Some Issues of Long-Term Investigations on Genetic Consequences by theChernobyl Accident
Lazjuk G.I.1, Satow Y.2
1– Belarus State Medical University, Minsk, Belarus
2– Hiroshima University, Hiroshima, Japan

1. SUMMARY
Results of almost 20-year investigations of possible consequences of the Chernobyl accident for
Belarussian population, obtained by the National Research Institute for Hereditary and Inborn Diseases,
provide grounds for the conclusion that at least four facts, related to genetic consequences, had connectedto the Chernobyl accident: three could be defined as proven and one – as probable. The first three are:•Significantly increased level of chromosome aberration in pregnant women and their newborn babies,
who resided in 1986-1988 in zones with 137Cs contamination of 555 kBq/m2 and higher;•

Significant three-year increase of prevalence of embrional development defects in the same
abovementioned zones and in the same years, which lead to the increase of prevalence of congenital
anomalies in social abortuses, fetuses and newborns;•January peak of babies with Down syndrome, born by women who were in the zones of maximum
irradiation in the period 26-30 April 1986;
Of possible but not yet proven consequences we shall mention investigation in contaminated andcontrol zones before and after the Chernobyl accident of the ratio of de novo structural chromosomal
aberrations (SCA) to inherited SCA, which induce chromosomal diseases. This investigation revealed anincrease of the share of de novo SCA in after-Chernobyl period. Etiology of observed changes is notuniform. While an increased level of chromosome mutations, including trisomies, is essentially induced byadditional ionizing radiation, many congenital anomalies which determined increased frequencies ofdefects in 1987-1989, belong to the group of multifactoral defects, i.e. for their etiology important areradiation as well as nutritional problems, hormonal and immunological upheavals.
2. RESULTS OF INVESTIGATION OF CYTOGENETIC EFFECTS
Cytogenetic effects in pregnant women and their newborn babies who have lived in the regionswith most severe contamination by Chernobyl fallouts (Gomel and Mogilev oblasts of Belarus) wereinvestigated. Standard practices were used for cultivation of peripheral blood lymphocytes and registrationof chromosome aberrations (G. Lazjuk et al., 1999). As could be seen from Table 1, all pregnant womenand their fetuses received biologically effective doses of ionizing radiation, which resulted in increased
numbers of dicentrics and ring chromosomes.
It appeared that mutagenic effect in evacuated pregnant women (group 1) was higher than inwomen who became pregnant 0.5-1 year after the disaster (group two) and women, who have lived morethan 2 years on the territories with the soil contamination of 555 kBq/m2 and higher. The level ofdicentrics and ring chromosomes in newborns was also higher than in their mothers (0.38% and 0.32% in
Gomel oblast, 0.21% and 0.19% in Mogilev oblast, respectively).

- 129 -Table 1. Frequency of dicentrics and ring chromosomes in pregnant women and newborn babies incontaminated and non-contaminated regions of Belarus.
Regions
Investigated groups
Number of investigatedFrequency of rings andmetaphases
dicentrics
1st group*
14645
0.32
Newborn babies of 1stGomel oblast
9167
0.38group
2nd group**
7753
0.14
3rd group***7715
0.19Mogilev oblast
Newborn babies of7486
0.21
3rd group
CONTROL
Novopolotsk
4th group****
4965
0.04
Minsk
Newborn babies
96700.04• * - 1st group – pregnant women evacuated during May-June 1986 from districts of Gomel oblast
with maximum contamination;• ** - 2nd group - pregnant women who have lived more than a year in zones with 137Cs contaminationof 555 kBq/m2 and higher;• *** - 3rd group - pregnant women, who have lived more than two years in zones with 137Cs
contamination of 555 kBq/m2 and higher;• **** - 4th group – pregnant women of control group from the city of Novopolotsk
3. RESULTS OF INVESTIGATION OF THE PREVALENCE OF EMBRYONICDEVELOPMENT DISRUPTIONS
Embryonic development disruptions were investigated by registration of congenital anomalies insocial abortuses, infants and foetuses.
3.1.

Results of investigation of social abortuses
By social abortion we understand the product of conception (embryo or fetus) was obtained after
the termination of pregnancy on woman's request. Since the material was collected without sampling, itmeans that in fact this is a population investigation. Pregnancy terminations were carried out in specialized
medical facilities by gynecologists, by curettage of uterine cavity when gestational age was 5 to 12 weeks.
This material was investigated by embryologists of the National Research Institute for Hereditary andInborn Diseases on non-formaline-fixed material with stereomicroscope and on histological sections.
When necessary, cytogenetic investigations in cultivated tissues of embryos were carried out. The
prevalence of embryonic development disruption was calculated for the number of investigated organs.
The total number of investigated abortuses exceeded 31,000, of which 2,701 were received from theChernobyl zone and the remaining were from Minsk, they were used as control. The frequency ofembryonic development disruption in social abortuses from the contaminated areas was significantly
higher than in Minsk during the same period (7.2% and 4.9%, respectively). Increase in malformations
was observed in all systems of organs, while more significant prevalence was observed for cleft of lip
and/or palate, dubling of kidneys and ureters, polydactyly and neural tube defects. The overwhelming
majority of malformations in social abortuses are etiologically heterogenic and due to this reason an
accurate estimate of the potential share of ionizing radiation in increased prevalences is impossible.
Moreover, in our investigations we have not observed neither higher number of aneuploids, nor cluster
death of cells during organogenesis, which are indicative for radiation effects.

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3.2.

Results of investigation of congenital anomalies prevalences
Prevalence of congenital anomalies was investigated in medical abortuses, obtained aftertermination of pregnancy due to genetic indications, in stillborns and newborns. Data of the nationalregistry of congenital anomalies (collected since 1979 at the National Research Institute for Hereditaryand Inborn Diseases) were used to this end. The details on the Belarus registry could be found in: G.
Lazjuk et al., 2003 (7). In this paper we describe only the results of investigation of prevalence of strictregistration congenital anomalies (SR CA). To this group belong anomalies which could be unambiguosly
diagnosed in prenatal and neonatal periods. So, to SR CA group belong: anecephaly (Q00), spina bifida(Q05), cleft of lip and/or palate (Q35, Q37), polydactyly (Q69), limb reduction defects (Q71, Q73),
digestive system atresia (Q39, Q39,2), anal atresia (Q42, Q42,3), Down syndrome (Q90), multiple
congenital anomalies (Q86, Q87, Q89,7, Q91-93, Q96-99). Analysis of SR CA prevalence was carried outin 4 groups. The first group was represented by the material from 17 districts of Gomel and Mogilev
oblasts, where there are territories with the surface density of soil contamination by 137Cs from 555
kBq/m2 and more, the 2nd group – control for the 1st group – 30 districts of Belarus in which the level ofcontamination by cesium was less than 37 kBq/m2 , the 3rd group – all territory of Gomel and Mogilev
oblasts (oblast centers excluded), not taking the level of radioactive contamination into account, the 4thgroup – control for the 3rd group - all territory of Minsk and Vitebsk oblasts (without the capital andoblast centre of Vitebsk oblast).
It is easy to see from Figure 1 that while the initial prevalences of anomalies in both groups arepractically equal, during the first three years after the Chernobyl disaster the prevalence of SR CA is muchhigher in the first group than in the control.

Figure 1. Prevalence of SR CA in 17 contaminated (Zone of Strict Radiological Control, ZSRC) districts(N=982) and 30 control districts of Belarus (N=1876)
After these three years, the prevalence of anomalies in two compared regions was not statistically different,
but there existed an annual smooth growth, and during 1990-2003 the level of prevalence of investigatedanomalies in both groups reached the level that was observed in the most contaminated districts (Table 2)
between 1987-1989.

- 131 -Table 2. Prevalence of SR CA in ZSRC and control districts during three periods (1981-1986,1987-1989, 1990-2003)
Contaminated districts of ZSRC
Control districts
Districts(N=17)(N=30)
Years
1981-1986 1987-1989 1990-2003 1981-1986 1987-1989 1990-2003
Number of liveborns
58128
23925
72143
98522
47877
153680and stillborns
Total number of SR
237
187
558
430
239
1207
CAPrevalence (1:1000)
4.08
7.82*
7.73
4.36
4.99
7.85
When prevalence of SR CA is compared on regional (oblast) level in the groups 3 and 4, there
could be seen a trend to increased prevalence of anomalies during the first 3 years, bur this rise was not as
distinctive as in zones of maximum contamination.

Figure 2 - Prevalence of SR CA in contaminated (Gomel, Mogilev; N=5692) and control (Vitebsk,Minsk; N=10008) oblasts.
The reason for a less clear 3-year rise of SR CA prevalence on oblast level as compared with theresults obtained for districts, apparently is a "diluting" of the results of 17 districts severely contaminatedby Chernobyl fallouts (with soil contamination by 137Cs of 555 kBq/m2 and more) by material obtainedfrom other districts of the same oblasts where population lives on territories with low contamination orrelatively clean areas. Moreover, there were territories in Minsk oblast (4th group) with soil contaminationthat exceeded 185 kBq/m2.
Relative risk of SR CA for 17 most severely contaminated districts of Gomel and Mogilev oblasts
increased from 0.9 in 1981-1985 to 1.6 in 1987-1989. After that (in 1990-2003) the relative risk fell to 1.0.
The clearest increase, and hence the higher relative risk, was observed for polydactyly, limb reduction
defects and multiple congenital anomalies. Significant input of dominant mutations, for which ionizing
radiation is believed to be important, is characteristic for these anomalies. Summing up, in the mostcontaminated by Chernobyl fallouts regions of Belarus a three-year (1987-1989) increase in prevalence ofCA was observed. In the following years the prevalence of CA increased in all areas indiscriminately tothe level of contamination and there was practically no difference between "clean" and contaminatedregions. Thus, if investigations of the prevalence of CA in Belarus were started 4-5 years after theChernobyl disaster, as it happened in Japan after the nuclear bombardment, the difference between
prevalence of CA in contaminated and non-contaminated zones would not have been detected.
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4. RESULTS OF INVESTIGATION OF THE CONSEQUENCES OF CHROMOSOME AND
GENOME MUTATIONSAs it was demonstrated by numerous investigations, the irradiation of population by radioactive
fallouts of Chernobyl has induced an increase of mutations level in somatic cells (I.Eliseeva, 1991,M.Pilinskaya, S.Dybinskiy, 1992; G.Lazjuk et al,1995). It's not impossible that commeasurable changes
did occur in gametal cells, but there are no investigations of this potential aftermath oft the Chernobyl
disaster. Indirect assessment might be conducted by usage of the National Research Institute for
Hereditary and Inborn Diseases results of investigation of prevalence of births with Down syndrome andprevalence of chromosomal diseases caused by non-balanced structural changes of chromosomes before
and after Chernobyl period.
4.1. Investigations of prevalence of Down syndrome revealed that while variations of annual prevalence
were in general low (about 1 case per 1000 births throughout the country and slightly higher variation inindividual oblasts). In January 1987 a high increase (by the factor of 2.5) of births with Down syndrome
was observed in Belarus. In Gomel oblast this factor reached its maximum – 3,6%о. These prevalences ofDown syndrome were 2-3 times higher than expected (Table 3).
Table 3. – Territorial distribution of children with Down syndrome born in January 1987.
Prevalence (‰)
RegionОЕО/Е
95% СIJanuary 1987
1981-1989
Belarus
2.5
1.0
31
13.9
2.2
1.5
3.2
Gomel oblast
3.6
1.18
2.6
3.1
1.4
6.2
Minsk oblast
3.1
1.1
6
2.2
2.8
1.0
6.0
Minsk city
2.7
1.1
6
2.6
2.3
0.9
5.1
Vitebsk oblast
2.2
1.0
4
1.8
2.1
0.6
5.7
Grodno oblast
1.7
0.9
3
1.6
1.9
0.2
4.6
Mogilev oblast
1.2
0.9
2
1.5
1.3
0.2
4.9
Brest oblast
1.0
0.8
2
1.8
1.1
0.1
4.0
Notes:
О – observed number of Down syndrome cases
Е – expected number of Down syndrome cases
CI – confidence intervalInvestigation of possible reasons for abrupt increase in the prevalence of Down syndrome(G.Lazjuk et al, 2002; G.Lazjuk et al, 2003) allowed for ruling out such factors as a change of mothers'
age at birth, prenatal diagnostics and possible effect of increased (due to extraordinary situation) attention
to this anomaly. After numerous discussions of these results it was defined that the only reason is an
impact of short-term intensive irradiation of Belarus women's gametes. This conclusion is supported by
the time period when the increase appeared (9 months after irradiation, when babies conceived in theperiod of the maximum increase of radiation were due to be born); by territorial distribution of numbers ofsuch babies, which resembles a trajectory of air masses during first days after the accident; and by aknown high radiosensitivity of mammals at the stage of ovogenesis preceding conception, whichcoincided with the maximum level of irradiation.

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4.2. Investigation of frequencies of chromosomal diseases caused by sporadic structural changes ofchromosomes
One of causes of chromosomal diseases is non-balanced sporadic structural changes ofchromosomes (sporadic chromosomal aberrations - SCA). Such chromosomes could be found in gonadsof parents (SCA de novo) or more remote ancestors (inherited SCA). By observing changes of the ratio
SCA de novo to SCA inherited it is possible to estimate the pressure of mutagenic factors, including
ionizing radiation, on hereditary structures.
Investigation of the ratio of SCA de novo to SCA inherited in the contaminated and the control
zones before and after the Chernobyl disaster was carried out at the National Research Institute for
Hereditary and Inborn Diseases of Belarus. For this purpose material of the Belarussian National Registryof congenital anomalies collected in 1979-1998 was used. Altogether, 209 families with various
chromosomal diseases caused by SCA were examined. Of them, such children were born in 72 families
before the Chernobyl disaster, and in 173 – after. As follows from Table 4, during the pre-Chernobyl
period there was no statistical difference (t=0.9; P=0.58) between ratios of SCA de novo to SCA inherited
in two compared regions. The ratio of inherited SCA to SCA de novo in families which had children withsame diseases during 1987-1998 period shifted in favor of SCA de novo both in the contaminated and the"clean" zones, but the increase in the contaminated zones was more significant (89% and 68%,
respectively, where t=2.99; P<0.01).
Table 4 – Comparison of sporadic (de novo) and inherited structural changes of chromosomes inchildren with chromosomal diseases in Belarus
Zones contaminated byZones free from radionuclide
Years of birth
Totalradionuclides
contamination
de novoinheritedtotal
de novoinherited
total
11(61%)
71828(52%)
2654
1979-1986
72
24(89%)
32775(68%)
35110
1987-1998
137
1979-1998
351045
103
61
164
209
Thus, in spite of the fact that the presented data need more wide population investigations, alreadyobtained data that the ratio of SCA de novo to SCA inherited has changed in favor of SCA de novo
support the assumption that the pressure of mutagenic factors on hereditary structures increases, which iseven more visible in zones with high contamination by Chernobyl fallouts.
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