, especially those parts that require significant revisions in the light of new data. Particularemphasis is given to those data that are relevant to theevaluation of genetic radiation hazards in man.

I.

A.

HUMAN DATA

NATURALLY-OCCURRING HEREDITARYDISEASES AND DEFECTS

2. In the 1977 report, the results of the British
Columbia Survey (TI) on the frequency of liveborn
individuals affected by hereditary or partially hereditary defects and diseases were presented. These resu l!sand considerations based on the degree ofcompleteness of reporting in the Registries used asdata-source and possible bi.ises due to delay in disease
onset, migration etc., allowed an estimate of 9.44% for
the total frequency of diseases believed to be of genetic
origin (0.12% autosomal dominant and sex-linked
diseases, 0.11% recessive and 0.20% chromosomal ones,
4.28% congenital malformations and 4.73% other multifactorial ones).

3. The Committee reappraised the above figures,
taking into account Stevenson's data from the Northern
Ireland Survey [SI]. the results from several ad hoe
surveys for specific dominant conditions (reviewed inreference [Vil), data from newborn surveys for chromosomal anomalies and the uncertainties involved in the
aetiology of diseases classified as congenital malformations, multifactorial diseases and irregularly inherited
diseases. It was concluded that for the purpose of
estimating genetic radiation hazards in man, it isappropriate to use the following revised figures (adding
up to a total of 10.5%): (a) 1.0% dominant and X-linked
diseases; (b) 0.1% recessive diseases (excluding thosemaintained through heterozygous advantage); (c) 0.4%
chromosomal diseases; and (d) 4.3% congenital malformations, and 4.7% other multifactorial and irregularly
inherited diseases, together, 9%.
·
4. Some new information has become available sincethe 1977 report. Czeizel [C1] has published the results ofa nation-wide survey on congenital malformations in1970 in Hungary. The classification of these malformations into the various categories and sub-categories has
been based on the International Classification of
Diseases [WI), with some modifications. The data covera 7-year period (1970-1976) and involve a total of
1 188 509 births of which 10 658 were stillbirths, the rest
being livebirths. The frequency of malformed babies
varied from 2.2% in 1970 to 3.7% in 1976 with anaverage of 3.1%. These figures are very similar to thatgiven as a minimal estimate (3.6%) for the British
Columbia data by-Trimble and Doughty [Tl); the latter
estimate however relates to livebirths only. Czeizel et al.
[C2] noted that, for the period 1972-1975, the incidenceof multiply-malformed babies ranged from 7.5 to 8.5%of all notified congenitally malformed ones suggestingthat from 2.6 to 2.9 per 1000 total births showed
multiple malformations; the majority of these were
found to be severe: 6.9% of such babies were stillborn
and 45% of those that were liveborn died during
infancy.

5.

The Hungarian Congenital Malformation Monitor,
operational since the beginning of 1973. makes use of
the so-called indicator congenital malformations 1 tomonitor the temporal and spatial trends in theincidence of these malformations. During the period
I Those that can be diagnosed easily and unequivocallywithin the first six days of life: anencephaly, spina bifida,hydrocephaly, cleft palate, cleft lip ± palate, oesophageal
atresia, rectal atresia,hypospadias, reduction deformities of thelimbs, congenital hip dislocation and Down's syndrome.

1973-1976, trends for a continuous increase were found
for three of the indicator traits: congenital dislocationof the hip, congenital limb reduction and hypospadias[C3]. Czeizel [C3] suggests that these trends may berelated to the more complete notifications although theincrease in limb reduction deformities is only partly
explained by this factor. Other trends noted were of atransitional type, i.e., increases for short periods (e.g ..
anencephaly in the fourth quarter of 1974; spina bifida
in the second quarter of 1974, in the third quarter of1975 and in the fourth quarter of 1976; cleft lip ±palate in the third quarter of 1973). While statisticalanalysis revealed that these trends are not due tochance, Czeizel has stressed the point that the contribution of three possible technical biases (changes indiagnosis, notification and evaluation of the given
congenital malformation) must first be excluded before
the trends become amenable to meaningful interpretations or to the search for causal factors.
6. In their extensive paper, Myrianthopoulos andChung [M52] have reported the results of a comprehensive prospective study of congenital malformations
in children born in the Collaborative Perinatal Project(CPP: a cooperative endeavour of twelve institutions
throughout the United States and the National Instituteof Neurological Diseases and Stroke of the National
Institutes of Health, set up in 1959). Pregnant women
have been followed from the first months of theirpregnancy through labour and delivery and thechildren born to "project mothers" were followed up to
one year of age. The project population was classified
by the researchers in the United States as about 45%''white" and 55% "non-white".2 The collection of information, medical examinations and laboratory tests havebeen done in uniform fashion and according to preestablished protocols.
7. The total data pertain to 53 394 single deliveries
including 52 390 live births and 1004 foetal deaths: in
137 of the total, the sex of the children was not known
either because they were macerated foetuses or because.
for one reason or another, they were lost to the study.
All analyses were based on 53 257 deliveries withknown sex: 15.6% of the children (8288 out of 53 257)
were born with known malformations, 13.0% or 6906
with single and 2.6% or 1382 with multiple malformations.
8. The authors point out that the high rate of malformations found in this study (relative to others publishedin the literature) can be explained on the basis of theperiod of time through which the malformations wereobserved and the conditions which made almost
complete ascertainment possible: only about one-thirdof malformations observed during the first year of life
were diagnosed at birth.
9. Other interesting findings that emerged from thisstudy include the following: (i) major malformations(e.g., anencephaly, microcephaly, congenital dislocation of the hip, cataract, cleft palate. cleft lip, pyloric
stenosis, hypospadias, cystic kidney etc.,) were present
in about 7% of the children, minor malformations (e.g.,polydactyly, syndactyly, low set ears, supernumerarynipples etc.,) in about 7% of the children and a combination of major and minor in about 1% of the cases; ofthe major malformations. about 42% were multiple and
2 The mention of racial or ethnic groups reported here orelsewhere in this report does not imply that the United
Nations accepts or recognizes such categories.
427

of the minor malformations, about 25% were multiple;
the cardio-vascular system had the highest frequency ofmultiple malformations (about 800/o); (ii) the highest
incidence of malformations was found among neonatal
deaths and deaths which occurred during the first yearof life; (iii) males had significantly more malformations
than females and this was entirely due to an increase in
the frequency of major malformations: and (iv) there
were no significant differences in the overallfrequencies of major malformations between "nonwhitcs" and "whites", but the "non-whites" had significantly more minor malformations than "whites",largely due lo an increase in "non-whites" ofpolydactyly, branchial cleft anomalies and supernumerary nipples; the frequency of multiple malformations was significantly higher in "whites" than in "nonwhitcs".
10. Leck [L2] summarized the estimates on prevalence
rates at birth for several potentially lethal or handicapping malformations in the United Kingdom(excluding Down's syndrome: data derived fromdifferent sources; see Leck [L2) for details). For thispurpose, data on cardiac malformations, pyloric
stenosis, non-postural talipes equinovarus, hydrocephaly, penial and perineal hypospadias and manyothers were included. Conditions of minor importance(i.e., those that cause no appreciable handicap or threat
to life) such as accessory auricle, glandular hypospadias, most postural foot deformities, polydactyly,
syndactyly, etc., were excluded. The overall estimate is
24.4 cases per 1000 total births. In terms of severity(expressed as percentage alive five years after birth),
about four-sevenths of the children with cardiac malformations (prevalence at birth: 6.5 per 1000) and twothirds of all the malformed survive up to that age.
11. Leck also examined the transmissibility of thecommon malformations mainly using figures onfrequency in sibs and offspring of index patientspublished by Carter [C6]. These data, summarized inTable 1, show that the percentages of first-degree
relatives affected (in each case by the same malformation as the index patients) all lie between 2 and 5%,
except for pyloric stenosis and hip dislocation (which
are very much commoner in one sex than in the other);
the recurrence risk seems to be higher when the index
patient is of the less frequently affected sex. Thesefindings are consistent with the hypothesis that theaetiology of each of the common defects involves a
multiplicity of causes, some genetic and some environmental. The rates are all much lower than expected if
single genes with complete penetrance for major effects
were involved.
12. Altukhov [Al) compared the rates of occurrence ofrare electrophoretic variants (i.e., those with an alteredelectrophorctic mobility or activity) in normal healthy
newborns (group a), in premature infants and in babies
with multiple congenital malformations (group b). The
sample sizes for groups (a) and (b) were, respectively.
504 and 227, although the number of individuals
screened for any given enzyme varied from 156 to 504(a) and from 82 to 227 (b). Over twenty genetic locicoding for the synthesis of enzyme proteins and erythrocyte antigens were studied. Five variants were foundin group (a) and 15 in group (b). As it was possible toexclude familial variants, it would appear that a muchhigher rate of incidence of these variants in prematureinfants and in those with multiple congenital malformations is of significance.
428

13. Recently, there has been considerable discussion
by Neel [Nl, N2, N3] on the contribution of mutation
to ill-health in man. He has argued that current andanticipated developments in research) are likely to leadto a significant upward revision of the UNSCEAR [Ul)estimates of the frequencies of dominant, sex-linked
and chromosomal diseases; and, more importantly. thatthe "UNSCEAR report probably grossly underestimates the contribution lo disease of mutations which
technically must be classified ns 'recessives"'. The latterargument rests on the following considerations.
14. The existence of a wide range of diseases known
to be due to the absence of activity of an enzyme or of atransport or receptor protein is now amply
documented. For instance, many of the classical"inborn errors of metabolism" (reviewed in [HI. Kl))are associated with the absence or near-absence of
enzymatic activity as are some of the inherited bleeding
disorders, thyroid disorders (reviewed by [S2)) and aclass of non-spherocytic haemolytic anaemias due tothe absence or near-absence of enzymes such as
pyruvate kinase, hexose kinase, glucose-phosphate
isomerase, etc. (reviewed by [MI]). The defects in DNA
repair mechanisms now known in the various forms of
xeroderma pigmentosum, ataxia telangiectasia andFanconi's anaemia are the result of enzyme
deficiencies. Familial hypophosphatemic rickets.
Hartnup disease and a dozen other rare entities areprobably due to the absence or malfunction of atransport protein (reviewed in [S3]), and testicularfeminization and the severe form of familial hypercholesterolaemia are due to absence or malfunction of a
receptor protein [A2, G1, M2]. These defects are all due
to what in the past have been termed "null" mutations,
usually with, in classical terminology, a recessive formof inheritance although heterozygotes when properly
studied show impaired activity as well. Since it isdifficult to envisage heterozygote advantage for thesenull mutants, it seems likely that most, if not all, aremaintained by mutation pressure.
15. A rough idea of the magnitude of the total impactof this type of mutations can be arrived at through thefollowing lines of reasoning. Based on a study of fiveenzymes in Drosophila, Mukai and Cockerham (M3]estimated that null mutations (characterized by the lossof enzyme activity) arise at a rate of 1.0 10-S/Iocus/
generation whereas electrophoretic variants arise at amuch lower rate (0.2 10-S/locus/generation) giving aratio of 5 nulls: 1 electrophoretic variants. In
Amerindians. Neel et al. [N4) estimated that mutations
resulting in electrophoretic variants of a series ofproteins of the blood serum and erythrocytes occur at a
rate of 1.6 10-5/Iocus/generation. If it is assumed thatthe rate in man is only 1.0 10-5/Iocus/generation forelectrophoretic variants, and if the ratio of nulls toelectrophoretic variants is only 2, then null mutations
for a given polypeptide should be expected with afrequency of 2 10-S/locus/gcneration.
16. In man, there must be at least 5000 proteins whose
absence or failure of function can lead to diseases suchas those mentioned in the preceding paragraphs.
Assuming no allelism, equilibrium between input and3 For instance, McKusick's 1978 catalogue [M 16) lists 736
proved autosomal dominant ( + 753 probable ones), 521
proved autosomal recessive ( + 596 probable ones) and I 07
proved X-linked ( + 98 probable ones) diseases in man. In the1975 catalogue [M 17) the respective numbers were: autosomal
dominants: 583 ( + 635): autosomal recessives: 466 ( +481) and
X-linked ones: 93 ( + 78).

loss of mutants in the population, no heterozygous
advantage or disadvantage and neglecting linkage, theprobability that a zygote would be homozygous for atleast one of these is (1-0.99998SOOO) or 0.095. While
there is no doubt that this estimate needs to be viewed
with many reservations, it does serve to illustrate thepoint that the impact on health in toto of this class ofmutations may exceed the commonly visualized grossphenotypic abnormalities.
17. To what extent null mutations contribute to foetal
loss in humans is not known. In Drosophila, nullhomozygotes or null/deficiency heterozygotes at 12 out
of 13 autosomal loci studied are viable and fertile [01.
02]. Neel points out that this is certainly not the casewith all null mutants in humans and that the apparent
difference between Drosophila and man may be an
artifact. i.e., flies with the degree of impairment experienced by many of the human null homozygotes areprobably so inviable as to preclude scoring. He speculates that the null homozygotes may make a significant
contribution to the relatively high foetal loss in humans,
but the demonstration that as much as 50% of recognized foetal losses are due to one or another kind ofchromosome anomaly [C4] "preempts a large part ofthat selection arena" [Nl, N2, N3]. While theproportion of null homozygotes that survive to term is
not known, it is probably a sizeable fraction.
Furthermore, since the accumulation in the gene poolof null mutations should facilitate the expression ofclassical recessive genes, one cannot, by invoking intrauterine selection against most of them, dismiss the nulls
as scarcely contributing to the social burden of
mutation [Nl. N2, N3].
18. Carter [C51] who recently examined the above
arguments and their implications, points out that thethesis that almost 10% of foetuses are homozygous for anull mutation and that a substantial proportion of nullhomozygotes may survive to term is difficult toreconcile with the current stillbirth, infant andchildhood mortality figures which in some areas areeach well below 1% and the majority of which arecaused by prematurity and congenital malformations,which are not recessive conditions; spontaneousabortions which occur at about 150 per 1000 recognizedpregnancies offer more scope. but, as Neel notes, asmany as half of these are due to chromosomal abnormalities. and others will have purely obstetrical causes.
Neel's estimates imply that, on the average, every
individual is heterozygous for about 50 null mutants;
this is also difficult to reconcile with the health of mostchildren born to first-cousin marriages, since zygotes
conceived in such marriages, would be homozygous for
one to two null mutants on the average: furthermore,
first-degree incestuous unions (where zygotes would be,on the average, homozygous for six null mutants)
would be almost incapable of producing viable children
and this is not the case. As Carter stated, if .. recessive"null mutations do occur with the frequency Neelsuggests, then " ... one must assume that their genefrequency is kept low in the population by selection
against them in heterozygotes and ... are best classedwith the dominants" [C51].
B.

EFFECTS OF RADIATION: HIROSHIMAAND NAGASAKI STUDIES

19. Neel et al. [N20], Satoh et al. [S132], Schull, Otaka
and Neel [S130] and Schull et al. [S131) have presented
some preliminary results of their continuing studies onmutations affecting protein structure in the children of
atomic bomb survivors of Hiroshima and Nagasaki.
The papers of Satoh et al. [S132] and of Schull et al.
[S 131] arc the most recent ones. The study populations
consisted of children born to "proximally exposed"
parents whose average conjoint gonadal dose wasapproximately 0.59 Sv and those of "distally exposed"
parents estimated to have received less than 0.01 Gy.
The total number of children identified in each of thegroups is well over 27 000. The mutation data pertain tovariants of 28 different (erythrocyte and plasma)proteins analysed using one-dimensional electrophoresis and involved the equivalent of 419 666 and282 842 locus tests, respectively in the first and second
groups. Once a rare variant was encountered. its occurrence was verified in a second sample and studies ofboth parents and available siblings were carried out. In
the event that neither parent exhibited the variant,
appropriate serological studies were performed toresolve possible discrepancies between the stated andbiological parentage.
20. Thus far two probable mutations have been
observed in children of proximally exposed parents.
One is a slowly migrating variant of glutamic pyruvatetransaminase and the other, a slow migrating variant ofphospho-glu<;:omutase-2. No probable mutations havebeen found in the children of distally exposed parents.
Schull et al. [S131] point out that the number ofmutations observed is still too small to provide ameaningful estimate of mutation rates. (Data on
chromosomal aberrations in the children of survivors ofHiroshima and Nagasaki are discussed in Section C.)
C. NUMERICAL AND STRUCTURAL
CHROMOSOME ABNORMALITIES
1.

Surveys of newborn children

21. In its 1977 report, the Committee discussed theresults of surveys carried out in different parts of theworld on the cytogenetic analysis of chromosomes inperipheral blood lymphocytes of livebom infants. The
data available at that time showed that out of 55 679
babies examined, 336 (0.60%) had abnormal chromosome constitutions (pooled data). The break-down of
the above frequency was: 0.22% sex chromosomal
anomalies:
0.14% autosomal trisomies; 0.19%
autosomal structural euploid abnormalities (Robertsonian and reciprocal translocations) and 0.5%
autosomal structural aneuploid anomalies. The karyotypes were examined with conventional staining
techniques except in the Hamilton Survey [Ll] in whichbanding methods were used.
22. The compilation of Hook and Hamerton [H3]focuses attention on consecutive newborns only, andincludes additional data from the Boston survey [W2]but excludes the data of Lin et al. [Ll] and those of
Bochkov et al. [81] (these were included in the 1977
report). The basis for exclusion of the data mentioned
above was the use of banding techniques in the work of
Lin et al. (and conventional techniques in the case ofothers) and the possibility of some selection in the studyof Bochkov et al. However, the frequencies of chromosomally abnormal infants recorded in these two surveys(0.48% in the work of Lin et al. and 0.76% in that of
Bochkov et al.) fall within the range of frequencies
recorded in the other surveys (0.48% in London,
Canada; 0.47% in Winnipeg, Canada; 0.83% in Arhus,
Denmark: 0.67% in Edinburgh, United Kingdom;429

0.61 % in_ Boston, United States and 0.50% in New
Haven. United States).
23. Buckton et al. [820] and Maeda et al. [M53] have
now published the results of other newborn cytogenetic
surveys carried out in Scotland and Japan, respectively(referred to as Edinburgh-UK-II and Kanagawa, Japanin Table 2). The Edinburgh survey includes: all babies
born alive in one of the Edinburgh hospitals sampledpreviously [J2]; and all babies born alive in 1976 andmost of 1977 in a maternity hospital in the Fife region.
A total of 3993 babies were karyotyped of which 3835
could be analysed using G-banding. The Japanese data
pertain to 2626 consecutive newborns screened in one
hospital. Banding techniques were used. The data fromthese studies are summarized in Table 2. Not includedin this table are the data of Turner and Wald [T3) andthose of Higurashi et al. [H36, H48]; the reasons for thiswill be discussed later.
24. It can be seen that of the 424 (0.63%) chromosomally abnormal infants, 158 (about one-third) carrysex-chromosomal anomalies. There are 95 (about onequartcr), numerical autosomal anomalies; there are 134(about one-third), balanced structural anomalies4 and37 (about one-tenth), unbalanced structural anomalies.
The incidence of sex-chromosomal anomalies alone is 3
per 1000 male births and 1.5 per 1000 female births. Of
the autosomal numerical anomalies (1.4 per 1000
births), the + G anomalies (Down's syndrome)
constitute the predominant group. Among the balanced
autosomal structural anomalies (2 per 1000), reciprocaltranslocations and Robertsonian translocations areabout equally frequent; among the latter, those
involving two D group chromosomes are morecommon (48 out of 60) than tho'se involving D and G
group chromosomes. Finally, aneuploid structuralabnormalities occur at a frequency of about 0.6 per
1OOO births.
25. Turning now to results not included in Table 2, thework of Turner and Wald [T3] on newborns at Magee
Women's Hospital in Pittsburg was carried out between
1962 and 1964 and was published only in 1970. In thisstudy which involved 1000 infants (517 males and 483
females), very strict attention was paid to randomization: neonates born were selected for study by the useof a random sampling frame in which one of the six
four-hour time periods of each of the first four days of
the week was chosen by random numbers; the first fourdeliveries of the selected periods were studied. Detailsof other aspects of the randomization procedures are
given in the paper of Turner and Wald [T3).
26. The number of chromosomally abnormal babies
in the above study was 33 (i.e., 3.3%; 2% with sexchromosomal anomalies and the remainder with
autosomal anomalies). This frequency is about fivetimes higher than that reported by others and different
from that of any other single study (see Table 2). The
increase was in all types of abnormalities with the
exception of 47, +21. Hook and Hamerton [H3] havesuggested several possible reasons for this discrepancy,
but none appear to be satisfactory and no further information from this study appears to be available.
At least in two of the three studies in which banding
procedures were used (Hamilton and Edinburgh-II), thefrequencies of balanced reciprocal translocations and inversions tend to be slightly higher than in those in which suchprocedures were not used. This may suggest that without theuse of banding procedures the frequencies of chromosomal
abnormalities of these kinds may be underestimated.
4430

27. The design of the study of Higurashi et al. [H36]on the incidence of chromosome anomalies innewborns in a Tokyo maternity hospital differed inseveral respects from those of others. Firstly, cytogenetic analysis of the karyotypes was not carried out
for all the babies. The babies were first screened forclinical manifestations during the first day of life; abuccal smear was obtained for an examination of both
X and Y chromatin (primary screening method). A
secondary screening included repeated buccal smears
and lymphocyte analysis for Y chromatin after two or
three months and this was done to ensure that there
were no false positives or negatives. All suspected cases
were examined by detailed chromosome analysis.
Secondly, babies thought to have congenital malformations were re-examined and this included a study of
their dermatoglyphic patterns (in the experience of theauthors, malformations associated with mental retardation and abnormal dermatoglyphic patterns werestrongly suggestive of autosomal aberrations [H37]).
Those judged abnormal by the criteria of malformations, dermatoglyphic patterns, low birth weight (andhistory of abortions in the mothers) were thenexamined through analysis of karyotypes.
28. Of the 3311 phenotypically normal male babies
studied through analysis of sex chromatin, 31 weresuspected of possibly carrying sex-chromosomal
anomalies; chromosome analyses of these showed twocases of 47,XXY, two of 47,XYY and one of
46,XY,-D,5 t(Dp;Yq). In 2054 phenotypically normal
female babies likewise examined, sex-chromosome
anomalies were suspected in 21 and out of the latter,
one had a 45,X karyotype.
29. For autosomal anomalies, the total number ofbabies initially screened was larger. Of the 12 319
babies (total sample), 694 were suspected of having
autosomal anomalies (353 males and 341 females). Of
the 694, two were + 13, three were + 18 (with one caseof mosaicism), eleven were + 21 (with one case ofmosaicism), one with B5p partial trisomy and one
which was 5p- (cri-du-chat syndrome). The totalfrequency of chromosomally abnormal individuals inthis study (25 in 12 319) cannot be readily comparedwith those obtained in other studies because the design
is different; this is true also of some individual classes(sex-chromosomal aneuploidies, autosomal trisomies).
30. The other study of Higurashi et al. [H48] was
focused on ascertaining the birth frequency of multiple
congenital anomalies in new-born infants (14 430 newborns out of which 7455 were males and 6975 werefemales). It was found that 33 of the babies had
multiple congenital anomalies. The birth frequencies of
the three major trisomies (13, 18 and 21) were, respectively, 0.14, 0.21 and 1.11 per 1000 births, in good
agreement with those recorded in the other surveys
listed in Table 2. The authors point out that most casesof sex-chromosomal anomalies remained undetected asthese showed no obvious manifestations at birth.
2.

Clinical significance of chromosome abnormalities

31. Hook and Hamerton [H3] used the data pertaining
to the 56 952 babies reviewed in their paper to estimate
the frequency of "clinically significant" abnormalities.
The authors included in this category all the nonmosaic XXY and 45,X instances, XYY and XX (male)genotypes, all autosomal trisomies and all unbalanced
structural rearrangements reported to have been

associated with congenital malformations at birth. Thebalanced structural abnormalities and sex-chromosomal mosaics were excluded. The reasons for the
exclusion of the latter were: (a) the variation in ascertainment between the studies; (b) the lack of information on the extent of abnormalities in the tissue
concerned: and (c) the inability at present to decide
about the clinical significance of mosaicism detected inperipheral blood lymphocytes m phenotypicallynormal babies.
32. The estimate arrived at is 2.91 per 1OOO, i.e., about
one-h:1lf of the total of all chromosomal anomalies
detected in newborns. lf the XYY and XX (male)karyotypes are excluded, the rate is 2.27 per 1000. An
analysis by sex of those affected indicated that the rate
in male newborns is about twice as high as in females
primarily because of the unequal contribution of thesex-chromosomal abnormalities judged by theseauthors as "significant". If one excludes the XYYs andXX males, the rate is still 60% higher in males.
33. An extension of the criteria used by Hook and
Hamerton to the total data given in Table 2 gives a rateof about 3.3 per 1000 for the abnormalities that may bedeemed to be "clinically significant", again about
one-half of all the abnormalities detected in newborns.
If the XYY and XX (male) genotypes are excluded, therate is 2.6 per 1000. These figures are in good agreementwith those reported by Hook and Hamerton.S
34. There are several reasons why the estimatesarrived at in paragraphs 32-33 may be underestimates.
Firstly. only long-term follow-up studies will provide
definitive answers to the question of what proportion of
the anomalies may have clinical significance. While it istrue that the clinical significance of certain chromosomal conditions such as trisomies for chromosomes
21, 13 or 18 can be relatively easily diagnosed at birth,
this is by no means true for all abnormalities. Secondly,
the frequency of sex-chromosome mosaics detected inmany newborn surveys may be lower since the numberof cells analysed may not be adequate and, todetermine the extent of mosaicisrn, more cells need to
be analysed. Furthermore, as Hook and Hamerton havepointed out. it is difficult to assess the clinical significance of mosaicism from chromosomal analysis ofperipheral blood lymphocytes of phenotypicallynormal individuals. Probably, at least some individuals
with 45,X/46,XY 45,X/46,XX or related karyotypes
may eventually prove to be of clinical significance. but
this depends on the magnitude of mosaicism and thetissues involved. Only long-term follow-up ofindividuals detected in such surveys may provide
clear-cut answers.
35. Thirdly, data showing that apparently balanced or
euploid structural rearrangements (translocations andinversions) in man can have deleterious phenotypic
effects (and thus assume clinical significance) areslowly accumulating. Jacobs [Jl] examined the datafrom the Edinburgh survey of the general population,of newborns and of mentally subnormal groups andfound a significantly higher proportion of .. mutant"balanced rearrangements in the mentally retardedgroup (excluding Down's syndrome) than in the others(5 out of 7 rearrangements in the mentally retardedgroup were of de novo origin, whereas in the other twogroups combined the respective figures were 7 out of
5 lfthe XXX condition is included among "clinically significant" abnormalities, the figures would be slightly higher.

39; see also [El] for a recent discussion of these data).
Breg's updated results [B2] on chromosome analysis of
the mentally retarded at the Southbury Training Schoolin Connecticut [83] show a similar situation: a total of 9balanced structural rearrangements (1 Robertsoniantranslocation, 6 reciprocal translocations and 2 inversions) were detected in 1087 individuals. In this study,
however, the relative proportions of familial versus
de novo rearrangements were not ascertained.
36. Other clinical data come from the work ofTharapel et al. [T4], Funderburk et al. [Fl], Aurias et al.
[A3] and Fryns and van den Berghe [F2]. Tharapel et al.
[T4] found 6 cases of de novo apparently balanced
reciprocal translocations which were associated withmental retardation and multiple congenital abnormalities (5 cases) or with ambiguous genitalia and multiple
congenital anomalies (1 case). Funderburk et al. [Fl]reported that the incidence of balanced chromosome
rearrangements was higher among mentally retarded
children (7 in 455) than among patients with psychiatricdisorders ( 4 in 1679). In the latter group, all the four
were pericentric inversions. The more recent results of
Aurias et al. [A3] show that among 2341 children withmalformations and/or mental retardation, 13 hadbalanced reciprocal translocations (of which 7 werefamilial), 5 had Robertsonian translocations and 2 hadpericentric inversions. In addition. in 762 children withtrisomy 21, three familial balanced reciprocal translocations were observed and none of these affected chromosome 21.
37. The studies of Fryns and van den Berghe [F2] on
lymphocytes of 12 160 patients (using currently
available banding techniques) showed that 32 of thesepatients were carriers of apparently balanced, reciprocal autosomal translocations. Eleven out of the 32
were detected in patients with mental retardation
and/or some malformation. In 7 of these, the translocation was familial; in one newborn with multiple
congenital anomalies, one of the parents could not bekaryotyped and in the remaining 3, the translocations
were of de novo origin. The authors point out that while
the occurrence of mental handicap with or without
congenital anomalies in patients with a de novo translocation may be explained as due to the possible occurrence of a deletion (during the formation of the translocation) which may be undetectable by present
techniques, it is hard to envisage such a situation in thecase of familial translocations.
38. Data bearing on the clinical significance ofchromosomal anomalies are also being collected in the
Collaborative Perinatal Project (CPP) mentioned
earlier. The paper of Patil et al. [Pl] summarizes someof the main findings from cytogenetic studies carriedout on the children when they were 7 or 8 years old infive of the twelve centres involved in the study (thesechildren have extensive neurological, developmental.
psychological and other clinical and family datasystematically recorded from birth onwards without
knowledge of their chromosome constitution andtherefore the cytogenetic study of the 7 or 8 year oldchildren is an unbiased one).
39. A total of 4342 children (2156 females and 2186
males) were examined and 21 (0.48%) showed major
chromosomal anomalies. There were 8 translocations, 3
pericentric inversions (1 autosomal and 1 each in an X
and Y chromosome), 2 trisomy 21 's, 3 X chromosome
mosaics, 2 other X chromosome aberrations and 3
XYYs. Of the 8 translocations, 3 were balanced Robert431

sonian and the rest balanced reciprocal ones. The
frequency of sex-chromosomal anomalies in females
was 0.23% (5/2156: 2 mosaics and 3 structuralanomalies) and in males, 0.23% (5/2186: 1 pericentric
inversion of the Y, 1 mosaic (47,XXY /46,XY) and 3
XXYs). No partial autosomal monosomies or trisomies
were detected. Table 3 in which the overall frequencies
observed in the CPP are compared with those innewborn surveys shows that these are in good
agreement except in the case of autosomal trisomies.
The lower frequency of these in the CPP results ispresumably due to the fact that infants with trisomies
13 and 18 and some of the children with trisomy 21
died (or in the latter case were institutionalized) andconsequently were not included in the sample.
40. Six of the children carrying translocations(although of normal weight and length at birth) had
minor clinical problems including clubfoot, reading
disability, abnormal hearing and an abnormal skull
shape. Three of the children who had de novo translocations had at least one of the above-mentioned abnormalities. All the five chromosomally-abnormal female
children (including mosaicism) had one or another kindof problems such as mental deficiency, neurologicalabnormalities, abnormal speech and motor development. small height and weight throughout development, and so on.

3.

Chromosome anomalies in perinatal deaths

41. Only a few studies [A4. B4, K2, M4, S5, S86] haveso far been carried out to examine the prevalence ofchromosomal anomalies in perinatal deaths (i.e., thosebabies who die before or during delivery or during thefirst week). The frequency of anomalies have been
estimated to be of the order of 5-6%, this being higher
among macerated stillbirths than in fresh stillbirths andin early neonatal deaths [A4]. The recent compilation of
results from four different centres [S86) shows that thefrequency of chromosomal abnormalities in macerated
stillbirths is 11.6% (13/112) dropping to 3.8% (13/340)
in non-macerated stillbirths and to 5.0%, (41/824) inearly neonatal deaths. Among the anomalies recorded,
trisomies predominate, particularly those involving
chromosomes of group E, followed by structuralanomalies, triploidy and others.

4.

Chromosome anomalies in spontaneous abortions

42. The incidence of chromosomal anomalies inspontaneous abortions in humans was extensively
reviewed in the 1977 report. The recent summary of
results presented by Carr and Gedeon [C4] and otherpapers published in the literature [H4, H49, K29]
support and extend the conclusions of the Committee
given in the 1977 report, which follow:
The overall frequency of chromosomal anomalies
among spontaneous abortions may be as high as
50% when corrections are made for non-hospitalized patients and for undetected induced
abortions:(b) Trisomies as a group constitute the most common
accounting for about 50% of all chromosomal
anomalies among abortuses, followed bymonosomy-X (18%); triploidy (17%), tetraploidy(6%) and others (7%; includes double trisomies,
mosaics and structural rearrangements);
(a)

432

(c)

Trisomies for all members of the chromosome
complement have been found among abortuses
except those for chromosome 1 and 5, allhough therelative involvement of the different chromosomes
is different; thus, for instance. trisomy 16 is clearly
the most common amounting to 30% of all
trisomies; trisomies for chromosomes 6, 11. 12. 17,
19 and X are rare; trisomy 21 and 22 have approximately equal frequencies (10% each):(d) Unbalanced translocations account for about 2 to
4% of all abnormalities observed in foetuses andthis frequency is much higher than among
liveborns.

43. Evidence for the maternal age-dependence fortrisomies involving acrocentric chromosomes (D and G
groups) was discussed in the 1977 report. The more
recent results of Hassold et al. [H50] document andextend the earlier findings. In this study in which datafrom 362 trisomic and 790 chromosomally normal
spontaneous abortions were compared with respect tothe age of the mothers, it was found that lrisomies as agroup were associated with a substantial increase inmaternal age, although there were considerable differences in the magnitude of the effect between different
trisomies. The effect of maternal age was mostpronounced for trisomies involving the small chromosomes, both acrocentric and non-acrocentric. Trisomy
16 was conspicuously different from trisomies for allother small chromosomes, both in the reduced importance of increased maternal age and in the highfrequency with which it occurred. The effect ofincreasing maternal age on trisomies for chromosomes
in groups A, B and C was less clear than for the small
chromosomes.
44. Hassold et al. [H50] speculate that the maternal
age-dependent trisomies may result from precocious
disjunction of the bivalents and random segregation of
the resulting univalents, a process which would affectchromosomes with the fewest chiasmata and whichmight be more prevalent in oocytes of older women.
They further suggest that true non-disjunction (i.e., thefailure of bivalents to separate at anaphase) may also
result in the production of trisomies and that thisprocess may be independent of, or only slightly influenced by, increasing maternal age, but be affected by
the presence of large blocks of heterochromatin.
45. With the advent of banding techniques to study
human chromosomes, it became clear that several
chromosomes contain heteromorphic regions which are
inherited like Mendelian genes and that these heteromorphisms are frequent in the acrocentric chromosomes. Applied to trisomic cases, these markers prqvide
a powerful tool to ascertain, in favourable situations, inwhich sex and at which meiotic division nondisjunction has occurred. This has been done fortrisomies for certain chromosomes in abortus material
and in the case of Down's syndrome.
46. The data summarized by Jacobs and Hassold [J15)given in Table 4 permit the following inferences: fortrisomy 16, non-disjunction can occur at any one of themeiotic divisions in either sex with meiotic I error in thefemale predominating; for others (trisomy 13, 14, 15, 21
and 22), non-disjunction seems to occur almost exclusively at division I in the female. The predominance of
meiotic I errors in the female for both age-related (Dand G group chromosomes) and in apparently ageunrelated (trisomy 16) is of importance in considering
the mechanism of non-disjunction (see also [F21)).

5.

J\.lutation rates

from the paper of Sankaranarayanan [S6] and modified
to take into account the frequencies of different kindsof anomalies discussed in this Annex provides asummary of these data. In drawing this figure, it has
been assumed that the level of spontaneous abortions isof the order of 15% and that 2% of the children die
perinatally. Some other important aspects ofaneuploidy and structural aberrations in humans, notcovered in Figure I, will be briefly dealt with in thefollowing paragraphs.

47. The 1977 report presented estimates of mutation
rates for the different kinds of chromosome anomalies
that result in liveborn children. For numerical errors ofautosomes, the estimated rates were 7.5 }~/gamete/
generation for sex-chromosomal errors and 6.7 I~/
gamete/generation for autosomal errors (giving a total
rate of 14.2 1~/gamete/generation). The estimates
based on the results summarized in Table 2 are nearly
the same, being 8.3 J()-4/gamete/ generation for sexchromosomal errors and 6.9 1~/gamete/generation
for autosomal errors (giving a total of 15.1 1~/
gamete/generation).

50. For monosomy-X, there is indirect evidence thatmaternal meiotic non-disjunction may not be the mainunderlying cause. It has been shown [C53, K30, W23]
that maternal age is not elevated in the mothers of XO
concept uses; in fact. the incidence of XO appears to behighest among young women, a finding which suggests
either that there is an increase in events leading tomeiotic or early cleavage errors in younger women, or
possibly that a greater proportion of their XO conceptuses survive to a stage of becoming recognizable
pregnancies [W23].

48. The earlier estimates [Ul] for balanced structural
rearrangements of autosomes and for unbalanced
rearrangements were, respectively, 1.9 1~/gamete/
generation and 0.45 1()-4/gamete/generation. In two
recent papers, Jacobs [J3, J16] has given revised
estimates based on the data for 48 650 and 59 452
babies, respectively. Much of the information on whichthese estimates are based overlaps with that given in
Table 2 and, consequently, these rates may beconsidered lo reflect our current state of knowledge inthis area. Jacobs [Jl 6] has also presented some estimates
based on the incidence of structural (balanced andunbalanced) chromosomal anomalies in spontaneousabortions. All these, taken from her more recent paper,are summarized in Tables 5. 6 and 7.
6.

51. For women with Turner's syndrome, Sanger et al.
[S87] have estimated that 77% of the propositae have amaternal X chromosome. Garron and Lindsten (G34]
found that X monosomic patients have, on the average,
more brothers than sisters. This finding suggested to theauthors that the X chromosome is more often lost
during spermatogenesis than the Y chromosome.
Paternal sex-chromosome loss from XX or XY zygotes
at early cleavage could also play a role in the genesis of
X monosomy in humans.

An overview of the importance of aneuploidy andstructural aberrations

52. With respect to their reproductive potential, thechromosomally abnormal types can be roughly divided
into four major categories [C52]: the viable steriles (XO,
XXY conditions, all male and some female reciprocal
X-autosome translocation heterozygotes, Y-autosometranslocation heterozygotes and some purely autosomaltranslocation heterozygotes), viable semi-steriles (mostbalanced structural heterozygotes, mainly the translocation and inversion carriers), viable but non-repro-

49. Three recent papers have extensively dealt withdifferent aspects of spontaneously arising aneuploidy
and structural aberrations including their contribution
to foetal wastage and genetic ill-health in humans [C52,
F21, S6]. An overall perspective of their relative
contributions can be gained by relating the incidence
frequencies recorded in new-born surveys, perinatal
deaths and in spontaneous abortions_ Figure I taken

150000 spont.1neous ibof"tiOlls

850000 births....---_..__ _ _ _ 11000
pr11n..n.1I deJths

I

833 OOO chiktrrn

8SO
chromosom.!IIV

lbno""''
5248
ch1omo1,0m:ilfy

640

170

,bnormaltnsomitl

1t1uctural aberrat1:rn1

l 5l3 nul••
1 960
sex•chromosomallyaneuploid~
{

40

{
{

44 7 frrn,d~,polypl04d~1

41,XYY:
41,XX.
Y:
M,1$.aie1

533
521

7~ OOOard othe>t1:

459

c.tuomosoma11v.ibno1m.1I

4 S.X

2S

:l.;!~C:298

an:! othEn:

124
37
100
1005
31

39975

14 100 45,X
12300

769
732
149

fflSOffllCS1• 13: 1 678-18: 2136·21: 3051 i

tr1plo1di.

4200 trtr.iploidl3075 !lructural abe,ut•ons
1125 mos.1cs

459
unbalimC!d st1uctut•I

225 oUwu

lber,atlons !nd 01h~1

Figure I. A summary ol the estimates ol chromosome anomalies (per 1~
conceptions) tn spontaneous abortions, perinatal deaths and In chtldren.
Modified alter [S6]433

ductive types (viable trisomy 21 individuals and viable
carriers of unbalanced structural rearrangements) andviable fertile types (XXX and XYY conditions). A
recent workshop [878, S91] was devoted to chromosomal aspects of male sterility in mammals including
humans.
53. The defect in XO women and XXY men appears
to be related to germ cell survival and sex-chromosomal
make-up [1361]. Germ cells are present in the ovaries ofhuman XO foetuses [S88], but loss begins late in foetal
life and by birth few oocytes remain [C54]. The
generally observed sterility of XXY males both in man
and in many other mammalian species investigated inthis respect has led to the postulate that the presence of
two X chromosomes in a testicular germ cell results in
its perinatal death [861). In female carriers of balanced
reciprocal X-autosome translocation, the risk of infertility seems to be brought about by gonadal dysfunction
in a proportion of the cases. Summitt et al. [S89]reviewed the literature on this subject and found thateach female carrier in which the X breakpoint falls
between bands Xq13 and Xq27 is liable to show infertility, with primary amenorrhoea in most cases, while
carriers with X breakpoints in other regions are fertile.
54. In male carriers of an X- or Y-autosome reciprocal translocation, and in some cases of autosomeautosome translocations in humans [C55. C70] as in themouse [S90] the infertility seems to be associated with
spermatogenic arrest. For the purely autosomal reciprocal translocations, those with one point of exchange
close to the centromere and the other fairly distal seemto be associated with infertility [C55] and this is truealso in the mouse [C56, S90, S92]. In humans, among
the cases so far described, an acrocentric chromosome
frequently seems to be involved in such male-steriletranslocations [C55]. The sterilizing effects of theseautosome-autosome translocations in both mice andhumans appears to be limited to male heterozygotes. In
humans, where the translocation has been shown to be
familial [B62, C57, L39], sterility and azoospermia havebeen reported in more than one male heterozygote, but
no effects on gamete production in females carrying thesame translocation have been apparent.

55.

A sizeable proportion of structural heterozygotes
are effectively semi-sterile since these individuals
produce gametes carrying unbalanced segregation
products that can lead to zygotic loss, spontaneousabortions and birth of congenitally malformed
children. Each individual translocation. however, islikely to be unique with regard to the level of imbalance
produced and its consequences. Very little is known
about the reproductive potential of unbalanced translocation heterozygotes, but where meiotic studies havebeen performed on occasional males, they have shown
severe impairment of the spermatogcnic sequence [F22].

2-5% arc due to translocation, the most frequent beinga translocation of a chromosome 21 with a D or G
group chromosome. Chromosome 14 is the one mostfrequently involved in the D group [HS] althoughchromosome 15 is also rarely involved [N6]. GIG translocations arc either t(21q21q) or t(21q22q). About 50%of the DIG and 90% of the GIG translocations are denovo ones, and the remainder are familial. Between I
and 2% of Down's syndrome patients are mosaics, themost common being 46147, +21.
57. Although there are no clinical differences between
patients carrying the standard trisomic type and thosewith translocations, there arc some important differences regarding their actual or potential family history.
Rare exceptions apart, the standard trisomic condition
arises by non-disjunction during gametogenesis in oneof the parents, more often in the mother. It has been
known for a long time that the risk of bearing a childwith Down's syndrome increased with advanced
maternal age. After the parents have had one child with
Down's syndrome the risk of recurrence appears
slightly elevated above the risk for the general
population. Carter and Evans [C18] estimated the recurrence risk in Britain as 1-2% irrespective of maternalage.
58. If chromosome 21 is translocated to anotherchromosome, the situation is different because suchtranslocations may be transmitted from generation to
generation in the balanced state. The actual risk of
producing a child who is effectively trisomic varies,
depending on which chromosomes are involved and onwhether the father or mother is the translocation
carrier. As stated earlier, the majority of DIG translocations involve chromosomes 21 and 14 and it has been
estimated on the basis of family data that a mother who
carries the translocation has a 10% chance of producing
a child with Down's syndrome; if the father is thecarrier of the balanced translocation, the risk of Down's
syndrome is thought to be only 2-3%. These estimates,
however, are preliminary and it is likely that the realrisk of having children with Down's syndrome may behigher at least in some families [M6].
59. The recurrence risk of Down's syndrome infamilies with a GIG translocation also varies
depending on the sex of the carrier and on the chromosomes involved. Although the data are not extensive, inthe case of a t(21 q22q), the female carrier has about 9%
chance of producing a child with Down's syndrome.
Reliable data are not available for carrier fathers, but
the risk appears to be small [M7, S9]. With a t(21 q21 q),
the risk is 100% irrespective of the sex of the carrier,since all gametes will be either disomic or nullisomic
for chromosome 21, which means that all children
surviving to term will be affected.

Parental origin of the extra chromosome in trisomv
21 and in translocation Down's syndrome. In the first60.
7.

Progress in work with Down's syndrome

56. General considerations. Down's syndrome is thebest known autosomal aneuploidy in man on which alarge amount of literature exists (see [810, L3, PS, S 16,
S93] for comprehensive reviews). The incidence isbetween 1 and 2 per 1000 births among various populations [H6. H7, H8, K31, K32, L40, MS, M54, M55, N22,
S94, Tl]. Three cytogenetic types of Down's syndrome
are known: trisomy 21, translocation and mosaics.
Trisomy 21 accounts for over 95% of the cases; about434

publication using chromosome hcteromorphisms tostudy the origin of the extra chromosome 21, Licznerski
and Lindstcn [L4] traced it to the mother. Since then, anumber of studies have been conducted [B11, M9, M10,
M56, LS, R2, SlO, U2, W4]. These studies haveestablished that the extra chromosome can be eithermaternal or paternal in origin and furthermore, that the
disjunctional errors arise in either of the two meiotic
divisions. Verma et al. [V2] compiled the results ofbanding analysis of 67 '·informative" cases of Down·s
syndrome and their parents. Non-disjunction wasmaternal in 44 cases (65.7%) and paternal in 23 cases(34.3%). In 37 or the 44 maternal-origin cases, nondisjunction occurred in meiosis I and in the remainder.
in meiosis 11. In the paternal origin group, in 14 cases. it
occurred in meiosis I and in the remaining 9, in meiosis
11. These conclusions are similar to those or
Langenbeck et al. [L5] and or Magenis et al. [~119].
61. In a more recent paper, Mikkelson et al. [M56]
have compiled data from the literature (including someof their earlier ones) in addition to presenting somenew data for two areas or Denmark, on the parental
origin of trisorny 21. Considering first the literaturecompilation. out of 145 informative cases, the extra
chromosome was maternal in origin in 112 (72.8 %) andpaternal in origin in 33 (22.8%). In the first group, 96
out of the 112 cases (86%) were due to division I errors,
the remainder being due to division II errors. In thesecond group, 20 out of 33 cases were due to firstdivision errors and the remainder due to second
division errors.
62. The new data or Mikkelsen et al. [M56) pertain to
Down's syndrome children born in the Danish islandsof Funen and Zealand (the earlier paper of Mikkelsen
et al. [M9] was on Down's syndrome in Zealand). The
total material comprised 125 families with Down's
syndrome children out of which 95 were informative(76%). In 77 children (81%), the extra chromosome
could be traced to the mother and 18 (19%), to thefather. In the new material alone, paternal failures wereobserved in 11 o/o of the cases in Fun en (5/ 45) and 23.5%of the cases in Zealand (8/34).
63. Jacobs and Morton [J4) have argued that themethodology used in many of the reports and/or theway in which the data are recorded, leads to the loss ofmuch of the potentially useful information. For
instance, Mikkelsen et al. [M9] and Wagenbichler et al.
[W4] summarized their results, without giving the actual
observations, for those "informative" cases for whom
the origin of the chromosome(s) could be established.
By not reporting all the observations, the authors haveintroduced a bias into their series and have made thecalculation of the relative probabilities of the different
mechanisms of origin of the extra chromosome
difficult. By applying a maximum likelihood analysis tothe data available to them, Jacobs and Morton [J4]reached the conclusion that " ... it appears that trisomy
21 is due to first division maternal non-disjunction
although there are case reports of second division nondisjunction, both paternal and maternal ..." andsuggested the need for complete reporting of the data
and large systematic samples.
64.
Data on the parental origin of translocation
Down's syndrome are limited. The information
summarized by Mikkelsen et al. [M56] and by
Chamberlin et al. [C58) suggest that in about two-thirds
to three-quarters of the cases the translocation wasmaternal in origin.
65. Maternal age. Maternal age has long been known
to be an important factor in Down's syndrome (see [PS]and references given therein). This correlation between
increasing maternal age and Down's syndrome applies
to 95% of the cases which are primary trisomies forchromosome 21 and which result from non-disjunction[PS, M 11 ]. For other types such as translocation Down's
syndrome, both spontaneous and inherited, and formosaics, no age-dependency has been proved [G2, R3].
Thus. among all the cases of Down's syndrome, there isa predominantly maternal-age-dependent and amaternal-age-independent class.

66. If the mother is less than 20 years of age at thetime of conception, the risk of producing a child withstandard trisomy 21 is about 1 per 2500 livebirths [PS,
C7]. The risk gradually increases until 35 years of age,
after which there is a more steep increase in thefrequency such that a mother over 45 years of age has
about 1 in 50 chance of having a child with Down's
syndrome [P5, Sl 1]. In more recent papers. Hook andFahia [H6], Hook and Chambers [117) and Hook and
Lindsjo [H8] have analysed the data on the incidence of
Down's syndrome in livebirths by single year intervals
in maternal ages for. respectively, the Stale of Massachussetts (1958-1965), the Stale of New York excluding
New York City. (1963-1974) and for Sweden. The main
finding is that the increase in the incidence of Down's
syndrome is gradual from maternal age 20 to about
30-31 and more pronounced thereafter. The effect ofmaternal age has also been confirmed by the results ofthe second Baltimore case-control study [CS].
67. In their 1980 paper, Lamson and Hook [L41]analysed the data published in the literature in which
the rates for Down's syndrome had been given by
I-year maternal age intervals to define the shape of thecurve describing maternal-age-specific· rates. There
were a total of 3613 Down's syndrome cases born tomothers or ages ranging from 20-49. Cases born tomothers below 20 years of age were excluded because
the analysis suggested that some factors operative atages 15-19 are not pertinent to rates at higher ages. Age
49 was chosen as the upper limit because of concern
about the accuracy of reporting and coding of data forhigher ages.
68. The statistical model used for analysis ("Theconstant plus exponential model" in the authors'terminology) is represented by the equation
y =a+ exp(b + ex)

where y is the rate of Down's syndrome in live births, x
is the maternal age and a. b and c are constants. The
authors point out that the above model gives a good fit
to the data "about as well as the approach that used
separate equations", and that it does not postulate asharp transition in biological processes aroundmaternal age 30, but rather a process continuously
accumulating at a constant exponential rate, superimposed upon a constant background rate. The equation
predicts that there is one group of conditions that
occur with a pooled constant rate a (matemal-ageindependent?) and a second group of conditions that
operate over the entire age-spectrum 20-49, its contribution increasing at an exponential rate with slope c(maternal-age-dependent?). They caution. however,that although their model may be more appealing statistically (and perhaps biologically as well, because its
equation has fewer parameters). this does not imply
that this model is necessarily more likely to be correct
than the others. Furthermore. the calculations of thematernal-age-independent and dependent categories
are consistent with the observed distributions, but are
not the only possible inferences from them.
69. The e.[fect of paternal age. Although it is widely
accepted that the most important variable in theincidence of Down's syndrome is maternal age. thepossible association with paternal age has also been
considered. A number of investigations [L3. P5, S 12].
however. have failed to detect any significant effect ofadvancing paternal age in addition to that accounted
for by maternal age.
435

70. Stimulated in part by a number of case reports on
the paternal origin of the extra chromosome 21 detected
through the use of the quinacrine banding techniques
mentioned earlier, the search for paternal-age-effect has
once again begun. Stene et al. [S13] have reported theresults of an investigation conducted in the Copenhagen Metropolitan area to study the effects of paternal
age on the incidence of Down's syndrome. Twohundred and twenty-four Down's syndrome patientsborn during the period 1960-1971 provided thematerial. The control was a random sample of 6053
births from the same period. By developing andapplying a new statistical technique (detailed in [S14]},
the authors found that: (a) there was an increasing
incidence of Down's syndrome with advancing
paternal age for a given maternal age; and (b) men
above the age of 55 years have a significantly increased
risk of begetting children with Down's syndrome. The
Japanese data presented by Matsunaga et al. [M13) aresupportive of the Danish findings: there was an excessof Down's syndrome infants born to fathers ;;i. 55 yearsof age.
71. The regression analysis of Hook et al. [H51] of
Down's syndrome cases born in 1964-1976 andreported by the British Columbia Registry for Handicapped Children showed that, after adjustment formaternal age effects, the data were consistent with anincrease of about 1.024-fold for each year of paternal
age throughout the entire age range (thus differing fromthe results of Stene et al. [S 13) and Matsunaga et al.
[M13] where the evidence was found only in men of 55
years and over). Among Down's syndrome cases for theperiod 1952-1963, however, for which ascertainment
appears likely to be less complete, there was noevidence for a significant paternal age effect.
72. Erickson [E2] has published the results of ananalysis of the data collected from 29 states and twolarge cities in the United States by the National Cleft
Lip and Palate Intelligence Service (NIS) during
1961-1966. The data pertain to 4000 white infants with
Down's syndrome and about 86 OOO normal whitebabies. His analysis confirmed the maternal-age
association with Down's syndrome with a high degreeof statistical significance but did not demonstrate any
independent effect of paternal age; in fact, the rates atpaternal ages over 45 years appeared to be nearly thesame. Erickson's conclusions, however, have beendisputed by Stene and Stene [Sl5]. The latter authors
have argued that the NIS data contain too few Down's
syndrome cases with older fathers and thus are lesssuited for an investigation of a possible paternal age
effect. Furthermore. they point out that the statisticaltests used by Erickson have relatively low resolving
power.
73. In a more recent paper Erickson [E3] examinedagain the question using two new sets of data derived
from two sources: the Metropolitan Atlanta Congenital
Defects Surveillance Programme and the National
Centre for Health Statistics; the former pertained to theperiod 1968-1976 and the latter to 1973-1975. Analysisof these data (taking into account the criticisms of Steneand Stene [S15] and improving the methods of statistical analysis) showed however no overall excess of
Down's syndrome infants born to older fathers in eithercase. The Atlanta data suggested an increased numberof Down's syndrome infants born to older fathers who
had children by women < 34 years; however, there wasa small deficiency of Down's syndrome infants born toolder fathers by women ;;a. 35 years. Erickson
436

concluded that the possibility of a paternal age effectremains open, but the available data suggest that, if itexists, it is quite small.

14. Effect of radiation. In its 1977 report, theCommittee reviewed the results of surveys designed toinquire whether parental (in particular, maternal)
irradiation may increase the risk of producing Down's
syndrome (see also [U3)). The main findings of all theretrospective and prospective surveys are recapitulated
in Table 8 which includes also the recent results of theBaltimore Case-Control study [C8]. This study,
however, in contrast to earlier findings [Sl9], found no
significant effect of maternal irradiation on theincidence of Down's syndrome. (The Indian study [K4]has been excluded from Table 8 owing to problems ofstatistical analysis, as discussed in the 1977 report [Ul].)
Thus the only studies that show a positive effect arethose of Alberman et al. [AS), Sigler et al. [SI9] andUchida et al. [U4, US]. In conclusion, as Uchida [U6)stated ". . . it may still be premature to say withconviction that radiation as a cause of non-disjunction,
increases the frequency of 21-trisomy. However, it
seems logical to avoid unnecessary exposure to
mutagens that might add to the genetic burden ofhumans".
8. Satellite associations: their possible functionalsignificance and relevance for autosomal trisomies
75. The satellite regions of human acrocentric chromosomes (Numbers 13, 14, 15, 21 and 22) are frequently
located near one another in metaphase chromosome
preparations. This relationship called "satellite
association" (SA) was first described by FergusonSmith and Handmaker [F3] and Harnden [H9] and has
been found to occur both in mitosis and in meiosis [F4].
The length of the satellite stalk or secondary
constriction, rather than the size of the satellite, is correlated with the frequency of associations [E4, S21, Zl].
76. SA is thought to be the result of the involvementof the acrocentric chromosomes in nucleolus formation[F4, HlO, 03) and the connectives between the satellite
regions which can sometimes be observed in stained
mitotic preparations [22) represent remnants of thenucleolus. Both the secondary constrictions of aerocentric chromosomes and the connectives have beenshown to contain DNA (rDNA) coding for 18S and 28S
ribosomal RNA (rRNA) [E4, Hll, H12, ClO].
According to a recent estimate [YI] there are approximately 50 such genes, i.e., about 5 ribosomal genes oneach acrocentric chromosome. It is recognized that the
number of RNA genes on a given chromosome isvariable [e.g., E4, Dl, H12] and it has been suggested
that such variations may be related to the frequencies
with which particular chromosomes are found insatellite associations [H 12, M 15, W5].
77. The frequency of SA may vary within the
population and a variety of in vivo and in vitro conditions (e.g., age, sex, thyroid autoantibodies, viral
infection, chromosome culture methods, etc.) have beenshown to have an effect on the frequency of SA (seeHoughton [H16) for a citation of the relevant papers).
There is a recent report showing that SAs are distorted
when colcemid is used to collect metaphases [R64]. In
part, interest in the problem of SA has been stimulatedby the finding that the majority of the chromosomal
abnormalities in liveborn children involve the aerocentric chromosomes and that these aneuploidies arecaused by non-disjunction and by structural rearrangements such as reciprocal lranslocations and Robertsonian translocations; and are also stimulated by the
speculation that SA, if it occurs in germ cells, may havean aetiological role in the development of these abnormalities {F3, H9, Cl 1, Cl2, R5, 03, Z3].
78. Several workers have concluded that participationin SA is random [e.g., CB. C14, l-118, JS, N7, R6, S22]
while a number of others found that some particularassociations were more frequent than others [e.g., C 15,
N8, A6. P7]. For instance, Cohen and Shaw [C13] foundthat there was a distinct tendency for G group chromosomes to be associated more frequently than D groupelements; in multiple associations of specified size
within a given number of D and G chromosomes, thetype of associations appeared to be random. Jacobs etal. [JS] noted that there was very significant heterogeneity among individuals in the frequency with which
different chromosomes entered into associations andwere unable to obtain evidence for preferential
association between any particular chromosomes. either
homologous or heterologous. The existence of differences between individuals has also been recorded by anumber of investigators [e.g., M15, H17, Z2]. On theother hand, Patil and Lubs [P7] found that the chromosomes most frequently involved in Robertsonian translocations6 (i.e., 14, 21 and 13) were also most frequently
involved in satellite associations. The observations of
Ardito et al. [A6] show that while the pattern ofassociation of 0-D, D-G and G-G groups seem to berandom, there exists some preferential association particularly between pairs of13-14, 13-13, 13-21 and 21-21.
79. The results of studies on Down's syndrome
patients and their parents have also yielded conflicting
results. Some studies have shown a significant increase
in SA in blood cultures of Down's syndrome children[e.g., R7] and it has been reported that the parents of
Down's syndrome children showed significant deviations from random association even though there was arandom distribution for the children themselves [e.g.,
C12, R5]. Other workers could not demonstrate any
difference between Down's syndrome patients, theirrelatives and normal controls [e.g., K37, T5]. Mattei etal. [M18] studied SA patterns in a large sample ofparents of normal children and parents of Down's
syndrome children. In the latter group, more SAs andmore complex associations were found. There were alsosignificant differences in the composition of theassociation complexes: in parents of Down's syndrome
children. chromosome 15 was less frequently involved
than normal and all associations involving chromosome 22 were increased except for 22-15. For chromosome 21, 21-22 was more frequent than normal.
80. Houghton [H 16] investigated the effects of gamma
or neutron irradiation of blood derived from normal
males and females, Down's syndrome males andfemales and the parents of both normal and Down's
syndrome children on satellite association. In the rangeof gamma exposures employed (0.05 to 0.6 Gy) no
6 Analysis of the data pertaining to over 10 OOO patients
examined (for various reasons) at the lnstitut de la Progenesein Paris, gives the following frequencies of involvement of thedifferent chromosomes: total Robertsonian translocations
detected: 84; 13/14: 27 cases; 14/21: 21 cases; 21/21: 15
cases; 13/21: 7 cases; 21/22: 5 cases; 13/13: 3 cases; 15/21: 2
cases; 13/22, 14/22, 15/22, and 22/22: I case each. A similar
analysis of published data from newborn surveys pertaining toover 42 OOO infants gives the following results; 13/14: 21
cases; 14/21: 5 cases; 13/22, 14/22, 15/22 and 14/15: 1 caseeach (total 30 Robertsonian translocations) [06].

effects on SA were apparent; the results obtained using
the silver staining technique (which permits a more
precise evaluation) were also the same. With neutrons
however, while there was no change in the overallfrequency of SAs, there was a change in the composition of the SA complexes: there appeared to be apreferential participation of chromosome 13 in SA overthe dose range of 0.05 to 0.6 Gy. The author has no
explanation for this observation.
81. In a similar study involving blood from four
healthy persons and with x-ray doses of 0.05 to 0.5 Gy(4 levels), Stenstrand [S95) found that the pattern of SA(the involvement of specific chromosomes) varied
between the different individuals and that in two cases,
irradiation seemed to have a definite influence on thispaltern although the chromosomes involved were not
the same ones. The changes in the SA tendency were
almost opposite to each other.
82. In summary, in spite of the considerable amountof work that has gone into studies on satellite associations, no clear conclusions can be drawn with respect totheir relevance in the context of the aetiology oftrisomies. Furthermore, the spectrum of chromosome
abnormalities in spontaneous abortuses does notsupport the idea that acrocentric chromosomes are
preferentially involved in non-disjunction; the datasuggest, rather, that there may be differences in theextent to which the different resultant trisomies (foracrocentric and non-acrocentric chromosomes) survive
foetal life.
9.

Non-disjunction in the human male studied throughdirect examination of the germ cell stages{a)Spermatozoa

83. The 1977 report considered some data bearing on
the detection of aneuploidy in human spermatozoa.
Briefly, the findings were:(a) The Y chromosome appears as an intensely fluorescent dot in interphase nuclei after staining
with quinacrine dichloride [P2];(b) With similar staining, the Y chromosome can beseen throughout the male germ cell series [P3]including the spermatozoa [85, S7].
These findings raised hopes that these F (fluorescent)bodies may be potentially useful for estimating nondisjunction rate of the Y chromosome. In initial studies,
it was found that between 1 and 3% of humanspermatozoa contained two F bodies [P3, 86) and thesefrequencies were confirmed in a subsequent study [P4].
As was pointed out in the 1977 report, the assumptionthat each F body in 2F spermatozoa corresponds to a Y
chromosome yields very high estimates of nondisjunction rate for the Y which are inconsistent with
the number of XYY individuals (zygotes) found in the
liveborn (or abortion) studies.
84. Further work by Beatty [87, 88, 89] and Sumnerand Robinson [SS] has clearly demonstrated that not all
Y chromosomes are represented by F bodies and that
not all F bodies represented Y chromosomes. In one
study [88], only 83% of the Y chromosomes were represented by F bodies; 7% of the haploid heads and 14% of
the diploid lu:ads contained one or more "adventitious
bodies" in~inguishable from true F bodies. Indirect
DNA estim.ates of Sumner and Robinson [SS] also lend
credence to the idea that a one-to-one correspondence
between 2F and YY is unlikely and that many of the437

2Fs are not YYs. Furthermore, it is known that single
Y chromosomes may have a bilid structure and extra
dots in spermatozoa may be explained by single Y
chromosomes being bilid (sec also [B9] for a treatmentof the problem).
85. All these lines of evidence strengthen the conclusions reached in the 1977 report namely, that the Fbodies may not at present provide a useful means ofestimating the rate of Y chromosomal non-disjunction.
86. Notwithstanding these considerations, Kapp [K3]has argued for the use of Y bodies as a tool to monitor
Y chromosome non-disjunction in males. His data
pertain to a normal male with no known exposure to
mutagens, two patients (one who underwent
adriamycin treatment for ostcogenic sarcoma and who
had a prior history of chemo- and radio-therapy andthe other who underwent serial x-ray therapy forseminoma), a physician who began nuoroscopy
residency, an individual with intestinal amoebiasis who
underwent diagnostic irradiation 9 days before startingon a 10-day regimen of Flagyl. a group of 18 men who
had experienced occupational exposure to dibromochloropropane (DBCP) and 50 unexposed controls. In
the case of the normal male, the average frequency of"2F" sperm was 1.3% (30 samples over 400 days: range:
0.7 to 2.2%). Likewise, 43 out of 45 controls from the
DBCP study had "2F" sperm in the range from Oto 2%.
In individuals undergoing chemical or radiation
treatment, the frequency was in general elevatedreaching levels of between 3 and 6% in about a monthafter the beginning of the treatment. In the case of
DBCP workers (duration of exposure not specified), 16of the 18 had frequencies of "2F" sperm over 2% whilefor 2 of them, the frequency was in the range of Oto 2%.

(b)

Meiotic stages

87. Holm and Rasmussen [H13, H14], Holm,
Rasmussen and von Wettstein [H15] and Rasmussen
and Holm [R4, R65] carried out a detailed analysis of
the meiotic prophase and metaphase I of humanspermatocytes through three-dimensional reconstructions of the meiotic nuclei from electron micrographs ofserial sections. The reconstructions comprise 4
leptotene [H13], 4 early-mid zygotene [R4], 10 latezygotene [R4], 21 early pachytene [R4], 22 mid-latepachytene [H13] and 3 metapahse [H14) nuclei andelucidate details of chromosome pairing, chiasma
formation and disjunction in man. Of interest in thepresent context is their linding which suggests thatprimary non-disjunction can arise in either of two
ways. The first is the failure of homologous chromosomes to form a chiasma, their entering the metaphaseplane as univalents with the possibility of orientation of
the centromeres towards the same spindle pole. The
second is premature dissolution of the synaptinemal
complex or chromatin chiasma 7 leading to univalents inthe meta phase plane with the possibility of their subse7 Chromosome pairing andsynaptinemal complex
formation are intimately related events in meiotic prophase.
With the exception of the Drosophila male (and probably
other dipteran males as well) which lack synaptinemal
complexes, the regular disjunction of homologues appears to
be connected with the presence of synaptinemal complexes. In
organisms with achiasmatic meiosis and/or lacking crossing
over, the entire synaptinemal complex complement is retained
until 1he separation of homologous chromosomes at anaphase
I. Jn most organisms however, rhe bulk of the synaptinemal
complexes is shed from the bivalents after pachytene leaving
only short fragments behind. It is generally believed that these438

quent movement to the same spindle pole. Holm et al.
(H 15] suggest that the retention of the synaptinemal
complex chiasmata until mctaphas_e. I P!ovides theopportunity to study causes of non-d1sJunct1on and thatthe method used holds potential to investigate theeffects of radiation and chemical agents on humanmeiosis.
10.

Detection of chromosome anomalies in humans11erm through direct cytological analysis: interspecific cell-fusion studies

88. Rudak et al. [R 1) described a technique for a
direct analysis of the chromosome constitution ofhuman spermatozoa. In this method, humanspermatozoa (in semen samples) are fused with zonapellucida-free eggs of the golden hamster (Mesocricetus auratus) using the eggs as "reactivating
vehicles". To obtain large numbers of eggs, adultfemale hamsters were induced to superovulate by i.p.
injection of 25 IU pregnant mares' serum gonadotrophin on day 1 (the day of ovulation) of the animals'
oestrous cycle, followed by an i.p. injection of 25 JU
human chorionic gonadotrophin on day 3. The animals
were killed 17 h after the second injection, theiroviducts dissected out and the cumulus mass containing
the ova removed; after suitable washing and clearing of
the ova, the zonae pellucidae were digested off with
0.1 % trypsin at room temperature. Approximately
40-50 eggs were recovered from each superovulated
female and eggs from 4 animals were routinely used foreach semen sample. The zona-pellucida-free eggs were
subsequently transferred to sterile petri dishes
containing the medium and mineral oil.
89. To effect sperm penetration, two to three drops ofthe preincubated sperm suspension were ?r?pped fr~ma Pasteur pipette onto the surface of the 011 111 each dishand mixed with the eggs. The dishes were incubated at
370c in 5% C02 in air for 3 h. Under the conditions of
the experiment, approximately 75% of the eggs which
had been incubated with sperm reached the fixation
stage. Of the fixed eggs, slightly more than halfcontained discrete haploid sets of both the hamster andthe human metaphase chromosomes. Of the 60 sperm
analysed, 31 had a 23,X and 23,Y constitution while 3
were aneuploid (with 22,X, -G; 22,X, -F. and 24,X,+ mar, + ace complements). The frequency ofaneuploidy in this sample is therefore 5%. The authors
suggest that their technique for the lirst time permits the
preparation and analysis of sperm chromosomes withthe same precision as has been achieved for thechromosomes of somatic cells and that " ... the way is
now open to studying directly the chromosome constitutions of a population of sperm ... and to assessing
the effects of various natural and experimentallyinduced phenomena on the chromosomes ofmammalian gametes".
11. Cytogenetic studies in offspring of atomic bomb
survimrs of Hiroshima and Nagasaki: further data

90. Somatic chromosomes of the children of atomic
bomb survivors and controls have been examined since
1967 in an attempt to determine whether atomic bomb
exposure of parental germ cells may have led to an
retained fragments :ire the ultrastructural counterparts of thesites where crossing over has occurred (the chiasmata) and thatthe fragments stabilize the cross overs, thereby holding the twohomologues of each bivalent together (see [R4, R65] for details
and pertinent literature).

increased risk of genetic damage expressed as anincreased frequency of children with induced chromosomal abnormalities. The data of Awa [A7] presented in
the 1977 report showed that among 2885 children of
atomic bomb survivors, a total of 18 individuals (0.62%)
with chromosome anomalies were found. In thematched controls (1090 subjects) there were 3
individuals with chromosome anomalies (0.2So/o). There
was a suggestive, but statistically non-significant
increase in the frequency of sex-chromosomal
anomalies in the children of exposed parents (0.31
versus 0.09%). Finally. the total frequency of chromosomally abnormal children of atomic bomb survivors
was in the same range as that which has been reported
in several newborn surveys (see Table 2).
91. Awa et al. [AS] have now updated this information(see also Ref. S131). Chromosome analysis has been
completed for a total of 10 820 children comprising5058 controls (children of distally exposed parents) and
5762 children of proximally exposed parents with anestimated conjoint gonadal exposure of 0.87 Sv. The
results are that in the controls, 25 (0.49%) were identified as having an abnormal chromosome constitution(11 with balanced autosomal rearrangements, 1 unbalanced rearrangement and 13 sex-chromosomal
aneuploids). Among the children of the exposedparents, there were 30 chromosomally abnormal
individuals (0.52%) the break-down being, 11 balanced
autosomal rearrangements, 3 unbalanced autosomal
rearrangements. and 16 with sex-chromosomal
anomalies. The present data, based on more than twice
the sample size. suggest again no significant differencein the frequencies between controls and the children of
exposed parents.
12.

New chromosomal abnormalities and birth defects

92. The 1966 report of the Committee [U7] dealt withsome of the well-known chromosomal anomalies inhumans such as trisomy 21. trisomy 18, trisomy 13, Cridu-chat syndrome (deletion of the short arm of chromosome 5), partial trisomy for chromosome 21, deletions
particularly involving the short or the long arms ofchromosome 18, DID and DIG translocations and thesex-chromosomal anomalies. In the 1972 report [US],further information on chromosomal anomalies particularly on reciprocal and Robertsonian translocations
was presented including methods of ascertainment(through a balanced or an unbalanced proband) andtheir relationship to the transmission of the translocations.
93. The application of banding techniques (reviewed
by Dutrillaux (D5] and Dutrillaux and Lejeune (D2]) to
study human chromosomes has revolutionized the fieldof human cytogenetics and has led to major advances.
Among these, the following may be listed:
(a)
(b)
(c)

The confirmation of well-established chromosomal syndromes (e.g. + 8, + 13, + 18, + 21, 4p-,
5p-. 18p-. 18q-. etc.):
A precise identification of previously suspected
trisomies (e.g., trisomy S and monosomies such as
those involving chromosomes 21 and 22);
A sub-division of classicalchromosomal
syndromes according to the chromosomal
segments involved (e.g., partial deletions involving
the proximal one-third to one-half and the distal
one-third to two-thirds of the long arm of chromosome 13; partial deletion of chromosome 18: 18pand 18q- syndromes: the 21q- syndrome):(d) The delineation of new chromosomal syndromes
involving practically every segment of thedifferent chromosomes of the human complement:(e) A more precise definition of known chromosomal
anomalies (e.g .. the identification that the relevant
chromosomal segment in the Cri-du-chatsyndrome (5p-) is in the mid-position of 5p15band);.
(f) The discovery o( fragile sites in certain chromosomes:(g) The demonstration of extensive chromosomal
heteromorphisms in humans and their applications:(h} The demonstration of an association between (i)certain genetic diseases and specific chromosomal
anomalies (e.g., retinoblastoma: specific loss ofband 13q 14) and (ii) certain neoplasias andchromosomal aberrations (e.g., chronic myeloid
leukaemia (CML) and the Philadelphia (Phi)chromosome);(i) Progress in gene mapping:(j) Evolutionary studies in primates.
94. Most of the above items have been adequately
covered in several recent reviews [02), [G3], (S16]. (N9,NlO]. (R8, R9], (V4], (PS], (Y2]. [F5], [W6], (H19].8 (KS],[S23], (C19]. [M21], (LS], [B12]. (D3] and (D4]. In what
follows therefore. only certain important features will
be summarized with particular reference to partialmonosomies and trisomies and fragile sites.

(a)Partial monosomies and trisomies

95. As mentioned earlier. new chromosomal defects.
particularly deletions and duplications involving
almost every chromosome of the human complement
have been discovered during recent years (see Table 2
in [S23] and Table 1 and Figure 1 in [L7]). The rate at
which information is accumulating justifies theconclusion that the incidence figures for chromosomal
anomalies summarized in Table 2 may need upwardrevision. Most of the currently available information onthese partial deletions and duplications. however. is in
the nature of case reports. For some such as Cri-du-chatsyndrome, the recent review of Niebuhr (N9] shows thatthe incidence rate may be of the order of 1 in 45 OOO
and among mentally retarded individuals the rate may
be of the order of 1.5 per 1000. There was a significant
excess of females with this syndrome.
96. Several chromosome deletions with distinctive
features have counterparts in single gene defects which
are inherited as autosomal dominants. This seems to be
the case with retinoblastoma which is associated withan interstitial deletion of the long arm of chromosome
13, specifically, band 13q14 [Y3]. Lewandowski andYunis [L7] have cited several other possible instances ofthis kind.
97. In general, partial trisomies seem to be more
frequent that partial monosomies. presumably because
the former are less deleterious. Roughly two-thirds ofthe reported cases (83 out of 129) summarized by
Sanchez and Yunis [S23] are partial trisomies and therest, monosomies. From their detailed analysis of 95
balanced reciprocal translocations (the break-points,
the chromosomes and the chromosomal segments
8 It is worth mentioning here that what have hitherto been
considered cases of trisomy-22 are really translocations
involving chromosomes 11 and 22 with I I q being the predominant trisomic segment [D6].

439

involved, the type of segregation observed in thefamilies ascertained, etc.) Aurias et al. [A3] reached asimilar conclusion, that trisomies are relatively better
tolerated than monosomies. Their results show that in
the case of 1 :3 segregation (leading to monosomies),
there is an average imbalance of 1.68 LJ9 whereas in thecase of 3:1 segregations (leading to trisomies) the
average imbalance is 4.22 U. Furthermore, with 2:2
segregations, the segment in triplicate is generally
longer than the monosomic segment (TM 10 translocations: 3.85 U long trisomy for a 0.47 U longmonosomy: non-TM translocations: 2.63 U trisomy for
1 U long monosomy). The authors point out, however,that there are some exceptions and that other causes in
addition to length may therefore be involved in innuencing the severity of chromosome disorders.

tuted by the so-called "heritable fragile sites". Dekaban[D 18) first reported on a fragile site on the long arm of a
C group chromosome and Lejeune et al. [L42) demonstrated that such a site on the long arm of chromosome
2 (2q1) was heritable. Sutherland [S96) has proposedthat a fragile site is a specific point on a chromosome
which is liable to show the following features: "(i) anon-staining gap of variable width which usually
involves both chromatids: (ii) the site is always atexactly the same point on the chromosome in the cells
examined from any individual patient or kindred; (iii)the site is inherited in a Mendelian dominant fashion:and (iv) fragility must be evident by the production(under appropriate conditions) of acentric fragments,
deleted chromosomes, triradial figures and the like" (inmetaphase preparations).

98. Another finding of interest that emerges from thework of Aurias et al. [A3) is that there is an excess ofbreakpoints for chromosome arms 4p, 9p, lOq, 21q and
22q and a deficiency of breakpoints in lp, 2p and 6p.ll
With the exception of chromosome 22, all the others (4,9. 10 and 21) are implicated in the aetiologies ofrelatively frequent chromosomal disorders (for reviewssee [G2, R8, R9, Y2]). As one plausible explanation, theauthors suggest that monosomies and trisomies of thesesegments may be relatively well tolerated and that thetranslocations involving these chromosomes are
therefore more readily ascertained, especially inchildren carrying unbalanced karyotypes.

102. Heritable fragile sites have been found on anumber of metacentric or sub-metacentric chromosomes (2, 10, 11, 16, 20) and at least one is known on
the X; however, they have so far not been found in anyof the live acrocentrics (13-15, 21, 22) or the Y. They
are never seen in 100% of the cells examined.

99. Although trisomies and monosomies may involveany chromosome, the amount of excess or deficientmaterial does not generally exceed 5% of the total
genome (see table 2 in Sanchez and Yunis [S23]). A
concept that seems to be gaining increasing currency inrecent years is that duplications or deletions of latereplicating regions are less harmful than those
involving earlier replicating regions. Positive Q- and Gbands are now known to represent late replicating
regions [G4, C17, Cl6, D5] and the chromosomal
segments generally involved in the chromosomal
syndromes are partict!larly rich in Q- or G-positive
bands.
100. In
contrast to"classical" chromosomal
syndromes (e.g., trisomy 21, 18, 13, etc.) which are
relatively well-defined entities (and which can be recognized on clinical grounds alone) some partial deletions
and duplications are presently difficult to diagnoseeither because of the absence of a specific relationshipbetween certain phenotypes and chromosomal
segments or because of overlapping phenotypic effects.
In addition, the chromosomal segments involved mayvary from patient to patient and consequently. thephenotype may show considerable variation. For
instance, offspring from carriers of balanced reciprocaltranslocations may receive derivative chromosomes.
This leads not only to partial monosomy or trisomy. but
usually to a combination of both which can be translated into various mixtures of two given syndromes.

(b) Heritable fragile sites
101. A class of chromosomal entities that currently
engages the attention of human cytogeneticists is consti9 U is the unit length of the autosome (total length: 280
units).
10 TM: breakpoints in the telomeric and median regions.
11 p and q refer, respectively, to the short and long arm of
the chromosome.

440

103. Lubs [L43] examined DNA replication by autoradiography in a female with a site Xq27 (or 28) andfound that the X with the fragile site did not appear to
be selectively inactivated. Fraccaro et al. [F23] similarly
studied a site at 2ql and found that in most cells there
was no detectable asynchrony in DNA synthesis
between homologues. Sutherland and Leonard [S97]showed that the chromosomal gaps associated with thefragile sites at 2qll, 10q23, llq23, 12pll, Xq27 (or 28)
do not stain with silver nitrate as the nucleolar regionsof the acrocentric chromosomes do.
104. Sutherland [S96]demonstrated thattheexpression of fragile sites in metaphase chromosomes
obtained from lymphocyte cultures occurred only when
culture medium 199 (which is relatively deficient infolic acid) was used, compared to several other mediai.e., their expression depends on the composition of theculture medium. This was true for sites 2ql 1, 10q23,
1lq13, 16q124, 20pll, Xq27 (or 28) but not for the site
at 16q22. The expression of these sites (except that at
16q22) was inhibited by folic acid, thymidine, folinicacid and probably BUdR. The inhibition, however,
could be reversed by a folic acid antagonist, methotrexate. In addition, there was a correlation between thefrequency of the sites and the pH of the medium for thesites at 2q, lOq and Xq. It was therefore postulated that
there may be at least three different biochemical classesof fragile sites, as judged by their response to pH, folicacid and methotrexate. In a recent report, Schmid et al.
[S98] showed that the presence of the antibiotic
distamycin A in the medium can reveal the fragile site
at 16q22 although there were interfamilial differencesin its appearance.
105. In a recent study, Glover [G38] confirmed thefindings of Sutherland, namely that folic acid andthymidine inhibited the expression of the fragile site on
the X-chromosome and further showed that the
inhibiting effect of folic acid, but not that of thymidine,can be negated by the addition of 5-nuorodeoxyuridine(FUdR) to the culture medium. He suggests that thisobservation can be explained by the fact that FUdR isintra-cellularly converted by thymidine kinase to
5-nuorodeoxyuridine monophosphate (FdUMP) which
in turn, is a potent inhibitor of thymidylate synthetase.
In the absence of exogenous thymidine, the pool ofdeoxythymidine monophosphate (dTMP) is depleted.

thus arresting DNA synthesis. Exogenous thymidine
bypasses this block by conversion to dTMP catalysedby thymidine kinase in the "salvage pathway". In otherwords, the observations are consistent with the
hypothesis that the fragile X is expressed by limiting thedTMP pool and, thus, the deoxythymidine triphosphate(dTTP) pool available for DNA synthesis. The data do
not support the notion that there is a deficiency inthymidylate synthetase in individuals with the fragile X
since inhibition of this enzyme docs not result in fragile
X expression in control males.
106. In 1980, Sutherland et al. [S99] reported finding a
new fragile site at 10q25. This site differed from othersin that it required BUdR (at a concentration of
5-10 mg/litre) in the medium for maximum expression
frequency, and was not inhibited by folic acid concentrations of up to 20 mg/litre or by pH. High concentrations of thymidine however, tended to inhibit
expression. The finding of BUdR-requiring fragile site
at 10q25 has also been reported by Scheres and Hustinx[SlOOJ.
107. Most of the fragile sites discussed above havebeen found either in the course of population cytogenetic studies or in individuals suggested to be chromosomally abnormal. Sutherland [S101] points out thatwith autosomal fragile sites, there is no association withabnormal phenotypes and that the detection in the
instances mentioned earlier is probably a reflection of
the material analysed. However, the fragile site at Xq27
seems to be associated with, and may even be the causeof, the form of mental retardation with macroorchidism [e.g., G37, H52, H53, H54, 117, S99, SlOl,
S102, S103].
108. In a study of 21 mentally retarded males withmacro-orchidism, 13 obligate carrier females and 26
potential carrier females, Sutherland [S102] found thatin the males, the frequency of cells showing the fragilesite Xq27 ranged from 4 to 56%. Among the obligate
carriers, only 5 showed any evidence of the fragile site
and all of them were younger than 35 years; in 7 of theremaining 8 and who were older than 35, the fragile site
could not be demonstrated. In the last case, the fragilesite was readily demonstrated at age 30, but not at age
32. In only 9 of the potential carriers could the fragilesite be shown to occur. The ages of these individuals
ranged from 2.5 to 21 years. After reviewing these andother data published in the literature, Sutherland [S102)
concluded that the diagnosis of X-linked mental retardation with macro-orchidism remains difficult; that not
all the retarded males with the fragile site have macroorchidism; that the fragile site can often be demonstrated in only a small proportion of metaphases fromsome retarded males even when the diagnosis isvirtually certain on clinical grounds and from a studyof the family history including other affected relatives;
and that the detection of the fragile site in females isstill inadequate despite the methods developed tomanipulate the culture medium.
109. A recent report by Daker et al. (019) has raised
the possibility that an X chromosome with a fragile site
typical of X-linked mental retardation can occur innormal individuals; the Xq28 was found in a malepatient (referred to for cytogenetic examination forother reasons) and in his brother, both of whom
appeared to be of normal intelligence. The authors
point out that ". . . although one case can hardly
undermine the importance of fra(X) in the diagnosis of
X-linked mental retardation, nevertheless, theknowledge that this fragile site may occur in individuals
of normal intelligence will make genetic counsellors
feel a little uneasy, especially if prenatal diagnosis of
the fra(X) becomes a reality ... this case therefore
clearly indicates the need for more information aboutfragile sites, especially in the 'normal' population".
I3.

Summary and conclusions

110. The available results of 10 cytogenetic surveys of
neonates (carried out in different parts of the world)show that 0.63% of the babies (424/67 014) are chromosomally abnormal; 158 children (about one-third)
carried sex-chromosomal anomalies, 95 children (about
one-quarter) numerical autosomal anomalies, 134
children (about one-third) balanced structuralanomalies of the autosomes and the remainder (37/424)
unbalanced structural anomalies. The incidence of sexchromosomal anomalies alone is about 3 per 1000 malebirths and 1.5 per 1000 female births.
111. Of the autosomal numerical anomalies (about 1.4
per 1000 births), trisomy 21 constitutes the predominantgroup. Among the balanced autosomal structuralanomalies (about 2 per 1000 births) reciprocal translocations and Robertsonian translocations are about
equally frequent. Among the latter, those involving two
D group chromosomes are more common (48 out of the60) than those involving D and G group chromosomes.
112. About one-half of all the abnormalities detected
at birth may be deemed to be clinically significant(about 3.3 per 1000 births). These abnormalities include
all the non-mosaic XXY and 45,X cases, XXX, XYY
and XX (male) conditions, all autosomal trisomies andall unbalanced structural rearrangements reported tohave been associated with congenital malformations atbirth. There are several reasons why this frequency islikely to be an underestimate.
113. The data on the incidence of chromosomal
anomalies in newborn infants and other results bearing
on whether these are familial or newly arisen, havebeen used to arrive at estimates of mutation rates.
For those abnormalities resulting in livebirths, the estimated rates are the following: numerical errors of autosomes, 6.9 lo-4/gamete/generation; sex-chromosomal
numerical
errors,8.3
lo-4/gamete/generation;balanced Robertsonian translocations, 0.40 lo-4/
gamete/generation; balanced reciprocal translocations,
1.3 lo-4/gamete/generation; unbalanced Robertsoniantranslocations, 0.23 lo-4/gamete/generation: andunbalanced non-Robertsonian structural rearrangements, 0.58 lo-4/gamete/generation.
114. In perinatal deaths, the frequency of chromosomal anomalies has been estimated to be of the orderof 5 to 6%. Among the anomalies found, trisomies
predominate.
115. Further data on the incidence of chromosomal
anomalies in spontaneous abortuses (published subsequent to the 1977 report) confirm and extend theconclusions reached in the 1977 report: about 50% of
spontaneous abortuses are chromosomally abnormal
and trisomies as a group account for over one-half of
all chromosomal anomalies recorded in the abortuses.
The trisomies have been found to show a maternal-age
dependence and the latter is pronounced for those
involving the small chromosomes, both acrocentric andnon-acrocentric. Trisomy 16 is different from the other441

trisomies in that there seems to be no demonstrable
maternal-age dependence.
116. Insights into the origin of the extra chromosomes
in some trisomies have been gained through the use ofchromosomal heteromorphisms as cytogenetic markers.
The conclusions that may be drawn from the data arethat in the abortus material, for trisomy 16, nondisjunction can occur at any one of the meiotic
divisions in either sex, with meiotic I error in the female
predominating. For others (trisomy 13, 14, 15, 21 and
22). non-disjunction seems to occur almost exclusively
at division I in the female. Trisomy 21 in livebirths
seems to arise primarily (in over 70-80% of the cases) as
a result of non-disjunction in the mother (division I).
117. There are now extensive data demonstrating thatin the case of Down's syndrome, there is an increase in
the frequency with increasing maternal age. There arealso some reports suggesting that increased paternal age
may also play a role.
118. The question of whether there is an increase in
the frequency of Down's syndrome children among theprogeny of irradiated mothers is not yet settled: theseveral prospective and retrospective epidemiologicalstudies carried out thus far to specifically investigate
the problem have not provided unequivocal evidence inthis regard.
119. Studies aimed at testing whether or not satellite
associations between acrocentric chromosomes seen inmetaphase preparations of lymphocytes may be related
to the aetiology of trisomies for these chromosomes,
have not provided evidence for such a relationship.
Irradiation was found to cause changes in the pattern ofsatellite associations, but the significance of suchchanges is not amenable to any satisfactory interpretation.
120. The use of banding techniques to study' humanchromsomes has led to a number of major advancesamong which are the discovery of new chromosomal
defects particularly partial monosomies and trisomies.
and heritable fragile sites. In general, partial trisomies
seem to be more frequent than partial monosomies.
Heritable fragile sites have been found on a number ofmetacentric or sub-metacentric chromosomes and at
least one is known on the X. Their expression depends
on the composition of the tissue culture medium. The
relationship between the heritable fragile sites and birthdefects is not yet clearly established. However, thefragile site on the X (Xq27 or 28) is usually associatedwith the form of mental retardation with macroorchidism in males; there is however one recent reportwhich raises the possibility that an X chromosome witha fragile site typical of X-Iinked mental retardation canoccur in normal individuals.

D.

GENES, CHROMOSOMES AND CANCER
I.

Monogenic disorders and neoplasia(a)122. The better known of these traits include
xeroderma pigmentosum (XP), ataxia telangiectasia(AT). Fanconi's anaemia (FA), Bloom's syndrome (BS)and retinoblastoma. All these except retinoblastoma are
inherited as autosomal recessives. In AT. FA and BS,
spontaneous breakage of the chromosomes occurs ·inperipheral blood lymphocytes and in cultured fibroblasts. On this basis, these syndromes are collectively
referred to as "chromosome instability syndromes". In
recent years, other disorders such as porokeratosis ofMibelli (autosomal dominant). nevoid basal cell
carcinoma (autosomal
dominant). incontinentia
pigmenti (X-linked) and scleroderma (multifactorial)
which may fall under chromosome instability
syndromes have come to light. German [G35, G36],
Hecht and McCaw [H21] and Paterson [P33] havereviewed the main findings. A workshop [W24] recently
held in England was entirely devoted to progress inresearch with AT. In what follows, some salient featuresof XP, AT, FA. BS and retinoblastoma will besummarized with special reference to neoplasia.

(b)

Xerodemia pigmentosum (XP)123. The main feature of XP is a marked sensitivity ofthe skin to sunlight-induced damage. manifested as
sunburns. freckling, hyperpigmentation and keratoses,
eventually leading to multiple skin carcinomas andmelanomas which are the final cause of death usually
before the age of 30 [R l OJ. The disease has now beensuccessfully diagnosed in utero [Rl l). Clinical heterogeneity of XP is manifest by a subgroup characterized
by mental retardation and neurological abnormalities(De Sanctis-Cacchione syndrome). The basis for predisposition to cancer is a metabolic abnormality in the
repair of UV-induced damage to DNA and isconsidered in a later section.
124. XP patients do not show increased numbers ofchromosomal aberrations, although there are isolated
reports of a pseudodiploid clone [G6] and of anincrease in abnormalities in fibroblasts from XP
individuals at late but not~at early passage in culture[H22). The levels of sister chromatid exchanges (SCEs)
appear normal [813. K7, W7].

Introduction

121. Many single gene traits predispose to, or arecomplicated by. neoplasia [G5, J6, K6, L9. M22, M23,
S24]. From the fourth edition of McKusick's [M 17]
Catalogue, Mulvihill [M23] could extract over 200
conditions with neoplastic tendencies, i.e., with benign442

or malignant neoplasia or tumour as the sole feature, afrequent concomitant or just a rare complication (seetable I in [M23]). Among these 200 conditions, about
one-half are autosomal dominant, one-third autosomal
recessive and one-sixth, X-linked; for some. evidence
for Mendelian behaviour is clear-cut while for otherssuch evidence is inconclusive. Some of the traits,
because of their rarity, are represented by only single
case reports. Notwithstanding these limitations,
Mulvihill's analysis shows that a substantial number of
all known single gene traits in humans can be
manifested as neoplasias; that a large number of geneloci might be involved in cancer susceptibility. and byinference, the number of "normal" genes contributing
to resistance to neoplasia is large, and nearly all bodily
systems and histological types of tumours are represented including the commonest malignancies of skin,breast, colon and lung.

125. XP individuals have been found in all
geographic groups although their freqency seems tovary in different populations. For the populations from
North America and Europe, the frequency has been
estimated at about 1 in 250 OOO [RlO]; in Japan this has
been estimated to be higher, being 1 in 40 OOO to1 OOO OOO [T27]. While homozygotes arc very sensitive
to sunlight-induced cancer (and die due to this), thesituation in hetcrozygoles is not yet clear [S25, T27].
(c)

Ataxia telangiectasia ( A '/J

126.
The major findings associated with AT areprogressive cerebellar ataxia, conjunctival andcutaneous telangiectasia, frequent sinopulmonary infections with abnormal immunity (not in all patients), a
generally hypoplastic lymphoid system and a predisposition to cancer (see [1114, 1-1211). Most of the cancers
reported in AT patients involve the lympho-reticularsystem; less frequently, epithelial tumours andleukaemia have also been reported [H23]. Death often
occurs before the age of 20 either from sinopulmonary
infections or from malignancies so that it is difficult toestimate the absolute risk of malignancy (AT patientswith cancer are more likely to be reported). There ishowever no doubt that the risk of malignancy, at leastof the reticuloendothelial system, is greatly increased in
AT [H21, S25]. An extensive comparison of the many
clinical aspects of XP and AT has been made by
Kraemer [KS].
127. In many, but not all, AT patients, increased
chromosome breakage is evident in lymphocytes, andJess strikingly, in fibroblasts [G16, H21, H23, H29, Ll 1].
The SCE frequencies are in the normal range, although
there is some variation between different patients [G7,
B13, H24). The non-random chromosomal changes thathave been recorded in AT individuals are discussed in
the next section.
128. Homozygotes for the AT gene may occur as often
as 1 in 40 OOO births [S25, S26]. From this, the frequency
ofheterozygotes(assuming
Hardy-Weinberg
equilibrium) can be estimated to be about 1% of the
population (the latter calculation assumes that AT is
genetically homogeneous which it probably is not; see,for instance, [H21, P37)). One report about AT patients(cited in [S25]) noted a number of cancers in family
histories in their clinical records. The relatives had nosigns of AT and many may have been heterozygous for
the AT gene. Swift et al. [S27] found that for blood
relatives of AT individuals (27 families) there was anincrease in deaths from all types of malignancy.
primarily in younger persons ( ,,s;;; 45 years). Below age 45,
there were 15 deaths due to malignancy (5.2 expected)
and below age 75, there were 59 deaths (42.6 expected).
There were actually fewer deaths from cancer than
expected in persons dying after 75 years of age.
Furthermore, the ratio of observed to expected deaths
from malignant neoplasms increased with an increasein the probability of hetcrozygosity for the AT gene
[S25, S27J.
129. The estimates of risks for hcterozygotcs dying ofcancer (relative to normal controls) varies by factors of
between 2 and 10 depending on how the data are
analysed. For instance, the relative risk factor is 2 whe·ndeath due to all malignancies is considered; it is 5.5
when cancers occurring below age 45 years alone areconsidered and it rises to 10 when ovarian tumours inwomen of<; 55 years are taken into consideration. These
values of relative risks multiplied by the estimatedheterozygote frequency give a value which is a usefulmeasure of the proportion of all cancer patients whocarry the AT gene. For instance, over 5% of all persons
dying before age 45 from any malignancy may carry the
AT gene [S25].

(d)

Fa neon i's anaemia ( FA)130. Fanconi's anaemia. also termed Fanconi's pancytopaenia or Fanconi's constitutional infantile panmyelopathy is a chromosome instability syndrome
associated with progressive marrow failure [F6]. The
clinical features include progressive underproductionof red cells, white cells and platelets leading toanaemia.
leukopaenia
andthrombocytopaenia.
hypoplasia or aplasia of the radius and thumb, growth
retardation and brownish pigmentation of the skin
[B15, G6, H21]. Other skeletal malformations andanomalies of the heart and kidney also occur. Deathoccurs mainly in the early years, but those who survive
longer have an increased risk of acute leukaemia,
especially myelomonocytic. Affected patients are also
at a greater risk for developing squamous cell
carcinoma of mucocutaneous junctions. such as aroundthe mouth and anus and for hepatic adenoma,
especially following prolonged androgen therapy for
their pancytopaenia [H21].
131. FA patients show increased chromosome
breakage and rearrangement, most evident in freshbone marrow preparations and in lymphocytes cultured
for short periods of time such as two to three days;
these occur also in fibroblasts cultured for longer
periods. The breaks are usually of the chromatid type[S38, S39, S40, Wl2] and the chromatid interchanges
observed (unlike in Bloom's syndrome patients) aremainly between non-homologous sites. The levels ofsister chromatid exchanges are normal [H25, K7, L16].
132. Dutrillaux et al. [011] made a study on the localization of chromatid breaks in lymphocytes of three FA
patients using three consecutive stains (Giemsa, Q andR banding). The breakpoints were almost exclusively
located in the interbands between R and Q bands, theonly true exceptions being the secondary constrictions.
The breaks seemed over-represented in the larger
autosomes 1-13 (excepting 4, 8 and 10) and underrepresented in the smaller ones (excepting chromosome17); the sex-chromosomes were only rarely affected.
There was a clear over-representation of breaks at threesites: lq12, 9q12 and the interband between 6p21 and6p22. The remaining breaks were randomly distributed.
133. The incidence at birth of FA is about 1 in 350 OOO
for the North American population [S25, S31] and may
be higher (1 in 70 OOO) in mid-Europe [W8]. For theformer population, a heterozygote frequency of about
0.33% can be estimated. In eight families of patients. 25
deaths from malignancy (among 102 deaths) were
found, a frequency which is significantly higher than
the 15.6 expected [S25, S31, S32]. This finding ofincreased cancer risk for FA heterozygotes does notappear to have been substantiated in some otherfamilies studied by Swift.
(e)Bloom's syndrome ( BS)134. Three main clinical features of BS are: severe
growth retardation, a telangiectatic erythema on
exposed areas and sun-sensitivity (816, G6, G9. G10,
H21]. Many patients have serious respiratory and intestinal infections and the immune system is impaired.
The risk of cancer is increased in BS patients. Primarycancer develops in approximately 1 out of 6 patients.
About half of the cancers are leukaemias of the nonlym phocytic type [H21, Gl 1]. Roughly half of the cases
recorded in the literature have been Ashkenazi Jews. A
443

founder effect is evident and the affected Ashkenazi
Jews have been traced to a small area at the border of
Poland and the Ukrainian Soviet Socialist Republic. It
is not known whether relatives of patients have an
increased risk of malignancy.
135. The cytogenetic hallmark of OS is the symmetrical quadriradial figure, which is rarely seen in otherchromosome instability syndromes. Lymphocytes andfibroblasts show an increase in quadriradials. The
quadriradials involve homologous chromosomes [GIO,
G12. S30). This is so characteristic of the disease that,
according to German [GlOJ, BS is not diagnosed unlessthese quadriradials are found. The exchanges occur
preferentially near the centromere [G6, G13, S33] andare distributed non-randomly along the chromosomes.
In the bone marrow such interchanges have not beenfound though other aberrations have been detected insome patients [G6, S33, S34].
136. The cells from BS patients contain highly
elevated frequencies of sister chromatid exchanges(approximately 90/cell: leucocytes, fibroblasts andbone marrow [B13, C20, G14, S34, S35]). The only
known defect in cultured cells is a reduced rate of DNA
chain elongation [H55]. However, this impairment does
not alter synthesis past pyrimidine dimers in template
DNA i.e., post-replication repair is normal [G22].
137. Some reports suggest that the characteristicallyhigh level of spontaneous SCEs in BS cells can be
reduced. In studies involving co-cultivation of BS andCHO cells, van Buul et al. (821] showed that the SCE
frequencies in BS cells can be reduced by about 20%;
the effect was observed only when cell-to-cell contact
was present with CHO cells without any effect on the
SCE frequencies in CHO cells. Bryant et al. [B22]reported more dramatic results: in euploid cell hybridization studies, they were able to demonstrate that thehigh SCE frequencies in BS cells could be reduced tonormal levels thus resulting in a complete "correction"of the mutant phenotype.

(j)

Retinoblastoma

138. Retinoblastoma, an embryoma of the precursorsof the rod and cone cells in the retina, is a malignant
eye tumour of children [B17, D1 OJ. Mortality is
associated with direct extension of the tumour into thecranial cavity to involve the brain and leptomeninges.
The incidence figures for this condition reported in theliterature (reviewed in ref. [V5]) range from about 1 in
34 OOO (Holland. 1927-1929) to about 1 in 10 OOO (twoAfrican populations; recent figures). Vogel [V5]considers that the most reliable estimates range between
1 in 28 OOO and 1 in 15 OOO and are based on studies
which involved a more complete ascertainment.
139. Retinoblastoma is often considered a classicalexample of a dominantly inherited tumour. As is now
well-known, this is not true of all retino-blastomas.
Analysis of the data indicates that about 60% of all
retino-blastomas are unilateral and non-hereditary, 15%
are unilateral and hereditary and 25% are bilateral andhereditary. In hereditary cases, the tumours tend to
appear a year earlier than in non-hereditary cases [K9].
For hereditary cases, the penetrance is of the order of
90 to 95% [KlO, V5]. Patients with bilateral, andpossibly in general with hereditary, retinoblastoma run
an increased risk of becoming afflicted with other444

tumour diseases, such as bone sarcomas in later life
[F24, F25].
140. The idea that retinoblastoma is a direct effect ofan autosomal dominant gene has been challenged [Z7].
Knudson [K 10, Kl 1] proposed a two-mutation model
for both the hereditary and non-hereditary retinoblastoma, i.e., the first event a germinal mutation thatmakes all of the cells susceptible and the second eventa somatic mutation that transforms this mutant cell into
a tumour cell. Vogel [V5] has suggested that in the nonhereditary variant, a single mutational step, possibly asmall chromosome deletion, may be enough to produce
a tumour.
141. The possibility that at least in a minority of retinoblastoma cases, there may be an association with apartial deletion of the long arm of a D group chromosome has long been surmised [LIO, T6, Wll]. Orye etal. (05] used the banding techniques to the chromosomes of a patient with retinoblastoma and a deletionof a D group chromosome and identified the chromosome as number 13. This finding has been confirmed
in several cases [06, PB]. Six of the ten cases with aninterstitial deletion of chromosome 13 reviewed by
Niebuhr [NlO] had bilateral tumours and one withbilateral tumours had a ring chromosome.
142. Cytogenetic evidence suggests that the locus forretinoblastoma is on the long arm of chromosome 13(the proximal part of 13q21 or the adjacent 13ql4
region [L7].) Most recently, Yunis and Ramsey [Y3]have refined the localization to a portion of band q14
of chromosome 13.
143. Czeizel et al. [C59] examined lymphocyte
chromosomes from 12 of the 43 cases included in theirsurvey of Hungarian patients [C60]. These cases wereselected solely for technical feasibility of examination.
The breakdown of the selected cases was sevensporadic unilateral cases that had been treated withsurgery only, two sporadic unilateral cases, twosporadic bilateral cases treated with surgery and xirradiation and one familial unilateral case treatedsurgically and with x-irradiation. It was found that
there was a significantly higher number of aneuploidcells and cells carrying structural chromosome
anomalies such as chromatid and iso-chromatid breaks
and stable chromosome-type aberrations. The increase
was found not only in the x-irradiated cases, but also inthe seven unirradiated ones (the latter sporadic andunilateral). More recent studies by Knight et al. [K33]
on twelve patients with matched controls failed to show
any increase in chromosome instability in lymphocyte
cultures of retinoblastoma patients.
144. There is at least one report [T28] of increased
sister chromatid exchanges in fibroblasts from a childwith del(13) retinoblastoma. The skin biopsy was
performed before the clinical onset of the tumour. The
observed frequency of 19.7 / cell was significantly higher
relative to that in a normal control.

(g)Aniridia- Wilms' tumour-urogenital abnormalities
association

145. Aniridia (absence or defect of the iris; specifically congenital hypoplasia of iris) is usually bilateraland is transmitted as an autosomal dominant trait; it
affects about 1 in 50 OOO of the general population[M57, M58]. About 30% of the cases are sporadic andare presumed to represent new germinal mutations[817]. Wilms' tumour is an embryoma of the kidney
derived from metanephric blastema. The incidence rate
has been estimated to be of the order of 1 in 10 OOO live
births or 6-7 per year per million in children under age
15 [Y7]. Wilms' tumour is discovered most often
between ages 3 and 4 at which time it is extremely
malignant [G39]. These tumours are bilateral in 5 to
10% of the cases, and the bilateral tumours may develop
simultaneously or sequentially [B 17].
146. Familial Wilms' tumour occurring in siblings has
been reported by a number of investigators (863. 1364.
K34, MS9]. Knudson and Strong [K34] reviewed andsummarized data on 58 familial cases. They concluded
that bilateral tumours are more likely to be familial,that familial tumours result from two mutations, one
germinal and one somatic and that sporadic tumours
result from two somatic mutations.
147. It has been found that the presence of aniridia
somehow renders the affected child prone to the development of Wilms' tumour [B 17, 1\160]. Aniridia ispresent in 1 out of 80 Wilms' tumour cases. The
sporadic cases seem more at risk, as about a third ofthese develop Wilms' tumour. The risk of developing
Wilms' tumour seems highest when sporadic aniridia is
accompanied by genito-urinary tract malformations
and mental retardation. Approximately 6% of patientswith Wilms' tumour exhibit upper urinary tract
anomalies [118, K35].
148. Since the original report that the aniridia-Wilms'
tumour association with mental retardation and genitourinary abnormalities in males is caused, at thecytological level, by an interstitial deletion of the shortarm of chromosome 11 [F26, R66], there have been
several confirmatory observations [A26, F27, Y8].
Francke et al. [F27] concluded that a specific deletionof 11 p 13 appears to cause aniridia with a 1 in 3 risk forthe development of Wilms' tumour and an even greaterrisk for mental retardation. It is interesting to note thatthe gene coding for catalase has been recently mapped,on the basis of enzymatic studies, to the same region ofchromosome 11 (band 1 lp13) [Jl9}. Junien et al. [Jl9}have pointed out that "from a practical standpoint, anassay of catalase activity would thus become a usefulcomplementary test in patients with aniridia appearing
to be new mutations. A low catalase activity would thendemand surveillance of the kidneys and gonads, even in
the absence of a visible chromosome deletion".

2.

Specific chromosomal defects in cancer

149. It is quite common to find that cancerous cells
have a highly aberrant chromosome number, but thisaneuploidy probably results from the rapid uncontrolled mitotic activity of such cells. rather than being
the cause of it. Banding techniques have permitted togain some insights regarding the possible role of somechromosomes (or chromosomal changes) in the originof some neoplasias. More data, however, would beneeded for a precise definition of the relationships
between specific chromosomal changes and cancer andfor an understanding of the mechanisms involved.
Mitelman and Levan [M24], Sanchez and Yunis [S23],
Harnden [H26], Rowley [RI2] and Hecht [H20] havesummarized most of the available information in this
area.

(a)

Chronic myeloid leukaemia and the Philadelphia(Phi) chromosome

150. ln 1960. Nowell and Hungerford [Nl I] reported
the first consistent chromosomal abnormality in ahuman cancer when they described the abnormallysmall G group chromosome that they observed inleukaemic cells from patients with chronic myeloid
leukaemia (CML). This chromosome, which appeared
to have lost about half of its long arm. was called thePhiladelphia (Phi) chromosome from the city of its
discovery. A number of laboratories subsequently
reported that 100% of patients with CML showed thePhi chromosome in their bone marrow cells. Others
reported that up to 30% of patients with CML were Phi
negative. In a number of the early cases. only
peripheral blood was studied and this might explain
why some of the patients were classified as Ph I negative(see Rowley [R12] for a review and citation of the earlyreferences).
151. By using banding techniques, Caspersson et al.
[C21] and O'Riordan et al. [04] independently reported
that the Phl chromosome was no. 22 and that it should
be identified as 22q-. The question regarding the natureof the Ph I chromosome was answered in 1973 when
Rowley [R 13] reported that the Ph 1 chromosome represented a translocation. rather than a deletion as many
investigators had previously assumed. The first reportpresented data on 9 Phl positive patients all of whom
had additional dully fluorescent chromosomal material
at the end of the long arm of one no. 9 (9q + ). It wastherefore proposed that the abnormality in CML wasan apparently balanced translocation t(9:22)(q34;qll).
Subsequent measurements of the affected pairs (9 and22) showed that the amount of DNA added to number
9 is equal to that missing from the Phi [M2S}.
152. The original report on the translocation, and anumber of reports confirming the observation, notedthat the translocation occurred only between number 9
and number 22 (see for instance [D8. P9. PIO, Pll, W9.
Wl 01). However, subsequently. translocations between
number 22 and other chromosomes (numbers 2, 13, 16,
17, 19 or 21) were also reported [e.g., F6, H27, H28,
M26, R14].
153. When patients with CML enter the terminal
acute phase, about 30% appear to retain the 46,PhL
positive cell line unchanged, whereas other chromosomal changes also occur on the PhLpositive cell lines
in 70% of patients (see table 2 in Rowley [R12]). Achange in the karyotype is a grave sign and, with rare
exceptions, heralds the acute blast phase.
154. In a workshop [D9] which was organized toreview the clinical and cytogenetic data in CML andacute non-lymphocytic leukaemia (ANLL). data on 223
patients with Phi.positive CML were compiled andanalysed. The prerequisites for inclusion of patients inthe series were that bone marrow mitoses had beenstudied by banding and that sufficient clinical data
were available. Of the 223 patients, 122 were studied in
the chronic phase, 59 in both the chronic and acutephases, 37 (who were known to have CML) only in theblast phase and 5 (with no prior history of CML) in theblast phase.
155. The major findings were that the translocation
between chromosomes 9 and 22 was found in 92% (205)of all patients; that of the remainder, 8 had a two-way
translocation involving chromosome 22 and another445

chromosome, and 9 had three- or four-way translocations, all of which involved both chromosomes 9 and 22
and some other chromosomc(s) (see also [P34)); thatone patient with a 22q- lacked an obvious translocation: that fewer than 10% of the patients in thechronic phase had other karyotypic abnormalities. In
contrast, at least 75% of those in the acute phaseshowed changes in their karyotype. In some instances,such changes preceded the onset of clinically apparent
blast crisis by up to 18 months, although the usualinterval was 1 to 4 months. It was found that theadditional abnormalities seen in the chronic phase.
most often a double Ph I chromosome (5%) or + 8 (2.4%)
were also those most frequently seen in the blast phase.
Also, the possible isochromosome for the long arm of
17 [i( I 7q)] was considered to be a reliable marker forthe blast phase, and other structural rearrangements
independent of the Phi translocation occurred in about
10% of the patients.
156. Reports of patients with CML whose cells havebeen analysed with banding have included those who
are PhLnegative. The PhLnegative patients account for
about 18% of the cases studied in chronic phase [RI2].
These patients tend to be older, with a large percentage
of males. They show a smaller elevation of the whiteblood cell count than do Phi-positives [Wto], andrespond poorly to treatment and therefore have a much
shorter mean survival (15 months as compared to 42
months for the Phi-positive patients). A number ofinvestigators have suggested that the Phi-negative
variant could represent a different disease. At present,
the tendency is to include both the PhLpositive andPhLnegative patients within the category of CML.

(b)

ified as number 7 in six cases. Five patients had an 8;21translocation.
159. The summary report of van den Berghe et al. [09)on acute non-lymphocytic leukaemia (ANLL) in 279
patients is in general confirmatory of Rowley's
analysis. They found that out of the 279 patients withAN LL, 140 had an apparently normal karyotype and
139 were chromosomally abnormal. Among the lattergroup, 22 cases had +8, 20 cases were -7, 11 cases hadt(Sq-;21 q +), 9 cases had 5( l 5q +; 17q-) and 5 cases
were t(9q + ;22q-). Of the remaining 139 patients 72
had modal chromosome numbers as follows: less than
46 (19 cases); equal to 46 (30 cases) and higher than 46(23 cases). The survival of patients was related to thekaryotypes of the marrow cells. Patients with only
normal cells (NN), with a mixture of normal andabnormal cells (NA) and with only abnormal cells (AA)
had median survival times of 6, 5 and 4 months, respectively. The correlation between karyotype and survival
was most significant for patients with AML in which
the median survival was 8 months for NN patients, but
2 and 3 months for AN and AA patients, respectively.
160. It would thus appear that AML and CML in theacute phases have some chromosomal changes incommon, namely, an additional number 8 and, lessfrequently in the former, an i(17q). Other changes
appear to be relatively specific for one disease oranother. The Phl chromosome is restricted to CML andan extra F, shown to be number 19, is found in CML
and not in AML. Loss of Y may occur in up to 10% of
Phl-positive males, but is rare in AML. The absence of
number 7 or an X in females or the (8;21) translocation
appears to be limited to AML [RI2].

Acute /eukaemias(c)157. In contrast to the observations discussed in thepreceding section on CML in which a specific chromosomal abnormality, the Phl chromosome, is found inover 90% of the patients, the chromosome patterns inacute leukaemias (either myelogenous (AML) or
lymphoblastic (ALL)) are quite variable, althoughchromosomal abnormalities have been detected inabout 50% of the cases. Sandberg et al. (S36] firstsuggested that patients with AML are more likely tohave diploid or hypodiploid chromosome numbers
whereas those with ALL are more likely to have hyperdiploid chromosome numbers. Although chromosomalchanges in bone marrow cells of acute Ieukaemic
patients are diverse, an extra C group chromosome (8or 9 or sometimes 10 or 11) had been repeatedly
reported in bone marrow cells of leukaemic patients aswell as in patients with other haematopoietic disorders[J7, R15]; a missing or deleted chromosome 7 [P12, R16]
or an isochromosome for the long arm of chromosome
17 has also been found [F7, M27].
158. Rowley [R 12] recently analysed the banding
patterns of chromosomes of 60 patients with AML,
acute myelomonocytic leukaemia (AMMoL) or erythroleukaemia (EL) (see table 8 in reference [R 121). It
was found that there is a surprisingly narrow range ofmodal chromosome numbers, with 22 individuals
having 45 chromosomes, 16 having 46 and 15 having 47:
5 had 42-44 and 4 had 48-50 chromosomes; the chromosomal abnormalities can be grouped into three major
types: gain of one autosome, loss of one autosome andbalanced translocation. It was further found that 13
patients had one extra autosome identified as number 8
in ten cases. Nine showed loss of one autosome, ident446

Testicular tumours

161. In 1967, Martineau [M28] reported the occurrence of a long submetacentric marker in 8 out of 9
patients with testicular tumours (seminomas) but so far
no banding studies have been reported on thesetumours.

(d)

Burkitt's lymphoma

162. Burkitt's lymphoma is a sporadic disease ofchildren. First described in Africa, it is also known tooccur in virtually epidemic proportions in New Guinea.
It shows involvement of the peripheral lymph nodes(e.g., in the jaw) or with a lymphomatous mass in thelower abdomen. The course of the disease is usuallyshort resulting in death within a few years. Burkitt's
lymphoma is now known to occur worldwide, including
the Americas and Europe. In such areas, the children
tend to be a little older when they contract the disease,to be more resistant to drug therapy and to die evenmore quickly after diagnosis than in Africa or in New
Guinea [W6].
163. The most interesting difference between the
African (and New Guinean) (AffiL) and the American
types (ArnBL) is related to the close association with the
Epstein-Barr virus in the majority of the cases of theformer type whereas this is not true of the latter.
Biopsies and cell cultures from patients with AfBL
show an abnormal chromosome 14 with an additionalterminal band [JS, M29] in many cases. Zech [Z4) and
Zech et al. (212) have provided evidence suggesting thatthe extra R band at the distal end of the long arm ofchromosome 14 is the result of a balanced translocationfrom chromosome 8, i.e .. t(8q-; 14q + ).
164. Studies of cells cultured from two children with
AmBL showed that in one there was no detectable
Epstein-Barr virus while in the other, it was present- In
both cases. the t(8q-;14q+) was found and was indistinguishable from that observed in the Afl3L [E5].

(e)Meningiomas

165. Cytogenetic studies of human meningiomas haveshown that the majority have a hypodiploid cell line
and the G group chromosome missing in many cases isnumber 22 [M30, Z5]. In addition, the loss of chromo·
somes 8. 9, X and Y have also been reported in a few
cases [M31, Z6].

(I)

Ataxia telangiectasia

166. In blood lymphocytes and fibroblasts frompatients with AT, increased spontaneous chromosome
breakage has long been known [H21. H23, H29, G16,
Ll 1]. More recently, chromosomal rearrangements ofthe translocation type have been described inassociation with chromosome breakage [B18, P14].
Banding studies have shown the specilic involvement ofchromosomes 7 and 14 in translocations, generating inparticular, t(14:14) and t(7;14) [H30, M32, 07, R17].
The involvement of chromosomes 7 or 14 with otherchromosomes has also been reported [M32, 07).
167. In their study, McCaw et al. [M32) found translo·
cations involving 14q in lymphocyte clones obtained
from 7 out of 8 AT patients; the other patient had a ring
14 chromosome. The breakpoints in chromosome 14
involved in the translocation were in the q12 band
whereas those in the recipient chromosomes were at ornear the end. The breakpoints and the extent ofprobable deletion in the ring 14 chromosomes were notdetermined. The authors had an opportunity to study
the chromosomes of one patient before and after the
onset of chronic lymphocytic leukaemia. Before
leukaemia was diagnosed, the patient had a lymphocyte
clone with a 14q translocation in about 20% of thelymphocytes sampled. After the onset of the leukaemia,
100% of the cells sampled from peripheral blood were
leukaemic and showed only one of the two number 14
chromosomes, namely one with extra material on its
long arm (14q + ). The authors consider that theevolution of the leukaemic clone from the pre-existingtranslocation clone was not fortuitous and that theleukaemic transformation was intimately related to thestructural rearrangement of 14q. They also believe thatthe increasing evidence provided by others for the non·random involvement of 14q in African-type Burkitt
lymphoma and other lymphoid neoplasms support their
hypothesis.
168. Aurias et al. [A9] have reported the results of astudy on R-banding of lymphocytes and libroblasts
from 11 AT patients and 6 relatives (parents. siblings)of the patients. Among a total of 927 lymphocytes
analysed. there were 158 chromosomal rearrangements
and out of 187 fibroblasts examined. 33 were chromosomally abnormal giving frequencies of 0.17% forlymphocytes and 0.18% for libroblasts. The mostfrequent rearrangement is a pericentric inversion ofchromosome 7 and this is true of both lymphocytes andlibroblasts. The relative frequencies of inv(7) and otherrearrangements are: 29,inv(7); 8,t(7q;l4q): 9,t(7p;14q);
6,inv(14); 24 other rearrangements involving chromosomes 7 or 14; 104 rearrangements involving otherchromosomes and a few other rearrangements of acomplex type involving chromosomes 7 or 14. The 191
rearrangements detected corresponded to 316 recognizable breakpoints, 35% of which involved chromosome 7, 15% involved chromosome 14, the remainder
involving other chromosomes. Among the 112 breakpoints in chromosome 7, 41 seemed to affect band p14
and 40. band q35; an analogous non-random situation
existed with respect to chromosome 14: bands q12 andq32.3 are predominantly affected.
169. These results thus demonstrate that inv(7) is themost common single type of rearrangement in AT
patients and are at variance with those reported byother investigators who had found t(14;14) and t(7;14)
to be the predominant types. The basis for thedifference is not clear at present, but may possibly be
related to methodological problems (the present work is
the lirst one to use R banding systematically for all cells
examined), geographical differences, age, severity ofthe disease, etc.
170. Turning now to the results from the study of therelatives of AT, in two of the three parents, 2 rearrangements of chromosome 7 and 14 (one, an inv(7) andanother a t(7p:14q)) were found in 225 cells. Among 2of the 3 siblings. 6 rearrangements of chromosomes 7
and 14 were found in 205 cells. In a further study of 17
AT heterozygotes. Aurias et al. [A9) confirmed theabove linding with respect to the specificity ofrearrangements and their rate of occurrence.
171. It is worth pointing out here that several investigators have independently reported the occurrence oft(7 ;14) in lymphocyte cultures of apparently normal
individuals [AlO. 819. H31, W13, Z8]. The apparent
breakpoints on each of the two chromosomes were
nearly similar in all these cases (chromosome 14: q12 orq(l-2); chromosome 7: q13 or qter). Aurias et al. [A9]stress that in most of the other studies on non-AT
patients, inversions had not been detected and this
could have been due to biased analyses. Inversions ofchromosome 7 and 14 were among the most common if
not the most common chromosomal change. both incells from AT patients and in cells from presumed
normal individuals. In both categories the frequency of
inversions was probably underestimated because of the
difficulty in detecting them. Their data lend credence tothe possibility that in AT individuals and AT heterozygotes, the frequencies of rearrangements involving
chromosomes 7 and 14 may be, respectively, 40 and 9times higher than in presumed normal cells.
172. The specilic chromosomal defects in cancer
discussed in this section and some others not discussed
are summarized in Table 9.

3.

Summary and conclusions

173. Many single gene traits (autosomal dominant,autosomal recessive and X-linked) predispose to or arecomplicated by neoplasia. The well studied ones are
exemplified by xeroderma pigmentosum (XP). ataxia
telangiectasia (AT), Fanconi's anaemia (FA), Bloom's
syndrome (BS) and retinoblastoma. All these except
retinoblastoma are inherited as autosomal recessives.
Conditions such as AT, FA and BS are collectively
447

referred to as "chromosome instability syndromes" on
the basis of the fact that spontaneous breakage of thechromosomes occur in peripheral blood lymphocytes
and in fibroblasts from these patients cultured in vitro.
174. The most notable abnormality in XP is hypersensitivity of the skin lo solar radiation and is reflected by
pigmentation changes, elevated erythema and multiple
neoplasms; basal and squamous cell carcinomas are themost prevalent types. Clinicians distinguish two formsof XP: the classical XP displaying skin (and ocular)
complications only and neurological XP in which awide range of central nervous system defects
accompany the skin lesions. XP heterozygotes do notseem to be at any increased risk for developing cancers.
175. AT is a complex neurovascular and immunodeficiency syndrome with a predisposition to cancer ofthe lymphoreticular system. Increased spontaneouschromosome breakage is evident in lymphocytes andless strikingly, in fibroblasts. More recently chromosome rearrangements of the translocation type
involving chromosomes 7 and 14 and inversions inchromosome 7 have been described. There is evidence
that the presence of the translocation containing clones
in peripheral blood lymphocytes may herald the development of cancer; in one AT patient with chronic
lymphocytic leukaemia, the neoplastic lymphocytes
appeared to descend directly from a pre-malignant
clone marked by a 14q translocation. Heterozygotes for
AT appear to be at an increased risk for the development of cancer.
176. The predominant clinical features of FA are
haematological disturbances involving all elements ofthe bone marrow, diverse anatomical malformations,cutaneous lesions and growth retardation. The affectedindividuals usually die in childhood from excessive
bleeding or overwhelming infection and those who
survive to adulthood are prone to acute leukaemia(particularly
myelomonocytic),squamouscellcarcinoma of mucocutaneous junctions surrounding theoral and anal cavities and hepatic adenoma. The modal
karyotype is normal in FA (this also holds true for XP
and AT). Both blood lymphocytes and dermal fibroblasts are characterized by a high spontaneous
frequency of chromatid-type breaks and gaps. The
chromatid rearrangements are mainly between nonhomologous sites. Heterozygotes do not seem to be at
an increased risk for cancer.
177. BS is characterized clinically by severe growth
retardation, a telangiectatic erythema on exposed areas,
increased sun-sensitivity and impairment of theimmune system. The risk of cancer is increased in BS
patients and about half of the cancers are leukaemias of
the non-lymphocytic type. The cytogenetic hallmark of
BS is the symmetrical quadriradial figure which israrely seen in other chromosome instability syndromes.
The cells from BS patients show highly elevatedfrequencies of sister chromatid exchanges in leucocytes,
fibroblasts and in bone marrow cells. There are no dataon whether heterozygotes are at an increased risk forcancer.
178. Retinoblastoma is a malignant eye tumour ofchildren. About 60% of the retinoblastomas are unilateral and non-hereditary, 15%, unilateral and hereditaryand 25%, bilateral and hereditary. The mode of inheritance of the hereditary variety of retinoblastoma is
autosomal dominant with over 90% penetrance. Cytogenetic evidence suggests that the locus for retina-

448

blastoma is on the long arm of chromosome 13 at band
q14.
179. There is good evidence for the association
between aniridia (an autosomal dominant trait). Wilms'
tumour and urogenital abnormalities and a specificdeletion of chromosome 11 (11 p 13) appears to cause
aniridia with a 1 in 3 risk for the development ofWilms' tumour and an even greater risk for the development of mental retardation. The gene coding for the
enzyme catalase has been mapped to the same region asthat which is involved in the aniridia-Wilms' tumour
association.
180. Over the last two decades, the thesis that somespecific chromosomal changes may be involved inneoplasia has gained increasing support. Thus for
instance, in chronic myeloid leukaemia. a translocation
between chromosomes 9 and 22 has been diagnosed ina majority of the cases. In acute leukaemias, thechromosomal patterns are variable although chromosomal abnormalities (some specific) have been detected
in about 50% of the cases. In Burkitt's lymphoma, themain chromosomal change seems to be a translocation
involving chromosomes 8 and 14.
E.

HUMAN
DISORDERSSHOWING
INCREASED SENSITIVITY TO THE INDUCTION
OF GENETIC DAMAGE BY PHYSICAL AND
CHEMICAL MUTAGENS; THE ROLE OF
DNA REPAIR

181. In the 1977 report, some asp~cts of the sensitivityof cells derived from individuals suffering from certain
inherited disorders to UV and ionizing radiation andthe role of DNA repair processes were dealt with. Thissection will be devoted to an updating of the information in this area. For more extensive reviews, see[Al 1, A27, C22, C61, H32, P33, P36. P37, P38, S4L
S42].
182. The disorders that have been extensively studied
from the standpoint of increased sensitivity to DNA
damaging agents are XP, AT, BS and FA. Besides,
some information is available for some other disorders.
The increased sensitivity of affected individuals to aphysical or chemical agent has been a useful indicatorof a possible cellular defect in the ability of the cells torecover from induced DNA damage. Thus for instance,
the increased sun sensitivity and the finding that XP
individuals developed skin cancer at early ages
prompted Cleaver's work with XP cells. This led to thediscovery that XP cells are deficient in DNA repair[C23] of UV-induced damage and catalysed the searchfor other disorders that may show repair defects, notonly with respect to UV-induced damage but also withregard to damage induced by other mutagens.
1.

Sensitivity at the indh'idual level

183. It is now known that, in addition to XP, BS andCockayne's syndrome patients show increased sunsensitivity although the repair defects may be of adifferent nature. The same is also true of FA patients.
There are three reports [C24, Gl8, M33] of AT patients
showing unusual radiosensitivity. Gotoff et al. [Gl8]reported a ten-year-old boy with AT and a malignant
lymphoma who, after receiving a maximum dose of3000 rad to the nasopharynx (out of a planned tumour
dose of 4000 rad) was noted to show marked symptoms

of cutaneous erythema and clinical signs indicated deep
tissue damage. Following his death eight months later
autopsy revealed deep tissue necrosis and it was
concluded that the radiation was directly responsible
for his death. The second report [M33) concerned anine-year-old boy with AT and 1-Iodgin's disease who
received a partial dose of 2843 rad (out of a planned
dose of 4000 rad) to the mediastinum. The patientdeveloped severe oesophagitis. skin damage and respiratory problems and died four months later. Lastly,
Cunliff et al. [C24) reported a seven-year-old boy with
AT and a malignant lymphoma in the upper lobe of theright lung. After 20 Gy, dysphagia and erythema werenoted and, at 30 Gy, the treatment was stopped becauseof worsening symptoms. He died three weeks later.
Again, death appeared to be due to the radiation
treatment.
184. There are reports (e.g., [B23]) of patients withbasal cell naevus syndrome showing severe responses toradiation therapy (the syndrome is an autosomal
dominant condition characterized by multiple basal
naevi, which frequently develop into carcinomas and avariety of minor malformations). In the case of familial
retinoblastoma, it is known that the gene carriers are
susceptible to other tumours, especially osteogenic
sarcoma; the latter may affect 1% of gene carriers [110,K17]. When gene carriers are irradiated, this risk rises
sharply; with very large doses of x rays to the orbit, theincidence of osteogenic sarcoma of the orbit may rise to
30% [S51].
2.

Sensitivity at the cellular level

185. A number of studies have been carried out toexamine the sensitivity of cells derived from thesepatients to the lethal, chromosome-breaking andmutagenic effects of radiation and of chemicals. Thesestudies have revealed that the patterns are complex andnot all of them are amenable to simple interpretations
as will be discussed below.
(a)or another condition associated with a predisposition tomalignancy) fell in this range. Cell strains identified assensitive came from AT patients (0 0 : 0.46 to 0.52 Gy),
progeria (Do: 0.96 to 1.39 Gy), the two genetic forms ofretinoblastoma (Do: 0.94 to 0.98 Gy) and partial
trisomy for chromosome 13 (D 0 : 0.75 to 0.95 Gy).
188. If the sensitivity of AT cell strains is expressed interms of a dose-reduction factor (ORF) relative tonormal strains, this corresponds to a value of about 3[P36. P37, P38, P39]. This is true irrespective of whether
the cells arc irradiated under oxic or hypoxic conditions. AT cell strains also display a uniform response toinactivation by 14 MeV neutrons; however they are
only from 1.6 to 2 times more sensitive to this densely
ionizing radiation than are normal strains [P37. P38].
189. While AT strains are consistently hypersensitive
to killing by ionizing radiation, their response to many
chemical carcinogens is less uniform. AT strains ingeneral seem to be sensitive to those chemicals whose
biological effects mimic those of ionizing radiationsuch as methylmethane sulphonate (MMS) and Nmethyl-N'-nitro-N-nitroguanidine (MNNG); AT cells
are inactivated at a normal rate by far UV (chiefly 254nm) light or UV-mimetic chemicals, such as N-acetoxyacetylaminofluorene (N-acetoxy-AAF) (see [Al 1, P37,
P38] and references cited therein). There is however,much more interstrain variability in response totreatment with radiomimetic chemicals than is observedfor ionizing radiation.
190. XP cells, with the exception of the XP variants,
are very sensitive to the lethal effects of UV-irradiation(reviewed in [C25]). XP variants in contrast, are only
slightly more sensitive than normal cells [L13]. XP
strains display cross-sensitivity to certain chemical
carcinogens, including reactive forms of polycyclichydrocarbons(e.g.,"K-region"
epoxidesofbenzo(a)pyrene) and aromatic amides (e.g., 4-NQO;[Tl2]) but respond normally to ionizing radiation,
monofunctional alkylating agents (e.g., MNNG) andthe DNA-cross-linking agent (mitomycin-C) [A18, F9,
M38, S41].

Cell-killing effects

186. In the work of Arlett and Harcourt [A28], thegamma-ray sensitivity to killing of over 50 lines ofhuman diploid fibroblasts (including some derived
from individuals suffering from one or another of thediseases mentioned above) was examined. It was foundthat the normal sensitivity could be described by arange of D 0 values of 0.97 to 1.80 Gy. All ten AT strainstested proved radiosensitive and gave a mean D 0 valueof 0.57 ± 0.15 Gy and these represent the most radiosensitive human skin fibroblasts currently available.
Representative cell strains from familial retinoblastoma, FA, Hutchinson-Gilford progeria occupied
positions of intermediate sensitivity. as did one of the
two AT heterozygotes. Six X P cell strains together with
two Cockayne's syndrome cell strains (all known to besensitive to UV) fell in the normal range, indicating an
absence of cross-sensitivity between UV and gammairradiation.
187. In the x-ray study of Weichselbaum et al. [W26],
again involving over 50 cell strains, the sensitivity of six
cell strains from normal individuals was described by
D 0 values in the range from 1.4 to 1.52 Gy with an
overall range, based on the extremes of their standard
errors, of 1.28 to 1.64 Gy. About three-quarters of thosestudied (including those derived from patients with one

191. The pattern of sensitivity of FA fibroblasts todifferent physical and chemical agents is somewhat
different than that of XP or AT fibroblasts. FA cells are
hypersensitive to bifunctional alkylating agents (e.g.,
mitomycin-C, nitrogen mustard) or to psoralen-plusblack light, but are at most only slightly more sensitive
to far-UV or gamma-irradiation, 4-NQO or MMS [F9,S104].
192. Fibroblasts from BS patients are not unusuallysensitive to UV- or x-ray-induced killing, but there areresults [K 13] showing that BS lymphocytes may behighly sensitive to EMS-induced killing. Fibroblasts
from Cockayne's syndrome patients are also hypersensitive to UV-induced killing [M37, S45] but shownormal sensitivity with respect to x rays.
193. Some of the main findings discussed in this subsection are summarized in Table JO.
(b)

Host-cell reacrfration

194. Several cell strains derived from patients withhereditary disorders such as XP, AT, etc., have been
assayed for ability to support the reproduction ofmutagen-inactivated viruses, a phenomenon known as449

host-cell reactivation (HCR). The XP cells have a
reducedcapacitytoreactivate
UV-irradiatedadenovirus 2 assayed on the basis of either plaqueforming ability [D21] or production of viral structural
antigens [R67]. Similar results have been obtained with
UV-irradiated SV-40 virus, herpes simplex and vaccinia
virus [A15, A16, US; see also S105]. Several AT strains
reactivate MNNG or x-ray-damaged adenovirus
normalJy [022, R67] despite their hypersensitivity tokilling by these two agents; however, HCR of far-UVirradiated virus is slightly reduced, using both plaqueforming ability and synthesis of viral (V antigen)protein as end-points [R67] although AT cells are inactivated at normal rates by far- UV light. These observations suggest that repair functions presumed to be
deficient in AT cells are not required to promotesurvival of x-ray- or MNNG-damaged virus but are
required to assist in viral recovery from a component of
far-UV damage to DNA. There is some evidence forprogeroid fibroblasts showing a reduced capacity toreactivate gamma-irradiated adenovirus [R69] and for
FA cells showing a reduced capacity to produce viralstructural antigens after infection with UV or gammairradiated adenovirus [R68].

(c)

Mutation induction

195. Maher et al. [M35, M38. M39] have shown that
UV irradiation induces significantly higher frequenciesof 8-AG resistant mutations in both classical XP
and variant XP cells than in normal cells. Likewise,
the XP cells were found to be more susceptible(by a factor of 2 to 3) to the induction of mutations by
the "K-region'' epoxide of benzo(a)pyrene, 7,12dimethylbenz(a)anthracene and dibenz(a,h)anthracene;
the XP variant cells (from a patient) were also found to
be more sensitive to mutation induction by hydrocarbon epoxides [M34]. Thus, at least in the case of the
XP cells, there is a reasonably good correlation between
cell killing and mutagenic effects of UV. The preliminary results of different investigators mentioned by
Arlett and Lehman [Al 1] for AT cells suggest, incontrast, that these cells may be hypomutable or even
immutable by ionizing radiation. A similar lack ofcorrelation between sensitivity to killing and to
mutation induction is also observed in the case of AT
cells treated with mitomycin-C. It is tempting to
speculate that error-prone repair pathways which innormal cells give rise to gamma-ray or mitomycin-C
induced mutations may be inoperative in the AT and
FA cells, respectively.

(d)

Induction of chromosome aberrations andsister-chromatid exchanges

196. XP strains display more chromosome breakage
than normal cells upon treatment with UV light or"UV-like" carcinogens but not with "ionizingradiation-like" chemicals fB 13, S43, S106, Wl 7). The
chromosomal sensitivity to UV appears to be insufficient to account for the increased lethality, suggestingthat the chromosome aberrations are probably not the
principal cause of cell death in XP [M36]. Most, but notall, XP cells show an elevated rate of UV-induced SCEs
[D12, P15, S47]. Wolff and co-workers [W17) reported
that a virus-transformed XP cell strain from complementation group A showed increased induction of
450

SCEs by a variety of chemical mutagens, even those(such as EMS) to which XP cells exhibit a normal
repair and cell-killing responses. The results of Perry et
al. [PI 5] support those of Wolff and co-workers. Heddle[H34] found that elevated levels of SCE induction by
EMS were not obtained in three untransformed XP cellstrains from complementation group A. In XP variants,
UV exposure results in normal levels of SCE [D12.
W17].
197. Ionizing radiation produces a much higher
frequency of chromosomal aberrations in AT than innormal cells: furthermore. it has been shown thatlymphocytes of AT patients when irradiated in Go or G1
show both chromosome-type and chromatid-type
aberrations, in contrast to the normal situation of only
chromosome-type aberrations [T7]. Natarajan and
Meijers [N 12] studied the x-ray-induction of chromosome aberrations in peripheral blood lymphocytes aswell as in skin fibroblasts from AT patients and foundthat in G 0 , G1 and G2, more aberrations were inducedin AT cells than in normal cells. These results as well as
those of Taylor [T9] demonstrate that base damage
which needs an S-dependent repair is not entirely
responsible for the increased frequency of x-rayinduced aberrations in AT cells. The frequencies of
SCEs induced by x rays (as well as those induced by anumber of chemical mutagens) are in the normal range[G20].
198. FA cells show an extreme specific sensitivity toboth the lethal and chromosome-breaking effects of
DNA cross-linking agents such as mitomycin-C [F8, F9,S44]. The induction of chromatid-type aberrations bymitomycin-C is markedly elevated in FA lymphoctyes[S44] and this is also true of x-ray exposure [H56].
Diepoxybutane. another bifunctional agent. also
increases the yield of chromosome aberrations atconcentrations that produce no increase in normal cells[A14]. In FA cells, a lower than normal number of
SCEs are induced in blood cells (but not fibroblasts) bymitomycin-C [L16).
199. It has been reported that cells (erythrocytes) fromtwo unrelated FA patients are deficient in superoxide
dismutase [J9] and that treatment with this enzyme
reduces the spontaneous level of chromosome breakage
in cultured cells [NB]. Raj and Heddle [R19] tested
whether or not treatment with superoxide dismutase(among other enzymes chosen) will lead to a greater
proportional reduction in chromosomal damage(measured using the induction of micronuclei as thecriterion) of mitomycin-C treated FA fibroblasts. The
results showed that while the enzyme treatment reduced
both the spontaneous and mitomycin-C-induced
chromosome breakage, there was no consistentpronounced effect in FA cells.
200. BS cells do not show increased frequencies ofchromosome aberrations following UV- or gammairradiation [15] but they seem to show an elevated SCE
response following exposure to EMS [K13]. Cockayne's
syndrome cells show an increased sensitivity to the UVinduction of SCEs [M36, S45]. In the study of Marshal)
et al. [M36), at any UV dose, approximately 2.5 times
more SCEs were induced iitCockayne's syndrome cells
than in normal fibroblasts.
201. Some of the main results pertaining to chromosome aberrations and SCEs are summarized inTable 11.

3.
(a)

DNA repair

Xeroderma pig111c11tos11m (XP)202. There are now extensive biochemical andbiophysical data on the DNA repair properties of UVirradiated XP strains to support the idea that theabnormal UV response of XP cells is due to a molecular
defect in the repair of UV-induced DNA damage. The
defect is not complete, however, but may be over 90%
in the cells of some individuals and only 50% in others[C25, K8, S41]. Cell strains established from all neurological XP patients and from most classical XP patientsare deficient, to varying extents. in excision repair. Thisconclusion is supported by data on several molecular
end-points: removal of dimers [C25, C26), disappearance of UV-endonuclease sensitive sites [P39) andrepair synthesis levels as monitored directly by unscheduled DNA synthesis (UDS) or repair replication[C26] or indirectly by photolysis of incorporated
bromodeoxyuridine (BrdUrd) [R70].
203. The XP strains that are deficient in excision
repair have been subdivided on the basis of complementation analysis, using the technique of somatic cellhybridization [K14]. Two strains are assigned todifferent complementation groups if, upon fusion, both
nuclei of binuclear hybrid cells exhibit near-normal
levels of UV-induced UDS: alternatively, if the UDSlevels remain reduced in the hybrids, the two strains arc
allocated to the same complementation group. Thus far,seven complementation groups have been identified[A17. 013. 014, K14, K15]. The strains designated as
XP variants constitute a minority of the strains frompersons having the classical form of XP; such strains
are proficient in excision repair, but are deficient inpost-replication repair after UV treatment [L12]. Thesevariants like the excision repair strains possess reduced
levels of photolase activity [S107) although the residuallevels vary between different variant strains. Table 12
summarizes some of the main DNA repair properties ofdifferent genetic forms of XP.
204. There is considerable evidence for the thesis thatthe defect in most, if not all, of these groups is in theincision step. Firstly, following UV-irradiation of XP
cells of groups A-D, only small numbers of single
strand breaks (SSB) are observed compared with thenumber of dimers in the DNA [C26, FlO]. Secondly,
when T4 endonuclease V is introduced into UVirradiated XP cells of groups A-E. UDS approaches
normal levels and the introduced enzyme increases
survival [TIO. TI 1]. Thirdly, Ciarrocchi and Linn [C27]
showed that T4 endonuclease restores repair replication
activity in a cell-free system obtained from XP-A cells.
Smith and Hanawalt [S47) characterized repair replication activity in isolated human cell nuclei, anddemonstrated that the activity restored to XP-A cells byaddition of T4 endonuclease closely resembled repair
replication in normal human cells. The observation thatthe incision endonuclease can allow cells from several
different complementation groups to perform the subsequent steps in excision repair suggests that all are
deficient in incision but not in excision-resynthesis.
205. It would thus appear that mutation in any of anumber of genes might lead to the loss of incision
activity in human cells. However, the existence of sevencomplementation groups in XP does not necessarily
indicate that seven different proteins are required forincision. Some of the groups may represent genes determining polypeptides that interact to form a single

functional complex; others may renect intragenic
complementation, mutations in regulatory genes ormutations in genes whose products facilitate the endonucleolytic event [H32].
206. Some support for the last possibility mentioned
above comes from the work of Mortelmans et al. (M40).
They found that normal human cells disrupted bysonication were capable of specifically excisingpyrimidine dimers both from purified DNA that had
been heavily irradiated. and from their endogenous
cellular DNA. However, sonicated XP cells fromgroups A, C and D also excised dimers from purified
DNA: but sonicated XP-A cells were unable to excise
dimers from their endogenous DNA. This was shown to
be a deficiency in enzyme activity rather than aproperty of the endogenous DNA. as DNA-freesonicates of normal cells were able to promote dimer
excision from the XP-A DNA. These findings led to thesuggestion that these X P cells are not deficient in theendonuclease activity per se but in some other activity
necessary for incision in vivo. Alternatively, theexcision of dimers from purified DNA may represent
the activity of enzymes not normally associated withexcision repair in vivo. Although the inability ofsonicated XP-A cells to excise dimers from theirendogenous DNA mimics their excision properties
in vivo, this is not true of XP-D cells in which excision
is observed in vitro but not in vivo.
207. It was mentioned earlier that cells of the XP
variant class have normal or near-normal sensitivity to
UV light and normal excision repair. These have adefect in post-replication repair [L12], a process which
may be defined as "the ability of UV-irradiated cells toachieve the eventual synthesis of high molecular weightdaughter strands of DNA despite the presence of
unexcised damage in the template strands'' [Al 1]. It has
been demonstrated that the molecular weight of newly
synthesized DNA in UV-irradiated XP variants is
considerably lower than in normal cells [L12J. Thissuggests that gaps in the daughter DNA strands(presumed to be opposite damage in the template
strands) persist for much longer in XP variants than innormal cells. In addition, caffeine has been found to
inhibit the sealing of these gaps in XP variants. but tobe without effect on normal cells [L12].
208. Park and Cleaver [Pl6) studied DNA synthesis innormal cells and in excision-defective (group A) andXP-variant cells after irradiation with UV. The sizes of
DNA synthesized during brief pulses of tritiatedthymidine 1-2 h after irradiation were decreased. theXP variant showing the smallest molecular weight.
Once synthesized, however, the labelled DNA
increased in size at the same rate as in control in all
strains, and the rate was relatively insensitive tocaffeine. After 2-3 h, labelled DNA in each cell typereached a maximum size that was less than in thecontrol cells, indicating the presence of long-lived
blocks to DNA chain growth. These authors argue thatin the studies of Lehman et al. [L12, Ll3] where one or
two chase times were used, the major difference
between XP variant cells and normal cells was
expressed in the size of the labelled DNA made, not on
its subsequent rate of elongation. On the basis of theirresults, the authors proposed a model alternative to thepost-replication repair model: their model assumes
normal chain elongation and termination mechanisms
in which the dimers and other damaged sites act as allor-nothing blocks to the progress of the replication
forks. Therefore, although the XP variant has a unique451

response to UV damage, this does not involve a defectin the bypassing of dimers during a post-labelling chase(i.e., no gaps opposite dimers) but only blocked forks atdimer sites {see also [C6 l]).
209. The mutation frequency induced by UV in XP
variants is well above normal not only when expressed
per unit UV fluence but also per survivor [M38, M39].
In contrast, the XP strains deficient in excision repair
are only hypermutable when the mutation frequency isgiven as a function of UV fluence and not survival[M38]. These observations provide good biologicalevidence that post-replication repair is relatively errorprone whereas, excision repair is error-free, at least in
response to UV damage.
210. The fact that all XP cell lines are defective in one
or more repair pathways for UV damage have led to the
speculation that UV-induced skin carcinogenesis innormal human beings has a low probability because
most of the lesions are removed and DNA synthesis
beyond any that remain is relatively error-free. In
excision-defective XP cells, many dimers remain andreplication beyond them, although relatively error-free,makes an appreciable number of mistakes and hence
gives a high possibility for neoplastic transformation.
In the XP variants, there are a few more dimers than innormals (because of a defect in post-replication repair)but replication beyond dimers is error-prone and, as in
the case of conventional XP's, an appreciable numberof mistakes is made [S41].
211. XP cells are also defective in the repair ofdamage induced by a number of chemical agents while
they are repair-proficient with respect to the damage
induced by certain other chemicals, as well as byionizing radiation: these are listed in Table 13. It
should be realized that the classification of chemicalcompounds as making reparable or irreparable damage
in XP cells, although useful, is complicated by the factthat most, if not all, agents each produce a number ofdifferent DNA lesions. The repair of a fraction of theselesions can be impaired in XP cells while the remainder
is normal. This seems to be the case with alkylation
damage to DNA. Both normal and XP cells are able toremove readily N-7-alkylguanine, but only normal cells
can do it for the minor, but biologically more important
product 0-6-alkylguanine [G21].
212. Earlier studies with 4-NQO demonstrated that
XP cells were more sensitive than normal cells forcytotoxic effects [Tl 2] and that XP cells had a relatively
low level of DNA repair synthesis [C28. S48]. Ikenega
et al. [12] found that three major stable purine adducts
formed by 4-NQO treatment were removed from the
DNA of normal cells but such removal was not detectable with the SV-40 transformed XP strain of complementation group A: a less stable guanine adducthowever, did disappear from XP DNA, but the rate ofremoval was lower than in normal cells.
213. The similarity of effects of UV and 4-NQO in XP
prompted Zelle (Z9] and Zelle and Bootsma [210] toinvestigate the problem in greater detail. The hypothesis
was that if 4-NQO lesions are (predominantly) removedby the same pathway as the pyrimidine dimers and are
dependent on the same gene products, then the classification of the different XP strains into different complementation groups should be similar with respect to UV
and 4-NQO repair in the strains. DNA repair wasstudied by determining the extent of UDS in the
exposed cells by means of autoradiography. The strains
452

that are classified into the same complementationgroup on the basis of their repair of UV-damage also
did not complement each other after 4-NQO treatment.
Strains belonging to different complementation groups(because they do complement each other for theexcision of UV lesions), also showed complementation
for the repair of 4-NQO-induced damage. In the purestrains, the degree to which UDS after 4-NQO
treatment was depressed followed the same pattern as
was seen for the repair of UV-damage. From theseresults, the authors have drawn the conclusion that
repair pathways of UV and 4-NQO lesions have steps
in common and that the gene products responsible forthe repair deficiency in the groups A, B, C, and D are ofequal importance for the repair of the majority of thedamage induced by 4-NQO.

(b)

A taxia telangiectasia

214. The DNA repair characteristics of AT fibroblaststrains after irradiation or other mutagen treatments are
summarized in Table 14. The 13 strains examined thus
far, can be divided into two broad categories, denoted
as exr- and exr+, on the basis of their capacity (relative
to that of normal strains) to execute DNA repair
synthesis (i.e., DNA repair replication and UDS)
following hypoxic gamma-irradiation [P37). The diminished level of gamma-ray-induced repair synthesis
observed in the exr- strains does not seem to stem froma defect in strand-rejoining, because all AT strains
restitute both single-strand (including alkali-labile
lesions) and double strand-breaks with normal kinetics,
as judged by several independent criteria [Ll 7. Pl 8, 17].
Instead, the reduction in repair synthesis can be
ascribed to a defective capacity to remove alkali-stableradio-products which are detected as sites in DNA
sensitive to the strand-incising activity of lesion recognizing enzymes present in crude extracts from Micrococcus luteus [P18, P36].
215. The site removal data imply that certain AT
strains lack a fully functional enzyme (endonuclease or
DNA glycosylase) or co-factor involved in the initial
incision reaction in an excision-repair process. The
radioproducts whose removal is presumed to be
defective in exr- AT strains have not been identified:
the whole spectrum of base, sugar and cross-link lesions
are all candidates with the exception of thymine
glycols. AT strains. both exr+ and exr-, apparently
repair this numerically important class of modified
bases normally [C62, R71].
216. The pattern of DNA repair replication for six AT
strains when treated with MNNG resembles thatobserved after exposure to hypoxic gamma-irradiation:
four exr- strains exhibit diminished levels and two exr+strains, normal levels [S110). Recently. Lehman et al.
[L45] reported that they were unable to confirm theabove observations of Scudiere [S1101 regarding
defective repair synthesis in AT3Bl (exr-).
217. In spite of the enhanced sensitivity of some AT
strains to the lethal effects of MMS, all strains have anapparently normal capacity to repair damage caused bythis alkylating agent, at least as reflected by DNA
repair replication. In agreement with cell survival
studies, the AT cells arc proficient in the repair of
far-UV light lA18, P17] and AAF-induced [Al9]damage.
218. Although considerable success has been achievedin elucidating the DNA properties in AT strains, theprecise biochemical defect responsible for the enhanced
radiosensitivity observed at the cellular and cytogenetic
levels remains unknown. Enzymological studies haveprovided little insight into the nature of the underlying
defect: cell extracts of both exr+ and exr strains
contain normal levels of activity of uracil-DNA glycosylase [K36] and AP endonuclease [I3, M62, S 111 ].
219. Inoue et al. [13, 17] have shown that the ability ofcell-free extracts to increase the priming activity (in aDNA-polymerase assay) of gamma-irradiated DNA isseverely reduced in several AT strains. A comparison ina similar assay of three AT homozygotes, one heterozygote and normal strains showed that homozygotes
had substantially lower activity than normal strains, but
no difference between heterozygotes and normal strains
was found.
220.
Cell fusion analyses have allocated three exrstrains to two complementation groups: ATI BE andAT3Bl to group A and AT2BE to group B [P17; seealso 17]. AT is thus genetically heterogeneous as is XP.

(c)Bloom's syndrome221. The nature of the DNA repair defect in BS is notknown, but Hand and German [H35] have demonstrated a lowered rate of DNA chain growth in S-phasefibroblasts which may account for the observation thatthe sedimentation of pulse-labelled DNA after UVirradiation is somewhat slower than in normal cells[022].

(d)Fanconi's anaemia

222. The unusually high sensitivity of FA cells to
DNA cross-linking agents has already been mentioned.
It has been suggested that FA cells are defective in the
repair of DNA cross-links [F9, SSO]. The DNA of FA
cells analysed on alkaline gradients immediately after
treatment with mitomycin-C sediments more rapidly
than that from normal cells [F9]. This fact may beconsistent with the explanation offered by Latt et al.
[L16], namely, that mitomycin-C damages one polynucleotide chain (as do monofunctional alkylating agents)
but removal of the fragment connected to the otherchain by an inter-strand cross-link cannot be effected
normally. The steps for the removal of such a fragmentin mammalian cells are not defined and this is true alsoof the fundamental molecular lesion in FA. Poon et al.
[P18] observed defective removal of thymine dimers
following large UV doses; with 4-NQO, normal endonucleolytic strand scission, and normal levels of UDS
were obtained. Remsen and Cerutti [R72] found that in
two out of four FA strains, the ability of cell nuclear
preparations to excise thymine glycols from gammairradiated exogenous DNA was reduced. For all FA
strains thus far investigated, the repair of x-ray-induced
single-strand breaks is not deficient. A recent report[K16] has described a significant decrease in DNA
ligase activity observed in fibroblasts and lymphocytesof a patient with FA and his mother (following UVirradiation). No differences were found in the othersteps of repair.

(e)

Cockayne's syndrome

223. The nature of the molecular defect in Cockayne's
syndrome is not yet known. Wade et al. [W18] havereported that the fibroblasts derived from seven
Cockayne's syndrome patients show increased UV- but
not x-ray sensitivity; reduced amounts of UDS
following UV-irradiation; reduced incorporation of3Hthymidine into small molecular weight single-stranded
DNA after UV; normal excision of UV-induced
pyrimidine dimers; and complementation of the ability
to repair UV-induced DNA damage in cell hybrids
formed between some of the fibroblast strains. Assays
on crude extracts of 5 of the 7 strains examined thus far
show that all 5 contain less than 50% of the normal
DNA polymerase activity.
4.

Summary and conclusions

224. The best studied human genetic disorders fromthe standpoint of sensitivity to mutagens (both at theindividual and at the cellular levels) and DNA repair
aspects are xeroderma pigmentosum (XP), ataxia telangiectasia (AT), Fanconi's anaemia (FA), Bloom's
syndrome (BS) and Cockayne's syndrome. XP, BS andCockayne's syndrome patients show increased sunsensitivity and AT patients are highly sensitive toionizing radiation.
225. XP cells (with the exception of the so-called
variants) are very sensitive to the killing effects of UV
and of certain chemicals such as some derivatives ofacetylaminofluorene (AAF) and nitroquinoline oxide(4-NQO) which form large adducts to DNA. Their
response to ionizing radiation and to relatively simple
alkylating agents such as MMS and EMS is normal. XP
cells are deficient in host-cell-reactivation of viruses.
XP cells are also more sensitive to ·mutation induction(8-AGR) by UV and chemicals such as the "K-region"
epoxide of benzo(a)pyrene, 7, 12-dimethyl-benz(a)anthracene and to the UV-induction of chromosomebreakage events and sister-chromatid exchanges(SCEs).
226. There is now a substantial body of evidence
supporting the premise that the XP strains are defectivein the repair of UV-induced DNA damage; all strains(with the exception of the XP variants) are deficient, tovarying extents, in excision repair. The variant strain isexcision-repair proficient, but post-replication repair
deficient.
227. When unscheduled DNA synthesis (UDS) after
UV irradiation was examined in the nuclei of heterokaryons formed by fusing cells from different XP
patients (their cells being deficient in excision repair).
certain combinations appeared normal in excision
repair capacity. On this basis, seven complementationgroups designated A to G have been defined.
228. The AT cells represent the most radiosensitive (toionizing radiation) human cells known but their
response to many chemical carcinogens is not uniform.
In general, the AT cells are more sensitive to thosechemicals whose biological effects mimic those ofionizing radiation. Host-cell reactivation as well as
response to far-UV are normal in AT cells. Preliminary
results suggest that AT cells are less mutable thannormal cells by ionizing radiation.
229. Ionizing radiation produces a much higher
frequency of chromosomal aberrations in AT than innormal cells. AT cells display an unusual pattern ofchromosome aberrations following irradiation in either
Go or early G1 phases in the sense that the aberrations
453

produced are both chromosome-type and chromatidtype. On the basis of their capacity to perform UDS
following hypoxic gamma-irradiation (relative tonormal cells), the AT strains can be divided into two
broad categories, those which are excision-repair proficient and those which are deficient in this respect.
Three excision-repair deficient strains have been
allocated to two complementation groups A and B, on
the basis of complementation studies. The precise
biochemical defect responsible for the enhanced radiosensitivity observed at the cellular and cytogcnetic
levels still remains unknown.
230. FA cells arc hypersensitive to bifunctional
alkylating agents and to psoralen-plus-black light, but
are only slightly more sensitive than normal cells to
far-UV, gamma-irradiation, 4-NQO or MMS. The
induction of chromatid aberrations by mitomycin-C iselevated in FA lymphocytes and this is also true of
x-ray exposure; diepoxybutane also elicits a higher
response in FA cells.
231. Fibroblasts from BS patients are not unusuallysensitive to UV- or x-ray-induced killing, but there aresome data showing that BS lymphocytes may be moresensitive to EMS-induced killing. Fibroblasts from
Cockayne's syndrome patients are hypersensitive to
UV-induced killing, but show normal sensitivity withrespect to x rays. There are some data which suggestthat some Cockayne's syndrome strains may have
reduced levels of DNA polymerase activity (in crude
extracts).
F.

OTHER RELEVANT DATA

232. Although a detailed review of the data bearing
on the radiation-induction of chromosome aberrations
in somatic cells per se is not within the scope of thisAnnex, the following data are discussed in view of their
topical interest and importance.
I. Chromosome aberrations in lymphocytes ofindividuals living in an area of high radioactivity

233. Pohl-Rilling and Fischer [P20] have summarized
the results of their studies on chromosome aberrations
in peripheral blood lymphocytes of individuals living
and working in Badgastein, Austria, an area known tohave a high natural radioactivity. The thermal radoncontaining springs constitute the main source of thisradioactivity. Five million litres of hot water containing
high levels of radon are delivered daily and most of thewater is conducted to big reservoirs and from there tohotels and spa houses where it is used for treatment.
Almost all of the 222Rn is discharged into the air. In
addition, radon emanates from the ground in the whole
region. The air activity is lower in the periphery (zone
II: 80-150 mR a-t, open air; 100-190 mR a-I, room air)than in the vicinity of the springs (zone I: 80-170 mR al, open air; 120-300 mR a-t, room air). Higher levels
occur in the various rooms with treatment facilities andthe highest air activity is found in the "thermal gallery"(1500 mR a-1), a former gold mine near Badgastein inwhich more than 5000 patients are treated per year. The
radiation burden of the population is derived frominhaled radon and daughters in addition to external
gamma irradiation. However, the alpha dose differs
widely, being dependent on site of habitation andoccupation and type of work. The total dose is lower
for inhabitants of zone II than for inhabitants of zone I,454

higher for attendants at the thermal baths and administrative personnel of the spa house, and highest for the
train drivers and doctors who spend several hours a dayin the thermal gallery.
234. Chromosome studies were carried out in 180
blood samples from 122 persons grouped into live
categories with increasing radiation doses, according totheir geographical position within the Badgastein area
and their occupations in the thermal baths, spa house or
thermal gallery. Category A comprised members of the
population living and working in Badgastein and its
surroundings who were continuously irradiated by the
background radiation; category B consisted ofindividuals who received occupational irradiation daily
six times per week for 4 to 6 h (Bl, bath attendants) or 8
to 10 h (B2, thermal gallery personnel) in addition to
the Gastein area background irradiation; category C
included doctors and train drivers (miners) who
received the dose pattern B2 and in addition a highalpha dose six times per week during one (Cl) or two(C2) 2 h period of duty within the mine. In addition,
there were other individuals who were considered a
special group (caretaker who lived on the premises andothers who had received diagnostic irradiation etc.).
The different groups of individuals studied had
accumulated "blood burdens" of 110 to 340 mR a-t of
gamma ray dose and 1 to 1600 mR a-I of alpha dose.
235. The main findings are:(a} Even at these very low dose levels, dose-effectrelationships were observed with the mean valuesof aberration frequencies (fragments, dicentrics
and interstitial deletions) increasing from A to C;(b) There was a weak dependence of aneuploid cells
on both age and dose only within groups A and B;(c) The frequency of fragments showed an age-dependence for all groups. When these were normalized
to an age of 50 years, the age-corrected meanvalues increased from groups A to C, although thedose-response patterns within each group showed
differences (the slope was flatter in C than in A
and B). At comparable doses, the number offragments was higher in group A than in B and in
B than in C. Within A, there was a strong dependence on alpha dose (expressed as mR per month),but no gamma-ray dose dependence. In group B, aweak dependence on both dose components waspresent and in group C, only to the gamma-ray
dose:(d) The results for dicentrics and interstitial deletions
within groups A and B were similar to those forthe fragments, namely, alpha dose dependence ingroup A and dependence on both alpha- andgamma-ray dose in group B. No linear
relationship between dose and two-break aberrations could be established for group C as a whole
although a weak alpha dose dependence waspresent in group Cl (in group C2, there was adecrease in aberration frequencies at the highest
dose levels).
2.

Chromosome aberrations in lymphocytes of nuclear
dockyard workers

236. Evans et al. [E6] published the results of a study
on the incidence of chromosome aberrations inperipheral blood lymphocytes of 197 dockyard workers
followed up over a JO-year period. These workers had
been exposed to mixed neutron + gamma irradiation
during the refuelling of nuclear reactors, but most

exposures were below the internationally acceptedmaximum permissible level of 0.05 Sv per year. Details
about the study population and methods of analysis arc
summarized in the following paragraphs. When thefacility for refueling of nuclear-powered submarines
was started in England in 1968:(a) The majority of the workers who joined theestablishment had not received previous occupational exposure to radiation;(b) Blood samples were taken before their classification as "radiation workers" to give backgroundcontrol samples and serial blood samples werelater obtained at periodic intervals as the dose
accumulated;(c) The blood was cultured using procedures standard
to their laboratory; the cells were orcein-stained
and those with 45 or more centromeres werescored for dicentrics, rings, acentric fragments,
minutes, abnormal monocentrics, additional orabsent monocentrics (aneuploidy), a medium-sized
chromosome with abnormal centromere separation (almost certainly an abnormal X chromosome) and chromatid aberrations;(d) Dose estimates in rems, from film badges, were
provided by the Admiralty Radiation Records
Centre;(e) The radiation sources were nuclear submarines
undergoing refit and emitting mixed neutron +gamma radiation, although the exposures werestated to involve "almost exclusively gamma
radiation".
237. The main results are:(a) When the cumulative doses over the ten-year
period were grouped into 0.05 Sv intervals, there
was a positive correlation between the incidence ofcells containing all types of aberrations with dose;(b) In view of evidence from a variety of populations
for an increase in the spontaneous frequency ofaberrations (in the absence of known radiation
exposure) with increasing age it was expected (andin fact found) that older workers and samples
from later years contributed more to the higher
dose categories, i.e., there was a positive correlation between dose and age, and dose and year of
culture and aberration frequency;(c) In view of the evidence from radiotherapy patientsand from individuals accidentally exposed to highdoses of radiation that the· frequency of unstable
aberrations decreases with time following theexposures, it was expected that, for a given time ofblood sampling, ·an exposure a few days or weeks
prior to sampling would result in higher detected
incidence of induced unstable aberrations than anequivalent exposure received a year or more prior
to sampling; this was in fact found;(d) When all these considerations were taken into
account, significant effects of dose were evident
for the incidence of dicentric aberrations, acentric
fragments and cells with unstable aberrations (Cucells), but not for cells with symmetrical rearrangements: for the former type of aberrations (Cu). alldata are consistent with a linear dose response;(e) A significant age-effect (but no dose-effect) was
found for aneuploid cells, for chromatid aberrations and for X chromosomes with abnormal
centromere separation, as expected (the majorityof peripheral lymphocytes are G 1 at the time of
exposure and consequently no chromatid type ofaberrations would be expected);(I) For all categories of Cu aberrations, the dependence on "recent dose" is greater, although notsignificantly so, than on "early dose". These data
are compatible with the conclusion thatconsidered overall, the rate of increase of dicentricaberrations is 1.4 I o-4 dicentrics per cell per
0.01 Sv.
238. The authors have stressed the point that the
population examined is small in number, subject tovery low levels of radiation exposure for periods of up
to a maximum of ten years and is therefore unlikely toprovide useful data on the incidence of malignant
disease. But it is clear that the yield of dicentric aberrations in cells from individuals obtained prior to occupational exposure (or following exposure to Jess than 0.01
Sv) was about 1 in 700 cells rising approximately
four-fold after accumulated doses of 0.2 to 0.3 Sv; theobserved increase is not large, but is believed to be adirect expression of damage to genetic material consequent to radiation exposure. As the relationshipbetween the yield of dicentrics in blood lymphocytes
and reciprocal translocations in the germ cells varies
between species, these data cannot also be used forpredicting genetic hazards in the progeny of exposed
individuals.
3.

Chromosome aberrations in Iymphoetyes of nuclear
power plant workers

239. In a study similar to that of Evans et al.,Bauchinger et al. [B65] made chromosome analyses of
57 healthy male employees of six German nuclear
power plants; they were metal workers, technicalengineers or radiation protection workers mainly inmaintenance or refuelling crews. All of them hadreceived annual doses below the maximum permissible
limit of 0.05 Sv a-1 and had worked with radiation for
periods ranging from 1 to 14 years. The exposure wasmainly to external sources of gamma rays and higher
energy x rays. The controls for this study were 11
healthy males with no radiation history except natural
background.
240. The frequencies of dicentrics and acentrics in theradiation workers were significantly higher than in thecontrols; and there was no evidence for a positive
correlation between the aberration yields and theaccumulated total dose, even when only the recent
annual dose of the workers was considered.
Furthermore. multiple regression analysis of aberration
frequencies on dose and age did not show any significant dependence on these. These observations are thus
not in agreement with the findings of Evans et al. In
addition, although the total dose-ranges were similar inthese studies, the observed frequencies of aberrations(the data arranged in 0.05 Sv intervals) in the nuclear
power plant workers were in general lower than thosein the dockyard workers. The authors attribute thedifferent nature of their findings to a combination ofseveral factors such as the limited number ofindividuals studied, lack of adequate data on the dose
accumulation patterns in the years preceding blood
sampling etc.
4.

Chromosome aberrations in lymphocytes of classified
radiation workers

241. Lloyd et al. [L49] have also compared thefrequencies of dicentric and acentric aberrations in
unirradiated control subjects and classified radiation
workers exposed to gamma irradiation within permis455

sible limits at a nuclear establishment in the United
Kingdom and routinely monitored with film badges
and thermoluminescent dosimeters. All those exposed
had consistently recorded doses in the range of 0.015 to
0.05 Sv per year for al least the four years immediately
preceding sampling, and in many cases for more thanten years. The incidence of both dicentrics andacentrics was significantly higher in the exposed
workers than in the controls. When allowance wasmade for the turnover of lymphocytes for the period
over which each worker had worked with radiation. a
linear dose-response relationship was found. The rateof induction of dicentrics was (2.22 ± 0.94) I Q-4 per
J0-2 Gy and for all unstable aberrations, (8.24 ± 2.8)
1Q-4 per 10-2 Gy. These rates are in reasonableagreement with dose-response data obtained in vitro.

5.

Chromosome aberrations in lymphocytes of uranium
miners242. Brandom et al. [B66] have studied the incidenceof chromosome aberrations in peripheral blood
lymphocytes of 80 underground uranium miners and 20
controls (in Colorado). The exposure estimates werebased on mine-air measurements and undergroundworking time. One working level (WL) is defined as any
combination of radon and radon daughters in 1 litre ofmine air which will result in the emission of 1.3 105
MeV of alpha-particle energy. One working levelmonth (WLM) is 1 WL times 170 working hours. Alphaparticles from short-lived 21s Po and 214Po deliver themain radiation dose to the tracheobronchial epithelium
and excess long-lived 210Pb in bone and blood isreported to be related to the WLM estimates.
243. The difference between miners and controls in
the incidence of dicentrics and rings is not significant
although, collectively, there is a three-fold increase in
the frequency of these aberrations in the lymphocytesof the miners. The frequencies of inversions and translocations, as well as those of terminal and interstitialdeletions were higher in the miners. The frequencies of
all aberrations (other than dicentrics and rings), showeda dose-dependent increase in the miners ·up to an
estimated dose of 3000 WLM. Finally, in the mosthighly exposed group of miners(> 3000 WLM), there
was a marked decrease in the prevalence of dicentrics
and rings, relative to other exposed groups.

6.

244.

Chromosome aberrations in lymphocytes of workers
with internal depositions of plutonium

In another study, Brandom et al. (867] conductedchromosome analyses of peripheral blood lymphocytesof 343 workers from the United States Department ofEnergy facility at Rocky Flats, Colorado, and 68 nonexposed controls from Rocky Flats and the Greater
Denver area. The radiation dose to the workers derives
mainly from internal depositions of a mixture of
239Pu0 2 (93-94%), 240Pu (6%) and 241 Pu (0.5%). Physicaldose estimates of incorporated plutonium were derived
by two methods, urine assay ("systemic burden") andlung counters ("lung burden"). External doses (x,gamma rays and neutrons) were estimated with x-ray
film badges until 1970 and from 1970-1979, by thermoluminescent badges. Although plutonium enters the
body primarily through inhalation, because of its differential organ distribution, the investigators did not have456

any individuals with only lung burdens. There were
workers with estimates of solely systemic burdens andthose with both systemic and lung burden estimates.
The systemic burden estimates ranged from about
37 Bq to 370 IJq in the different workers with only
systemic burdens and from about 37 Bq to more than
1.5 kBq in those with both systemic and lung burdens.
The average external radiation estimates varied from0.002 to 0.02 Sv for the different individuals and theaverage years of exposure from 11.8 to 15.2; the mean
cumulative Sv value in each exposure group varied
from 0.03 to 0.33 Sv.
245. The individuals were classified into a number ofsub-groups based on estimated exposures. Approximately 100 cells were analysed for each subject. The
chromosomes were trypsin-banded and C-banded forkaryotypic examinations and all chromosomes in every
cell were analysed for numerical and structural aberrations. The data were categorized into: complex aberrations (dicentrics + rings + inversions + translocations); and total aberrations (complex aberrations +deletions).
246. In the group with only systemic burden
estimates, there was no measurable increase in thefrequency of aberrations relative to controls. The
authors point out however that caution must be
exercised in interpreting these data since the dose
estimates are subject to some uncertainty; consequently. the Jack of significant increase in aberration
frequency may be due to limitations in the sensitivity or
accuracy of the urine assay for systemic burden
estimates, or may reflect a true biological indication of
no response at these relatively low dose estimates.
247. In the group with both systemic and lung burden
estimates, there were significant increases in aberration
frequencies from the least to the most highly exposed
persons, in both the complex aberrations and total
aberrations (up from 0.5 per 100 cells in controls toabout 3.5 per 100 cells, complex aberrations; up fromabout 1 per 100 cells in controls to about 5 per 100 cells,"total" aberrations). The frequencies of deletions
strongly contributed to the total yield of aberrations,especially in the lowest estimated exposure group.
248. When the data were appropriately pooled based
on total burden estimates and re-analysed, there wasagain, a significant increase in the incidence of complex
and "total'' aberrations with increasing dose. While theincrease in aberration frequency with dose was statistically significant (P < 0.01 ). it was not marked, risingfrom an average of about 1% of cells with somecategory of structural aberrations among the controls toabout 5% of cells affected in the highest exposuregroup.
249. Stepwise linear regression analyses demonstrated
that lung burden estimates, cumulative external irradiation and age entered as significant independent
variables. The relative contribution of cumulative dosesof external irradiation to the aberration yields cannot
be accurately estimated. For instance, the frequency ofaberrations in the categories "complex" and "total'" wasmarkedly higher in a group with an estimated external
dose of 0.15 Sv than in another with more than twice(0.33 Sv) that dose. The mean plutonium burden
estimate for the first group was 4.4 kBq and for thesecond, 1.3 kBq. It would thus seem that the differencein aberration yields noted above is probably primarily
due to the amount of internal plutonium.

7.

Chromosome aberrations in atomic bomb sun·ivors ofHiroshima

250. In earlier investigations on the somatic chromosomes of atomic bomb survivors of Hiroshima andNagasaki, it was shown that cells with radiationinduced chromosome aberrations persisted among thecirculating lymphocytes for at least three decades afterradiation exposure and that the frequency of aberrant
cells was in general proportional to dose. The majorityof such aberrant cells were identified as having symmetrical exchanges (reciprocal translocations and inversions) while the frequency of unstable aberrations(dicentrics and rings) was an order of magnitude lessfrequent {A20, A21]. ·251. Sofuni et al. [S52] made a further analysis ofradiation-induced chromosome aberrations in atomic
bomb survivors by comparing the results derived froma conventional staining and a trypsin-Giemsa banding
method. Twenty-three atomic bomb survivors from
Hiroshima were selected for this investigation. Theirestimated doses ranged between 1 to 8.5 Gy of mixed
gamma and neutrons; however, these dose estimates are
subject to revision. Lymphocyte cultures were
established for each individual and the chromosome
preparations were made using both the ordinary (0)staining and the trypsin-Giemsa banding method (G).
The data are summarized in Table 15 from which it canbe seen that:(a)(b)

In general. there is a dose-dependent increase in
the frequency of aberrant cells;
The frequencies are clearly higher in the G(banding stain) than in the O (ordinary stain)
series. Not shown in the table is the finding thatthe asymmetrical aberrations constituted only 5%of the total aberrations (17 348 cells identified ashaving aberration by one or the other method). In
addition to easily detectable interchanges
involving two breaks, the symmetrical aberrations
identified included paracentric inversions, severaltranslocatypes of insertional and reciprocal
tions and some quite complex translocations
involving more than three breaks.
8.

Summary and conclusions

252. Chromosome studies in peripheral blood
lymphocytes of people living and working in an area ofhigh natural radioactivity in Austria (radiation burdensfrom inhaled radon and daughters in addition toexternal gamma radiation); and of workers exposed toradiation in a number of different occupational settings(nuclear dockyard workers in the United Kingdom.
nuclear power plant workers in the Federal Republic of
Germany. uranium miners in the United States, workers
in the United States with internal depositions ofplutonium) have been carried out. Further results fromcontinuing studies of the atomic bomb survivors ofHiroshima have also become available.
253. In the Austrian study, where the different groups
studied had accumulated "blood burdens" of 110 to 340
mR a-1 of gamma-ray dose and 1 to 1600 mR a-1 ofalpha dose, the mean frequencies of aberrations (dicentrics, interstitial deletions and fragments) increased
with increasing dose, even at these relatively low
exposure levels.
254. In the British nuclear dockyard workers(primarily gamma-ray exposures below the maximum

permissible limits), significant effects of dose (linear
dependence) were evident for the incidence of dicentricaberrations, acentric fragments and cells with unstable
aberrations: for all categories of unstable aberrations,the dependence on recent dose was greater (but notsignificant) than on early dose.
255. 1n the case of the nuclear power plant workers of
the Federal Republic of Germany (external gamma ray
and higher energy x-ray exposures: also below
maximum permissible limits). although the frequencies
of dicentrics and acentrics were significantly higher inthe workers than in controls, there was no evidence fora positive correlation between aberration yields and theaccumulated total dose even when only the .. recent"annual doses were considered. However. in a survey ofUnited Kingdom radiation workers, a linear doseresponse relationship was found after appropriate
weighting of results to allow for turnover of lymphocytes. The rates of induction of dicentrics and of all
unstable aberrations were in reasonable agreement within vitro dose-response data.
256. In uranium miners in the United States exposure
to radon and daughters up to and exceeding 3000 WLM(1 WL is defined as any combination of radon anddaughters in 1 litre of mine air which will result in theemission of 1.3 10s MeV of alpha-particle energy; one
WLM is 1 WL times 170 working hours) the frequencies
of all aberrations (including inversions, translocations,terminal and interstitial deletions, but excluding dicentrics and rings) showed a dose-dependent increase up toan estimated dose of 3000 WLM.
257. In the case of workers in the United States withinternal depositions of plutonium (mean cumulative
exposures in the range from 0.03 to 0.33 Sv), there was asignificant increase in the frequencies of complex(dicentrics + rings + inversions + translocations) andtotal (complex aberrations + deletions) aberrations.
258. The results of the study of chromosome aberrations in lymphocytes of the survivors of the atomic
bomb in Hiroshima confirm those obtained earlier,namely, a dose-dependent increase in the frequency of, aberrant cells (dose range: 1 to 8.5 Gy; mixed neutronand gamma-ray exposures). Furthermore, with the useof Giemsa banding techniques, around 20% moreaberrations could be identified. relative to conventional
orcein staining technique.

II. EFFECTS IN EXPERIMENTAL
MAMMALS AND OTHER SYSTEMSA.

DOMINANT LETHALS AND
REPRODUCTIVE CAPACITY

259. The 1977 report considered in some detail thedata on the radiation induction of dominant lethals inmice and other experimental mammals. A modest
amount of data including those from a comparative
study of the effects of 239Pu. fission neutrons andgamma irradiation in male mice have since accumulated; these are reviewed in the following paragraphs.
1. The mouse260. Grahn et al. [G23) conducted a large-scale study
to assess the induction of dominant lethality (among
other things) in male mice by incorporated 2J9Pu and by457

external gamma and fission neutron irradiation. Hybrid
B6CF1 male mice 100-120 days old received injectionsof monomeric 239Pu citrate in the tail vein at dose levelsof 0.19 and 0.37 M Bq/kg body weight. Following theinjections. they were mated to 100-150 day old female
B6CF1 mice (I male x 2 females per week up to 45
weeks). In the neutron series, the male mice Wl're
exposed to 0.8 McV neutrons from the Janus
Biomedical Research Reactor (this neutron source has a
gamma-ray contamination of Jess than 3%); single
exposures in the range from 0.1 to 1.6 Gy were administered at rates of 0.04 to 0.12 Gy per minute. Weekly
exposures {for a total of 6 to 24 weeks) were in therange of 0.008 to 0.13 Gy and were delivered during a
45 minute exposure period weekly; the dose rates
ranged from 2 104 Gy to 3 10-3 Gy min-1. All doses
were midline tissue absorbed doses (MDL) as measured
in a tissue equivalent phantom. Dose to the testes may
have been up to 10% higher.
261. All gamma irradiation exposures employed 60Co
sources. Single gamma irradiation dose levels, in termsof MLD, were in the range of 0.45 to 5.7 Gy and weredelivered at 0.3 to 0.4 Gy min-t. Weekly doses ofbetween 0.08 and 2.1 Gy were delivered in a 45 minuteperiod each week concurrently with the weekly neutron
exposures and dose rates were 2 10-3 to 4.7 10-2 Gy
min-1. Continuous (22 h d-1) exposures were given at
two MLD levels, 0.03 and 0.06 Gy d-1 delivered at 2.5
10-s and 4.5 10-5 Gy min-1.
262. The extent of dominant lethality in the different
experiments was assessed by dissecting pregnant
females from 10 to 17 days after conception andcounting the numbers of corpora lutea, uterine implants(IMP), live implants (LE) early deaths occurring at or
around the time of implantation, late deaths and preimplantation losses. However, only the data on postimplantation foetal survival are given in the paper,
since the aim of this study was to compare the effects of
239Pu with the other radiations and Pu exposure was notfound to influence pre-implantation losses.
263. Concerning first the retention and microdistribution of 239Pu in the testis which was also assayed inthis work (a total of 19 mice at the 0.19 MBq/kg and 23
mice at the 0.37 MBq/kg levels), it was found that Pu
was retained in the testes with no change over the
420-day observation period, with the average retention(both dose levels) being about 0.05% of the initial
injected dose. In autoradiographs, about one-half of thealpha tracks were in the interstitial tissue, the remainder
occurred in the tubule, mostly originating fromplutonium deposited along the basement membrane of
the spermatogenic tubule. The heterogeneity ofdeposition was such that more than 83% of the gonad
was radiation-free. In an earlier study from Harwell,
Green et al. [024) examined the inherent heterogeneityof this distribution and concluded that the spermatogonia within a 10 µm concentric ring inside thebasement membrane would receive a dose 2.5 times
higher than the whole-organ absorbed dose. Russelland Lindenbaum [R21] have recently confirmed thisvalue and noted that the localized dose to the gonia
may be up to 4 times higher than the integrated dose.
Initially, a 0.37 MBq/kg dose produces a total testicularburden of about 5 Bq or about 20 Bq/g equivalent to adaily exposure of about 1.5 10-3 Gy or about 1 10-2 Gy
per week to the whole gonad.
264. One important observation related to the findingthat the testes continued to decrease in weight, while458

retaining 0.05% of the initial dose. Therefore, the actual
dose rate to the gonad would slowly increase with age
and duration of exposure. For the purpose of theiranalysis, the relevant genetic dose had been assumed tobe the whole gonad dose and to remain unchanged
during the course of the study. This dose was taken tobe 1.5 J0-3 Gy d-1 at 0.37 MBq/kg and 7.5 104 Gy d-1 at
0.19 M Bq/kg.
265. The data on plutonium-induced dominant lethals
are presented in Table 16. These data were examinedfor evidence of statistical heterogeneity within matingtime sequences; it was found that the weekly variation
in LE/IMP proportions were not significant. There washowever a dose effect, as shown by the difference
between the 0.19 and 0.37 M Bq/kg data. A linear
regression analysis of these data within and acrossmating time sequences and within dose levels, demonstrated that the regression of post-implantation survival
on time after injection (an indicator for accumulatingdose) was not significantly different from zero slope.
Therefore, the dominant lethal rate was concluded to be
independent of accumulating dose and to principallyreflect dose rate. Searle et al. [S53] had discussed these
aspects in connection with their 239Pu work and hadconcluded that the observed dominant lethality was
mostly induced in meiotic and post-meiotic cell stages.
The gonadal doses for these latter stages of germ cell
development were estimated to be 0.021 and 0.042 Gy
for the 0.19 and 0.37 MBq/kg regimes. Under these
conditions, the dominant lethal rate could be estimatedas (64 ± 11)104 gamete/I 0-2 Gy of alpha frradiation to
the whole gonad.
266. The results from chronic gamma-irradiation
together with estimates of doses are given in Table 17.
These data yield a rate of dominant lethality of(5 ± 0.6)104/gamete/J0-2 Gy, for post-meiotic germ
cells. The estimates of rates from other data (single andweekly gamma-ray exposures, single and weekly
neutron exposures) are summarized in Table 18. Also
shown in the Table are the estimates for 239Pu andchronic gamma-irradiation.
267. Inspection of Table 18 will reveal that, for postmeiotic stages:(a) There are no statistically significant differences indominant lethal rates for gamma-irradiationdelivered either singly or weekly; for chronic
gamma-irradiation, however, the rate is only about
one-half of the above rates;(b) There are no significant differences with fission
neutron irradiation delivered singly or weekly;(c) Single gamma-irradiation exposures are more
efficient than weekly or chronic exposures in
inducing dominant lethality in pre-meiotic stages;(d) The effects of single or weekly neutron exposuresof pre-meiotic stages are not significantly
different.
The RBE estimates for these data are given in Table 19
from which it can be seen that alpha irradiation of postmeiotic stages is nearly as efficient as fission neutrons;for pre-meiotic stages, fission neutrons are 19 times
more effective than chronic gamma irradiation.
268. In subsequent work, Grahn, Frystak and Lee{G25] have compared the induction of dominantlethality (among other things) by low single doses ofneutrons (1 10-2 to 40 10-2 Gy) and of gamma rays (0.23
to 1.45 Gy) in male mice. The strain of mice used, age,etc., are the same as those of the study discussed in thepreceding paragraphs. The data pertain to the first fiveweeks of mating following irradiation. The average
number of Jive implants/pregnant female was slightly
reduced and this effect was significant after 0.2 and 0.4
Gy of neutrons and 1.45 Gy of gamma rays. Pre-implantation mortality was slightly increased (significant at all
neutron doses except at 0.01 and 0.1 Gy); the increases
in the gamma ray series did not reach statistical significance. Post-implantation mortality was slightly higher
in all irradiated groups except after 0.01 Gy ofneutrons. There were some indications that at the very
low doses employed (0.01 and 0.025 Gy of neutrons and0.23 and 0.45 Gy of gamma rays), post-implantationmortality was higher than expected on the basis ofextrapolation from higher doses in earlier work.
269. In an extension of the 239Pu studies to 241Am
another transuranic element presumed to have ~slightly different metabolic behaviour, Grahn et al.
[G26] injected a single dose of 0.37 MBq/kg of 241Am(intravenous) and examined the testicular distribution
pattern and dominant lethality. It was found that the
gonadal retention was only 50 to 60% of that seen for
239Pu. Retention through the first JOO days after
injection remained unchanged (as for plutonium) andpreliminary autoradiography indicated that the microdistribution was similar to that seen for plutonium. The
estimated testicular dose for the measured burden of
about 13 Bq per gm of tissue was 9.2 J()-4 Gy d-1,
slightly above the dose delivered by 239Pu dose of 0.19
MBq/kg. The results of a 10-week dominant lethal
series conducted between 125 and 195 days after
injection suggested that the amount of intrauterinemortality was low and not significantly different fromthat in controls.
270. Shevchenko et al. [S 133] studied the induction of
dominant lethals in mice by incorporated 14C, Labelled
glucose solution (5.4 104 Bq/g, 12.4 105 Bq/g and
25 105 Bq/g) was administered orally to adult hybrid(CBA x C578L) male mice. The midline absorbed dosesin the testes were, respectively, 0.22. 0.5 and 1.0 Gy. It
was found that the amount of dominant lethality in
post-meiotic germ cells increased linearly with anincrease in dose. The authors estimated that the RBE
for beta rays from incorporated t4C (relative to x or
gamma rays) was not significantly different from 1.
271. In a series primarily designed to study the
induction of autosomal recessive lethals and to assess
the length of the sterile period, Luning et al. (Ll 8)
irradiated 60--70-day old CBA male mice with 14 MeV
neutrons at 1.5 and 2.5 Gy. The irradiated males weremated to unirradiated females of the same strain(1 male x 3 females) for three consecutive weeks. The
pregnant females were killed and examined for intrauterine deaths on the 17th day after the beginning of thematings. The frequency of dead implants was between 8
and 9.5% in the controls (week 1, 9.5%; week 2, 8.5%
and week 3, 8.3%). With 1.5 Gy, these frequencies
increased from 21.1% (week 1) to 25.3% (week 2) and to
37.8% (week 3). At 2.5 Gy the corresponding figures
were: 23.4% (week 1). 32.4% (week 2) and 49.5 % (week3). As no parallel experiments with x-irradiation weredone, no RBE values could be calculated. However incomparison with previous experiments with the s;mestrain [F12], the authors concluded that 14 MeV
neutrons may be between one and two times as
effective as x rays.
272. Yusof [Y9] compared the yields of dominantlethals in caffeine-fed hybrid (C3H x 101) male mice
irradiated with 2 Gy of either x rays (0.7 Gy min-1) or

6DCo gamma rays (0.002 Gy min-1) and mated tofemales on either the eighth or fifteenth day after x- andgamma-irradiation, respectively, to sample treatedspermatids. The live embryo/corpus luteum ratio inpregnant females killed on about the fourteenth day ofpregnancy was 0.51 for x rays and 0.67 for gamma rays.
These corresponded to rates of induction of dominantlethals of about 17 J()-4 and 10 1()-4 per gamete per
10-2 Gy, respectively. Caffeine had no significant effect.
273. The above differences in induction rates might
have been due to dose rate and/or to quality effects. Jn
order to investigate this, Searle and Ueechey [S54] gave
(C3H x 101) hybrid male mice doses of 3 Gy of x- or
gamma-irradiation at the same high and low dose rates
of about 0.6 and 0.002 Gy min-1. All litters wereconceived 12-16 days post-irradiation and so were
derived from treated spermatids as in the previous
experiment. Live embryo/corpus luteum ratios were0.59 and 0.52 for protracted and acute gamma-irradiation, 0.40 and 0.38 for protracted and acute x-irradiation. These ratios correspond to rates of induction of
dominant Jethals per gamete of 0.39, 0.50, 0.77 and 0.83,
respectively. Although for both x- and gamma-irradiation, acute exposures were more effective thanprotracted ones (protracted/acute ratios of 0.92 and
0.78, respectively), the differences were not significant.
However, there were significant quality effects. therelative effectiveness of x- versus gamma-irradiation
being 2 at low and 1.7 at high dose rates. In both experiments of Yusof and of Searle and Beechey, thefrequencies of abnormal spermatozoa were significantly increased 7 to 8 weeks after irradiation, but there
was no consistent effect of radiation intensity or
quality. In the experiment of Searle and Beechey, there
was no significant effect of dose rate on either testes
mass or sperm count in the x-ray series but there was asignificant effect in the gamma-ray series, with greater
survival at the lower intensity. This result is in line withother evidence which suggests a greater effect of dose
rate after gamma-irradiation than after x-irradiation
over the same range.
274. Generoso et al. [G27] have recently reported on
an experiment designed to examine whether the oocytes
in female mice are capable of carrying out repair ofgenetic damage induced in the male genome. Suchexperiments although known for a long time in Drosophila (see [S55] for a review) have so far not been
carried out in mammals with this specific objective. In
the present work, 12-week old males of one stock(either (101 x C3H)F1 or the reverse hybrid (C3H x10l)F1) were irradiated with 5.5 Gy of acute x rays (ortreated with one of four chemicals) and mated tofemales from different stocks (T, (SEC x C57BL)F 1,(C3H x 10l)F1 and (C3H x C57BL)F1). Dominantlethality was assessed through dissection of pregnant
females in the usual manner. focusing attention on
pregnancies that occurred during 0.5 to 3.5-day matinginterval (x-ray series), 3.5 to 7.5-day mating interval(IMS), 6.5 to 9.5-day mating interval (TEM), etc. The
results showed that, while there was no difference in theyield of dominant lethals in the x-ray series, marked
differences were noted in the experiments withchemicals. particularly with IMS: the frequencies
ranged from 9% ((C3H x C57BL)F1). to 50% ((SEC x
C57BL)F1) and to 81% (T stock). all at 65 mg/kg bodyweight (the dominant lethal frequencies were calculated
from the ratio of live embryo per pregnant female in theexperimental group to those in the controls).
275. Favor et al. [Fl 1] used a modified dominantlethal test to assess the extent to which dominant lethals459

were expressed during the later stages of gestation (i.e.,late dominant lethals). In this study, 10-week old
B6D2F1 hybrid male mice were irradiated with 600 R of
x rays and then mated to females of the same genotype
and age (I male x 2 females) for seven days. The
females were checked daily for the birth of new littersand the numbers of live and dead at birth wererecorded. The progeny were weaned at three weeks ofage after which the parental females were sacrificed
and their uterine horns examined and scored for live
and dead implantation scars according to the method
described by Soares [S56, S57]. Unirradiated controls
were run concurrently. The data showed that theradiation treatment caused a significant increase in thenumber of late deaths (defined as the difference
between the number of "live scars" and the number of"live born"): ·the percentage of late deaths increased
from a control mean of 7.32% to 28.6% in the irradiatedseries. The scar method used in this work has theadvantage that the females need not be killed at mid
pregnancy and that the incidence of dominant lethality
can be assessed after the birth of litters.
276. The authors are aware of the fact that the methodof assessing live and dead implantations by the scartechnique underestimates dead implantations andoverestimates live implantations. Using an estimate oferror rate (the calculation of which is outlined in theirpaper) the data collected by the scar technique can,however, be corrected to be more accurately representative of the live and dead implantations.
277. Goldstein and Spindle [028] studied the x-rayinduction of dominant lethals in male germ cell stages
which are expressed from the cleavage stage to the early(trophoblast) outgrowth stages in cultured mouseembryos. Random-bred male mice of the Dub:(ICR)
strain aged 10-12 weeks were irradiated with 4.5 Gy ofhigh dose rate x rays (0.6 Gy min-1) and mated tofemales of the same strain sequentially (1 male x I
female twice a week for the first four weeks after irradiation of the males and once a week for the next fourweeks). The females, prior to mating, received injectionof pregnant mares' serum gonadotrophin and humanchorionic gonadotrophin for induction of superovulation. In each group. on day 2 of pregnancy, thefemales were killed and the oviducts were flushed out
to obtain uncleaved and two-celled embryos. The ratioof uncleaved ova to two-celled embryos provided ameasure of fertilization. The embryos were cultured
and mortality at various stages of development wasrecorded (Table 20).
278. The data show that:(a) In the irradiated group, there is a higher incidence
of developmental failures in early cleavage, at thelate morula stage and at the late blastocyst stage
than in the controls;(b) Dominant lethalsl2 are induced more frequently ingerm cells exposed as early spermatids andspermatocytes and next most frequently in germ
cells exposed as spermatozoa: of the experimental
two-cell embryo fertilized 14-28 days after irradiation (spermatids-spermatocytes), 35.9% arearrested during cleavage, primarily at the two- or
three-cell stage and this is more than twice the
12
1

proportion found in controls for the same period.
Furthermore, of those fertilized 14-28 days after
irradiation that developed to the morula stage.
26.8% did not form blastocyst after 72 h in culture
while only 7.8% of the control embryos failed at
this stage;
The germ cells irradiated as early spermatids andspermatocytes manifest about equal proportionsof dominant lethals at each developmental stage
whereas those irradiated as sperm manifest
dominant
lethality
predominantlyattheblastocyst. The overall pattern of stage sensitivity
as observed in this study agrees well with what has
been known from conventional dominant lethal
studies [824].

(c)279. In subsequent work with the same strain of miceand techniques, Goldstein et al. [G29] used four lower
x-ray doses (0.9. 1.8, 2.7 and 3.6 Gy). The main observations were the following:(a) When the germ cells used for fertilization were
spermatozoa or spermatids at the time of irradiation, the fertilization index (i.e., the ratio of 2-cellembryos to uncleaved eggs) was not affected atany dose level; with spermatocytes, however, thefertilization index was significantly lower than in
the controls at all doses except the lowest one;(b) With spermatozoa, there was no significant
increase in the frequency of embryos arrested indevelopment before blastocyst formation but there
was a small, dose-independent increase in thesefrequencies (between 5 and 9%) after blastocyst
formation;(c) Embryos derived from germ cells irradiated as
spermatids showed increased developmental arrest
both before and after blastocyst formation;
furthermore, the dominant lethals manifesting
before blastocyst formation were about equallydistributed at all cleavage stages. This latter observation, however, is in contrast to that noted at 4.5
Gy (paragraph 278) by the same workers: at thisdose, developmental failures were found primarily
at the 2-cell stage. The overall frequencies ofdominant lethalsl3 over the range 0.9-4.5 Gy gavea satisfactory fit to a model which incorporates alinear and quadratic component.
280. Eiche [E7] conducted a study to examine theeffects of low x-ray doses (0.04 and 0.08 Gy) given to
young (1-, 2- and 3-week old) female mice and tofemale foetuses irradiated in utero (at two weeks of age)on intrauterine death. The choice of these groups was
dictated by the fact that oocytes in very young females
are very sensitive to killing [R22] and the oocytes in the
15-day old foetuses are at a stage when the DNA
synthesis is most conspicuous [P21]. Young females or
foetuses (CBA x CBA and CBA x AJax) were irradiatedand, when 63-64 days old, were mated to CBA or
C57BL males. On the I 8th day after the beginning of
the matings, the animals were killed and examined for
intrauterine contents (live foetuses, early deaths andlate deaths).
28 I. The data showed that there were no significant
differences in intrauterine death rate between the
13 Total dominant lethality =Percent dominant lethals:(_ [(I-fraction arrested al a given stage, experimental;)] x IOO.

I -fraction arrested al the same stage, control

The stage may be early cleavage, late morula or late blastocysl.

460

1

[

-

1-frnction of experimental embryos arrcsled)lbefore trophoblastic outgrowth( I-fraction of control embrvo< arrested)
before trophoblaslic ou1gmw1h

x OO.
I

control and irradiated groups within any experiment.
although the controls in two out of the three experiments gave low values; however, these latter values
were within the range of intrauterine death rate of nonirradiated series in earlier experiments from the samelaboratory. In the experiments in which similar type offemales were mated to males of two different strains,there was a considerable difference in the mean numberof implants as well as in their distribution. The observation that the mean number of implants per female in
the two series in which the females had been irradiatedduring the first week was considerably lower than in theother series, however, was not borne out in a subsequent study [E8].
282. Baev et al. [825) exposed adult female mice of the
H strain to whole-body chronic gamma-irradiationfrom a 137Cs source over a 35-day period at a meandose of about 1 lo-4 Gy min-1 (total dose: 5 Gy). Afterthe completion of the exposure the animals were mated(2 females x 1 male) to males of the same strain and age
for a 7-week period. The females were checked from the13th mating day onwards and those found to bepregnant were killed and the numbers of corpora lutea,
live and dead embryos were counted.
283. It was found that the frequency of pregnant
females was lower in the irradiated groups (58%) thanin the controls (96%). There was a marked fall in
fertility beginning with the second week; from week 3
through week 7, fertility rates varied between 3 and 9%
versus 27 and 58% in the controls. Mean corpora lutea
counts in the irradiated females were normal at week 1,
but declined progressively thereafter through week 7.
Counts of implants showed the same pattern of decline,with the rate of decrease even more marked. These dataand estimates of dominant lethality [B25] show that:(a)

The induced post-implantation mortality rate israther low, varying from 2.6 to 6.1 % (apart fromweek 6 where the estimated rate has a negativesign) with no statistically significant difference
between the different weeks;(b) The induced pre-implantation mortality rate, on
the other hand, varies over a wide range: (3.1%,
week 1; 5.1 %, week 2; 15.9%, week 3; 3.2%, week
4; 7.5%, week 5; 17.7%, week 6; 3.9%. week 7;
0.3%, week 8 and 14.9%, week 9);(c) Consequently, the increase in total dominantlethal rate can be accounted for primarily by preimplantation loss.
However, the latter (c) is known to include non-genetic
effects. such as unfertilized eggs and it is a less reliable
index.
284. A comparison of these data with the results ofSearle and Beechey [S58) for weeks 1 and 3 after acutex-irradiation exposures in the range of 0-4 Gy (0.7 Gy
min-1) shows that a decrease in dose rate to I 10"'4 Gy
min-1 reduces the rate of post-implantation mortality.
The rate observed in the present study with 5 Gy ofchronic gamma irradiation is of the same magnitude asthat after 1 Gy of acute x-irradiation.
285. Searle et al. [S59) compared the breeding
performance of hybrid (C3H/HeH female x 101/H
male) F1 female mice given 239Pu (0.19 or 0.37 MBq/kg
body mass in 1% trisodium citrate bJ, the tail vein) or
kept in a 0.1 Gy d-1 or 0.2 Gy d-1 6 Co-gamma-irradiation field for up to six 4-week periods (but mated in
the control area) or unirradiated. The injected (orgamma-irradiated) females and the contemporaneouscontrol females were mated to males of the PT stock. In

the plutonium series, most of the females were mated 24
h after injection and were allowed to breed until theyfailed to produce any live-born litters within twomonths of the previous one; some other females were
killed 24 h after injection or at later intervals for radiochemical or autoradiographical studies. In the
gamma-ray series, the mice were initially put together
as trios (1 male to 2 females) in the control area and afemale was moved into the radiation field when avaginal copulation plug was found; she was removed tothe control area on the 18th day of gestation and theappropriate male added to allow a mating at postpartum oestrus. One day after the birth of the litter (oron the day of birth if a vaginal plug was recorded then)she was returned to the radiation field and only
removed when the litter was 18 days old and ready to
be weaned. She was then paired with the male again
and the procedure was repeated until sterility ensued.
286. The ovarian dose rates from the injected
plutonium were initially 8 10-3 and 1.7 10-2 Gy d-1,
respectively in the two groups, changing little thereafter. Actual gamma-ray dose rates averaged around8 10-2 and 16 10-2 Gy d-1, respectively; the highest dose
received was in the first 4-week period 2.6 or 5.2 Gy,
declining to about two-thirds of these values by the
fourth 4-week period. As mentioned earlier, the females
were irradiated until the onset of sterility.
287. The results show that both gamma-ray treatments
affected the reproductive performance more than theplutonium injections with respect to duration of fertility
and offspring per litter in successive 4-week periods,
though the overall mean litter sizes were not significantly less than controls. In the gamma-ray series, thepercentage of fertile females dropped to zero by thefifth and eighth 4-week periods (respectively, in the 0.2
Gy and 0.1 Gy d-1 groups). In the plutonium series, asimilar drop was noticed after 12 and 15 4-weekperiods, respectively in the 0.37 and 0.19 MBq groups.
The mean number of offspring per litter in the
gamma-ray series dropped to one-third of that incontrols in the 0.1 Gy d-t group and to one-sixth in the
0.2 Gy d-1 group. In the plutonium groups, this drop
was less pronounced reaching only two-thirds of thecontrol level even in the 0.37 MBq group. From theseand other data, the authors estimated that the RBE forthe effects on reproduction attributed to germ-cellkilling is about 2.5 for the alpha particles relative togamma rays, a value which is lower than that found fortestis mass reduction (10-15) in an earlier study [S53].
They suggest that this low RBE may be connected with
the inhomogeneity of the alpha-particle dose within theovary.

2.

Other species

288. Chambers and Chapman [C29] studied theinduction of pre- and post-natal lethality (among otherthings) in rats that were given testicular x-ray exposuresof either 600 R or 450 R, using litter size and thenumber of progeny alive after birth at day 1 and at day
21 as criteria. Male rats of the yellow Cu2 strain were
irradiated (either with a single acute exposure of 600 R
at 10 weeks of age or with a fractionated exposure of
450 R given in three fractions of 100, 150 and 200 R at
10, 12 and 14 weeks of age. respectively; 85-90 R
min-1). Nine weeks after irradiation (a period of time
sufficient to ensure that irradiated spermatogonia will
be sampled) the males were mated to females and thenumbers of progeny born alive and those that survived
461

until day 1 and day 21 were recorded. The data show
that:(a) There is a reduction in litter size following
spermatogonial irradiation;(b) Based on the litter sizes in the progeny, the rate ofinduction of such effects can be estimated to lie between (2.0±1.4)1()-4/gamete/R to (3.0 ±2.3)1()-4/
gamete/R.
These values are in agreement with those calculated by
Taylor and Chapman [Tl3] in an earlier study with rats,(1.4 ± 0.8)1<>-4/gamete/R, and also with those in mice:
Luning's [Ll9] mouse data yield estimates of 1.8 1()-4
and 2.2 I ()-4/gamete/R based on litter size at birth andweaning, respectively. Estimates based on the same
traits from the mouse data of Lyon et al. (L20] are
1.4 lQ--4/gamete/R for both traits.
289. Caine and Lyon [C30] reported on the effects of
x-irradiation on reproductive capacity and dominantlethal induction in female guinea pigs and in the
Djungarian hamsters (Phodopus sungorus). The latter
species resembles the mouse in body size, is physiologically closer to the hamsters, has a relatively low
chromosome number (2n28) and is easily
maintained under laboratory conditions. Female
random-bred, albino guinea pigs and Djungarian
hamsters were irradiated with 4 Gy of x rays at 3-5months or 8-12 weeks of age, respectively (bilateral
irradiation, each side being exposed in turn; 0.5 Gy
min-1). The irradiated females were mated to males(guinea pigs: 4 females x 1 male; hamsters: pair-mating)
24 h after irradiation and left to reproduce for two
years, litters being expected at approximately 2-3
month intervals for guinea pigs and ~ week intervals
for the hamsters. Dominant lethal studies were carriedout only with the guinea pig at the first oestrus and at 3
months, while in both species the reproductive capacity
was assessed.
290. The following results were obtained:(a) In the guinea pig, the irradiated females produced
fewer offspring in the first litter, but the difference
from the controls was not significant;(b) The mean litter size of irradiated guinea pigs was
reduced in the first six months (2.9 versus 4.6 inthe controls), but this reduction was barely significant; in the 6-12 month interval and in theremainder of the period there were no differences;
there was no significant alteration in the overallmean number of litters per female during the
2-year period, although the irradiated females
produced a smaller mean number of offspringthan the controls (22.4 versus 31.2 in the controls);(c) In the guinea pig again, irradiation caused a significant increase in dominant lethals at the firstoestrus matings with a lower non-significant
induction at three months; the dominant lethal
yield at first oestrus matings was due primarily to
pre-implantation loss while at three months, postimplantation loss was higher; most of the postimplantation death occurred soon after implantation;(d) In the Djungarian hamster, irradiation produced adramatic sterilizing effect, i.e., a lowering of boththe total number of litters and litter size; only 12
out of the 48 females in the irradiated group werefertile and these produced only one litter each (incontrast to controls with a mean of 11.8 litters/
female) as a consequence of which the total reproductive capacity was drastically reduced (3.3
versus 43.3 offspring per female in the controls).
462

291. These data demonstrate that the female
Djungarian hamsters are at least as sensitive to the sterilizing effect of radiation as the mouse, and considerably
more sensitive than the Syrian hamster (Mesocricetus
auratus) in which some animals may remain fertile forthree months after a dose of 4 Gy [C31 J. The
Djungarian hamster thus represents another species forthe study of the differences in sensitivity of oocytes toirradiation.
292. In Mikamo's experiments [M49], mature female
Chinese hamsters were x-irradiated with 50, 100 or
200 R and mated to unirradiated males to assess theamount of dominant lethality in oocytes at the first,
third or fifth oestrous cycle after irradiation. The
uterine contents of pregnant females were examined at
18.5 days of gestation. There were a total of 436 females(80 controls, 88 for the 50 R group, 121 for the 100 R
group and 147 for the 200 R group). The results showed
that, with one possible exception. there was no statistically significant increase either in pre-implantationmortality (range: 6.5 to 8.5% in the different irradiation
series versus 6.4% in the controls) or in the frequency ofabnormal foetuses (range: 8.8 to 10.7% versus 10.8% in
the controls). In the third oestrous cycle after 100 R, thefrequency of abnormal foetuses was slightly higher(12.8%) and this was correlated with an increase inchromosomal abnormalities in oocytes of females
cytologically examined in parallel experiments (seeparagraph 378).
3.

Summary and conclusions

293. Further data on the radiation-induction of
dominant lethals and on the effects of radiation on
reproductive capacity have become available fromstudies with some experimental mammals. Male mice
were injected with 239Pu (0.19 and 0.37 MBq kg-I) andmated at weekly intervals to unirradiated females andthe amount of dominant lethality was assessed bydissecting the pregnant females at mid-pregnancy andscoring live and dead implants. It was found that the
weekly variation in the ratio of live implants to the total
number of implants did not show significant differences for the different weeks, but there was a doseeffect as shown by the differences between the 0.19 and0.37 MBq kg-I data (estimated gonadal doses of 0.021
and 0.042 Gy). The amount of dominant lethality
observed (mostly induced in meiotic and post-meiotic
germ cell stages) was consistent with a rate of 64 1Q--4
per gamete per 10-2 Gy.
294. In the gamma-ray experiments, the rates ofdominant lethality were nearly the same irrespective ofwhether the exposures were administered singly (in therange of 0.45 to 5.7 Gy) or as weekly doses of between
0.08 and 2.1 Gy (sampling of post-meiotic male germ
cell stages); for chronic exposures (at the rate of 3.36 10-2
Gy d-1 and 5.98 10-2 Gy d-1 with total accumulated
exposures of between 0.59 and 1.06 Gy and between
1.05 and 1.89 Gy), the rate of induction of dominantlethals is 5 1()-4 per gamete per 10-2 Gy which is
one-half of that after single or weekly exposures.
However, single gamma-ray exposures were more
efficient than weekly or chronic exposures in inducing
dominant lethality in pre-meiotic stages. The rates (pergamete per 10-2 Gy) are, respectively, 1.1 1()-4, 0.35 lQ--4
and 0.141()-4.
295. With fission neutron irradiation of male mice,
there were no significant differences in rates in post-meiotic cells between single exposures (in the range
from 0.1 to 1.6 Gy) or weekly exposures (in the range
from 0.008 to 0.13 Gy for a total of 6-24 weeks).
Furthermore, the effects of single or weekly neutron
exposures of pre-meiotic stages were not significantly
different.
296. In terms of relative biological effectiveness,
alpha-irradiation of post-meiotic stages is nearly as
efficient as fission neutrons; for pre-meiotic stages,
fission neutrons arc 19 times more effective thanchronic gamma-irradiation.
297. With low single doses of neutrons (2 to 40 J0-2
Gy) and of gamma rays (0.23 to 1.45 Gy) to males(sampling of germ cells during the first five weeks),
there were slight but measurable increases in postimplantation mortality.
298. Fourteen MeV neutrons (1.5 and 2.5 Gy) may be
between one and two times as effective as x rays ininducing dominant lethals in post-meiotic male germ
cell stages.
299. The frequency of dominant lethals induced inspermatids by acute x-irradiation (2 Gy) is 1.7 times
that induced by protracted (0.002 Gy min-1) gammairradiation. Pre-treatment of the males with caffeine
prior to irradiation did not affect the dominant lethal
yields with either kind of irradiation. Irradiation of
spermatids (3 Gy) with low dose rate (0.002 Gy min-1)
or high dose rate (0.6 Gy min-1) x or gamma rays
showed that the relative effectiveness of x- versus
gamma-irradiation was 1.9 at low and 1.6 at high dose
rates. There were no statistically significant effects ofdose rate on testes weight or sperm count in the x-ray
series, but there were significantly less severe effects on
both with protraction of the gamma-irradiation.
300. The extent to which oocytes in female mice arecapable of carrying out repair of genetic damage
induced in the males (sampling of mutagenized
spermatozoa) has been investigated by irradiating (ortreating with one of four chemicals) males of a given
strain and mating them to females of different strains
and assessing the amount of dominant lethality. It was
found that, while with x-irradiation, there were no
significant differences between the different femalestrains, with chemicals, particularly with isopropyl
methane sulphonate, the frequencies of dominantlethals were markedly different with certain strains offemales.
301. In one study with mice, a modified dominantlethal method was used to assess the extent to which
dominant lethals were expressed during the late stagesof gestation. The results (600 R of x rays; sampling of
spermatozoa) showed that radiation caused a significant increase in the number of late deaths. In experiments designed to examine x-ray induction of
dominant lethals in male germ cell stages of the mousewhich are expressed from cleavage stages to the early
trophoblast outgrowth stages, it was found that thestage at which the embryos die (early cleavage, latemorula, late blastocyst) varied depending on theradiation dose and the germ cell stages that were
sampled; for instance, with 4.5 Gy, embryos derived
from germ cells that were spermatids at the time ofirradiation showed developmental arrest primarily atthe 2-cell stage. With lower doses, however, (0.9 to 3.6
Gy) and with sampling of the same germ cell stages, thedominant lethals manifesting before and after

blastocyst formation were about equally distributed at
all cleavage stages. The overall pattern of stage sensitivity as observed in this study agrees well with what
has been known from conventional dominant lethal
studies.
302. When adult females were exposed to chronic
gamma-irradiation over a 35-day period (total dose: 5Gy). mated to males and the pregnant females analysed
for intra-uterine mortality of the embryos, it was foundthat the induced post-implantation mortality was rather
low (2.6 to 6.1%) in the different mating weeks: theinduced pre-implantation mortality varied over a range
from 0.3% to 18% in the different weeks. The increase indominant lethality can thus be accounted for primarily
by increase in pre-implantation losses.
303. When female mice were injected with 239pu or
chronically irradiated with gamma rays and then tested
for breeding performance, it was found that there wasan adverse effect with respect to the duration of fertility
and the number of offspring per litter, although theoverall mean litter sizes were not significantly Jess thanin the controls. In the gamma-ray series (0.1 and 0.2 Gy
d-1 for up to six 4-week periods), the percentage offertile females dropped to zero by the fifth and eighth
4-week periods (respectively in the 0.2 and 0.1 Gy d-tgroups). In the plutonium series, a similar drop wasnoticed after the twelfth and fifteenth 4-week periods,
respectively, in the 0.37 MBq and 0.19 MBq groups.
From these and other data, it has been estimated that
the RBE for the effects on reproduction attributed togerm cell killing is about 2.5 for alpha-particles relative
to chronic gamma rays.
304. When rats were given testicular exposures of 450
and 600 R and germ cells irradiated as spermatogonia
were sampled, there was a significant reduction in litter
size and this was consistent with a rate of induction ofsuch effects of between 2 and 3 1()-4/ gamete/R.
305. Irradiated (4 Gy of x rays) female guinea pigs
produced fewer offspring in the first litter and the meanlitter sizes were slightly reduced in the first six months:
from this time onwards up to two years, there was no
pronounced alteration in the overall mean number oflitters per female, but the irradiated females produced asmaller mean number of offspring than controls.
306. In the female guinea pig, irradiation caused asignificant increase in dominant lethals at the firstoestrus matings, one that was mainly due to an increasein pre-implantation losses. Post-implantation losses
were higher 3 months after irradiation.
307. In the female Djungarian hamster, x-irradiation(4 Gy) produced a marked sterilizing effect, i.e., alowering of both the total number of litters and litter
sizes.
308. In experiments involving irradiation of mature
female Chinese hamsters (50-200 R) it was found thatthe amount of dominant lethality in oocytes at the first,
third or fifth oestrus cycle matings was not significantly
increased, relative to controls, with one exception: inthe third oestrus cycle after 100 R. the frequency ofabnormal foetuses was slightly higher relative tocontrols and this was correlated with an increase inchromosomal abnormalities in oocytes of females
cytologically studied in parallel experiments.
463

B.

TRANSLOCATIONS
I.

depending on the exposure and exposure rate and thetestes were processed for cytological preparations.

Introduction

309. Since the publication of the 1977 report, somenew data have become available on the radiationinduction of translocations and other exchange typeaberrations in male and female germ cells of the mouseand in spermatogonia of the rhesus monkey. These data
pertain to the induction of reciprocal translocations inspermatogonia following irradiation of males (andanalysed cytogenetically in descendant spermatocytes),of chromatid aberrations in meiotic stages of male andin oocytes of female mice (also analysed cytologically),of heritable translocations in females (studied using
genetic techniques and subsequently verified using
cytological methods) and of reciprocal translocations insperrnatogonia of the rhesus monkeys (studied cytologically in descendant spermatocytes).

313. The data are presented in Table 21 and show thatthe yield of translocation decreases over the range of
100-0.003 R rnin-1 with no significant difference
between 0.001 and 0.003 R min-t. These data are very
similar to those of Pomerantzeva et al. [P22. P23] andSearle et al. [S53) discussed in the 1977 report andpermit the conclusion that there is no increase in translocation yield at very low exposure rates. The rate per R
at the high exposure rate of 100 R min-1 is about 16
times that at the lowest rate of 0.001 R min-1 when acorrection is made for the relative biological efficiencyof gamma rays relative to x rays. The finding of a lackof increase in the rate of translocation recovery at very
low exposure rates is also qualitatively in line with thatfrom specific locus experiments [R23, R24) discussed in
the 1977 report.

310. Ford et al. [Fl4] compiled most of the relevant
cytogenetic data that bear on the induction of reciprocal translocations in mouse spermatogonia (eight
different studies involving examination of a total ofover 70 OOO spermatocyte preparations of irradiatedmales and examination of spermatocyte preparations of
681 sons of irradiated fathers). In one of the two studies[S 113] involving cytogenetic analysis of spermatocytesof 531 sons of irradiated fathers (spermatozoa! irradiation), one male progeny heterozygous for an induced
reciprocal translocation was also a mosaic for a Robertsonian translocation: about half of the spermatocytes
examined contained a typical "Robertsonian trivalent"
which was replaced by two normal bivalents in theremainder.

314. In the work with plutonium alpha rays, gamma
rays and neutrons reported in the section on dominant
Jethals, Grahn et al. [G23] also studied the induction ofreciprocal translocations in spermatogonia. Testes
preparations were made from 8 to 60 weeks after
injection of plutonium and the spermatocytes at
metaphase I were screened for translocations. The
frequencies of translocation configurations observed
were such that when they were plotted against total
accumulated dose (minus the 13 days of meiosis
preceding metaphase I) no dose-effect relationship was
evident. However, there was a SU!!!!estive indication thata peak response may be obtained at 0.15-0.20 Gy andthis possibility is being tested at present.

311. Ford et al. point out that mosa1c1sm indicatesthat the Robertsonian translocation would have originated during embryonic development, possibly as earlyas the first cleavage division and that this was presumably a spontaneous event. Apart from this, there were
no instances in any of the other studies for theradiation-induction of Robertsonian translocations.
The authors point out that, although it is likely thatsome cases of Robertsonian translocations could havebeen misclassified as reciprocal ones on the basis ofmetaphase I configurations (and all the investigations
referred to in their paper were carried out before the Cbanding procedure was introduced), the number ofRobertsonian translocations so missed could have been
only very few. As they stated " ... it can be concluded
with confidence that if Robertsonian translocations are
induced by ionizing radiation at all, they are formed
with negligible frequency compared to reciprocal translocations".
2.

Reciprocal translocations in male germ cells of the
mouse

(a)

Spermatogonia

312. Brewen et al. [826] compared the yields of translocations obtained at low exposure rates of 60Co
gamma-irradiation in the range of 1-0.001 R min-1(range: 100-800 R; spermatogonial irradiation) withthose after x-irradiation at 100 R min-t. Adult CD1
male mice which were 8-10 weeks old at the start of theirradiations were used throughout the study with the
exception of a few animals that were 40 weeks oldwhich served as an aged control. The animals were
killed at different times after the end of the irradiations

464

315. In contrast, weekly doses of fission neutrons up
to total doses of 1.2 Gy produce a linear response witha slope of (6.8 ± 0.6)1Q-4 per 10-2 Gy for cells withtranslocations. The response to single doses of neutrons
was non-linear and was best fitted with a powerfunction with a coefficient of 0.79 ± 0.04. For gamma
rays, the weighted linear regression coefficients for theeffects of single weekly and chronic gamma irradiationsare (1.53 ± 0.074)1Q-4, (0.76 ± 0.077)1Q-4 and (0.175 ±0.017)1D-4, respectively. The decrease in effectivenesswith decreasing dose rate is consistent with earlier
studies of Searle et al. [S53]. The lowest coefficient fromthe chronic exposure data is almost identical to thevalues recorded by Searle [S53] and Pomerantzeva et al.
[P22, P23) for comparable low dose rate exposures.
316. In their other study discussed earlier, Grahn,
Frystak and Lee [G25] obtained suggestive evidence fortranslocation induction after single neutron doses of
0.025 to 0.40 Gy and 0.225 to 1.45 Gy of gamma rays.
The increases were small but significant at all doses
employed except at 10-2 Gy of neutrons.
317. In the same work reported in the section on
dominant lethals, Shevchenko et al. [S133) also
obtained cytogenetic data on the induction of reciprocal translocations in mouse spermatogonia by incorporated 14C. The frequencies were 0.34%. 0.84% and0.60% at the estimated absorbed doses of 0.22, 0.5 and1.01 Gy, respectively. Comparing the yields of translocations recorded in this study with those published in
the literature (chronic gamma irradiation experiments),
the authors concluded that the RBE value for 14C beta
rays is about 1.
318. In the study of Yusef [Y9] discussed in thesection on dominant lethals, translocations were also

scored in the spermatocytes (descended from irradiatedspermatogonia; 2 Gy of high dose rate x rays or 2 Gy of
60Co gamma rays at low dose rate) of males which had
been given 0.1 % caffeine in their drinking water foreight weeks. As expected, the frequencies of translocations were significantly lower in the gamma-irradiationgroup (2.8% versus 5.2% in the x-ray group). Caffeine
treatment did not have :rny measurable effect, but in the
gamma-ray group, the caffeine-treated males tended tohave a somewhat higher incidence of translocations,although the effect was non-significant. The frequency
of autosomal univalents was higher after acute x-irradiation than after gamma-irradiation and the univalentfrequency tended to be lower in the irradiated groups
that had received caffeine (2.9% versus 5.6%, x rays and1.7% versus 2.0%. gamma rays).
319. In the 1977 report, the work of Cattanach et al.
[C32) on the induction of translocations in mouse
spermatogonia by fractionated (unequal fractions)
x-ray exposures was discussed. In these experiments,
the yield of translocations depended on the size andsequence of the exposure fractions. Thus, when a1000 R exposure was administered as 100 R followed by
900 R 24 h later, the yield of translocations (22%) was
similar to that which can be obtained by extrapolationfrom lower exposures (assuming linearity) and also tothat after a 500 + 500 exposure, 24 h apart. However,when the 900 R exposure preceded the 100 R exposure,
the response was much lower (7.4%) yet still higher thanthat produced by a single 1000 R exposure (4.5%). The
same order of effectiveness was observed for the lengthof the sterile period.
320. From these results, the authors concluded that24 h after the initial exposure the surviving stem cells are
more sensitive than earlier, both to killing and to the
induction of translocations; and they are no longer
heterogeneous in their radiosensitivities so that
increasing yields of translocations may be obtainedwith increasing exposures. Evidence for this Joss ofheterogeneity came from the observation that numbersof spermatocytes with 0. 1. 2 ... translocations gave agood fit to a Poisson distribution in the 100 + 500 R,
100 + 700 R, and 100 + 900 R series, but often
showed an excess of cells with two or more translocations (suggesting heterogeneity with a more sensitive
sub-population) in other series [C33].
321. In further experiments aimed at studying theradiation-induced loss of heterogeneity of the spermatogonial stem cell response to the induction oftranslocations, Cattanach and Crocker [C33] obtained results at
two further exposure levels, namely at 600 and 800 R.
The main observation was that the yield of translocations was highest after fractionation (24 h interval)
when the treatment regime comprised the 100 R as the"conditioning" exposure followed by the larger"challenging" exposure. The results thus substantiate
the earlier observations [C32] and also support the 100+ 500 R data of van Buul and Leonard [B27] inshowing that the elevated response also occurs at lower
exposures. All these data are thus consistent with thethesis that the stem cell spermatogonia surviving aradiation exposure become sensitized to genetic
damage 24 h later and at this time, little of the original
heterogeneity in radiosensitivity typical of the unirradiated testis remains [C32, P24].
322. In another study, Cattanach et al. (C63] reported
that if the chemical mutagen triethylenemelamine(TEM) was given to male mice as a '"conditioning"

exposure, followed 24 hours later by 900 R of x rays,
then high translocation yields were obtained as with
100 + 500 R. TEM + 500 R 24 hours later gave a small
but non-significant increase above normal response to500 R. while TEM + 500 R four days later gave a subadditive yield (as did the reverse order treatment). as
had 100 + 500 R five days later in a previous study[C64]. The authors thought it unlikely that TEM and xrays would both synchronize the cell cycle of surviving
stem cell spermatogonia in a similar fashion.
323. Cattanach et al. [C63] therefore postulated thatthe common mediating cause was the depletion of thestem-cell population, probably by preferential killing ofcells actually in cycle [C65]. This might have "triggered"
the long cycling survivors from a static out-of-cycle
condition or Go phase which may be highly radioresistant [C65] into a more active and shorter cell cycle(see also [P24]). The authors consider that 24--48 hours
later, a very high proportion of these cells may havebeen synchronously brought into either a sensitive stageof the cell cycle proper or a sensitive longer lastingtransitional phase, before having begun a series of
rapid cell divisions to repopulate the germinal
epithelium. The sharply reduced translocation yields
with the fractionation intervals of3-16 days after 500 R
may have then typified the response of the rapidly
cycling cells, which seems similar to that found in theactively proliferating mouse testes [C65].
324. In an extension of their earlier study [B27], vanBuul and Leonard [B28] gave unequal fractionatedx-ray exposures to male mice (spermatogonial irradiation) to define the magnitude of the conditioning
exposure that would sensitize the As spermatogonia tothe challenging exposure 24 h later. In this work, a total
exposure of 1000 R was administered in the following
way: 100 + 900 R; 75 + 925 R; 50 + 950 Rand 25 +975 R. Appropriate single exposure controls were done
concurrently. The results showed, however, that when
the conditioning exposure is below 100 R, there was noenhancement of the translocation frequencies. The
frequencies recorded were the following: 25R: 0.4%; 50
R: 0.76%; 100 R: 1.3%: 1000 R: 2.5%; 25 + 975 R:
3.3%; 50 + 950 R: 5.0%; 75 + 925 R: 5.0% and 100 +900 R: 16.1 %. These results support the idea that
depletion of the stem-cell population is the importantcause in triggering survivors into the more active cycle
as has been postulated by Cattanach et al. [C63] because
at exposures below 100 R, stem-cell depletion would be
relatively slight though there would still be major
killing effects upon differentiating spermatogonia.
325. Van Buul et al. [B29, B69] studied the response offour different stocks of mice (with the Swiss
random-bred genetic background (Cpb(SE)S)) to the xray-induction of reciprocal translocations in theirspermatogonia. The stocks were the following:
(a)
(b)
(c)
(d)

Normal mice;Mice heterozygous for a reciprocal translocation
involving chromosomes 1 and 13;
Mice that were trisomic for the translocatedchromosome but with normal phenotypic
appearance:
Mice that were trisomic for the same translocatedchromosome, but characterized by severe underdevelopment, skull malformations and abnormal
growth of the upper and lower incisors ("teeth
trisomics").

326. In the first experiment (which involved the first
three stocks) the irradiation exposure was 3 Gy. The
465

frequencies of translocation recorded were: 8.8 ± 3.5%
(normal mice); 6.1 ± 1.9% (translocation heterozygotes) and 9.6 ± 2.6% (normal trisomic mice) showingthat while the normal and trisomic mice have similarsensitivities, the translocation heterozygote may have alower sensitivity. The latter observation has been
confirmed in experiments involving 2.5 and 5.0 + 5.0
Gy (24 h interval) in which it was found that the translocation heterozygotes had a lower sensitivfty thannormal mice (11.4% versus 19.7%, 700 cells scored ineach and 24.9% versus 33.8%, 800 cells scored in each).
In the second experiment (with a different radiation
set-up) in which the comparison was between normaland "teeth trisomic" mice after 3 Gy, the frequencies oftranslocations were 5.8 ± 2.3% in the normal mice and5.6 ± 2.2% in the latter showing no significant
difference.
327. In another study, van Buul [830) examined theradiosensitivity of male mice descended from a mouse
population which had been exposed to 2 Gy ofwhole-body x-irradiation every generation (at 26 ± 2days after weaning) for 69 generations. Non-irradiatedmale descendants of the 69th generation were obtained
from Spalding and at the age of 12 weeks were given awhole-body 400 R x-ray exposure. Control mice of thesame strain without radiation history received the same
x-ray exposure. After 10-13 weeks, the mice were killed
and meiotic chromosome preparations were made. The
results showed that the frequencies were the same inboth the groups (8.7 and 8.8%) as were the nature of thetranslocation configurations. The ratio of ring versus
chain configurations was somewhat higher in the groupwith radiation history (1.5) relative to controls (0.9).
However, the mean chiasma frequencies were similar inboth groups. Van Buul concluded that the radiation
history did not alter the radiosensitivy of the males tothe x-ray induction of reciprocal translocations in theirspermatogonia. These results are in agreement withthose reported by Sheridan [S60, S61] in the mouse andby Sankaranarayanan [S62] in Drosophila.

(b)

Meiotic stages

328. Adler [A23] investigated the sensitivity pattern ofdifferent stages of meiotic prophase of spermatocytes
for gamma-ray-induced chromatid aberrations. Ten- to
twelve-week-old hybrid male mice (C3H x 101) were
irradiated with 300 R of gamma rays (60 R min-1) andprimary spermatocytcs were sampled on day 1(diplotene), 5 (mid-pachytene), 9 (zygotene) and 11(leptotene). The results show that:(a) Zygotene is the most sensitive stage for the
induction of rearrangements, the rank order being
zygotene > pachytene > diplotene > leptotene;(b) The frequencies of fragments as well as those of
autosomal and sex-chromosomal univalents did
not vary significantly between the different stages;(c) At zygotene, the exposure-frequency relationshipfor chromatid interchanges was consistent with amore-than-linear increase with exposure (Y = aD
+ bO)) and this was also true for fragments.
329. These results are at variance with some others
published in the literature. For instance, Tsuchida et al.
[T14] found that with 300 R of gamma-irradiation at alower exposure rate (29 R min-1), diplotene andpachytene were equally sensitive to the induction ofrearrangements. but the pachytene stage was lesssensitive than diplotene (10.5% versus 16.0%) for the
induction of fragments and breaks outnumbered466

rearrangements. The picture that emerges from thework of Walker [W19] shows that radiosensitivity
progressively increases during prophase, diakinesis
being the most sensitive (this stage was not investigatedin the work of Adler) with respect to both rearrangements and fragments. Her work also showed that acutex-irradiation (0.72 Gy min-1) and protracted gamma
irradiation (2 Gy: 1 1()-4 Gy min-1 over 13 d) wereequally effective in inducing structural aberrations if
the mean frequencies were weighted for each stage withrespect to their time span.

(c) Relationship helll'een partial sterility of translocation
heterozygotes and the length of the translocated segment
330. It has long been known that the degree of partial
sterility of male translocation heterozygotes may varyfrom substantially lower than 50% to substantiallyhigher than 50% of normal fertility. The former ismainly dependent upon the proportions in whichbalanced and unbalanced gametes are represented in
the ejaculate, which in turn is a function of meiotic
segregation. On the other hand, the formation ofmultivalent associations observed in meiotic preparations is assumed to be dependent upon the size of thetranslocated chromosome segment, which influences
the possibility of chiasma formation between the translocated segment and its homologous segment in the
intact chromosome.
331. Generoso et al. [G41 J tested the possibility thatthe degree of partial sterility of a male translocation
heterozygote is correlated with the frequency at which
multivalents are observed in the diakinesis-metaphase I
spermatocytes. The index of partial sterility used is thepercentage of dead implants in females that have beenmated to translocation heterozygotes. Only males thatcarried single reciprocal translocations were includedin the analysis (45 males identified from analysis of 25
metaphase I spermatocytes). The percentage of dead
implants was based upon 6 pregnancies from each of 41
males, 9 pregnancies from each of 2 males. 5
pregnancies from 1 male and 4 pregnancies fromanother. The percentage of multivalents was determined from 25 cells scored for each male.
332. The results demonstrate a significant positive
correlation between the degree of partial sterility andthe frequency of multivalents in meiotic preparations;this means that the length of the translocated segment
has some influence on the proportion of unbalanced
gametes in the ejaculate. When the translocatedsegment is short, the probability of scoring a cell withmultivalent is reduced, but the proportion of sperm in
the ejaculate with balanced translocation is increased.
The reverse is true when the translocated segment islong. What this means is that cytological scoring may
be biased in favour of translocations with translocatedsegments which have a lower probability of transmission. However, it should also be remembered that if
the translocated segment is short, there is more chanceof post-natal survival of unbalanced zygotes.
3.

Heritable reciprocal translocations in female mice

333. In the 1977 report, the results of Searle andBeechey [S63) and of Krishna and Generoso [K 18) on
the x-ray induction of heritable reciprocal translocations in female mice were presented. In the study ofSearle and Beechey, none out of 386 sons of females

given 3 Gy of x rays showed evidence of translocation
heterozygosity. although there were 3 confirmed translocations in 294 female progeny. With the sameradiation exposure (300 R), Krishna and Generoso
found that 4 out of 800 male progeny were partiallysterile (and subsequently confirmed cytologically astranslocation carriers) and 2 were sterile (and werecytologically normal).
334. The testing of the female progeny from the same
experiment has now been completed [K 19]. The results
show that out of 935 sons tested, 4 are partially sterile(and have been shown to be translocation heterozygotes
through cytological analysis), 2 fully sterile (cytologically normal): in addition. 1 daughter with an XO
constitution is also semi-sterile. Besides, 7 XO females
and 1 XO/XX mosaic have been recovered. These
results demonstrate that reciprocal translocations canbe recovered in both male and female progeny ofirradiated females. If one restricts attention to semisterile males alone. a total of 8 translocations have been
recovered among 1735 progeny (males + females)
which gives a frequency of 0.46% or a rate of 0.15 10-4
per R per gamete, about one-half of that after spermatogonial x irradiation [Ul]. The control rate in the workof these authors is 1 in 4392 [040] such that correction
for controls will not affect the rate appreciably.

4. Chromatid-interchanges and other aberrations
in mouse and Chinese hamster oocytes: in vitro studies
335. Other studies on aberration induction in oocytes
have used the technique of culturing oocytes in vitro. In
these, at different times after irradiation, the female
mice are killed. the oocytes with germinal vesicles
recovered and cultured in vitro and then screened foraberrations in metaphase I. The general findings were
that:(a) The frequency of chromosomally abnormal
oocytes increased with time after irradiation;(b) The variation in the yield of aberrations as afunction of time between irradiation and ovulationagreed well with the variation in sensitivity todominant lethal induction over the same period;(c) From the frequency of aberrations observed in theoocytes, it was possible to predict the frequency oftransmissible reciprocal translocations. Studies ofthis kind reported in the 1977 report included
among others, those of Brewen et al. [831] and of
Searle and Beechey [S63].
336. Since then, the results of three studies on thesame general problem have been published. Caine and
Lyon [C34] conducted experiments to compare theeffects of x rays and some chemical mutagens on theyields of aberrations. The x-ray dose was 4 Gy and wasgiven to mature females that were 8-12 weeks old. The
oocytes were recovered after one and three weeks,
cultured in vitro and processed for examination ofaberrations. The results confirm the earlier findings.
namely, that the yield of aberrations is significantly
higher in week 3 than in week 1 and this is true of the
proportion of abnormal cells in the two sampling times(59.5% versus 41.5%). The aberrations studied included
chromatid gaps and breaks. isochromatid gaps.
fragments and rearrangements. Fragments, usuallyisochromatid, were the most common aberration typeand more aberrations were found in week 3 (all four
categories) with the frequency of rearrangements being
more than twice that in the first week (22% versus 8.5%).

337. Brewen and Payne [B32] conducted a study toanalyse in detail the radiosensitivity of mouse oocytes
from the standpoint of the induction of aberrations.
Four x-ray exposures (50, 100, 200 and 300 R) wereused. Eight- to ten-week-old female mice of the CD1strain were irradiated and the oocytes were collected atvarious intervals ranging from 1.5 days to 28.5 days.
The types of aberrations scored were chromatid
deletions, isochromatid deletions and chromatid interchanges. The results showed that, as expected, the sensitivity was different depending on the degree ofmaturation of the oocytes: the least sensitive oocytes
were those that were 0.5-1.5 days from ovulation(probably corresponding to stages 7 and 8); the sensitivity gradually increased with longer intervals between
irradiation and ovulation until a stage of peak sensitivity was reached at 9.5 days. From this time. theaberration yield remained relatively constant until thefemales became functionally sterile.14
338. The data were analysed by the authors in three
ways. Firstly. the data from all time intervals at eachexposure were pooled. Secondly, the data from the leastsensitive time intervals at each exposure were pooled.
Thirdly, the data from the period of uniform sensitivity
at each exposure were pooled. Exposure-frequency
regression analyses were done on these pooled data andthe best fits were to the models Y = a + bD + cD2 andY = a + cD2 for both deletions and interchanges (theterms a, b and c correspon~ to the coefficients of the
spontaneous. one-track and two-track terms, respectively). These analyses have thus demonstrated that theaberrations under consideration result from a predominantly two-track process. The data on which thesecalculations were made are summarized in Table 22.
339. Brewen. Payne and Adler [B33] carried out astudy to examine the induction of chromosome aberrations in mouse dictyate oocytes after fractionated x-ray
as well as after chronic 60Co gamma-ray exposuresusing procedures similar to those employed in theirearlier work [831). In the first series, a total exposure of
400 R of x-rays was split into two fractions separated
by time intervals of 90, 135, 180 and 1440 min. In thesecond one, the same total exposure was administeredin unequal fractions (100 + 300 R or 300 + 100 R)
separated by 90, 135 and 180 minutes. In the third
series. chronic gamma-ray exposure was given tofemale mice over an eight-day period, 8-16 days prior
to ovulation and the exposures were 117, 240, 348 and
483 R. Appropriate single exposure controls wereconcurrently run. The frequencies of interchanges anddeletions were determined in metaphase I oocytes.
340. Considering first the results of series I, it was
found that with 90- and 135-minute intervals between
fractions, the yields of interchanges did not significantly deviate from those expected on the basis of interaction of chromosome breaks produced by the two
fractions (the yield with the 90-minute fractionatedinterval was identical to that after the single exposure;with the 135-minute interval, it was lower). With
intervals of either 180 min or 24 h, the observed
frequencies of interchanges were similar but lower thanthose with shorter intervals between the fractions and
14 The authors have defined functional sterility as theinability to super-ovulate a sufficient number of oocytes tomake slides. For instance, after 300 R, only about 35 oocytcs
were obtained from 100 females at the 28.5-day interval. Thisdegree of oocyte killing makes cytogenetic studies difficult,but does not preclude the possibility of some females being
capable of producing a few offspring.

467

were not significantly different from the expectation
based on additivity. With deletions, the frequency wasconsistent with interaction with the shortest interval (90minutes) but not at other intervals.
341. The results of the second series of experiments
indicate that there was no difference in aberration yieldand thus in the rejoining time, irrespective of whether
the first fraction was JOO or 300 R. For interchanges for
instance. the frequencies were the following: 100 + 300
R, 90 min: (74.7 ± 5.0)%; 300 + JOOR: (62.4 ± 7.1)%;
JOO + 300 R. 135 min: (62.8 ± 5.6)%; 300 + 100 R:(61.5 ± 5.1)%; JOO + 300 R, 180 min: (52.9 ± 4.3)%;
300 + JOO R: (52.5 ± 4.3)%. The authors consider thatthese data " ... argue strongly that the mouse oocyte's
repair systems, al least for chromosome aberration
formation, are not drastically altered by the magnitudeof the x-ray dose, and that this repair occurs within
hours and not days or weeks".
342. The data from the chronic gamma irradiation
series show that the frequencies are much lower thanafter acute irradiation and this is true for both interchanges and deletions; and the frequencies observed
are consistent with a linear increase with exposures.
These data demonstrate that when the exposure rate is
reduced from 100 R min-1 (x rays) to 0.04 R min-1(gamma rays), the yield of exchanges is reduced to onetenth at a total exposure of 478 R. The magnitude of
reduction in the yield observed in this study is lower
than that observed in specific locus work involving
maturing oocytes. The combined data from thefractionation and low exposure rate exposures led theauthors to conclude that the exposure-frequency
relationships for both exchanges and deletions inducedby x-irradiation are due to the involvement of two-track
processes.
343. In the Chinese hamster, Mikamo [M49)
conducted a study to assess the chromosomal radiosensitivity of the oocyte stages sampled from x-irradiated
5-month-old mature females. Oocytes sampled fromfemales irradiated at 85, 59, 35 and 19 hours before
ovulation (and analysed at metaphase II) manifest a
relatively low level of sensitivity to the induction ofchromosome aberrations (mainly chromatid breaks
from 0.3 to 4.1 %). From 17 hours before ovulation, thesensitivity begins to rise (10% breaks) reaching a peak at
11 hours before ovulation (43.3%): the stage of peaksensitivity corresponds to diakinesis just prior to theonset of prometaphase I. Prometaphase I andmetaphase I stages (9 and 7 hours before ovulati?n)retain a relatively high level of sensitivity (aberration
frequencies of 31.4 and 25.3%) although this is not ashigh as diakinesis. The exposure-frequency relationships for chromatid breaks at the most sensitive
diakinesis stage appears consistent with a greater thanlinear increase in yield with increasing exposures(50-200 R range).

5.

Reciprocal translocations in spermatogonia of therhesus monkey and comparison with results fromother mammalian species

344. In the discussion of the data on the induction ofreciprocal translocations in the spe.rmatogonJa of therhesus monkey in the 1977 report, 1t was pomted out
that:(a) The frequencies in the rhesus monkey are much
lower than in man, marmoset and the mouse:
468

(b)
(c)

Peak yields of translocations are obtained ataround 1-2 Gy in the monkey, levels that are much
lower than in the mouse:
There are significant differences in the response
between the different animals even at the same
dose level and in the frequencies recorded by Lyon
et al. [L23] on the one hand and by van Buul [834)on the other.

345. Van Buul [835, B36] has now collected more dataon translocation induction in the spcrmatogonia of therhesus monkey and these arc presented in Table 23 (thetranslocations were scored in C-banded preparations).
It can be seen that:
(a)

(b)
(c)

The spontaneous frequency of translocations in
the rhesus monkey is low and comparable to thatrecorded for other mammals studied so far in thisrespect such as the mouse, marmoset, rabbit,
guinea pig and golden hamster;
The dose-response curve is humped with amaximum around 1 Gy and a humped curve has
been found for all mammalian species studied;
The chiasma frequencies in the rhesus monkey aremuch higher than in the mouse, rabbit, golden
hamster, etc., and consequently the ratio of ringversus chain configurations is much higher in therhesus monkey than in other species.

346. Van Buul [836) fitted the translocation data tolinear and linear-quadratic equations (0, 0.5 and 1 Gydata) and found that these gave a good fit to the linear
model Y = a + bD and the fitted values of a and bare,respectively, 0.0233 and 0.0086. A comparison of thevalues of the slopes for the data of the rhesus monkey
and those of other species (mouse, rabbit, guinea pig,
marmoset and man) show that the value for the monkey
is significantly lower than that of other species except
the guinea pig (see also [B68)). These comparisons are
summarized in Table 24.
347. In a cytogenetic study, Benova et al. [B79)compared the sensitivities of the spermatogonia of themouse, rabbit, Syrian hamster and the rat to the
gamma-ray induction of reciprocal transloeations. The
doses were in the range of 0.5 to 5 Gy and the dose rate
was either 1.23 Gy min-1 or lQ-4 Gy min-1. It was foundthat for exposures given at the high dose rate, thesequence (in decreasing order of radiosensitivity) was
the following: rat, rabbit, mouse and the Syrian
hamster. For low dose rate exposure, the sequence was:rabbit, rat, Syrian hamster and the mouse.
6.

Summary and conclusions

348. Reciprocal translocations are the predominant
kind of structural aberrations induced by ionizing
radiation in mouse spermatogonia. An examination of
all the relevant cytogenetic results that bear on theradiation-induction of translocations in mouse spermatogonia support the thesis that, if Robertsonian translocations are induced, they are formed with a negligible
frequency relative to reciprocal translocations.
349. In a cytogenetic study, a comparison was madeof the yields of reciprocal translocations after spermatogonial irradiation of mice at different expo~ures. a~d athigh and low dose rates (x- and gamma-Jfrad1at1on).
The results showed that the yield per unit dose
decreases over the range of exposure rates from 100 to
0.003 R min-1 (a maximum of 16-fold difference) withno further decrease at still lower exposure rates. Theseresults support those from earlier studies discussed in
the 1977 report.
350. With plutonium alpha-ray irradiation of mouse
spermatogonia, there are indications that the peak yieldof reciprocal translocations may be obtained at doses ofbetween 0.15 and 0.2 Gy. Caffeine treatment of malemice prior to irradiation (spermatogonial x- or gammairradiation) does not affect the yield of translocations.
351. A number of additional experiments (subsequent
to those reported in the 1977 report) involving irradiation of mouse spermatogonia with unequally fractionated x-ray exposures (100 + 900 R, 100 + 500 R
etc., in this or reverse order with a 24-hour interval
between the fractions) have been completed. The yieldof translocations was found (as has been the case inearlier studies) to depend on the size and sequence ofthe exposure fractions. With a small fraction precedinga large one, the yield is high and is equal to that linearly
extrapolated from lower exposures. With the reversed
sequence of exposures, the yield is low, but higher thanthat after a single acute exposure. These observations
have been interpreted on the assumption that 24 hours
after the first fraction, the surviving stem cells are in the
more sensitive stage than before, both to killing and totranslocation induction and that they are less heterogeneous in their radiosensitivities at the time theyreceive the second fraction (the degree of synchrony isdependent on the magnitude of the first fraction). In
other fractionation experiments involving unequal
x-ray exposures (100 + 900 R, 40 + 950 R, 25 + 950 R
and the single exposures) it was found that when theconditioning exposure was below 100 R, there was noenhancement of translocation yields. These results
support the idea that depletion of the stem-cell
population is the important factor in triggeringsurvivors into the more active cycle and that at
exposures below 100 R, stem-cell depletion would be
relatively slight.
352. Heterozygosity for a specific reciprocal translocation involving chromosomes 1 and 13 in miceappears to decrease the radiosensitivity (relative tonormal mice) for the x-ray induction of reciprocaltranslocations in their spermatogonia. But tertiary
trisomic mice (trisomic for the same translocatedchromosome) however, do not differ in radiosensitivity
from normal mice, with respect to the same end-point.
353. When male mice descended from a populationthat had a previous radiation history (for 69 generations; exposed to 2 Gy per generation at 26 days after
weaning) were tested for their radiosensitivity (translocation induction in spermatogonia) and compared with
non-irradiated descendants, no differences could bediscerned.
354. A study has been conducted to examine whether
reciprocal translocations induced in mouse spermatogonia are subject to selection between the stage at
which they are induced and the spermatocyte stage at
which they are scored. The results are consistent withthe view that there is probably no selection against
spermatogonia carrying translocations in the exposure
range from 50 to 300 R.
355. There are results which document the premisethat in male mice which are heterozygous for a reciprocal translocation, there is a significant positive correlation between the degree of partial sterility of thesemales and the frequency of multivalents in meiotic
preparations.

356. The completed studies on the x-ray induction ofheritable translocations in female mice demonstratethat reciprocal translocations can be recovered in bothmale and female progeny of irradiated females and thatthe rate of 0.15 1~/R/gamete is about one-half of thatafter irradiation of spermatogonia.
357. Subsequent to the publication of the 1977 report,
further studies on x-ray induction of aberrations infemale mice (using the technique of culturing theirradiated oocytes in vitro) have been conducted. The
results obtained confirm those discussed in the 1977
report in showing that the frequency of chromosome
aberrations in oocytes recovered three weeks after
irradiation were significantly higher than those inoocytes recovered in week 1. In another investigation, it
was found that the least sensitive oocytes were thosethat were 0.5-1.5 days from ovulation and that thesensitivity gradually increased, reaching a peak around9.5 days from ovulation; from this time onwards, theaberration yield remained relatively constant until thefemales became functionally sterile.
358. Again in studies using in vitro culturing of
irradiated mouse oocytes, when the x-ray exposures
were fractionated with intervals of between 90 and 180
minutes and of 24 hours between the fractions, it was
found that with 90 and 135 minute intervals. the yields
of interchanges did not deviate from those expected on
the basis of interaction of chromosome breaks
produced by the two fractions; with intervals of either
180 minutes or 24 hours, the yields of interchanges wereconsistent with the additivity expectation. With
deletions, the frequency was consistent with interaction
with the shortest interval (90 min), but not at otherintervals. Similar studies with chronic gamma-irradiation of female mice and scoring for aberrations intheir oocytes in vitro demonstrated a pronounced dose
rate effect: at an exposure of 478 R, the yield ofchromatid interchanges was only one-tenth after
chronic than after acute exposures.
359. In the Chinese hamster, oocytes sampled fromfemales irradiated 11 hours before ovulation (andanalysed at metaphase II) manifest the highest level ofradiosensitivity to the induction of chromatid breaks
relative to other stages. The stage of peak sensitivity
corresponds to diakinesis prior to the onset of prometaphase. In this stage, the frequencies of chromatid breakincrease faster than linearly with an increase in x-ray
exposures.
360. More extensive data on the induction of reciprocal translocations in the rhesus monkey spermatogonia have now become available. These confirm theconclusion reached in the 1977 report in showing thatthe rhesus monkey is much less radiosensitive thanmost of the mammalian species studied in this respect.
The peak yield is obtained at around 1 Gy.
C.

LOSS OR ADDITION OF CHROMOSOMES:NON-DISJUNCTION
1.

Introduction

361. The 1977 report considered the importance ofexperimental models to study non-disjunction together
with the data that were then available in the mouse,mouse-tobacco mouse hybrids and in the northern field
vole. Microtus oeconomus. In this section, the information that has accumulated since then will be469

discussed and placed in perspective with the earlier
work that has been done in this area. Useful reviews on
this subject with particular reference to the mouse !R25]
and to experimental mammals in general (H39, H40]
have been published.
2.

l\tcthods to study aneuploidy362. The methods that have so far been used can bebroadly divided into cytogenetic and genetic ones. The
cytogenetic methods, which are currently in extensive
use in several laboratories, involve chromosome
analysis of second meiotic metaphase in oocytes [H4 I,
R26, R27, UlO, Ul I) or spermatocytes !842, 08, S67):
pre-implantation embryos at the first cleavage stage[015, Fl5, Fl6, K20, M45] or morulae and blastocysts[Fl7, G30, Y4]: post-implantation embryos [Fl7, S68,
Tl7, Y4, Y5, Y6]: and newborn offspring (in mice)[G31].
363. Methods for chromosome preparations fromoocytes and from pre-implantation cleavage stages
involve modifications of Tarkowski's air-drying
technique [Tl8]. The technique of Evans et al. [EIOJ for
early post-implantation embryos has also been
modified and "banding techniques" have been
employed for a better identification of the chromosomes. Chromosomes from spermatocytes at metaphase
I I are usually prepared according to the method ofEvans et al. [Ell]. All these methods make use of direct
chromosome analysis to assess the amount ofaneuploidy in male or female germ cells or in embryos
at various developmental stages.
364. Some of the genetic methods, particularly those
aimed at studying sex-chromosomal non-disjunction
have been in use since the early 1960s [K2 l, R25, R28,
R29, R30) and involve studying the segregation of sexlinked marker genes in genetic crosses of appropriate
stocks. The genetic method described by Lyon et al.
[L30] in 1976 using Robertsonian translocations has not
yet been employed in any further published study,neither have other possible methods that would use
marked autosomes [R25].
3.

Spontaneous incidence of aneuploidy

365. Data on the spontaneous incidence of somenumerical chromosome anomalies of interest indifferent mammalian species are summarized in Tables
25 and 26. It can be seen that in most species, theincidence of aneuploidy in early embryos is rather low
in contrast to the situation obtained in humans. Not
mentioned in the tables is the finding that the incidenceof aneuploidy in the first cleavage stages of the embryos
varies between different strains of mice and is generally
higher when fertilization is effected in vitro than in vivo
[F15].

4. The mouse366. Chandley and Speed [C35) and Speed andChandley [Sl 14] have recently reported their results on
x-ray-induced non-disjunction in male and female
mice. In the male series, random-bred Q strain adultmice were irradiated with 1 Gy of x rays and mated tofemales live weeks after irradiation (to sample spermatocytes) or seven weeks after irradiation (to sample
spermatogonia). Appropriate unirradiated controls
were also run. Pregnant females from week 5 and week470

7 and control matings were killed at 9-10 days ofgestation and chromosome preparations made from all
viable foetuses or their membranes. The data to be
discussed below are from the paper of Speed andChandley [St 14) since the earlier paper [C35] was apreliminary report.
367. In the above investigation. the overall frequency
of abnormalities in the controls was 1.1% (6/571) andincluded 2 trisomics (41,XXY), 1 triploid (60,XXY) and3 mosaics (39/40); the frequency of trisomies alone is
0.35%. In week 5 of the irradiated series, the frequency
of abnormalities was 2.0% (20/1005) and included 2
monosomies (39,X), I trisomy (41,XY,+ 16), 1 tripletrisomy (43,XXY, + 10. + I 7), 5 triploids, 2 tetraploids, 8mosaics and 1 with miscellaneous aberration(40.XY,lq + ). In week 7, the frequency of chromosomally abnormal embryos was slightly higher being,
2.8% (20/688: 2 monosomies, 7 trisomies, 8 mosaics, 1
triploid and 2 tetraploids). The frequencies of trisomies
alone were, respectively, 0.20% (2/1005) and 1.0%
(7/688) in weeks 5 and 7 and were not significantly
different from the control frequency of 0.35%.
368. In the female series, there were three irradiatedgroups (6-8 week old females irradiated with 5 10-2 Gy;
9 month old females irradiated with the same dose andmated: and 6-8 week old mice irradiated with the same
dose and mated when 9 months old) and two controls(young and aged). Techniques for making chromosome
preparations were the same as those mentioned earlier.
369. When young females were irradiated, thefrequency of chromosomally abnormal embryos was
1.5% (2/129; I trisomy and I mosaic) and not significantly higher than in controls (1.1%; 6/571; same asgiven in paragraph 367). When young females were
irradiated, aged and then mated, the frequency was
2.1% (3/145: 1 monosomy, 1 trisomy and 1 mosaic): thecorresponding frequency for irradiation of aged
females was 3.6% (6/168: 3 trisomies, 3 triploids). The
frequency of chromosomally abnormal embryos in theaged female control group was also 3.6% (6/168; 1
monosomy, 1 trisomy, 2 mosaics, 1 triploid and 1
tetraploid). Thus, apart from a general increase in thefrequency of chromosomally abnormal embryos withan increase in maternal age, there is no measurable
effect due to irradiation at this dose level.
370. Max [M63] irradiated virgin female mice (froman inbred CDA strain) of 6, 15 and 46 weeks of age(groups 1, 2 and 3, respectively) with 2, 4, 8 or 16 R of xrays and mated them to young males of the same strain
when the irradiated mice were, respectively 16 or 32-35
weeks old (groups 1 and 2). Group 3 mice were matedsoon after irradiation. The foetuses were examined forchromosomal abnormalities, particularly aneuploidy.
There were concurrent controls. In the controls (all age
groups pooled), there were 2 trisomic and 2 triploidembryos out of 213 screened; the former were found irigroup 3 controls {2/27) while the latter were in group 2{2/78). In the irradiated series (all radiation groups)
there were I trisomic and 6 triploid embryos among 642
embryos; the single trisomic was found in group 2(1/289) and the triploids were in groups I (4/307) andin group 2 (2/289). Thus in these experiments, while
there is some suggestive evidence for an increase inchromosome abnormalities with increasing maternalage, no radiation effects could be demonstrated.
371. In the experiments of Strausmanis [S68] virgin
inbred C57DL females aged eleven months wereirradiated with 4, 8 or 16 R of x rays and placed withyoung untreated males of the same strain. five days
after irradiation. The pregnant females were killed 10days after vaginal plugs were observed and the conceptuses processed· for chromosome analysis. Aneuploidembryos classified as alive (heart beats observed while
dissecting) were 1 monosomic in the control group (outof 496 embryos) and 2 trisomics in the irradiatedgroups together (out of 568 embryos). The number ofaneuploid embryos classified as dead was 4 trisomics inthe control and 3 trisomics in the irradiated groups.
These data show that trisomic embryos are notuncommon in the mouse but die after implantation. In
any case there is no evidence for an increased
frequency of chromosome abnormalities in embryos ofaged female mice x-irradiated before mating as
compared to non-irradiated ones.
372. In the study of Hansmann et al. [H39, H40]
female mice of the NMRI/Han strain (8-12 weeks old)
were x-irradiated with 20 R or 200 R and mated tounirradiated males. Cytological preparations of
foetuses were carried out 9.5 days after detection ofvaginal plugs on the morning after irradiation. The
results showed no evidence of aneuploidy among 90
karyotyped control foetuses and among 95 embryos inthe 20 R series. However, one embryo out of the 22
karyotypes in the 200 R group was monosomic(chromosome 19) and another trisomic (chromosome17) and these findings were confirmed in all
metaphases examined after banding.
373. In another experiment, Hansmann [H39] andHansmann et al. [H42] irradiated 8-12 week old malemice with 20 or 200 R and mated them from day 2 today 36 after irradiation to unirradiated females of thesame age and strain. Foetal preparations were made on
day 9.5 post coitum. Out of 211 karyotyped foetuses incontrols, there were no aneuploids. In the 20 R series,
there were 3 aneuploids among a total of 216 foetuses
analysed (1.4 %) and in the 200 R series, there were 7
aneuploids among 385 foetuses analysed (1.8%). The
genetic constitutions were (with the origin in terms ofthe day of mating given in parentheses): 20 R:
41,XX,+11 (21); 41,XY,+2 (21) and 41,XX,+11 (31);200 R: 39,XO (4); 39,XY,-8 {5); 41,XX.+14 (7);41,XY, + 13 (16); 39,XO (25); 41,XYY (28):40.XO, + 13 (32). It is worthy of note that the inductionof aneuploidy is not significantly enhanced by thehigher exposure relative to the lower one. Irradiation
did not seem to enhance the incidence of polyploidy inthis study.

result from breakage-related chromosome loss as well
as from non-disjunction). Irradiated (200 R; x rays; 1
day before mating) or control females ranged in age
from 2.5 to 12 months at conception. Over 13 OOO
offspring have been scored with only one case ofmaternal trisomy (XMXMY /XMY mosaic) derived froma 12-month old irradiated female and one of paternal
trisomy (XMXPY), and no clear-cut differences in either
oxr or XMO frequencies with age.
5.

Other species

376. Although the Chinese and Syrian hamsters havebeen used for the study of oocytes and pre- and postimplantation embryos in recent years [843, H43, H44],
radiation data are very scanty. The unpublished observations of Hansmann quoted in his paper [H39] showthat following x-irradiation of female Chinese hamsters
and examination of metaphase II oocytes there is not asingle case of aneuploid oocytes either in the group
irradiated with 20 R or 200 R (147 and 131 oocytes,
respectively, were examined) or in the control group(121 oocytes).
377. In the Chinese hamster study of Mikamo [M49]discussed earlier, chromosome analyses were also
carried out (at metaphase II) in oocytes of 5-month-old
virgin females that had received 50, 100 or 200 R of xirradiation; of 16-19 month old females irradiated with
50 R. In the first series, in each of the first, third andfifth cycles after irradiation, unfertilized eggs werecollected and processed for chromosome analysis atmeta phase II; in the second series the oocytes collected
were those in the first cycle after irradiation.
378. In the first series, 8197 oocytes from 1200 females
were chromosomally analysed (1747 eggs from 254
control animals, 1812 oocytes from 309 females in the
50 R group, 2300 oocytes from 336 females in the 100 R
group and 2338 oocytes from 301 females in the 200 R
group). The data showed no significant increase in thefrequency of aneuploid eggs except in the 200 R, firstcycle group where there was a slight but significant
increase in the frequency of aneuploid eggs (3.4 versus
2.1% in the controls). With respect to structural abnormalities, again there were no significant increases
except in one group: in the third cycle eggs of the 100 R
group, the frequency of these anomalies was 1.1%
versus 0.2% in the controls (see also subsection II.A.2).
The author has no explanation for the statisticallysignificant increase in these two particular samples.

374. In 6 of the 10 observed aneuploid foetuses, themal-segregation could be allocated to meiosis I or II;
the other 4 foetuses. however. were derived from sperm
irradiated in the vas deferens (39,XO and 39,XY,-8) orthe' epididymis (41,XX. + 14) or irradiated as midspermatids (41.XY,+ 13). A chromosome loss mostprobably may explain the XO karyotype. Mitotic nondisjunction during early cleavage stages could lead tothe two trisomic foetuses (trisomy 13 and trisomy 14)
generated 7 and 16 days after irradiation [H42].

379. In the second series (with aged females irradiatedwith 50 R), there was a demonstrable effect of maternal
age with respect to the production of spontaneous
aneuploids (4.1% in the aged controls versus 2.1% in theyoung controls of the first series), but no effect ofirradiation was detected in the treated group (4.0%).
With respect to structural aberrations, there was no
measurable effect of either maternal age or irradiation(0.2% in the young controls, 0.4% in the aged controls,
and none in the treated group).

375. Russell et al. [R75] have used a genetic method todetermine whether advancing age affects nondisjunction in irradiated or unirradiated female mice.
Sex-chromosome markers were built into the cross sothat maternal non-disjunction (XMXMY or OXP) could
be distinguished from paternal non-disjunction(XMXPY or XMO) (any XXX types would be only
questionably detectable by phenotype; and XO can

380. The other results obtained by Mikamo [M49]relate to the induction of aneuploidy in oocytes
sampled from irradiated Chinese hamster females
irradiated at 85 to 7 hours before ovulation. In theseexperiments (200 R), the frequencies of hyper-haploideggs nuctuated around a mean of 1.5% (1526 oocytes
sampled in 10 different periods before ovulation) with arange from 0% (35, 15 and 7 hours before ovulation) to471

3.4% (59 and 11 hours before ovulation). The meanfrequency of hypo-haploid oocytes was slightly higher(2.4%) with a range of between 0% (13 hours before
ovulation) and 5% (11 hours before ovulation). The
control frequencies of hyper- and hypo-haploid oocytes
were, respectively, 0.8% and 1.3% ( 1839 oocytes
sampled). In one stage (oocytes sampled 11 hours
hefore ovulation: as will be recalled, this stage showed
the highest sensitivity to the induction of chromatidaberrations). which was studied in detail, the data at
exposure levels or 50, 100 and 200 R show small but
non-significant increases (the latter probably due
mainly to the small numbers of oocytes that could besampled) in the frequencies of hyper- and hypo-haploidoocytes at SO R (2.1 and 4.2%, respectively; 1/48 and2/ 48 versus the control rates of. respectively 0.8 and1.3%) with no consistent increase at higher exposurelevels.
381. 1n the 1977 report, the preliminary results ofTates {T19] from studies on non-disjunction in the
Northern field vole, Microtus oeconomus, werereported. In this species, C-banding techniques haveshown that the X chromosomes have large blocks ofcentromeric heterochromatin and the Y chromosome is
C-band positive along its entire length. This permits theidentification of spermatids having single Xs, two Xs
and two Ys. Using this technique, Tates obtained goodevidence for the induction of non-disjunction (in prespermatid stages) at x ray exposures as low as 50 R, but
the calculation of the exact frequencies was complicated by the frequent variability between animals
within exposure levels and within and between
sampling intervals.
382. In their 1979 paper, Tates et al. [T20] presented
the results on the x-ray induction of sex-chromosomal
non-disjunction and of diploidy induced in prespermatid stages of Microtus, and scored cytologicallyin the descendant spermatids. The following conclusions may be drawn:(a) In controls, the frequency of non-disjunction
spermatids is about one-fifth of that of diploid
spermatids (0.5 1()-4 versus 2.6 1Q-4):(b) In irradiated animals (range 0.25 to 2 Gy), particularly in those given relatively high doses, there is apronounced induction of non-disjunction and of
diploid spermatids at most of the sampling times;
the exposure-frequency relationships for nondisjunction spermatids show, however, no uniform
pattern at the different sampling times. On days 1
and 12, the frequencies increase with increasing
exposures, but at days 2, 4 and 8, the pattern isirregular, particularly at lower exposures. The
induction of diploid spermatids shows in general abetter exposure-frequency relationship;(c) At any given exposure level, the mean frequencies
of non-disjunction spermatids and of diploid
spermatids vary at different sampling time;(d) The induction of non-disjunction spermatids andof diploid spermatids occurs during the first as
well as the second reduction division.
383. Tates et al. [T20) noted that the induction of nondisjunction of sex-chromosomes and of diploid
spermatids are not necessarily linked, in the sense thatsometimes there is a significant induction of one kindof event and not of the other. The usefulness of thissystem for the study of non-disjunction is to someextent marred by the occurrence of significant heterogeneities between animals, within exposures andbetween experiments and sampling times.
472

384. In a relatively large-scnle extension of this work
involving 4 different x-ray doses (0.25, 0.50, 1.00 and 2Gy), 6 different sampling limes (1, 4, 6, 7. 9 and 12 days
after irradiation) and 6 animals per dose point, Tates
and de Vogel [T21] were unable to demonstrate any
significant increase in the frequencies of non-disjunctional (for the sex-chromosomes) spermatids over thecontrol level. However, the frequencies of diploid
spermatids increased linearly over the range of doses
tested, but the slopes for the different sampling times
were different. The cell stages most sensitive to the
induction of diploid spermatids were sampled on days
4 and 9 after irradiation (day 4: primary spermatocytes
in late pachytene, diakinesis or metaphase and possibly
some secondary spermatocytes at the time of irradiation; day 9: leptotene, zygotene and early pachytene at
irradiation).
385. The lack of response to the induction of sexchromosomal non-disjunction is puzzling. The animals
used in this and in the earlier studies were derived froma colony initiated in 1974 with 2 pairs of animals and 3
young. No specific breeding scheme was used exceptthat in every generation, breeding pairs were usuallyformed by taking into account factors such as fertility,
fecundity and absence of cannibalism. It may be that
increased inbreeding might have selected againstpresumed non-disjunction-prone individuals. Current
studies with a new colony established from new wild
animals which are under way, may help to throw lighton this possibility.
6.

Summary and conclusions

386. A number of cytogenetic and genetic methods
are currently available to study spontaneously-arisingand radiation-induced chromosome losses and gains in
the germ cell stages of experimental mammalian
species. Most of the recent data have come from the useof cytogenetic methods (e.g., chromosome analysis ofearly cleavage stages, embryos at 9-10 days ofgestation, oocyte stages at metaphase II, etc.).
387. The spontaneous incidence of monosomics andtrisomics in early embryonic stages of most mammalian
species studied in this respect is quite low, being of theorder of about 0.5 to 1%. This is in contrast to thesituation obtained in humans.
388. When male mice are exposed to x irradiation(100 R), mated to unexposed females and the embryos
derived from irradiated meiotic and spermatogonialstages are analysed for aneuploidy, there is no
measurable increase in the frequency of either
monosomic or trisomic embryos over the control level.
One study with a lower exposure of 20 R provides someevidence for a possible increase in the total frequencyof aneuploids (monosomy and trisomy) and for the
possibility that non-disjunction may occur at meiosis I
or II; in the same study, at the higher exposure of 200
R, there seems to be no further increase in aneuploidy.
389. The problem of whether small x-ray exposures tofemale mice (in the range from 2 to 16 R) will lead to anincrease in the frequency or non-disjunctional gametes
leading to monosomic and trisomic embryos has been
investigated by a number of workers. The available
data suggest that this effect could not be demonstrated
in either young or aged female mice.
390. The results of a genetic study in the mouse haveprovided no convincing evidence for irradiation

causing an increase in the frequency of X-chromosomal
11011-disjunctional progeny in irradiated young or aged
females.
391. Studies involving irradiation of female Chinese
hamsters (young and old; 20-200 R range) and subsequent culturing of their oocytes in vitro have provided
no clear-cut evidence for an increase in the frequencyof aneuploid eggs; there was no demonstrable effect ofmaternal age either. Other experiments with the same
species aimed at ascertaining the oocyte sensitivity to
the x-ray induction of aneuploidy (irradiation of
females 85 to 7 hours before ovulation; 10 different
time periods) show that there may be an increase in thefrequencies of hyper-haploid and hypo-haploid eggs
after irradiation with 200 R; the increases for any
individual stage, however, are not significant in view of
the relatively small sizes of the samples. In oocytes
sampled 11 days before ovulation (and which manifest
a high sensitivity to the induction of chromatid structural aberrations) for which data at 50. 100 and 200 R
are available, there are indications that there may be anincrease in the frequency of hyper-haploid and hypohaploid eggs, but it is by no means as striking as it is in
the case of chromatid aberrations.
392. In the Northern field vole, Microtus oeconomus,
contradictory results have been obtained on theradiation-induction of sex-chromosomal aneuploidy inmale meiotic stages: earlier experiments provided
positive evidence while the later ones showed no significant induction (dose of up to 2 Gy); however, there isgood evidence for the induction of diploidy and the cellstages sampled on days 4 and 9 after irradiation seem to
be most sensitive in this respect.
D.

I.

POINT MUTATIONSSpecific-locus mutations in male mice: effects of3H and 239Pu

393. In the 1977 report, the preliminary results ofCumming et al. [C36, C37] on the induction of specificlocus mutations by tritiated water in the germ cells ofmale mice were presented. More complete results fromthis work have now become available [R31]. Briefly,(101 x C3H) F1 wild type male mice were injected
intraperitoneally with tritiated water (1.85 or 2.78 10-2
MBq per gram of body weight) and mated to females of
the tester stock. The offspring were scored forpresumed mutations at the seven loci and the presumed
mutants were bred to establish allelism of the mutations
and to determine the viability of the mutations in thehomozygous condition. Both post-spermatogonial andspermatogonial stages were sampled. The weighted
mean dose for the experiments with irradiated postspermatogonial stages was calculated by estimating theaccumulated dose for each succeeding day after HTO
injection and weighting by the number of offspring
conceived that day. For the experiments with irradiatedspermatogonial stages, the weighting was by weekly,
rather than daily, intervals. The data are presented inTable 27. These data permit an estimate of an induction
rate of 4.4 I0-7/locus/10-2 Gy for post-spermatogonialstages and of 1.5 10-7/locus/10-2 Gy for spermatogonia
after correction for control rate (historical control: 28
mutations in 531 500 offspring).
394. An examination of the distribution of themutations in the offspring (Table 28) shows thefollowing features:(a)

For spermatogonial irradiation, the pattern is not
significantly different from that which has beenrecorded for x- or gamma-irradiation where a low
frequency has always been observed at the a andse loci;(b) The mutations in the offspring from irradiation of
post-spermatogonial stages appear to be more
evenly distributed among the loci, a characteristicof those obtained in x-irradiation experiments
involving these stages [R32];(c) Although no deficiencies involving d and se locisimultaneously has been recorded in the present
study (these are common after x-irradiation of
post-spcrmatogonial stages [R32, R33]) there isother evidence for the association of some of themutations with aberrations: three of the mutants
were sterile and an s locus mutant listed as"untested" had a high frequency of sterility in her
offspring;(d) In the spermatogonial series, 10 out of the 18
tested mutants were viable in the homozygous
condition and this proportion was 3 in 11 in the
post-spermatogonial group.
Altogether, these data present no evidence for any
striking disparity from the spectrum and properties ofmutations recovered in x-irradiation experiments.
395. Russell et al. [R31] have estimated the RBE
values for mutation induction by 3H relating themutation rates observed in the present work with thoserecorded in earlier investigations with x- or gammairradiation. For post-spermatogonial stages, the resultsof experiments with 300 R of x rays (90 R min-1) waschosen as the standard although the dose rate in the 3H
study was much lower than the rate of 90 R min-1. The
justification for this is that the mutation rate in postspermatogonial stages appears to be independent ofdose rate or at least not markedly affected by it [R34].
The x-ray data (based on the progeny from the first two
weeks of mating) yield a rate of 6.1 10-7/locus/l0-2 Gy(25 mutations in 18 693) after correction for controls[R35]. (The reason for using these data is that in the 3H
experiinents 95% of the progeny were conceived in thefirst two weeks after injection.) The rate in the 3H
experiments namely 4.4 10-7 /locus/I 0-2 Gy divided by
the rate cited above for x rays gives an RBE of 0.7 (after
making a correction from R to Gy) for the induction of
specific locus mutations in post-spermatogonial stages.
With the limited number of mutations scored in the 3H
series, the above RBE values are not significantly
different from 1.
396. For spermatogonial stages, as is well known, dose
rate is very important [R34, R36]. In the 3H experiment,
the dose rate is relatively high in the first few days after
injection as compared to what it is later, but even in thefirst half day, it probably does not average much morethan about 0.001 Gy per minute. Consequently, the data
most suitable for comparison are those obtained withgamma rays at 0.8 R min-1 and below. The recent calculations of Russell and Kelly [R 77, R78] show that for all
such data, the straight line of best fit is described by Y
= (8.04 1Q-6 ± 1.19 1Q-6) + (7 .34 1()-8 ± 0.83 10-8)0 in
which Y is the mutation frequency per locus and D isthe exposure in R. This result does not differ greatly
from the regression formula Y = (8.34 JQ-6) + (0.659
10-7)D calculated by Searle [S69] who restricted hisanalysis to the data then available at exposure rates of
0.009 R per minute and lower. Dividing the rate
obtained with 3H (1.5 J0-7) by the rate for gamma rays
estimated by Russell and Kelly (with correction for thechange from R to Gy), one obtains an RBE value of 2473

for 3H relative to chronic gamma ray exposures ofspermatogonia. Because of the limited number ofmutations in the sample, uncertainty as to the numberof independent events involved when clustering occurs,
and some uncertainty as to the true doses, Russell et al.
[R31] believe that it is unlikely that the RDE value of2.0
differs significantly from 1. They, however, stress thepoint that "it would seem prudent at this time to assume
that the RBE for exposure of stem cells in the testis totritiatcd water might be approximately 2" and that thisvalue might be used in the context of risk evaluations.
397. In the 1977 report, a review was made of theavailable data on the induction of dominant lethals[L33, S53] and cytogenetic damage [S53, 844) in malemice by 239Pu. Experiments have been initiated in Oak
Ridge [R37] to study the induction of specific locus
mutations with this radioactive isotope. In this work
(101 x C3H)F1 male mice were injected intravenouslywith 0.37 MBq/kg body weight (- 0.925 MBq/mouse)of monomeric 239Pu citrate. Thirteen weeks after
injection, the males were mated with untreated femalesof the tester strain and the offspring are being scoredfor mutations at the seven specific loci. Until now, 11
presumed mutations have been observed in 54 679
offspring. This is highly significantly above the control
frequency.

2.

Specific-locus mutations in female mice

398. In earlier work discussed in the 1977 report,
Lyon and Phillips [L31] investigated the mutational
response of maturing mouse oocytes to x-irradiation
with a total dose of 2 Gy given in 20 fractions of 0.1 Gyeach.IS The offspring conceived within the first sevenweeks (and later) after the last irradiation were scoredfor mutations at the seven loci of the PT stock. Appropriate controls with 2 Gy given acutely were run. The
results showed that the yields with the fractionation
regimes were lower than that after acute irradiation.
Based on those data and earlier fractionation data ofRussell [R39] Lyon and Phillips concluded that ·• ... itseems reasonable to suppose that in our work, the effectof each 0.1 Gy dose was low, and equal to 1/20 of theobserved effect of twenty such doses . . . it seems
probable that the effects per unit dose of a 0.1 Gy doseis indeed less than that of 0.5 Gy and hence the doseresponse relationship is highly curved. There is asuggestion in Russell's data that the mutation rate perunit dose is still increasing at dose levels of 200 R to 400
R, but this needs further work"'. The experiments of
Lyon et al. [L32] considered below were designed to
examine the mutational response at relatively higher
doses.
399. Adult female mice were given doses of 2, 4, or 6
Gy of x rays at 0.52 or 0.72 Gy min-t and matedimmediately. Offspring conceived in the first sevendays (i.e., using oocytes which were mature at the timeof treatment) were scored for specific locus mutations
at the seven loci. The earlier data from their work at 2
Gy (acute irradiation; conceptions up to 10 days after
treatment) were added to the results of 2 Gy in thepresent work: the control data were taken from Russell[R38].
400. The results are presented in Table 29. Statisticalanalysis was carried out by fitting the data to a linear
model (Y = c + bD), a linear-quadratic model (Y = c
15 4 fractions of 0.1 Gy at 2-h intervals every day for 5
successive days or 20 daily fractions on 5 days of 4 weeks.

474+ aD + bD2) and to a square-law model (Y = c +bD2). With the linear model, the values of slope varied
from (3.13 ± 0.50) 1()-6 to (3.06 ± 0.50) J()-6 dependingon the control frequency, with the departure fromlinearity being marginally significant at the 5% level.
With the linear-quadratic model, the values of a varied
from (0.42 ± 1.05)1()-6 to (0.23 ± 1.05)1()-6 and those ofb from (6.22 ± 2.60)10-9 to (6.47 ± 2.60)10-9 again
depending on the control frequency assumed. The P
values (from tests of goodness of fit) were from 0.49 to
0.50, showing that the fit of the data to the model wasgood. It may be noted that the linear term is not significantly different from zero. With the last model, the bvalues ranged from (6.99 ± 1.15)10-9 to (7.19 ±1.15) 10-9 and the P (goodness of fit) values, from 0.71 to
0.77 showing that the fit to this model is slightly better
than that to the previous one.
401. The authors point out that the good fit of the data
to the linear-quadratic or to the square-law models does
not necessarily imply that these relationships give agood representation of the biological phenomena
involved; that the observations are also amenable tointerpretations based on dose-dependence of repair
processes, as has been suggested earlier by Russell (see[R38] for a recent discussion); and that they prefer theinterpretation based on the repair hypothesis. Theirreasoning for the last conclusion is discussed in the next
section.
402. Other useful information that was obtained in the
study of Lyon et al. [L31] pertain to the distribution of
the mutations among the different loci, their viability
pattern, the induction of dominant or X-linked visible
mutations and those with irregular inheritance. The
spectrum of mutations resembled that found by Russell
et al. IR40) and others [S69] in mouse spermatogonia inthat approximately 50% occurred at the s locus. whereas
mutations at the a and se loci were rare~Therc were no
simultaneous d-se mutations (presumed to arise as
deletions) although Russell [R33] had found such
deletions to be common after irradiation of oocytes.
The proportion of those which was lethal in the homozygous condition was 78%, in good agreement with thatobtained by Russell et al. [R40] for spermatogonia andnearly all the ~ and ~ mutations were homozygous
lethal. The dominant and X-linked visible mutations
included 2 viable repeats of tabby (Tu), two lethal
splotch ~ alleles and a lethal W allele. In addition
there was a new X-linked mutation (broad-headed;Bhd) and two further mutations caused a light coatcolour and/or spotting. Six additional mutants withirregular inheritance occurred and these had tail kinks,
light coats, behavioural abnormalities and small size
either together or in various combinations.
403. Selby et al. [S70] studied the mutational responseof the oocyte stages in female mice shortly before birth.
These mice were given 300 R of either x-irradiation athigh exposure rate (93 R min-1) or 300 R of gammairradiation at 0.8 R per minute. At maturity, theirradiated animals were mated to males of the tester
stock to score for mutations at the seven specific loci. In
the acute x-ray series, 3 mutations were recovered
among 16194 Ft progeny; in the gamma-ray series, 1
mutation was found among 37 218 progeny. These
results are therefore consistent with the existence of amarked dose-rate effect of the kind recorded formaturing oocytes and the possibility that the repair
capacity of the oocytes in mice shortly before birth may
not be different from that of maturing oocytes in adultfemale mice.

3.

(a)

Nature of specific-locus mutations

Dose-response kinetics and the nature of specificlorns 11111/ations.

404. The 1977 report of the Committee considered indetail the arguments of Abrahamson and Wolff [24)which led these authors to conclude that:(a) The dose-rate effect for low-LET irradiation foundin specific-locus experiments with mouse
spermatogonia and oocytes is a consequence or
the fact that a large proportion of mutational
events at high dose rates are two-track events;(b) The relative contribution of one-track and twotrack events to the mutational yield could be
estimated (for oocytes this was done from data on
acute x-irradiation at 50, 200 and 400 R and forspermatogonia, the linear component estimatedfrom the available low dose rate data was used toestimate the magnitude of the two-trackcomponent after acute x-irradiation);(c) The coefficients for one- and two-track components so obtained can be used to calculate
expected frequencies of mutations in the otherexperiments;(d) As the magnitude of the one-track component foroocytes is substantial (and since the oocyte data
are used to predict genetic risks for irradiatedhuman females) there is reason to consider that theearlier hazard evaluation (which assumed that therisk to human females from low-LET irradiationof mature and maturing oocytes at low doses or at
low dose rates is only one-twentieth of that at highdoses and dose rates) is too low and to revise it
upwards.
405. In their recent paper on x-ray stage sensitivity ofmouse oocytes, Brewen and Payne [832) have drawn
attention to the line of reasoning pursued byAbrahamson and Wolff discussed in the preceding
paragraphs, in the interpretation of the mouse oocyte
results. Brewen and Payne compared the yields ofcytologically-scored chromosome deletions (observedin their study of oocytes irradiated in the intact animals
and cultured in vitro with subsequent processing forchromosome aberration analysis) and specific-locus
mutations (in Russell's studies). They found that, whenappropriate corrections are made for changes in oocyte
sensitivity with time after irradiation, both the data on
deletions and specific-locus mutations gave good fits toa power law model of the form Y = kD 0 where theslope of the line (in a log-log plot) is a first approximation of the dose exponent, n. The exponent n
approximated a value of 1.7 when the data were plottedby individual stages of sensitivity. i.e., week 1 fordeletions and mutations, weeks 2 to 4 for deletions andweeks 2 to 6 for mutations. The data pooled over theentire time span tested, gave a slope of 1.7 for deletions
over the entire exposure range studied; for mutations
this was true from 50 to 200 R but between 200 and 400
R n was equal to 1.1 (for deletions too, if the analysis
was restricted to week 1 data at the higher doses, thesame phenomenon was observed, namely, a lower n).
406. On the basis of these analyses, Brewen and Payne
stated •· ... the similarities in the variations in sensitivityof induction as a function of oocyte maturation and thedose-response characteristics, when this stage sensitivity
is accounted for, of both structural chromosome aberrations and specific locus mutations lead us to conclude
that they are produced by the same general mechanism
following ionizing radiation ... We suggest that thismechanism involves, principally, the interaction of two
independently induced lesions when low-LET radiation
is employed and consequently follows approximate 02
kinetics. This proposal does not require any more
complicated hypotheses to explain the data and is inaccord with other radiobiological theory ... this would
explain the very low mutation yields following chronic
or multiple small fractionated exposures ... "407. However, ever since his first discovery of
dose-rate effects in spermatogonia and oocytes, Russell[R38) has continued to favour the alternative hypothesis(on the basis of a number of further studies and a solid
body of supporting data) that the mutations themselves
are single-track phenomena and other track events are
involved in damaging or saturating the repair processes
at higher doses and dose rates; that the hypothesis thatthe dose-rate effects observed may be predominantly aconsequence of repair of one-track mutational events
also fits the data indicating that the dose response for
low-LET radiations for induction of point mutations inmammalian cells is probably curvilinear (concave) athigh, and linear at low dose rates; and that theapproach used by Abrahamson and Wolff is not areliable one for estimating hazards in man.
408. It may be recalled from subsection 2 that Lyon etal. [L32) consider that their oocyte specific-locus data
are biologically more consistent with an interpretation
based on repair mechanisms. Their arguments are that
W.L. Russell [R38, R41] had shown that in young
females, mutation rate varied with time after treatment.
Weeks 2-6 were more sensitive than week 1, and fromweek 7 onwards, no mutagenic effects were obtained.
The increased sensitivity of weeks 2-6 does not appear
to occur at all doses. A similar variation with time after
treatment is found for chromosome aberrations [B45,
B46, C34) and dominant lethals [C34]: the frequency
rises with time until sterility sets in, and, as with genemutations, the amount of increase is dependent onradiation dose [C34]. Further there is another factor
which had been shown to affect sensitivity of oocytes tomutagenesis, namely, the age of females at irradiation;
Russell [R36, R41] found that old females gave a higher
mutation rate than young females, particularly insecond litters. Females irradiated on the day of birth oras 17.5 day old foetuses however gave a lower mutation
rate than those irradiated when adult, but the mutations
occurred at later ( > 7 weeks) intervals. Lastly, it is thus
easy to see that all these different responses cannot beeasily explained in terms of radiation hit kinetics.
409. Lyon et al. [L32] believe that the assumption ofdiffering activities of compensating error-free anderror-prone repair systems in oocytes such as thosepostulated to exist in microorganisms (see [K22] for a
recent review) would provide ample ground for
explaining the observed variations in mutability. First,
the combination of sensitivity to cell killing andresistance to mutagenesis shown by small oocytes,
resting in small follicles (up to stage 3a [P27]) andsampled later than seven weeks [09] is consistent withthe absence of error-prone repair. One may thus
postulate that small oocytes are characterized by weakerror-free and absent error-prone repair. Any potentially mutagenic insult would lead to death of thesecells; such an absence of error-prone repair would
protect the germ cells from excessive mutagenesis at theexpense of increasing cell death. Second, in growing
follicles sampled in weeks 2-6, repair enzymes(including error-prone systems) would be among theproteins becoming functional in the developing oocyte.
475

The finding of Pedersen and Mangia [P28] that UDS in
response to UV treatment was higher in growing than in
resting oocytes is in line with this reasoning. The abilityof the oocytes to survive mutagenic insults would
increase, but at the expense of an increase in mutagenic
response. Finally, in the mature follicle, in which UDS
is high [M46], error-free repair would become stronger
so that resistance to both cell killing and mutagenesis
would improve.
410. Lyon et al. [L32] suggest that the above model
involving varying levels of error-free and induciblelevels of error-free and error-prone repair, although
admittedly speculative, would lit the data on mutagenesis
in mouse oocytes well. It would also be possible toexplain variation among species, or among strains
within a species, in a similar way. The details of these
phenomena however, remain to be elucidated.

(b)

Further data from the analysis of the albino locus"c" region

411. In the 1977 report, some data of L.B. Russell et
al. on the c (albino) locus mutations were presented.
The study 1s now completed [R42, R43, R44, R79].
Altogether, 119 presumed mutations involving the £locus were recovered in more than two decades of work
by W.L. Russell et al. on the radiation-induction of
specific locus mutations in various germ cell stages andwith different kinds of irradiations and regimes andthese constituted the material for the study of L.B.
Russell et al. Of these 107 were fully tested for allelism
and for viability in the homozygous condition; of theremaining 12, one was tested for allelism only, four
died before they were old enough to reproduce and 7
were not mated.
412. The 107 tested mutations may be subdivided on
the basis of(a) Viability in the homozygous condition (viable,
subvital and neonatally or prenatally lethal, designated with v, s and 1, respectively, as part of theirsuperscript); ·(b) Whether with respect to pigment phenotype invarious combinations, they mimicked the "albino"
allele (mutants designated with ~ as part of theirsuperscript} or were intermediate between £ and £(designated with eh or ~ as part of their superscript). Fifty five of the mutations were viable andalbino (£8v}, 13 were viable and of various intermediate pigment types (_£xv), 4 were subvital (_£as ands?s). 7 neonatally lethal albinos (£3 1) and 33 prenatally lethal albinos (£•I).
413. All the prenatally lethal and at least one of theneonatally lethal £ locus mutations (£•'} classes areprobably deficiencies. Since the absence of the locus
mimics albino in phenotype, the intermediates are
assumed to result from intragenic changes. There isevidence that the class of viable albino mutants areeither intragenic changes or very small deficiencies.
414. The distribution of the major classes of themutations are given in Table 30 from which it can beseen that:
(a)

476

Among the x- or gamma-ray-induced mutations,
34 of the 51 induced in spermatogonia (67%} arehomozygous viable; this frequency is slightly
lower for neutron-induced c locus mutations (9 out
of 15);-The total number of mutations that were available
from other cell stages is relatively small;(c) The proportion of the mutations that are lethal
homozygously is of the order of about 30% for
those recovered after spcrmatogonial irradiation(x- or gamma- or neutron-irradiation); for othercell stages. the overall proportion of lethals is
almost twice as high (58%; 14/24);(d) The proportion of intermediate types among the
34 non-lethal, non-mosaic c locus mutations
recovered from irradiated spermatogonia (x- or
gamma-irradiation) is 26%, which is nearly thesame as that among spontaneous mutations (28%);
none of the 9 whole-body non-Jethals derived fromthe neutron-irradiated spermatogonial group wasof the intermediate type. It would thus appear that
low-LET irradiation of spermatogonia increases
the absolute frequency of viable c locus mutations
without changing the spectrum from that of
spontaneous ones;(e) The proportion of homozygous viables is highest
for the spontaneous £ locus mutatJons.
(b)

Not shown in Table 30 is the finding that there was no
significant dose rate effect on the relative proportionsof c locus mutations that were homozygous lethal. L.B.
Russell et al. [R42] consider that these findings support
the view that most of the c locus mutations induced inspermatogonia even by high dose rate X· or gammairradiations are of a type most likely to result fromsingle-track events (62% £~v, £xs and £"v plus 16%
presumed deficiencies not involving the closest marker)
and that most of the reduction in mutation frequency at
low dose rates is not due to a change in relative
proportion of two-track and one-track ionizing events.
415. Turning now to fractional c locus mutations, 16of them were recovered among the total of 119 [R43J.
These 16 mutations were distributed evenly among
controls and irradiated groups, suggesting that thefractionals observed are all presumably spontaneous in
origin. (At the c locus, the bulk of spontaneous
mutations have been fractionals.) The overall progeny
ratios from the fractional mutants indicated that the
mutations could have occurred in one strand of thegamete DNA, in a daughter chromatid derived frompronuclear DNA synthesis, or in one of the first two
blastomeres prior to replication.
416. The stage at which homozygotes die was determined for 28 c locus mutations of which 26 had earlier
been found to be probably prenatally lethal (R45].
Uterine dissection experiments involving 796 dissected
females and 7615 corpora lutea [R44] indicate that theprenatally lethal mutants die either around early preimplantation (13 mutants) or around the time of
implantation (13 mutants). None of the £ locus
mutations kills between the latter time and the timearound birth, when the neonatal lethals (7 mutants) die.

4.

Autosomal recessive lethals in male mice

417. The primary aim of the work of Liining et al.
[Ll 8] described earlier in the section on dominantlethals was to assess the effectiveness of acute andchronic irradiation with 14.5 MeV neutrons in inducing
autosomal recessive lethals in mouse spermatogonia.
Adult CBA male mice were irradiated with 1.5 or 2.5
Gy (acute) or 2.5 Gy (chronic: about 7 10-3 Gy h-l, 8hours a day for 5 days a week through 11 weeks). The
two important findings from this study are that:

(a)There is no measurable difference in the rate ofinduction of autosomal recessive lethals inmouse spermatogonia between neutrons delivered
acutely or chronically;(b) The rate of induction is about 2 JQ-4/10-2 Gy/
gamete, 14.5 MeV neutrons being about twice aseffective as acute x rays.

5.

Sex-linked recessive lethals in male mice and rats

418. In the 1977 report, the details of an X-chromosome inversion ln(X)l H described by Evans andPhillips [E12] were given. This inversion covers about
85% of the physical length of the X chromosome and.
therefore. covers slightly over 5% of the mouse genome.
Lyon, Phillips and Fisher [L50] have now reported on
the use of this inversion to study the x-ray induction of
X-linked recessive lethals in spermatogonia. Males
were irradiated as young adults with a fractionateddose of 5 + 5 Gy of x rays (0.9 Gy min-1) with a 24 hinterval. It was found that 2/536 irradiated and 0/529
control X chromosomes carried a confirmed lethal.
These frequencies correspond to a rate of induction of
1.9 1G-6 per 10-2 Gy per X chromosome for single
exposures (allowing for the enhancing effect offractionation). The results are considered as fully
consistent with previous experiments in which X-linked
lethals were not detected and indicate the value of using
inversions for this work and the need for large-scale
experiments. The results are also consistent with thoseon the induction of autosomal recessive lethals
although there were indications that some X-linked
lethals may be eliminated in the heterozygous state.
419. Chambers and Chapman [C29] have recently
reported on the rate of induction of sex-linked recessive
lethals in rat spermatogonia. The total x-ray exposure
was 450 R given in three fractions of 100, 150 and 200
R at 10, 12 and 14 weeks of age, respectively. The data
used for estimating the rate of sex-linked recessive
lethals were those on litter size on day 1 and on day 21.
The rates arrived at in their two dose groups are 1.1 lQ-4
and 2.1 lQ-4/X chromosome/Rand in good agreementwith the earlier estimate of 1.6 1Q-4/X chromosome/R
by Taylor and Chapman [T13].
6.

Autosomal recessive lethals in female mice

420. Liining and Eiche [L34) have collected data on
the induction of autosomal recessive lethals in maturingoocytes of mice of their CBA strain. The procedures
and test schemes were essentially those used earlier inconnection with work on the determination ofradiation-induced autosomal recessive lethals inspermatogonia [L36, L37]. The x-ray exposure was 250
R to sexually mature females; the irradiated females
were mated to males immediately after irradiation andwere allowed to produce one or two litters conceived
during the first six weeks following irradiation. The
data are consistent with a rate of induction of 1.3 IQ-4/
R/gamete by one method of calculation [H58] or of 0.8
to 1.2 1Q-4/ R/gamete by another method [L35]. In any
case it is clear that these estimates are about the same asthat arrived at for spermatogonia [L47].

lated exposure: 300 R) it was found that the mortality in
the F2 crosses was no higher than in controls. Thissuggests that the germ cells of female foetuses may not
be more sensitive than maturing oocytes of adultfemales and that the risk from foetal exposure is nohigher than that from adult exposures.
422. Ronnback and Sheridan [R46] irradiated female
CBA mice chronically with 137Cs gamma rays in utero
during either of two periods, the 10th to 14th days ofgestation or 14th to 18th days of gestation. The doses
administered were 0.34 Gy/generation in the first groupand 1.6 Gy/generation in the second group. The dose
rates were 3 10-3 Gy h-1 in the first and 1.7 10-2 Gy h-1
in the second group. The irradiation exposures wereadministered through nine generations and at the end,
the female progeny were tested for the induction of
autosomal recessive lethals. The data obtained areconsistent with rates of induction of 1.5 lQ-4/10-2 Gy/
gamete (in the group that received 0.34 Gy/generation
during days 10-14) and 0.3 lQ-4/10-2 Gy/gamete in thegroup that received 1.6 Gy per generation during days
14-18. The rate of 1.5 lQ-4 is in accordance with thatreported by Ronnblick [R47], i.e .. 6.3 lQ-4/10-2 Gy/
gamete (with a range of 0.7 to 11.8 lQ-4: 95% confidence
limits) after a single chronic gamma irradiation
exposure of female foetuses (1.6 Gy) during the 10th to14th days of gestation.
7.

Biochemical mutations detected by electrophoresis

423. In the 1977 report, data on the induction of
mutations in mouse spermatogonia, using nine electrophoretically detectable markers [M47] and haemoglobin
loci [R48] were discussed. Narayanan et al. [N14] has
now obtained some data in a spermatogonial irradiation experiment in which biochemical mutations at 20
loci were studied. Adult C3H males were irradiatedwith mes gamma rays (100 + 500 R, separated by a 24
h interval) and mated to females of the 101 strain. Liverbiopsy was performed on the offspring in order toscreen for biochemical variants. Liver extracts werethen submitted to isoelectric focusing on polyacrylamide gels, an electrophoretic method that is capable ofseparating proteins from one another differing in as
little as 0.01 pH unit in their isoelectric points. Among
2100 F1 animals so far screened, three isoenzyme
variants (two esterase and one lactic dehydrogenasevariants) were recovered. In the controls, two esterase
variants were found among 12 800 animals. A puzzlingfeature of the variants recovered in this work is thatthey were not transmitted beyond the F1.
424. In another study, Pretsch [P40] used a thin-layerchromatographic method to detect the induction of
mutations causing hyperaminoacidemias. Adult C3Hmales or (101 x C3H)F1 males were given 100 + 500 Rof mes gamma-irradiation (24 h interval) and mated tofemales of the 101 or T strain, respectively. Both preand post-meiotic stages were sampled. The blood fromthe F1 animals was used for chromatography. No
mutants, however, could be detected in a sample of5786 animals.
8.

421.
In other experiments with irradiation of female
foetuses [L34] ( x-irradiation of pregnant females with afractionated exposure: 25 R d-1 for four days from day
10 to day 13 of pregnancy plus 50 R d-1 for a further
four days from day 15 through day 18; total accumu-

Dominant mutations

425. In the 1977 report, the unpublished results of
Selby and Selby on the induction of mutations causing
dominant effects in the skeleton of the mouse were
described. These data and discussions about their477

relevance for hazard evaluations have now been
published [E16, El7, E18, R49, S71, S72, S73, S74, S75,
SI 17). In this work, adult male mice received afractionated gamma-irradiation exposure (JOO + 500 R,
separated by 24 h; 60 R min-1) and were mated withuntreated females. The Fi sons conceived during thepost-sterile period were processed for examination of
their skeletons after they were allowed to produce
progeny. Thirty seven of the 2646 F1 males were judged
to have dominant mutations that caused one or morerare skeletal abnormalities; 31 of these were shown to
be mutants by breeding tests and the remaining 6,
having no progeny, were counted as mutants based
only on criteria supported by the data.
426. In breeding tests, the authors found that thedominant mutations affecting the skeleton showedvariable expressivity and incomplete penetrance formany or all of the effects that they caused. A number ofthem severely affected viability. With the experimental
procedure used, both incomplete penetrance anddecreased viability would have caused an underestimate of the mutation rate. Thus, some Fis actually
having a mutation might not show it because of low
penetrance, some mutant Fis . having defective
skeletons might not be classified as mutants if
penetrance were too low to permit proof of transmissibility, and mutants that died before examination would
not be counted. Note, however, that the first of thesethree cases does not lead to any underestimation of first
generation genetic damage.
427. In order to know if some of the skeletal
mutations might actually be gross chromosomalchanges such as reciprocal translocations or
aneuploids, cytogenetic examination of the testes ofmutation-bearing males was carried out on 9 of theskeletal mutants (6 of which were proved mutants and 3of which were counted as mutants on the basis ofpresumed-mutation criteria), 2 non-skeletal mutants
and one sterile F1. These were chosen for cytogenetic
examination because they were either sterile or hadpartial sterility. Mutant numbers 1268, 2490 and 2691
were all found to be balanced reciprocal translocation
heterozygotes; a heterozygote for a non-skeletal
mutation (a belly-spot; mutant number 2971) which
was partially sterile was also found to be a translocation carrier [S72]. Subsequent breeding tests involving
mutant numbers 1268, 2691 and another mutant(number 1163) revealed that every mouse that had thereciprocal translocation had the skeletal defects andconversely, every one that did not have the translocation did not have skeletal defects. It thus appears thatat least for these mutations, the association between thepresence of a balanced reciprocal translocation andskeletal defects is strong and suggests that some of thebalanced reciprocal translocations are in factassociated with dominant phenotypic effects.
428. In further experiments [S75] Selby tested eight
other skeletal mutations for effects in homozygous
condition. It was found that all of them were lethal as
homozygotes; for seven of them, death occurred after
implantation and before birth, and for the remaining
one, 10 days after birth. Thus, at least in this limited
sample, the majority of mutations having dominant
effects on the skeleton in heterozygous carriers also act
as recessive lethals. The follow-up experiment in whichmales known to be heterozygous for a skeletal mutation(mutant number 1629) were mated to normal ( + / +)females, showed that the intra-uterine death rate washigher than what would have been expected on the478basis that the mutation had no heterozygous effects on
dominant lethality. From these results and other considerations, Selby has concluded that recessive lcthals
often have dominant harmful effects.
429. In addition to the skeletal system discussed
above, there is one other system that has already beenshown to be useful in studies on the induction of
dominant
mutations. This concerns dominant
mutations causing cataracts in the eye of the mouse.
The fact that cataracts can be caused by dominant
mutations in mammals (including humans) is known[E19, M 16, P30, W21, W27]. The experiments of Eh ling
and colleagues [El3, E20, E21, E24, K23, K24, K42)
have validated the usefulness of the cataract system forboth radiation and chemical mutagenesis studies. The
paper of Ehling [E24] is the most recent on this subject.
The radiation work of these authors consists of threeexperiments, one involving a total exposure of 910 R
given in two equal fractions separated by a 24 h interval
and the other two involving single exposures of 534 R
and 600 R, respectively. In all experiments, adult (101x C3 H)F1 male mice were gamma-irradiated at a rateof 53-55 R per minute and mated to females of theseven-locus tester stock (to score, in the same experiment, for specific locus mutations) and the eyes of the
Fi progeny at about 3 weeks of age were examinedbiomicroscopically with the aid of a slit lamp to detectlens opacities. All the presumed mutants were progenytested to confirm the genetic nature of the lens opacity
phenotype. Specific locus mutations were scored using
standard procedures.
430. The data are summarized in Table 31a whichshows that the mutation rate for post-spermatogonialstages is higher than for spermatogonia and that
exposure fractionation has an augmenting effect on
mutation frequency. These responses have long been
known from specific locus work and the present work
has demonstrated that similar responses are obtainedwith cataract mutations. The mutation rate estimatesthat can be derived from these data are: 0.45-0.55
mutation per 106 gametes per R for single high dose rate
gamma ray exposures and 1.26 mutations per 106
gametes per R for the particular fractionation regimeused.
431. Small lens opacities frequently occurred in theoffspring of the experimental as well as control groups(opacities of the anterior embryonic suture, opacities ofthe posterior embryonic suture, small white patchesdiffering in form and location and remnants of thepupillary membrane). The total frequency of offspringwith any small lens abnormality was 10% in the control
group and 11% in the experimental group. Breeding
tests of approximately 300 carriers provided theevidence that these small lens abnormalities are notcaused by single dominant genes [K42]. These abnormalities were therefore excluded from the data
presented in Table 31a.
432. The properties of the transmissible radiationinduced dominant cataract mutations are given in
Table 31 b. It can be seen that apart from two mutants
which were sterile, the remainder were fertile. The
penetrance and expressivity properties of these mutants
are similar to those affecting the skeleton.
433. When one compares the overall frequencies of
induced cataract and specific locus mutations (columns
4 and 7, respectively, in Table 3 la), it is clear that therecessives outnumber the dominants by a factor ofabout 2.5 for spermatogonial and 2.7 for post-spermatogonial irradiation. In humans, 20 well-establisheddominant cataract mutations are currently known[M 16]. If the number of loci at which dominant cataract
mutations can arise in the mouse is the same as inhumans, then one is scoring for events at 20 loci as far
as dominant cataract mutations are concerned,
compared to events at 7 loci scored in the specific locus
experiments (a factor of 3). Thus. on a per locus basis,radiation induces approximately 8 times (i.e. 2.5-2.7 x
3 "" 8) more recessive visible mutations than cataract
mutations [E24].
9.

Histocompatibility mutations

434. In the 1977 report, the studies of Kohn andcolleagues on the induction of histocompatibility (H)mutations in mouse spermatogonia were described. As
is well known. the H-system in mammals comprises agroup of co-dominant genes located throughout the
genome, and their action (production of cell membrane
alloantigens) determines the acceptance or rejection ofdermal grafts. For operational reasons, the H-loci inmice are divided into two classes distinguished fromone another in the F1 hybrids of the B6 and C lines thatare used. The class-I loci. at least 30 in number [B73],
have different alleles in the parental lines and are
therefore heterozygous in the F 1 hybrid. The class-IIloci have similar alleles in the parental lines and are
therefore homozygous in the hybrid; the number ofclass-II loci is unkown, but a conservative estimate is of
the order of about 50 loci [G42].
435. The procedure to detect new mutations is toexchange tail skin grafts orthotopically between F1
hybrid mice (derived from mutagenized germ cells)
from the two strains mentioned above and classify theprogeny as resulting from "gain" type mutations(appearance of a new antigenic specificity. i.e .. grafts
donated by the putative mutant rejected) or "loss" typemutations (loss of specificity i.e., grafts placed on theputative mutant rejected) or "gain-loss" type ofmutations (one specificity replaced by another). Class-I
mutations are distinguished from class-I I by their"loss" or "gain-and-loss" phenotypes for loci on
autosomes and X chromosomes; class-II mutations
could produce only "gains" unless the Y chromosome
is involved (see [K38] for detailed description of themethods).
436. The earlier results of Kohn et al. [K38, K39)
showed that there was no evidence for the recovery of
x-ray induced histocompatibility mutations (spermatogonial irradiations). This result was attributed by theauthors, not to the failure of the system to detectmutations, but rather to the very low mutability of theseloci (relative to the seven or six specific loci that havebeen used in radiation studies with mice). Theysurmised that this could happen if the x-ray induced Hmutational lesions failed to result in viable progeny (seealso [K40]).
437. In a further study, Dunn and Kohn (D23] tested
for the induction of H-mutations in post-meiotic malegerm cell stages. The doses used were 3.5, 6.5 or 3.5 +3.0 Gy with a 24-h interval. Altogether 8 H-mutations
were found in nearly 3000 progeny (including 1101
control progeny). Two of them were clusters andtherefore could not have occurred in sperm; one class- I
mutation was not relevant because it occurred in the B6
genome of the unirradiated mother. Of the relevant

five, two were class-I losses (1 from the 6.5 Gy group;
1/565: the other was in the 3.5 + 3.0 Gy group; 1/514)
and the remaining three were class-IT mutations of the"gain" type: one on the control (1/1101), one in the 3.5
Gy group (1 /809) and one in the 3.5 + 3.0 Gy group(1/514).
438. A comparison of these results with those for
specific locus mutations in post-meiotic male germ cells
and with spermatogonial mutation rate for the H-Iociclearly indicates that in the first comparison, the rate
for the class-I H-loci is only about 1/9 of the specificlocus rate; in the second comparison, the two rates do
not significantly differ from one another. At face value,
the spermatogonial rate for the H-loci is only about
1/60 of that for specific-locus mutations. In any case,the very low radiation-induced mutability appears to bea general property of these loci, one which does notdepend on germ cell stage.
10.

Induction of congenital anomalies and tumours by
irradiation of mouse germ cells

439. Recently, Nomura [N23] published a paper inwhich he demonstrated that congenital anomalies andtumours could be detected in the progeny of irradiatedmice and has thus identified a potentially useful model
system for the study of these effects following irradiation of germ cells. Mature male or female mice (63-65
days old) were x-irradiated with doses in the range from
0.36 to 5.0 Gy and mated to unirradiated animals.
Living foetuses on day 19 and offspring surviving morethan 7 days after birth were examined for the incidenceof congenital anomalies. (The germ cell stages sampled
are not specified.) The results are summarized in Table
32.
440. It can be seen that there is a significant inductionof congenital anomalies following germ cell irradiationand that the frequencies decrease (relative to thoseobtained in Jiving foetuses) in live-born progeny. This isdue to the fact that some anomalies (cleft palate,cxencephalus etc.) are lethal shortly after birth. Since
the data are presented as frequencies pooled over allradiation doses employed, no conclusions can be madewith respect to whether there are dose-effect relationships or whether certain specific kinds of anomalies
predominate at lower versus higher doses.
441. In the other part of the study dealing withtumours, the progeny of exposed parents (same doses asin the congenital anomalies part of the study) derived
from irradiated spermatozoa, spermatids, spermatogonia and maturing oocytes were screened for thepresence of tumours in their internal organs. The total
yields of tumours in the offspring for all male germ cellstages sampled were significantly higher than incontrols. Tumour incidence and lung tumour frequency
were slightly higher when x-irradiation was administered 8-14 days before mating than at other intervals.
Exposure of oocytes in early follicular stages (8-21 days
before ovulation) induced significant yields of tumours
while mature oocytes (1-7 days before ovulation) wereresistant to 2.16 Gy of irradiation. When the dose wasfractionated (2 equal fractions separated by 24 hours),
increased yields (relative to single doses) were foundfor irradiated spermatogonia and mature oocytes. but
not for spermatozoa and spermatids.
442. Kirk and Lyon [K43] have now confirmed
Nomura's findings with respect to the induction of479

congenital anomalies in the offspring of exposed
female mice. These were irradiated with 1.08 to 5.04 Gy
acute x irradiation and mated at intervals of 1-7, 8-14,
15-21 and 22-28 days, with uterine examination in latepregnancy to detect early foetal deaths (dominantlethality) and late malformations. At each weeklyinterval, the incidence of abnormalities (with dwarfism
and exencephaly the commonest types) tended lo risewith increasing dose, and at any given dose theincidence tended to rise with time after irradiation.
Changes in incidence of dominant Jethals and ofabnormal foetuses paralleled each other closely, withhighest incidences in week 3 ((59 ± 5)% for dominantlcthals and (12.5 ± 3.1)% for abnormal foetuses after
5.04 Gy). This increased radiosensitivity of Jess mature
oocytes is similar to that reported previously for othergenetic effects.
11.

Summary and conclusions

443. Subsequent to the publication of the 1977 report.
more data have been obtained on the induction of
specific-locus mutations in the germ cell stages of malemice by tritium (given as tritiated water by i.p. injections). The data permit an estimate of induction rate of
4.4 1Q-7 /Iocus/10-2 Gy of beta-irradiation for postspermatogonial stages and of 1.5 10-7/Jocus/l0-2 Gy
for spermatogonia. The RBE estimate (relative to highdose rate x- or gamma-irradiation) for post-meiotic
germ cells is not significantly different from unity. For
spermatogonia, the RBE value (relative to chronic
gamma rays) is about 2.2 although this value may not
be significantly different from 1.
444. An examination of the distribution of themutants among the seven loci reveals that the pattern is
not significantly different from that recorded for x- or
gamma-irradiation for spermatogonial mutants: themutants obtained from irradiation of post-meiotic germ
cells are more evenly distributed among the loci, acharacteristic of those obtained in x-irradiation experiments involving these stages.
445.

The preliminary results obtained in studies with

239Pu show that this radioactive isotope is capable of448. Further data on the nature of mutations inducedby ionizing radiation in mouse germ cells have been
published pertaining to the analysis of the mutations
recovered at the c (albino) locus in different radiation
experiments. These show that for spermatogonial irradiation, nearly two-thirds of the x- or gamma-ray induced
mutations are homozygous viable. The proportion isslightly lower for neutron-induced £ locus mutations.
Most of the lethal mutations are probably deficiencies.
Since the absence of the locus mimics albino
phenotype, the intermediate types (with respect topigment phenotype) which were recovered are assumed
to result from intragcnic changes. The proportion ofintermediate types among the 34 non-lethal, nonmosaic c locus mutations recovered from irradiatedspermatogonia (X· or gamma-irradiation) is nearly thesame as that among spontaneous mutations (26% and28%, respectively). The viable albinos (as well as theintermediate types) are concluded to result from onetrack events. There was no dose rate effect in therelative proportion of _£-locus mutations that were
lethal.
449. The 14.5 MeV neutrons are about twice aseffective as acute x rays in inducing autosomal
recessive Jethals in mouse spermatogonia. At doselevels of 1.5 or 2 Gy, there is no dose rate effect for the
induction of recessive lethals.
450. The rate of induction of autosomal recessive
Jethals in mature mouse oocytes after x-irradiation(high dose rate) is about the same as that recorded forspermatogonia; the germ cells in female foetuses(fractionated irradiation from day 10 through day 18 ofpregnancy) do not appear to be more sensitive thanmaturing oocytes in adults.
451. Further studies with the skeletal mutations inmice have shown that some of the skeletal mutations
may be associated with balanced reciprocal translocations; put in another way, some of the balanced reciprocal translocations are associated with dominantphenotypic effects. Other data on skeletal mutations
show that all the eight tested were lethal in the homozygous condition.

inducing specific-locus mutations in sperrnatogonia.
446. Further data have been obtained by Lyon andcolleagues on the x-ray induction of specific locus
mutations in maturing mouse oocytes at dose levels of
2, 4 and 6 Gy. When these data were analysed statistically, it was found that they fitted all three models tried(linear, linear-quadratic, power-law model) although
the linear-quadratic and power-law models gaveslightly"better fits. It has been pointed out that the good
lit of the data to the linear-quadratic and power-law
models does not necessarily imply that these relationships adequately reflect the biological phenomena
involved. Lyon and colleagues have expanded on the
repair model originally proposed by W.L. Russell to
explain these results.
447. The frequencies of specific locus mutations
recovered from irradiation of oocyte stages in female
mice shortly before birth at a low exposure rate of 0.8 R
min-t (gamma rays: 300 R) were significantly below
those obtained after the same exposure given at a highexposure rate (93 R min-1); this observation suggeststhat the repair capacity in these oocyte stages may not
be very different from that in oocytes of adult female
mice.
480

452. New data have become available from studies on
the induction of another kind of dominant mutation,
namely, those that cause cataracts in the eye of themouse. The induced cataract mutations are qualitatively similar to those affecting the skeleton in terms ofdominance. penetrance and expressivity.
453. New data on the induction of histocompatibility
mutations in post-meiotic male germ cell stages of themouse show that the rate of induction by x-irradiation
is much lower than that for recessive specific locus
mutations; these data and those on irradiation of
spermatogonial stages (in these stages too, the rate ismuch lower than that for specific locus mutations)confirm the view that the H-loci in general are muchless mutable than the specific loci at which mutationinduction has been extensively studied.
454. The studies of Nomura have shown thatcongenital anomalies and tumours can be recovered in
the progeny of irradiated male and female mice. It thus
appears that the mouse can serve as a useful model forthe study of these kinds of effects following irradiationof germ cells.

E.

GENETIC EFFECTS OF INTERNALEMITTERS

455. In earlier reports of the Committee as well as inthis Annex, data an the induction of genetic (and someother biological) effects by incorporated radioactive
isotopes have been dealt with. The purpose of thissection is to present a broad synthesis of all this inform'ation (for a recent review, see [S76]).
456. Studies on the genetic effects of incorporated
radioactive isotopes present some special problems
which are not encountered in other branches ofradiation genetics and which, in many ways, are very
similar to those encountered in chemical mutagenesis.
Thus, for working with radioactive isotopes it isimportant to know the extent to which the nuclide
actually reaches the gonads and how long it remains
there, as well as its actual relationship to the germ cells
themselves. Except with internal gamma-emitters,
track-lengths are usually too short to allow the germ
cells to be affected by any extra-gonadal material.
Sometimes, the nuclide can become incorporated into
the hereditary material itself and then its exact position
and what chemical changes follow its decay may affectthe likelihood of a mutational event after the transmutational one. These and other complex phenomena
associated with the disintegration of a radioactive
material mean that its actual effectiveness in mutationinduction will not be determined solely by the characteristics of the emitted radiation.
457. Table 33 gives details about some internallydeposited radionuclides of special genetic interest.
Three of the ~-emitters included are of obvious interest
because they can be incorporated into DNA. The
penetrating gamma radiation from 137Cs will reach the
gonads from anywhere in the body, but ~-radiation fromgonadally deposited material is of importance as well.
The three alpha emitters are known to reach soft tissues(including gonads) after being taken into the body andto be retained there for long periods [14, R51]. Environmental contamination from these three radionuclides
arises in various nuclear operations, such as mining andmilling and fuel processing, while it has been estimatedthat thermonuclear reactors would produce 105 times
as much tritium per megawatt as fission reactors [S77].
458. A summary of some of the main results obtainedwith different radioactive isotopes studied in mammals
is given in Table 34. It is clear that the work done so far
in this area is relatively meagre and diffuse but it has
already exposed some intriguing aspects of biologicalresponse. For instance, there is the apparent high cytogenetic sensitivity of rat spermatogonia to low doses ofcertain ~-emitters [847], the later intra-uterine deaths
after 239Pu alpha exposures which continued into thenext generation [L33] and the declining translocation
yield with prolonged exposures of male mice to 239Pu
despite high retention [844, G23]. All these and otherproblems need more detailed studies.
F.
1.

OTHER RELEVANT DATA

Biological effects in mice and rabbits kept in an areaof high natural radioactivity

459. Leonard et al. [L21] have reported on their observations of biological effects in male mice and rabbits
artificially kept in area near Lodeve in South-westernFrance. Exceptionally high concentrations of uranium(of the order of 1% and sometimes up to 7-8%) arefound at certain sites, giving rise to a very high naturalradioactivity. Correspondingly high concentrations ofradon occur in the atmosphere. At a site where the dose
rate amounts to about 8 10-5 Gy h-1, a rabbit hut was
built and cages with laboratory rabbits were placed on
its floor. Gamma-ray dose was determined by placing
individual lithium fluoride dosimeters around the neckof each rabbit. Air samples inside the hut were taken inspring and autumn for the determination of 222Rn. The
rabbits were kept in the hut for a period of 12 months,
and blood samples were taken at 4-month intervals to
study chromosome aberrations in lymphocytes. Control
animals were kept in a nearby site with very much
lower level background radiation, as well as in thelaboratory.
460. Male mice of the BALB/c strain were also placedin the hut during summer; they could not be
maintained for longer periods owing to their sensitivity
to climatic variations. Control mice were kept in thesame hut as control rabbits. The effects studied
included those on fertility and the induction ofheritable chromosome aberrations.
461. The external gamma radiation dose received byindividual rabbits varied between 0.13 and 0.26 Gy
after 120 days, 0.15 to 0.53 Gy after 240 days and 0.21
to 0.71 Gy after 360 days. The concentration of radonin the rabbit hut was - 5 kBq J-1 in autumn and- 90 8q 1-1 in the spring. It was estimated that at theseradon concentrations, an annual dose of about 5-10 Gy
would have been delivered to the bronchial region, thedoses to other tissues being much smaller (e.g., gonads:
annual dose of about 8 10-3 to 1 10-2 Gy). In mice, thetotal accumulated gamma dose was estimated to be 0.14
Gy for the 3-month period.
462. The cytogenetic observations on rabbit lymphocytes showed that in those cells sampled prior toradiation exposure, the only aberrations noted werechromatid and chromosome gaps and chromosome
fragments and this was true of controls as well. Afterthe exposure, in addition to these aberrations, dicentrics were found; the total frequency of abnormal cells
rose to 1.90% by four months, 2.63% by eight months
and 3.9% by one year (the control value was one-thirdof the last mentioned figure after one year). In the micein which both the irradiated males and their F1 sons
were studied cytologically for the presence of translocations or other aberrations in their spermatocytes, none
were found.
463. In a subsequent paper, Leonard et al. [L22]extended these observations to a further eight months
for rabbits and also conducted further studies withmice. In rabbits, the lymphocytes of which were
sampled at 16 months, difficulties were encountered tostimulate the lymphocytes to divide and the aberration
frequencies became very variable between the different
animals. In general these frequencies did not exceed thelevel observed after 12 months and in fact showed areduction. By 20 months, there were practically no
aberrations (1000 cells from 7 animals). Male mice kept
in the radiation area for three months showed slightincreases in litter size, the mean number of offspring
sired and in the mean number of offspring weaned overa 6-month period (estimated external dose: 0.15 Gy).
Female mice, whose biological response was a/so
studied, however, showed slight reduction in the mean
number of litters, mean number of offspring sired andin the mean number of offspring weaned. Model experi481

ments with radon exposure of laboratory rabbits undercontrolled conditions (to concentrations that wereroughly live times the total exposure of the rabbits
maintained in Lodeve for eight months) showed nochromosome aberrations, suggesting that the chromosome aberrations observed in the earlier study were
probably not due to radon exposure but essentially to
gamma irradiation.
2.

Further data on the relationship between chromosome arm number and relative radiosensith·ity indifferent mammalian species

464. It may be recalled that in the 1977 report, the"arm number hypothesis" proposed by Brewen et al.
[ 1339] and the data collected by other authors to further
examine the validity of the hypothesis were discussed(sec also [S64)). It was concluded that the arm number
relationship (i.e., the linear relationship between theyield of dicentrics and the effective chromosome arm
number after low-LET irradiation) was not adequately
documented to be used at present to predict fromlymphocyte data of one species the expected
frequencies of dicentrics in lymphocytes of another, orto estimate the frequencies of reciprocal translocationsin spermatocytes of one species from those of another.
Furthermore, the two-fold higher sensitivity of human
lymphocytes to the induction of dicentrics (relative tothe mouse) could not be conlirmed.
465. Subsequent to the publication of the 1977 report,
some new data have become available. Considering
first the comparison of the sensitivities of human andmouse lymphocytes to the induction of dicentrics, theearlier data of Brewen et al. [839] had been collectedusing culture times of 60-63 h for the mouse and 54 h
for human lymphocytes. The work of de Boer et al.
[1340] demonstrated that, in the above investigation, thefrequencies of dicentrics scored in mouse lymphocytes
were based on cells that were both in the lirst andsecond division after irradiation; when a 36 h culture
time was used (scoring only lirst division cells), thefrequencies of diccntrics were nearly the same as thosein human lymphocytes and this was true after 1 Gy as
well as after 2 Gy of x rays, i.e., there was no
relationship between chromosome arm number andrelative radiosensitivity to the induction of dicentrics(mouse: 40 chromosome arms; man: 81 chromosomearms).
466. Preston and Brewen [P26] re-examined the above
problem by studying the frequencies of induced dicentrics using different fixation times (42 and 48 h forhuman and 36 and 48 h for the mouse lymphocytes)
and a range of exposures (25-250 R). It was found that:(a) For human lymphocytes, the dicentric yields withthe 42 h lixation· time were higher for two donors
while these were nearly the same as those from adifferent donor the lymphocytes of whom were
fixed at 48 h:(b) When the yields at the later fixation times werecorrected appropriately by assuming that a cell
containing a dicentric without an accompanying
acentric fragment was at its second. mitosis after
treatment, the yields at the 42 h fixation time wasstill higher; this suggested to the authors that theincreased yield at the earlier lixation time was notentirely due to the fact that only the lirst division
cells were being analysed;(c) In mouse lymphocytes, the dicentric yields werehigher at the earlier (36 h lixation time) than at the482

later one (48 h); when corrections similar to thosecarried out for human lymphocytes were made forsecond division cells, again the frequencies werestill higher at the 36 h than at the 48 h lixation time;(d) Considering all data together, it appeared that thedicentric yields in human lymphocytes were from
1.5 to 2 times higher than in those of the mouse,
thus substantiating their earlier contention.
467. A further repeat of this work by Van Buul andNatarajan [B74] with blood from 8 different humandonors, x-ray doses of I or 2 Gy, lixation times of 42
and 48 hours in two experiments and several lixation
times (40-60 hours) and FPG-staining in another,demonstrated that the "mixing-up" of first and second
cell cycle at later sampling times cannot explain theobserved variation in the frequencies of chromosome
aberrations, but that donor-donor variation is a
predominant factor influencing aberration yields. Jnfact, the condition of the donor seemed to be mostimportant since repeats on the same donor showedmarked variability in sensitivity. Whether the interdonor variations are due to different proportions of
sub-populations of lymphocytes with different radiosensitivities could not be answered. Confirmatory results
showing that the frequencies of radiation-induced
dicentrics were nearly the same at different lixation
times when corrected for cells in their second and third
mitoses were also obtained by Leonard and Decat [L26]
and Scott and Lyons [SI 16]. In using blood from four
different donors, the latter authors noted that in one
donor, the frequencies of radiation-induced dicentrics
were signilicantly different between two experiments.
468. Jn the study of de Boer et al. (840] dealing withradiosensitivity of mouse and human lymphocytes tothe induction of chromosome aberrations consideredearlier, some results on the induction of dicentrics inlymphocytes of normal mice, mice heterozygous for atranslocation between chromosomes 1 and 13, tertiary
trisomic mice carrying the same translocated chromosome and either normal or abnormal in appearance
were also presented. One of the findings was that theseabnormal ("teeth trisomic") mice manifested a higher
level of radiosensitivity than normal mice. However, in
their recent work, Van lluul and de Boer [869] could
not conlirm the above observation. They point out thatsince the tertiary trisornic mice occur in a variety ofphenotypes and the splitting up into "normal-looking"and "teeth trisornics" is based on some phenotype
properties only, it is likely that the genetic factor(s) thatmight have caused the high frequencies in the earlier
study were missing in the "teeth trisomic" mice used in
the later experiments.
469. Another mammalian species from whichconflicting results had been obtained in the past is the
rabbit. Scott and Bigger [S65] and Muramatsu andMatsuoka [M44] observed that the yields of x-ray
induced dicentrics in the rabbit lymphocytes were lessthan one-half of those in human lymphocytes; Bajerska
and Liniecki (841] found however, that the sensitivities
were the same (both species have the same effective
chromosome arm number). With a lixation time of 48 h
Leonard et al. [L29] found that the sensitivity of rabbit
lymphocytes is in fact less than one-half of that ofhuman lymphocytes. This finding was confirmed by
Liniecki et al. [L28) who had earlier reported similarsensitivities of rabbit and human lymphocytes (1 to 4 Gyof x rays; 40 h lixation time for the rabbit and 44-48 h
fixation time for human lymphocytes). In the same
study Liniecki et al. also assessed the sensitivity of pig

lymphocytes to the induction of dicentrics (1--4 Gy of xrays) and found (despite the fact that the chromosomesof the pig have 64 effective arms) that this was similar
to that of rabbits (31 h fixation time for pig lymphocytes).
470. The recent and more decisive experiments ofFabry and Leonard [F13] using BUdR-Giemsa
techniques (which permit unequivocal distinction
between cells in M1. M2 and M3) demonstrated that
there exists no significant differences in the frequencies
of dicentrics in human and rabbit lymphocytes (200 Rof x rays) provided that only cells in the first divisionwere included in the calculations. Their results further
show that at 48 h (the fixation time used in most of thestudies on rabbit lymphocytes published in the literature and referred to in the preceding paragraph)around 50% of the cells are in the second and about
30% of the cells in the third division.
471. The finding of Murarnatsu and Matsuoka [M441
discussed in the 1977 report. namely, that the lymphocytes of cat (arm number: 71) manifested only about
one-fifth of the radiosensitivity of human lymphocytes
to the radiation-induction of dicentrics, has now been
confirmed by Stephan et al. [S66]. These authors foundthat the ratio of the yields of dicentrics in human ascompared to cat lymphocytes is 1.0 : 0.27 (100--400 R).
472. In primates, Leonard et al. [L29] studied thechromosomal radiosensitivity of lymphocytes from thechimpanzee (Pan troglodytes), a hominoid ape phylogenetically and chromosomally closely related to man(48 chromosomes and 81 chromosome arms). No significant differences were observed in the radiationinduced frequencies of dicentrics and fragments(100--400 R; 48 h fixation time for both). The mean areas
covered by the lymphocyte nuclei are, however, very
different for the two species: 48.4 µm2 for man and only
23.3 µm2 for the chimpanzee. In the gorilla (Gorilla
gorilla) however (chromosome arm number: 81) the
sensitivity to the induction of dicentrics appears higher
than in humans [D24].
473. Takahashi et al. [T15] compared the yields ofdicentrics after acute and low dose rate gamma irradiation of the lymphocytes of man and the crab-eatingmonkey (Macaca fascicularis; 83 chromosome arms).
Doses of 1--4 Gy were administered to heparinizedwhole blood samples at dose rates of either 0.5 Gy min-1
or 0.17 Gy h-1 (0.0029 Gy min-1). With acuteirradiation. the yields of dicentrics were similar in both
species as had been found in an earlier study [H38).16 At
the low dose rate. the yields were lower in both species,
as would be expected from the kinetics of induction ofdicentrics (Y = aD + b02). The surprising result wasthat, except at 1 Gy, the yields were significantly lower
with monkey lymphocytes. A comparison of the valuesof the a and b coefficients after acute and low dose rateirradiation showed that:(a)(b)

The magnitude of the linear components was not
significantly different either between the species or
between the radiation regimes;
There was a drastic decrease in the magnitude of
the quadratic component in the monkey (by afactor of about 30) whereas this reduction wasmuch less with human lymphocytes (by a factor of 4).

16 This study showed in addition that the yields of induced
dicentrics (as well as dicentrics and rings) were similar to thosein man, crab-eating monkey, squirrel monkey (Saimiri
sciureus; 77 chromosome arms) and slow loris (Nycticebus
cougang; 99 chromosome arms).

These results permitted the authors to conclude that thechromosomal damage leading to dicentrics can be
repaired in unstimulated (G 0 ) lymphocytes and thatsuch repair capacity is different in the two species.
474. Takahashi et al. [T15] also looked into thequestion of whether there was any preferential elimination of cells with dicentrics during the course of low<lose rate irradiation. This was carried out by
incubating the cells for varying periods in the medium(2, 4, 6 and 24 h) after acute or chronic irradiation with
4 Gy prior lo PHA stimulation. It was found that:
With lymphocytes of both species, there was adecrease in mitotic indices and dicentric yields
with post-irradiation incubation, although the time
when these reached their lowest values wasdifferent (2 and 4 h after irradiation for mitotic
index and dicentric yields, respectively); with the
24 h interval, the reduction was by one-quarter for
dicentric yields for both the species while that for
mitotic indices was by about 30% and 60% for man
and monkey, respectively;(b) At comparable time intervals between irradiation
and PHA stimulation, the yields of dicentrics weresimilar in both the species;(c) There was no evidence for preferential eliminationof cells with multiple dicentrics in either species.
These results. particularly those showing speciesindependence for the elimination of aberrations withtime (post-irradiation incubation prior to PHA stimulation), strengthen the view that the different yields ofdicentrics obtained after low dose rate irradiation in thetwo species may be a reflection of primarily a speciesspecific G 0 repair mechanism.

(a)475. Takahashi et al. [T16] have now extended theirstudies to the induction of chromosome aberrations at
low gamma-ray doses (0.05 to 0.5 Gy; 6 levels). The
methods used (48 h cultures; BUdR technique) were thesame as in the earlier work. The results showed that asin the earlier work, there were no differences between
the monkey and human lymphocytes with respect to the
induction of dicentrics. The human data gave a satisfactory fit to a linear model (i.e., a linear increase inaberration frequency with dose), whereas this was not
the case with those for the monkey. There was somesuggestive evidence for the existence of a plateau in
aberration yields between 0.1 and 0.3 Gy for themonkey and between 0.2 and 0.3 Gy for human
lymphocytes, but more data would be needed to verify
this suggestion, particularly for human lymphocytes.

3.

Molecular mechanisms inrnlved in the production ofchromosome aberrations

476. In the 1977 report, some of the available information on the relationship between radiation-induced
lesions in the DNA, their repair and their relationshipto mutations and chromosomal aberrations wasreviewed. Some new data have been collected sincethen which shed further light on the mechanisms
involved in the formation of chromosome aberrations
in eukaryotic systems, and these will be reviewed in thissection.
477. Kihlman et al. [K.26) used the 5-bromodeoxyuridine labelling technique to explore the mechanisms
involved in the formation of chromosomal aberrations.
The rationale for using this technique is the following:
the incorporation of BUdR into the DNA of achromatid alters its staining properties and its scnsi483

tivity to chromosome damage by UV and x rays. A
chromatid that has incorporated BUdR into bothstrands of its DNA stains more weakly with the nuorescence plus Gicmsa (FPG) technique than a chromatidthat has incorporated the BUdR into only one strand of
its DNA, and such a single-substituted chromatid inturn does not stain as strongly as a completely unsubstituted chromatid. The same dose of x rays produces
about three times more breaks in unifilarly substituted
chromatid than in an unsubstituted one. The extreme
case is represented by long-wave UV (i.e., wavelengthsof between 310 and 350 nm) which produces aberrations exclusively in chromatids having BUdR-substituted DNA.
478. Although the thesis that two lesions are required
to produce one exchange aberration is not a new one inradiobiology (it was arrived at long ago on the basis of
dose-effectrelationshipforradiation-induced
exchanges [L38, M67, S78]) direct evidence has beenlacking. The experiments of Kihlman et al. [K26] were
designed to obtain such evidence.
479. Root-tip cells of Vicia faba were exposed in theG2 phase to long-wave (320-380 nm) UV radiation or to
x rays (40 R); before the irradiation exposures, BUdR
had been substituted for thymine in various numbers of
DNA strands in these chromosomes. The experiments
involved cells with chromosomes of the following
constitutions: TT-TT (both chromatids of the chromosome containing unsubstituted DNA), TT-TB (onechromatid with unsubstituted DNA and one withunifilarly substituted DNA). The sister chromatids inchromosomes of the TT-TB and TB-BB constitution
could be distinguished by differential staining with the
FPG technique.
480. The results show that:(a) Long-wave UV induced no aberrations in chromosomes with unsubstituted DNA:(b) In chromosomes with BUdR-substituted DNA.
long wave UV, like x rays, induced subchromatid
and chromatid aberrations; because these aberrations were found in the first mitosis after exposureof G2 cells. the effect of long wave UV was of the
S-independen t, ionizing-radiation -type;(c) The sensitivity to the production of aberrations by
x rays increased with increasing number of BUdRsubstituted DNA strands, i.e., TT-TT < TT-TB <TB-TB < TB-BB;(d) The increased sensitivity of TB-TB chromosomes
over the TT-TB chromosomes was particularly
striking.
481. The question of whether a damaged chromatid
may interact with an undamaged one to form an
exchange (as has been suggested in the model ofResnick [R54)) was studied by making use of thefinding that in cells with chromosomes of the TT-TB
constitution. long wave UV produced no breaks in TT
chromatids, whereas x rays produced about three times
as many breaks in the TB chromatids as in TT
chromatids. In the latter case, if the assumption that
two lesions are required to form one exchange is true,
then, there should be nine times more exchanges
between TB chromatids than between TT chromatids.
If. on the other hand, one lesion can give rise to an
exchange, there should be three times as manyexchanges between TB chromatids as between TT
chromatids. The results were in line with the first
assumption. These results provide direct evidence that
two lesions are required to produce one exchange.
484

482. Natarajan and Obe [N15) tested the hypothesis
whether or not double-strand DNA breaks are responsible for radiation-induced chromosome aberrations.
They made use of the finding of Tanaka et al. [TIO) who
demonstrated that the introduction of T4 endonucleasein Xeroderma Pigmentosum (XP) cells in vitro in thepresence of inactivated Sendai virus led to the ability ofthese cells to perform unscheduled DNA synthesis. This
indicated that, as XP cells are deficient in the first(incision) step of excision repair, this first step can be
mediated by the endonuclease and when this is done.
the other steps in the sequence can be carried out by thecells' own enzymatic machinery. According to theaccepted model of excision repair, following treatment
with a mutagen causing direct breaks (x rays) or where
the repair processes generate single-strand breaks (UV),transient short stretches of single-strand regions should
be present in the chromosomal DNA of the treatedcells. If single-strand-specific endonuclease, such as
Neurospora endonuclease. is introduced in these cells,
one would expect to induce double-strand breaks in the
single-stranded regions of the DNA. If double-strand
breaks are responsible for radiation-induced chromosome aberrations, under these conditions, there would
be an increase in the frequency of aberrations for agiven dose in the ensuing mitosis.
483. CHO cells were irradiated with x rays or
short-wave UV or treated with chemicals (MMS,
bleomycin, mitomycin-C) in G2 stage in the presence of
the inactivated Sendai virus and Neurospora endonuclease and the aberrations were scored in the ensuingmitosis. In the x-ray series, the above treatment led toan enhancement of the frequencies (by a factor of about
2 at the lowest exposure of 50 Rand much higher at 100
and 200 R) of breaks, exchanges and gaps. These results
have been interpreted by the authors as due to theconversion of some of the x-ray induced single-strand
DNA breaks into double-strand breaks by the enzyme.
Similar results were obtained after treatment with MMS
and bleomycin but not after UV or mitomycin-C: withthe latter two, however, there was a clear increase in thefrequency of gaps.
484. The possible reasons for the difference in
response between x rays, MMS and bleomycin on the
one hand and UV and mitomycin Con the other are thefollowing: ionizing radiations produce chromatidaberrations in G2 and the effect is S-independent. It
does not require DNA and chromosome replication to
be expressed as chromosomal aberrations. Bleomycin is
known to act like x rays, i.e., to be S-independent.
Although the aberrations induced by MMS are
S-independent, MMS is known to behave more like xrays with regard to excision repair, namely. "smallpatch" repair [R55]. MMC, on the other hand, is across-linking bifunctional alkylating agent and theaberrations are of the delayed type and S-dependent.
Short-wave UV induces dimers which are implicated as
being responsible for UV-induced chromosome aberrations; these are of the S-dependent type. It is known
that in addition to dimers, UV induces strand breaks.
During excision repair of UV-induced lesions, longpatches of single strand regions are expected to occur.
It would appear that single-strand stretches following
the "long patch" repair even if initiated in G2 are notconverted into double-strand breaks by the en don uclease and it may be that this type of repair relevant toinitiation of chromosome aberrations is confined to the
S phase only.
485. In a subsequent study, Natarajan et al. [N16]extended their observations to CHO cells irradiated inthe G1 stage of the cell cycle, in addition to examining
the duration of availability of single-strand gaps foraction by Neurospora endonuclease in irradiated G2
cells. The results show that after G2 irradiation,(50-200 R) all classes of chromatid aberrations
increased, as noted in the earlier study. In G1 cells(75-300 R) an increase in chromosome-type of aberrations was found but there was also a marked inductionof chromatid aberrations. The increase in chromosome-type aberrations in irradiated G1 cells treated with
Neurospora endonuclease has been interpreted as due
lo the conversion of DNA single-strand breaks or gaps
to double-strand breaks by the enzyme; the inductionof chromatid aberrations in G1 was assumed to be due
to conversion of some of the damaged bases into
strand-breaks by the enzyme. The authors haveprovided evidence for the conversion (by the enzyme)of single-strand breaks induced by x rays into doublestrand breaks using neutral sucrose gradient centrifugation.
486. The data from experiments designed todetermine how long the single-strand breaks or gaps
produced in G2 by x rays remain available for action by
the enzyme show that immediate post-irradiation
treatment with the enzyme leads to a marked increasein the frequencies of chromatid gaps, breaks andexchanges. Later post-treatments, i.e., after 60 or 90
min, increase the frequencies only of breaks, but not of
exchanges. It would thus seem that single-strand
regions are available even 60 min after irradiation, but
the induced double-strand breaks are not able tointeract effectively to produce chromatid-type aberrations. This may be due to changes in spatial arrangements of chromosomes in later G2 or prophase cells
prior to mitosis, which restrict interaction of breaks. ·487. Kato [K27] demonstrated that the frequencies of
UV-induced sister chromatid exchanges (SCE) in rat
kangaroo cells were reduced on photoreactivation withvisible light, suggesting that pyrimidine dimers are
involved in the production of SCEs. Reynolds,
Natarajan and Lohman [R561 irradiated CHO cells with
far UV and near UV (broad-spectrum) and determined
the frequencies of SCEs over a range of doses; inparallel experiments, enzymatic assays were performed
to assess the numbers of pyrimidine dimers making
use of dimer-specific endonuclease from Micrococcus luteus. It was found that both types of UV irradiation induced SCEs, which showed a linear increase
with exposure time (dose); in addition, the enzyme
specific sites (ESS) showed a similar increase and theratios of SCEs to ESSs were nearly the same over thedose range studied. These data thus suggest that dimers
are related to SCE induction. However, a substantial
number of dimers need to be produced in the DNA ofCHO cells before one SCE can occur and their calculations show that about 20 OOO pyrimidine dimers need to
be induced for each additional SCE.
488. Recently, in experiments with chick embryonic
fibroblasts (which possess photoreactivating enzymes).
Wolff [W22J found that photoreactivation (PR)following UV irradiation leads to the disappearance of
dimers but not of SCE's. The interpretation was thatsome other minor photoproduct and not the dimers
may be responsible for the induction of SCE's. Similar
results were obtained by Natarajan et al. [N17] after 5
and 10 J/m2 UV irradiation followed by PR; there wasa reduction in the number of dimers (i.e., ESS) but noreduction in the frequencies of SCEs. The frequencies
of SCEs seemed to saturate around 20 per cell.

489. An examination of the chromosome preparations
showed that at these UV doses. there was a considerable
mitotic delay and a high frequency of chromosome
aberrations in cells which were still in their first mitosis.
This would indicate that only a small proportion ofcells came through to a second cell cycle. In subsequent
experiments therefore, Natarajan et al. used lower UV
fluences (1 and 2 J/m2). The results showed that:(a) There was a considerable amount of dimer
removal (by about 95%) after PR;(b) There was a reduction in the frequencies of SCEs
by about 50%.
490. In order to investigate the effect of fixation timeon the frequency of SCEs, an experiment with 2 J/m2
was conducted and the cells were fixed at 5 h intervals
between 24 and 35 h. The data clearly demonstrated
removal of dimers with PR (to the extent of about 85%)and that, at all fixation times, there was a significant
reduction in the frequencies of SCEs which varied
between 25 and 40%. These results. therefore, show that
there is a relationship between SCEs and pyrimidine
dimers. The discrepancy between these data and thoseof Wolff [W22] is probably due to the possibility thathigh UV fluences were used in his study.
491. Using Potorous cell line PtK2, Ishizaki et al. [181found that the frequency of UV-induced SCEs could be
reduced by post-irradiation exposure to visible light. In
their experiments, UV fluences of 5 and 10 J/m2 wereused. Moreover, the effect of PR light was temperaturedependent; the authors therefore concluded that the
reduction in the frequency of SCEs is probably
mediated through an enzymatic reaction.
492. In more recent work, van Zeeland et al. [211]conducted
experiments withfibroblasts
from
Xenopus laevis which possess photoreactivating
enzyme to study the influence of photoreactivation on
UV-induced pyrimidine dimers, sister-chromatid
exchanges, cell-killing and point mutations to ouabain
resistance. The results clearly showed that thefrequencies of all the biological end-points studied werereduced on photoreactivation and this was paralleledby a decrease in the frequencies of pyrimidine dimers(determined as endonuclease sensitive sites). However,an absolute quantitative relationship could not beestablished between the photoreactivation-mediatedreduction in the amount of pyrimidine dimers and thedecrease in the frequencies of SCEs, chromosomal
aberrations, point mutations and the extent of cellkilling and this could be due to a number of causes.
Nonetheless, these studies show a direct relationshipbetween biological effects and UV-induced pyrimidine
dimers in this system.
4.

A test of the hypothesis of whether there is proportionality between spontaneous and induced rates ofmutations493. One of the main assumptions involved in the useof the doubling-dose method for risk evaluations in
man is that of proportionality between the average
spontaneous and induction rates of mutations. An
example will serve to illustrate this point. Suppose thatin species A, the average spontaneous rate is 1Q-5 pergene and the average rate of induction is 10-7 per unit
dose per gene. The doubling dose then is 100 dose units
and the mutational risk per unit dose of radiation
exposure is 1/100 of the spontaneous incidence.
Suppose that in a related species B, the average485

spontaneous rate is lower, say I Q-6 per gene. It will bevalid to apply the doubling dose of 100 dose units tospecies B only when it is assumed that the average rateof induction in species Bis also lower, say, 1o-s per unit
dose per gene such that 10-5/10-7 - IQ-6/10-S = 100. If
for instance in B, the rate of induction is 10-7 (i.e., thesame as in A), the doubling dose will be 10 dose units
and the mutational risk will be an order of magnitude
higher, namely 1/ 10 of spontaneous incidence (insteadof 1/100 of the spontaneous incidence) in spite of thefact that the amount of damage induced will be thesame in both cases.
494. One way to test the validity of the assumption of
proportionality between spontaneous and induction
rates is to examine the average induction rates ofmutations in related species or strains of organisms thatdiffer from one another in their spontaneous rates andsee whether such a proportionality is in fact obtained.
Another method is to examine within a species whether
or not such a proportionality between spontaneous andinduction rates is obtained on a locus-by-locus basis fora number of gene loci. Shukla, Sankaranarayanan andSobels [S79] adopted this latter approach to study thisproblem in Drosophila melanogaster. These investigators collected data on the induction of specific-locus
mutations at 14 X-chromosome loci following spermatozoa) irradiation (x rays; 3000 R). The mutational
spectrum obtained in the radiation work was comparedwith the spectrum that Schalet [S80) has observed in his
work on spontaneous mutations using the same set ofloci and stocks. The conclusion that emerged from theirwork was that the data were not out of line with theassumptionofpostt1vecorrelation
betweenspontaneous and induction rates of mutations for theloci under study but that more extensive data, both on
spontaneous and induction rates would be required
before the evidence could be considered conclusive.
Furthermore, a proportionality across the spectrum of
mutations for spontaneous and radiation-induced
mutations in spermatozoa may not hold for spermatogonia, since it has been shown in the mouse that the
spectra for induced mutations in these two germ cellstages are not the same.

these data are consistent with the assumption of proportionality between spontaneous and induced mutations.
496. Glickman et al. [033] conducted a study on
gamma-ray induction of mutations in the lacl gene of
Escherichia coli, a locus which codes for the lac
reprcssor. Exposures from 5 kR to 40 k R were used andthe lacl mutants recovered (among which werenonsense mutations ranging from 1.4 to 10.8% in the
different experiments) were analysed for changes atmore than 70 nonsense sites (amber and ochre) within
the lacl gene. Contemporary controls were run and theconclusions drawn pertained to 98 and 135
independent nonsense mutations isolated in thecontrols and 30 kR radiation experiments, respectively.
497. Among the spontaneous mutants, both transitions and transversions were frequent and there were
three "hot spots'' in the amber spectrum at sites 6, 15
and 34. These sites had previously been shown byMiller et al. [M48] to correspond to the location of 5methylcytosine residues in the DNA; this naturallyoccurring modified DNA base gives 5-methyluracil(thymine) by spontaneous deamination and therefore
occasionally results in errors in the DNA that go uncorrected by uracil-N-glycosidase [C39). Gamma rays also
induced both transitions and transversions but theprominent amber "hot spots" seen with the
spontaneous mutants were absent, suggesting that
gamma rays presumably do not cause extensive deamination. Transitions constituted 55.6% of the
gamma-ray induced amber mutants compared with
71.4% transitions among the spontaneous ambermutants: the difference is statistically significant at the
5% level. When the amber data were analysed again
with the amber "hot spots" excluded, the distribution oftransition and transversion events in the spontaneousand induced mutants was similar. The authors havedrawn the conclusion that the spectra of induced andspontaneous mutations are similar with the exceptionof the spontaneous "hot spots".

5.

495. In another study, Racine, Langley and Voelker[RS7] accumulated enzyme mutants by exposing abalanced lethal strain of Drosophila melanogaster(heterozygous at seven allozyme loci) to chronic gamma
irradiations (0.07 Gy h-1) for 14 generations (196 days;
total accumulated dose: 335.52 Gy). Following the 14
generations of exposure the flies were screened by gelelectrophoresis for newly-arisen null mutants and/or
mobility variants. Among other things, the rank orderof mutability observed in this work was compared withthe one recorded by Mukai and Cockerham [M3] andtheir own unpublished results on spontaneous
mutations at the same set of loci. This analysis revealed
the following rank order for radiation-induced
mutations (the numbers of mutants are shown in parenthesis): aGpdh (6); Hex-C {4); cMdh (2); Got-2 (1);Adh (O); Dip-A (0) and aAmy (0). For spontaneous
mutations, the order was the following: aGpdh (7);Hex-C (5): cMdh (2); uAmy (1); Got-2 (1): Dip-A (0)and Adh (0).17 It can be seen that there is a good correspondence between the two rank orders suggesting that
17 aGpdh: a-glycerolphosphate dehydrogenase; Hcx-C
hexokinase-C; cMdh: cytoplasmic malate dehydrogenase
Got-2: mitochondrial glutamate oxaloacetate transaminase
Adh: alcohol dehydrogenase; Dip-A: dipeptidase-A; aAmy
a-amylase.

486

Chromosomal evolution in primates and its possible
relevance for inter-specific comparisons and forassessing the chromosomal basis of human pathology498. Dutrillaux [D4] has published an exhaustive
review of the chromosomal evolution in primates andhas proposed a tentative phylogeny from Microcebus
murinus (a Prosimian which seems to have retained arather primitive karyotype) to man. The chromosome
studies were carried out after whole blood culture or
fibroblast culture after skin biopsy. Detailed comparisons of the karyotype of man with those of about 60
species (of the approximately 200 species of the orderof primates) were made, on a band-by-band basis forevery chromosome using all the available banding
techniques. Almost all the data used for these comparisons have been collected by the author and hiscolleagues. The major conclusions of use to theCommittee that emerged from this work are summarized in the following paragraphs.
499. To facilitate discussions, the reconstructed evolutionary tree showing the sequence of chromosomalchanges that have occurred is diagrammed in Figure 11.
An examination of the above figure shows that thepattern of chromosomal evolution is not the same in the
different lines. The types of rearrangements that haveoccurred vary from one group (suborder, family, genus)

.......... .
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A

Legend: Each species is designated by a three-letter code:

HSA: Homo sapiens
PTA: Pan troglodytes
GGO: Gorilla gorilla
PPY: Pongo pygmaeus(man)(chimpanzee)(lowland gorilla)(orangutan)

MMU: Macaca mulatta
MFA: Macaca fascicularis(rhesus monkey)(crab-eating
macaque)(pygmy chimpanzee)

PPA:
CGA:
EPA:
MTA:
CAE:
CMI:

Pan paniscus
Cercocebus galeritus
Erythrocebus patas
Myopithecus talapoin
Cercopithecus aethiops
Cercopithecus mitis

rr•

Plfl

I

Pongidae

Cercopithecidae(patas monkey)(several species)
Colobidae

CVE: Colobus vellerosus
CCA: Cebus capucinus
ATR: Aotus trivirgatus',~._.......r,(capuchin monkey)(owl monkey)

MIM: Microcebus murinus(red-fronted lemur)
LFF: Lemur fulvus fulvus
LFA: Lemur fulvus albocollaris
LFC: Lemur fulvus collaris
LMA: Lemur macaco(crowned lemur)
LCO: Lemur coronatus(ring-tailed lemur)
LCA: Lemur catta
HSI: Hapalemur simus
HGO: Hapalemur griseus occidentalis(gentle lemur)
HGG: Hapalemur griseus griseus
HGS: Hapalemur griseus subspecies
WA: Varecia variegata
PFU: Phan er furcifer} Cebidae

Lemuridae

Figure II. Reconstruction of the sequence of chromosomal changes that have occurred during primate
evolution from the most ancestral karyotype seen in
Microcebus murinus [04]to another. For instance, Robertsonian translocations
are preponderant among the Lemuridae (44 of the 57
changes are of this type), but are non-existent among
the Pongidae. Chromosome fissions are very frequent
among the Cercopithecinae (26/51, including new
information), but are not found elsewhere, andpericentric inversions are preponderant in the evolutionof Pongidae and the human species (17 /28).
500. There is a very close similarity of chromosome
banding patterns between the simians studied and man.
All the quantitative and some of the qualitative variations detected involve the heterochromatin. Approximately 70% of the bands are common to the simians
and to the lemurs (prosimians). In the remaining 30%,
technical difficulties
prevented
a meaningfulcomparison but this does not exclude the possibility
that a complete analogy may exist. It thus appears thatthe chromosomal evolution of the simians (andprobably of all the primates) has occurred without
detectable duplication or deficiency of the euchromatin.

501. The reasons why particular kinds and/or
sequence of changes have occurred in one but not in
another line can only be conjectured but the answers
presumably lie in the breeding structure and size of theevolving populations, the selective advantages or disadvantages of given rearrangements, the genie contents ofthe chromosomes concerned, the functional alterations
that may accompany structural alterations (position
effect), etc. The available data suggest that of all these
considerations,evolutionbystructural-changemediated position effects appears least likely.
502. As mentioned earlier, the kinds and relative
frequencies of the different rearrangements aredifferent in the different lines of evolution. For
instance, a closer look at Figure II, segment B- HSA
will reveal that from the last common ancestor of all
simians to man, 50% of the changes are pericentric
inversions, 13% complex intrachromosomal rearrangements and 16% complex, imprecisely-defined interchromosomal ones. In the direct ancestors of man(segment D-HSA; Figure 11) again, 8 of the 15487

changes arc pcriccntric inversions, the remainder being
made up of others (3 other intrachromosomal, 3interchromosomal and I paraccntric inversion) with noRobertsonian translocations.
503. In contemporary human populations, as was
discussed in chapter I, the two kinds of rearrangementsthat are predominant are the Robertsonian and reciprocal lranslocations; the pericentric inversions
constitute a minor class. It would thus appear that thecategories of rearrangements most frequently observedin humans are not those that occurred in the evolutionof our ancestors.
504. Some of the types of chromosomal changes thathave been noted during the evolution of primates arealso known in chromosomally abnormal humanindividuals. Apart from the Robertsonian and reciprocal translocations mentioned earlier, pericentric
inversions appear to be common to both human
evolution and human pathology, although the relative
frequencies are different. It would therefore appear
instructive to examine whether these inversions that are
rarely observed in man are not those that are"frequently" observed in evolution. In the work
reported [D4], Dutrillaux could identify 44 pericentric
inversions among which 21 occurred either on chromosomes that were already identical to those of man or on
those which were at the last stage before giving rise tohuman chromosomes. Two-thirds of the latter could beconsidered as possible "convergent mutations" (in thiscontext, referring to the occurrence of similar structuralchanges in species belonging to different lines ofdescent) and one-third, "reverse mutations" (the occurrence of structural change leading to ancestralchromsome(s)). From the data available for patients(over 10 OOO of them) at the Institut de Progenese,
Dutrillaux could extract 26 independent pericentric
inversions; in addition, there were three independentcases of paraccntric inversions.

505. A comparison of these 29 inversions with those
detected during evolution permitted the conclusion that
8 of the former could be considered as possible "reverse
mutations" and 1 a possible "convergent mutation". Of
these 8, 7 were pericentric inversions and 1 a paracentric inversion; out of the first 8, 1 was observed 3times and another 2 times. Considering the fact that the
number of breakpoints and consequently the number ofdifferent inversions is theoretically very large, it would
appear that the correlation between changes that haveoccurred in human pathology and in human evolution
is more than mere coincidence.
506. The implications of these findings for interspecific comparisons of chromosomal sensitivity toradiation (or other mutagens) to the induction ofdifferent kinds of aberrations can only be speculated on
at present. Two questions, yet unresolved, are: "can theevolutionary history provide any clue with respect tothe inducibility of a given kind of chromosomal
aberration in different species and in man and thepathological consequences that may derive from such
induced aberrations in man?" and "can quantitativeand qualitative comparisons be based on the inductionof one kind of aberration in different species provide aproper perspective and a basis for predicting therelative radiosensitivity of human chromosomes todamage that is relevant in the context of induced pathological states?"
488

6.

Summary and conclusions

507. Experiments were conducted in which mice andrabbits were kept in huts in sites of high concentrationsof uranium in the soil. The radiation exposures werefrom external gamma-irradiation and from inhaledradon. Periodical blood samples were taken from the
rabbits to assess the amount of chromosome damage;the mice were used in tests on fertility and for cytogenetic studies on induced reciprocal translocations(spennatocytc analysis). ,508. 1n the rabbits, the frequency of dicentrics in thelymphocytes rose from zero per cent (al the beginningof the experiment) to 1.9% after 4 months exposure(gamma-ray doses in the range from 0.13 lo 0.27 Gy for
individual rabbits), to 2.6% after eight months(gamma-ray doses of between 0.15-0.53 Gy for
individual rabbits) and to 3.9% after one year. After a
16-month period, there was no further increase in thefrequency of aberrations and after a 20-month period,
the frequency actually dropped to zero. The radon
exposure estimates were 5-10 Gy per year to thebronchial region and about 1 1Q-2 Gy per year to the
gonads. From model studies with radon exposuresalone to rabbits, it was concluded that the chromosome
aberrations observed were all due to gamma irradiation.
509. Male mice kept in the radiation area for threemonths showed slight increases in litter size. the mean
number of offspring sired and in the mean number ofoffspring weaned. Female mice (also kept in theradiation area) showed slight reductions in all theabove three indicators of radiation effects. Neither theirradiated male mice nor their sons showed any
evidence for the presence of translocations or otheraberrations in their spermatocytes. The estimate of theexternal gamma-irradiation for the 3-month period was
0.15 Gy.
510. Additional data on the radiation-induction ofaberrations in lymphocytes (dicentrics) that havebecome available since the publication of the 1977 reportconfirm the conclusion reached by the Committee in its
1977 report, namely, that there is no simple relationshipbetween the effective chromosome arm number of thespecies and its relative radiosensitivity to the inductionof these structural aberrations. The mammalian species
studied in this respect included the rabbit, the cat, thechimpanzee, the gorilla and the crab-eating monkey.
Furthermore when it is ensured that only cells in theirfirst mitosis after irradiation are scored for dicentrics,
there are no differences in sensitivity between mouseand human lymphocytes, and between rabbit andhuman lymphocytes.
511. Whereas after acute gamma irradiation thefrequencies of radiation-induced dicentrics in thelymphocytes of man and the crab-eating monkey are
similar (at similar doses) after chronic irradiation, theyield in monkey lymphocytes was lower. The difference
after chronic irradiation has been explained on theassumption that chromosomal damage leading to dicentrics can be repaired in unstimulated (Go) lymphocytes
and that such a repair capacity may be different in thetwo species.
512. Direct evidence for the thesis that an exchangeaberration is the result of interaction of two lesions has
been obtained using root-lips of Vicia faba in whichprior to irradiation with long-wave UV or x rays, BUdR

was substituted for thymine in various numbers of
DNA strands in the chromosomes with a consequentchange in radioscnsitivity, this increasing withincreasing numbers of substituted strands.
513. Data demonstrating that double-strand breaks in
the DNA are responsible for radiation-induced (x rays)
chromosome aberrations has been obtained in CHO
cells in vitro. The experiments involved the introduction of Neurospora endonuclease into cells madepermeable prior to the x-ray exposure. The results
showed a marked increase in the frequency of aberrations under these conditions relative to controls whichwere not treated with the enzyme. Similar results wereobtained with bleomycin and MMS, but not with UV or
mitomycin-C. Possible reasons for these differences are
discussed. In the x-ray work. there is evidence showingthat the single-strand breaks produced by irradiation
are available for action by the enzyme even 60 minutes
after irradiation, but the induced double-strand breaks
are not able to interact effectively to produce
chromatid-type aberrations as the interval between
irradiation and the enzyme treatment increases.
514. The frequencies of UV-induced sister-chromatidexchanges in rat kangaroo cells and in a potorous cellline are reduced on photoreactivation with visible light,
suggesting that UV-induced pyrimidine dimers are
involved in the production of SCEs. Using anothertechnique, the involvement of dimers in UV-induced
SCEs has also been demonstrated in CHO cells.
515. In chick embryonic fibroblasts (which have the
PR enzyme), PR following UV-irradiation led to thedisappearance of the dimers but not of SCEs in somestudies. The reason for this has now been clarified:higher UV fluences which were used in these studies led
to a considerable mitotic delay and, consequently, onlya small proportion of cells came through to a second
cell cycle. With lower UV-fluences, clear evidence has
been obtained for removal of dimers by PR treatment
after UV as well as for a reduction in the frequencies of
SCEs.
516. The hypothesis of whether there is proportionality between spontaneous and radiation-induced
mutation rates (an assumption which is central to theuse of the doubling-dose method for risk evaluations)has been tested in Drosophila and in E. coli. In Drosophila, the data on spontaneous and induced mutation
rate estimates for a number of individual loci areconsistent with the hypothesis. In E. coli where thecomparison was between spontaneous and induced
mutation rates at more than 70 sites in the Jacl gene. if
the three amber "hot-spots" (predominant in the
spontaneous mutation spectrum) were excluded, there
was correspondence between spontaneous and induced
mutation rates for the different sites.
517. Extensive data on chromosomal evolution inprimates have been published in which detailed
comparisons of the karyotype of man with those ofabout 60 primate species have been made (on a bandby-band basis for every chromosome using all theavailable banding techniques). It has been found thatthe pattern of chromosomal evolution is not the same inthe different branches of the evolutionary tree (i.e., thetypes of rearrangements that have occurred vary fromone group to another). From the last common ancestorof all simians to man 50% of the changes are pericentric
inversions. However, in contemporary human populations, the pericentric inversions constitute a minor

class. The possible implications of the finding of
pericentric inversions in chromosomally abnormal
individuals are brieny outlined within the framework of
the evolutionary history of our species.

III.

EFFECTS OF X-IRRADIATION ON
SURVIVAL KINETICS OF SPERMATOGONIAL CELLS IN MICE AND
RATS

518. Oakberg [010] conducted a study to investigate
the effects of x-irradiation on the survival of stem cell
spermatogonia in the mouse and to obtain doseresponse curves for bpth single and fractionatedexposures in order to determine if the cell populations
surviving these treatments are qualitatively different.
This study is an extension of the author's earlier work[011] discussed in the 1972 and 1977 reports of theCommittee.
519. One group of adult C3H x 101 hybrid male micereceived three injections of 0.46 MBq or 3H-thymidine
at 9 h intervals and x-irradiation (100. 300, 500, 600,
1000 R or the first half fraction of a 1000 R exposure)
24 h after the last injection. The mice were killed 120 h
and 207 h (in one experiment, 414 h) after irradiation.
The rationale for choosing 120 and 207 h is that it is
known from previous work [012] that some surviving
stem cells will divide between these two intervals,
although intervals of five days or more are required forthe process of degeneration to run its course. A second
group of mice received a single injection of 0.46 MBq
of 3H-thymidine one hour before x-irradiation at levels
similar to those mentioned above. Appropriate controls
were maintained. Testes preparations were made for
autoradiography and for scoring of survival of the stem
cells: cell survival was measured by counting stem cells
in 99 tubule cross sections per slide (198 per mouse)
distributed among the stages of the cycle of the seminiferous epithelium: labelling was scored by counting 100
As spermatogonia per slide (200 per mouse).
520. The stem-cell survival data 120 and 207 h after xirradiation are given in Table 35. The mean number ofAs cells in the unirradiated mouse is reduced by the
injection of 3 H-thymidine and likewise, irradiated mice
given 3H-thymidine show lower cell counts than micethat received radiation alone. Compared to the 120 hdata, the number of cells scored in the unlabelled group(experiment 1) after 207 h is higher at 300, 500 and 600
R, lower at 1000 R and the same for the 500 + 500 R
exposure; in the mice receiving 3H-thymidine survival
after 207 h is higher than after 120 h at 300, 500 and 600
R, and lower for both 1000 R and 500 + 500 R
exposures. At both intervals, with and without 3Hthymidine. the data lit a curvilinear relationship withno evidence of discontinuity over the 100-1000 R
range, though it should be noted that there are no
points between 600 and 1000 R.
521. The data from experiments on the labelling of As
spermatogonia are summarized in Table 36. The
percentage of labelled cells at 207 h is markedly influenced by the total exposure and by exposure fractionation; for instance, in the 3 x 0.46 MBq group, thepercentage of labelled cells does not differ significantly
between controls and the 100-oOO R groups, is significantly lower in the 1000 R group and significantly highin the 500 + 500 R group. At 414 h, there is no significant difference between 100, 300, 500, 600 and 500 +489

500 R groups (all .ire higher than controls) while thesingle I OOO R exposure is lower than in the controls justas al 207 h. When irradiation is given I h after lHlhymidine injection, very few labelled cells survive anyof the exposures used with values ranging from 2.2% to6.6% compared with 21% for controls.
522. From these results. Oakberg [010) has concluded
that the surviving stem cell population is qualitatively
the same for that portion of I he dose-response curve
giving a linear increase in mutation frequency, butdifferent for both 1000 R single and fractionatedexposures. This parallelism between survival of labelledcells and mutation frequency in spermatogonial stem
cells summarized in Table 37 suggests that a stage in thecell cycle 24-42 h after DNA synthesis is resistant tocell killing but sensitive to mutation induction. The
mutation rate after a single 1OOO R exposure is low
because labelled mutation-sensitive cells have been
selectively killed. The mutation frequency after the 500
R exposure is increased because of synchronizationinduced by the first fraction combined with theselective killing of unlabelled cells by the second one.
Irradiation one hour after the labelling with 3Hthymidine demonstrated that the S phase of the
spermatogonial stem cell cycle is sensitive to radiationinduced cell killing.
523. There are some interesting differences between
the dose-response relationship reported by different
authors for effects of low-LET irradiation on somedirect measures of spermatogonial survival. As alreadystated, Oakberg [010) found a curvilinear (quadratic)
response for survival of type As spermatogonia scored
207 h after x-irradiation, with no sign of discontinuity
at 600 R. De Ruiter-Bootsma et al. [R76) reported an
exponential relationship over the 4-12 Gy range forspermatogonial stem-cell survival measured 3 weeks
after irradiation by the tubule repopulation method,again with no sign of discontinuity around 6 Gy.
524. Cattanach [C40], however, reported an exceptionally high 600 R point (giving a plateau between 600
R and 700 R) in the otherwise exponential doseresponse curve for the median day of return to fertility(i.e., length of the sterile period which results from
spermatogonial killing) after 300-1000 R x-irradiation.
He interpreted this as due to the presence of twostem-cell populations with different radiosensitivities toradiation killing. Lu et al. [L48] assayed levels of
the X-isozyme of lactate dehydrogenase, LDH-X(providing a measure of the number of spermatocvtes
plus spermatids) and numbers of sperm-heads in testicular homogenates 56 days after 0-14 Gy of acute
gamma-irradiation. Both curves had very large
shoulders with inflection points at 5 and 6 Gy. The
authors concluded that there was a radioresistant
subpopulation of stem-cells which predominated after
doses greater than 6 Gy.
525. Thus, results of the two histological assays are inagreement with each other, as are those of the twofunctional assays. As the former two assays measured
the stem-cell survivors at an earlier post-treatment stage
than the latter two, the possibility arises that some
temporal factor (possibly connected with a feed-backmechanism) alters the form of the response between theinitial phase of spermatogoniul proliferation and thefinal phase of sperm production. Oakberg [010)suggested that the 600-700 R plateau in return tofertility found by Cattanach might be connected withthe dynamics of repopulation at higher doses when the490

number of surviving colonies is low. This might affectthe return to sperm numbers adequate for fertility in amanner which is dose-dependent. However, thishypothesis may need modification in view of the more
recent results of Lu et al. [L48) already discussed.
526. Huckins and Oak berg [H59, H60, H6 l J haverecently carried out further analyses of the behaviour ofstem-cell spermatogonia in normal and irradiated rat
and mouse testes, mainly using whole mounts of seminiferous tubules. When their conclusions are comparedwith those of Cattanach and co-workers [C32, C63.
C64, C65] derived from translocation studies andalready discussed in section 11.8., a consensus seems toemerge. The only spcrmatogonia which survive anacute exposure of 100 R or more (apart possibly fromsome A1 cells) are some of the radioresistant longcycling stem cells.
527. According to Huckins and Oakberg [H61] thesesurvivors are likely to be in a prolonged "protective" G 1phase, while Cattanach and Crocker [C63] havedescribed it as Go phase. Probably as the result of thedepletion of other spermatogonial stages. these longcycling surviving cells are triggered from the indeterminate "A-phase" into the determinate "B-phase" [Sll 8]of active mitotic proliferation, with nearly synchronousentry into DNA synthesis 2 to 3 1/2 days later [H61].
Most stem-cells then go into a short cycle, as the resultsof de Ruiter-Bootsma and colleagues indicate [R76].
Some stem-cells start to differentiate into subsequent
stages before the complete rebuilding of the undifferentiated population [H61].
528. At 24-48 h after irradiation the surviving As
spermatogonia synchronously arrive at what isprobably a transitional phase sensitive to the inductionof mutations and chromosome aberrations, but inwhich some cells could still survive a large radiation
dose. The sub-additive mutational response at longer
fractionation intervals (3-15 days) presumably reflects
the sensitivity of the short cycling stem-cells. These are
the only type found in the immature testis. which also
has a reduced radiation response [C64, E22, Sl 19). The
exact relationship between the long-cycling and theshort-cycling stem-cell spermatogonia is still obscure. It
is possible that the short cycle precedes differentiation,or that short-cycling cells periodically and randomly
enter a longer cycle [H61 ].
529. Although the long- and short-cycling cells can be
regarded as more resistant and more sensitive subpopulations, it seems difficult to equate them with theentities thus described by Cattanach et al. [C40] and Lu
et al. [L48] since the shorter cycling cells seem todisappear at doses which are decidedly lower than the> 6 Gy postulated. However, it seems clear that heterogeneity in sensitivity to killing and to mutationinduction must remain within the long-cycling A, cells
at stage G 0 or G1 which would alone survive doses of 6
Gy or more, since otherwise it would be very difficult to
explain the humped type of dose-response curve for the
induction of point mutations or translocations. The
exact nature of the mechanism which triggers active
stem-cell proliferation after irradiation is still unknown,
but it should be noted that neither Cattanach et al. [C641
nor Cunningham and Huckins [C66) have been able todemonstrate a chalone effect in the irradiated testis.
530. In the 1977 report, the work of Hsu andFabrikant [H45] on the cellular response and cell
population kinetics during spermatogonial cell renewal

in the mouse testis exposed to continuous gamma
irradiation at 1.8 10-2 Gy d-1 and at 0.45 Gy d-1 wasdescribed. The results were that:(a) At the lower dose rate for seven days, the A,
spermatogonial cells showed no reduction in cellnumber; at the higher dose rate, the number of A,
cells was reduced to 50% of that in controls during
the first three days of continuous irradiation andfrom day 4 to 10, this ligure was 80%. From day 11
onwards, control levels were reached:(b) In the group irradiated at the higher dose rate for
two weeks, the repopulation of the seminiferous
epithelium commenced with increased cell proliferation in the A, cells. This was supported by thelinding of an increase in the As mitotic index.
Labelling with 3H-thymidine was used in thisstudy for the analysis of cell population kinetics.
531. Erickson [E14] has recently reported the resultsof a similar study in rats with a broader spectrum of
low dose rates but without using any radioactive label.
Sprague-Dawley rats were irradiated continuously with
60Co gamma rays at dose rates of 1 10-2, 3 10-2 or 6 10-2
Gy per 23 h day (7 1~ Gy min-1, 2.1 10-5 Gy min-1 and4.2 10-5 Gy min-1) for periods ranging from one month
to six months. At the termination of the radiation treatments in the different groups, the animals were killed
and testes preparations were made. Spermatogonia
were counted in whole mounts of seminiferous tubulesthat were isolated from the testes.
532. At 1 10-2 Gy d-1, there was no statistically significant effect on stem cell number and this was soirrespective of the duration of exposure (i.e.,
irrespective of the total dose delivered); at 3 10-2 and6 10-2 Gy d-1, there was an initial drop (after one andtwo months of irradiation, respectively) to about 80 or
60% of the control level, followed by a slower decrease
reaching values of 60 and 40% of the controls.
533. One month after irradiation, counts of differentiating spermatogonia were reduced to a dose ratedependent level that remained essentially unchanged
during the succeeding five months of irradiation; theproduction of Ai spermatogonia (a population whose
size depends on spermatogonial generations A1-A3) was
not significantly affected by 1 10-2 Gy d-1 and averagevalues for dose rates of 3 10-2 Gy and 6 10-2 Gy d-1 were
60 and 30% of controls, respectively; testicular weight
was also not significantly affected by 1 10-2 Gy d-1, but
3 10-2 Gy d-1 resulted in a final value of 73% of control
and that for 6 10-2 Gy d-1 was 49% of control. Erickson
concluded that a reduction of stem cell mitotic activity
may be the principal effect of continuous low-level
irradiation on spermatogenesis in the rat.

IV. TIMING OF OOCYTE MATURATION IN
THE MOUSE AND ITS RELEVANCE TO
RADIATION-INDUCED CELL KILLING
A:'ID MUTATIONAL SENSITIVITY
534. In the 1977 report, the preliminary results of
Oakberg and Tyrell [014] from their autoradiographic
studies on the timing of oocyte development in theadult mouse were brieny discussed. Oakberg (09] has
now published these results and has also compared thenuclear morphology of arrested and stage 3 oocytes in
the mouse, guinea pig and the human female. The
results of Oakberg and those of some others notconsidered in the 1977 report are summarized in thissection.

535. The importance of this problem derives from thefact that in specific-locus experiments with irradiatedfemale mice, the mutation rate drops to zero in theprogeny derived from conceptions that occurred after
six weeks and it had not been possible so far to relatespecific oocyte (and follicular) stages to specific postirradiation litters. Pedersen's extensive analyses of follicular dynamics in the female mouse [P31] were basedon lH-thymidine labelling of follicle cells: his results
showed that it took 19 days for a stage 3b with about 20
cells to reach ovulation. Duration of stages 7 and 8.
however, could not be measured by this technique.
Other difficulties in using 3H-thymidine labelling arethat beta rays from the tritium kill follicle cells [B48).
Follicle cells have different cell cycle times. as a consequence of which undue weight may be given to rapidly
dividing cells. thereby shortening the estimate of transit
times.
536. In their earlier work using N-3H-thymidineacetyl-D-glucosamine, Oakberg and Tyrell [015)estimated that 35 days were required for maturation ofstage 3b follicles. Although the problem of oocyte
timing was not discussed by Haddald and Nagai [H46],
the results of these authors with labelled L-fucose gave
results similar to those of Oakberg and Tyrell. showingthat the estimated time for maturation of 3b oocytes
was longer than that in the work of Pedersen [P31 ).
537. In the work recently reported by Oakberg (09]the question was asked whether the drop in mutation
rate after six weeks might be attributed to the samplingof arrested stage 1 oocytes or whether it did occur after
the initiation of follicular growth when species differences in chromosome morphology are minor. Fourlabelling experiments were performed, the first two
with N-3H-acetyl-D-glucosamine, the third with D-1JH-glucosamine and the last one with L-1-3H-fucose. In
experiment 1, the mice were given labelled acetyl-Dglucosamine (3 x 925 kBq at 9 h intervals) and killed atintervals ranging from 6 h to 25 days. In experiment 2,
the females were irradiated with 50 R of x rays (group1) or given single intraperitoneal injection and 50 R of
x rays 24 h later (group 2) or the labelled compound
alone (group 3). While some of the mice from thesethree groups were used for histological studies of theovaries. some were pair-mated with 101 x C3H males.
In experiment 3, the mice received D-J-3H-glucosamine(either in a single injection of925 kBq or in three equal
fractions spaced 9 h apart) and killed at intervals
ranging from 24 h to 28 days after injection. Labellingwith L-J-3H-fucose was achieved by two 925 kBq injections given 4 h apart and the animals were killed 1, 7,
14, 21 and 28 days after injection. The progressive
appearance of unlabelled oocytes (unlabelled in zona
pellucida) were used to compute the transit and thematuration time of the different stages.
538. The results show that:(a) Of the three compounds tested, L-1-3H-fucose
gave the best labelling with the lowest dosage;(b) Approximately four weeks are required for stage
4a oocytes (with a second layer of follicle cells) toreach ovulation, thus confirming the earlier
finding [014]; the duration of stage 3b, however. isabout two weeks instead of one week as suggested
earlier;(c) Adding these two estimates gives six weeks as thetime interval from initiation of stage 3b 10
ovulation;(d) Although there was some evidence for a reductionin the numbers of stage 3 and 4 oocytes in the N491

(e)lH-acetyl-D-glucosamine-injected females, anextensive ten-week breeding test showed no effecton breeding behaviour or litter size of females
given the labelled compound;
There was no evidence that either 50 R or
pregnancy had any effect on the progression oflabelled follicles.

539. Thus, conceptions within six weeks after irradiation sample oocyles exposed in stages 3b-8 and littersconceived after six weeks arc derived from stages l-3a.
The numbers of surviving stage 1 and stage 2 oocytes
are so low (after irradiation) that no more than one or
two litters are produced from these and at least one
litter must be derived from stage 3a. The nuclear
morphology of both stages 3a and 3b are similar to one
another and also to stage 3 of guinea pig and humanoocytes and yet there are striking differences inmutational sensitivity of the 3a and 3b stage oocytes in
the mouse; furthermore, the change in mutational sensitivity of the mouse oocyte with time after irradiation asshown by Russell [R38, R60] occurs in a cell with"typical" diplotene chromosome configuration. i.e., it
does not parallel the change from the arrested dictyate
to the more characteristic diplotene of oocytes
contained in a follicle with a single layer of cuboidal
cells. These findings demonstrate that the degree ofchromosome condensation does not appear to be areliable criterion of oocyte sensitivity to either cellkilling or mutation induction.
540. The high sensitivity to cell killing and the morediffuse (dictyate) condition of the chromosomes of thearrested mouse oocyte compared to the radiation
resistant "typical" diplotene of the arrested humanoocyte has raised doubts concerning the relevance ofgenetic data in the mouse for the estimation ofradiation hazards to the human female. The data of
Caine and Lyon [C30] and of Cox and Lyon [C41),
however, show that the guinea pig, where the oocyte isarrested in a condensed diplotene, with a highresistance to cell killing, also shows a low incidence ofradiation-induced dominant lethals. just as the arrested
dictyate oocytes of the mouse and hamster.
541. There is therefore no consistent correlation,either negative or positive, between sensitivity to cellkilling and the frequency of mutation observed [C30,
R38]. The evidence so far suggests that low mutational
sensitivity may be a general property of arrested
mammalian oocytes (irrespective of nuclear configuration) but the number of species studied from thispoint of view is still small. Moreover. it should bepointed out that although the usual pattern fordominant lethal induction is one of high sensitivity ofthe maturing oocyte and low sensitivity of the immatureone, Caine and Lyon [C30] found a somewhat higher
frequency of post-implantation dominant lethals in theimmature guinea-pig oocytes than in the mature,
although the yield was still low.
542. As the authors point out, a considerable part of
the high pre-implantation loss in first oestrus matings
may have been due to oocyte damage rather than todominant lethals. The evidence for dominant lethal
induction was accompanied by a reduction in littersize, lasting for many months after irradiation. The
extent to which this reduction was the result of genetic
damage is not yet clear. Caine and Lyon emphasize theneed for further work on this, pointing out that "ifgenetic damage were detectable in guinea-pig oocytes
several months after irradiation it would not be safe to492

conclude that such damage would not persist in human
females". Therefore it would seem incorrect to assume
that the mutational radiosensitivity of the immature
human oocyte is necessarily as low as that of theimmature mouse oocyte. Obviously, more data areneeded.

V.

SENSITIVITY OF MAMMALIAN FEMALE GERM CELLS TO KILLING BY
IRRADIATION

543. The 1972 report of the Committee [US]considered in some detail the sensitivity of oocytcs toradiation-induced cell killing in different species ofmammals. In this chapter, the main findings recordedin the above report will be first summarized before
considering new data.
544. Female mammals are born with a finite numberof oocytes formed already during embryonic development. These so-called primordial oocytes are
surrounded by a single layer of follicular cells. Withmaturation, the oocytes grow and multi-layered follicles
are formed. In young adults of both the rat and rhesus
monkey, the number of growing oocytes amounts toabout 10% of the total population, the remaining 90%
being primordial follicles [B49).
545. In the oocytes, the sequence of nuclear changes
comprising meiosis is arrested at the diplotene stage
which lasts until the time of ovulation. The nuclear
morphology of the arrested oocytes varies between
species. Thus. a typical diplotene is characteristic ofman, the rhesus monkey, the goat and the dog. A
synizesis-like diplotene (chromosomes clumped into a
dense knot) is characteristic of the guinea pig and adiffuse interphase-like diplotene (dictyate) is present in
the mouse and a few related species of rodents such as
the hamster. the deermouse and the gerbil.
546. The chromosomes in the nucleus of theprimordial oocytes in man and the rhesus monkey areof the so-called lampbrush type, similar in form to
those of amphibia and other lower vertebrates. The
oocytes in the growing follicles in all the species
examined possess lampbrush-type chromosomes.
547. In humans, there is evidence [S81] that the oocyte
chromosomes synthesize a large body of nucleolarmaterial and that the synthesis is amplified during the
diplotene stage. In pachytene, the oocyte nucleus shows
1 to 2 main nucleoli (connected with the satellites orsecondary constrictions of D and G group chromosomes) and micronucleoli are rare. In diplotene
however, the main nucleoli (2 to 3) become voluminousand numerous, micronucleoli appear and do not seemto be connected with the acrocentric chromosomes.
They arise at the contact zones of the heterochromatic
regions and differ from the nucleolar organizers on
acrocentric chromosomes; they are connected in part tocentromeric
hetcrochromatin
includingvarioussecondary constrictions.
548. In terms of radiation-induced killing ofprimordial oocytes, there are drastic differences insensitivity between the different species. The responseof the oocytes in the growing follicles, however, is not
strikingly different.
Information on theseissummarized in Table 38.

549. A few papers (among them two reviews) dealing
with the effects of irradiation on mammalian female
germ cells have been published during the last few years[B48, B50, B51, H47]. Some of the information
contained in the review papers [B50, B5 I]. although notnecessarily new or recent, covers a broader spectrum of
mammalian species than was the case in theCommittee's 1972 report. These data. however,strengthen the Committee's earlier conclusions, namely.
that the sensitivity of the human oocytes to the killing
effects of x-irradiation is more similar to that of therhesus monkey than to that of rats or mice. In what
follows, those aspects of radiosensitivity to killing notcovered in the 1972 report will be presented with particular emphasis on the data from the rhesus monkey andman.
550. Oogonia in the ovaries of the rhesus monkeys
and humans [B52, B53, B54] are more resistant than thecorresponding cells in rodents. For example, Baker and
Beaumont [B52] showed that the exposure of foetal
rhesus monkeys aged 4-4.5 months to 350-600 R of xrays caused a 7% reduction in the population ofoogonia; when the post-irradiation interval was
extended to 10-14 days, the depletion of the germ cells
was only 4%, reflecting the repopulation of oogonial
cells by mitotic divisions. The proportion of oogonial
killing was exposure-dependent; by increasing theexposure to 1000 R, the population was reduced to 43%of that in controls.
551. Baker and Neal [B54] showed that the sensitivityof oogonia in the ovaries of mice, rats and rhesus
monkeys remains virtually the same irrespective ofwhether they are exposed to x-irradiation in organ
cultures in vitro, or in vivo. Furthermore, they showedthat exposure of 2000 to 4000 R eliminates only aproportion (80% during the sixth month of gestation) of
the oogonia in human ovaries in vitro. This finding
suggests that the human oogonia may be even moreresistant than those of the rhesus monkey.
552. Data on the radiosensitivity of oocytes in foetal
rhesus monkey are scanty. The available ones show that
exposures between 200 and 400 R have no measurable
effects on the population of oocytes [016]. Baker and
Beaumont [B52] found that none of the foetuses aged
two months to full term (six months) was completely
devoid of germ cells after 350-600 R of x rays and thata severe reduction of the number of oocytes occurred
only after 1000 R or more. The most marked effect was
found after exposure during the fifth month ofgestation, a period associated with a high rate of
spontaneous atresis and with the cessation of mitotic
activity in oogonia [B52, B55].
553. Baker and Neal [B54] and Baker [B53] compared
the structure of the irradiated and control humanovaries (from foetuses aged 2-7 months post-coitum) at
various intervals after the onset of organ culture.
Exposure to 2000-4000 R affected the germ cells at allstages in their development, although oogonia undergoing mitosis appeared to be the most sensitive. Quantitative studies of a foetal ovary from a six-month old
foetus showed that 4000 R x-irradiation caused a 65%
reduction in the number of germ cells within 7 days oftreatment. A similar response was obtained in foetal
rhesus monkeys after exposure to 2000 R and confirmsthat human oogonia and oocytes are very radioresistant.
554. The radiosensitivity of the oocytes of somejuvenile and adult mammals has already been

considered (Table 38). Most of the other mammalian
species for which quantitative data are available suggestthat they are intermediate between the mouse and therhesus monkey. The LDso/30 for primordial oocytes in
the guinea pig is about 500 R, although 15 OOO R is
required for 100% killing ((15], see also [017]). This vastdifference between the LDso and LD100 values is presumably due to the fact that there are two distinct populations of primordial oocytes: one, a "large" type, withappearance similar to those of other species such as themonkey and man and the other. a "contracted" type, inwhich the chromosomes appear to be condensed
toward the centre of the nucleus. "Contracted" oocytes
are radiosensitive: they are either killed by exposure to
x rays or are transformed into the larger types (15].
555. Only qualitative data are available for the rabbit
and the hamster. Oocytes in these species seem to haveradiosensitivities comparable to those in the rat [B56.
M50]. Thus, doses of less than 7 Gy destroy the majorityof primordial follicles and also a proportion of thosethat have completed their growth phase. Females of
species that have relatively long foetal or post-natal
development, in contrast to those of rapidly developing
species (such as rodents), are not sterilized by acuteradiation exposure. This is owing to the greater
asynchrony of oocyte stages in the former species. Evenin the slowly developing species, however, continuousor fractionated exposure has revealed a highly sensitive
developmental stage of limited duration. This has beenfound to be the case for bonnet monkeys (Macaca
radiata) [A31], squirrel monkeys (Saimiri sciureus)[D25], and juvenile dogs [A32], species in which thearrested oocyte is resistant to radiation-induced cell
death. Continuous exposure of foetal squirrel monkeys
to tritiated water indicated a sensitivity of developing
oocytes even higher than that observed for the mouse.
The finding that primates. as well as mice, have oocyte
stages that are vulnerable to radiation suggest that thehuman oocyte may also pass through highly sensitive
stages in development. The general pattern of sensitivity of oocytes to radiation among mammalian species
may be more similar than is commonly thought.
556. Preovulatory maturation of oocytes within
Graafian follicles commences with the onset of the socalled "LH surge" (Luteal hormone) which occurs, forexample, about 13 hours before ovulation in the mouseand 36 hours before ovulation in man [B50]. Thereafter,
radiosensitivity varies according to the stage of meiosis
attained by the oocyte and increases by a factor of 10 as
the cell passes from the dictyate stage to metaphase I in
the mouse [M51].
557. Hobson and Baker [H47] studied the effect ofovarian x-irradiation in the rhesus monkey on
menstrual cycle length, duration of menstrual bleeding,excretion of gonadotrophin in the urine, concentrationof gonadotrophin in the pituitary gland. ovarian
histology and breeding performance. It was found thatat exposure below 4000 R, there was no significant
effect on any of the above parameters measured.
However, exposures of between 400 R and 6000 R
rapidly induced amenorrhoea in most animals. but noincreased excretion of gonadotrophin was observed.
The reproductive capacity of the animals used in the
study was poor. No births occurred before irradiationand only three confirmed pregnancies thereafter.
558. Baker and McLaren [B48] conducted experiments to measure the cell-killing effects of
3H-thymidine on the developing oocytes of mice using493

a multiple injection method similar to that in the workof Callebaut [C42]. Pregnant Q strain mice received
seven injections of 3H-thymidine (148, 1480 kBq and14.8 MBq per injection) between the 13th and 16th dayof pregnancy at about 12 h intervals. The animals were
either killed on the 17th day of pregnancy and the
foetal gonads removed for analysis or they wereallowed to give birth and the ovaries of the progeny
were studied.
559.
It was found that:(a) The ovaries of the foetuses on the 17th day ofgestation and on the day of birth contained
oocytcs which were predominantly at the zygotene
or pachytene stage of prophase I and the majorityof these cells were labelled;(b) The highest intensity of silver grains was over theoocytes;(c) Ovaries from experimental mice aged up to one
month appeared normal, although smaller than in
the controls; the proportion of the oocytes undergoing degeneration was higher than in the ovaries
of control mice and in the treated ovaries, theatretic oocytes being more heavily labelled;(d) In 5-months old experimental mice, the primordial
follicles were mostly normal in appearance inovaries from the low dose group (148 kBq); in thehigh dose groups, however, there was an increasein the proportion of grossly abnormal follicles andsome ovaries were devoid of oocytes;(e) There was a reduction in the total number ofoocytes in the ovaries of experimental mice andthis was proportional to the dose of the isotope
used and affected primordial follicles more thanmultilayered follicles: by 5 months of age, thenumbers of oocytes in the 1480 kBq and 148 kBq
groups were reduced to about 1% and 50% of thecontrol values, respectively:(f) At 13 months of age, ovaries from mice in the 14.8
MBq group were devoid of oocytes and corpora
lutea, while in the 1480 kBq group some corpora
Jutea remained, but virtually no oocytes. These
results permitted the authors to conclude that themouse oocytes are highly sensitive to internal betaradiation from 3H-thymidine incorporated during
embryonic life.

VI.

SOMATIC CELL GENETICS

560. Only a limited amount of data has accumulated
since the publication of the 1977 report on mutationinduction in somatic cells by ionizing radiation. The
papers concerned and some others dealing with otherkinds of radiations will be briefly reviewed in thefollowing paragraphs.
A.

MUTATION INDUCTION AT THE HG-PRT
LOCUS
I.

Chinese hamster ovary (CHO) cells

561. It is known that several factors, such as theanalogue used, its concentration, cell-seeding density,
time of addition of the analogue to the mutagen-treatedcells (expression time), the source of serum used in theselective medium, interclone metabolic co-operation
etc., affect the recovery and type of mutants obtained.
Jostes et al. [J 11 J investigated the role of de-aminationof 8-azaguanine (8-AG) to 8-azaxanthine (8-AX) by

494

serum under conditions where cell density andexpression time were controlled. It was found that the
reduction in toxicity of 8-AG which results from its deamination to the 11011-toxic product 8-AX leads to theselection of many mutants which are resistant only todrug concentrations lower than that added to theselecting medium. That is, at lower concentrations one
may be selecting preferentially for mutants with partial
enzyme activity or for non-mutant cells. In fact, ananalysis of mutant clones selected under conditions
where drug toxicity was maintained revealed that mostof the mutants having partial enzyme activity were
eliminated. The elimination of partial mutants agreed
well with the approximately 2-fold reduction in
frequencies of spontaneous and x-ray induced mutants
when drug toxicity was maintained by single 30 µg
AG/ml and by changing the drug medium once.
562. Burki [B80] found that when exponentiallygrowing CHO cells are exposed to 50-kVp x rays, thesurvival curve shows a shoulder and the induction of 6TGR mutations is curvilinear with dose (2-10 Gy),
responses similar to those reported by other investigators for exposures of CHO and V-79 cells to moreenergetic x rays. When the cells are synchronizedwithout the use of drugs, the x-ray-induced cell kiJJing
and induced 6-TGR follows a characteristic pattern. For
cell killing, the sensitive periods of the cell cycle are theG1, G2. M and early S periods, as others have reported.
For mutation induction, the sensitive stage is the G 1
period with the maximum sensitivity near the boundary
between G 1 and S: other periods of the cell cycle
appear to be very refractory to the induction of 6-TGR
mutations.
563. Jostes et al. [J20] conducted a study in which
synchronous CHO cells were x-irradiated (300-kVp xrays) at various stages in the cell cycle and analysed forthe frequency of 8-AGR mutants. The induced mutant
frequencies were highest in mitosis (40 10-5 after 5 Gy),in early G1 (30 1Q-5) and at the G1/S border (30 I Q-5);
were low in mid-to-late G1 (15 10-5) and were lowest in
S phase (6 1Q-5). Qualitatively, the variation in sensitivity during the cell cycle for induction of mutants
corresponded with that reported for the induction ofchromosomal aberrations. However, a quantitative
comparison of the two end-points and plots of thelogarithm of survival versus mutant frequencies oraberration frequencies indicated that the mutant
frequencies were much higher than expected when thecells were irradiated in mitosis or at the 01/S border.
The mutants recovered were classified as complete (i.e.,
failing to survive in azaserine-hypoxanthine medium
and incorporating tritiated hypoxanthine at a rate Jessthan 1o/o of that for wild-type cells) or as partial (i.e.,
surviving in azaserine-hypoxanthine medium at a rate
greater than 1o/o of that for wild-type cells). The
percentage of mutants classified as partial was 0-22%
for selection in 30 µg/ml 8-AG and 15-60% forselection in 5 µg/ml 8-AG. However, the number ofpartial relative to complete mutants had little or nodependence on radiation dose or phase of the cell cycle
irradiated.
564. In another investigation [J21], CHO cells were
given two 4.5 Gy doses of x rays separated by 1 or 2 h.
during which interval the cells were held at room
temperature to minimize progression through the cell
cycle. The frequency of induced mutations to 6-TGR
was co.mpared with that of mutations induced by asingle dose of 4.5 or 9 Gy. Mutation frequencies
induced by the split dose were intermediate betweenthose induced by the two single doses, suggesting that"premutational'' lesions were repaired.
565. In the study of Cleaver [C43] cultured CHO cells
were labelled with 6-JH-thymidine or 5-mcthyf-JHthymidine, frozen and allowed to accumulate damage
from JH decays for varying periods of time. Two seriesof experiments were carried out with each of these. At
the end of various "dose accumulation periods", thecells were thawed to 37°C and used for the determination of 6-TOR mutations. Appropriate controls weremaintained. In parallel experiments, mutationinduction by UV (up to 24 J/m2) and x rays (up to 10Oy) was also studied.
566. The results showed that, in the range of doses
employed, the dose-response curves were linear for all
three experiments. JH in the 6 position produced 2-3
times more 6-TOR mutants than 3H in the 5-methyl
position, indicating that a local effect associated withtransmutations at the 6 position in the DNA produces
mutations more efficiently than the emitted beta
particle does. No difference between 3H decays at the 6
position and the 5-methyl position was observed when
DNA damage in the form of single-strand breaks wasmeasured. In another study, Cleaver [C44] examined
whether or not x-irradiation would induce an errorprone repair process that would increase the frequencyof 6-TOR mutants in CHO cells. The cells were xirradiated at times from Oto 17 h before being irradiatedwith UV. Only one x ray dose (3 Oy) and one UV dose
(13 J/m2) were used. No synergism however, wasobserved.
2.

Chinese hamster V-79 cells

567. Thacker, Stretch and Stephens [T23] examined
the induction of 6-TOR mutants in the V-79 Chinese
hamster cells after gamma irradiation. After irradiation,
the cells were grown in non-selective medium fordifferent time intervals before respreading into medium
containing 0.5 to 0.7 µg/ml 6-TO; in some experiments,
colonies arising in 6-TO medium were counter-selected
in medium containing the glutamine-analogue
azaserine, which distinguishes mutants with very little
HO-PRT activity. Only these mutants were found to be
increased in frequency by irradiation, the maximum
measured frequencies occurring in cells respread after
two days of growth in non-selective medium. The
results showed that over the range from 1-8 Oy thedose-effect relationship for induced mutations per
viable cell was non-linear (induction rates of 5 10-S per
10-2 Oy to 3 10-1 per 10-2 Oy). However, a plot of theinduced mutation frequency against log surviving
fraction gave an approximately linear relationship. The
same linear relationship holds for recently publisheddata on human and mouse cell cultures, so that all threemammalian cell types exhibit the same fixed probability of mutation induction relative to the extent ofinactivation caused by ionizing radiation (about 4 I0-5
mutants per lethal event) (see also [T33]).
568. Asquith [A25] studied the mutagenic and lethal
effects of single and fractionated doses of gamma
irradiation in the same cell line. The induction of 8AOR mutants was scored. The results showed that:(a) The dose-effect curve after single doses (0.5 to 10Oy) was non-linear:(b) The lethal and mutagenic effects of fractionateddoses were always less, relative to those after
single exposures;(c)

When the cells were exposed to graded single
doses of up to 6 fractions (each of about 3.5 Oy),
the rate for fractionated doses always was lower
than that for the corresponding single doses; and(d) When a total dose of 8.34 Oy was administeredeither singly or in 2, 3. 4. 6 or 12 fractions of equal
size, there was an increase in survival withincreasing number of fractions paralleled by aconcomitant decrease in mutation frequency, suchthat there appeared to be a constant relationshipbetween mutation and survival.
569. Thacker et al. [T24] studied mutation to 6-TG
resistance in V-79 Chinese hamster cells after irradiation with accelerated helium, boron or nitrogen ionscovering a LET range from 28 to 470 keV ~Lm-1. It was
found that for all radiation qualities, a dose-dependent
increase in mutation frequency was obtained for doses
giving surviving fractions greater than about 0.20.
The effectiveness per unit dose for both inactivationand mutation induction increased with increasing
LET of the radiation to a maximum in the range of
90-200 keV µm-1. However, the maximum mutagenic
effectiveness (relative to gamma rays) was about 2 ormore times that for inactivation.
570. Unique RBE values cannot be given for thesedata because of the differences in the shapes of thedose-effect curves at different LETs. The linear coefficient taken from the quadratic fit to each set of data
gives one estimate of RBE which emphasizes thedifference in effectiveness at low doses. This "initialslope RBE" for helium ions (for mutation induction)
range from 2.9 to 17 in the range of LETs from 20 to 90
ke V µm-1; for boron ions. at both LETs tested (110 and
200 keV µm-1) the RBE values are the same, while fornitrogen ions this is 14.
571. In a subsequent paper, Ooodhead et al. [043]
used carbon-K characteristic ultrasoft x rays of photon
energy 0.278 keV. These x rays produce electrons of"range" .;;; 7 nm which is an order of magnitude smaller
than those for aluminium x rays and is only about threetimes the diameter of the DNA double helix. The
effective ranges are less than 7 nm owing to the very
tortuous path of such slow electrons; each electron
produces a total of only about 14 ionizations and these
are not along a clearly defined path. The dose distribution through the cell is highly non-uniform being 100%on the entrance surface and decreasing exponentiallywith depth in the cell. Under the assumption that thetargets are uniformly distributed within the cell of
uniform thickness 7 µm, the average dose to the targets
is 24% of the dose at the entrance surface. Despite thevery low energy and short track length, the authors
found that the above ultrasoft x-irradiation caused
inactivation and induced 6-TOR mutants. With certain
assumptions about the position of the sensitive sites
within the cells, it was concluded that carbon x rays are
more effective than gamma rays and are probably atleast as effective as long tracks of helium ions of similar
LET. These data extend the conclusions previously
drawn from the observed effectiveness of aluminium xrays [C67, 044] regarding the sizes of the sub-cellulartargets involved in inactivation and mutationinduction. They imply that the sensitive sites are smaller
than about 7 nm and that highly localized energy
depositions consisting of ~ 14 ionizations are sufficient
to produce biological effects.
572. The increasing use of photochemotherapy,
involving combined treatments with 8-methoxypsoralen495(8-MOP) and long-wave UV light (UVA: em1ss1on
range: 305-450 nm with a maximum at 355 nm) for
treatment of psoriasis in man prompted Burger andSimons to study the effects of similar treatments(PUVA) on mutation induction and cell-killing in V-79
Chinese hamster cells [B57] and in diploid human fibroblasts [858] this study is considered later in this chapter.
Treatment with 8-MOP alone (50 µg/ml, 4 h) or UVA
alone (9000 J/m2) did not cause any significant
induction of 6-TG mutants. Combined treatment(PUVA) induced both cell-killing and mutations. This
was also observed under conditions approaching
patient treatment (PUVA) with respect to the concentration of 8-MOP in the skin and the amount of UVA
received by the epidermal cells. A simple relationshipproved to be applicable for mutation induction under
different conditions: 5.5 )(rll per J/m2 per µg of
8-MOP.
3.

Mouse lymphoma (L 5178Y) cells

573. Nakamura and Okada [N18] investigated the
gamma-ray (137Cs) induction of 6-TGR mutations in
L5178Y cells at 0.5 Gy min-1 and 8 10-3 Gy min-t. In
addition, they examined cell killing, the relationshipbetween mutation frequencies and variations in dose
rate in the range of 0.5 to 8 10-3 Gy min-1 at a dose of
2 Gy, the effects of temperature (±OOC versus 37°C
during irradiation at 0.5 or 8 10-3 Gy min-t: 2 Gy) andthe effects of adding dimethyl sulphoxide (DMSO) atvarious concentrations to the medium containing thecells during irradiation.
574. For cell killing from 2 to 8 Gy the dose-response
curve was sigmoidal at high dose rate and exponential
at low dose rate. In the same dose range, the frequencyof 6-TGR mutations increased faster than linearly withhigh dose rate irradiation, but was nearly linear at low
dose rate. At a dose of 2 Gy, the mutation frequency
continued to decline (to about one-half of that after
high dose rate irradiation) with a decrease in dose rateuntil the latter reached about 3.3 10-2 Gy min-1, below
which there was no further reduction. At 0°C. thefrequencies of mutations were nearly the same at boththe high {0.5 Gy min-1) and low {8 10-l Gy min-1) dose
rates, whereas at 37°C the frequency at the lower dose
rate was less than one-half of that at the higher one.
DMSO exhibited a radioprotective effect both withrespect to survival and to mutation induction; thereduction in mutation frequencies became more
pronounced with increasing DMSO concentration
following irradiation at 0.5 Gy min-t but were notmeasurably affected by irradiation at the low dose rate.

4.

Human diploid fibroblasts

575. In the experiments of de Ruijter and Simons[R61J, human diploid fibroblasts were x-irradiated (100,200 and 300 R) in suspension and mutation induction
at the HG-PRT locus was studied using the 8-AG or
6-TG selection systems; in addition, the length of theexpression time for these mutants was ascertained byseeding the cells for selection at 0, 3, 6, 10 and 14 days
after x-irradiation. The results showed that:
(a)

496

Direct expression of at least a proportion of themutants occurred on day O followed by anincrease in mutant frequency over the entire
culture period; the latter, however, was found to
be entirely due to an increase in spontaneous

(b)

(c)

mutations, suggesting that for human diploidfibroblasts, culturing after treatment is notnecessary for the expression of HG-PRT deficientmutants.
In practice, however, a culture period is needed as
the number of clone-forming cells that can beseeded without culture after treatment is very low,
and the number of mutants that can be selected isconsequently small, even in large-scale experiments.is
The exposure-frequency relationship does notappear to deviate from linearity; the mean
mutation rate is 2.1 10-7 per R which, in the
exposure range used, is about twice that obtainedin rodent cells.

576. Cox and Masson [C45] studied the induction ofcell killing and mutations to 6-TGR in cultured human
diploid lung fibroblasts {HF 19 strain) after exposure toionizing radiations with LET in the range from 20 to
470 keV µm-1. It was found that, for all radiations
studied, the dose-response curves were exponential(range: up to 2.5 Gy). Helium ions of increasing
average LET showed increasing effectiveness in theorder: He{20) < He(28) < He(50) < He (70) < He (90).
The Do values decreased from 0.92 Gy at 20 keV µm-1
to 0.32 Gy at 90 keV µm-t. Correspondingly, theRBE values increased from 1.4 to 4.0. Boron ions ofincreasing average LET showed decreasing effectiveness in the order B (110) > B (160) > B (200). The
D 0 values increased from 0.34 Gy at 110 keV µm-1 to 0.5
Gy at 200 keV µm-t. The RBE values correspondingly
decreased from 3.7 to 2.5. Nitrogen ions of 470
keV µm-1 were less effective than B ions of200 keV µm-1;
the D 0 was 0.73 Gy and the RBE, 1.7. In view of thefact that the survival curves were exponential, the RBE
values for inactivation were not dose-dependent; theRBE maximum lies between LETs of 90 and 110
keV µm-1 and is of the order of about 4.
577. The dose-response relationships for mutationinduction were approximately linear for all radiation
types. Helium ions of increasing average LET showed
increasing mutagenic effectiveness in the same order asthat for cell killing; the induced mutation rates
increased from 3.9 10-s Gy-1 at 20 keV µm-t to 22 10-s
Gy-t at 90 keV µm-1. Correspondingly the RBEs
increased from 1.3 to 7.1. Boron ions of increasing
average LET showed similar mutagenic effectiveness:the induced mutation rates were between 17.8 and20.7 10-s per Gy. The RBE values were between 5.7 and6.7. Nitrogen ions of 470 keV µm-1 were considerably
less effective than boron ions, the induced mutation
rate being 8.5 ]0-5 Gy-1 and the RBE 2.8.
578. The mutation data suggest that the RBE-LET
relationship has a humped form similar to that forcell inactivation. However, while the RBE values forinactivation and mutation induction differed only
slightly for radiations in the LET range between 20 and
50 keV µm-t, at higher LET these values for mutation
were about twice those of the corresponding RBEs forinactivation. The RBE maximum for mutationinduction is in the range 90-200 keV µm-1. Although
this range is similar to that obtained for the induction
18 It is instructive to recall that in the work of Cox andf\lasson [C7 I J discussed in the 1977 report, it was demonstrated that, with respect to the induction and selection of
6·TGR mutants, the maximal yield was observed when thecells surviving the irradiation had completed 3-4 doublings(6-7 days of growth) in a non-selective medium.

of 6-TGR mutations in V-79 Chinese hamster cells [T24],
the comparison of RBE is complicated by the fact thatthe hamster cell RBEs are not unique values.
579. In experiments with aluminium soft x rays andcarbon soft x rays. Cox et al. [C67) and Goodhcad et al.
[G43] demonstrated that these irradiations are capableof causing cell inactivation and inducing 6-TGR
mutations in human cells. The general conclusions arc
similar to those arrived at using V-79 cells.
580. Burger and Simons [B58) investigated cell killingand induction of6-TGR mutations in dividing and nondividing (i.e., under liquid-holding conditions) humanskin fibroblasts (derived from a healthy boy) fromtreatment with 8-MOP and long-wave UV (UVA). Two
8-MOP concentrations (0.25 and 10 µg/ml) and a range
of UVA doses (up to 600 J/m2 in combination with 10µg/ml 8-MOP and up to 5333 J/m2 in combination
with 0.25 µg/ml 8-MOP) were used. Under liquidholding conditions, both the amount of cell killing andthe frequency of induced mutations are lower than for
dividing cells under the same 8-MOP/UVA conditions;the effect of liquid-holding on cell survival is lesspronounced (reduction by 40%) than on mutations(reduction by 80%). The number of mutations induced
per unit dose ( = per µg 8-MOP/ml per J/m2) individing cells is 3.3 1Cr8/cell (for 10 µg/ml 8-MOP and
UVA dose range up to 100 J/m2 and for 0.25 µg/ml
8- MOP and UV A range up to 3500 J / m2) this finding
being qualitatively similar to that obtained with V-79
cells [B57). These data thus suggest that there is a linear
relationship between mutant yield and the product of
8-MOP concentration times UVA dose. The cytotoxic
effect of PUV A treatment, however, is dependent on
the actual concentration of 8-MOP and UVA dose andthis result is also in agreement with the results with V-79
cells. Calculations show that, for instance, at 50 and
10% survival levels, the decrease of 8-MOP concentration by a factor of 40 (from 10 to 0.25 µg/ml) can becompensated by an increase of UVA exposure by afactor of 10. This suggests that the increase in UVA
exposure needed does not bear a simple proportionality
to the decrease of 8-MOP concentration with the
combined treatment.
581. Burger and Simons have used the above data tocalculate the risk of mutation induction in epidermal
cells for PUV A therapy of psoriasis patients under theassumptions that the mutational response of the basal
epidermal cells is similar to that of skin fibroblasts; thatthe concentration of 8-MOP in the skin during anormal PUVA treatment is 0.25 µg/ml: that about 30%of the dose of UV A reaches the basal layer; and thatabout 10% of the epidermal cells are dividing and 90%
are in Go, In clinical studies, Burger et al. [855) used astarting dose of 18 OOO J m-2 for fair-skinned
individuals which, for the basal layer of the epidermis
would mean a dose of 5400 J m-2. The weighted averagefrequency of mutations per PUV A session thenbecomes
5400 x 0.25 x 3.3 10- 8 x 0.10 (for dividing cells) +5400 X 0.25 X 0.6 J0- 8 X 0.90 = 1.17 JQ-5
Patients given 36 maintenance treatments a year for 30
years will accumulate 30 x 36 x 1.17 1Q-5 - 1.26 1Q-2 percell. This figure might be of some relevance in thecontext of assessing potential risk of cancer induction(on a mutation model) for patients given PUVA therapy
if such therapy can be shown to have a carcinogenic
effect.

5.

Human peripheral blood lymphocytes

582. In 1977, Strauss and Albertini [S120) reported on
an autoradiographic method to quantitatively detect 6TGR variants in human peripheral blood lymphocytes.
In subsequent papers, Albertini [A30] and Strauss andAlbertini [S 121] discussed in detail the experimental
procedures and the results obtained in studies withlymphocytes of normal individuals, from cancer
patients treated with cytostatic chemicals or x-radiation
therapy and from Lesch-Nyhan syndrome (LN)
patients.
583. Albertini [A30] and Strauss [S120, S121) made useof the cytotoxicity of 6-TG to human lymphocytes
possessing normal HG-PRT levels to distinguish andselect for viable 6-TGR variants. In autoradiographic
studies, such variants were shown to undergo DNA
synthesis (incorporation of 3H-labelled thymidine) andsurvive in the presence of normally toxic levels of
6-TG, following PHA stimulation. Experiments withartificial mixtures of lymphocytes from LN patientsand normal individuals showed that the LN cells werevirtually all detectable even when present in low
frequency ( 1Q-5). 6-TGR lymphocytes were found in
healthy normal individuals at median frequencies of11()-4 and 1.1 1()-4 when determined at 2 10-3 M and2 1()-4 M concentration of the selective agent. Theirfrequencies were not found to be age-related. The
distribution of the frequencies of 6-TGR variants incancer patients (treated with chemotherapeutics)
differed from that for normal controls in that more thanhalf of the patients had the variants in frequencies
higher than the highest seen in controls. Such anincrease in variant frequency over control levels was
also noted in lymphocytes from radiotherapy patients[A30].
584. In their studies. Strauss and Albertini also foundthat lymphocytes from even LN patients which wereresistant to 6-TG at concentrations 10 OOO times overthose which inhibit normal cells, were not absolutely
resistant; thus a marked difference in the apparent
frequency of 6-TGR cells was seen when LN cells were
tested at 2 1()-4 M and 2 1~3 M: only the cells at thehigher concentration were able to incorporate 3Hthymidine. Secondly, in the chemotherapeutically
exposed cancer patients, the 6-TGR fraction of cells wasdifferent at 2 10-3 M or 2 1()-4 M, suggesting that manyof the 6-TGR lymphocytes had properties similar to LN
cells. Thirdly, in some of these cancer patients, thelevels of 6-TGR cells were higher even before chemotherapy with further rises either after the initiation ofchemotherapy, or after its re-initiation after a nontreatment interval. Fourthly, PUY A treatment forpsoriasis also leads to elevated variant frequencies.
Finally. the authors have evidence to suggest that somecells that synthesize DNA in vitro under the conditions
used for selection may not be mutants but rather may
be phenocopies.
585. Considering all the data, Strauss and Albertinisuggest that at least some of the variants isolated aresomatic cell mutants and that the system in its simplest
application may be valuable as a retrospective
monitoring system for unknown environmental
contaminants, for combination of agents, etc.
586. Evans and Vijayalaxmi [E23] have now collected
data on the x-ray and mitomycin-C induction of 8-AGR
variants in in vitro studies with human lymphocytes. In
parallel experiments, determinations of chromosome497

aberration frequencies (after x rays) and of SCE
frequencies (after MMC) were also made.
587. The reason for using 8-AG for variant selection
has been stated as follows by the authors: "We werestrongly innuenced by the fuel that 6-TG is incorporated into DNA and that inhibition of DNA synthesisby excess thymidine protects against the toxicity of
6-TG, but not 8-AG. In contrast, 8-AG is incorporated
into RNA and inhibition of RNA synthesis protects
against the killing effects of 8-AG, but not of 6-TG. The
short-term culture of lymphocytes in vitro is inappropriate for selecting for resistance to cell killing
post-DNA synthesis, and since the blast formation oflymphocytes by PHA necessitates a considerable
amount of RNA synthesis, we elected to use 8-AG
(2 1()-1 M) in preference to 6-TG in all the experiments"[E23].
588. The main results are that the incidence of 8-AGR
variants varied from 0.80 1()-1 to 3.99 1()-1 in the blood
samples from 26 donors whose ages ranged from 16 to82; although there was considerable scatter, there wasnevertheless a clear age dependence (the frequencies
increased with age); there was no sex-difference in thefrequency of these spontaneous variants; significant
increases in 8-AGR variant lymphocytes occur
following exposure to quite low doses of x rays and thedose-response over the range 0-2 Gy is curvilinear; thedata give a good fit to a quadratic equation with a negligible linear term or to a power-law function with nequal to 2.1. Assuming that n = 2, then the linear term
is equal to (6.90 ± 0.11) 1()-1 and the quadratic term,(6.81 ± 0.20) J(}-4; the kinetics of dose-response for the
x-ray induction of 8-AGR variants is similar to that for
x-ray induction of chromosome aberrations; with
MMC (treatment times of 1, 5 or 10 h in the concentration range 10-9-JQ-5 M) the frequencies of thevariants increased with MMC concentration with eachdose-response curve being of the form y = a + bD
where y = variant frequency. a = control frequency of(8.38 + 0.37) l(}-4 and D = MMC concentration. The
values of b (for treatment durations of 1, 5 and 10 h)are. respectively, 0.83, 0.92 and 1.06; the maximum
increase in 8-AGR variants is around 12-fold at thehighest MMC concentration, but significantly increased
frequencies are evident following exposure to low
doses. of the order of 10-S M over short time periods
and the data on SCEs show that these are induced atvery much higher frequencies relative to the 8-AGR
variants per cell, but the shape of the dose-response
curves for these two end-points are very similar. The
authors have suggested that x-ray induced 8-AGR cells
may be true mutants (the spontaneous variants areprobably deletions involving the terminal region of the
X-chromosome containing the locus for HG-PRT) andthat on the basis of their evidence, for every 8-AGR
event in a cell population, there are around 10 visible
chromosome breaks in an active X-chromosome. The
MMC-induced· 8-AGR variants are considered torepresent "cells in which large MMC-guanine adducts
have prevented normal transcription of the HG-PRT
locus to give functional HG-PRT".
B. MUTATION INDUCTION ATTHE
THYMIDINE KINASE (TK) LOCUS
589. In the study of Knaap and Simons [K28]mentioned earlier, mutation induction at the TK locus
was also investigated in the L5178Y mouse lymphoma
cell line heterozygous for TK. The frequency of TK-

498

deficient (bromodeoxyuridine resistant) mutants(following UV or x-irradiation) appeared to reach aplateau two days after treatment, an expression time
which is much less than that needed for TG-resistantmutants. The dose.effect relationship was linear ( 1-4
Gy. x rays; 1.25 to 5 J m-2, UV) and the induction rate
for TK-deficiency was higher by a factor of 2 relative tothat for TG·resistance.
590. Jacobson et al. [J12] found that unfiltered broadspectrum radiation emitted by black light (BL), coolwhite (CW) and black light blue (RLR) nuorescentlamps and a sunlamp (SL) is both toxic and mutagenic
to L5178Y mouse lymphoma cells when the cells were
irradiated in phosphate-buffered saline. The increase inmutant frequency was linear throughout the range of
exposures tested. To facilitate comparisons between the'different nuorescenl sources, the authors defined aparameter called joule-equivalent mutagenesis (iem)and this was equal to the number of mutants per I ()5survivors per joule per square meter; jem values were
calculated using the integrated irradiance of each lamp.
Based on these values. the relative mutagenic efficiencyof the various lamps (compared to the germicidal UVlamp) was 3.0 10-3 for the sunlamp; 1 J(}-4 for the black
light and cool white lamps: and 3.0 JQ-5 for the black
light blue lamp. Since some of the lamps have relatively
higher emission in the UV spectrum than others, thisproperty may be responsible for the differences
observed. Unpublished observations of the authors
have shown that filtration of wavelengths shorter than
388 nm effectively eliminates the toxic and mutagenic
effects of CW lamps. Although other wavelengths may
have effects, a comparison of the spectral radiance of
the BLB, BL and CW lamps over 10 nm intervals in the
UV region shows that these lamps emit about 100-foldless radiation than the SL from 290-330 nm. This is ingood agreement with the 100-fold lower rate of mutagenesis of the BLB and a 30-fold lower rate of the BL
and CW lamps compared to the SL. The BLB lamp
emits appreciably less radiation than the BL and CW
lamps from 290 lo 300 nm, which may account for its
mutagenesis rate being about one-third of that of theBL or CW lamps.
C.

MUTATIONS TO OUABAIN RESISTANCE(OUAR)

591. Thacker et al. [T25] have reported on their studies
on mutation induction to ouabain resistance (OUAR) in
Chinese hamster V79-4 cells by EMS and by gammairradiation (ouabain is a specific inhibitor of the plasma
membrane enzyme (Na+ + K+)-dependent ATPase(Na/K ATPase)). With EMS, reproducibly large
increases in the frequency of OUAR mutants were
found in cultures treated with various concentrations (1to 4 mg/ml) and re-spread in 1 mM ouabain for up to 8
days after treatment. The concentration-frequency
curve was linear in the range from 1 to 3 mg/ml
concentration, followed by a very marked increase toabout 30 1Q-5 at the highest concentrations of 4 mg/ml.
In contrast, gamma rays were found to be ineffective ininducing these mutations despite exploration of the roleof variables such as radiation dose, ouabain concentration, post-treatment interval before selection, celldensity in selective medium and clonal state of the cells
at the time of adding ouabain (in situ versus
respreading method). A similar result was obtained foraccelerated helium ions for which the RBE had beenshown to be about 10 (relative to gamma rays) for 6-TG
resistance in these cells [T24]. The authors have some

evidence for an interaction between cellular radiation
damage and ouabain (irradiated wild-type cells weremore rapidly inactivated by ouabain than unirradiatedcells) but this damage seems insufficient to account for
the inability to detect OUAR mutations after ionizing
radiation.
592. Chang et al. IC47] irradiated Chinese hamster
V-79 cells with an unequally fractionated UV dose
(UV,. 3J/m2 + 17J/m2) separated hy 4. 6 or 12 h. withor without cycloheximidc or caffeine present during theinterval between the fractions. for part or whole of theperiod. Among others, the effects of these different
regimes on post-replication repair, survival andmutation induction to OUAR were studied. The data on
post-replication repair (collected using alkaline sucrose
density gradient methods) show that irradiating cellswith an initial small dose of UV, 4-6 h before a larger
UV dose. significantly increases the rate by which small
DNA, found immediately after irradiation is converted
into high molecular weight DNA: the presence of UVdamaged DNA for at least 1.5 h before UV2 irradiation
appears to be sufficient to enhance the rate of postreplication repair. This enhancement is inhibited bycycloheximide treatment during the interval between
fractions; a similar inhibitory effect was observed withcaffeine.
593. The data also demonstrate that with fractionatedUV irradiation, the colony-forming ability was higher
relative to the unfractionated dose; however, themutation frequencies were either reduced or were notaffected. The results from cycloheximide treatments
gave two different kinds of effects. depending on the
protocol used; a 4 h treatment immediately before thesecond irradiation increased survival but reduced
mutation frequencies whereas a 6 h treatment (ortreatment long before UV2) tended to reduce survival
and increase the mutation frequency. While themechanisms for the two different effects of cycloheximide treatment are not clear. the authors speculate that
this chemical may have dual effects, one promoting theaction of an error-prone system (i.e., causing theobserved increase in mutation frequency) and the otheran error-free system (causing the observed reduction in
mutation frequency). With respect to caffeine. theresults show that caffeine pre-treatment or treatment
between the fractionated UV doses always increases themutation frequency. Since caffeine docs not effectexcision repair in Chinese hamster cells, these data
indicate that caffeine pre-treatment may inhibit anerror-free post-replication repair system. while allowing
error-prone repair to occur.
594. In Cleaver's studies on the induction of TGresistant mutants in CHO cells by radioactive
thymidine discussed earlier in this chapter OUAR
mutations were also sought for, but none found. His
other experiments [C44] on synergism between theeffects of UV and x rays for mutation induction to
OUAR provided no evidence for such an effect.
D.

RESISTANCE TO METHOTREXATE (MTXR)

595. In the work of Nakamura and Okada on the
gamma-ray induction of 6-TGR mutations in L5178Y
cells the induction of MTXR mutations was alsostudied. It was found that the dose-response curve forthese mutations was linear, irrespective of the mode ofdelivery (high versus low dose rate) of the irradiation
although the rate of increase with increasing dose wasless after low dose rate irradiation. As in the case of 6TGR mutations, presence of DMSO in the medium at
the time of high dose rate irradiation afforded a radioprotective effect, this effect increasing with increasing
DMSO concentration.
E.

NATURE OF RADIATION-INDUCED
MUTATIONS IN SOMATIC CELLS

596. In 1978, Cox ;111d Masson [C46) presented
evidence that gross structural changes involving the X
chromosome constitute the genetic basis of a significant
proportion of radiation-induced 6-TGR mutations inhuman fibroblasts. Gene mapping experiments haveassigned the HG-PRT locus in humans to the terminal
region of the long arm (q27) of the X chromosome[P41]. Cox and Masson determined the patterndisruption points (PDPs) for 23 6-TGR mutants induced
by 250 kV x rays. carbon ultrasoft x rays, helium ions of
90 keV/µm, alpha particles from plutonium (- 140
keV/µm) and nitrogen ions of 470 keV/µm. Thesemutants were selected by resistance to 3 µg/ml 6-TG.
seven days after irradiation at dose levels that gave
surviving fractions of 0.2 (about 2 Gy of x rays). The
hypothesis was that, if radiation-induced mutations to
6-TGR arise as a consequence of structural changes of
the X chromosome. a proportion of the more extremechanges should be detectable cytologically, using
banding techniques.
597. It was found that aberrations (exchanges anddeletions) consistent with the mapped position of the
HG-PRT locus were apparent in the X chromosomes of
up to 40% of TGR mutants. In the case of exchangeaberrations, the independence of the mutants described
was clear, since all the exchanges were different. The
majority of mutants with X chromosome deletions weredetected in a single experiment using nitrogen ions andit is possible that two examples of del(X)(q26) wererepeats of a single clone. With a single exception (anXp exchange probably not associated with the mutant
phenotype) all PDPs occurred in the q arm of the X
chromosome.
598. Analysis of 20 spontaneous mutant karyotypes
failed to reveal any structural abnormalities in the X
chromosome. Since a direct association between
induced TG resistance and X-chromosomal aberrations
would require that such aberrations in non-mutant cells
surviving the radiation dose should be rare, 25 nonmutant viable clones were also examined C)1ologically(alpha particles from plutonium were used): no aberrations were found.
599. The conclusion that structural changes of the X
chromosome are associated with the loss of HG-PRT
function raises the question of whether the functions ofother genes located on the long arm of the X are also
affected. As a preliminary test of this possibility. theauthors examined the G-6-PD activity using semiquantitative histochemical staining techniques. As
judged by the staining intensity, the variations in
G-6-PD activity among the alpha-particle induced TGresistant mutants were considerably larger than thoseobserved among non-mutant surviving clones, with up
to 5% of the mutant clones showing very low activity
and a similar number showing hyperactivity. In electrophoretic enzyme assays, two karyotypically defined Xq
exchange mutants were completely devoid of HG-PRT
activity but were not obviously deficient or super-activein G-6-PD activity. However, because almost all mutant499

clones showing atypical G-6-PD act1v1ty in histochemical assays showed very poor growth, it has notbeen possible to carry out truly representative
karyotype and electrophoretic analyses and hence thequestion or multiple gene effects in radiation-induced
TO mutants still remains to be answered.
600. Brown and Thacker [B75] stress that the methods
or human fibroblast HG-PRT mutant selection and thelimited lire span or mutant clones preclude precise
estimates or the proportion or radiation-induced
mutants with recognizable X-chromosome aberrations.
The 40% figure quoted in the paper or Cox et al. [C46)
was an average figure for a variety of different qualities
of ionizing radiation and in these preliminary experiments. no attempt was made to avoid the problems of
mutant fitness and consequently there was considerable
experimental variation in the proportion of chromosomal mutants detected. However, Brown et al.
generally observed that 250-kV x rays generated a lower
proportion (5-25%) of such mutants than radiations ofhigh-LET (20-60%). Since the proportion of suchmutants observed was innuenced by the duration of the
post-irradiation growth (for mutant expression) andmany mutant clones showed such poor growth that they
could not be characterized, these authors are disinclined to put too much emphasis on these figures;
instead, a good case for the gross nature of theradiation-induced HG-PRT mutants can be made on
biochemical evidence. Such evidence has now beenobtained.
601. The evidence comes from HG-PRT mutants in
V-79 Chinese hamster cells [875]. Each of these mutants
was independently isolated (the experimental design
ensured this) although inevitably, some spontaneous
mutants will be included in those isolated after irradiation. The analysis pertains to a total of 50 mutants
isolated after a 5 Gy gamma-ray exposure (6-TGR
mutants) and to similar numbers of spontaneous and
EMS-induced mutants. All of these were examined incell-free extracts for HG-PRT activity. Approximately
10% (5/48) of radiation-induced mutants showedmeasurable (i.e., more than 1% of the activity of
wild-type cells) HG-PRT activity while 50% (23/46) of
spontaneous mutants showed such activity. Since theradiation treatment gives only a 5-fold increase inmutant frequency over that found spontaneously at thisdose, it is possible that all those mutants withmeasurable activity found after irradiation are of
spontaneous origin.
602. Other evidence to support this idea is that thefrequency of mutants with measurable HG-PRT
activity does not increase with radiation dose, as wasdemonstrated earlier by Thacker et al. [T30]. In
addition, out of a small number (15) of independentlyisolated mutants induced by alpha particles at a dose
giving a 14-fold increase in mutant frequency, none
showed measurable HG-PRT activity.
603. Brown et al. (875] checked for the presence or
HG-PRT protein in those mutants which showed nomeasurable HG-PRT activity, by producing anantibody to purified HG-PRT. It was found that only 2(or possibly 3) of the radiation-induced mutants lacking
HG-PRT activity showed a cross-reaction to thisantibody. However, it is again possible that these crossreacting mutants are or spontaneous origin, since as
many as 4 or 5 of the mutants selected after radiation
treatment could be spontaneous mutants with nomeasurable HG-PRT activity (from the relative mutant
500

frequencies and the fact that 50% of spontaneous
mutants show no measurable HG-PRT activity, seeabove). None of these isolated mutants show loss of
G6-PD activity, but a small number show changes in
the X-chromosomc arm known to carry the HG-PRT
locus (see for instance [T31] for a description of aradiation-induced (Pu) mutant which has a clear
X-chromosome rearrangement, probably a pericentric
inversion of the Xq-X-chromosome with PDPs in the
p2-q I region).
604. Waldren et al. [W28] have presented some resultsfrom a study involving a CHO hybrid cell line
containing a single human chromosome 11: on thishuman chromosome are genes for cell surface antigens
a1. a2 and a3 and for lactic dehydrogenase-A (LOH-A).
The a 1, a2 and a3 loci cause the formation of specific cellsurface antigens that render the cell sensitive to killingby specific antigens in the presence of the complement.
The a1, a3 and LOH-A are on the short arm while a2 ison the long arm. In the mutagenesis experiments, thecells were either x-irradiated (100-600 R) or treatedwith MNNG and aj mutants were isolated and tested
for loss of only a1, a1 and up to 2 others and all four'
markers. The results are summarized in Table 39 whichshows that the frequency of single marker loss is quite
low after x-rays (as compared with MNNG andcontrols): limited marker loss (at and up to two others)
is higher for both x rays and MNNG (relative tocontrols). Total marker loss is highest in the x-raygroup. These data therefore suggest that at least for theloci studied, the radiation-induced mutational events
predominantly involve chromosomal deletions.

F.

MUTAGEN-SENSITIVE CELL STRAINS

605. Recent years have witnessed an increasing
interest in the isolation of cultured mammalian celllines which are sensitive to specific mutagens. The
impetus came from similar work with human cellstrains derived from patients with inherited disorders
and it is hoped that the isolation and study of mutagensensitive mutants of cultured mammalian cell lines may
also contribute to our knowledge of DNA repair
processes and their relationship to mutagenesis. A
number of mutagen-sensitive mutants have been
isolated using replica plating methods [K41, S122], viralsuicide method [S123] and others [T32].
606. Sato and Hieda [S82, S83, S84] have reported theisolation and characterization of mutant mouse cellstrains isolated from L5178Y cells mutated with nitrosoguanidine, which have been found to be sensitive tophysical and chemical mutagens. Thus. for instance, theline designated as MlO [S83] which was originallyisolated as being sensitive to methylmethanesulphonate, was later found to be more sensitive also to
the killing effects of x rays. The UV sensitivities of theparental and mutant lines however, were similar, as
were plating efficiencies and doubling times.
607. Shiomi et al. [S134] compared the gamma-ray
induction of 6-TGR mutations in the L5178Y and the
MIO lines and found that in the parental line thefrequencies of induced mutations increased steadily
with an increase in exposure (25-500 R; 2-3 10-7 R-1);
in the MIO line however, the frequencies increased in
the range from 25-75 R, followed by a sharp decrease
therearter (100--150 R). In the lower exposure range, therate of induction per unit exposure in the M10 line wasabout 4 times that in the parental one. When the
induced mutation frequencies were plotted against log
survival, the relationship was linear only up to 20%
survival in the MlO line (the curves for LS178Y andMIO were superimposable); in the LS178Y cells, a
linear relationship was obtained over the whole range
down to about 2% survival (see also (T23] and [T33]).
608. Another line isolated by these authors, designated as Q31 (also from LS178Y cells, after nitrosoguanidine treatment) was sensitive to 4-nitro-quinoline1-oxide (4NQO), i.e., showed no growth in a platecontaining SO ng/ml 4NQO [S82). Further tests revealed
that 10 ng/ml of 4NQO completely inhibited thegrowth of Q31 cells, but not that of parental cells. Q31
was also found to be more sensitive to the killing effects
of UV (D 0 of 1.6 J m-2 versus 3 J m-2) but did not show
any enhanced sensitivity to x-irradiation. Chromosome
analysis revealed that the cells of the parental line
contained 41 chromosomes while those of Q3 l,
39 chromosomes.
609. In a subsequent study, Sato and Hieda [S84]compared Q31 and LS178Y cells with respect to the
induction of 6-TGR mutations by UV and caffeine
sensitivity. The maximum yield of mutants was
obtained after 7 days post-irradiation in L5178Y cells
and 14 days in Q31 cells. The mutation frequencies in
Q31 are higher after low doses of UV, but show adecline after higher (more than 2 J m-2) doses (whilethat of LS 178Y continues to increase up to 12 J m-2). A
plot of the induced mutation frequency as a function of
the logarithm of surviving fraction again indicates
hypermutability of Q31 cells as compared to theparental strain. Caffeine affected the cell-killing effectof UV in both cell strains to a similar extent, indicatingthat the defective (repair?) process in Q3 l was caffeineinsensitive.
610. Thompson et al. [T32) have reported on theisolation of mutagen-sensitive clones by mutagenizing
CHO cells with EMS, UV, MMC and ICR-171. Two of
the UV-sensitive clones studied in detail had a D31 doseof 1.0 J/m2 compared to 7.0 J/m2 for the wild-type
cells. and each was shown to have no detectable repair
replication following exposure to UV doses up to
26 J/m2. Although these mutants resemble XP mutants
in humans with respect to their repair defect and crosssensitivity to the carcinogen 4-NQO, one of the twoclones is characterized by extreme hypersensitivity to
MMC (80-fold, as compared to the wild type). Clones
having hypersensitivity to alkylating agents but not UV,
were obtained using MMC and EMS. In the latter case,the two clones had significantly increased sensitivity to
the killing effects of 60Co gamma rays.
611. Busch et al. (B76] isolated 54 UV-sensitive clonesof CHO cells, including two from a parent cell line
which is hypersensitive to EMS and is also sensitive tox rays (EMS and ICR-170 were used to mutagenize thecells). Most of the UV-sensitive clones studied thus far
appear to be five-fold more sensitive than the original
strain, in terms of the slopes of the survival curves. All
the seven clones examined for DNA repair competence
using a repair replication assay (measurements of repair
using alkaline isopycnic gradients) exhibited a DNA
repair defect (0-34% of normal) resembling that seen in
XP cells. Furthermore, in two of ihe repair-replication
defective clones, there was an approximately nine-foldenhancement of UV mutagenesis (Ouabain resistance,
6-TGR and 8-azaadenine).

G.

SUMMARY AND CONCLUSIONS

612. Further studies on the role of some factors
affecting the recovery and type of mutants obtained
have been performed. With CHO cells, it was shownthat de-amination of 8-azaguanine to 8-azaxanthine byserum under conditions where cell density andexpression time were controlled leads to the selection ofmany mutants which are resistant only to drug concentrations lower than that added to the selecting medium.
613. With synchronized CHO cells, it has been shownthat for x-ray-induced cell killing, the sensitive periodsof the cell cycle are G1, G2, M and early S, whereas formutation induction (6-TGR or 8-AGR) the boundary
between G1 and S shows maximal sensitivity.
614. In CHO cells, 6-3H-thymidine and 5-methyl-3Hthymidine induce 6-TGR mutants and the dose-response
curves are linear. Tritium in the 6 position produces 2-3
times more 6-TGR mutants than tritium in the S-methyl
position, suggesting that a local effect associated withtransmutations at the 6 position in the DNA produces
mutations more efficiently than the emitted beta
particles.
61 S. In V-79 cells, the dose-effect relationship for the
gamma-ray induction of 6-TGR or 8-AGR mutants is
non-linear. Fractionation of the dose into two or more
fractions leads to an increase in survival and a decreasein mutation frequency (8-AGR). In V-79 cells andhuman diploid fibroblasts, accelerated helium, boron or
nitrogen ions covering a LET range from 28 to 470
keV /µm produce a dose-dependent increase in thefrequency of 6-TGR mutants. The effectiveness per unit
dose for both inactivation and mutation induction
increases with increasing LET of the radiation.
Aluminium- and carbon-K characteristic ultrasoft xrays are capable of both causing inactivation andinducing 6-TGR mutants in Chinese hamster (V-79) andhuman cells. These data also suggest that the sensitivesites for mutation induction and inactivation aresmaller than about 7 nm.
616. In mouse lymphoma cells (LS178Y), theinduction by gamma rays (high dose rate) of 6-TGR
mutations follows a non-linear kinetics. High dose rateirradiation is more effective than low dose rate irradiation in the induction of these mutations. After a doseof 2 Gy, the mutation frequency continued to declinewith a decrease in dose rate (to about one-half of thatafter high dose rate irradiation) until the dose rate
reached about 3.3 10-2 Gy min-1 below which there wasno further reduction. Furthermore, the yields ofmutations were the same at both high and low dose
rates when the irradiations were carried out at ooc
whereas at 37°C, the yield was Jess than one-half of thatat the higher dose rate.
617. In human diploid fibroblasts, the dose-effectrelationship for the induction (by x rays) of 6-TGR
mutations is linear.
618. Analysis of all published data on x- or
gamma-ray induction of HG-PRT· mutations in humanand mouse cell strains shows that when the induced
mutation frequencies are plotted against log survival,
the relationship is linear (with a slope of about 4 1o-s
mutants per lethal event) suggesting that mutation
frequency curves can be predicted from a knowledge ofsurvival curves for each cell type.
501

619. Studies have been conducted to examine theeffects of the combination treatment (PUVA) involving
long-wave UV (UVA) and 8-methoxypsoralen(8-MOP). Treatment with 8-methoxypsoralen or UV(UVA) alone was not mutagenic and the combined
treatments induced both mutations (6-TGR) and cellkilling. The data suggest a linear relationship between
mutant yield and the product of the concentration of 8methoxypsoralen times the UV (UVA) dose.
620. The autoradiographic method devised by Strauss
and Albertini for quantitatively detecting 6-TGR
variants in human peripheral blood lymphocytes isdiscussed together with the results obtained by theseauthors with lymphocytes sampled from patients withLesch-Nyhan syndrome, normal individuals, andindividuals who have undergone chemo- or radiotherapy. Evans and Vijayalaxmi have extended theusefulness of the lymphocyte system for detecting
HG-PRT· mutations in in vitro studies using
8-azaguanine as the selection agent. X rays andmitomycin-C were the chosen mutagens. With both ofthese, increases in the yields of 8-AGR variants withincreasing exposures were found. However. while theradiation-induced variants are considered to be
mutational events, those induced by MMC are thought
to represent cells in which large MMC-guanine adducts
have prevented normal transcription of the HG-PRT
locus to give functional HG-PRT.
621. In L5I78Y mouse lymphoma cells, x rays andUV irradiation produce a linear increase in thefrequency of thymidine kinase-deficient mutants withincreasing dose. In the same system, unfiltered broadspectrum radiation emitted by black ligh 4 cool whiteand black light blue. fluorescent lamps and a sunlamp
arc both toxic and mutagenic when the cells areirradiated in phosphate buffered saline. But theirrelative mutagcnic efficiencies are different.
622. Gamma irradiation is ineffective in producing
mutations to ouabain-resistance in Chinese hamster(V-79) cells, but UV irradiation or EMS treatment are
effective in this regard. Lack of OuaR mutationinduction by ionizing radiation has also been demonstrated for CHO cells.
623. The effects of fractionated UY irradiation withcycloheximide or caffeine present during the interval
between fractions on mutation induction to ouabain
resistance have been studied. With cycloheximide
present between the dose fractions the effects weredifferent (an increase or a decrease in mutation
frequency relative to the unfractionated UV dose)
depending on the experimental protocol. Caffeine
given as a pre-treatment or between the UV dose
fractions always led to an enhancement of the mutation
frequency.
624. There is now good evidence that a sizeable
proportion of the HG-PRT mutations induced byionizing radiations (in human and V-79 fibroblasts) is
associated with structural changes of the X chromosome. With x rays, this proportion is of the order of
5-25%, whereas with high-LET radiations, it is of theorder of 20-60%. Other studies using a CHO hybrid cellline containing a single human chromosome 11 (onwhich arc present genes for cell-surface antigens, a1, a2
and a3 and that for lactic dehydrogenase-A) also
provide evidence supporting the thesis that radiationinduced mutations at these loci may be predominantly
chromosomal deletions.
502

625. A number of mutagen-sensitive cell lines havebeen isolated from cultured mammalian cells in recent
years and these arc proving to be useful in studies on
DNA repair, relationship between DNA repair andmutagenesis, etc.

VII. EVALUATION OF GENETIC
RADIATION HAZARDS IN MANA.

A SUMMARY OF THE MAIN CONCLUSIONSREACHED BY THE COMMITTEE IN ITS 1977
REPORT

626. The 1977 report of the Committee presented theavailable human and experimental data that wereconsidered suitable in the context of the evaluation ofgenetic radiation hazards in man; discussed theassumptions and uncertainties involved in making useof these data for such purpose; and gave quantitative
estimates of hazards using both the so-called "direct"
and the "doubling-dose" methods.
627. With the "direct method'", it was pointed out that,with respect to hazards from the induction of
mutations, what was desired was an assessment of therisk of induction of mutations causing dominant effects
in the progeny with some indication of handicaps anddisabilities that they may cause. To do this, the mouse
data on the gamma-ray induction of mutations causing
dominant effects in the skeleton were used. The
reasoning was, and still continues to be, that many of
the skeletal abnormalities recovered in the mouse
experiments are similar to rare dominants and rareirregularly-inherited dominant conditions in man
which together constitute a sizeable proportion ofhuman genetic diseases.
628. The overall estimate of risk arrived at using thedata on skeletal mutations with appropriate corrections
for low dose, low dose rate irradiation conditions, easeof diagnosis of skeletal defects in humans and severityof effects was 20 lo-6 per 10-2 Gy (or 2000 lo-6 per Gy)of paternal, low-LET, low dose or low dose rate irradiation. In other words, 2000 individuals per million born
will be expected to suffer from one or another serious
handicap due to the induction of mutations withdominant effects, per Gy of paternal radiation exposure
under the stated conditions. The figure therefore
subsumes the effects of mutations which are operationally classified as "dominants" as well as those of"recessives" which have effects in the heterozygous
condition.
629. The rate of 20 lo-6 per 10-2 Gy of paternal
exposure was arrived at by the Committee by multiplying the estimated rate of induction of skeletal
mutations 4 lo-6 per 10-2 Gy (of low-LET, low dose rateirradiation) by a factor of 10 and then dividing the
product by a factor of 2. The rationale was set forth asfollows: " ... Firstly, a perusal of McKusick's latest
tabulation of monogenic disorders in man [M 17] will
reveal that out of the 583 'proved' autosomal
dominants, 328 are clinically important: in the lattergroup, 74 (or roughly 20%) involve one or more parts ofthe skeleton to a varying extent. However, this figure isundoubtedly a reflection of the ease of diagnosis ofsuch abnormalities by phenotypic inspection and/or
radiography. The true figure therefore is likely to belower and, in the opinion of Carter and McKusick, is of
the order of 10%". (This means that only about 10% ofthe dominant mutations in man are likely to be
associated with skeletal defects. The reciprocal of this,i.e., 100/10, provides the multiplication factor 10 used
to convert the rate of induction of skeletal mutations
into one applicable to mutations having dominant
effects on any of the bodily systems in man.)
630. "Secondly, not ,ill of the skeletal abnormalities ofmutational origin studied in the mouse will impose aserious handicap in humans. Selby suggests that this
proportion of abnormalities (leading to serious
handicaps) may range from 25% to 75%: in Carter's
opinion, a ligure of 50% may be accepted as a tentative
estimate and this has been confirmed in a detailed
discussion of the mutants by Selby and McKusick"[U1]. (This is the basis for dividing 10 x 4 lQ--0 by 2.)631. Similar data on the induction of skeletal
mutations in mouse females were not available. The
Committee carefully considered the existing evidence
from specific locus studies in mouse females, in particular, the data showing that for radiation conditions
applicable to man, maturing oocytes manifest a very
low level of mutational sensitivity and immature
oocytes are virtually insensitive. It was argued that if
the mutational sensitivity of human oocytes weresimilar to that of the mouse. the risk for human females
will be low (and very much lower than that for males).
but the Committee refrained from giving any quantitative estimate.
632. For computing the risk from the induction ofbalanced reciprocal translocations (the predominant
kind of radiation-induced structural change), theCommittee used the limited human and marmoset
cytogenetic data obtained in experiments involving
acute x irradiation of spermatogonia. Two points
deserve mention here: firstly. although, to be on theconservative side. the above data were used, it wasnoted that the sensitivity of the rhesus monkey (aspecies more closely related to man than either the
marmoset or the mouse) to the radiation induction ofreciprocal translocations in their spermatogonia is far
lower than that of the marmoset or the mouse;secondly, it was assumed that balanced reciprocal translocations as such are not associated with adverse
phenotypic effects of clinical significance and that therisks stem primarily from the unbalanced products
generated during meiotic segregation in translocation
heterozygotes.
633. Analysis of the cytogenetic data (obtained inexperiments involving irradiation of the testes of
marmosets and men and screening of the spermatocytes
descended from irradiated spcrmatogonia) permitted
an estimate of about 7 IQ-4/10-2 Gy/cell. From this.
the rate of heritable translocations was estimated as
1.75 1()-4/10-2 Gy/gamete (assuming that the rate ofrecovery in the F1 will be one-fourth of that in spermatocytes). The rates for low dose x rays, low dose rate xrays and chronic gamma-irradiation were derived by
dividing the above figure of 1.75 J()-4 by 4. 2 and JO.
respectively. The rates thus derived (0.44 JQ-4, 0.88 J()-4
and 0.18 1()-4/JQ-2 Gy/gamete) were used to estimate
the proportion of unbalanced zygotes that will result( = twice the above rates; based on the segregational
properties of translocation heterozygotes) and the
proportion of the unbalanced zygotes that will result inchildren with multiple congenital anomalies ( = 6% of
unbalanced zygotes; based on human data: see [U8]).
These calculations showed that per 10-2 Gy of paternal
irradiation. between 2 and 10 per million children born

will suffer from multiple congenital anomalies which
can be attributed to the induction of reciprocal translocations in the spermatogonia of irradiated males.
634. The Committee stressed the point that the ratesof translocation induction used above were hased onhuman and marmoset cytogenetic data with corrections
for transmission and expected effects at low doses anddose rates being based on mouse data. It cautioned that" ... should it turn out that the rate of induction inhuman spermatogonia is more similar to that in therhesus monkey. the estimates may need revision. andconsequently the quantitative figures arrived at must be
considered provisional at present".
635. There were no data on the rate of translocationinduction in human females or in any primate species.
The data for mouse females showed that in maturingoocytes exposed to acute x-irradiation, the rate was
0.16 lQ-4/10-2 Gy/gamete (semi-sterility data). The
Committee stated that " ... although there is no direct
evidence on the response of immature oocyte stages tothe induction of translocations at low doses and dose
rates, the data on specific locus mutations and on Xchromosome losses strongly support the view that therate for translocations is also likely to be low, but noquantitative estimates can be given".
636. The Committee expressed the view that the risk
from the induction of structural aberrations other thanreciprocal translocations is likely to be very small sincemost of them act too early to constitute a real hazard.
For chromosomal deficiencies (which are also known to
be induced at relatively high frequencies in the mouseafter oocyte irradiation) it was stated that ". . . notenough is known yet about their probable over-all rateof induction or deleterious effects (especially in theheterozygote) to make any estimate of the genetic
damage they may cause".
637. The risk from the induction of sex-chromosome
losses was considered to be very low after irradiation ofmales and probably also very low after irradiation of
females, these conclusions being based on mouse data.
The Committee carefully evaluated the human as well
as mouse data on the induction of non-disjunctional
effects and concluded that information on this is very
inadequate or conflicting and therefore no quantitative
estimates could be given.
638. For arriving at estimates of risk using the''doubling-dose method" the Committee made use of
the following assumptions and data. The doubling-dosefor all genetic effects is probably of the order of 1 Gy
and the use of this figure in computations is not likely
to underestimate risk. The incidence of autosomal
dominant and X-linked diseases in man is 1%; theincrease in the frequency of these diseases as a result ofradiation exposure will be directly proportional to themutational rate. Autosomal recessive diseases occur inhumans at a frequency of 0.1%; their incidence is only
very indirectly related to mutation rate. The incidenceof numerical chromosomal anomalies and unbalanced
structural anomalies is of the order of 0.4%; theincrease in their frequency will be directly proportional
to mutation rate. Balanced reciprocal translocations per
se may not confer any risk to the carriers; the risk fromthe induction of such structural rearrangements mainly
stems from the unbalanced products generated by theseduring meiotic segregation. For diseases of complex
aetiology, such as irregularly-inherited dominantdiseases. multifactorial diseases, and congenital malfor503

mations (together constituting 9%), the mutational
component (i.e., the proportion of these diseases thatwill respond to radiation exposure in a manner similar
to that of simple monogenic dominant diseases) is of
the order of 5%. Lastly, under continuous radiation
exposure (10-2 Gy/gcneration), the population willreach a new equilibrium with respect to the incidence of
these diseases: the rate of approach to the equilibrium
as well as the incidence values at equilibrium and in thefirst generation following radiation exposure will bedifferent for the different classes of diseases; thus for
instance. the approach to equilibrium will be faster for
single-gene dominant diseases, very slow for recessive
diseases and somewhat intermediate for diseases ofcomplex aetiology. The first generation incidence
following radiation exposure (under conditions ofcontinuous radiation exposure) will be one-fifth of thatat equilibrium for single gene dominants and X-linked
diseases, nearly the same in the first generation and at
equilibrium for chromosomal diseases and one-tenth ofthat at equilibrium for diseases of complex aetiology.
639. All these considerations permitted an estimate of
the total increment expected in the first generation
amounting to 63 new cases of genetic diseases per
million progeny and 185 cases per million atequilibrium, when the population is continuously
exposed to low dose rate, low dose or chronic low-LET
irradiation at a rate of 10-2 Gy per generation.

B.

RELEVANT NEW INFORMATION THAT HAS
BECOME AVAILABLE SINCE THE PUBLICATION OF THE 1977 REPORT640. The new data that have become available since
the publication of the 1977 report (and considered indetail in the preceding chapters) can be arbitrarily
grouped under at least four categories, with someoverlap between them; (i) those that confirm andfurther document the Committee's earlier conclusions;(ii) those that help to shed light on the validity ofassumptions or tentative conclusions (arrived at on thebasis of limited data) or controversial view-points; (iii)
those that seem relevant in a qualitative sense but
which, as yet, cannot be used in a quantitative manner
for risk evaluations; and (iv) those which open up
potentially useful approaches to hazard evaluations
and/or those which may be of use in improving quantitative evaluation of hazards. Some of the mostimportant of these will be summarized in the following
paragraphs.

I.

Confirmatory data(a)Human studies

641. The incidence figures for congenital malformations in the Hungarian survey are similar to theestimate made by Trimble and Doughty in the British
Columbia survey. The data of Myrianthopoulos andChung based on an almost complete ascertainment ofcases of congenital malformations show that, if
anything, their incidence may be even higher. The
analysis of the transmissibility of some common
congenital malformations summarized by Leck (for allthese, see section I.A) serves to illustrate the viewexpressed by the Committee, namely, that the
mutational component of these diseases is probablyquite small.
504

642. The new data from the recent Edinburgh andJapanese surveys on the incidence of chromosomal
anomalies in newborns (subsection l.C.1. Table 2) show
that, despite the systematic use of banding techniques,
the frequencies of different kinds of abnormalities are
similar to those reported in a number of earlier surveys.
The currently available results from chromosomal
studies of children born 10 survivors of Hiroshima andNagasaki (subsection I.C.11) show that the frequencies
of chromosomal abnormalities are similar to those incontrols.
643. Reviews on the incidence of chromosomal
anomalies in spontaneous abortions and on aneuploidy(section I.C, Figure I) document and confirm that:(a) The overallfrequencies of chromosomal
anomalies in spontaneous abortions may be as
high as 50%;(b) Spontaneous non-disjunction plays a major role ingenerating aneuploidy;(c) Such aneuploidies are frequent among chromosomally abnormal foetuses (sub-section I.C.4) andin newborns (Table 2);(d) Non-disjunction occurs in the male as well as
female germ cells, both in meiosis I and in meiosis
II (subsection l.C.7 and Table 4), as suggested bystudies on spontaneous abortions and on Down's
syndrome;(e) Evidence for radiation-induced non-disjunction in
man continues to be equivocal (Table 8);(I) Direct studies on aneuploidy in humanspermatozoa now appear possible (subsection
I.C.10).
644. Many known single-gene traits in humans areassociated with neoplasia (section I.D .. Table 9). DNA
repair studies with human cells (subsection l.E.3) whichhave been in progress for some years now, have underlined the important role of these processes, particularly
with respect to their relationships to cellular response toradiation and other mutagenic agents (subsection
I.E.2).

(b)Studies with experimental organisms

645. Further evidence has been obtained in mice forthe induction of genetic effects by 239Pu (section I I.A).
Even low doses from 239Pu alpha rays are capable ofcausing significant increases in the frequency of translocations (subsection I I.B.2). Studies with lH (given as
tritiated water) have shown significant induction of
specific locus mutations in both pre- and post-meiotic
germ cells of male mice (subsection 11.D.1); themutational spectrum shows no striking disparity fromthat induced by x rays.
646. The dose-response curve for the induction of
specific locus mutations in maturing oocytes of female
mice (high dose rate x-irradiation) has now been
extended to include the 6 Gy dose point. All the highdose rate data obtained at different doses to maturingoocytes considered together confirm that the doseresponse is curvilinear (subsection Il.D.2,).
647. Confirmatory evidence for earlier findings that theyield of reciprocal translocations induced in spermatogonia decreases with decreasing dose rate of low-LET
radiation has been obtained in a new set of studies(subsection 11.B.2; Table 21). Further data on the
induction of heritable translocations in female mice arein line with earlier results in showing that the rate inmaturing oocytes of females is about one-half of that inmales (subsection 11.B.3). The frequency of chromaiidinterchanges induced in maturing mouse oocytes(scored in meta phase I) is lower by a factor of 10 at low
dose rate relative to that at high dose rate (subsection
I I. 0.4).
648. The weight of currently available evidence
suggests that, following irradiation of male mice(spermatogonial irradiation), Robertsonian translocations are recovered (if' at all) at very low frequencies.
649. A number of studies have further documented
the existence of differences in sensitivity for the
induction of chromosomal aberrations in male andfemale mouse germ cell stages (subsections I l.B.2 and
11.B.4) and of dominant lethals (subsection 11.A.1 andTables 20 and 22). The new data on dominant lethal
induction in female guinea pigs, Djungarian andChinese hamsters (subsection I I.A.2) serve to further
highlight the existence of species differences in radiosensitivity.

655. Studies on the timing of oocyte maturation in themouse show that a period of six weeks elapses between
the initiation of stage 3b to ovulation. This means thatin mutation experiments, conceptions within six weeks
after irradiation would utilize oocytes exposed in stages
3b-8 and that litters conceived after six weeks would bederived from stages l-3a. Since the nuclear
morphology of both stages 3a and 3b is similar to one
another and also to stage 3 of guinea pig and humanoocytes, it would appear that the change in mutational
sensitivity of the mouse oocytes occur in a cell stage
with "typical" diplotene configuration (chapter IV).
656. Evidence has been obtained that in human fibroblasts and Chinese hamster cells, a significant
proportion of x-ray and high-LET radiation-induced
HG-PRT mutations is associated with cytologicallydemonstrable deletions or other aberrations in theregion of the HG-PRT locus (section IV.A).
2.

650. A number of studies have been carried out on the
induction of aneuploidy by irradiation of male andfemale mice and female Chinese hamsters (subsection
11.C.4). While in mice in some studies the evidence forthe radiation-induction of aneuploidy (scored in utero)appears good, in others it is weak; in Chinese hamsters.
the evidence is not clear-cut.
651. Completed studies on x-ray-induction of reciprocal translocations in the spermatogonia of rhesus
monkeys show that the dose-response is "humped" witha peak around 1 Gy (thus being qualitatively similar towhat is known for other mammals studied in thisrespect) and with a rate of induction (up to doses of 1Gy) being substantially lower than what has beenrecorded for other mammalian species (subsection
11.B.5; Tables 23 and 24).
652. Studies on the acute x-ray induction of
autosomal recessive lethals in maturing oocytes of mice
have demonstrated that the rate is nearly the same asthat for spermatogonia. Germ cell stages in female
foetuses do not appear to be more sensitive to the x-ray
induction of autosomal recessive Iethals than maturingoocytes in adult females. There is a dose rate effect for
the induction of specific locus mutations in oocytes offemale mice irradiated shortly before birth. suggestingthat the repair capacity of these oocyte stages are notdifferent from that of maturing oocytes in adult females(section IJ.D).
653. Further data on the relationship between chromosome arm numbers and relative radiosensitivity to
the induction of dicentrics in lymphocytes confirm theview expressed in the 1977 report, namely, that chromosome arm number is not a reliable criterion for extrapolation from one species to another with respect to thesensitivity of the chromosomes to the induction ofdicentrics (subsection 11.F.2).
654. Irradiation of mice or rats at very low dose rates(of the order of 1 10-2 to 2 10-2 Gy d-1, gamma rays)causes no reduction in spermatogonial stem cellnumbers, although at rates ;;, 3 10-2 Gy d-1. the situation
is different (chapter III). Further data from labellingstudies of irradiated mouse testis show that thesurviving spermatogonial stem cell population is qualitatively the same for that portion of the dose-response
curve giving a linear increase in mutation frequency (upto 600 R acute irradiation).

Data that shed light on the validity of assumptions,tentath·e conclusions and controversial ,·iew-points

657. The interpretation of the dose-rate effectobserved for the induction of specific locus mutations(and thus, of the nature of the mutations induced) inexperiments with female mice has been controversial
for some time. While W.L. Russell has continued tofavour the hypothesis that the mutations themselves are
single-track phenomena and other track events are
involved in damaging or saturating the repair process athigh doses and dose rates, others (Abrahamson et al.
Brewen et al.) have preferred an interpretation basedon the premise that the mutations are predominantly
two-track phenomena. In the discussion of their recent
experimental results on dose-effect relationships for
specific locus mutations in maturing mouse oocytes,
Lyon et al. have supported W.L. Russell's interpretation and have detailed their reasoning for this(subsection I 1.0.3 ).
658. The question of whether the genetic radiosensitivity of the immature oocytes of the human female issimilar to that of the mouse has been kept undercontinual review by the Committee (see, for instance,
paragraphs 293-298 in the 1977 report). On the basis of
all the evidence available the Committee concluded in1977 that there was no consistent correlation between
the induction of genetic effects, cell killing and chromosome morphology in oocytes (in mice, guinea pigs andgolden hamsters); that even if one continues to consider
the possibility that the human immature arrested oocyte
might be mutationally as sensitive as the most sensitiveof all oocyte stages in the mouse, for radiation conditions applicable to man the genetic hazard of radiationin the female will still be less than in the male. The newdata from studies on the timing of oocyte maturation in
the mouse (chapter IV) support the earlier view that
nuclear morphology is not a reliable criterion of oocyte
sensitivity: the nuclear morphologies of stages 3a and3b oocytes are similar to one another (and also similar
to those of stage 3 human and guinea pig oocytes) andyet, strikingly different in mutational sensitivity.
659. The results of experiments in Drosophila andEscherichia coli have yielded results consistent with
one of the main assumptions involved in the use of the"doubling dose" method for risk evaluation, namely,that there is proportionality between spontaneous andinduced rates of mutations (subsection 11.F.4).
However, the consistency in Drosophila exists, so far,505

only for induced mutations in spermatozoa, and theconsistency in Escherichia coli is dependent on
excluding "hot-spots".
660. It may be recalled that in making estimates ofincrease of dominant and X-linked diseases (using the
doubling dose method) under conditions of continuous
low-LET radiation exposure at the rate of 10-2 Gy/
generation, the Committee in its 1977 report assumed
that the first generniion increment for these diseases
will be about one-fifth that at equilibrium. The recenl
calculalions of Childs [C68] show that the increment in
the lirst generntion is of the order of 15% of thatequilibrium, a figure which is quite similar to the 20%
used by the Committee.
3.

Data that seem relcl'ant in a qualitathe sense

661. The frequencies of chromosome aberrations inlymphocytes of individuals living in an area of highnatural radioactivity in Austria have been found to beelevated; this is also 1rue of nuclear dockyard workers
in the United Kingdom, of nuclear power plant workers
in the Federal Republic of Germany and the United
Kingdom, of uranium miners, of workers with internal
depositions of plutonium, and of atomic bomb
survivors of Hiroshima (section 1.F).
662. Studies have been made with rabbits and mice
keeping them artificially in huts in areas of high naturalradioactivity in France for periods up to 20 months(only four months in the case of mice). In rabbits there
was an increase in the frequencies of chromosomal
aberrations (lymphocytes) reaching up to about 4% by
one year; however, by 20 months, there were practicallyno aberrations. Male mice kept for four months,
showed no translocations in their spermatocytes. But,
when such "irradiated" males were mated to unirradiated animals. there were slight increases in litter size,
the mean number of offspring sired and the mean
number of offspring weaned over a six-month period.
Female "irradiated" mice in contrast, under similar
conditions showed slight reductions in all of the above
indicators (subsection 11.F.1).
663. Although it has been known for a long time thatcertain classical chromosomal syndromes in man areassociated with congenital malformations, mental andphysical defects, it is only in recent years that studies
are beginning to focus attention on the possible clinicalsignificance of other abnormalities such as balanced
reciprocal translocations. The currently available data,
although not based on random samples, are suggestiveof an association between apparently balanced reciprocal translocations (and some other structural
rearrangements) and mental and physical defects(subsection I.C.2) and point to the need for further
studies (e.g., follow-up of children studied as newborns
and who were found to have balanced structuralanomalies).
664. In the mouse it has also been shown that somebalanced reciprocal translocations can have dominantphenotypic effects on the skeleton (subsection II.D.8).
665. The preliminary results from tests of mutants
originally isolated because of the skeletal abnormalities
that they caused in the F1 offspring, show that most ofthem behave as recessive lethals. Put another way,radiation-induced recessive lethals can have dominantdeleterious effects (subsection I l.D.8).
506

666. The utilization of banding techniques to study
human chromosomes has, among other things, led tothe discovery that partial monosomics and trisomies forpractically every chromosome of the human
complement arc frequent, and are in fact more common
than was envisaged a few years ago (subsection l.C.12).
The recent discoveries of heritable fragile sites inhuman chromosomes have exposed another facet ofchromosome structural defects(?) whose significance inthe context of human pathology remains to beestablished.
667. Studies of chromosomal evolution in primatesusing banding techniques have shown that the sequenceand types of chromosomal changes in different lines arequite different (subsection II.F.5). However, thequeslions of whether the predominance of a particularkind of change in the evolutionary history of a given
species (for instance, the predominance of pericentric
inversions in the line of descent leading to
Homo sapiens) puts some constraints on or predispose
the species to similar inducible changes or whether theevolutionary history is "irrelevant" in the context ofstudies on induced aberration remain to be answered.
668. The arguments advanced by Neel in favour of
the thesis that the contribution to human disease ofrn utations technically classified as recessives iscurrently underestimated, have been considered(section I.A); however, at present. it is difficult to givequantitative estimates.
4.

Data useful for quantitative assessment of genetic
radiation hazards

669. The only new data that have become available
since the publication of the 1977 report and which canbe used in the context of quantitative assessment ofgenetic risks to man are those that derive from experimental studies on the induction of dominant mutations
causing cataracts in mice (subsection II.D.8). Further,
the data on the induction of reciprocal translocations in
the rhesus monkey (subsection 11.B.5), although notnew, can be used, at least to set an arbitrary lower limit
for the risk from the induction of reciprocal translocations.

C.

SOME RELEVANT RECENT PUBLICATIONSON QUANTITATIVEEVALUATION OF
GENETIC RADIATION HAZARDS IN MAN

670. In two papers, Selby [S75, Sll 7) has discussed,
among other things, the problem of quantitative evaluation of genetic radiation hazards in man and has
briefly summarized the risk estimates (including themethods and assumptions used) arrived at by
UNSCEAR in its 1977 report and by the BEIR
Committee in its report published in 1980 (877]. The
estimates of the latter Committee are discussed later inthis section and will not be gone into here.
671. Ehling [E17], Ehling and Kratochvilova [E13]
Kratochvilova and Ehling [K23) made a preliminary
estimate of genetic risks from the induction of
mutations having dominant effects, using the data on
cataract mutations in mice obtained in their experiments in which a gamma-ray exposure of 910 R was
given to male mice in two equal fractions separated bya 24 h interval (spermatogonial data). As will berecalled (subsection II.D.8), the rate of induciion

estimated in this study was 1.3 1()---0/gamete/R. This
figure was multiplied by 0.85 (to correct for theenhancement effect due to fractionation and based on
specific-locus data collected in the same study). by 0.3(correction factor for dose rate effect), by 1.2 (to correct
for DNA content in human cells relative to that inmouse cells) and by 32.4 (to extrapolate from data on
dominant cataract mutations to total dominant
mutational damage affecting all bodily systems; basedon the ratio of dominant cataract mutations to all
dominant mutations as estimated from the tabulationsof McKusick in 1975 [M17]). The resultant figure was
13 1()---0. In other words, following paternal low-LET
irradiation, there will be 13 progeny per million born(per R of irradiation) who would be expected to beaffected with one or another kind of serious genetic
disease of induced mutational origin.

672. In subsequent papers, Ehling [E20] and Ehling etal. (24] extended these calculations to data from studies
on the induction of cataract mutations by single acute
gamma-ray exposures of 534 R and 600 R. As discussed
earlier (Chapter II.D.8), the rates of induction
estimated from these data are: 5.5 10-7/gamete/R (534R) and 4.5 10-7/gamete/R (600 R). These rates were
multiplied by 36.8 (the "new" ratio of cataract to all
dominant mutations that can be calculated from
McKusick's more recent compilation of 1978 [M16]).
The resultant ligures were: 20 1()---0/gamete/R and
17 1()---0/gamete/R. In other words, following paternal,
low-LET, high dose rate irradiation. 17-20 affected
progeny per million per R of exposure will be expectedin the F1. The figures will be one-third of these for low
dose rate. low-LET irradiation.
673. In a recent paper. Childs [C68] has made adetailed analysis of published data on birth frequencies,
mutation rates and fitness of each of the important
dominant and X-linked diseases in humans. For
dominant diseases. the author made use of the list
compiled by Carter [C49. C50] with minor modilications. The frequency of rare dominant diseases wasestimated based on the frequency of diseases given by
Trimble and Doughty [Tl]. For X-linked diseases, thesource was the list compiled by Stevenson and Kerr
[S124] and selected data from Trimble and Doughty.
674. From his analysis. Childs estimated that these
diseases (dominant and X-linked) affect about 0.6% of
liveborn individuals of which 16% or 0.1% of livebirths
carry a newly-arisen mutation. Assuming that the
population is exposed to low-LET irradiation at a rateof 10-2 Gy/generation and that the doubling dose is
1 Gy, he estimated that at equilibrium, there would be
about 61 extra cases per million livebirths of serious
genetic disease; the expected increase in the first
generation following the radiation exposure would be
15% or 9 cases per million. The increase in the first twogenerations would be 24% of that at equilibrium and a
50% increase would occur by the ninth generation. For
dominant diseases alone, the increase would be 14% in
the first, 23% by the second and 50% by the tenth. For
X-linked diseases alone, the increase in the first
generation is 25%, and in the first two generations, 50%.
(As X-linked diseases have a birth frequency of only 4%of that of dominant diseases, the combined increase is
only slightly higher than for dominant diseases alone.)675. Childs considers that the estimates arrived atabove may be maximum estimates for two reasons.
Firstly. Neel et al. [N24] calculated that the minimum
doubling dose, based on mortality data of the childrenof atomic bomb survivors of Hiroshima and Nagasaki,
and mutation induction in mice at low dose rates.
should be 1.38 Gy for males and more than 10 Gy forfemales, i.e., a harmonic mean of about 2.4 Gy.
Secondly, some of the dominant disorders included in
the analysis (the two common disorders hypercholesterolaemia and otosclerosis account for 50% of the birthfrequency of dominant disorders) are likely to be
maintained by selection pressure alone and would
therefore not change in frequency with a change inmutation rate [N25].19 Childs concludes that the"overall dominant genetic risks from ionizing radiation
may have been overestimated by UNSCEAR (1977) bya factor of at least 6". Thus, using a doubling dose of
2.4 Gy and excluding the disorders mentioned above
and X-linked ones, the expected extra number ofdefective children would be 3 per million births and 12
per million births at equilibrium.
676. Other papers of interest are those of Neel, Schull
and Otake [N21], Schull, Otake and Neel [S130) and
Schull et al. [S131], the last of which is the most recent.
In these papers, the authors presented an analysis of all
the currently available genetic data obtained fromcontinuing studies of the Hiroshima and Nagasaki
populations. The data pertain to untoward pregnancy
outcomes,20 survival through childhood, incidence of
sex-chromosomal aneuploids and incidence ofbiochemical variants. In all the calculations, an RBE of
5 for neutrons has been assumed. As Schull, Otake andNeel [S130] point out "in no instance is there a statistically significant effect of parental exposure. But for all
indicators, the observed effect is in the direction
suggested by the hypothesis that genetic damage
resulted from the exposure". Doubling dose estimateshave been made only for the first three of the indicator
traits since the data on biochemical variants are
considered too preliminary to provide a meaningful
estimate for this end-point.
677. The gametic doubling dose estimates presented[S13 l) are the following: untoward pregnancy
outcomes: 0.69 Sv (standard deviation, 0.93); survival
through childhood: 1.35 Sv (standard deviation, 3.88);
sex-chromosomal aneuploids: 5.35 Sv (standard
deviation, 24.31). The weighted average of the estimatesis 1.39 Sv with a standard deviation of approximately
1.56. The authors [S130] consider that this estimate
should be multiplied by a factor of 3 to convert it into a
relevant estimate for low doses and dose rates.
678. The Committee examined the data and theanalysis presented and concluded that in view of thelack of statistically significant effects and high standard
deviations associated with the doubling dose estimates,
it would be premature to use these for genetic risk
assessments at the present time.
679. Genetic risk assessments for radiological protection
purposes. Oftedal and Searle [018] have summarized theconclusions of a Task Group set up by ICRP (hereafter
to be referred to as Task Group) to make a quantitativerisk assessment and to express the risks in terms
comparable to those for somatic risks. Most of the main
conclusions reached by the Task Group are similar to
those of UNSCEAR in its 1977 report. This is to be
19 It should be noted that the paper referred to by Childs
gives no evidence in support of this belief, which must be
considered speculative at present.
20 An untoward pregnancy outcome is one that terminatedin a child who had a major congenital defect, was stillborn, ordied in the neonatal period.

507

expected in view of the fact that the basic data andseveral of the assumptions used are similar in bothcases. To facilitate easy reference the summary table of
the Task Group is reproduced below as Table 40.
680. UNSCEAR used both the direct and the
doubling dose method for the computation of risks. The
Task Group, however, used the doubling dose method(except for reciprocal translocations to be discussed
later) because "(i) it allows the risk to be expressed interms of basic human hereditary damage and (ii) if an
overall genetic doubling dose is accepted, it allows an
overall genetic risk assessment to be made even in theabsence of direct experimental evidence on certain
categories of hereditary defect".
681. In the UNSCEAR 1977 report, the risks (calcu·
lated using the doubling dose method) are expressed asa certain number of cases of serious genetic disease per
million progeny following low-LET, low dose or dose
rate irradiation of a population (assumed to be stable insize) at a rate of 10-2 Gy/generation. The Task Grouphas expressed the risks, instead, as a certain number ofcases per million man-rem (which is another way of
expressing them, allowing for the possibility of
exposure to different kinds of irradiations withdifferent RBEs and LETs).
682. The doubling dose used by UNSCEAR is 1 Gy
(low-LET irradiation) and that by the Task Group 100
rem; with this method, the Committee computed the
expected increments for the different categories ofgenetic disease as a certain number of cases in the first
generation and at equilibrium. The Task Group gave in
addition, figures for the second generation as well.
683. For simple dominants and X-linked diseases, theexpected increments in the first generation and at
equilibrium computed by the Committee and by the
Task Group are the same (namely 20 per 106 in the first
generation and 100 per 106 at equilibrium).
684. For diseases of complex aetiology (incidence
figure of 9% or 90 OOO per 106), the Committee assumed
that the mutational component is of the order of 5%,
which is another way of saying that the incidence of
only a small fraction of these diseases (5% of 90 OOO per
106 = 4500 per 106) will respond in direct proportion to
mutation pressure (just like the simple dominants and
X·linked ones) while with the bulk of these, radiation
would not produce any increase in their incidence rates.
Thus with a doubling dose of 1 Gy, and under radiation
exposure at the rate of 10-2 Gy / generation, the expected
increase at equilibrium will be 45 cases per 106
individuals born (i.e., 4500 x 1/100 = 45). The
Committee made the further assumption (based on the
BEIR Report [860]) that one-tenth of these cases (orabout 5) will be expressed in the first generation.
685. The Task Group split up the category of diseasesof complex aetiology into dominants of incomplete
penetrance and multifactorial diseases maintained bymutation and multifactorial disease not maintained bymutation and stated that "these two categories ofgenetic damage are very difficult to study and theirbirth frequency in the population cannot be determinedwith any degree of assurance." That is, they did not use
the incidence figure of 9% (for both categories together)arrived at in the British Columbia Survey. Conse·
quently, the expected increments after radiation
exposure were arrived at in a way different from theone used by the Committee described above. The Task
508

Group " ... felt that the number of extra cases atequilibrium after a parental dose of I million man rem
could be taken as the sum of the equilibrium values of
the categories (unbalanced translocations, aneuploid
conditions and simple dominants), that is 100 + 30 +
30 = 160 of which 10% would become manifest in thefirst generation after a single exposure ... " (see Table
40). For the second category described above theexpected increment was given as zero. Thus, one of themain discrepancies between the conclusions of theCommittee ( 1977 report) and of the Task Group (45cases per 106 versus 160 cases per I 06) stems from thedifferent assumption and the way of calculating theeffects of irradiation on the category of diseases withcomplex aetiology.
686. Regarding diseases with a recessive form ofinheritance. the Committee in its 1977 report expressed
the opinion that the effect of low level irradiation on
the incidence of these diseases in the first generation
will be "relatively slight" while at equilibrium (which
will be attained after hundreds of generations) there
will be a slight increase .•687. The Task Group used the same lines of reasoning
as those used by the Committee in its 1977 report as will
be clear from the following statements: " ... The probability of a newly induced recessive mutation pairing up
with a previously existing mutant allele at the same
locus, so that the deleterious condition is expressed in
the first generation after exposure, is regarded as negligibly low. In general, homozygous effects of induced
recessives will be spread over hundreds of generations,with a very slow attainment of equilibrium ... for theabove reasons, and in the context of radiation
protection, it was thought that the true recessives would
probably not contribute significantly to the extra
mutation load
following low level radiation
exposure ... ".
688. The Task Group however mentioned that " ...
the evaluation of recessive mutational effects is very
difficult and, not surprisingly, members of the Task
Group were not unanimous in their views on thissubject ... Two corresponding members have statedthat the risk from 'nominal' recessive disorders,
although largely concealed for many generations, may
be a far graver problem than all other hazards
combined, especially if these so-called recessives havesignificant effects in the heterozygotes. However, in thepresent state of our knowledge, this aspect of the risk
problem is extremely difficult to quantify ...".
689. Turning now to chromosomal diseases, theCommittee in its 1977 report used an incidence figureof 0.4% (sex-chromosomal and autosomal trisomies,
XO, mosaics and unbalanced structural aberrations)and estimated that with a doubling dose of 1 Gy andradiation at the rate of 10-2 Gy/generation. there will be
about 40 cases of affected individuals per million; since
the reproductive fitness of these individuals will be
zero, there will be no accumulation over generations
and thus the effects seen in any given generation will beessentially those of new chromosomal changes of theabove kinds.
690. For the Task Group, the starting point, i.e., theincidence figure for these diseases was 0.5% (the overallfrequency of sex-chromosomal and autosomal trisomies
and the XO); this figure was multiplied by a factor of
0.6 to take into account the possibility that thefrequency of transmission (to the gamete) of aneuploidconditions may be lower after treatment of spermatogonia than of oocytes, as has been found in experimental studies with mice. It was stated that " ... since
all these aneuploids will be manifest in the first
generation and will not reproduce, the expected
frequency of extra cases for a doubling dose of 100 rem
will be 0.005 x 0.6 x 0.01 per rem which is a risk of 30
per million in the offspring of a person receiving lrem".
691. In the 1977 report, the risk of producing unbalanced gametes leading to congenitally malformed
children (stemming from the induction of balanced
reciprocal translocations in males) was estimated using
the combined marmoset and human cytogenetic data as
2 to 10 per million per rad. The risk for the irradiationof females was considered to be low, but no quantitative estimates were given.
692. The Task Group however, used the same database (marmoset and human data) and gave an estimate
for only low dose rate x-irradiation, i.e., a reduction
factor of 0.5 was used noting "that the human x ray
doses were below 100 rad". The rate so obtained was
doubled to take into account irradiation of males andfemales. The rationale for this procedure was set forth
as follows: ·'Heritable translocations can be induced infemale mice after x-irradiation of dictyate oocytes.
Although mutation rates are similar to those after
spermatogonial irradiation. it seems probable from theresults of specific locus experiments that the effect oflowering the dose rate will be more pronounced inoocytes than in spermatogonia. On the other hand,because translocations induced in oocytes would be in
the form of chromatid exchange, a gamete from anaffected oocyte would be six times more likely to havean unbalanced form than a balanced one [S135]. It
seems reasonable to regard these opposing factors ascancelling each other out. Therefore, the risks fromtranslocation induction in female germ cells have beentaken to be similar to those in male ones." It will thus
be clear that the nearly two-fold higher risk estimatedby the Task Group derives from the assumption ofequal sensitivity of males and females, one which was
not used by the Committee.
693. The BEIR Committee's assessments. To facilitate
discussion, the summary table from the above
Committee's 1980 report [B77] is given below (Table
41).
694. Two methods have been used. The first is theindirect relative-mutation-risk method used by the
BEIR Committee in its 1972 report (and what in
UNSCEAR reports is referred to as the doubling dose
method) and the second, the direct method for
estimating total phenotypic damage induced in a single
generation. With the first method, the estimates are
expressed in terms of risk per rem of added exposure.
695. The BEIR Committee adopted a range for the
relative mutation risk of 0.02 to 0.004 per rem (doubling
dose, 50-250 rem). As is pointed out "this is based
mainly on our best substantiated estimate of the
doubling dose, namely, 114 R for mouse spermatogonia(for x- and gamma-radiation, the Roentgen, R, and therem are virtually equal). We approximately halve anddouble this to get our range of 50-250 R, which we
believe overlaps the true value. Further reason forthinking that this range is broad enough comes from theestimates of 100-200 R obtained when data from both
sexes are combined ... The few human data suggestthat humans are not notably more sensitive, and areprobably less sensitive than mice".
696. For autosomal dominant and X-linked traits, therange of 40-200 (Table 41) under the heading··equilibrium" has been arrived at by multiplying thecurrent incidence figure of 10 OOO (per million) by the
relative mutation risk range of 0.02-0.004 mentioned in
the preceding paragraph. Although no corresponding
figure for the first generation is given (see Table 41 ), it
is pointed out that " ... if we were to use the BEi R I
method of estimating first generation expression fromequilibrium estimates, then a mean persistence of 5
generations would imply first-generation expression in
the range of ... 8-40 per million livcborn per rem ofparental exposure".
697. For irregularly inherited diseases, the BEIR
Committee assumed that the mutational component ofthese diseases is in the range of 5-50% (the same as thatused in their 1972 report). When the current incidence(9%) is multiplied by this range as well as by the relativerisk range, the range of 20-900 given in Table 41 is
obtained. Again, the BEIR Committee did not give theincrement in the first generation. However, it was statedthat " ... these mutants would be expected to persist for
longer periods than would the simple, autosomal
dominants. BEIR I assumed a mean persistence of 10
generations, which would lead to an expectation of afirst generation expression of about one-tenth theequilibrium expression".
698. For autosomal recessives, the conclusions of the
BEIR Committee (see Table 41) are essentially the sameas they reached in their 1972 report (this was also
discussed in the 1977 report of UNSCEAR).
699. Turning now to the range of 5-65 cases per
million per rem given in Table 41, this represents the
direct estimate of the total phenotypic damage in thefirst generation. The skeletal data obtained by Selby
and Selby and by Ehling in mouse studies were used forthis purpose and this was also the case with the estimateof UNSCEAR. The estimate of UNSCEAR was
however 20 cases per million per 10-2 Gy of paternal
irradiation. The reasons for the difference in the quantitative estimates are the following.
700. First, to convert the rate of induction of skeletal
mutations in mice to an overall rate involving all bodily
systems in humans, the UNSCEAR used a multiplication factor of 10 (i.e., 4 1~ x 10 = 40 1~). Thiswas divided by a factor of2 to exclude mutations whose
effects are slight: the BEIR Committee on the other
hand, used a range of 5-15 to make the first conversion
and used a range of 0.25 to 0.75 to make the second
conversion. In its view, these ranges reflect the uncertainties involved. These operations (i.e., 4 1~ x 5 x
0.25 and 4 1~ x 15 x 0.75) give a range of 5-45. Inother words, following paternal low-LET, low dose rateirradiation at a rate of 1 rem per generation, theexpected number of individuals (in the generation
following the exposure) who will suffer from the effects
of serious genetic diseases of induced mutational origin
will be in the range of 5-45 per million livebirths.
701. Second, to take into account the effects of irradiation of females, the BEIR Committee multiplied theupper limit of 45 given above by 1.44 (the UNSCEAR
1977 report assumed that the risk for irradiated human
females will be negligible and did not give any quantitative estimate). The rationale for this multiplication509

was set forth as follows: "The mutational response ofresting oocytes in mice is negligible, compared with thatof spermatogonia, and mature and maturing oocytes inmice have a mutation rate no greater than 0.44 times
that found in spermatogonia. We do not know which ofthese two classes of oocytes would have a mutational
response more similar to that of arrested oocytes inwomen. To incorporate this range of uncertainty into
our risk estimate for the combined effect of irradiationof both sexes, we have simply kept the lower limit of
our estimate the same as it was (assuming a negligible
mutation frequency in resting oocytes) and multiplied
the upper limit by 1.44 (assuming the maximal estimateof the mutation frequency in mature and maturingoocytes). This gives an estimate of 5-65 induced serious
disorders per million liveborn as the first generation
expression, after exposure of the entire population to I
rem per generation."
702. For estimating the risk from the induction ofreciprocal translocations, the U NSCEAR in its 1977
report used the marmoset and human cytogenetic dataas the basis and arrived at an estimate of between 2 and10 congenitally malformed children per million births
per 10-2 Gy of low-LET irradiation of males. Briefly,
the calculations were the following: 7 lQ-4 (rate oftranslocation induction: spermatocyte data) x 0.25 (multiplication factor to get the rate for heritable translocations in the progeny) x 0.1 or 0.5 (multiplication
factors to account for dose-rate effect after chronic
gamma and low dose rate x rays, respectively) x 2(multiplication factor to estimate the rate of productionof unbalanced products of reciprocal translocations) x
6% (the proportion of unbalanced products that was
assumed to give rise to viable, but congenitally
malformed progeny). The risk for the irradiation ofhuman females was considered to be small, but noquantitative estimate was given.
703. For the BEIR Committee's calculations of risks
for irradiated males, the starting point was the same
cytogenetic data as those used by UNSCEAR. The
estimate of risks (see Table 41) was also nearly thesame. but the method of calculations was different.
Some of the salient aspects of the calculations and therationale behind them can be summarized as follows.
704. In mice, the ratio of the observed incidence ofpartial sterility to that calculated on the basis of theincidence of multivalents in primary spermatocytes was
about 1:2 for 300 R and higher exposures, but was 1 :1
at 150 R, for reasons yet unknown. To take into
account the above uncertainty, the BEIR Committee
assumed an overall ratio of 1 :1.5. Thus from the rate of
7.7 lQ-4 per R (spermatocyte data; note that the
UNSCEAR used a figure of 7 lQ-4) the "rate of potentially transmissible rearrangements in spermatocytes"
was estimated as 4.7 lQ-4/rem (i.e., two-thirds of
7.7 IQ-4; the UNSCEAR's calculations imply a ratio of

1 :1 ).
705. To convert the above figure into one that will beapplicable at low total doses or at low dose rates. the
BEIR Committee used a reduction factor of 2. This
figure was arrived at by assuming a quadratic model fortranslocation induction in mouse spermatogonia,
applying it to the published mouse data of Searle et al.
(lSl25}; 600 R; different dose rates), estimating thecontribution of the linear and quadratic components tothe total yield at an exposure of 100 R (because thehuman and marmoset data pertain to exposures of 100
R and below) and thus computing the expected
dose-rate effect. The resultant rate was 2.3 1Q-4 per rem.
510

706. From the above rate and assuming that on the
average, alternate segregations occur in 45% of the
spermatocytes and that half of the recoveries carry thetranslocation, the BEi R Committee computed that theprobability of transmitting a newly-induced translocation to an offspring will be 5.2 10-s per rem (i.e.,2.3 \Q-4 x 0.45 x 0.50). It follows that "the combined
expectation for all adjacent segregations" would be 55%
of 2.3 I Q-4 or 1.3 1Q-4,21 Assuming further that "no morethan 5% of all translocations are capable of producing
viable aneuploids", the probability of generating thiswas estimated as 5% of 1.3 IQ-I or 6.5 1()-6 per rem.
707. The BEIR Committee stated " ... however, we
would expect only one of the four kinds of aneuploid
segregation products to be capable of giving rise to
viable zygotes. Taking into account that this might notalways be one of the less frequent products, dividing by
4 to accommodate the one-out-of-four expectation
gives the figure of 1.6 1Q-6. Using the order-ofmagnitude range of uncertainty ... gives the range 0.5
1()-6 to 5 1()-6 per rem" ,22708. For estimating risks for irradiated females, theBEIR Committee made the same assumption as thatused in their 1972 report. namely, that the rate ofinduction of reciprocal translocations in females may
be the same as that in males. "Thus, the expected
frequency of viable aneuploids for both sexes isassumed to range from 1 10-6 to 10 1()-6 per rem." The
BEIR Committee also used "an alternative andindependent approach based on litter-size reduction
observed after acute irradiation of mouse germ cells"
and pointed out that "the upper limit of 10 1()-6 for both
sexes combined may be an overestimate, and that thetrue value could indeed be near to zero".
709. In conclusion therefore, it can be stated that
there is no major disagreement between the quantitativevalues presented in the 1977 UNSCEAR report and in
the 1980 BEi R report, although some of the methods
used are not the same.

D.

CURRENT RISK ASSESSMENTS OF THE
COMMITTEE

1.

(a)Direct method

Mutational damage

710. As mentioned earlier, in its 1977 report, theCommittee estimated genetic risks using a direct and adoubling dose method. With the former (and using thedata on the induction of skeletal mutations in malemice as a basis), it was estimated that the risk from theinduction of mutations (which will be expressed in thefirst generation progeny as serious genetic diseases,
handicaps and disabilities) is of the order of 2000 cases
per million births per Gy of paternal, low-LET, lowdose or low dose rate irradiation. The Committee
considers that the above estimate is still valid.
21 Alternate and adjacent-I segregations have the same
meiotic consequences in translocations, providing there ischiasma formation in at least one of the interstitial segments,
which is normally the case (sec (S 126]). In the absence ofadjaccnt-2 segregation therefore, one-quarter of the sperm
produced by spermatocytes heterozygous for a translocation
will carry the translocation in balanced form. This is indeed amaximum figure, as stated in the BEIR report.
22 See however Dutrillaux et al. (D26].

711. An independent estimate of risk from theinduction of mutations in males can be arrived at using
the data on the induction or dominant cataract
mutations in male mice following spermatogonial
irradiation. These data discussed in subsection 11.D.8
permit estimates of 12.7 10-7/R/gamete (fractionatedgamma irradiation; 455 + 455 R. 24 h interval) and 5.0
10-7 /R/gamete (average estimate based on the datafrom the two single gamma-ray exposure experiments
involving 534 R and 600 R. respectively). These rates
however, need first to be converted into those that wil I
rellect the response under low dose. low dose rateirradiation conditions in the mouse, and, secondly, tobe transformed into quantities that will express the risk
in humans. The performance of these operations restson the validity of the following two assumptions.
Firstly. that the quantitative changes in response of thedominant cataract mutations and of recessive specificlocus mutations in mice to changes in dose rate anddose fractionation procedures are similar (and its
corollary. that. if the rate under one set of radiation
conditions is known, those for other radiation conditions desired can be estimated using the specific locus
data). Secondly, that since in man, about 2.7% (20/736)
of all known and proven dominant mutations areassociated with one or another form of cataract [M61],
the reciprocal of this (i.e., 100/2.7 = 36.8) can be usedin the context of estimating the overall genetic risk fromthe induction of mutational damage [E20).
712.
(a)

The relevant calculations are the following:
Expected rate of induction of cataract mutations
at low doses or low dose-rates of low-LET irradiation:(i) From the data in exposure fractionation
study:
12.6 10-1 = 3.5 10-1
1.2 X 3(the factor 1.2 comes from the enhancement
effect observed due to fractionation. inconcurrent specific locus studies; the factor 3
is the dose rate reduction factor):(ii) From the data on single exposures:

5 10- 13

- - = 1.67 10- 7(b)(the factor 3 is the same as in (i) above).
The average of these two estimates (weighted
by the number of mutants in the fractionationand single exposure series) is 2.6 10-7.
Overall risk from the induction of dominant
mutations causing serious effects in the first
generation progeny:
2.6 10- 7 X 36.8 :::< 10 I0- 6(the factor 36.8 is the same as that mentioned in
the preceding paragraph). In other words, about
10 individuals per million born will be affected by
one or another kind of clinically important serious
genetic disease (of induced mutational origin) per
10-2 Gy of paternal. low dose rate or low dose,
low-LET irradiation (or 1000 individuals affected
per million born per Gy of irradiation under thestated conditions). It is worth pointing out that inthese calculations, the multiplication factor 2 andthe division factor 2 used in similar computations
with the skeletal mutations to take into accountease of diagnosis and severity of effects. respectively (see Section Vil.A), have not been employed.

713. It is clear that the above estimate of 1000 cases
per million per Gy of paternal irradiation is similar tothat derived using the data on the induction of
dominant skeletal mutations in mice. The finding thatthe estimates derived from two different sets of mouse
data and using different correction factors are similar
strengthens the earlier conclusions of the Committee.
However, it bears reiterating here that all theseestimates involve a number of assumptions and thatthese estimates merely rellect the current status ofknowledge and may be subject to revision at somefuture date.
714. Since there are no experimental data on the
induction of either skeletal or cataract mutations infemale mice, it is not possible to use a similar approachto estimate the risk associated with the irradiation ofhuman females. However, the probable magnitude ofrisk to the latter can be derived in a very indirectmanner by comparing the specific locus mutation rateestimates for spermatogonia and mature (and maturing)
oocytes after low-level low-LET irradiation. As theCommittee stated in its 1977 report " ... the four rates
for low-level irradiation of mature and maturingoocytes estimated by Russell are only 0.17, 0.27, 0.33
and 0.44 times as effective, and only in the highest ofthese is the induced rate in oocytes significantly above
the control rate. Thus the ratio of effectiveness to thespermatogonial mutation rate could be zero".
715. If, for the sake of argument. it is assumed thatthese ratios will hold also for the induction of
mutations having dominant effects; and if it is acceptedthat the mutational response of the human oocytes will
be more similar to that of mature and maturing mouse
oocytes for low-level irradiation; then the risk from
irradiation of human females can be estimated to be in
the range from O to 0.44 of that from irradiation ofmales. In other words, irradiation of human females
may entail a risk of producing between O and 9 affectedchildren per million births per 10-2 Gy or between 0
and 900 affected children per 106 births per Gy of
low-LET low level radiation,
716. It should be stressed that the computation of thisestimate is not meant to suggest that a new risk from
irradiation of females has been uncovered, but rather,to take into account the possibility that the mutational
sensitivity of the immature human oocyte may not be as
low as that of the immature mouse oocyte. Thus theearlier conclusion of the Committee is still valid.
namely that: ..... even in the event that the humanimmature arrested oocyte does not respond like themouse arrested oocyte, but more like the most sensitive
stages in the mouse, it seems likely that the genetic
hazard of radiation in the female will still be less thanin the male". This applies to low dose or low dose rate
low-LET irradiation.
717. As discussed in chapter I of this Annex, the thesisthat the impact of spontaneous mutations in man thatare classified as recessives and which are null mutations
in a molecular sense (i.e., those which cause an absenceor near-absence of enzyme activity) on human health
may be currently underestimated remains speculative.
Nonetheless the Committee takes note of this point, but
wishes to point out that at present there is no way totranslate this concern into meaningful figures. It
believes that the risk from the induction of mutations
having dominant effects in the progeny far outweighsthat from the induction of recessive mutations per se.

511

718. Turning now to possible risks from the inductionof minor (polygenic) mutations, the UNSCEAR 1972
report [U8] staled the difficulties involved in making arisk estimate for this kind of mutations as follows:" ...
Experiments with Drosophila show that mutation
resulting in minor deleterious effects grossly outnumber
those with severe effects. The calculations ... do nottake into account this class of mutations which lead tominor disability and disease. Because of the greater
frequency of occurrence of these mutations, their total
effect in terms of genetic burden to the population
could be greater than that of a smaller number ofrelatively more serious conditions. . . There is,however, no way at present to assess their contribution
to the genetic burden of man". In the 1977 report, theabove general conclusion was implied (although not
explicitly stated) and no risk estimates for this class ofmutations were made. The situation has not changed in
the meantime and therefore, the Committee does not
sec a need to alter the above point of view. (For recent
reviews on the effects of spontaneously-arising andradiation-induced polygenic mutations on population
fitness in Drosophila, see [S127, M68].)719. In its 1972 and 1980 reports, the BEIR
Committee expressed a similar opinion. The 1972
report stated the situation as follows: " ... Perhaps the
major reservation that we have about our estimates isthe failure to take adequately into account mutations
that have very mild effects ... this is the most frequentclass of mutations in Drosophila and because they
persist longer in the population than those with more
drastic effects, each mutant affects a correspondingly
larger number of persons . . . Perhaps the humancounterparts of these mutations, in addition to causing
a slight reduction in life expectancy, are responsible forgreater susceptibility to disease, impaired physical ormental vigor, or a slight malformation of some organ. . . Despite a concern for this effect, we shall not
attempt to estimate it quantitatively.. . At least in
Drosophila, the evidence is now good that this class ofmutations is relatively less frequent among radiationinduced
mutations
than
among
spontaneous
mutations ... The empirical experiments on mice argue
that such genetic mutations are not making any
substantial impact on mouse populations for up to 45
generations of continuous radiation, far longer than weare able to consider in any meaningful way for thehuman population".

(b)

Chromosomal damage

720. As was discussed earlier, the Committee madeuse of the limited human and marmoset cytogenetic
data to give estimates of risk from the induction ofreciprocal translocations in males in its 1977 report.
The risk was estimated as 2 to 10 cases of congenitally
malformed children per million births per 10-2 Gy (or200 to 1000 such cases per million births per Gy) of lowlevel, low-LET irradiation and the risk was assumed tostem primarily from the unbalanced products generated
by radiation-induced balanced reciprocal translocations (see Section VII. C for a recapitulation of theprocedure used in the calculations).
721. Studies on rhesus monkey spermatogonia using
improved techniques have yielded far lower rates oftranslocations than those previously reported forhuman and marmoset spermatogonia. Since there is noa priori reason to assume that human spermatogonial
sensitivity is similar to those of the marmoset and since512

the possibility exists that human spermatogonia may
manifest a pattern similar to that of the rhesus monkey,
one can use the rhesus monkey data to define aprobable lower limit of risk; this procedure will notmaterially alter the Committee's earlier assessments aslong as it is assumed that the sensitivity of humanspermatogonia may lie anywhere between the limits
defined by those of rhesus monkey and marmoset.
722. If this line of' reasoning is accepted, thencorrection factors similar to those used in the 1977
report can be used to arrive at an estimate of risk asfollows (all rates are per 10-2 Gy):
Rate of induction in rhesus monkey
0.86
spermatogonia; cytogenetic data(b) Rate of induction that relates torecoverable translocations in the F 1
0.215 10-•progeny [divide (a) by 4](c) Rate after low dose rate x rays [divide(b) by 2] based on mouse cytogenetic
0.1075 lO-·
observations(d) Rate after chronic gamma-irradiation[divide (b) by 10) based on mouse
0.022 10-•
cytogenetic observations(e) Expected rate of unbalanced products:
0.215 10-•for (c)[multiply (c) and (d) by 2]:
0.043 10-•for (d)(f) Expected frequency of congenitally
malformed children in the F 1 assumingthat about 6% of unbalanced products[item (e) above] contribute to this:low dose rate x rays
1.3
I o- 6chronic gamma irradiation-0.3
10- 6 •(a)Thus, on the basis of the rhesus monkey data, one canestimate that the risk of producing congenitally
malformed children (as a consequence of the inductionof balanced reciprocal translocations in the fathers) is
between 0.3 per 1Q6 and 1.3 per 106 per 10-2 Gy (orbetween 30 and 130 per 106 per Gy) of paternal low
level irradiation. Taking into account all the primate
data, it can be estimated that there will be between
about 30 and 1OOO cases of abnormal children per
million progeny per Gy of paternal low level irradiation, stemming from the unbalanced products ofradiation-induced balanced reciprocal translocations.
723. Although the risk estimated above is based
entirely on unbalanced products of balanced reciprocaltranslocations, the Committee takes note of the observations in humans (chapter I) and in mice (subsection
I I.D.8) that some balanced reciprocal translocations areassociated with dominant phenotypic effects. The risk
from these is not, however, ignored: it forms part of thetotal risk estimated for mutational events withdominant effects. Thus, some of the dominant skeletal
mutations are associated with, and probably caused by,balanced reciprocal translocations. The basis fordominant effects of balanced reciprocal translocations
has not been elucidated, although at least two formal
possibilities can be envisaged: loss of chromosome
material at the site of chromosome breakage, perhaps
too small to be detected, and position effect. In
humans, the documented cases of position effects
involve only the X chromosome [D16, T26] and areassociated with abnormal phenotypes. In mice, in
addition, there is evidence that position effects can also
be generated in the case of autosome-autosome translocations.
724. The rate of translocation induction in human
females is not known and there are no marmoset or
rhesus monkey data. In its 1977 report, the Committeestated that " ... the data for mouse females show that inmaturing oocytes exposed to acute x-irradiation, therate is 0.16 lQ-4/gamctc/rad ... although there is no
direct evidence on the response of the immature
oocytes stages to the induction of translocations at low
doses and dose rates, the data on specific locus
mutations and on X-chromosome losses strongly
support the view that the rate for translocations is also
likely lo be low, but no quantitative estimate can begiven".
725. It is now possible to make further arguments(necessarily indirect) and calculations to show that theabove statement is probably correct for low dose rate
gamma irradiation. One can start with either of thefollowing two assumptions: for radiation conditions
applicable to humans, the human immature oocyte will
respond in a manner similar to the mature andmaturing mouse oocyte, and the immature humanoocytes will respond in a manner similar to that of theimmature mouse oocytes. In the latter case, the risk isnegligible or zero. The following discussion focuses on
the consequences if the first assumption is correct.
726. In mice, as discussed earlier, maturing andmature oocytes are only one-half as sensitive as
spermatogonia to the induction of heritable translocations. There is a pronounced dose-rate effect(subsection 11.B.4) for the induction of chromatid interchanges in maturing oocytes. If these findings are applicable to humans, marmosets and rhesus monkeys, thefollowing two rates of heritable translocation induction
can be computed for high dose rate low-LET irradiation (all rates per 10-2 Gy): 0.875 lQ-4 (marmoset andhuman data base; 0.5 x 0.25 x 7 x lQ-4) and 0.108
lQ-4 (rhesus monkey data base; 0.5 x 0.25 x 0.86 xlQ-4). At low dose rates, these rates will be an order ofmagnitude lower (i.e., 0.0875 lQ-4 and 0.0108 lQ-4).
727. Since heritable translocations recovered from
irradiated oocytes are induced as chromatid interchanges, a gamete from an affected oocyte would be six
times more likely to have an unbalanced form of thetranslocation than a balanced one (see references [Sl28,
Sl35]). In other words, the rates for unbalanced
products will be six tirries those quoted above (i.e.,
0.5275 lQ-4 per 10-2 Gy and 0.0648 lQ-4 per 10-2 Gy).
Assuming as before that about 6% of the unbalanced
products will result in congenitally malformed children,
it can be estimated that there will be 3 children per
million who will be affected per 10-2 Gy (or 300 per
million per Gy) (marmoset + human data base) or 4
affected children per 10 million births per 10-2 Gy (or40 per million per Gy) (rhesus monkey data base) of
maternal, low-LET, low level irradiation. In either case,
it is clear that the risks are low for irradiated human
females. It is worth reiterating here that if the sensitivityof the human immature oocytes is similar to that ofimmature mouse oocytes, the risk will be close to zero.
728. With respect to structural aberrations other thanreciprocal translocations, the Committee's earlier viewthat the risk from their induction is probably small(since most of such changes may act too early toconstitute a real hazard in liveboms) is still valid. It is
known that deficiencies are induced and no doubt someof these will contribute to dominant effects. The risk forthese. like that for balanced reciprocal translocations, isincluded in the scoring of mutational events withdominant effects. Likewise, the Committee's earlier
conclusion (based on mouse data) that the risk from theinduction of sex-chromosome losses in males is very

low or nil is still valid. For chronic gamma irradiationof maturing oocytes of mouse females, L.B. Russell(R30] has estimated (from the data of W.L. Russell andcolleagues) an induction rate of 5 1D-6/R; for irradiation of immature oocytes, the induction rate is zero.
These findings would suggest that if the human oocytes
respond like those of the mouse, the risk is probably nohigher than 5 lD-6/R (or about 500 lD-6/Gy) for irradiation of females. Similarly, the Committee's earlier
conclusion that the risk from the induction of nondisjunction (leading to viable trisomies) is small,
although it cannot be quantified at present, still stands.
729. The "expected rates" of induction of different
kinds of genetic damage (derived from the relevant data
discussed in this section) are summarized in Tables 42
and 43.
2.

Doubling dose method730. The estimates of risk arrived at by the Committee
using the doubling dose method are given in Table 44.
They are essentially the same as those given in its 1977
report, except for three changes: (a) the current
estimates are based on an assumed exposure of 1 Gy/
generation (instead of an assumed exposure of 10-2 Gy/
generation, as was the case in the 1977 report) of low
dose rate, low-LET irradiation; (b) on the basis of thecalculations of Childs [C68] for dominant and X-linked
diseases, discussed earlier, the Committee has now
assumed that the first generation increment of these
diseases is 15% of that at equilibrium, instead of the
20% figure assumed in the 1977 report; and (c) the
Committee has refrained from applying the doublingdose of 1 Gy to the overall incidence of chromosomal
diseases in order to estimate the increment which would
be expected to result from irradiation. Instead, it hasapplied the doubling dose only to the structuralcomponent of these diseases, for the reasons discussed
below.
731. Chromosomal diseases are divided into two very
distinct components, namely, those based on structuraland those based on numerical changes. Structuralchanges in the form of reciprocal translocations were
included in the mutational end-points from which an
overall doubling dose of 1 Gy for low dose, low-LET
irradiation was calculated. Therefore, it seems appropriate to apply the same value to the structural anomalies
in Table 44. However, data on trisomies which result
from the process of non-disjunction rather than chromosome breakage, were not used in doubling dose
calculations and the results of more recent experiments
do not permit a doubling dose for this category to be
estimated with any confidence. No experiments havebeen carried out under chronic exposures and noclear-cut dose-response relationship has been obtained
under acute exposures. Moreover, there are complicating factors like maternal age which lead to considerable heterogeneity of response. Therefore, no attempt
has been made to estimate the likely effect of 1 Gy/
generation on the incidence of numerical anomalies.
This effect is likely to be very small.
732. For the purpose of doubling dose calculations,the incidence of diseases stemming from structuralaberrations of chromosomes has been derived from thefigures for structural aneuploids given in Table 2 of thisAnnex. However, aneuploid Robertsonian translocations have been omitted because of the evidence thatthese are not induced by radiation (see text); the513

"others" category has also been omitted because they
are mainly mosaics and therefore probably result fromevents in early development rather than in either
parent. For the same reasons, mosaics have also been
omitted from calculations of the incidence of numericalanomalies.
733. Other data and assumptions that are now used toderive risk estimates are the same as those used in the
1977 report. Among these are the following: the use of adoubling dose of 1 Gy to estimate risks at low doses oflow dose rate, low-LET irradiation: the assumption of
the same incidence figures for the different classes ofgenetic diseases as those used earlier (1% dominant andX-linked diseases); 0.25% recessive diseases, including
those maintained by heterozygous advantage, but thisinclusion does not affect the risk estimate: 0.34%
chromosomal diseases and 9% diseases of complex
aetiology; the assumption that under conditions ofcontinuous exposure to low level low-LET irradiation,
the incidence of diseases in the population will reach a
new equilibrium with an elevated incidence rate; andthe assumption that the equilibrium frequency, the rateof approach to equilibrium and the expected effects inthe first generation will be dependent on the kind of
disease under consideration.
734. It should be noted that the genetic risk estimates
given in Tables 43 and 44 refer to gonadal radiation
exposures before or during the reproductive period, i.e.,
all the dose is genetically significant. When dealing
with population exposures, it is sufficient to assume forthe purposes of calculation that the child expectancy
per parent is 1.0 until the mean age at conception andzero thereafter. Thus, if the mean age at conception is
30 years, then the genetically significant dose will bethat received by the gonadal germ cells up to the age of
30. If the mean life expectancy in the population is 70
years, then the genetically significant dose will be 3/7of the mean lifetime gonadal dose.
3.

Index of harm, genetic detriment and the impact ofgenetic disease(a)Introduction

735. The quantitative figures of risk arrived at earlier(Tables 43 and 44) refer to expected numbers of casesof "serious genetic disease" due to radiation-induced
mutations and chromosome aberrations in the progenyof those exposed to irradiation. The term "serious
genetic disease" used in this context connotes ill-health,handicap or disability of genetic origin which can set in
at any time from birth onwards; it does not, however,discriminate between the impact of these diseases on
the individual, family, society or health-care facilities,
to mention only a few. As Newcombe has stressed [N5]," ... such numbers are poor indicators of harm if one
lacks a satisfactory measure of the spectrum of severities among the various individuals affected by thehereditary conditions". For instance, no one doubtsthat Huntington's chorea and Down's syndrome areserious genetic diseases, but yet they are different:
Huntington's chorea is a disease in which there is a
gradual but very serious degeneration of the central
nervous system with onset during the third to fifth
decades of life. Down·s syndrome children suffer froma multiplicity of problems from birth onwards.
736. What is obviously needed are some objective andquantifiable indices of severity such as years of life lost514

due to the disease, the relative durations of hospitalization or medical care needed, etc., which can, at leastin principle, be used to "weight" the different diseases
to arrive at an overall estimate of genetic detriment.
Only on the basis of such an estimate (or a group of
estimates, depending on the criteria used) can one makemeaningful comparisons between, and realistic
appraisals of (i) the impact of diseases of different
genetic aetiologies and (ii) the relative contribution ofsomatic and genetic effects to human ill-health. Thispremise is valid for both spontaneously-occurring andinduced effects.
737. These considerations would suggest that, in thecontext of comparing genetic and somatic effects ofradiation, equating the number of cases of induced
genetic disease per unit amount of radiation with thenumber of cancer deaths (and then adding the two
together as a measure of total harm or detriment) isneither wholly satisfactory nor entirely adequate. An
example will make this point clear: if a fatal induced
cancer involves, say, 10-12 years of loss of life and if
the average age at death from what are classified as
major genetic defects were at age 15 (i.e., with about 60
years of loss of life expectation), there would immediately be a factor of 4 or 5 greater average detriment foreach major genetic defect than for each fatal cancer, as
judged by only life loss. and apart from the difference
in disability during life.

(b)

Indices of harm

738. A recent ICRP document [I6] considered indetail the problems involved in developing indices ofharm from the standpoint of recommending appropriate limits for any occupational or other exposure toradiation and the assessment of the safety of an
occupation involving such an exposure and comparing
it with· the safety of other occupations. In that
document, both the limitations and utility of certain
criteria such as fatality and mean loss of life, various
occupational injuries and their severity (expressed for
instance as the total number of working days lost) weredealt with and compared with similar consequences ofsomatic and genetic effects of radiation exposures. It
suggested that the index of time lost (an integrated
measure taking into account all these criteria) from afull and normal working life (expressed as man-years
per year per 1000 employed) is a possible approach,despite a number of limitations.

(c)Genetic detriment739. The reasons why, in spite of its importance. theproblem of developing adequate measures of genetic
detriment has been largely neglected thus far, have been
succintly stated by Trimble and Smith [T2) and can besummarized as follows. It is difficult to define
parameters that could be considered valid measures ofoverall burden: it is equally difficult to amass large
volumes of objective data covering the whole life spanof both diseased and normal individuals, and suchresearch is still generally thought to be scientificallyunrewarding. Notwithstanding these difficulties, a few
attempts have been made to develop an index of harmfor genetic diseases. Although all these attempts
concern spontaneously-occurring genetic diseases, theremainder of this section will be devoted to a discussionof these, if only to illustrate the methodology that coulde~ - los Yos
e~ = -I00-OOO------

eventually be used to assess the genetic effects ofradiation.
740. Several tangible criteria have been used to assessand quantify the actual burdens imposed by genetic
diseases on the individual, the society and public healthfacilities. These include mortality (and consequent
reduction in life expectancy). number of days of hospitalization, frequency of hospital readmission, etc. These
do not include however entities such as the reduction in
the quality of life for the carrier of a given genetic
disease nor does it include the anguish experienced by
the parents of a child with a genetic defect. There is no
doubt that these are important. but they do not readilylend themselves to quantification.

(i)171e use of years of life lost as an index of genetic
detriment

741. As has been emphasized by the lCRP document[16] and by Jones [J13, Jl4], a life-shortening genetic
disease is not necessarily a cause of death in the sense
one uses the word in the context of death due to an
automobile accident or drowning. Genetic conditions
may shorten one's life by altering one's risk of mortality
over a considerable period of time. Unlike a cause ofdeath which acts at the time of death only. a genetic
condition is a risk-altering state that may act from birth
onwards. A person with a genetic disease is born into a
different life table with different risks of death thanother people.
742. Years of life lost can be defined as the number ofyears of life that would eventually be gained if thecause or condition under study were somehow eliminated [113, 114]. Jones [113] has stressed the point that" ... it occasionally happens that an investigator calculates the years of life lost by taking the difference
between the age at death and life expectancy at birth ...
this procedure is incorrect". For instance, an individualof age x has already survived many risks of death andcan expect to live to an appreciably riper age than hecould have as a newborn. It is thus clear that for aproper estimation of years of life lost, one should take
into account the age and sex-specific mortality rates ofindividuals with and without the condition considered.
743. Jones [J13, 114] has illustrated the use of years oflife lost (YLL) index for genetic diseases with respect to
Down's syndrome (OS) which manifests itself at birthand Huntington's disease (HD}, one with a delayed
onset. For Down's syndrome the procedure is asfollows: c~nsider the average age at death for a personwith DS, Yos. and the expectation of life at birth foreveryone else.~- If Down's syndrome were eliminated,then everyone who would have lived YDS, years now
lives ~ years. Hence for each person. the gain in yearsof life equals(~ -Yos). If Ios is the incidence of Down's
syndrome per 100 OOO born, then years of life lost
through Down's syndrome is

100 OOO - losSubstituting in equation (I) gives

YLL

- 1

os -

Ds

(e' - - ) + It>s (e~ - fos)o
Yos
100 OOO - Ins(3)744. The data and assumptions used are thefollowing: the incidence figure for Down's syndrome atbirth estimated by Carter et al. [C48] of 1 in 660 in
England is a reliable one and can be considered applicable for the United States; although the sex distribution at birth appears slightly to favour the males, withcomplete ascertainment at birth, the female and maleneonates with Down's syndrome would be of equal
numbers; and the data from two large studies ofmortality, one an American and the other a Danish, canbe used; in the first, Fabia et al. [F20] have presented
sex-specific life tables up to 10 years of age, based on
all Down's syndrome children born alive in Massachusetts from 1950 through 1966 (a total of 2421 cases). In
the second, Oster et al. [019] have presented similartables from 5 to 80 years of age for all the Down's
syndrome cases (526 cases) born in a certain area ofDenmark in 1949.
745. From these data, Jones calculated that the
average age at death for Down's syndrome males is 35.7
years and for females, 35.5 years. In 1970, the life
expectancy at birth in the general United States
population was 67.1 years for males and 74.8 forfemales [N19]. Applying equation (2), he arrived at a
YLLos figure of 5364.2 years per 100 OOO persons born
alive, or a little more than 53.5 years for every 1000
livebirths.
746. With diseases such as Huntington's chorea, thesituation is somewhat different. In these cases, having
the genotype (but not the disease) is usually not a riskaltering state. Since the onset is often gradual, fixing apoint in time in the natural history of the disease withdelayed onset (where the risks to a patient's life firstdiffer from the risks for other people) is difficult. It canconservatively be assumed that until onset as conventionally defined for that disease, the person's life issubject to the same forces of decrement as others.
Account must also be taken of the fact that many
people with the genotype for the disease never develop
it because they die before the onset. In a disease withdelayed onset, the incidence at birth of the underlying
genotype is always higher than lifetime incidence, i.e.,
the number of persons relative to (say) 100 OOO born
who will develop the disease at some time in their lives.
In calculating years of life lost, it is the latter number(lifetime incidence) which is important, since under theassumption used, the lives of people who die before
onset have not been shortened by the genetic disease forwhich they are at risk [113].
747. Jones [113) has shown that lifetime incidence,
although rarely reported in the literature as such, can be
estimated from the relationship

YLLos = los (e0 - fos) years per I 00 OOO liveborn (I)Ios and yos can be determined from reports on Down's
syndrome and ~ can be inferred from the same information and published life expectancy figures. It is not,however, the same as published life expectancy at birth,~. because the published figures include the deaths ofpersons with Down's syndrome, whereas ~ does not.
The two figures are related according to the equation:

(2)

lg

Bg

=-=-

(4)

Sg

where I8 represents lifetime incidence per 100 OOO born;
Bg is the number of persons in the life-table populationsaffected at a given time: and 8 is the average durationof disease g. In other words, incidence = prevalence +duration. He has also shown that once 18 is determined,515

the remainder of the calculations is essentially the same
as for a disease which manifests itself at birth (e.g.,
Down's syndrome considered earlier). The equation is.

YLl.-g =B

1: (p,lg) (e, - Sg.• ) = ~ (e - Sg),~o~years per 100 OOO born(5)

~here p, is the proportion of 18 with onset at age x; ands8,, is the expected duration of illness for a person withonset .at age x.
748. The data used by Jones arc those published byReed and Chandler [R63) for Michigan for which theprevalence was estimated by Reed and Chandler as 4.1
per 100 OOO; to obtain this figure, these authors determined the number of choreics living in the Lower
Peninsular of Michigan on April 1, 1940 and divided
this number by the total Lower Peninsular populationon that day. Jones however based his calculations on
the national 1970 life-table population which contained
more choreics per 100 OOO than reported by Reed andChandler. Weighting the age-specific prevalences from
the Michigan study according to the 1970 age-distribution yielded an overall prevalence in the 1970 lifetable population of 4.8 choreics per 100 OOO. The 1970
life-table population numbered 7 085 472 persons, andthe total number of choreics in the study population
was 338.
749. In the Reed and Chandler study, the average
duration of illness was essentially the same for both
sexes: 15.85 years. Using equation (4), the number ofmen and women per 50 OOO born who became choreic
at some time in their lives can be estimated as
169/15.85 = 10.7 persons; for both sexes together, thelifetime incidence is 21.3 persons per 100 OOO. Examination of the age distribution at onset revealed that the
average life expectancy at onset was 36.1 years formales and 41.2 years for females. Using equation (5)YLLHD = lg (e - sg) = I 0.7 (36.1 - I 5.85) == 216.7 years
for every 50 OOO males and 10.7 (41.2 - 15.85) = 271.2
years for every 50 OOO female births. For both sexes
together, a little less than 5 years of life are lost due to
1-1 D for every 1000 persons born.
750. A comparison of the above figure with thatobtained for Down's syndrome will reveal that theeffect is about an order of magnitude higher for thelatter when the criterion of life loss is used. In otherwords, the amount of genetic detriment associated with
Down's syndrome is much higher than that with
Huntington's disease, partly owing to the seven times
higher incidence of Down's syndrome. It bears reiterating that the detriment measured here pertains to life
loss only and does not include the personal or family
hardship and the trauma associated with having a
genetic disease.
(ii)

Does a gfren kind of genetic disease lead more
frequently to early mortality? The results of the
British Columbia study

751. Thus far, the most extensive and perhaps themost illuminating studies, from the standpoint of theassessment of the relative impacts of different classes of
spontaneously-occurring genetic diseases, are those by
516

Trimble and Smith [T2] and by Newcombe [N5). Boththese represent an extension of the earlier work by
Trimble and Doughty [TI] on the incidence of genetic
disease in the Canadian province of British Columbia
with a current population of over two million people.
Using automated record linkage, ill-health records ofvarious kinds have been linked to the records of allbirths (approximately 800 OOO). Trimble and Smithestimate that nearly 90% of all potentially linkable pairsof ill-health and birth records were successfully brought
together and linked. The specific examples, to be
discussed below, were obtained using the healthhistories of 835 774 children who were born in theprovince between 1946 and 1970, including the histories
for 370 children with known single-gene dominantdisorders, 559 with identified recessive diseases. 928
with chromosomal diseases (of which 43 were with sexchromosomal diseases and the remainder with
autosomal disorders, primarily Down's syndrome) and
14 460 with irregularly inherited congenital malformations.
752. One of the questions asked was whether a given
kind of disease leads more frequently to early mortality.
As Table 45 shows, within the first year of life, approximately 2.5% of all liveborn children die from one cause
or another: this value is about 4 times higher forchildren with dominant or recessive diseases and about
5 times higher for children born with irregularly
inherited conditions: the overall risk of childhood
death drops after the first year of life to about 2 per1000 livebirths in the second year of life, 1 per 1000 in
the third and to nearly half this figure for the fourthand fifth years; for children with genetic diseases, while
the absolute risk of mortality decreases, the relative
risks do not; children with dominant disorders appear
to have as great, if not greater, relative risk of death in
the second through fifth years of life compared to thesame risk for infant mortality: for surviving children
with recessive diseases, there is an almost 20-foldincreased risk of death in the second year and thisrelative risk becomes greater during the third to fifth
years of life: ·children with congenital malformations,however, appear to have a fairly constant, 4- to 6-foldhigher risk of dying at all ages up to five years, whencompared to all livebirths: and by ages 4 and 5.
children with single-gene disorders, especially thosewith recessive diseases, appear to have even greater
absolute risks of dying compared to children born withirregularly inherited disorders.
753. Figure III (taken from the paper of Newcombe[N5]) compares the age-specific cumulative mortality
among cases in different categories of genetic diseases
over the first nineteen years of life; mortality isexpressed as a factor by which it exceeds the expected
numbers of deaths based on all births in the same years.
It can be readily seen, with this criterion, that recessive
diseases are associated with the highest severity; thatdiseases classified under the headings "multifactorial","environmentally caused" and "unknown aetiology"
are associated with the least severity; and that theremaining classes fall in between.
754. As Newcombe [N5] cautions, these different
degrees of severity apply, however, only to the casesthat actually got into the different registries and areclearly not applicable to those manifestations that were
too mild to be registered as handicapping conditions.
Thus for instance, whereas the registration of Down's
syndrome in the British Columbia registries can beconsidered complete, the same is not true of other

40

,o

5
YEARS

OF

19

LI FE

Legend: REG: recessive diseases; AC:autosomal chromosome disorders;
DOM: dominant; SC: sex-chromosomal
diseases; CM: congenital malformations; SL: sex-linked gene disorders;
MULT: multifactorial disorders excluding
congenital malformations; ENV: environmental; UNKN: unknown aetiology

Figure Ill. Age-specific cumulatlve mortality among cases of chromosomal
and non-chromosomal disorders andother handicapping conditions [NS]chromosomal anomalies. Newcombe has estimated thatabout two-thirds of the total cases of chromosomal
anomalies are not registered in the above registries. The
exclusions, however, are of the less severe traits. In
assessing the public health impact of these diseases, one
should clearly not take data on degrees of severity asderived from cases that have attracted special attention
and then assume that these severities are typical of thetotal number of cases as derived from the surveys thathave aimed at complete ascertainment.
755. While mortality is a useful measure of severity
and data on this are more readily obtainable, one
should not over-emphasize its importance. For
instance, for chromosomal diseases, mortality per se isperhaps one of the least useful indicators of severity
and this would be particularly true of Down's
syndrome which may result in prolonged stays in institutions from an early age. In such circumstances theburden to society is perhaps inversely related tomortality. The same is true of several single genediseases which have a late onset in life and of sexchromosomal anomalies which tend to be mild and to
escape notice until after puberty.
(iii)

Overall estimates of lost life and impaired life for
spontaneously-arising genetic diseases

756. Recently, Carter [C51, C69] has provided somerough estimates (Tables 46-49) of the average disability
caused and the average length of life lost by the morecommon genetically determined diseases in adeveloped country. Carter did not give similar
estimates for irregularly-inherited diseases, but theCommittee has made some crude estimates for these
diseases (see Table 50) taking into account the list of
Trimble and Doughty [Tl], but wishes to caution that
there may be considerable errors in these estimates. In
considering the information presented for single-gene
dominants, X-linked recessives and autosomal recessives (Tables 46-49), the following points made byCarter are worthy of note.

757. The estimates of birth frequency (equivalent to
the life-time incidence figures used by Jones [J13, J14])
given in the above tables are mostly those given inreview articles by Carter [C49, C50]. They are derived
from the prevalence estimates by multiplying the latterby the average duration of life in the population(assumed to be 70 years) divided by the average
duration of clinical illness. The birth frequency
estimates are underestimates, since these do not include
those who die from other causes before the disease
becomes clinically manifest. However, in developed
countries, this will usually be a small proportion of thewhole, and in them, the genetic disorder cannot be said
to have caused lost years of life. Three chronic
dominant neurological disorders have been added tothose quoted in Carter [C50]. Estimates of theirprevalence are variable [S129] but they are notuncommon disorders in neurological practice.
758. The estimates of age of onset, duration of clinicalillness and age at death are reasonably well established,though in debilitating disorders, where intercurrent
infection is the usual final cause of death, modern
antibiotics are substantially prolonging life. The
estimates of average degrees of disability are inevitably
somewhat arbitrary and subjective. The rough guide has
been limitation of working capacity in adult life
and/or, in childhood, educability. The life-longdisability of congenital blindness is somewhat different
from a slowly progressive disorder such as dominantcerebellar ataxia, which at first causes little disability
but, towards the end, is totally incapacitating; or fromneurofibromatosis, which causes little disability in somepatients but severe disability in others. While all
estimates are approximate, they are perhaps useful forcomparison with similar estimates for radiationinduced neoplasms.
759. An examination of the summary Table 50 will
reveal that, ·depending on the index of detriment used,
the ranking of severities varies (columns 4 and 5 inTable 50). Thus in terms of years of impaired life, therank order is: chromosomal diseases > X-linked
diseases > recessive diseases > dominants > irregularly inherited. If years of life lost is taken as the index
of detriment, then the rank order becomes: recessive
diseases > irregularly inherited diseases > X-linked
diseases > chromosomal diseases > dominants. The
ranking for the degree of impairment is: recessive
diseases > chromosomal diseases > X-linked diseases> dominant diseases. Finally, for impaired life
weighted for degree of impairment the rank order is:recessive diseases > chromosomal diseases > X-linked
diseases > dominants. The finding that dominantdiseases as a whole rank lower than others is not
unexpected; nearly one-half of all dominant diseases
included in the calculations have a late onset (giving
unimpaired life durations of 30 years or more) whereasa sizeable proportion of diseases belonging to the othercategories have an onset in childhood.
760. The last two columns in Table 50 provide somerough idea of the social impact in terms of impaired orlost life per 106 births. As can be seen, the rankings are
now different. On the whole, spontaneously-arising
genetic diseases account for about 2 300 OOO years of
impaired life per J06 births and about 3 OOO OOO years oflife loss per 106 births (the assumed average life expectancy at birth for the general population is 70 years or
70 106 per 106 births).
517

(iv)

Utilization of hospital services as an index ofgenetic detriment761. A number of investigators have used utilizationof hospital services as a rough measure of the degree ofthe detriment associated with genetic diseases (e.g., [C5,D17, H2, P32, S85)). In these studies, medical charts ofthe patients were examined for given periods, thepatients subdivided into different categories and dataon the number of admissions, length of hospitalization(and in some cases, costs), etc., were collated. Since thediagnostic criteria varied in the different studies,precise comparisons are not possible. The study of Hallet al. [H2] is illustrative of the principal aspects and will
be discussed below.
762. This study pertains to cases admitted to theChildren's Orthopaedic Hospital and Medical Centre(COHMC) in Seattle area. 4115 medical charts were
examined and the patients were assigned to one of fivecategories which were:(a) Clearly genetic disorders:(b) Multifactorial/polygenic conditions;(c) Development anomalies:(d) Familial disorders;(e) Non-genetic disorders.
Each patient was assigned to only one category,irrespective of the number of admissions. The results of
the analyses showed that:(i) Of all admissions. 4.5% had clearly genetic
disorders (0.6% chromosomal, 1.2% autosomal
dominant, 2.2% autosomal recessive, 0.5% Xlinked recessives), 22.1 % had multifactorial/
polygenic conditions, 13.6% developmental
anomalies, 13.2% familial disorders and 46.6%
non-genetic disorders;(ii) Patients with clearly genetic disorders (category a)
had an average of 5.3 admissions as compared to
1.3 for patients with non-genetic conditions;(iii) Of "genetic" patients (category a), 12.8% had morethan 20 admissions as compared to only 1.2% for
all patients studied;(iv) The length of hospitalization for "genetic" patientswas 3.4 days as compared to 2.5 days for nongenetic patients;(v) In terms of general costs, the "genetic" patients(and their families) incurred more expenses thanothers.
763. The frequency of genetic diseases among hospital
admissions in the above study is compared with similar
data from some other studies in Tables 51 and 52. It canbe seen that the results are roughly similar, except forsome of the entries in the last row. Penchaszadeh (P32]
points out that this difference is due to several factors
among which the most important is the persistentburden of environmental infectious and nutritional
diseases in the paediatric age population in Venezuela.
764. In the British Columbia study of Trimble andSmith [T2] mentioned earlier, data on the utilization of
hospital services by individuals with different genetic
conditions were also collected. These are summarizedin Tables 53 and 54. Excluded from the Tables are
hospitalizations due to common childhood disorders
such as respiratory and infective diseases. It can be seen
that: for 1000 livebirths, there are some 200 hospital
admissions in the first year of life, dropping to about
one-third of this figure by the second year and to about
one-lifth during the fifth year of life; that children withdominant or recessive diseases or congenital malformations are, on the average, admitted to hospitals 5-7
518

times more often up to age 1, with the relative risk
gradually increasing with age, except for those withcongenital malformations; that with respect to hospital
stays, considering all livebirths, there are over 200 daysof hospitalization per 100 children during the first yearof life and this figure decreases to about one-fifth byage 5; that children with dominant diseases account for
9-13 times as much in-patient hospital usage per capita
during the first year of life and this value increases
drastically for those who survive this period; that forchildren with recessive disorders, the amount of
hospital usage per affected child is 12-24 times greaterthan for all livebirths, and these children have average
lengths of stay per admission per affected child of
13-19 days during the first year of life; and thatchildren with congenital malformations spend consistently slightly less time, on average, in hospital thanthose with either dominant or recessive diseases. butthey have a 7-11 times greater use of in-patient services
per capita than normal children. It is worth pointing
out that these figures are qualitatively similar to those
discussed in paragraph 762.

(d)

Genetic detriment for radiation-induced genetic
diseases765. In principle, it is possible to use one or more of
the indices discussed in the preceding paragraphs tocompute the amount of detriment that is likely to result
from the estimated induction of genetic diseases byradiation. It hardly needs to be stressed however thatsuch an attempt is beset with considerable uncertainties, as will be outlined below.
766. Firstly, for those diseases for which a proportionality between spontaneous and induction rates was
assumed (i.e .. single-gene dominants, X-linked diseases
and a small proportion of diseases of complex
aetiology), it is necessary to make the additional
assumption that the spectrum of detriment for"induced" diseases will be similar to that for
spontaneous ones. For instance, for dominant diseases,
the numerical estimates of risk given in Tables 43 and44 subsume diseases with early as well as late onset.
Whereas for spontaneously-arising diseases one has
sufficient knowledge of the degrees of severity, thiscannot be said to be true for ''induced" ones. The
reason for this is that the quantitative estimates of risks
from the induction of mutations having dominant
effects are based on rates of induction estimated fromanimal experiments and consequently are subject to thelimitations inherent in the extrapolation procedure
employed.
767. Secondly,
spontaneously-arising
autosomal
recessive diseases are associated with a considerable
degree of detriment (see Table 50). Our risk estimatesfor radiation exposure however, do not include
recessive diseases per se, since their incidence is notexpected to increase appreciably in the foreseeable
future as a result of radiation exposure.
768. Thirdly, the major component of spontaneouslyarising chromosomal diseases is constituted bynumerical anomalies. However, as discussed earlier, it
has not been possible to provide an estimate for theradiation-induction of numerical anomalies and therisk has been assumed to stem primarily from theunbalanced products of induced balanced reciprocaltranslocations.

769. Finally, for the class of diseases which is numerically most frequent among spontaneously-arisingdiseases, namely, the irregularly-inherited ones, it isdifficult to make the kind of estimates (in terms of
impaired life, life loss, etc.. ) which Carter has made forother classes. The figures for those given in columns
3-7 of Table 50 are no more than crude guesses andmay be associated with considerable errors. This
limitation doubtless applies also to estimates of
detriment associated with radiation-induced irregularly-inherited diseases.

progeny per million births per 10-2 Gy who will sufferfrom the effects of induced mutations having dominant
effects. The data on the induction of dominant skeletal
mutations in mice were used to make this estimate. For
structural aberrations of chromosomes-predominantly
reciprocal translocations-the risk was estimated to lie
between 2 and 10 per million livebirths per 10-2 Gyunder similar radiation conditions. The cytogenetic
data on radiation-induction of reciprocal translocations
in marmoset and human males were used for thispurpose.

770. In spite of these problems and difliculties, theCommittee considers it worthwhile to attempt someestimates of detriment for radiation-induced genetic
diseases, if only to illustrate a possible method and to
gain some rough idea of the impact of these relative tothat for spontaneously-arising ones. Such estimates are
given in Table 55. It is worth reiterating that thenumerical values are only approximate and must be
viewed in the light of the number of reservations
mentioned earlier.

775. The risk for irradiation of human females, bothfrom the induction of mutations having dominant
effects and from the induction of reciprocal translocations was considered low, but no quantitative estimates
were given.

771. It may be noted that the numerical figures given
in column 2 of Table 55 (induced cases per 106 births)
are those from Table 44, but the dominant and Xlinked categories are shown separately. Furthermore,
following Childs [C68], the first generation incidence
for dominant and X-linked diseases is assumed to be
14% and 25%, respectively, of the equilibriumincidence. For chromosomal and irregularly inherited
diseases, the figures given in column 2 are the same as
those given in Table 44. For impaired life and life loss,
the figures used are the same as those given in Table 50,
except that for chromosomal diseases. the figures given
in Table 49 for autosomal structural aneuploidy are
employed.

777. The risk estimate arrived at using the doublingdose method was that, under conditions of continuousradiation exposure to low-LET, low dose rate irradiation at a rate of 10-2 Gy/generation, the additional
number of cases of genetic disease will be about 63 per
million births in the first generation and about threetimes this frequency at equilibrium (over and above the105 200 per million births occurring spontaneously).
The doubling dose assumed was 1 Gy.

772. The general conclusions to be drawn from Table
55 can be stated as follows: if a population is exposed
to low dose rate, low-LET irradiation at a rate of 1 Gy
per generation, the expected increment in genetic
disease is of the order of about 2000 cases per 1Q6 births
in the first generation; this frequency is about oneseventh of that at equilibrium. These diseases are likely
to cause about 50 OOO years of impaired life per 106
births and an equal amount of life loss per 106 births in
the first generation. At equilibrium, the figures areabout 6 to 7 times higher. A comparison of these figureswith the magnitude of detriment associated withspontaneously-arising genetic diseases (Table 50) willshow that the former are relatively small for the statedradiation conditions. The Committee wishes to stressagain that these figures (Tables 50 and 55) are crude,
but may be useful in the comparison of detrimentassociated with spontaneously-arising and radiationinduced cancers.

E.

SUMMARY AND CONCLUSIONS

773. In its 1977 report, the Committee made use ofboth the "direct" and "doubling dose" methods toobtain quantitative estimates of genetic radiation
hazards in humans. The main conclusions were thefollowing.
774. Using the direct method. the Committee
estimated that following low-LET, low dose rate irradiation of males, there will be about 20 cases of affected

776. The risk from the induction of sex-chromosome
losses in either sex was also considered low, for theradiation conditions applicable to humans.

778. Since the publication of the 1977 report, newdata have become available. Among these are thosewhich confirm and further document the Committee's
earlier conclusions: those that help to shed light on thevalidity of the assumptions and tentative conclusions(arrived at on the basis of limited data) or controversial
view-points; those that are relevant in a qualitative
sense, but which as yet cannot be used in quantitativerisk assessments; and those that are of relevance forquantitative risk assessments. These have been briefly
reviewed in this chapter. The new data pertain to the
induction of dominant cataract mutations in mice andto the induction of reciprocal translocations in therhesus monkey. Use was made of these data (inaddition to those that were used in the UNSCEAR 1977
report) in quantitative hazard evaluations.
779. New publications on quantitative estimation ofgenetic hazards in humans (those of individual authorsand of scientific bodies) have appeared since the
UNSCEAR 1977 report. Brief summaries of the main
conclusions reached in these are given, in addition tosome detailed discussions on the similarities and differences between the conclusions reached by the
UNSCEAR in 1977, an ICRP Task Group and the
BEIR Committee in its 1980 report. It is pointed outthat the conclusions reached by all three scientificbodies are similar and where differences exist, theystem from the different assumptions used (the basic
data for all three are the same).
780. The Committee's current estimates of genetic
hazards have also been made using the direct anddoubling dose methods. With the former method, therisk from the induction of mutations having dominant
effects in the progeny has now been estimated to lie in
the range of 1OOO - 2000 cases of affected individuals
per million born per Gy of low-LET, low dose rate519

irradiation of males. For the irradiation of females, therough estimate of risk under similar conditions is 0-900
cases per million births. The lower limit of this estimate
assumes that the mutational sensitivity of the humanimmature oocytes will be similar to that of mouse
immature oocytes whereas the upper estimate assumes
that the human oocyte will respond in a manner similar
to that of maturing mouse oocytes under conditions ofchronic low-LET irradiation.
781. The risk from the induction of reciprocal translocations has now been estimated to lie in the region of
about 30 to 1000 cases of affected individuals per
million births per Gy of low-LET, low dose rate irradiation of males: for irradiation of females, the very
indirectly estimated risks are lower (range of 0-300
cases of affected individuals per ]06 births).
782. As in the 1977 report, the Committee has used adoubling dose of 1 Gy to estimate risks using the
doubling dose method (the argument that the doublingdose is likely to be higher than 1 Gy was considered,but it was decided to keep the figure of 1 Gy for thisAnnex until more data on this aspect accumulates). The
quantitative estimates of risk arrived at in this Annex
are slightly different from those arrived at in the 1977
report. It is now estimated that under conditions ofcontinuous irradiation at a rate of one Gy per
generation (low-LET, low dose rate), the expected total
increment in the frequency of genetic diseases is about
2000 cases per million births in the first generation(instead an estimated 6300 cases per million) and about
15 OOO cases of affected individuals per million births atequilibrium (instead of 18 OOO cases per million). The
reasoning for this change has been: recent calculations
indicate that for dominant and X-linked diseases, thefirst generation increment is 15% of that at equilibrium(thus lowering the number of cases from 2000 per
million to 1000 per million); the conclusion of theCommittee (arrived at on the basis of all available
evidence) that the assumption of a doubling dose of 1
Gy for all chromosomal disorders (most of which are
numerical anomalies of chromosomes) rests on particularly uncertain grounds; the Committee's current
assessments relate only to the structural component ofchromosomal disorders; the risk from the induction ofnumerical anomalies is considered to be very small.
783. In this Annex, the Committee has reviewed datathat bear on severity or detriment associated withgenetic diseases and has also made a first attempt togive some crude estimates of genetic detriment basedon a number of assumptions, for spontaneously-arisingand radiation-induced genetic diseases. Under theassumption that the average life expectancy at birth is
70 years (and thus, for a million liveborn, 70 J06 years),
it has been estimated that overall, spontaneouslyarising genetic diseases cause about 2 300 OOO years of
impaired life per million livebirths and about 3 OOO OOO
years of life loss per million livebirths. For a population
exposed to low-LET low dose rate irradiation at a rateof one Gy per generation, the additional cases ofgenetic disease induced, would cause about 50 OOO
years of impaired life per million livebirths and an
approximately equal amount of life loss per million
livebirths in the first generation following the radiation
exposure. At equilibrium, the comparable figures are,340 OOO years of impaired life per million livebirths andabout 286 OOO years of life loss per million livebirths.
The Committee wishes to reiterate that these estimatesare very crude ones, but are illustrative of at least one
method to estimate genetic detriment.
520

VIII.

SUGGESTIONS FOR FUTURE
RESEARCH

784. In this Annex, the progress that has been made in
mammalian and human genetics, cytogcnetics, somatic
cell genetics and in other areas pertinent to the evaluation of genetic radiation hazards in man has beenreviewed, and revised estimates of genetic risks havebeen presented. The Committee feels that, in order toincrease our precision in risk assessment. more research
effort along the following lines will be useful (the orderin which these are listed do not renect the order ofimportance).

(a)

Human studies

Continuation of surveys on hereditary diseases inhuman populations and correlation of clinical data andchromosomal defects: studies on the contribution of
mutations to irregularly-inherited disorders; continuation of studies on genetic disorders such as ataxia
telangiectasia in which the cells derived from patients
suffering from the disorders show enhanced sensitivity
to damage induced by radiation and by other mutagens,using all possible approaches and comparisons.

(b)Studies with mammals and other higher eukaryotes

Continuation of studies on the nature of radiationinduced dominant and recessive mutations at defined
gene loci; studies on the induction of mutations in germ
cells and somatic cells at low doses and low dose rates;
studies on factors modifying radiation-induced genetic
damage and on mutational assay systems in somatic
cells; studies on the possible influence of genetic
background on the induced frequency of dominant
mutations in higher eukaryotes.

(c)Studies at the chromosomal level

Studies on the induction of reciprocal translocations(including primates and human testis material whenpossible) using cytogenetic techniques. especially at low
dose rates and low doses of radiation: studies on the
induction of structural aberrations in mammalianoocytes; studies on factors innuencing the induction
and recovery of chromosome aberrations in germ cells
and somatic cells in suitable mammalian systems.

(d)Biochemical studies using suitable prokaryotic andeukaryotic systems

On: the relationships between DNA damage. its repair
and the origin of mutations and chromosome aberrations; mechanisms of constitutive and induced DNA
repair by physical and chemical agents and theirrelevance for rnutagenesis; mechanisms of regulation of
DNA repair and of genetic recombination (possible
role of hormones and growth factors) and their role indifferentiation and carcinogenesis; DNA repair during
gametogenesis; relationship of DNA lesions to changes
in DNA sequences.

(e)

Research 011 biological dosimeters to monitor
radiation exposures

New approaches on the use of chromosomes as
biological dosimeters; development of biochemical andimmunological techniques for monitoring changes in
DNA sequences and their application to estimate
cumulative doses arising from exposure to physical andchemical agents.

T a b 1 e

Recurrence risks of common malformations!L2. C6, WJ~
Preva 1ence at birth (%)
Type of malformation

Anencephaly, spina bifida
Malformations of heart and great vessels(same type in index patients andrelatives}
Cleft lip(!:. cleft palate)
Infantile hypertrophic pyloric stenosis
Male index patients
Female index patients'Hon-postural' talipes equinovarus
Dislocation of hip(s} in patientsnot screened at birthMale index patients
Female index patients

In sibs ofindex patientsln offspring ofindex patients

5

4
2-4

2-3
accordingto typeaccordingto type

4

3

5
7

13

4

3

6
2

5
2

521

Ta b 1 e

V,

N
N

2

Incidence of chromosomal abnormalities in newborn infants

I01. ll20, HJ, Ll, M53, Oi, W2]

Autosomal anomalies

Sex-chromosome anomalies

f

+-'
C:

Males

..,
(1J

~

Females

Numerical (trisomics)

Number of infants

>

~

V,

Male

Female

Total

al
1

493
1066
3 7176
4 5761
5 784962072
7 13751
8 21849 1303
10 13932

47, 47, 0th. 45,
XYY XXVX

930~/ 2437
41015 2081
6763 13939
45387 11148
33831 11680 10
1921
3993
4
13751
11
2182 4353h/ 31197 2500:,:. 1233 2626
2

Total
43048 23966 67014

•D

•E

+G

0th.

10
66
93
78
29
84
22
19
18

0.54
0.48
0.47
0.83
C.67
C. 73
C.61
0.51
0.76;1
0. 69,:.

424

0.63

5

1
1
6
6
9

2
9
5

5

I

37

3
1
2

5 2
7 3
sf/ 2
J,:..

9 12
4
1 6
2

43 42

47, 0th.
XXX£_/

FreStructural (aneuploid)- - - - - - - - - - - - - Tota 1 quency
Robert- Rcci(%)
sonian procal Inver- Robert- Reci- Dele- Super~~- T andsions sonian pro- tions numer- 0th.
cal T
ary
DID DIG inserb/
tionalStructural (cuploid)

l

-

3
3
2

24

10

3

8

2
14
16
17
3
19
3
4
3
81

1
12
15
6
3
5
2
2

3

1
2
4

11
15
10

4

3
1
1
2

12
3
3

48

14

60

5

.at

1
1
2
2
4

12

I

6 d/
2

2

5

6 e/
1
2

3

-

3

5

14

6

~

158 (0.24 %)

95 (0.14 %)

134 (0.2 %)37 (0.06 %)a/ Survey centres: I: llamilton, Canada; 2: London, Canada: 3: Winnipeg, Canada; 4: Arhus, Denmark: 5:Edinburgh I, United Kingdom; 6: Edinburgh II,
United Kingdom; 7: Boston, United States; 8: New Haven, United States; 9: Moscow, USSR; 10: Kanagawa, Japan.
b/ Most of these are mosaics.
cl Included 1 twin-pair and 1 triplet.
di Unbalanced Y-autosome translocation.
e/ Supernumerary small metacentric chromosomes including two mosaics.
T/ Also had inversion.
gl One Y-autosome trans 1oca t ion.
hi These 2500 infants are a random sample of 10237 infants born during the study period (1969-1972) and included 15 twin-pairs, 29 newborn
infants with various congenital malformations, 5 stillborn and 13 delivered prematurely [81].
i/ The authors observed 7 infants with a pericentric inversion of chromosome 9 and 1 with a pericentric inversion of the Y, but for somereason, did not include these in their tabulations.
l.'OTE:

Data on heritable fragile eites are not inaluded in this Table.

T a b 1 e

3

A comparison of the fre_ciuencies of chromosome abnormalities
in newborn aiidrn 7-and 8-jear old children(based on Table 2 and reference [Pt;)
Newborn surveys

7 and 8-year old

N = 67014

N = 4342

0.24 % (158) b/
0.14 % (95) c/
0.20 % (134) -0.23 '1. (10)0.04 % (2) d/
0.21 % (9) -Type
Sex-chromosomal abnormalities a/
Auto soma 1 tri somi cs
Autosoma 1 s true tura 1 rearrangementsa/Includes sex-chromosomal aneuploids, mosaics, deletions, inversions,etc.
Number of chromosome anomalies given in parenthesis.
81 out of 95 were+ G (trisomy-21).
Both the autosomal trisomics were + G (trisomy-21).

b/

c/

a/

T a b 1 e
Non-disjunctional

4,n of the extra chromosome in autosomal trisomies
stu 1es 1n srontaneous a ort1ons

Orl

J15]

There were 49 infor.natiVP. ccses in 124 caoes e:i:amined.

Male
I

Male

11

Female Female
I
II

13

14

15

+
+

Total

Chromosome

Origin

+
+
+

3

2

+

5

21

22

2

2

1

2
0

11

]

8 %

4

2

12
1
1

3

3

33
92 %
2
10 ]

4

17

8

14

49

+
+

16

1

523

T a b 1e

5

Mutation rate estimates for balanced structural rearran ements
6

Reciprocaltranslocations

Robertsonian translocations
Population

NumberNumberexamined abnormal

Spontaneousabortions
5726
16
113
Live births
59452
Percentage:
Spontaneous abort ionsLive births
Gametic mutations rate:
Spontaneous abortions
Live births
All recognized conceptions

Total

Inversions

DIG

OIO

de
novo

Familial
Pat, Mat.

0
2

1 3
12 15

de
novo

0
12

Familial
Pat. Mat.

0
2

0
6

0
3

0.070
0.069

0.017
0.018

0
-4
0.24 10_4
0.20 100.16 10· 40.16 10·4

?

de
novo

Familial
Pat. Mat.

1
0

4
13

1 4
16 14

?

T a b l edeFamilial
novo Pat. Mat.
0
9

0
1

1
3

?

0
4

de
nova

Familia 1
Pat. Mat.

4
18

3 7
37 36

0.157
0.087

0.035
0.015

0.279
0.190

-4
3.49 10_4
1.31 10_4
1.63 10

40.09 10"0.09 10·4-43.99 10.4
1.88 10_4
2.20 106

Mutation rate estimates for unbalanced Robertsonian translocationsl

DID

Population

NumberNumberexamined abnormal

Spontaneousabortions5726
46
4
live births
59452
Percentage:
Spontaneous abortions
Live births
Gametic mutation rate:
Spontaneous abortions
Live births
All recognized conceptionsa/Includes two sibs.

de
novo

15
1

Familial
Pat. Mat.

1

DIG

?

1 11-~-I 6
1
0 1

de
Familial
novo Pat. Mat.
4
0

0
0

Total

GIG

42-I
0

de
nova

2
0

Familial
Pat. Mat.
0
0

0
0

de
nova

2
0

20
2

Familial
Pat. Mat.
1
0

15 10
0 1

0.576
0.005

0.175
0

0.052
0.002

0.803
0.007

-4
16.00 10_4
0.13 10.4
2.51 104.37 10· 4
00.66 10" 4-42.60 10_4
0.10 10_4
0.48 1022.32 10·4
0.23 10·4
3.54 10·42
22

Tahle7

Mutation rate estimates for unbalanced structural rearran ements

Population

NumberNumberexamined abnormal

Spontaneousabortions5726
42
Live births
59452
18
Percentage:
Spontaneous abortions
Live births
Gametic mutation rate:
Spontaneous abortions
Live births
All recognized conceptionsa/Stable structurally
Rings
abnormalchromosomes
FamilialdeFamilialdenova Pat. Mat,nova Pat. Mat.
15
3

~/ 6
1 I

1
0

10
2

0
0

0
0

non-Robertsonian types

Supernumerary

1

de
nova

2
0

0
2

Total

Familial
Pat. Mat.
0
I

0
5

de
nova

0
3

16
5

Familial
Pat. Mat.
8
2

6
6

0.681
0.012

0.052
0

0
0.018

0.733
0.030

-4
17.60 10_4
0.36 10_4
2 .95 10

2 ,6 10- 4
00.39 10- 40-40.23 10_4
0.20 10-4
19.53 10_4
0.58 10_4
3.42 1012
5Includes three sibs.

Table

8

Radiation and Down's s ndrome: e idemiolo ical studies
S6,
Country
Canada----UGl

1968
Denmark

Study type

RetrospectiveJapan---r962

Prospective

United Ki n~dom
Scotland, 1959

Retrospective

N. I re 1and, 1962
England, 1970
England, 1972

United States

Outcome

Ref.

Retrospective 81 DSM a/ Significant increase in D~/ [U4]incidence in exposed mothers(abdominal exposures or
fl uoroscopy)
Significant increase in DS
861 M
Prospective[US]in exposed mothers-moEngl and, 1961

Cases

?

No significant radiation
effect.

[VJ]

15034 M£1 Frequency of DS in the progeny '.SIB]
of exposed mothers was lessthan half of the controls;
not significant;117 Dsr.':!/ flo significant radiation[LG]effect.
Non-significant increase of [C9;Retrospective 51 OS'4
OS in controls.
No significant radiation(Sl7;
Retrospective 197 DSM
effect.
~o significant radiation
630 M
Prospective[S20]
effect.
Siqnificant increase in DS[AS]
Retrospective 465 OSP
in exposed mothers who hadreceived radiation 10 years
or more before the conceptionof the cases.

1965

Retrospective 216 D5P

1969

Retrospective 61 DSM

1977 e/Retrospective

128 DSP

Siqnificant increase in OS
in exposed mothers.
Ila significant radiation
effect.
No significant radiation
effect.

(S19]
[M14;
[C8j

a/ DSM: mothers of llown' s syndrome cases.
DS: Down's syndrome.
cl M: Mothers.
o/ DSP: Parents of Down's syndrome cases.
~/ A follow-up of the 1965 survey above [Sl9].
o/525

Table9Specific chromosomal defects in some cancers( from [1120, R12) and other sources)
DisorderMain chromosomal
anomalies

Comments and reference

Chronic mye 1oi cll eukacmia

Ph 1-chromosome:t(9;22)(q34;qll)i ( l 7q)t(l4q-;14q+)

Present in over 90 % of patientsin chronic phasein blast phase 1 Rl2, D9]'M32, l/25 J

Chronic lymphocyti c
1eukaemi aAcute non-lymphatic
leukaemia+8; -7; t(Bq-; 2lq+); Anomalies in 50 % of the cases;t(15q+;l7q-);[091
t(9q+;22q-)[P35)

Durkitt lymphoma a/- African type -t(8q-;14q+)

Lymphoma usually associated with
Epstein-Barr-virus (EBV) [24, 212]
rlot usually associated with EBV'1t61 J
(RIB)
[020, P35, 020]

- American typet(Bq-;14q+)
Uon-Burkitt lymphoma 14q+
Hodgkin's lymphoma !I 14q+6q-; +8;
lymphob las tic
leukaemiat( 4; 11 )(q13;q22)
14q+lymphocytic
lymphoma !I
Hultiple myeloma
14q+
Plasma cell leukaemia 14q+
Meningiomas-22; -8; -9; -X; -YLong
submetacentric
Semi nomas !I
marker chromosome
Aniridia-1:i lms'del{llplJ)
tumour - gonadoblastoma association
Retinoblastomadel(13ql4)
Chronic lymphocytict( 14q-; 14q+)
leukaemia in ataxia
telangiectasia'.RIB)
1 \Jl4)f1H4)lt131, M30, 25, 26][M28]'.F26, F27, R66]
'.VJ]
rm2 J

!I Based on 1-2 cases only.
T a b 1 e

Cross-

Cells

UV

AAF

Ionizing
radiation

1inkers

XP

SS

SS

N

N

XP variant

,N

II

H

II

AT

N

u

SS

L5

N

BS

[~

[~

Cockayne' s
syndrome

SS

[~

EMS

MtJliG

ilQO

References

N

N

H

s

N

il

[C25, ll4,
M34, T12][Al2, C25,
ll4, f.135)(HJJ, llJ,
ll4, PJB,T]][FB, F9,ll4, 5104 J[A28, Gl9,
Kl3]
;A28, 545,
W!S, H37)[ S or U [ S or ll
ii

FA

10

N

tl

SS

[~

Ii

Ii

s

"

N

rS
'N

s
s

111

AAF:
acetylaminofluorene
MMS:
methylmethane sulphonate
EMS:
ethylmethane sulphonate
Cross-linkers: mitomycin C, psoralen • UV light; nitrogen mustard
tllmG:
1i-methyl-N' ni tro-ll-ni troguanid i ne
riQO:
4-nitroquinoline oxideSsensitiveSSvery sensitive!lnorma 1[~conflicting results.
E

526

Table11
disorderso muta ens

Cells

UV

XP

s

Ionizing
radiation

MF

CrossIi nkers

msllili1G

NQO

References

il

II

SS

(M36, S43]

llN

l'Y·!S

Chromosome breakage effects
AT
FA

s

11

BS

u

tl

XP

s

SS

[ NI 2, T8, T9;

SS(~[Al4, 1134,
S44j

SS

[EIS, K!3,
Kt2;

SCE-induction

AT
FA
SS
Cockayne's
syndromeS[~
N[H34, wl7,

Pts:

H

[G20}
[L!6:

less than il

s

[K13)

s

[M36, S45)

MHS;
methylmethane sulphonate
EMS:
ethylmethane sulphonate
Cross-linkers: mitomycin C, psoralen + UV light; nitrogen mustard
MNNG:
N-methyl -ll' ni tro-rl-ni troguanidi ne
NQO:
4-nitroquinoline oxideSsensitiveSSvery sensitiveN
normal[~conflicting results.

Ta b 1e

12

DMF

UDS

a/

b/

9.6

0-5

4.8
9.9

10-15
25-50
40-60
10
10-15
60-100Some

Clinical features

Group

A
B
C
D
E
F

b/

c/
~/

rieuro1ogica l

+
+

+

+

+

+

+

1.4

+

G
Varianta/

Cutaneous

+
+
+

+/1.6

3-7

Endo-sites£_/

Photo lase

0
0-5
10

36
0

10

8
49

60-70
60

d/

16

0

1

100

20

Average dose modifying factors (UV), ratios of D0 values for normal tomutant, from survival curves.
Percentage of normal cell LIDS in autoradiographs.
Loss of endonuclease sensitive sites 0-16 hours post UV-irradiation,
relative to normal cells, in per cent.
Per cent of normal.

527

Tab 1 eDama ina ents or roducts
ce s are re a1r- ro

Proficient

Deficient

Ionizing radiation
strand breaks
anoxic4-HQO (minor compound)110-carbaryl
NO-methyl guanidine
HNNG
11/IS
MNU

UV

El!S

N-7 alkylguanine
Proflavin + light
Propane sultone
Mi tomycin C~/

13dimersprotetn DNA links
strand breaks
Ionizing radiation
anoxic4-llQO/IAF damage
JCR-170
J\flatoxin
K-region epoxides
Er benzanthracene
nr2 tie benzanthracene
EMS

0-6 alkyl guanine
Psora len + 1i ght
Chlorpromazine + light
CCNU
HtW 2
Decarbomyl mitomycin C

Cells are categorized on the basis of survival, host-cell
reactivation, or chromosomal, or biochemical, or biophysicalmeasures of repair (a listing in both categories means that
there are several products of an agent or that all celllines are not the same).
For abbreviations, see Table 10.
T a b l e

14

DNA repair properties of AT fibroblast strains~P37]
LlHA-damaging
agent

Repair hallmark

Hypoxic y rays DNA repair replication
Unscheduled DHA synthesis
H. luteus endonuclease-sensitivesite removal
Single-strand break rejoining:velocity sedimentation
Oxic y rays
Thymine glycol removal:in cells
by cell extracts
Single-strand break rejoining:velocity sedimentation
alkaline elution
endonuclease S
Double-strand brlak rejoining:velocity sedimentation
unscheduled OIIA synthesis
Bleomycin
Single- and double-strand
break rejoining:velocity sedimentation
4UQO
Alkali-labile lesion removal
HtmG
illiA repair rep 1ica t ion~lMS
DIIA repair replication
Far-UV light
UV endonuclease-sensitivesite removal
Dt{A repair replication
Unschedu 1ed DUA synthesis
Post-replication repairt;-acetoxy AAF DIIA adduct remova 1
Dl,A repair replication
a/

b/

528

Strain~/exr

rt!- 1

exr +ReferencesP~/[Pl7, P18]

D
D

P

P

'.P36][Pl7, P36JPP

[Pl 7, P36]

P
P

P
P

[C62]
;R71]

P
P
P

p

[T7;

P
P

[F28]
[Sl09]

P
D

p

[L17]

il

[V6;

P

P

[F28, L44]

il,P

D

;5112;

D
P

P
P[5110;[SllOJ

P
P
P
P
P
P

P

[Pl 7, A29 j

P[5110, P17;

P'.P37, A29]

p'.Ll3;

P

[Al9J
[A29J

exr-: deficient and exr• proficient in Dr:A repair replication inducedby hypoxic gallllla rays;
exr; strains: AT!bE, AT2BE, ATJBI, ATSICTO, AT194CTO;
exr strains: AT3BE, AT4Bl, ATSB1, AT7Bl.
D: deficient; P: proficient; no entry: not tested.

Ta b l e
Fre uenc15

of aberrant cells b dose in 23 heavil
atomic om survivors oex osed

[~S~!

Dose
group
(Gy)

!lumberof cases

Mean

1.00-1. 99
I !)7 .8
2.00-2.99 258 .2
3.00-3.99 331.7
4.00-4.99 405.7
5.00+
710.7
Total
exposure 311.1!lumberof cells
analysed

Number of aberrant ce 11 s
0 (%) 2-I

G (%) 2./78 (26.4)
92 (35.8)
63 (46.0)
29 (34. I)
80 (65.6)
342 (38.2)

8
6
3
3
3

295
257
137
122

68 (23.1)
80 (31.1)
52 (39.0)
25 (29.4)
68 (55.7)23896

239 (32.7)

85

a/ 0 is ordinary stain, G is banding stain.

Ta b I e

16

Post-implantation foetal survival ciata
for different matin eriods after 1nject1on of lutonium-239
3,
Exposure level (MBq/kg)
Experiment
number
1
2

20-31
12-15
22-33
43-48
11-15
21-25
31-35
41-45

3

a/

Mating period(weeks after
injection)

IMP:
LE:

0

0.19

IMP

LE/IMP!?

727
409
926
464
626
582
505
605

0.95740.95600.96000.95470.94730.9691
0.94850. 9570

IMP

595
612
588
573

0.37

LE/111P!/

HIP LE/IMP!?

0.94120.93460.93030.9564

744
415
981
501
626
576
488
540

0.94490.93490.93780.94410.92810.91670.90780.9333

total number of uterine implants;
total number of live implants.

Ta b l e17eriodsPost-im lantation foetal
after 1rra 1at1on o continuous woe- o y externa co a - garrrna-1 rra iation(AZZ matings were Llithin the ?-35 day post-irradiation interval);Gz3;
Exposure level
Mating periodExpt.
(weeks fromnumberstart ofexperiment)

Control
IMP

LE/IMP

Dose

3.36 x 10- 2 Gy d-l

5.98 x 10- 2 Gy d-l

U:P

LE/IMP Dosea/

I:!P LE/ll\P Dose

0. 9379 0.59
0.9377 0.94
0. 9297 1.06
0.8870 1.06
0.9108 1.06
0.9027 1.06
0.8791 1.06

246
320
513
453
631
442
291

a/

2

3

28,30,32,34
14-17,24,26
10-13
10-23
9
21
32

267
274
533
402
689
579
566

0.95880.94530.95680.9527
0.94190.94820.9576

0
0
0
0
0
0
0

290
321
526
460
583
473
455

!_/

0.92680.88750.85770.83890.87370.88010.8900

I.OS

1.67
1.89
1.89
1.89
1.89
1.89

a/ Mid-line tissue absorbed dose in Gy accumulated over 5-1·1eek period prior
to mating and adjusted for radiation-free periods.

529

Ta b 1e18

Dominant lethal mutation rates, er amete er 10- 2 G ,ase upon post-1mp antat1on oeta surv va

IG23!

Mutation rate (x 10)

Radiationqua 1 ityCe 11 stage
exposed60co y rays

Pos tmei ot i c~/~~
IU.l +·U,bJ d/

Premeiotic b/

1.1 - 0.2

Postmeiotic~/,54 - 4.0

88 -Premeiotic b/,3.9 .:!:. 0.9

2.6 .:!:. 0.6,

Neutrons

239Pu
a-particles
a/
b/

r:1

al

Singleexposure

Weeklyexposure

t

~

+

-

t

54 -l 2.2 a/+

0.14 - 0.07,

0.22 -l 0.06 di
21,

-

-

2.7 :i. 0.54 d/

64 ! 11

Rates based upon total dose delivered up to 5 weeks prior tomating and adjusted for radiation-free period;
Rates based upon total dose accumulated prior to mating;Rate based upon total dose delivered over a 4-week period:
Rates based upon pooling of all data in both sets 11ithin the brace.

Dominant lethals
Postmeiotic stages
Premeiotic stages
Translocations
Fragments
Abnorma 1 sperm
Testis weight loss

530

-+

A11 stages £1

Genetic end pointb/

5 .:!:. 0.6,0.35 - 0.06

t

Table

a/

Continuous
exposure

H

Respon~e CQ~fficient(x 10 10 Gy) !I

Ratio

a

nf

Ye

a/ye

nf/yc

a/nf

64.0

54.0

5.0
0.14
0.18
2.8
0.11
380

13.0 + 3.0

11.0
19.0
38.0

1.2
El.0

10.0
6 .1

2.5
1,6

2.6
E6.~/

6.8

93.0

2.7

3600

1.1
2300

E38.0 + 5,0
33.0 + 5.0
25.o .:!:. a.o
9.5 .:!:. 4 .oFrequency per 2gamete or cell per 10 Gy, except testis weight loss
as mg per 10 Gy.
Assumes that initial portion of dose-response curve corresponds tothat seen following weekly neutron irradiation.

Ta b 1e20

Freguencies of dominant lethals LlLM ex
mouse "embryo deve opmen t 1 n v1 ro at various(4.5 Gy)[G28)

Germ ce 11
stage
irradiatedSperm

Day after
i rrad iati onof males0,t

Spermatid

7
II

14
18
21
Spermatocyte 24
28
35
Spermatogonia 49 d/

atsta es of

1mes

Fraction arrested
beforemorula stage

Frequency
of-DLM a/

Fraction arrested
before~lastocyst stage

Frequencyof DLM b/

Fraction arrested Frequency
before trophobla5t of DLM c/outgrowth stage

Experimen ta 1

Contro 1

Per cent

Experimental

Control

Per cent

Experimental

Control

Per cent

99/590214/956
142/966
148/709244/731397 /971
279/867
170/441
75/23952/29740/26433/21973/60869/47978/37729 /286
73/542l l l /576
94/58076/57483/68681/641

5

82/49140/742
127 /824
132/561
93/487210/574
155/588
57/27135/16460/24536/224

9/491
89/53583/41065/20916/25751 /469
41/46522/48683/49859/603
99/560

14
12
-6
2
14
29
19
17
6
16
2

95/4092371702
164/697
115/429
145/394
154/364
132/433
58/214
19/1297/185
23/18833/17737 /446
13/32725/23425/24135/41849/42433/46422/41551 /544
54/461

5
28
20
18
29
37
21
22
9
-6

13

0
0
26
32
22
26
21
7
3

a/

arrested at earl cleava e sta e, ex erimental) 1
Per cent of OLM = [ l - (1 - fraction·
ract1on arreste at ear y c eavage stage, con ro

X 100.

b/arrested at late morula sta e, ex erimental))
Per cent of DLM = [l - (1 - fraction- ract1on arreste a ate moru as age, contro

X 100.

cl
d/

-

-1

- fraction arrested at late blastocyst stage, exeerimental}) X 100.
- fraction arrested at late b1astocyst stage, control
Data from day 42 are not included because fewer than fifty 2-cell experimental embryos were produced.
Per cent of OLM= [1 -T a b 1e21

Fro uenc of reci rocal
gamma-1rrad1at1ona/b/induced er R ofose rates

Exposurerate(R min- 1 )Trans locations /R

0.00120.0035
0.012
0.105
1.0
100.0

-5
1.3 10_5
1.5 10_5
2.1 10_5
4.0 10_5
6.7 102.0 10-\1a/Goodnessof fitP > 0.30
P < 0.05
P > 0.30
P > 0.40
P > 0.05 ,P > o.n1£'

Presented as the linear coefficient "b" of the doseresponse curve, Y = bD, where Y is the yield and "D"
the dose.
These data were for x-irradiation and so the translocation
yield per R was multiplied by 0.8 to account for the relative biological effectiveness of gamma rays relative tox rays.

£I

This P value is not very informative, because for comparative purposes the data were fitted to a linear curve,
although it is known that there is a significant two-trackcomponent.

531

Ta b 1 e

hase-1 mouse ooc tes
ow1ng x-1 rra 1a 10n

Fre uenc of chromatid

0 R
Interval(days)

22

50 R

100 R

200 R

300 R

!lumber of
Number of
Number oftlumber of
Number ofcells D X cells D X cells D X cells D X cells D X
a/ b/
a/ b/
a/ b/
a/ b/
2_/ !>_/

1.5
500
3.5
5.5
7.5
9.5
13.5 to 14.5
17.5
21.5
24.5
28.5

l

0

150
125
160
150
125
150
166
125
100
75

0
1
1
1
2
2
2
2
2
1

1
1
1
1
1
2
2
2
0
1

225
3 2
150 2 1
170 4 4
175 5 4200 5 6265 11 11
200 9 9188 13 10
125 5 4

150
175
225
143
125
350
125
162
92

5 3
10 5
10 8
a 7
15 13
31 46
17 17
17 17
15 11

160
170
128
169
200
361
153
200
125

9
4
12 16
16 17
25 35
52 71
99 145
51 39
48 44
39 34

a/ D; deletions.

[I X; interchanges.

Ta b 1e23Frequencies of reci eroca 1 trans l oca ti ons
i nduc eel in die seermato2on1a of rhesus monKeys
tins, B3ii]

Dose
(Gy)
0
0.5
1.0
2.0
3.0

NumberofmonkeysflumberoftestesNumberof
cells
scoredTranslocations

15
6

16
10
11
9
4

1500
2750
4650
3350
1475

0
0.36
0.86
0.99
0.68

7

7
4

Tab 1 e(%)

24

A comeari son of the s lo~ of the 1i near regress ion "b"estimated for the monkey w1
those est1mated for other species
for the induction of reci rocal translocations ins ermato onia a/,B
Anima 1b lOij: + sd lOi\'.

MonkeyMouse

0.86 ± 0.04
1.92 ± 0.22
2.90 ± 0.34
2.51 % 0.20
1.53 ± 0.17
1.29 ± 0.02
1.96±0.18
1.48 ± 0.13
0.91 ± 0.10
7.44 ± 0. 95
3.40 ± 0.72

RabbitGuinea pig
Marmoset
Man
a/

532

p

Ref.

< 0.01< 0.01< 0.01<01< 0.01< 0.01

[L24]
'.E9]
[M43;
:1~20:[837]'.P25)
[L25]
[L25]
[B38)
'.838][636)o.

< 0.01> 0.05< 0.01< 0.01The linear regression coefficients were estimated for all the animals
using the data given by the different authors at doses to those giving
peak yields of translocations.

Ta b l e

25

andEmbryonic
stage

Species

Mouse

Numberstudied

1-ce 11Chinesehamster 4-8 cell
Sheep
2-8 cell
Rabbit5.5 dayPig
10 dayCow
12-16 day
1·1ouse8-11 day9-10 dayRat
11 dayrolyplaid

n+l

al
1

616
516
338
193

1-2 cell

n-1

a/

12
a/
5"

1

3

8

226
89
463
88
12
607
561
410

1
4
4

5
8

Aneuplaid

Polyplaid

(%)

(%)

6
1
3

[1:45]
[M45;
:015;
[K20;

1.9

1.2
0.9
0.5

1.5
4.1

0.9
4.5
0.9

2.2

[B43!
[L46]

:F29;

1. 7
8.0

7

3
2

Ref.

0.5
0.4

[tl64 '.
[1:65]
iF17]
[C35]
[B70]

1.0
0.2
0.7

a/ Not studied.

Ta b l e

26

Incidence of "s ontaneous" ~on-dis ·unction in oo enesis
rom severa ro ents a(arter 1 H40]l
Incidence of
Number ofoocytes ·or Number
aneuploidy
embryos hyperploid(%)(hyperploidanalysed
X 2)

ReferenceSpecies

Aneuploidy
assessed inI-louseoocytes

5853

28

0.96

pronuclei

2902

24

1.65

IM4S;

455
226
455
197

0
1
1
0

0
0.89 b/0.44
0'H39, H43]
1843]'.B72, H43]

llaanster
Chineseoocytes
4-8 cell embryos
Syrianoocytes
Dj ungari anoocytes[B7l,H41,H57,
M66,R26,R73,
R74 ,$115 ,UlO]£1~/ The data are put together, although different methods have been used(in viva/in vitro maturation, hormone induced ovulation, spontaneous
ovulation, different strains, etc.) for the different groups.
b/ One embryo affected by a monosomy was reported by the authors.
c/ Hansr.iann and Probeck, unpublished.

T a b l e

27

~1utation frequencx at 7 specific loci in offspring of male mice
1nJected with tr1t1ated water
tR31]

Cell stage exposed
to radiation
Post-spermatogonial

Spermatogonial a/

Experiment
1-1
1-2
1-3
2

~/

p_l

Injected
amount(MBq/gra ofbody weight)

Numberofoffspring

28
18
18
28
18
18

515
3327
4101

!lumberofmutations

Estimatedweightedmean dose togerm cells
(Gy)

1
4

4.30

2408
18218

6
3
13 b/

6.15

11481

7Y

A negligible portion (< 1 %) of the dose was received in post-spermatogogonial stages.
The number includes both mutants of a cluster of two in the offspring of
one male in this experiment.

533

T a b 1 e 283Distribution of H-induced mutations in mice according tolocus anCI v1ali1 lity or liomozygote[~~I]
flumber of mutations at specified locus

Result of
viabi 1ity
test

Cell stage exposed
to radiation
Post-spermatogonial

Spermatogonial

a

b

d

se

s

Total
3

ViableSublethal a/Lethal b/ Sterile-cl
Untested

1

3
3
I

Total

3

ViableSub lethal
LethalUntested

3

5

2

11

2

1
1

1

2

10
3
5
3

4

21

2
4

2

2

Total
al
Iii
cl

p

C

4

5

1
2

3

Defined here as lethal after perinatal period and before breeding age;
Lethal before birth or perinatally;llutants themselves were sterile and, therefore, could not be tested.

Table

29

Specific locus mutations after irradiationof maturing roouse oocytes[L32)

Dose (Gy)

Number ofmutants

Total
progeny

11utation rate
per_ ocus
per 10 Gy x 107

0 al
2 b/
2 Tnew data)
2 (tota 1)

2. 3 or 8
3204639
10379
8488
18867
7501
9875

2.65
3.33
6.27

4

6

7
7
26

a/
Ii'/

Reference [R38].
Reference [L31].

4

Ta b 1 e

230

Distribution of major classes of c-locus mutations induced in the mouse,R 21

Germ-ce 11 stage
irradiatedType ofradiationr,umber ofmutations

Spontaneous ~I
Spermatogonia

x or gamma

neutrons

51
15

Postgonial

x or ganrna

5

Oocytes

al
Fil
cl

534

18 E_/

neutrons
x or gamma
neutrons

3
7
9Type of mutation (%)
ViableSubvital

Lethal
a/

94 .1
66.7
60.0
40.0
33.3
57 .1
22 .2

5.9
2.0
6.7
0
0
14.3
0

0
31.4
33.3
60.0
66.7
28.6
77.8

Includes prenatal and neonatal lethals.
Control group, plus mosaic mutants from all groups.
One of these not tested for homozygous viability.

T a b 1e

31a

Gamma-ray indl:,lction of dominant cataract mutations in ma le mice2( t''o1• oompari svnR, f.hf! n1m11",ers af PPc•,•nttf1,e uiv-~ei .fi f~ lom"u nn,tati onH
1•e<...ovcred in tJze 4Utme (::rperlme>!lil ,u•e gi,,,,,i in tJte la:::t ,-olurrrn.1

Exposure(R)
0 a/
455+45"5 ~/534
600
455+455 ~/
534
600

!_/

bi

Germ-cell
stage
treatedSpermatogonia
Spermatogonia
Spermatogoni a
Post-spermatogenial stages
Post-spennatogenial stages
Post-spermatogenial stages

Number ofF
offspring!lumber ofcataract
mutants

Frequency
pergamete5(x 10 )

Rate pergameteper R
6(x 10 )

riumber of
specificlocus
mutations

8174
5231
10212
11095
272

0
6
3
3
I

114.7
29.4
27 .o
367 .6

1.26
0.55
0.45
4.04

9

14
2

1721

58.1

1.09

3

865

115.6

1.93

3

2
7

For specific locus mutations, the historical control currently stands at
6 mutations in 103 218.
Fractionated irradiation separated by a 24-h interva 1.

535

Ta b 1e31b

reatures of radiation-induced dominant cataract mutations in mice[E2tl. E2il. ~:J]

MutantProv i sional
gene
symbolMale
001 ~/

Vlrn

female]60
Female]]6female

lac
Nzc
Nuc

Expressivi ty

Fertility

constant

normalvariable

normalconstant

norma 1constant

reducedincomplete va ri ab 1e
Anterior pyramidal cataract
with corneolenticular attachment and remnants of thepupillary membrane, uni- andbilatera 1
Anterior polar cataract,complete variable
posterior synechiae, uni- andbilateral
Anterior capsular cataract,incomplete variable
posterior synechiae, uni- andbilateral

norma 1PeneLrance

Man ifes tat ion

Exeosure 9roue 455+455 R
Vacuolisation of the wholecompletelens. microphthalmia, irisadhesion, bilateral
Iris anomaly with cataract,completelong teeth, bilateral
Nuclear and zonular catara'ct, complete
bilateral
complete
Nuclear cataract, bilateral

165

Female

Apyc

132

Male

Apoc

143

Female

Ace

206

Male
284 ~/

Alm

Male
257
Male
236
Male
223

Mei
Ide
Anc

336 ~J
340
341

395

a/

536

Exeosure 9roJe 534 R
Anterior lenticonus, microcomplete constantphthalmia, white spotting on
the belly, bilateral
Microphthalmia with ea taractof the left lens
Iris dysplasia with cataract, complete constantspotting on the belly, bilateral
Anisocoria, ovoid pupils,
incomplete variable
occasionally with cataract,uni- and bilateral
Ex~sure group 600 R
Anterior polar cataract
Nuclear and posterior
incomplete constantsuture cataract
Anterior polar cataract,incomplete constantpupillary membrane
Anterior polar cataract,
corneal lens attachment,
mi c rophtha lmy

complete

Derived from post-spermatogonial irradiation.

constant

reducednormalreducedsterilenorma 1
norma 1sterilenorma 1males
normalfemales
reducednorma 1

Ta b l e

32

Incidence of conof male or ema e micerin
x irradiation

Living foetuses on day 19
p

Incidence(%)

45/2041(2.2) < 0.001

25/942(2.7) < 0.001

4/1026(0.4)

Offspring surviving more than 7 days

Details a/

Incidence(%)

pllale parents irradiated(0.9) < 0.05
14 OE, 4 Ex,
1 Hy, 1 Ga.
Female parents irradiated
8 CP, 3 T, 4 0, 29/1750 (1.7) < 0.01
10 OE, 2 Ex,
1 Ga.
Con;rols
1 0, 1 OE,
1/809
(0.1)
1 Ex, 1 PD.
8 CP, 5 T, 13 0, 20/2314

Details a/

3 T, 7 0,
3 OE, 6 TA,l A.

lOT,160,
1 Lu, 1 l i ,

1 A.

1 T.

a/ CP, cleft palate; T, tail anomalies (kinky and/or short): D, dwarf (lessthan 75 % of body weight of untreated groups); OE, open eyelid; Ex, exencephalus: Hy, hydrocephalus; Ga, gastroschisis; TA, testicular atrophy,
Lu, lung anomaly (mislobulation); Li, liver anomaly (mislobulation);A, atresia hymenalis.

T a b 1 e

33

Some internal emitters of interest for the genetic risk'.S76!
Radionuclide

Ha lf-1 ife

Mode of
decay

3H

12 a

6

14c

5730 a14 d
30 a1600 a24390 a
458 a

6

32p
137Cs
226Ra
239Pu
241Am

6
6,Y

a
a
a

Hean track
1ength (µm)

42
1900
380
40
40
40

Remarks
Possible transmutation effect
11hen in DNA
As above
As above; skeletal effects
All tissues irradiatedMain dose to skeleton
Main dose to skeleton, liver
As above537

Table34

Some genetic results with radioactive isotopes in mammals
IS76]
Radionuclide

Activity

End point
I.

Ref.

ResultBeta-emitters in rodents

Specific locus mutations(male mice)

Significant induction'R31 Jin pre- and post-meiotic·
cells
Significant induction
Dominant lethals (mice,
rCJ0J- 110 M!lq
in both sexes
ml waterboth sexesr K25]- 0.2-1 Mllq Dominant lethals (female Significant increase
per mousemice)
Evidence for induction 'B47]- 0.035 t1Bq Dominant lethals (maleper gramin premeiotic cells
rats)
Evidence for induction !R52]
F 1 translocations (male- 0.93 MBq
in post-meiotic cells
per mousemtce)
No significant effectDominant lethals (male- 0. 75 11Bq
(F19]
in post-meiotic cells
per mousemice)
131 1 0.0075-0.026 MBq Dominant lethals (maleSignificant increases'R53]
per mouse . mice)(post-meiotic cells)
0.13 11Bq
Oominant lethals (raale
Evidence for induction '.847]
per gramin post-meiotic cells
rats)
1 5133]Significant increase
0.55 MBq
Dominant lethals (maleper grammice)
1.24 t1Bq
Significant increase'5133]
Translocations in
per gram
spermatogonia
2 .SO ltBq
Significant increase[S133]
Translocations in
per gram
spermatogoni a- 10-15 fl[Jqper gram2.

Alpha-emitters in male mice

239Pu
0.37 MBq/kg Trans locations
239Pu 0.0018-0.018 MBq Dominant lethals,
per mousesemi-sterility
239Pu- 0.15 MBq/kg Dominant lethals fragments, translocations
239Pu
0.37 itBq/kg Specific locus m~tations

Significant increase
Extra intra-uterine
death, also in r 1
RBE about 23 (relative
gamma rays}
Significant increase

[844]
'L33]

239Pu 0.18-0. 37 1-lBq/kg Dominant lethals, fragments, translocations

RBE estimatesfrom 13-40 (relative
to gamma rays)

1

Note:

1'01•

'.553]'.R37]
G23]

routes of aa>tinict:ration and ot•ier detailo, see ,he cited 1•eferencec.

Tab l e35

rtean number of A~ spermatogonia scored per mouse
120 and 07 h after x-1rradiat1on[010!

Experiment
Treatment

x rays only
120 h

207 h

Experiment 2( 3HJ~Thd + x rays~/
120 h

207 h

Control
147.5,:3.2s£{41.5,:3.25 133. 25+5 .16 133.25+5.16
100 R
300 R
39.5+2.40 69 +1.58 24 +2.20 65.5 +5.95
500 R
16.5+1.71 33.5+2.02 13.75+1.65 25.5 +3.43
600 R
13.7+1.89 23.7+2.81 12.25+0.85 16. 75+2 .10
lOOOR
5. 2+1.03 2 .0+0.58
2.75+0.85 1.25+0. 75
500+500R~/ 5. 0+1.08 5 .0+0.82
8.5 +1.55 2.0 +0.63
a/
Ii/

c/

al
538

•3H'dThdx rays only ~ x'rays £_/
120 h

207 h

118.25+4.29 105.21+3.36
98.25+7 .53 84.25+6.61
60.5 +3.01 48.75+3.97
27.75+3.59 21.0 +0.58
15.25+1.44 10.5 +2 .02
3.75+0.95 o. 75+0.25
2.75+0.63 0.75+0.25

0.46 MBq [ 3HJdThd 1 h befo e x rays.
3 injections of 0.46 MBq 1\JdThd at 9 h intervals. x rays 24 h after last
injection.
Standard error of the mean.
24 h between fractions.

Tab l e36Frequency of labeled /\l spermatogonia 207 and 414 hafter acu ex-ray exposure[010]
Experiment 1
0.46 MBq [3HJdThd 2._/207 hTreatment

Control
100 R
300 R
500 R
600 R
1000 R
500+500 R
al

Experiment 2
3 x 0.46 tlBq [ 3HJdThd ~I
207 h

Numberof cells

labelled

800

21.0

800
800
800
228
226

6.0
2.9
2.6
6.6
2.2

%

414 h

Nu1nberof cells%
Numberlabelled of eel ls

1000
800
800
200
800
166
216

29.20
1600
29.00
800
24.25
800
27.50 di 800
26.25 800
10.24 el 800
47.22 c1 800%

labelled
22.81
33.75 cl33.25 cl39.88 c1
36.50 cl1s.25 e/35.50 c1

1 injection of 0.46 MBq [~H]dThd l h before irradiation.
3 injections of 0.46 HBq ( H]dThd given 9 h apart. Irradiation 24 hafter last injection.
Significantly above control.
Based on only one mouse.
Significantly below control.

o/
cl

a/
e/

T a b 1e37

A corn arison of cell survival, mutation fre uency and ercenta eo labe e
spermatogon1a a ter x-,rra 1at1on o the ma e mouse[010]

Exposure
(R)

0
100
300
500
600
1000
500+500,
24 h apart
a/

s1

I.I

di

et

6 x 0.46 MBq
3tt-thymidine
24 hbefore irradiation(% labelled cells)al

3 x 0.46 MBq
3H-thymidine
24 hbefore irradiation(% labelled cells)

207 h

414h

207 h

414 h

7.8
15.6

0.7
1.6

16.3

l. 7

2.4
39.1

0.2
3.1

29.2
29.0
24.3
27.5
26.3
10.2 cl47.2 -

22.8
33.8 d/33.8 al39, 9 di36.5 di15.3 el
35.5 d/Cell survival(% of control)
Minimumcl

207 h
i nterva 1

18.0
10.3
9.2
0.9

80.0
46.3
20.0
10.0
0.7
0.7

Mutations
per locu~
per R 10
b/

0.75

1.5

8.72
13.29
9.28
49.91

From references (011, 013].
From reference [R58].
These values are calculated from Table 35; the first three entries
correspond to 120 hand the last two to 207 h.
Significantly above control, 5 % level.
Significantly below control, 5 % level.

539

Table38

X-ra ex osures R re uired to kill all ovarian ooc tes
1nerent mallllla 1an species
IB50]
SpeciesPrimordial foll icles~-7
Juvenile

Adult

15

50
110-15)
315
(100)
15000
(500)
(>500)(>900)
7000(5000}
5000?
(2000)?

Mouse-

(7}

Rat

100

Guinea pig
Pig
Cow
Monkey

(500)
(900}
2000?

Human£/"Growing" andgraafianfollicles
2200
4400

- 5000Note: The data avail.able az>e not matched for species
differences in the rate of oocyte development. Thisis important, since, for e:wmpl.e, if sul".,ivaZ. ofoocytes in the rat has been recorded after a somm.,hat
longer survival. time inter·.1aZ, a nr.<ch Zol,/61' e.rposu1'e
LJOuld have given a 100 i kiZ.Zing.

~/ Figures in parentheses are L0 50 exposures.
b/ Varies with age, strain and radiation procedure.
c/ Depends on authority and on fractionated doses
to women under 35 years.
Table

39

Fre uenc of occurrence of different subclasses of a- clones
yr ce 1Tfiie"""""n mutagenes1s experiments w1[W28}

Markers 1os t
Only a 1a 1 and up to
two others
A11 fourx rays

Untreated controls
tlumber

Per cent

13

16

44
22

56
28

79

100

tl~mber

t1NNG

Per cent

Number

Per cent

2

8

28

30
16

64
34

19
2

65
7

47

100

29

100

Ta b 1 e40

enetic ill health
1ate
an s,ze,

Category of genetic effect
Unbalanced translocations; riskof malformed liveborn
Trisomics and XO
Simple dominants and sex-linked
mutations
Dominants of incomplete penetrance
and multifactorial disease maintained by mutation
Multifactorial disease not maintained by mutation
Recessive disease
Total

Equilibriu~

1 + 2 generation30

23 + 629

30

30 + 030

100

20 + 1636

160

16 + 14

30

0

0

b/
320

b/
89 + 36

a/ Over all generations following the generation exposed.

o/ No estimate given.
540

125

Table41

Current
incidence
per mi 11 ion
1iveDorn
offspringType of genetic disorder 2._/

Autosomal dominant, X-linked
Irregularly inheri tcd
Recessive

10300 ]
90300
1100

Chromosomal aberrations '!_I

6300

al
b/

c/

er;

el
f/

Effect of 1 rem per generation
per mill ion 1ivcborn offspringFirst generationbi

Equi 1i bri um

5-65 ~/

40-20020-900 e/
Very slow
increase

Very few; effects
in heterozygotes
accounted for in
top row
Fewer than 10 9./c/Increases
only slightly

Includes disorder and traits that cause serious handicap at some time
during 1ifetime.
Estimates directly from measured phenotypic damage or from observed
cytogenetic effects.
Estimates by the relative-mutation-risk method.
No first generation estimate available for X-linked disorders: theexpectation is that it would be relatively small.
N:B. A typographical error in the GEIR report is corrected here.
Some estimates have been rounded off to eliminate impression of considerable precision.
Includes only aberrations expressed as congenital malformations, resulting from unbalanced segregation products of translocations andfrom numerical aberration.
Majority of the Subcorrrnittee feels that it is considerably closer tozero, but one meni>er feels that it could be as much as 20.
Ta b 1e42

Ex ected rates of inductior er G of variousof genetic amage 1n umans at ow ose rates o

Kind of damage

1. Mutations having

dominant effects

2. Balanced reciprocaltranslocations (RT)
3. Unbalanced productsof item (2) above
4. X-chromosome loss

a/
~/

cl

f/

-1

t;

Based onA. Dominant s~eletal
mutations in mice
B. Dominant cataract
mutations in mice
A. RT in marmoset andhumansB. RT in rhesus monkey
Item A of (2) above
Item B of (2) above
X-chromosome loss inmice

Rate per 10 gametes
following irradiation of
Spermatogonia

Oocytes

400 al0-180 b/35 cl
16. 7 c/1750-8750 di

0-15

220-1080 d/
3500-17500 fl
440-2160 [Inegligible

0-110 el0-5250 r;/
0-660 511
0-500 hibi0-875 elSame estimate as that presented in the 1977 report.
Estimated from the spermatogonial data using the assumptions that the
in1nature human oocytes will be mutationally insensitive, i.e., similar
to the mouse irrrnature oocytes, or will have a mutational sensitivity
which is 0.44 times_~hat of sperm2togonia; see text for details.
The figure of 35 10 is igat derived from fractionation experiments
and the figure of 16.7 1- from the two single exposure experiments.
The lower rate is for chronic gam~a irradiation and the higher one isfor low dose rate x rays: based or cytogenetic results.
Under £gronic garrrna irradiation conditions; the upper limits of 880 or
100 10 are derived from the spermatogonial estimate for heritable
reciprocal translocations assuming that the oocytes will be one-half as
sensitive: the lower limit of zero is based on the assumption that theoocytes will be practically insensitive to the induction oftranslocations.
Assumed to be twice that of balanced RT.
Assumed to be six times that of balanced RT.
Based on results obtained with chronic ga1t111a irradiation of maturingoocytes; see text for details.
541

Table43

Risk of inductiona(See Table 44 for risk estimates using the doubling dose method)

Risk from the induction of

Expected frequency (per 10 ) of geneticallyabnormal children in the first generation
after irradiation ofMales

Mutations having dominant effects 2,_/
Unbalanced products of translocations

2.I
b/

c/

d/

e/

542

- 1000 - - 2000 b/- 30 - - 1000 d/

Females
0 - - 900 cl
D - - 300 '!_/

Includes the risk from the induction of dominant mutations, as well as
recessive mutations, deletions and balanced reciprocal translocations
with dominant effects.
The lower 1imit of - 1000 is derived from the data on cataract
mutations and the upper limit of - 2000 per 106 is derived from data on
skeletal mutations and is the same as the one arrived at in the 1977
report. A multiplication factor of 2 has been used in the skeletal
estimate but not in the cataract one; this factor is an attempt to allow
for the likelihood that many dominant mutations (especially those affecting
systems other than the skeleton) remain to be detected, A correction
factor of 0.5 to allow for skeletal mutations which are not clinicallysignificant is not required for the cataract estimate. See text for
further details.
The lower limit of zero is based on the assumption that the mutational
sensitivity of human immature oocytes i~ 6similar to that of mouse immature oocytes; the upper limit of 900 10 is based on the assumptionthat the sensitivity of human oocytes is similar to that of mature andmaturing mouse oocytes and that the latter is 0.44 times that of spermatogonia. See text for furt~ r details.
The lower limit of - 30 10 5 is based on rhesus monkey cytogenetic data;
the upper limit of - 1000 10- is based on combined marmoset and human
cytogenetic data.
The lower limit of zero is based on the assumption that the sensitivityof human immature oocytes to the induction of heritable reciprocal translocations will be similar to that of mouse immature oocytes with respect
to the i ngucti on of chromosome aberration phenomena; the upper 1imi t of
- 300 10 is based on the assumptfons that the sensitivity of the human
illillature oocytes to the induction of translocations will be one-half ofthat of human and marmoset spermatogonia (based on results with mice on
heritable translocations), that the frequency of unbalanced products will
be six times that of recoverable balanced reciprocal translocations andthat 6 % of the unbalanced products will result in congenitally-malformed
children. See text for further details.

Tab 1 e

44

of one nn
Gy(See Table 43 for risk estimates using the direct method)
Effect of 1 Gy per generation
Disease classification~/
Autosomal dominant andX-linked diseases
Recessive diseases
Chromosomal diseases
Structura 1
Numerical
Congenital anomalies,
anomalies expressed laterand constitutional anddegenerative diseases
Total

Current
incidenceFirst generationb/c/

10000 d/2500 ~/

1500
s 1ight

10000
slow increase

400 f/
3000 :§:/

240
probably
very sma 11

400
probably
very small

90000 h/105900450
2190

4500 i /14900

Equilibrium

Follows that given in the BEIR report fB60], except that chromosomal
diseases are divided into those with a structural and those with anumerical basis.
Based on the results of the British Columbia survey and other studies.
For details, see [Ul] and Table 2 of the present Annex.
The first generation incidence is assumed to be about 15 % of the equilibrium incidence for autosomal dominant and X-linked diseases (see text
for details), about 3/5 of the equilibrium incidence for structuralanomalies and about 10 % of the equilibrium incidence for diseasesof complex inheritance.
Includes diseases with both early and late onset.
Also includes diseases maintained by heterozygous advantage.
Based on the pooled values of Table 2 but excluding euploid structural
rearrangements, Robertsonian translocations and "others" (r:iainly
mosaics). See text for details.
Excluding mosaics; see text.
lncl udes an unknown proportion of numeri ea 1 ( other than Down's syndrome)and structural chromosomal anorralies.
Based on the assumption of a 5 % mutational component; see ru1J for
details.

a/
b/

c/

di

et

!I

i/

T a b 1 e

45

Deaths per 1000 living affected~/
DisorderA11 1i vebi rths
Dominants

23.6
98.0
(x4) £I
Recessives
98.5
(x4)
Congeni ta 1
130.0
ma lf onna ti ons (xS)

a/

b/

cl

2

Age (years)
3

1.8
19.4
(xll)
35.0
(xl9)
11.2
(x6)

1.0
4.2
(x4)
32 .6
(x33)
5.6
(x6)

4

5

0.6
4.7 b/(x7)13.1
27.0
(x39)
(x22)
3.3
3.0
(x4)
(x5)
0.7

All rates, in this and later tables, are based on individuals
who have survived to at least the beginning of the age being
considered and only for those data which cover the relevant
age groups.
Pooled estimate because of very small numbers of deaths atthese ages.
Numbers in parentheses, in this and later tables, are theapproximate increases in risk compared to the same risk for
all livebirths (e.g., 4 = 98.0/23.6).

543

Ta b 1 e

46

Estimates of load from mono9en i c dominant disorders
rest, cs9 J

Birthfrequency
per 4
10

Condition

Fanrilial hypercholesterolaemia
Deafness - congenital(dominant)- adult onset
Polycystic kidney
Huntington' s chorea

20

10
8

5

Multiple exostosis
0.5
lleurofi bromatos is
4
Retinoblastoma (untreated) 0.3(dominant)11yoton i c dystrophy
2

Average years of Lost
OnImpaired life
impaired life and years
life degree of
imair111ent

Cause of death

Coronary
thrombosis
none

55

10 (50 %)5

070 (30 %)

0

30
30
45

40 (20 %)
10 (50 %)
15 (50 %)

0
30
10

15
20
2

50 (20 %)
30 (50 %)
1 (50 %)

5
20
67

40

10 (50 %)

20

10
10

30 (10 %)
60 (50 %)30
0545 (80 %)

20
35
20
0

Dementia andinfection
CancerInfection
Aortic aneurysm
none

none
Renal failure
Cerebra 1
degenerationand infection
CancerCancerCancerDementia andinfection
Haemolytic crisis
noneCongenital spherocytosis
Blindness, early onset(dominant)Tuberose sclerosis

2
1

Multiple polyposis
Osteogenesis imperfecta
Marfan syndrome
Peroneal muscular atrophy(dominant)Spastic paraplegia(dominant)Cerebe 11 ar a taxi a(dominant)

1
0.4
0.4
2

30
2
30
lO

5 (50 %)
63 (40 %)
20 (30 %)
60 (20 %)

0.5

20

50 (30 %)0Infection

0.5

35

25 (SO%)10lnfecti on

Table

5

47

Estimates of load from autosomal recessive disorders[C51, C69

Condition

544

Birth
frequency
per 4
10

Cystic fibrosis(untreated)
Phenyl ketonuri a
Neurogenic muscle atrophy

5

Adrenal hyperplasia
Congenital deafness(recessive)
Early onset blindness(recessive)
Non-specific mental
retardation (recessive)

1
2

5

Average years of Lost
UnImpaired life
impaired life and years
life degree of
impai nnent

Cause of death2

8 (50 %)

60

Lung infect ion

C1

40 (95 %)
4 (90 %)

30
65

C
0

60 (30 %)
70 (50 %)10

0Infection
Paralysis andinfection
Electrolyte lossnone

5

65 (SO%)

0

none

0

50 (90 %)20

Infection

Tab 1 e

48

Estimates of load from X-linked recessive disorders
trn, C69)

Birthfrequency
per 4
10
males

Condition

Muscular dystrophy(Ouchenne type)

Average years of Lost
OnImpaired 1 ife
impaired life and years
1ife
degree of
impairment2

4

16 (60 'k}

50

0
0
0

50 (20 %)70 {15 %)
50 (80 %)20
020

Haemophilia A
X-linked ichthyosis
X-linked forms of mental
retardation

Tab 1 eCause of death

Debility andi ntercurrent
infection
Haemorrhage
noneIntercurrent
infection

49

Estimates of load from some selected chromosomal disorders{est, C69]

Birthfrequency
per 4
10

Condition

Average years of Lost
UnImpaired life
impaired life and years
1ife
degree ofim airment

Down's syndrome12035 (95 %)35

Edward's syndrome
Autosomal structuralaneuploidy
XXX
XXV
XYY

1
5

0
0

1 (100%)20 (95 %)

69

5
5
5

5
5

65 (30 %)
65 (30 %)
65 (20 %)

0
0
0

5

Table

Cause of death

Associatedmalformation
or infection

so
none
none
none

SO

A comparison of the estimates of load from different kindsof spontaneously-ar1s1ng genet1c d1sease
fC51)

Disease category

Frequen 6y
per 10births{A)

Autosomal dominant
9000
X-linked (males only) 1000
Recessive
2500
Chromosomal
4000
Irregularly
90000
inherited <:._/
Total

Years Years lgst
Average y~a rs of
impai reg per 10
Unbirths
per 10
impaired Impaired Lost births
life
life
life
{C)
{A x C) {A x 0)
(D)
(B)

1
2

25 (33%) a/ 13
40 (39%) a.1 28
35 (80%) a.1 32
44 (55%) 'F_! 24

20

20 (?)

33
I.510650022500011700020000 b/ 14000 b/
87500 80000 176000
96000

a/ 30 1,800000 2,700000
2,308500 3,007000

a/ Degree of impairment.

o/ Birth frequency is halved to take into account both sexes.

c/ Crude assessments by the COfllllittee.

545

Tab 1 e

51
ita l admissions

fre uenc of enetic disease amon
per cent o tota
fH2, P32J

Disease category
Numberstudied

9352
1089
200
4115
6161

Chromosomal
0.7
0.4
0

0.6
0.7

Single Multigene factorial
6.4
6.9
5.0
3.9
3.1

Develop- Familial Heterogeneous,
non-genetic Ref.
mentalor unknown
anomalies

31.5
3.9 ~ 22.8 • 18.9
16.5 ~ 53.0 • 36.5
22.1 • 35.7 • 13.6
3.3 - 3.4 • 0.1

53.2
63.0
25.5
46.6
92.7

8.2
6.9
16.5
13.2

rcsJ
f S85]
rD17]

rH2]

[P32)

Note: The studies mentioned above were carried out in hospitals in Baltimore(CS], Montreal [S85]. Boston [D17]. Seattle fH2] and Caracas '.P32].

52

T a b l e

Fre uenc of sin le- ene diseases amon aediatric admissions
per cent o tota a m1ss1ons(112, P32]
Autosomal
dominant

Autosomal
recessive)(-linked
recessive

Ref.

1.3
2.1
1.0
1.2
0.3

4.2
2 .1
3.5
2.2
2.5

1.3
2.7
0.5
0.5
0.4

[CS]
IS85]
[017]
fH2]
f P32]Ta b 1e53

Humbers of selected hos italor certain 1n S 0

1i vi ng affected
1sor ers

Age

2

3

4

5

201
1104
(x5)
1384
(x7)
1051
(x5)

70
527
(x7)
571
(x8)
420
(x6)

49
371
(x8)
470
(xlO)
275
(x6)

44
302
(x7)
443
(xlO)
256
(x6)

42
382
(x9)
287
(x7)
281
(x7)

T a b l e

54

All livebirths
Dominants
Recessives
Congenital
malformations

100 affected children

Numbers of da s hos
Wlt certain 1n

Age
All 1ivebi rths
Dominants
Recessives
Congenita 1
malformations

546

2

63
229
2022 803(x13)(x9)
2685 804(x12) (xl3)1500 569
(x7)
(x9)

3

4

5

38
473
(x12)
603
(xl6)
307
(x8)

33
424
(xl3)
799
(x24)
291
(x9)

30
981
(x33)
378
(xl3)
331
( xl 1)

T a b 1e

55
from the induct ion
to OW ose,
1 't. eer generation

A

Condition

Autosomal dominant
X-linked (both sexes)
Chromosomal a/
Irregularly inherited
Tota 1

Inducednumberof case~per 10births
(A )

1400
125
240
450

/\verage yearsof 1ifelmpai red

Lost

Years
impairegper 10births(C)(D)(A .. X C)

(A+ x D)

35000
5000
4800
9000

18200
3500
12000
13500

53800

47200

225000
20000
8000
90000

117000
14000
20000!35000343000286000FIRST GEttERATlOtl
13
25
40
28
20
50
30
20·

2215

Years
lost
per 106
birthsEOU IL I SR IUM

Autosomal dominant
X-linked (both sexes)
Chromosoma 1 a/
Irregularly Tnherited
Total
2_/

9000
500
400
4500
14400

25
40
20
20

13
28
50
30

Only unbalanced products of induced reci pro ea 1 translocations resulting
in livebirths considered.

547

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AI

A2

A3

A4

AS

A6

A7

A8

A9

AlO

A11

A12

A 13
A14

A 15

A16

A17

A18

Al9

A20

548

Altukhov, Yu.P. lvtonitoring of human populations forgenetic load: theoretical and experimental considerations. Paper presented at the Joint Expert Consultation
Meeting (UNEP/WHO) on Genetic l\lonitoring,
September 1978, Moscow.
Attardi, B. and S. Ohno. Cytosol androgen receptor
from kidney of normal and testicular feminized (Tfm)
mice. Cell 2: 205-212 (1974).
Aurias, A., M. Prieur, 13. Dutrillaux et al. Systematic
analysis of 95 reciprocal translocations of autosomes.
Hum. Genet. 45: 259-282 (1978).
Alberman, E.D. and M.R. Creasy. Frequency ofchromosome abnormalities in miscarriages andperinatal deaths. J. Med. Genetics 14: 313-315 (1977).
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