Human Gene Therapy

December 1984

NTIS order #PB85-206076
“Where two principles really do meet which cannot be reconciled with one another, then

each man declares the other a fool and heretic. ”

–Ludwig Wittgenstein, 1950-1951

“Even in the extreme case where disagreement extends irreducibly to ultimate moral ends,

the proper counsel is not one of pluralistic tolerance . . . We can still call the good good and

the bad bad, and hope . . . that these epithets may work their emotive weal.”

“Thus we do what we can with our ultimate values, but we have to deplore the irreparable

lack of the empirical checkpoints that are the solace of the scientist. Loose ends are untidy at

best, and disturbingly so when the ultimate good is at stake.”

—Willard Van Orman Quine, 1981

Recommended Citation:

Human Gene Therapy—A Background Paper (Washington, DC: U.S. Congress, Office of

Technology Assessment, OTA-BP-BA-32, December 1984.

Library of Congress Catalog Card Number 84-601155

For sale by the Superintendent of Documents

U.S. Government Printing Office, Washington, DC 20402
Preface

This background paper is the fourth in a series of OTA publications on genetics,

and the third in a series focusing on emerging biological technologies. * It was prepared

at the request of Representative Albert Gore, Jr., as Chairman of the Subcommittee

on Investigations and Oversight of the Committee on Science and Technology, U.S. House

of Representatives. Preparation of the paper involved extensive assistance from and

review by experts and other interested parties (apps. C and D), and included a workshop convened at OTA on September 25, 1984.

Interest in human applications of recombinant DNA technology has been expressed

by numerous scientific, medical, religious, civic, and government leaders by Representative Gore’s subcommittee and resulted in congressional hearings in November 1982,

Human gene therapy is currently preeminent among the the topics of concern. This

paper focuses on the imminent development of human gene therapy, emphasizing early

medical applications. The governmental concerns related to human gene therapy, as

for other medical technologies, will include protection of subjects involved in research

and clinical treatment, ensuring safety and efficacy of the techniques in specific applications, and public discussion and education.

Human gene therapy, if it is approved for use, will first be performed on patients

who have no better prospect for treatment, and who suffer from severe, rapidly fatal

diseases caused by defective genes. Treatment will involve inserting copies of the normal gene into cells where the new gene can be used to produce proteins that correct

a biochemical defect. Human gene therapy as currently envisioned would thus be applied to treat patients with specific rare genetic diseases, and not as the tool of a eugenic

social program intended to improve the human gene pool.

Gene therapy in humans will first be done in cells from an organ or tissue other

than germ cells, probably from a patient’s bone marrow. Such treatment would therefore not lead to heritable changes. Therefore, because cells that are used in reproduction are not involved, gene therapy of this type is quite similar to other kinds of medical therapy, and does not pose new kinds of risks. When considering gene therapy that

does not result in inherited change, the factor that most distinguishes it from other

medical technologies is its conspicuousness in the public eye; otherwise it can be viewed

as simply another tool to help individuals overcome an illness.

Public interest in gene therapy suggests that utmost care must be taken to ensure

that the process for approving its early application is fair, open, and thorough. Several

Federal agencies, including the Recombinant DNA Advisory Committee at the National

Institutes of Health and the Food and Drug Administration, are presently involved in

just this process.

It is generally agreed that gene therapy that affects only the patient is analogous

to other medical technologies. There is, however, no agreement about the need, technical feasibility, or ethical acceptability of gene therapy that leads to inherited changes.

Commencement of gene therapy that would involve inherited changes should not proceed without substantial further evaluation and public discussion.

*The other OTA publications on genetics are Impacts of Applied Genetics (April 1981), The Role of Genetic Testing

in the Prevention of Occupational Disease (April 1983), and Commercial Biotechnology: An International Ana&sis (January 1984). The other publications on novel biological technologies are Impacts of Applied Genetics and Impacts of ~Veuroscience (March 1984).

. . .

///
Advisory Panel for OTA Workshop on

Human Gene Therapy, Sept. 25, 1984

LeRoy Walters, Chairman,

Director, Center for Bioethics

Kennedy Institute of Ethics, Georgetown University

Non-Government Panelist s

Lori Andrews

American Bar Foundation

James E. Bowman

Professor of Pathology and Medicine, and

Committee on Genetics

University of Chicago

C. Thomas Caskey

Howard Hughes Institute Medical Investigator

and Professor of Medicine

Baylor College of Medicine

Theodore Friedmann

Professor of Pediatrics

School of Medicine

University of California, San Diego

Ola Huntley

Board of Directors

Sickle Cell Self-Help

Horace Judson

Henry R. Luce Professor

Writing Seminars

Johns Hopkins University

J. Robert Nelson

Professor of Theology

Boston University

Nanette Newell

Calgene, Inc.

Albert Rosenfeld

Consultant on Future Programs

March of Dimes

Seymour Siegel

Ralph Simon Professor of Ethics and Theology

Jewish Theological Seminary of America, and

Executive Director

U.S. Holocaust Memorial Council

Carol Struckmeyer

Genetic Associate and Program Coordinator

New Hampshire Genetic Services Program

Government Panelist s

W. French Anderson

Chief, Laboratory of Molecular Hematology

National Heart, Lung, and Blood Institute

John C. Fletcher

Assistant for Bioethics

Warren G. Magnuson Clinical Center

National Institutes of Health

Elaine Esber

Director, Office of Biologics Research and

Review

Food and Drug Administration

Judith A. Johnson

Analyst in Life Sciences

Science Policy Research Division

Congressional Research Service

Library of Congress

Henry Miller

Medical Officer

National Center for Drugs and Biologics

Food and Drug Administration

Robert Nicholas

Staff Director

Subcommittee on Investigations and Oversight

Committee on Science and Technology

U.S. House of Representatives

iv
OTA Project Staff for Human Gene Therapy

Roger C. Herdman, Assistant Director, OTA

Health and Life Sciences Division

Gretchen S. Kolsrud, Biological Applications Program Manager

Robert M.

Stephen K.

Cook-Deegan, Study Director, Senior Analyst

Teresa Schwab,1 Research Analyst

L. Val Giddings,l Analyst

Nanette Newell,2 Senior Analyst

Eleanor Pitts,3 Research Assistant

Eckman,

4 1984 Wharton Public Policy Fellow

Contracto r

Lawrence Wissow, Johns Hopkins University

Support Staff

Sharon Smith, ’ Administrative Assistant

Elma Rubright,3 Administrative Assistant

Linda Ray ford, Word Processing Specialist

ISince September 1984

‘Until April 1984.

3LJntil August 1984

4June to August 1984
Contents

WHY IS CONGRESS INTERESTED IN HUMAN GENE THERAPY NOW? . . . . . . . . . . . . . . .

History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . .

Concern Among Religious Leaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OTA INVOLVEMENT AND REVIEW PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TYPES OF GENE THERAPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Different Mechanisms of Gene Therapy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Somatic Versus Germ Line Gene Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Stages of Development of Gene Therapy Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TECHNIQUES OF GENE THERAPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Genes Are Copied and Passed on by DNA Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Isolation and Cloning of the Normal Gene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Insertion into Human Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BACKGROUND ON GENETIC DISEASES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chromosomes and Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Single Gene, Multigene, and Environmentally Modified Traits . . . . . . . . . . . . . . . . . . . . . .

Genetic Treatment Versus Eugenics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MEDICAL ASPECTS OF GENE THERAPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Genetic Corrections of Animals and Other Organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reasons Genetic Diseases Cannot be Eliminated ., , ..., ..., ., . . . ..., . . . . . . . . . . . . . .

Types of Genetic Disease That Are Poor Candidates for Gene Therapy Now . . . . . . . . .

Reasons Germ Line Therapy May Be Unnecessary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Criteria for Beginning Human Gene Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ISSUES THAT MAY ARISE FROM CLINICAL APPLICATION . . . . . . . . . . . . . . . . . . . . . . . .

Medical Malpractice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Parental Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Patents and Trade Secrets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SOCIAL IMPLICATIONS OF GENE THERAPY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Major Social Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . .

THE FEDERAL ROLE IN GENE THERAPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

International Interests in Human Gene Therapy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Federal Agencies Potentially Involved in Gene Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . .

Functions of the Federal Government . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Case Histories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONCLUSION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TECHNICAL NOTE 1

DNA Function . . . . , . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TECHNICAL NOTE 2

Genetic Engineering Techniques: Cloning and Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TECHNICAL NOTE 3

Violating Species Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page

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51

52
Contents—continued

TECHNICAL NOTE 4 Page

Fertilization, Implantation, and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

TECHNICAL NOTE 5

Hemoglobin Disorders: A Case Study of Genetic Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Sickle Cell Anemia... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Thalassemias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Other Unstable Hemoglobins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Diagnosis of Hemoglobinopathies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Treatment of Hemoglobinopathies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

APPENDIX A–DIAGNOSTIC TECHNOLOGIES FOR GENETIC DISEASES . . . . . . . . . . . . . . 63

Fetal Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Technologies for Fetal Tissue Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Tissue and Fluid Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

APPENDIX B—PRIVACY AND CONTROL OF GENETIC PATIENT DATA . . . . . . . . . . . . . . 69

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Privacy and Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Third Party Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

APPENDIX C–WORKING GROUP ON HUMAN GENE THERAPY, RECOMBINANT

DNA ADVISORY COMMITTEE, NATIONAL INSTITUTES OF HEALTH . . . . . . . . . . . . . . 80

APPENDIX D–ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

APPENDIX E–LIST OF ABBREVIATIONS AND GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . 82

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

APPENDIX F–REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

. . . Vlll
HUMAN GENE THERAPY

Advances in molecular biology have triggered

an unprecedented expansion of knowledge about

human genetics. The rise of new genetic technologies, and their implied power, has engendered

concerns among religious, scientific, and civic

leaders that these new technologies may be growing more rapidly than our ability to prudently

control and productively use them. The ability to

insert human genes into human patients to treat

specific genetic diseases–human gene therapy–

has been one of the concerns noted by those observing the evolution of genetic technologies.l

Human gene therapy will first be considered

in a clinical situation where it might be possible

to treat with a human gene an individual patient

suffering from a genetic disease. Gene therapy

would be attempted only when there is no other

therapeutic alternative, or when the alternatives

are judged to be of greater risk or less potential

benefit. Application of gene therapy for a human

genetic disease should require evidence that it is

safe, might prove beneficial, is technically possible, and is ethically acceptable. Judgments should

be made in a procedurally sound and objective

regulatory framework.

Some of the concern about the potential abuse

of gene therapy may be allayed by considering

the following points:

The most promising prospects for human

gene therapy involve treatment of specific

genetic diseases by methods that are not designed to cause inherited changes, and the

ethical concerns may thus be similar to those

associated with other medical technologies,

such as vaccination or drug administration,

currently in use (President’s Commission,

1983; Shinn, 1982; Fletcher, 1982, 1983;

Siegel, 1982, 1983).

The capability for human gene therapy will

almost certainly develop in small increments,

like other medical technologies. This like-

‘The ckwlopment of recombinant DNA and other adk’anced techniques of molecular biolo~l’ have permitted no~’el applications of

I)iological methods in industry and health care through the new

biotechnology. This background paper is not about industrial or

medical applications of biotechnolo~~’, but rather about cleliheratd]r

changing genetic information in humans.

lihood, combined with the lack of inheritance

of anticipated genetic alterations, suggests

that decisions to proceed will not lead to irreversible population effects.

Inherited alterations, the most controversial

potential applications of gene therapy, are

unlikely to be undertaken in humans in the

near future because they are technically too

difficult, are perceived as ethically problematic, and may not prove superior to existing technologies.

There is a regulatory framework already in

place for considering the first applications of

human gene therapy. The existence of established procedures cannot guarantee that they

will be followed, because some scientists or

physicians may choose to deviate from them,

but there are laws in place that can be enforced. The existence of such a regulatory

framework distinguishes gene therapy from

many other novel biological technologies.

The primary justification for attempting human

gene therapy is the number and severity of

genetic diseases. There are 2,000 to 3)

000 known

genetic diseases—i.e., diseases whose roots can

be traced to specific genes or known inheritance

patterns (McKusick, 1983), As many as 2 percent

of newborn infants suffer from a genetic disease

(Lubs, 1977). For most such diseases, the defective genes have not been identified or located. For

several, including some of the most severe childhood diseases, the gene that causes the disease

has been found, and for a few such diseases,

copies of the normal gene are available through

use of recombinant DNA technology. Human gene

therapy will be feasible only for those diseases

in which the defect has been identified and the

normal gene has been isolated and cloned. All of

the diseases presently under consideration for

gene therapy are rare.

Gene transfer experiments in animals have produced some inherited changes, but the ethical

questions and relative inefficiency of current techniques preclude application to humans. Because

most of the serious concerns that human gene

therapy might cause long-term changes in human

populations presume inheritance of characteris1
—

2 Human Gene Therapy—Background Paper

tics, the present state of the technology does not

pose fundamentally new ethical problems. Human

gene therapy that does lead to inherited changes,

however, would likely incite deep-seated apprehensions about premature application. There

should be ample opportunity for public discussion before germ line gene therapy is tested in

humans. The body of this background paper will

explicate these statements by surveying the technical prospects for human gene therapy and discussing the public policy considerations.

Direct genetic alterations have been successfully

practiced in bacteria, yeasts, fruit flies, and some

mammals. To date, scientists have not succeeded

in applying these same techniques to correct the

action of defective genes or directly to change the

genome of a human being. The barriers to correcting the genetic defects that cause a few

human diseases, however, are now primarily

technical, and these barriers may be overcome

within the next few years. There are already

grant applications to the National Institutes of

Health that could lead to clinical testing of human

gene therapy. Requests for permission to begin

the actual clinical research that would involve

humans have not, however, been received to date.

“Human gene therapy,” for the purposes of this

report, refers to the deliberate administration of

genetic material into a human patient with the

intent of correcting a specific genetic defect. This

would include, for example, replacement of the

defective gene in bone marrow cells of a child affected by genetic immune deficiency. Most discussion in this background paper centers on

noninherited gene therapy because it is the type

expected to be considered soon.

Gene therapy, as defined here, would not include genetically enhancing general characteristics such as behavior, intelligence, or physical

appearance. These are excluded from the definition, although the prospects for influencing such

traits in the population through genetic methods

are discussed in some sections because concern

about such prospects has been raised in public

debate (Subcommittee on Investigations and Oversight, 1982; Siegel, 1983; Rifkin, 1983; Foundation

on Economic Trends, 1984; National Council of

Churches, 1984; World Council of Churches,

1983). Enhancement of complex human traits may

never be practical or socially accepted and it is

not “therapy” for a specific disease.

The definition used in this report thus focuses

on correction of specific genetic defects in individual patients, except when social concerns

about other applications or general issues are explicitly recognized. This background paper summarizes the technical, medical, and social considerations that arise from consideration of genetic

manipulation in humans and how they relate to

Federal policy.2

——

%enetic techno]ogim that do not involve gene (Iwrap}r, including

agricultural, pharmacx~]tical, and other industrial applications, hai’e

been discussed in swreral twrlier reports issued bj the Office of Terhno]o&v Assessment (OTA) of’ the [ 1,S Congress. Impacts of Applied

Genetics, issued in 1981, dealt with non-human applications of biotechnology The Role of” Genetic Te~ting in the Prww]tion of’

Ocrupationa] Disease, issued in 1983, cwwed the usfl of geneti(’

sl’reening in the n orkplace; ,and Commercial Bm(wh/]()/ogt .41J International/ and.vsis, issued in January 1984, surveyed and anal}’zed

the commercial deleloprnent of biotechnolo@ in Japan \\’estern

Europe, and the Unitcxl States. Issues and topics considered in these

other OTA publications are not repeated here; rather, this

background paper explores new issues relating to gene therapj in

humans.

Why is Congress interested in human

gene therapy now?

Congressional interest in human gene therapy liberate “engineering” of humans who are physistems from general awareness of the rapid pro- cally or intellectually “superior” is morally repuggress in molecular genetics combined with con- nant or politically dangerous, and there is fear

cern about the potential power and impact of new that the new techniques might be used to attempt

biological technologies. Some believe that the de- such engineering (Rifkin, 1983; Foundation on
Why is Congress Interested in Human Gene Therapy Now? 3

Economic Trends, 1984). Human gene therapy

that leads to inherited changes, in particular, has

been identified as a “fundamental concern for the

protection of the integrity, value, and health of

human life, both of individuals and of large numbers. The putative possibility of performing germ

line therapy, however noble in intention, would

incur risks of unknown magnitude to future progeny” (Nelson, 1984b). Several events contributing to the public interest in molecular genetics

are of particular interest.

History

In 1972, scientists joined DNA fragments from

two species, resulting in the first deliberately created recombinant DNA molecule (rDNA) (see

Technical Notes 1 and 2 for further details). In

1973, rDNA molecules were first duplicated and

grown in bacteria. Concern about the safety of

recombinant DNA laboratory research led scientists to call for a worldwide moratorium on certain types of experiments. Several scientific and

political meetings, some of them quite contentious, were held that focused on issues of safety

(Wade, 1984). In 1974, the Recombinant DNA

Advisory Committee (RAC) was formed to advise

the National Institutes of Health in formulating

guidelines for research; the first guidelines were

issued in 1976 (Milewski, 1984).

Commercial interest in biotechnology became

evident in 1976 when the first new firm, Genentech, was established specifically to apply recombinant DNA technology to medicine and other

areas. Since that time, more than 200 firms have

been founded to exploit the new technologies (Office of Technology Assessment, 1984). Two patent decisions in 1980 highlighted the commercial

potential of new biological technologies. In one,

a bacterial strain was patented that had been developed using traditional methods of selecting for

genetic traits, and without resort to recombinant

DNA technology.3 This was the first patent issued

7’I’he first patent for a microorganism w as granted to ,Ananda

Chakrabart}’ of the General Electric Corp. for a strain of

I%whmmas bactwiom [hat di#%ts certain petrochemicals. Dr

Chakrabartj dcn’eloped the strain by growing rare and mutant forms

of the barteria in new artificial eni’ironments until a strain u’ith

the desired chararterlstics resulted. ‘J’he dwision to grant the patent was made hjr the [

 T S Suprww (:ourt in a 5 to 4 ~rotf’ on June

lo, 1980

for a living organism. The second patent was

issued for the technique of making certain types

of recombinant DNA molecules.4

Wall Street responded to the promise of biotechnology in 1981 by setting a record for the

fastest price-per-share increase when Genentech’s

initial public offering of stock rose from $35 to

$89 per share in 20 minutes. Optimism was again

noted in 1982 when Cetus made a large and successful initial public offering ($115 million). Early

commercial expectations were encouraged when

the first commercial product using recombinant

DNA technology was introduced to the market

in 1982: human insulin, sold as Humulin (Office

of Technology Assessment, 1984, ch. 4). Many of

the expectations of rapid economic bonanza have

been tempered by the length of time and magnitude of effort required to bring products to the

market, but long-term prospects for commercial

applications of biotechnology remain promising

(Office of Technology Assessment, 1984).

Developments in regulation, law, and finance

were attended by continued advances in genetic

research. The surprising discovery of “split” genes

occurred through the use of recombinant DNA

technologies in 1977.5 That same year, two independent techniques were developed for determining the DNA sequences that contain genetic information, permitting direct inspection of the

genetic material and analysis of its functions (Watson, 1984).

Advances in medical applications also occurred.

Recombinant DNA techniques were first used for

the prenatal detection of sickle cell disease in 1982

(Chang and Kan, 1982; Orkin, Little and Kazazian,

1982). Use of enzymes that specifically cut DNA,

in combination with probes that detect specific

—

4This patent was granted to Stanlej’ Cohen of Stanford t “ni\ersity and Herbert Boyer of the [University of California at San F’ran -

cisco for the basic process of constructing recombinant D N A

molecules. The patent is questioned by some, but has not been seriously challenged at the time this is written (Office of ‘J’echnology

Assessment, 1984, ch, 16). The patent has since been complemented

by a process patent for the same technolo~k that was granted in

August 1984.

‘Scientists confirmed [heir expectations that the genes were more

complicated in higher animals rompared to bacteria. Genes in higher

organisms are often dikided into regions: the sequence for a protein, for example, may be separated into several units, and the units

must be rearranged and “spliced” together to form the sequence

that is e~entually used to produce the protein (Leder, 1978),
4 Ž Human Gene Therapy—Background Paper

sequences of DNA, led to development of a method

for determining the location of genes, even when

their function had not been determined and the

genes had not been isolated (Botstein, 1980; Botstein, 1984). The technique, first described in

1980, has great promise for both promoting understanding of human genetics and assisting in

the diagnosis of hereditary diseases (see app. A).

In 1980, the first inherited alteration of genes in

the germ line of mice was achieved (Gordon and

Ruddle, 1981) and in 1982, the gene for rat growth

hormone was introduced into mice (Palmiter,

1982, 1983). The mice that incorporated the rat

growth hormone genes into their cells could be

induced, using a special diet containing zinc, to

grow to twice normal size. The response to zinc

was due to a special DNA sequence that the scientists had included with the growth hormone gene

that caused zinc to “turn on” the inserted gene.

The progeny of the genetically altered mice also

inherited the new foreign gene, making them

“mighty mice” as well.

The human experiments of Martin Cline, a physician from the University of California at Los

Angeles, contributed to the ethical apprehensions

of many observers. Dr. Cline attempted gene therapy using recombinant DNA in two patients suffering from thalassemia, a disease causing severe

anemia (see Technical Note 5)—one in Israel and

one in Italy. The propriety of the experiments was

widely questioned in the scientific literature

(Wade, 1980; Wade, 1981). Many scientists and

clinicians judged the human experiments premature (Fletcher, 1982a, 1982b; Anderson, 1982)

and pointed out that Dr. Cline did not even follow the protocol that had been approved by the

foreign human subjects review boards. He also

failed to wait for approval by such committees

in the United States (Talbot, 1982). Professor Cline

was penalized by the National Institutes of Health

by termination of two grants, and he resigned

chairmanship of his division at the University of

California (Sun, 1981, 1982; Talbot, 1982). (Dr.

Cline’s experiments and the dispute over their

propriety are described in greater detail below.)

The history of human gene therapy thus did not

have an auspicious start, although many scientists and clinicians would not consider Dr. Cline’s

experiments bona fide attempts at human gene

therapy.

Concern among religious leaders

Increasing commercial interest, progressive

movement of the technology into the relatively

unregulated private sector, possible premature

applications to humans, and impressive technical

improvements all attracted attention to molecular

genetics in the early 1980s. The general secretaries of three large religious bodies—the U.S.

Catholic Conference, the Synagogue Council of

America, and the National Council of Churches—

sent a letter to President Carter in 1980 in which

they expressed concern that prowess might surpass prudence in the human application of genetic

technologies. They noted that we had entered an

“era of fundamental danger triggered by the rapid

growth of genetic engineering)” and appealed to

the President to look into how molecular genetics

might be applied to humans (President’s Commission, 1982, pp. 95-96). The letter noted that there

was no governmental agency or committee investigating the ethical, social, and religious questions raised by the new technologies. Such questions included concern for fair distribution of

risks and benefits, control of genetic experimentation, and long-term consequences of genetic interventions.

The President’s Commission for the Study of

Ethical Problems in Medicine and Biomedical and

Behavioral Research (hereafter called the “President’s Commission”) responded by investigating

some uses of recombinant DNA in humans. The

Commission’s inquiry resulted in publication of

Splicing Life in November of 1982 (President’s

Commission, 1982). In that same month, the Subcommittee on Investigations and Oversight of the

Committee on Science and Technology, U.S.

House of Representatives, held hearings for 3 days

entitled Human Genetic Engineering.

A resolution signed by 56 religious leaders and

8 scientists and ethicists rekindled interest in

human genetics when it was sent to Congress in

June of 1983 and introduced by Senator Mark O.

Hatfield (Congressional Record, June 10, 1983, S

8202-8205). The resolution urged that ‘(efforts to

engineer specific genetic traits into the germ line

of the human species should not be attempted”

(reprinted in: Foundation on Economic Trends,

1984). The signatories of the resolution came from
OTA involvement and review process 5

a broad spectrum of political and religious viewpoints, including diverse Protestant, Roman Catholic, and Jewish representatives (signatories and

resolution printed in: Recombinant DNA Advisory

Committee, 1984). The resolution was accompanied by a discussion paper by Jeremy Rifkin,

author of Algeny and head of the Foundation on

Economic Trends, although the discussion paper

was not endorsed by all signatories of the resolution (Nelson, 1984a; McCormick, 1984; Dorfman,

1983). The discussion paper warned of many potential abuses of intervening in human genetics

(Foundation on Economic Trends, 1984; Recombinant DNA Advisory Committee, 1984). Delivery

of the resolution, and the involvement of Rifkin

and many of the signers attracted media attention, once again verifying the existence of public

and religious apprehensions about the rapid advances of genetic technologies (Harden, 1984).

Discussions following release of the resolution

have failed to demonstrate a consensus, even

among the signatories, but the document did generate the wide public discussion sought by many

who signed it (Nelson, 1984a; McCormick, 1984).

OTA involvement and review process

OTA convened a workshop in September 1984,

where potential consumers and experts in ethics,

medicine, and genetics convened to discuss the

technical feasibility and diverse implications of

human gene therapy. The panel for the workshop

and other workshop participants reviewed material prepared by OTA staff and contractors. Several drafts of the background paper were widely

circulated for external criticism before and after

the workshop, resulting in review by more than

70 ethicists, scientists, religious and civic leaders,

and other concerned parties. Drafts were also distributed for review at the National Institutes of

Health, the Food and Drug Administration, to all

members of the Working Group on Human Gene

Therapy of the Recombinant DNA Advisory Committee of the National Institutes of Health, and to

other government agencies.

Types of gene therapy

Human gene therapy encompasses a broad

range of technologies and may eventually be applied to a diverse group of genetic diseases. This

variety requires that several distinctions be kept

in mind when discussing the technology.

Different mechanisms of gene therapy

Gene therapy refers to the insertion of genetic

material to correct a defect. Gene therapy can

take several forms:

gene insertion, in which a new version of a

gene is introduced into a cell;

gene modification, in which a gene already

in place is altered; and

gene surgery, in which a particular gene is

excised and may also be replaced by its normal counterpart.

Such genetic alterations would involve insertion

of new material that directly codes for proteins

or that affects how existing genes are expressed

by suppressing or enhancing production of particular proteins.

Current prospects for human gene therapy do

not include either gene modification or gene surgery (Anderson, 1984) because these are more

complex than merely adding new genes to cells,

Such complicated manipulations can now be performed, however, in some viruses, yeast, and bacteria, and the necessary technologies may later

be discovered that would permit gene surgery or

controlled genetic modification in animals and

humans. Through the remainder of this background paper, gene therapy will refer to gene insertion, because this is the form likely to be applied first. The distinction is technically relevant,
—— —

6 . Human Gene Therapy—Background Paper

Gene Insertion

Another chromosome

or another part of

the same chromosome

Chromosome containing abnormal gene \

,- Viral sequences .6,1.

or attached DNA

Insufficient production of Increased production

protein or production of of protein or

abnormal protein production of normal

protein

SOURCE: Office of Technology Assessment.

but does not significantly affect the discussion of

public policy implications that will be addressed

because gene modification and gene surgery do

not raise moral or medical issues distinct from

those raised by gene insertion.

Somatic versus germ line gene therapy

Gene therapy might be performed in either

germ cells (sperm, egg cells, or the cells that give

rise to them) or in somatic cells (cells that comprise all other body tissues). Alterations in somatic

cells do not result in inheritance of the alteration,

while modification of germ cells results in changes

that could be passed on to subsequent generations

if the recipient patient were to have children.

Genes are comprised of deoxyribonucleic acid

(DNA). DNA, in turn, is composed of long chains

of molecules called nucleotides. All the genetic information that is inherited by a cell is encoded

by the sequence of nucleotides in its DNA (see

Technical Notes). DNA ultimately controls formation of all of the substances that comprise and

regulate the cell. Certain sequences of DNA contain information for specific proteins such as enzymes, hemoglobin (the oxygen-containing protein in red blood cells), or the variety of receptors

on the cell’s surface. Stretches of DNA that contain the information for a specific product are

called genes. The DNA of the gene would not be

different for somatic versus germ line therapy,

although there might be different sequences

added adjacent to the gene depending on how the

gene would be regulated in a particular experiment or treatment. The difference between

somatic and germ line therapy is which type of

cell is treated with DNA.

Somatic cell gene therapy is illustrated by following how physicians might attempt to correct

the genetic defects that cause ADA or PNP enzyme deficiencies. ADA deficiency is caused by

absence or inactivity of the enzyme adenosine

deaminase. PNP deficiency is a different disorder

with some clinical similarities, It is caused by

absence or inactivity of the purine nucleoside

phosphorylase enzyme. In ADA deficiency, the

DNA in the adenosine deaminase gene is abnormal, and for PNP deficiency, there is a corresponding defective PNP gene. The genetic defect

is due to an incorrect DNA sequence caused by

a mutation. The mutation could be in the form

of errant replacement of one nucleotide by

another or loss (or addition) of one or more nucleotides somewhere in the sequence. The altered

sequence encodes an abnormal enzyme that does

not function, or causes insufficient production of

the normal protein.

Because there is either not enough enzyme, or

it is present in a dysfunctional form, the chemical reactions mediated by ADA or PNP do not take

place normally in the cell. This leads to accumulation of some chemicals that would normally be

destroyed by ADA or PNP, and a paucity of those

chemicals the enzymes are responsible for making. In the case of both ADA and PNP deficiencies, it appears that toxic chemicals accumulate

that inhibit the action of cells that are involved

in body defences.

The diseases are inherited as recessive genetic

traits (the two diseases caused by the different

enzyme deficiencies are slightly different, but not

in a sense that is relevant here), and are usually

fatal before age 2 if not treated (Kredich, 1983).
OTA involvement and review process 7

Severe immune deficiencies can be treated by

bone marrow transplant (Friedrich, 1984), but not

all patients are eligible for transplant, and the procedure is quite risky and costly. ADA or PNP deficiency might be treated instead by somatic cell

gene therapy: removing an affected patient’s bone

marrow cells, inserting normal genes for the enzymes into them, and returning the treated cells

to the patient where they could grow and perhaps produce enough of the needed enzyme to

degrade the toxic chemicals, thus restoring immune function.

Although the details vary, most of the diseases

that might be approached by gene therapy conform to this model: they are genetic defects that

cause insufficient production of normal enzymes

or production of dysfunctional ones. Gene therapy attempts to restore enzyme function by inserting DNA to produce normal protein.

Rather than treating only bone marrow or

other somatic cells, germ cells or cells of an early

embryo might be treated to correct a genetic defect. Such germ line treatment would affect all

cells in the body, including both somatic cells and

germ line cells. In the case of ADA or PNP deficiency, germ line therapy would likely be done

by inserting the correct genes into an affected embryo within hours of fertilization. This might lead

to presence of a normal ADA or PNP gene in all

cells, and expression of the normal gene with production of a normal enzyme in the tissues where

it would be needed to correct the immune deficiency.

In somatic cell therapy, treatment affects only

cells in the patients’ organs and would not be

passed on to children, while germ line correction

would produce genetic changes that could be

detected in all cells in the body and could be

passed on to children.

TREATMENT OF SOMATIC CELLS

Many of the ethical and religious reservations

expressed about human gene therapy refer only

to alterations that might affect the germ line to

produce inherited changes, In the opinion of several ethicists and religious thinkers, treatment of

somatic cells by genetic methods does not pose

ethical problems different in kind from those presented by other types of experimental therapy

such as new drugs or novel surgical techniques

(Fletcher, 1983a, 1983b; Siegel, 1982, 1983). The

questions that need to be addressed in assessing

the appropriateness of treating somatic cells

include:

What is the likely impact on people’s regard

for the sanctity of human life? (World Council

of Churches, 1983; National Council of

Churches, 1984).

What are the risks of inadvertently affecting

the germ line?

What are the precautions taken against deliberate misapplication?

What scientific data are available to suggest

that the treatment might work to the patient’s

benefit?

How serious is the disease? What are the

realistic possibilities of benefit to the patient?

What are the risks to the patient? What is

the prognosis if there is no treatment?

What are the alternative methods of treatment? Is gene therapy likely to be more effective, less costly, safer, or otherwise more

acceptable than available alternatives?

How safe is the procedure, based on the best

available evidence? What are the data on

short-term effects and long-term consequences?

Are patients or their surrogate decisionmakers properly informed about the risks

and benefits of the therapy?

Are the side effects of the treatment reversible or treatable in the patient and in the

population?

These concerns are analogous to those that

would be raised for any other new medical treatment. The likelihood of inadvertently affecting the

germ line, however, is of greater concern for gene

therapy than for most other treatments. The risk

of genetically altering the germ line is not unique

to gene therapy because several other medical

practices —such as vaccination, cancer chemotherapy and radiation therapy—also carry this

risk (see “Safety” below).

A concern for deliberate misapplication of gene

therapy derives, in part, from a historic association between eugenics and oppressive political

movements (see below). Genetic “purity” or preservation of “superior” characteristics by genetic
8 Human Gene Therapy—Background Paper

means has been advocated by several political and

scientific groups in the past (Kevles, 1984), and

some fear that gene therapy technology might become part of a coercive social program. The rationale for gene therapy as currently contemplated–insertion of single genes to correct severely

debilitating specific genetic diseases (Anderson,

1984)—is extremely remote from such eugenic

motivations.

The question regarding the sanctity of human

life is one that has been addressed by religious

thinkers and philosophers (Siegel, 1982, 1983;

President’s Commission, 1982). This concern for

human dignity underlies the great care with

which proposals to undertake human gene therapy are now being scrutinized. Such concern suggests that public education and discussion must

precede and attend clinical application (Working

Group on Human Gene Therapy, 1984; President’s

Commission, 1982; Capron, 1984a,b).

TREATMENT OF GERM CELLS

If ever applied to humans, germ line therapy

could be done in several ways. Such therapy could

be directed at sperm or ova, or cells that produce

them, before the germ cells join to produce a fertilized egg. It could also be targeted at the early

stages of development, currently practical only

if performed within hours after fertilization, days

before the embryo is implanted in the uterus.’

Human gene therapy affecting germ line cells

raises several concerns in addition to those listed

for somatic cell therapy. These have been noted

by religious and civic commentators (Foundation

on Economic Trends, 1984; National Council of

Churches, 1984; President’s Commission, 1982),

and include:

propagation of unpredictable effects (both

positive and negative) into future generations,

diminishing genetic diversity among human

populations, and

long-term effects of changing genetic characteristics in human populations.

The different social and ethical considerations

that arise from somatic versus germ cell manip-

%’or further details on stages of fertilization and human cie\wlopment, see Technical Notes.

ulations are elaborated further in the sections

below on medical and social aspects of gene

therapy.

COMPARISON OF SOMATIC AND

GERM CELL GENE THERAPY

There are several technical and practical advantages to performing gene therapy on somatic cells

as opposed to germ cells. The primary advantage

of somatic cell therapy is that it can be performed

on individuals at any stage of development, while

germ line therapy as currently envisioned would

have to be performed early in embryonic development. Experiments on somatic cells may be

done on samples or parts of organs, rather than

an entire organ, lowering the risks of failure because a failed experiment does not cause loss of

the organ. Experiments involving somatic cells

may also be repeated in the same individual if they

fail, and the reliability of the gene transfer procedure does not have to be as high. Somatic cell

gene therapy is also advantageous because it

directly benefits the person to whom it is administered, rather than a person (who cannot consent to therapy) who develops from a treated

embryo.

Despite these advantages of somatic therapy,

there are several disadvantages. Somatic cell therapy may not be applicable to some disorders that

affect multiple tissues, because cells of each organ

would have to be altered. It may also not be effective for those tissues composed of cells that

do not divide, such as brain and muscle (although

symptoms of some diseases of nerve and muscle

cells might be treated by gene therapy in other

kinds of cells that influence brain and muscular

function). Which diseases and which tissues might

prove refractory to gene therapy of somatic cells

will be determined only by further study of the

specific genetic diseases in question.

There is at least one potential advantage to

heritable correction of germ line cells. Once a defect were fixed, it would be less likely to plague

the direct descendants of the person who developed from the treated embryo. This would not

eliminate the risk, however, because new mutations causing the same disease could spontaneously arise.
OTA involvement and review process 9

TREATMENT OF SPERM, OVA, AND

CELLS THAT PRODUCE THEM

While germ line therapy, until now, has been

performed on early embryonic cells, it is theoretically possible to perform it by inserting new

genetic information into gametes (sperm, ova, or

the cells that produce them).

Sperm may be difficult to genetically alter, because they are small, difficult to penetrate by

physical or chemical manipulations, and would

have to be treated in vast numbers. Millions of

sperm are usually inseminated before fertilization, although only one actually fertilizes the egg;

every sperm would have to be treated if gene

therapy were to be assured. It would be technically easier to genetically alter sperm by treating

the cells that produce them because such cells are

larger and less difficult to manipulate. There are

several complications with this strategy, however,

including the necessity to use invasive procedures

to obtain testicular cells, unavailability of methods for artificially inducing maturation of sperm,

and uncertainty over whether genetic changes in

sperm precursors would lead to genetic correction in all sperm. Substantial technological advances would thus be required for reliable gene

therapy of sperm or their precursor cells.

In contrast, ova, or egg cells, might be altered

after they were extruded from the ovary, and

before fertilization. Egg cells are larger and more

easily manipulated than sperm, suggesting that

eggs might be easier candidates for gene insertion. Methods for obtaining human ova are now

routinely practiced for in vitro fertilization techniques, and many do not involve highly invasive

techniques (Andrews, 1984c). Manipulations of

egg cells and early embryos differ primarily in

that the eggs could be altered before fertilization,

eliminating some ethical concerns of those who

regard fertilization as the beginning of human life.

Unless the gene therapy technique were extremely

reliable, however, methods would have to be

found for confirming that the desired alterations

had actually occurred. This would involve sampling of embryonic or fetal tissue, and would thus

not avoid all of the ethical questions that beset

embryonic manipulations.

Gene therapy of gametes thus offers some advantages in restricted applications, but it would

affect the germ line, and would not avoid the ethical dilemma associated with heritability of genetic

changes. The technical prospects for such therapy, however, are less promising than treatment

of either early embryos or somatic cells. For both

technical and ethical reasons, therefore, gametic

gene therapy is not imminent.

IN VITRO VERSUS IN VIVO

Gene therapy can theoretically be performed

either on cells that have been removed from the

body (in vitro), or on cells that are in their usual

place in the body (in vivo). The first attempts at

human gene therapy will be performed on cells

that are removed from the body, genetically

altered in vitro, and restored to the patient, as

in the example of ADA or PNP deficiencies (Anderson, 1984). This procedure makes the chances of

altering the germ line of the patient quite low,

and also reduces the probability of unintentionally

affecting other tissues that need not be treated

(Working Group on Human Gene Therapy, 1984).

Several disorders in addition to ADA and PNP

deficiencies are currently under discussion for

somatic cell gene therapy. Citrullinemia is caused

by deficiency of the enzyme arginosuccinate synthetase involved in protein and amino acid metabolism and nitrogen excretion (Walser, 1983).

The gene has been isolated and cloned (Freytag,

1984), and citrullinemia is considered a promising candidate for early application of human gene

therapy. Ornithine carbamoyl transferase deficiency can be quite severe, and the gene that

codes for it has been cloned (Horwich, 1984), making it also a potential candidate for gene therapy.

Lesch-Nyhan disease is a rare genetic disorder.

It affects primarily boys who appear normal at

birth but soon show abnormal uncontrollable

movements. Abnormal behaviors of self-mutilation such as biting off fingers or otherwise inflicting painful injuries are part of the syndrome,

as well as aggression towards others. These

bizarre symptoms are extremely distressing to the

patient and his family. Lesch-Nyhan syndrome is

caused by complete deficiency of the enzyme

38-803 0 - 84 - 2 , QL 3
10 • Human Gene Therapy—Background Paper

hypoxanthine-guanine phosphoribosyl transferase (HPRT), the same enzyme that is partially deficient in gout (Wilson, 1984). The gene has been

cloned (Miller, 1984; Jolly, 1982; Yang, 1984), and

proposals for human experimentation on gene

therapy for Lesch-Nyhan syndrome have been

submitted to at least one local Institutional Review

Board (Baskin, 1984; Merz, 1984). Proposals to

begin human experiments on Lesch-Nyhan syndrome are expected to be referred soon to the

National Institutes of Health (Anderson, 1984;

Jenks, 1984; Merz, 1984).

It may be possible in the future to alter specific

tissues while they are still in the body. It would

be desirable, for example, to selectively alter

nerve cells to treat diseases caused by metabolic

disruption of brain cell function, or to correct

only liver cells in genetic diseases that primarily

affect proteins produced by the liver. The worst

behavioral symptoms of Lesch-Nyhan syndrome,

for example, presumably involve disruption of

normal neural processes, and it might prove necessary to directly treat nerve cells. While methods for specifically targeting particular cells for

directed gene therapy are theoretically possible,

they have not yet been developed. Several possible methods of delivering specific genes to targeted cells may be found in the future, however,

by use of tailored viruses or antibodies attached

to artificial membrane sacs that contain the appropriate genes (see Technical Note 2).

Stages of development of gene

therapy technology

If human gene therapy becomes a viable medical technology, its development will fall into several stages.

Feasibility testing, involves animal studies and

in vitro experiments on human cells, but not

with patients.

Early clinical research involves a few human

patients with rare and severe diseases for

whom other treatment alternatives are too

risky, inapplicable, or less likely to be beneficial.

Clinical testing will occur only if a potential

for success has been demonstrated in early

clinical research and feasibility testing. Clinical testing might involve a wider range of

diseases and larger number of patients than

early clinical research if experience with

more severe diseases is fruitful. The final

stage would be

Standard medical practice in those specific

instances where gene therapy has been

shown safe and efficacious for a particular

disease or type of patient. Issues of fair access to the technology, methods of paying for

it, and proper quality assurance would

emerge as the technology made the transition to this final stage.

Somatic cell therapy is now in the first stage,

verging on the second. Germ line gene therapy

has not even undergone feasibility testing in a

form that might be applied to humans. Gene therapy for different disorders or specific kinds of

patients will beat different stages of development;

only a few diseases are now being tested for feasibility of somatic cell therapy (Working Group

on Human Gene Therapy, 1984; Anderson, 1984).
Techniques of Gene Therapy Ž 11

Techniques of gene therapy

Gene therapy involves isolating a gene, putting

it into cells where it will be used, and ensuring

that the inserted gene functions in the new cells

in a way that does not harm the patient.

Genes are copied and passed on

by DNA replication

Genetic information is transmitted from one cell

to its progeny by duplication, or replication, of

its DNA. When a cell divides, it copies its DNA

and distributes a copy to each of two offspring

cells. A new therapeutic gene introduced into a

cell in the laboratory can thus be reproduced

through the process of cell division when the cell

is placed into a patient and proliferates.

Many breakthroughs in molecular genetics have

come from discoveries about how DNA replicates,

how it can be specifically cut and reassembled,

and how to re-introduce the altered DNA back

into cells in such a way that its expression, or

translation into protein, can be controlled (Judson, 1980). Many of the techniques for splicing

and controlling the expression of genes were first

discovered between 1970 and 1974, using some

of the same techniques that led to the development of recombinant DNA (Watson, 1984).

Isolation and cloning of the

normal gene

The usual first step in approaching gene therapy is identification of the abnormal gene. (This

step can be skipped when the corresponding normal genes are already available, as was the case

for sickle cell disease.) Once the abnormal gene

has been found, then copies of the corresponding

normal gene must be isolated and copied. There

are several ways to identify abnormal genes.

These involve analysis of patterns of inheritance

of a disease, study of the metabolism of patients

who have the disease, and analysis of the genes

of those who have the disease, Identification of

the gene that causes a particular disease requires

hundreds of experiments, luck, and extensive resort to recombinant DNA technology.

Once the gene that causes a disease has been

identified, the corresponding normal gene must

be isolated, unless it is already available because

it has been studied for some other purpose. Using

an abnormal gene to find its normal counterpart

is usually done by exploiting the extensive similarity between the sequences of the normal and

defective genes; they rarely differ greatly in overall sequence (although the functional results are

quite different, or there would be no disease).

After the normal gene has been identified and

isolated, then it must be copied. The process of

making multiple copies of a single gene is called

cloning.7 Cloning involves combining the gene of

interest with DNA sequences that allow it to be

copied in lower organisms—usually bacteria or

yeasts. The DNA containing the gene of interest

is then inserted into bacteria or yeast (or, more

recently, into some types of mammalian cells

growing in culture). The DNA is copied as the cells

proliferate. The numerous copies of DNA are then

purified from other cell components, and the gene

of interest can be cut away from unwanted DNA

sequences, One now has millions or billions of

copies of a single gene.

These copies are then combined with DNA that

is suitable for insertion into human cells.

Insertion into human cells

The DNA that contains the normal gene can be

administered to human cells in several ways:

using viruses, physically injecting it, treating the

DNA chemically so that cells take it up, treating

the cells so that they are induced to take in the

DNA, or by fusing the cells with membranes that

T’r)r details of cloning, see the ‘1’echnica] Notes. (honing a gene

should not be umfused with cloning an organism, ‘1’}le term “cloning” refers to reproduction mrithout mating: in the case of a g[>nc

or DNA sequence, this merely means making copies of the relrwant

stretch of DNA. Cloning a whole organism, in contrast, in~’ol~ws cop)ring all of a cell’s DNA so that a completely new organism that

shares all its genes with the original is produced. The techniques

tor (loning grnes are completely’ different frum those for cloning

organisms. Cloning an indliidual human Jt’ouki not help in thr pre-

! ent ion of genet i(’ disease, and is not d irerth’ related to the (lues -

tions raised b~r human gent’ therap~
12 Human Gene Therapy—Background Paper

contain the DNA. In the distant future, designed

viruses or genetic elements may be used to transfer genes to specifically targeted human cells. At

present, however, more primitive methods are used.

VIRUSES

Viruses are small packages of genetic information in the form of DNA or RNA that enter cells

and either insert their information into that of

the infected cell or duplicate themselves using the

cell’s biochemical machinery. Viruses are usually

covered with a coat of protein or membrane, but

their most distinguishing characteristic is the

genetic information that they contain. Some

viruses promise to be practical for gene transfer

because they are relatively simple and controllable, and contain sequences that permit insertion

of genes into the host’s DNA. Modified viruses are

the most likely candidates for gene therapy in the

long run, because they are highly efficient, can

affect many cells, and are relatively easy to manipulate in the laboratory (Rawls, 1984).

Several scientists are developing viruses that

would not injure cells, would not propagate uncontrollably, and would enter only target cells

(Anderson, 1984). Such viruses have been successfully used to insert new genes into bloodforming cells of mice with relatively high efficiency (A. D. Miller, 1984; Williams, 1984). At

some point, scientists may be able to design a

virus that could be used for cloning as well as delivery, saving yet more steps.

MICROINJECTION

Microinjection of DNA involves putting the DNA

one wants to insert into a solution that can be

pushed directly into individual cells through extremely small needles made of glass. The technique is highly reliable, in that a high proportion

of cells that receive genes express them (Capecchi, 1981), but limited by the number of cells that

can be directly injected. Investigators can inject

hundreds or thousands of cells, at most, for a

given experiment, compared to billions that can

be treated using viruses or chemical treatments.

Microinjection has been the method of choice for

experiments involving gene transfer in mice, because of its reliability, but its applicability to

humans is questionable because it is not completely reliable, and often results in cell death (an

alternative that is ethically unacceptable for

human experiments) (Anderson, 1984).

CHEMICAL AND PHYSICAL METHODS

Some early experiments in gene transfer employed mixing DNA with chemicals and subsequently applying the DNA to a large number of

cells. Most cells would pick up the DNA, and some

would insert it into their own DNA, and, in some

cases, express it. The usual chemical treatment

employed calcium phosphate with relatively large

amounts of the desired DNA. The most common

physical method involved “electroporation”) in

which electrical treatment of the cells induced uptake of DNA and other constituents from the

fluids bathing the cells.

Chemical and physical treatments have the

advantage of not requiring a vector to cause insertion, but have two major disadvantages. First,

the DNA is only stably incorporated into a small

proportion of cells, usually only one in ten thousand to one in a million. (This small proportion

nevertheless usually represents hundreds or

thousands of times more cells than could be directly injected.) This feature requires that cells

that take up and incorporate the desired DNA

must somehow be separated from cells that do

not, and there must be a very large number of

cells to treat in the first place. Second, the DNA

usually inserts at random into the cell’s genome,

and often in multiple copies. DATA insertion following chemical and physical insertion methods

is thus relatively uncontrolled and unpredictable

(Anderson, 1984).

MEMBRANE FUSION

The final way to get DNA into cells involves putting it inside of membranes that can then be fused

with the outer membrane of target cells, allowing the contents to spill into the cells. The membrane sacs, called liposomes, can be made of artificially constructed lipid mixtures or derived

from specially treated cells such as red blood cells

or bacteria. The advantage of cell fusion is that

it is relatively simple, and large numbers of cells

can be treated. It is, like chemical treatment,

unreliable and nonspecific at delivery. The technique might prove useful in the future, however,

if membranes are constructed that target specific

cells with highly reliable delivery.
Background on Genetic Diseases 13

Background on genetic diseases

Chromosomes and inheritance

Higher organisms package their DNA into segments called chromosomes. Each chromosome is

composed of one very long stretch of DNA that

is bound to various proteins and other molecules.

There are two copies of each of 22 chromosomes

in the cells of a human. In addition, there are two

sex chromosomes. Females have two ‘(X” chromosomes and males have one “X” and one “Y. ” In normal human cells, therefore, there are 46 chromosomes: 2 sex chromosomes and 2 copies of each

of 22 other chromosomes (these non-sex chromosomes are called autosomes).

The 46 discrete aggregates of DNA and attached

protein that comprise the chromosomes are maintained inside the nucleus of somatic cells. In germ

cells, in contrast, a specialized phenomenon called

meiosis takes place. Cells divide so as to leave only

23 chromosomes in a sperm cell or ovum: one sex

chromosome (either an “X” or a “Y”) and one copy

of each of the autosomes. All ova contain an “X”

and 22 autosomes, because they derive from

female cells that contain two “X” chromosomes.

Sperm are divided into two groups; half have an

“X” and 22 autosomes and the other half have a

“Y” plus 22 autosomes.

During the process of fertilization, a sperm joins

with an ovum to restore the chromosome number to 46. If the sperm contains an “X” chromosome then a female is produced, and if it contains

a “Y” then a male results.

Single gene, multigene, and

environmentally modified traits

Diseases that might be treated by gene therapy

will, at least in the foreseeable future, be exclusively those caused by mutations in a single

gene. Such diseases are called single gene defects,

and contrast with diseases and traits influenced

by several genes or environmental factors. Genes

can cause disease through several mechanisms.

Most human diseases have a genetic component

inherited by the individual and an environmental

component that comes from outside the individual. The relative importance of genetic and environmental influences varies in both patients and

diseases. Some medical conditions, such as automobile accidents or war wounds, may have large

environmental and very small genetic contributions. Most diseases have a mixture of genetic and

environmental contributions (Harsanyi, 1981). In

several disorders, such as Huntington or TaySachs diseases, the influence of a single gene is

so large that the disorders are called genetic

diseases.

SINGLE GENE TRAITS, OR MENDELIAN TRAITS

When traits or diseases are primarily determined by a single gene, they obey the relatively

simple laws of inheritance first specified by

Gregor Mendel, a monk who lived in the last century and whose interests in agriculture led him

to discover several genetic phenomena in plants.

The same patterns of inheritance that Mendel first

described in plants, noted below, are also found

in several human diseases, and thus indicate that

the cause of the disease is genetic.

At the turn of the century, a British physician

and scientist, Archibald Garrod, first introduced

the idea that some diseases that followed definite

inheritance patterns might be caused by “inborn

errors of metabolism” (Stanbury, 1983; Kevles,

1984). He postulated that some diseases were due

to biochemical errors. He further speculated that

such biochemical defects might be caused by

genetic abnormalities that obey Mendel’s laws.

Several decades later, biochemical errors were,

for first time, traced to specific enzymes. These

discoveries confirmed Garrod’s hypothesis. Other

diseases were traced to molecular defects in nonenzyme proteins; the first “molecular disease” described was sickle cell anemia, in which an abnormal hemoglobin protein was found (Pauling,

1949). Research over the past three decades has

revealed more and more genetic diseases, and

greater understanding of many of them.

Many genetic diseases are due to changes in just

a single gene, such as ADA and PNP deficiencies.

More than two hundred specific enzyme defects
14 • Human Gene Therapy—Background Paper

cause known human clinical syndromes, and over

a hundred other genetic diseases have been biochemically characterized (Stanbury, 1983). Prominent disorders such as sickle cell anemia, familial

hypercholesterolemia, polycystic kidney disease,

Huntington disease, neurofibromatosis, Duchenne

muscular dystrophy, cystic fibrosis, achondroplasia, hemophilia, and many others are examples

of single gene disorders. Many common adult

disorders, usually excluded from pediatric statistics on genetic disease prevalence, such as Alzheimer disease and hemochromatosis, have forms

strongly influenced by genetics (Breitner, 1984;

Cook, 1979, 1981; Folstein, 1981; Cartwright,

1978, Dadone, 1982; Skolnick, 1982; Kravitz, 1979).

Single gene defects affect 1 to 2 percent of newborns (Lubs, 1977), and addition of adult genetic

diseases would significantly increase the estimated prevalence and cost of genetic disease.

Even diseases or traits that are due to a single

gene vary widely in severity, depending on environmental factors and other genes; the extent to

which patients have signs and symptoms of a

genetic disease is called “expressivity.” Diseases

can also be variably expressed in populations,

affecting some people and not others who carry

the gene. This is described as “penetrance.” Complete penetrance indicates that all who have the

defective gene also have the disease, while incomplete penetrance means that some people

have the gene but not the disease.

Single gene traits can be classified by how they

are inherited. They can be recessive, dominant,

or X-linked.

Recessive Disorders.--Recessive diseases occur

when one receives a defective gene from both

parents (see diagram). Diseases due to dysfunctional gene pairs are usually due to protein abnormalities that cause a biochemical imbalance.

Sickle cell disease and thalassemia affect globin,

the protein part of hemoglobin, which transports

oxygen through the blood to body tissues. Other

recessive disorders, such as Tay-Sachs disease,

ADA and PNP deficiencies, and phenylketonuria

(PKU), affect enzymes whose absence or dysfunction adversely affects cellular metabolism. Most

of the relatively well understood genetic diseases

are recessive disorders that can be traced to speRecessive Inheritance

Father Mother

Non-carrier Carrier Child

2 5 % 5 0 % with

disease

25%

Chromosome with normal gene

Chromosome with defective gene

SOURCE: Office of Technology Assessment.

cific defects in enzymes. However, the specific

molecular defect underlying many recessive diseases, including at least one common one-cystic

fibrosis—is not known,

Dominant Disorders.--Dominant disorders occur when offspring receive a defective gene from

either parent, and having just one such gene leads

to expression of the disease (see diagram). In some

cases the defect is known, such as some types of

porphyria, in which enzyme deficiencies lead to

abnormal disruption of biochemical pathways

that produce and degrade heme—the non-protein

part of hemoglobin found in red blood cells. In

most dominant disorders, however, the biochemical nature of the derangement is not known; the

molecular defect in dominant disorders is, in general, less well established than for recessive ones.

X= Linked Disorders.—X-linked disorders are

carried on the “X” chromosome. X-linked diseases

usually affect boys because males have only one

copy of the “X” chromosome: there is no set of

genes on a second “X” chromosome to balance the

effects of a defective copy of the gene. The inheritance pattern of X-linked disorders is distinc-
Background on Genetic Diseases . 15

Dominant Inheritance

Affected parent Unaffected parent

Unaffected Affected

chiId child

50% 50% 

Chromosome with normal gene

Chromosome with defective gene

SOURCE Off Ice of Technology Assessment.

X-Linked Inheritance

Mother Father

(carrier) (unaffected)

Non-carrier Carrier Affected Unaffected

daughter daughter son son

NOTE: x—Normal chromosome.

@ –Chromosome with abnormal gene.

SOURCE” Off Ice of Technology Assessment

tive: sons inherit the traits only from their mothers,

because a son always derives his “X” from his

mother and his “Y” from his father. Daughters

can get a defective gene from either parent, but

do not usually have the disease unless they get

the abnormal gene from both parents. X-linked

traits thus act like dominant traits inherited only

from the mother in boys, and are usually recessive in girls. Examples of X-linked disease traits

are hemophilia, Duchenne muscular dystrophy,

and Lesch-Nyhan syndrome.

There are apparently few traits, and no known

diseases, that are carried in genes located on the

“Y” chromosome, and expressed only in males.

Single gene defects are, in general, the best understood of genetic diseases; the early instances

of human gene therapy will be done to correct

the effects of single mutant genes.

MULTIGENE TRAITS

There are certain body characteristics and

other traits that accrue from the interactions of

several genes. Eye and hair color, for example,

are traits that are specified by genes, but do not

obey simple Mendelian patterns of inheritance because many genes are involved. Similarly, there

are genetic diseases caused by interactions of

multiple genes that are minimally affected by environmental influences. Such disorders are termed

polygenic or multigenic.

ENVIRONMENTALLY MODIFIED TRAITS

The vast majority of characteristics that define

individuals are determined by a combination of

genetic predisposition and interaction with the

environment. Height, for example, though determined genetically to a significant extent, is also

influenced by nutrition and other factors. Likewise, many diseases derive from interactions of

genes and the environment in which both components contribute significantly to the disease

process.

The type of diabetes mellitus that occurs in

younger people, for example, is now believed to

be caused by a special susceptibility of insulinsecreting cells to certain viral infections or other

environmental insults. The clinical disorder is thus

caused by an environmental agent acting in concert with genetic characteristics. Most common

diseases, including cardiovascular diseases, cancer, and many drug reactions appear to involve

multiple genes as well as environmental influences.

Most complex human traits, including physical

and intellectual capacities, are also multigenic and
16 Human Gene Therapy—Background Paper

environmentally influenced. The controversies

that have raged in the psychological literature

over the genetic and racial components of intelligence center on the relative importance of

genetic and environmental contributions, including nutrition, health care, cultural background,

and socioeconomic status. There is little doubt

that genetics and environment interact, but there

is vigorous contention about which factor predominates and how public policy should respond

to differences in complex traits such as intelligence,

Genetic treatment versus eugenics

Eugenics is the term applied to “the ‘science’ of

improving human stock by giving ‘the more suitable races or strains of blood a better chance of

prevailing speedily over the less suitable’ “ (Kevles,

1984, quoting Francis Galton). The eugenics movement is noted for promulgating social programs

intended to enhance desired human traits, such

as intelligence and physical strength, and to eliminate undesirable traits, such as “feeblemindedness)” criminality, and disease.

Eugenic social movements date back to the last

century, and the intellectual history of eugenics

extends much further back in history (Kevles,

1984). Deliberate eugenic interventions have been

decried several times in the 20th century. Eugenic

movements were popular throughout Europe and

the United States early in this century, and were

most overtly expressed by the National Socialist

(Nazi) Party in Germany before and during World

War II.

Federal legislation to restrict immigration passed

between World Wars I and II was based, in part,

on eugenic principles, and mandatory sterilization laws also supported by eugenicists still exist

in several States (Kevles, 1984; Reilly, 1977) and

are occasionally used (Bowman, 1984). Many

prominent geneticists were involved in the American eugenics movement in the early part of this

century (Kevles, 1984), and participated as “experts” in preparing legislation or otherwise promulgating social reform congruent with eugenic

aspirations.

Germs of eugenic thought persist in contemporary society, notably in regard to controversies about genetics and intelligence (Lewontin,

1984), and some fear that the technical advances

of molecular genetics may lend themselves to

abuse (Grobstein, 1984; Reilly, 1977). This is not

a criticism of the technology per se, but rather

a concern about its potential misapplication or affiliation with forms of social coercion (Powledge,

1984).

The distinction between gene therapy and

eugenics rests on several different points. Gene

therapy involves the informed participation of patients who suffer from a specific disease, while

eugenics involves social programs, sometimes involuntary ones, focused on general human traits.

Gene therapy is intended to benefit a particular

individual, while eugenics is intended to improve

the human general (or, often, national) population. Gene therapy is directed at correction of

symptoms due to genes known to cause disease,

while eugenics often dwells on polygenic traits

whose genetic components are controversial, and

whose expression is poorly understood.

Medical, scientific, technical, ethical, religious,

and social commentators have noted the difference between therapy for a specific genetic disease and interventions intended to enhance traits

such as intelligence and physical appearance

(Siegel, 1982,1983; Fletcher, 1983b; Friedmann,

1983). Genetic correction of specific diseases, if

it does not affect the germ line, is analogous to

other medical procedures that involve risk assessment by the patient and attending health professionals.

There is not a complete dichotomy, however,

between the correction of specific diseases and

eugenics based on social preferences for certain

traits. This is relevant in considering gene therapy because it vitiates any sharp distinction between correction of a specific genetic defect,

which might be treated by gene therapy, and

affecting a mildly undesirable trait, for which

gene therapy might be controversial. A genetic

condition might be considered serious by one person, and not by someone else. Baldness or brown

eyes, for example, might be considered treatable
Medical Aspects of Gene Therapy . 17

genetic defects by one family, and would scarcely

be noticed by another.

The distinction between individual decisions in

favor of gene therapy and social programs advocated by eugenicists can also blur if gene therapy becomes commonplace. Many individual decisions can culminate in wide social effects. The

social impact of gene therapy depends on how

often it is used, who has access to it, which conditions are treated, and what public policies are

erected to foster or inhibit it. As long as gene therapy is restricted to rare recessive disorders, it will

likely have minimal social risk and large benefits

to individual patients.

Application of gene therapy to enhance traits

such as intelligence or physical strength cannot

now be done because so little is known about the

genetic influence on such traits. Most traits that

some individuals might consider desirable to

amplify will likely prove to be polygenic or environmentally influenced, and thus technically approachable by gene therapy only in the distant

future, if ever. There is no guarantee, however,

that it will always be impossible to use the techniques developed for gene therapy to improve

socially esteemed mental or physical traits in at

least some patients. If desirable traits can be modified by methods developed for gene therapy,

then public policy for such applications may well

prove analogous to those now employed for cosmetic surgery. Cosmetic surgery is not generally

reimbursed as part of government or private

health insurance, but is usually paid directly by

individuals. Cosmetic surgery has not generated

major public policy dilemmas, although controversy might arise in gene therapy if parents were

attempting to secure “cosmetic” gene therapy on

behalf of an unborn

authorize germ line

reversible in future

infant or young child, or to

changes that would not be

generations.

Medical aspects of gene therapy

Early clinical experiments in human gene therapy will be performed on somatic cells of patients to attempt partial correction of life-threatening diseases. They will be performed to allay

the signs and symptoms caused by a defect in a

single gene whose normal counterpart has been

cloned, and whose correction does not require

careful control of expression. Gene therapy will

be considered when there is no preferable alternative treatment available to the individual patient. This prediction is based on analysis of several factors described below, and underlies the

analysis throughout this section. Predictions about

human gene therapy are based, in part, on results

of animal experiments. A short review of such

animal experiments is followed by a discussion

of relevant clinical considerations in humans. The

medical aspects of gene therapy include reasons

that genetic diseases can never be completely

eliminated from the population, why certain types

of genetic diseases are not good candidates for

gene therapy, why germ line therapy may never

be necessary or its use extremely restricted, and

which disorders might be approached using gene

therapy in the near future. The analysis is restricted to the early applications of human gene

therapy because technical predictions beyond this

time horizon are perilous, and because decisions

confronting Federal policymakers in the next few

years will be focused on early applications.

Genetic corrections of animals and

other organisms

Gene therapy is contemplated in humans only

because it has been performed in animals and

lower organisms. One of the most successful attempts to genetically alter organisms involved the

“cure” of a genetic defect in fruit flies (Spradling,

1983). Some fruit flies have an enzyme defect that

results in their having rose colored eyes. Scientists were able to correct this abnormality by delivering the correct gene into fly cells by using

DNA molecules specific to fruit flies that can carry

foreign DNA into the fly’s own DNA. The treated

flies that took up the normal gene transmitted the
—

18 • Human Gene Therapy—Background Paper

genes to their progeny, who showed normal eye

color.

Gene transfer experiments have also been done

in mice. Several traits have been artificially added

to mouse cells early in embryonic development.

In experiments involving transfer of rat growth

hormone to mice, the mice that develop from the

altered embryos express the foreign genes, although not in a way that is controlled like the normal gene would be. Scientists have had to use

special techniques to get mammalian cells to incorporate new genes, and the genes are inserted

into chromosomal or cellular locations that cannot be predicted or controlled. Examples of genes

that have been transmitted to progeny in mice

include the gene for rabbit hemoglobin, rat

growth hormone, and a DNA fragment with both

specific enzyme activity and antibiotic resistance

to neomycin (Palmiter, et al., 1982; Palmiter, et

al., 1983; Brinster, 1983; Wagner, et al., 1981;

Williams, et al., 1984).

The growth hormone experiment was especially interesting because expression of the gene

could be manipulated by the scientists, and this

feature was inherited by progeny of the treated

mice. Other transferred genes have also been

passed to the progeny, although genetic manipulations have occasionally resulted in undesired side

effects, such as sterility or induction of new mutations. These effects suggest that oversight committees will seek evidence that such side effects

are highly improbable when inspecting proposals

for experiments that involve human gene therapy (Working Group on Human Gene Therapy,

1984).

Most of the animal experiments noted above

resulted in germ line changes of the treated

mouse lines, The experiments were done to investigate animal development, rather than to pave

the way for human application of gene therapy.

More recent experiments have been done on somatic cells of animals, and are more directly

analogous to what would be done in early human

trials. Several groups of investigators have successfully inserted genes into the bone marrow

cells of mice, and have shown production of proteins from the inserted genes in cells that derive

from bone marrow cells (Kolata, 1984c; A. D. Miller,

1984; Williams, 1984; Anderson, 1984). These experiments used modified viruses as the gene

transfer agents in ways quite similar to those that

might be used in humans, although treatment of

the recipient mice was more drastic than may be

acceptable for humans, and data on long-term

risks (e. g., reversion to infectious virus type, induction of new mutations, predisposition to cancer, and integration into the germ line) were not

reported. The new studies show great promise,

and demonstration of technical feasibility should

encourage animal experiments to ascertain the

magnitude of the risks.

Other recent experiments demonstrate that

proper regulation of gene expression in the cells

of humans and other higher animals is more complex than in fruit flies and bacteria. Early attempts

at gene therapy in humans will probably, therefore, be conducted on diseases for which there

is reason to believe that precise regulation is unnecessary for therapeutic benefit, such as ADA

and PNP deficiencies. Early plans to apply gene

therapy to diseases in which regulation would be

important have been thwarted by the complexity of regulation, although such obstacles may

eventually be overcome. Hemoglobin disorders,

for example, will not be the first candidates for

human gene therapy because of the need for regulation of globin expression (Anderson, 1984).

Reasons genetic diseases cannot

be eliminated

There will always be patients who suffer from

genetic diseases. It will never be possible to eliminate even single gene defects, although the

prevalence of some disorders, especially some

dominant ones, could be significantly reduced.

New mutations causing genetic defects will always

occur, and so people will be born carrying such

mutations. Neither would it be possible to stop

the expression of recessive diseases by preventing those who carry one copy of any abnormal

gene from mating, because humans carry an estimated 5 to 10 recessive defects in their genome

on average, and so no one would be permitted

to mate.

It is already possible to prevent the birth of

children with some genetic disorders through
Medical Aspects of Gene Therapy 1 9

genetic counseling, prenatal diagnosis, and family

planning. The number of diseases for which this

is possible will grow as we learn more about

human genetics. It is unlikely, however, that current methods for preventing genetic disease will

prove practical for all, or even a large fraction

of couples in the near future. Most genetic disorders still cannot be detected prenatally, and

tests for carriers are available for even fewer diseases. Yet effective prevention requires such tests.

Furthermore, such tests must not only be available; they must also be used. Barriers to use include cost, complexity, and lack of public awareness. Given the large number of potential genetic

diseases, it is unlikely that any one screening test

will screen for all, or even most genetic diseases.

This means that for many disorders, couples will

only know that they are at risk after an affected

child has already been born. Thus, until the entire child-bearing population is screened for a

given defect, or prospective parents know of

special risks, even those diseases for which all the

relevant tests are available will persist.

It maybe useful to screen some populations for

some defects. Screening programs for Tay-Sachs

carriers among Jews of Eastern European descent, and for thalassemia among Mediterranean

populations have been successful in some instances. These successes cannot be generalized

to all genetic diseases, however, and are probably

relevant only to a few relatively common disorders.

Effective use of genetic screening and selective

testing presumes public awareness that such tests

are available and acceptable. Families must wish

to use the technologies and expect to benefit from

the information provided. This requires that there

be no stigma attached to carrying a potential

genetic defect and trust that genetic patient data

will be properly used. (Issues relating to control

of and proper access to genetic patient data are

discussed below, and in app. B.)

There are a few genetic diseases whose prevalence could be dramatically reduced. Huntington

disease is a dominant trait encoded in chromosome 4 that causes a debilitating brain disease that

usually becomes evident only in a patient’s 40s

or 50s (after reproductive decisions have been

made). All those who carry the gene for Huntington disease will develop the disease if they live

long enough. If carriers could be told whether

or not they had the gene before deciding to have

children, and if all those who carry the gene

decided not to have children, then the gene could

be eliminated in a single generation. This is true

of Huntington disease because it is almost always

inherited and only rarely due to a new mutation

(this is not true for many dominant disorders).

Elimination of the gene would, however, entail

large numbers of coordinated personal decisions.

Marjorie Guthrie, wife of the famous folk singer

Woody Guthrie who was afflicted with Huntington disease, posed a difficult question that

bears on any program to prevent the birth of

those with Huntington disease, “Does anyone

really think it would have been better for Woody

not to have come into the world-in spite of

everything?” (Cited in Rosenfeld, 1984). IS the dis-

.

ease so awful that the birth of potential Huntington patients should be prevented when they

would have several decades of relatively normal

life? This is just one of several difficult dilemmas

that emerge from advances in genetics related to

particular diseases. New genetic technologies for

determining the genetic makeup of humans may

provide the information about whether one is susceptible to Huntington diseases and other disorders, but cannot determine a moral choice that

involves social, religious, and personal values. In

the absence of compelling social justifications,

decisions are and should be left to individuals,

families, and health professionals in a particular

situation.

Even if all diagnostic tests are available, there

are families for whom the prospect of selective

abortion is unacceptable, or who choose not to

avail themselves of genetic testing technologies

for other ethical, religious, legal, social, or medical reasons. Such couples, while not at increased

risk of having children with genetic diseases, will

nevertheless inevitably bear some children with

genetic defects. The only way to avoid this would

‘A method of detecting Huntington disease hefore s~wlptoms

emerge, and men before hirth mav he ai,ailable within a decadt’-

a Whnique is alread~ a~ailahlr for ce]lain families (SW app A, it’ex -

Ier, 1984; Guse]la, 1%43: Rosenfeld, 198.$).
20 • Human Gene Therapy—Background Paper

be to circumscribe their liberty, making the judgment that the potential social benefit overrides

their autonomous right to choose what is best for

themselves and their families. The generally high

regard for personal autonomy in our society implies that such couples’ right to make reproductive decisions will be protected.9

Existence of new mutations, absence or unavailability of genetics tests, and freedom of choice

all suggest that genetic diseases will continue to

exist, and therapies for them in infants, children,

and adults will continue to be needed.

Types of Genetic Disease That Are

Poor Candidates for Gene Therapy Now

CHROMOSOMAL DISORDERS

In addition to genetic diseases that are caused

by mutation of single genes or small numbers of

genes, there are others caused by abnormal chromosomes. One group of genetic disorders is

defined by a surfeit or deficit of chromosomes

in cells of the affected individual: patients have

an abnormal number of chromosomes or parts

of chromosomes. The most common such disorder is Down syndrome, which affects one in

600 live-born infants. Chromosomal disorders

overall affect one in 200 newborns, and account

for half of all spontaneous abortions (Burrow and

Ferris, 1982).

Gene therapy for chromosomal disorders is not

scientifically possible now, even in experimental

animals. Chromosomal abnormalities involve the

improper placement, absence, or duplication of

fragments of chromosomes or entire chromosomes. Chromosomes typically contain hundreds

or thousands of genes, and there are no techniques presently available for inserting enough

DNA to correct such large defects in either somatic

or germ cells.

COMPLEX AND DOMINANT TRAITS

At present, there is a large technological gap

between those diseases for which gene therapy

is promising in the near term and those about

which so little is known that gene therapy cannot even be rationally contemplated,

‘L. Andrews, 1984d, citing Carey ~’. Population Sen’ices International/, 431 U.S. 678, 685 (1977).

Complex traits such as intelligence and physical stamina, are not sufficiently understood to

merit serious contemplation of any genetic intervention, and gene therapy could certainly not

be justified, both because such intervention might

not be considered ‘(therapy, ” and because there

is no gene whose insertion would likely be effective. Even if gene insertion could reliably alter

physical and mental abilities, many question

whether it would ever be used, because it would

have to be cheaper and more effective than other

techniques for altering human characteristics.

Genetic techniques would have to prove more effective or less costly than education, indoctrination, physical and mental training, and drugs.

Dominant traits, and poorly understood recessive diseases are also poor candidates for gene

therapy in the near future. Therapy of such

disorders will depend on the specific cause and

biochemical or metabolic manifestations of the

disorder. To date, no dominant disorder is sufficiently well understood to warrant an attempt at

gene therapy. 10 There are, however, a few dominant traits that could potentially be treated using

gene therapy. Gene therapy might eventually be

contemplated for those enzyme defects inherited

as dominant traits, and for diseases caused by

deletions of small amounts of DNA that could be

replaced (there is some evidence for such deletions in retinoblastoma and Wilm’s tumor—

cancers usually developed in childhood that are

inherited as dominant traits). In such cases, the

decision to undertake somatic cell gene therapy

for the dominant disorder will not significantly

differ from consideration of recessive traits.

Nevertheless, few dominant disorders have been

characterized biochemically, and simple gene insertion may not correct many dominant disorders. Correction of dominant diseases may require insertion of extensive amounts of DNA, gene

surgery to remove the defective gene, or both;

techniques for these more complex manipulations

have not been demonstrated in mammals. Prospects for gene therapy of dominant disorders are

therefore, in general, poorer than for recessive

enzyme defects, although a few dominant diseases

might be addressed.

l~rhls genera ]lzatlOn does not app]}’ to traits that are dominant

in males and recessit’e in females (X-linked traits).
Medical Aspects of Gene Therapy Ž 21

Reasons Germ Line Therapy

May Be Unnecessary

Germ line gene therapy may never be widely

practiced because treatment of abnormal embryos and gametes offers little advantage over

selection of normal ones.

Germ line therapy, as currently practiced in

animals, involves taking embryos in vitro, genetically altering them, and returning them to a

female for further development. In early embryonic stages, only a few cells are present. To

determine whether the embryo is normal or abnormal would require that one have a test that

provided a diagnosis without disrupting the few

cells. No such tests exist at present.11 There are

prenatal diagnostic tests, but these are useful only

later in pregnancy, when many more cells can

be sampled to make a diagnosis without harming the fetus, 12

In order to practice gene therapy on an early

embryo, one would have to treat either all embryos or only ones known to have a treatable

genetic defect (Harsanyi, 1982; Pembrey, 1984).

Treatment of just those embryos carrying genes

for a particular disorder would require a way to

identify them. If methods to identify embryos carrying the abnormal gene were available, though,

it would be easier and safer to merely select a

normal embryo rather than treat an abnormal

one (Harsanyi, 1982). If all embryos are treated,

then a significant fraction of normal embryos

would be unnecessarily subjected to the added

risks of gene therapy manipulations, The ratio of

normal to abnormal embryos depends on the type

of genetic defect being treated. In the most common scenario, involving two parents who are

1 ITeChnlqUeS for separating animal embryos and gro~’ing identical twins from them have, however, been de~eloped (Nlaranto,

1984b). These same techniqes, if applicable to humans, might eventually be used to do diagnostic tests on celLs separated from the

embryo early in development. This would permit preimplantation

and later prenatal genetic screening, and might also allow monitoring

of the efficac~’ of gene therap~~ without harming the embryo or fetus.

This might, howe~er, be ethically unacceptable.

12There are monomic and technical reasons, however, to intensify the search for techniques to detect genetic defects in single or

small groups of cells in early embryonic development. Techniques

of in litro fertilization im’olve great economic cost and failures cause

severe emotional distress; in this setting, a premium is placed on

ensuring the normal status of embryos before the}’ are implanted.

known carriers of a recessive gene, only one in

4 embryos would develop the disease, and so one

unaffected and two asymptomatic carrier embryos would be treated for every one in which

the disease was prevented. If parents have dominant or X-linked traits, at most half those treated

would develop the disease. The situations described are those that would yield the highest

fractions of abnormal embryos; most other types

of traits would have even less favorable ratios of

affected to normal embryos.

Gene therapy on embryos is also made less

likely because of the need to ensure that it has

been successful. Unless gene therapy were almost

certain to work, parents might seek to determine

that the defect had been corrected, much as they

can now ask for prenatal diagnosis. Checking the

success of gene therapy would require either a

test for the embryo before it were reimplanted,

none of which exists, or availability of a test later

in pregnancy and before delivery. If such a test

were available, it could be used for conventional

prenatal diagnosis. Gene therapy of embryos

would thus not avoid the ethical dilemmas already

associated with conventional prenatal diagnosis,

and would offer little advantage over selection of

normal embryos or fetuses, while significantly increasing risks. For cases in which parents did not

wish to check on the success of gene therapy, because of religious convictions or because they

would not change their actions based on prenatal

tests, this argument would not apply.

There are certain situations in which germ line

gene therapy might be contemplated. For example, if a man and a woman both had PKU or sickle

cell disease and wished to have their own children, then the parents and physician would know

in advance that all embryos would acquire the

disease because of the parents’ genetic constitution. This situation would eliminate the risk of unnecessarily treating unaffected embryos, but

might still require a method for ensuring that the

gene therapy had been successful (although parents might choose not to test this because of personal or religious beliefs).

The strength of the arguments against germ line

gene therapy would also diminish if gene transfer techniques became extremely reliable. How-
22 . Human Gene Therapy—Background Paper

ever, this would require dramatic technical improvements in gene transfer and would not

eliminate the ethical dilemmas.

The medical complications of gene therapy suggest that germ line therapy on early embryos may

never be ethically acceptable, even if it becomes

technically feasible, except in extremely rare

matings between parents whose genotype for a

genetic disease is known. Uncertainty about possible effects of such therapy in future generations

may preclude application of germ line gene therapy for even these instances.

Criteria for Beginning Human

Gene Therapy

The decision to approve the application of gene

therapy to humans should depend on satisfaction

of several requirements. The requirements will

be based on analysis of risks and benefits for the

individual patient and consideration of the wider

implications of approving gene therapy for any

given patient. The factors considered in analyzing which applications of human gene therapy

might be approved will include potential effectiveness, safety, reliability, presence or absence

of alternative treatments, severity of symptoms,

and prognosis. Each of these will be considered

in relation to a particular genetic disease in an

individual patient. Some generalizations about

these factors, however, apply to the technique of

gene therapy as a whole.

SAFETY

Judgments of the safety of gene therapy will

be based on animal data and comparison to similar human interventions. For those few genetic

disorders, such as thalassemia, that have counterparts in animals, short term safety can be assessed

by experiments that measure clinical improvements in animals. For other diseases, it will be

necessary to base judgments of safety on animal

data obtained in experiments that involve gene

transfer, although clinical benefit in the animals

cannot be measured. Experiments might be performed, for example, using the same gene and

delivery system as would be used in humans, and

the animals observed to see if they express the

gene or develop side effects.

Questions of safety include not only short term

effects, but also long term consequences that may

require years to ascertain even in animals (if such

long-term risks can be assessed at all). Intergenerational effects would be especially difficult to

assess, but would be of concern only if germ line

cells were affected. Long-term studies of multiple generations of animals may also be required

when and if germ line therapy is ever anticipated.

Defects that could affect a patient’s progeny

would be a concern if germ cells were affected

by gene therapy. Protocols for human gene therapy of somatic cells will therefore be reviewed

for evidence that ensures that germ cells are not

affected (Working Group on Human Gene Therapy, 1984). The risk of germ line effects has precedent in cancer chemotherapy, radiation therapy,

and some types of vaccination. Each of these technologies has a risk of inducing new mutations in

the patient that could be passed onto the patient’s

progeny. If somatic cell gene therapy is done outside of the body, the risk of germ line effects is

likely to be extremely remote. If, however, experiments involve administration of gene therapy to

the whole patient, then germ line side effects will

be a concern, and such risks must be outweighed

by the severity of the disease or the magnitude

of potential benefit in the individual patient. In

the case of ADA or PNP deficiency, for example,

the length of the patient’s life would be less than

2 years and would be of low quality without gene

therapy. For such a patient, the risk of germ line

effects might be acceptable, particularly if such

effects could be detected and the patient’s reproductive decisions informed by this knowledge.

There are some special risks of using viruses

to transfer DNA, and assurances of the safety of

such transfer viruses will be prominent in approval of human experiments (Working Group on

Human Gene Therapy, 1984). The special risks

of viruses include the possibility of rearrangement

of genetic material in the host that would lead

to formation of an infectious agent. It is quite

probable that scientists will be able to design DNA
Medical Aspects of Gene Therapy 2 3

derived from viruses that cannot revert to its

more infectious form (Rawls, 1984; Anderson,

1984).

One special concern relates to the potential

mutagenicity and carcinogenicity of gene therapy

using techniques now available (Rawls, 1984;

Anderson, 1984). It is not yet possible to control

how and where inserted DNA integrates into that

of the host cell. Insertion of genetic material may

thus lead to new genetic mutations in the cells

so treated (Gordon, 1981). It has also raised the

prospect that inopportune insertion of new DNA

may rarely cause or predispose a patient to develop cancer. Recent evidence about cancer genes

suggests that certain cancers may be associated

with abnormal expression of genes that are present

in normal cells. Abnormal expression has been

induced by viruses similar to those that are being developed to facilitate gene transfer, and

cancer-like characteristics have been induced by

techniques that closely parallel other methods

that might be used for gene therapy (Hayward,

1981). The frequency with which gene transfer

results in deleterious mutation or predisposition

to cancer appears quite low, perhaps one in ten

thousand to one in a million, suggesting that risks

may well be less than for cancer therapy, immune

suppression, or radiation (Working Group on

Human Gene Therapy, 1984). Nevertheless, evidence for low risk of carcinogenesis will be explicitly sought in the approval process preceding

early clinical trials (Working Group on Human

Gene Therapy, 1984).

The short- and long-term risks of gene therapy

are not known. It is thus inappropriate to attempt

gene therapy except in the face of otherwise extremely poor prognosis until more is known about

the risks. Determination of safety will likely derive from observations of animal experiments and

the early instances of human gene therapy undertaken in patients with severe diseases—such as

ADA deficiency, PNP deficiency, urea cycle defects, or Lesch-Nyhan syndrome–that lack a

preferable alternative therapy in a given patient;

for such patients, even a low probability of benefit may outweigh the uncertainties and risks of

treatment. If animal experiments and early human

applications prove safe, diseases with somewhat

better prognoses

therapy.

might then be treated by gene

EFFICACY

Human gene therapy should not be approved

until there is evidence that it might work; codes

of research ethics require this. Commencement

of experimental human gene therapy will require

evidence from tissue culture and animal experiments. in the small number of diseases for which

there is an animal model, judgments of efficacy

can be based directly on clinical correction of animal diseases. In other diseases, constituting the

majority of genetic disorders, it will be necessary

to base judgments on studies in tissue culture,

related human diseases, and relevant animal

studies. Experiments might produce evidence, for

example, that the human gene were expressed

in treated animals or could be expressed in the

patients’ cells in vitro. The disorders in which

gene therapy might soon be attempted do not

have exact animal models, and so the earliest experimental human treatments may well be based

on tissue culture studies and indirect animal experiments.

Demonstration of efficacy will require evidence

that a gene can be delivered to a tissue where it

can be effective, that it will remain in cells long

enough to have an effect, and that the product

of the gene is sufficiently expressed. In some

future cases, these factors may require that the

transferred gene serve as a direct replacement

for the abnormal host gene, occupying the same

location in the same tissue. In other cases, including those for which gene therapy is being

seriously considered now, it may not be necessary to correct the defect so precisely.

In the case of ADA or PNP deficiency, for example, it may require only a little enzyme produced in bone marrow cells to sufficiently compensate for the biochemical defect. The absence

of animal models indicates that the only way to

test this is to do a human experiment. This is seriously considered for ADA or PNP deficiencies

only because the diseases are rapidly fatal and

there is, for most patients, no alternative therapy.

Evidence for potential patient benefit for these
24 . Human Gene Therapy—Background Paper

diseases may thus require only that the ADA or

PNP enzyme be detected in bone marrow cells

of the patient following gene transfer.

Genetic diseases that affect the brain constitute

a particularly large group of disorders for which

the question of organ specificity is crucial. There

are several dozen genetic diseases whose most

prominent symptoms are neurological, including

Tay-Sachs disease, metachromatic leukodystrophy

Lesch-Nyhan disease, and phenylketonuria (PKU).

The brain differs from other organs in two important respects. First, the nerve cells, whose impaired function gives rise to symptoms, do not

proliferate like bone marrow cells after they mature. This implies that genetic material introduced

into one nerve cell cannot be amplified by allowing that cell to reproduce for many generations.

Second, the brain has highly selective mechanisms

for transporting substances from the bloodstream

to brain tissues. Correction of biochemical defects

elsewhere in the body may therefore not correct

the defect in the brain, and may not eliminate

neurological or behavioral symptoms.

Doctors and scientists do not know which brain

defects can be corrected only in brain cells and

which might be treated by modifying other

tissues. Lesch-Nyhan disease is due to the absence

of HPRT enzyme in all cells. Its worst symptoms

are due to disruption of brain functions. There

is uncertainty about whether or not the disease

can be treated by correcting the biochemical abnormality in cells other than brain cells (e.g., bone

marrow cells) (Anderson, 1984; Merz, 1984). Further, there is no way to test whether treatment

of bone marrow cells would cure the brain dysfunction except through human experiments. If

the disease could be treated by alteration of bone

marrow, then patients who already have this

severely debilitating disease could be treated.

Otherwise, the only currently conceivable alternatives are treatment of cells early in development

(that might also entail germ line changes), or prevention of the disorder by prenatal diagnosis and

selective termination of pregnancy.13

IWther alternatives, such as implantation of genetically altered

nerve cells or insertion of genetic material using engineered viruses

specific for nerve cells, are theoretically possible, but have never

been successfully demonstrated, even in animals.

Many questions about efficacy will be addressed

by future genetic and clinical research. Determinations about which diseases can be treated

and which methods are most successful must be

made before human gene therapy becomes routine medical practice.

RELIABILITY

Experimental or medical therapy should be

undertaken only if the procedures are sufficiently

reliable to suggest that the potential scientific and

clinical benefits outweigh the risks of ill effects

or failure.

Animal experiments involving gene transfer,

with the exception of those done in lower organisms, until recently had a relatively low probability of success in any one organism. This was

tolerable to the investigators because their interest was in gene expression and animal development, and they could select the most scientifically

interesting result from a large population of therapeutic failures. Such techniques are not acceptable for correction of genetic diseases in humans,

where there must be of potential benefit to the

individual treated.

Application of gene therapy in humans is now

seriously considered only because of advances in

the methods of delivering genes into cells and

stable expression of genes so delivered (Anderson, 1984).

ALTERNATIVE TREATMENTS

Gene therapy will be acceptable only if it offers

the best prospect of success among all potential

treatments for a given patient. Factors that might

be considered in comparing gene therapy to alternatives will include educated judgments about:

expected efficacy,

anticipated costs (to the patient or overall),

and

magnitude and type of risks.

Such judgments will vary from physician to

physician and patient to patient, as for any medical technology.

The genetic basis of a disorder does not imply

that its treatment must also be genetic. There are

several treatments that have proven effective in
Medical Aspects of Gene Therapy . 25

some genetic diseases. The clinical manifestations

of hemochromatosis can be prevented by periodic blood donation. Dietary treatments of PKU,

galactosemia, urea cycle defects, and several other

disorders considerably improve patient prognosis, although they are only partially effective and

impose substantial limitations on patients and

their families. Vitamin supplementation of those

with Wernicke-Korsakoff encephalopathy and

several other disorders can be quite effective.

Drug treatments can compensate for some

genetic defects. Clinical investigators have already

discovered two drugs that lead to partial correction of sickle cell disease by inducing expression

of a type of hemoglobin, normally only expressed

during fetal development, that can compensate

for the errant sickle cell protein (see Technical

Note 4). Clotting factors can be given to hemophiliac patients, and biotechnology may greatly

increase the availability and reduce the cost of

such factors.

Clinicians have also pursued the possibility of

directly administering enzymes that are missing

due to genetic defects (Desnick, 1981). Such enzyme therapy has not been clinically successful,

but advances in drug administration could render such therapy practical. Development of drug

pumps that reside in the body and deliver hormones, enzymes, or other chemicals for long periods of time may reduce the need for gene therapy. A new insulin pump developed by NASA, for

example, promises to work for years without

need for battery replacement (Langone, 1984).

Gene therapy is not the only way to restore normal genetic information to some organs of a patient with a genetic disease; some genetic defects

may be remedied by transplantation of whole

organs or tissues. Bone marrow transplantation

has been successful, for example, in treating

thalassemia, sickle cell disease, and immune deficiencies; liver transplants have been performed

for Wilson disease (Desnick, 1981; Friedrich,

1984). Transplantation is a serious prospect for

only a small minority of potential patients, however. This is because current methods require

tissue compatibility between the donor and the

recipient, a rare event, and because the methods

require highly risky treatments to prepare the patient to receive the transplanted cells or organs.

A final disadvantage of transplantation is its extraordinary cost.

There are thus several existing and prospective

treatment for genetic diseases that do not require

direct gene replacement or supplementation, but

all have limitations and many genetic diseases

have no treatment. As one physician summarizes

the status quo, “therapy of most genetic disorders

is still ineffective and inadequate” (Friedmann,

1983).

Gene therapy of somatic cells will therefore

probably prove technically superior to alternative treatments for selected patients with some

disorders.

SEVERITY OF SYMPTOMS AND PROGNOSIS

The patient expected quality and length of life

directly affect the potential benefit and acceptable level of risk of any medical or experimental

intervention. Extremely serious disorders, such

as Lesch-Nyhan disease and ADA and PNP deficiencies, have such poor prognoses that even

small potential benefits are welcome and large

risks may be acceptable to the patient and his or

her family because they pale in comparison to

continued life with the disease.

Some examples of diseases likely to be targets

for gene therapy are noted by category in table 1.

The number of patients likely to be treated are

noted in table Z.

DATA MONITORING

For clinical trials to be optimally productive of

new knowledge, investigators must have mechanisms for following patients, and have a protocol

for obtaining whatever tissues may be needed and

for analyzing them. Advance thought about how

data monitoring will be done and disclosure of

what it will involve to the human research Subjects should be an important aspect of any human

gene therapy experiments. Attention to data monitoring will thus be one requirement for approval

to begin clinical trials.

INFORMED CONSENT

Assurance that informed consent will be freely

and appropriately obtained is required for all ex38-803 0 - 84 - 3 : QL 3
.

26 . Human Gene Therapy—Background Paper

Table 1 .—Examples of Diseases for Which

Gene Therapy Might Be Considered

1. Protocols for human gene therapy in somatic cells

expected in next several years:

immunodeficiency caused by adenosine deaminase

or purine nucleoside phosphorylase deficiencies

(ADA or PNP deficiencies)

Lesch-Nyhan syndrome (complete hypoxanthineguanine phosphoribosyl transferase deficiency)

urea cycle defects caused by deficiencies of

arginosuccinate synthetase (citrullinemia) or

ornithine carbamoyl transferase (OCT, also known as

ornithine transcarbamylase)

2. Might be attempted in foreseeable future:

phenylketonuria (as improvement on current dietary

treatment)

familial hypercholesterolemia

defects of the urea cycle other than citrullinemia

and OCT deficiency:

arginemia (arginase deficiency)

mucopolysaccharidoses and other defined metabolic

defects:

Gaucher disease (some forms)

metachromatic Ieukodystrophy (arylsulfatase B

deficiency type with little brain involvement)

Hunter syndrome (enzyme detectable in normal

blood)

branched chain ketoaciduria (severe grades)

3. Farther off because protein expression may require

4.

5.

6.

—

regulation:

hemoglobinopathies: (see Technical Note 5)

sickle cell disease, hemoglobin SC disease

alpha and beta thalassemia

hormone production defects

Farther off because gene product may be easily

available for administration (diminishing the need for

gene therapy):

growth hormone deficiency; some other hormone

production defects

hemophilias

Unlikely unless new discoveries provide clues on how

to approach gene therapy:

(Some may require germ line therapy because of

access to tissue sites or immunologic problems with

gene product.):

Tay-Sachs disease and other metabolic defects that

primarily affect brain

cystic fibrosis

type 1A growth hormone deficiency

most diseases inherited in dominant pattern (e. g.,

Huntington disease, Marfan syndrome,

achondroplasia, etc.)

May not be applicable:

chromosomal disorders:

Down syndrome

environmental and multigenic disorders:

hypertension

diabetes

“Cloned human gene available

SOURCE: Wissow, 1984.

Table 2.—Numbers of Patients Who Might Be Treated

by Somatic Cell Gene Therapy in the Near Future

Number of patients

Disorder with the disorder

Adenosine deaminase

deficiency

Purine nucleoside

phosphorylase deficiency

Lesch-Nyan syndrome

Arginosuccinate synthetase

deficiency

Ornithine carbamoyl

transferase deficiency

40 to 50 reported

worldwide

9 patients in 6 families

reported worldwide

1:10,000 males, estimated

200 new cases in the

United States per year

53 cases reported

110 cases reported

SOURCE: Stanbury, et al., 1983, as modified by OTA.

periments involving humans (Code of Federal Regulations, 1983). In the case of human gene therapy experiments, this will include disclosure of

what can reasonably be expected about:

treatment for them,

• relative costs of alternative therapies,

therapies,

procedures that will be done to obtain clinical data on the gene therapy experiments,

procedures for dropping out of the study,

and assurance that it is the patient’s right to

do so.

All human experimental protocols should be reviewed by local Institutional Review Boards (IRBs),

as is the case with all experiments involving

humans. In the case of human gene therapy, however, the NIH recently revised the Guidelines for

use of recombinant DNA to state that research

proposals involving human gene therapy (proposed by institutions that receive Federal funds

for recombinant DNA research) must be submitted to NIH for approval, in addition to local

IRB review. These protocols will be reviewed first

by a Working Group on Human Gene Therapy,

then by the Recombinant DNA Advisory Committee, and finally by the NIH Director before ap-
Issues That May Arise From Clinical Application . 27

proval to proceed is granted. One purpose of this

special care is to further insure proper informed

consent of patients electing to participate in gene

therapy experiments. FDA also has the authority to oversee the adequacy of informed consent

in clinical experimentation involving new therapeutic products, and this might include gene insertion technologies (Esber, 1984).

One special aspect of human gene therapy, the

potential for wide publicity, may merit attention

in the process of securing informed consent.

Widespread interest in human gene therapy

among scientific, religious, and government

leaders in advance of its successful application

suggests that the early clinical trials will be subject to potentially intrusive publicity. It is unlikely

that government oversight bodies can assure the

privacy of subjects who agree to participate in

gene therapy experiments, and so acknowledgement of this risk may be necessary by investigators before commencing. Investigators may also

need to anticipate responding to the demand for

media information by developing mechanisms for

channeling interest through hospital spokesmen,

preparing families to deal with the press, and

careful observation of privacy safeguards. The

risk of media exposure is part of the process of

informed consent, because this may prove to be

the salient difference between gene therapy and

other experimental medical techniques.

Issues that may arise from clinical application

If gene therapy moves through the early stages

of development and reaches the stage of standard medical practice, several medical issues may

emerge. None of these is different in kind from

issues arising in connection with other medical

technologies, but the context of the new problems

would be different.

Medical malpractice

Issues related to malpractice may be raised by

gene therapy if it develops into a routine medical technology. Physicians could be sued, for example, for failing to treat a genetic disorder. A

patient who suffered an untoward side effect because of genetic changes induced by gene therapy might also bring suit. What would the standards of care for this technique be?

Several medicolegal issues might enter into

assessments of liability and responsibility, It is not

clear, for example, who would be qualified to

employ the sophisticated techniques of gene therapy if it were to become standard medical practice. Should all physicians do it? Only those certified by the American Board of Medical Genetics,

the National Board of Pediatrics, the Hematology

and Oncology subspecialty board in internal medicine, or the American Board of Obstetrics and

Gynecology? Should gene therapy take place at

.

all hospitals, or only in certain ones? Who would

practice gene therapy, and where, may well be

determined by decisions made by the court system, State and local Governments, national medical specialty boards, and other medical and legal

organizations.

Parental responsibilities

Parental views on religion and medical practice,

including those that might preclude even somatic

cell gene therapy, might pit the beliefs of parents

against standard medical practices. Many court

decisions about whether to allow blood transfusions to children of parents who reject such treatments on religious grounds exemplify this kind of

conflict. Some legal scholars have even contended

that parents who fail to intervene on behalf of

the health of their children might be forced to

do so. In one recent case, a woman who objected

to cesarian section on religious grounds was compelled to undergo the operation to preserve the

life of the fetus (Lenon, 1983; Finamore, 1983).

If gene therapy were widely available and standard medical practice, analogous conflicts might

arise.

Whether medical practitioners, courts, institutional committees, or parents decide on who is

treated will depend on how gene therapy and
28 • Human Gene Therapy—Background Paper

other medical technologies are handled by the

courts or in new legislation at the State or Federal level.

patents and trade secrets

The techniques involved in gene therapy involve

the use of recombinant DNA to clone and insert

human genes. The early applications, if they involve the diseases listed in table Z, are unlikely

to involve patentable agents or processes, because

the methods under development have been openly

published and developed at several centers, and

the recombinant DNA involved is available in several laboratories. Eventually, however, the complexity and variety of approaches to gene therapy might result in products or processes that

could be patented. Patents might be sought, for

example, for genetically altered viruses designed

to deliver the human gene to the target tissue or

that permit controlled expression. The criteria for

granting such patents will be patentable subject

matter, novelty, utility, and nonobviousness, the

same ones used for other recombinant DNA products (OTA, 1984, ch. 16). The public policy issues

of fair access to the technology and encouragement of innovation would also be analogous to

those for other medical technologies.

A few distinctive aspects of patents and trade

secrets are especially relevant to gene therapy.

The review process by the National Institutes of

Health (NIH) for approving experiments involving proprietary information might require closed

sessions, so that trade secrets were not disclosed

publicly. The guidelines for human gene therapy

formulated by the NIH (described below) are not

binding on private firms that do not receive Federal research funds, although companies would

be likely to seek NIH approval in any event to

avoid adverse publicity and to assure due process for questions that arise about liability and insurance. Finally, the flow of scientific and clinical information to other investigators might be

inhibited if trade secrets related to gene therapy

must be protected.

Insurance

Gene therapy might eventually be covered by

standard medical insurance, or it might require

special provisions. Gene therapy, if it follows the

model of other medical treatments, will not be

covered by insurance companies until its efficacy

has been established for its intended application.

Coverage by insurance will likely depend on the

particular disorder, the relative cost (for gene

therapy and the alternatives), and the safety and

efficacy of the techniques involved.

Social implications of gene therapy

Gene therapy, should it prove useful, would be

like other technologies in changing the character and kinds of decisions that individuals make.

It would provide new options for medical therapy and imply new responsibilities for making

such decisions fairly and for the benefit of both

individuals and society. In the view of many

religious and ethical thinkers, gene therapy restricted to somatic cell corrections of single gene

traits differs little from other medical therapies

(Neale, 1983; World Council of Churches, 1983;

Siegel, 1982; Fletcher, 1982, 1983a, and 1983b).

There are risks and benefits associated with beginning gene therapy, as with any new technology. Public policy, public education, scientific and

technical advance, and other factors can all influence which applications are pursued and

which eschewed. In an open and democratic

society, new technologies are greeted by different

social groups in different ways. Some may believe

that beginning gene therapy too closely resembles “playing God” or is too dangerous, while

others impatiently await its application to the disease affecting a loved one.

Background

The application of gene therapy to humans is

likely to be regarded throughout society as a significant step, whether done in somatic or germ
Social Implications of Gene Therapy 2 9

line cells. It will be a focus of attention because

it is unprecedented and technologically sophisticated, and because it permits alteration of something considered fundamental to each individual—

his or her genetic constitution. While genetic

changes have been technologically induced for

years—for example, in the use of some vaccines--

the changes have never been so premeditated nor

so direct as deliberately inserting new human

genes to cure a specific disease. As noted above,

however, the main difference between gene therapy and other medical technologies may be perceptual more than actual. The risks and benefits

of gene therapy are analogous to those for other

therapies, and many believe that it presents no

fundamentally new ethical problems, yet there

remains a gnawing discomfiture with the prospect.

In the absence of gene therapy after birth, an

individual has no role in the choice about which

genes he or she carries, and so bears no responsibility for carrying them. Once gene therapy is

available, this may not be the case, and individuals

ma-y play some role in selecting their genes. This

prospect is frightening to many because new

choices bring new responsibilities; new technologies can be misapplied. The magnitude of the

responsibility is, to a large extent, determined by

the power of the new technology. If, as suggested

above, gene therapy is not widely applied in the

near future because of limitations on the range

of diseases to which it is applied, then the social

impact of gene therapy is likely to be less than

that associated with many other accepted medical practices.

Most of the major social impacts of genetic

knowledge will almost certainly derive less from

gene therapy than from genetic screening or

other genetic testing. Some fundamental choices

about privacy of data on patients’ genetic constitution must be made as the new technologies provide greater amounts of such information (see

app. B). The new information will, however, not

be directly related to developments in gene therapy) but rather to diagnostic evaluations of patients’ predispositions to genetic diseases or

special health risks.

Some fear that increased knowledge about how

genes work may further promote a cold, abstract,

and mechanistic view of human life. To the extent that this is true, however, it does not relate

directly to gene therapy but rather to genetics

in general, and even more broadly to all of

science.

Social aspects of gene therapy that are mentioned below fall into several general categories:

What process will determine when to begin

gene therapy?

How important are evolutionary considerations? and

What might be the impacts on social institutions?

Major social issues

WHAT PROCESS WILL DETERMINE WHEN TO

BEGIN GENE THERAPY?

The process of deciding when to begin experimental human gene therapy includes several components. Some judgments are technical, involving assessment of the expression of the gene of

interest, for example, and such decisions are left

to scientific peers to examine experimental design

or determine which studies are relevant to a proposed project. Other judgments involve assessment of quality of life for a particular patient;

such decisions can only be made by the patient,

his or her family, the physician, or others who

are familiar with the details of a particular case.

Other judgments may involve determination of

acceptable risk to society, and these invite wider

public participation.

Many of the questions raised will be answered

only in the context of a particular patient in a particular family seen by an individual physician, and

the judgments of the parties most directly affected

will decide the case within the constraints set by

laws, regulations, and local ethics and human research committees. The context for making individual decisions will thus depend on peer review

and compliance with human subjects guidelines.

The criteria for peer review and setting of guidelines involve, in turn, government agencies that

must ensure fairness, completeness, and representation of diverse and often conflicting viewpoints.
30 . Human Gene Therapy—Background Paper

Judgments about whether a given experiment

conforms to the criteria will differ among individuals. Some of the differences will reflect life

experiences. A physician accustomed to treating

cancer patients will have different views from a

scientist whose primary interest is developmental biology. A hospital attorney may hesitate to

endorse an experiment that the parent of an affected child would eagerly embrace. One suspicious of technology in general might reject experiments involving any level of risk.

Some urge caution in approaching uses of gene

therapy.

Once we decide to begin the process of human

genetic engineering, there is really no logical place

to stop. If diabetes, sickle cell anemia, and cancer are to be cured by altering the genetic makeup of an individual, why not proceed to other

‘disorders’: myopia, color blindness, left-handedness? Indeed, what is to preclude a society from

deciding that a certain skin color is a disorder? . . .

With human genetic engineering, we get something and we give up something. In return for securing our own physical well-being, we are forced

to accept the idea of reducing the human species

to a technologically designed product. Genetic

engineering poses the most fundamental of questions. Is guaranteeing our health worth trading

away our humanity? (Rifkin, 1983, pp. 232-233).

In contrast, an urgent request for support of

gene therapy research is found in the words of

Ola Huntley, three of whose children suffer from

sickle cell disease:

I resent the fact that a few well-meaning individuals have presented arguments strong enough

to curtail the scientific technology which promises

to give some hope to those suffering from a

genetic disease. I have faith to believe that genetic

therapy research, if allowed to continue, will be

used to give life to those who are just existing

. . . .I, too, would like to ask the question, who do

we designate to play God? Aren’t those theologians and politician; playing God? Aren’t they

deciding what’s best for me without any knowledge of my suffering? I am very angry that

anyone would presume to deny my children and

my family the essential genetic treatment of a

genetic disease . . ..1 see such persons as simplistic moralists who probably have seen too

many mad scientist horror films. It’s like saying

that someone can deny others the right to drive

or ride in an automobile because there is an everpresent danger of an accident (Huntley, 1983, pp.

166-169).

Such conflicting views cannot be assuaged by

empty assurances, and public policy decision will

typically be made without consensus. There are

dangers in premature application balanced against

undue delays of useful medical benefits. Public

policy will be decided amidst great uncertainty.

As one doctor noted, “the ethical principle that

physicians have to be concerned about is that we

know what we’re doing before we promise that

we’re going to try and treat someone” (Ryan, 1983,

p. 172). In deciding when to begin experiments

on human gene therapy, the need for further

knowledge must be weighed against the benefits

that might accrue to patients with severe and fatal

diseases.

Most of the social and ethical questions raised

about gene therapy could also be raised in the

context of other medical interventions, such as

use of antibiotics or acceptance of surgery. It is

not the questions that are new, but rather a new

technology that forces their reconsideration.

Disagreement about the seriousness of the new

social and ethical consequences of using gene

therapy in humans hinges on incompatible judgments of how widely it will be used and how

revolutionary will be its perceived impact on how

humans view their own sanctity. Most scientists

and clinicians believe that gene therapy will be

only a small incremental medical advance applicable to a few patients, while religious and social

commentators may reflect on its cumulative effects over generations. The general interest in

human gene therapy has led some scientists and

medical providers to urge caution so as to avoid

political reaction against gene therapy among the

general population (Rosenberg, 1983; Grobstein,

1984).

Public policy will have to be based on consideration of patient welfare, social impacts, religious

precepts, and political realities. There is little reason to believe that differences in opinion about

the appropriateness of human gene therapy will

resolve spontaneously, or even after extensive

public discussion. Where there is no agreement
Social Implications of Gene Therapy . 31

on what decision to make, the only alternative is

a process for making the decision, and government agencies must demonstrate that the process is rational and fair (Bazelon, 1983).

Wide public discussion and agreement on a

process do not guarantee fair decisions or correct assessments of risk and benefit. Errors of

judgment may occur even with unassailable expertise and completely democratic participation.

Resort to fair and open process is not, therefore,

perfect, but merely the best practical solution to

assure fairness.

Given the anticipated public interest in and controversy about human gene therapy, any successful mechanism for permitting its commencement will involve a public process including

discussion among individuals with different informed perspectives. Such discussion may arrive

at consensus, but if it does not, documentation

of the fairness and rationality of the decisionmaking process will be the only practical course. The

Federal Government will be involved in decisions

about human gene therapy because of its involvement in medical research, health care, and issues

that attract wide public interest.

There are several Federal agencies already in

place that can educate the public and make decisions about when to begin human gene therapy.

These include the Recombinant DNA Advisory

Committee of the NIH, the Food and Drug Administration, and several other bodies within the department of Health and Human Services. These

will be described below in the section on the Federal Role in Gene Therapy.

HOW IMPORTANT ARE EVOLUTIONARY

CONSIDERATIONS?

Direct manipulation of the genome inspires visions of mankind controlling its own evolution,

depleting the diversity of genes in the human

population, and crossing species barriers to create

new life forms. The magnitude and rapidity of

change caused by direct genetic intervention,

however, are likely to be far smaller than the large

effects caused by relaxing historic selection pressures on the human population through changes

in the environment, sanitation, and health care.

Discussion of germ line gene therapy is most

relevant to permanently changing the human

gene pool because it would lead to inherited

changes. At present, however, such discussion is

necessarily vague and speculative because the

technology does not exist and may never be used.

There will doubtless be continued public interest in ensuring fair and open debate on whether

human germ line gene therapy would be appropriate. It is impossible, however, to make estimates of the potential magnitude of its impact on

human populations now.

The effects of somatic cell gene therapy will depend on how many patients receive such therapy, and to which conditions it is applied. It is not

possible to make firm predictions about how

many patients might eventually be treated by

gene therapy, because it is not now certain that

even somatic cell gene therapy will prove medically useful. The effect that somatic cell therapy

would have on human population genetics would

be no different in kind than that from other technologies that affect the patient and do not lead

to inherited changes, Most of the changes would

be due to preservation of the lives of those who

would otherwise die before reproducing, the

same effect that results from diet therapy in PKU,

or clotting factor replacement in hemophilia.

While it is not possible to estimate the number

of patients that might eventually be aided by

somatic cell gene therapy, it is possible to estimate

the impact of correcting those genetic defects that

are currently targeted. These will be the potential genetic impacts that must be assessed by those

approving the early experiments in gene therapy.

As can be seen in table 2, the diseases for which

gene therapy is now contemplated are quite rare.

The total number of patients with these conditions that might be treated using somatic cell gene

therapy would likely be less than 300 per year

in the United States, and would probably be far

fewer until the technology were accepted. This

figure compares to the approximately 4 million

births in the United States each year.

Changing the Gene Mix in Human Populations.—Somatic cell gene therapy would have no

direct effect on the mix of genes in human popula-
32 Human Gene Therapy—Background Paper

tions, and would have only the indirect effects

noted above. Germ line therapy, in contrast,

would alter the prevalence of some genes, although the magnitude of such effects is impossible to predict because so many factors are involved.

Direct germ line gene therapy of recessive

disorders would, for most diseases, have a noticeable effect on human evolution only if widely

practiced for hundreds of generations. The number of generations needed to have a significant

effect would depend on the type of gene being

corrected, its prevalence in the population, when

the disease were expressed (in adulthood or

childhood), the severity of the disease caused by

it, and many other factors. If gene therapy were

used only to treat single gene recessive traits, then

it would take several hundred generations measurably to alter the prevalence of the gene in the

population. For defects that are present on one

percent of chromosomes in the human population, for example--corresponding to a genetic disease much more common than any under consideration for gene therapy now—it would take

1,500 years to increase the frequency to 2 percent. 14 If germ line gene therapy were widely

practiced for a large number of diseases, including common dominant traits, then alterations

might be noticed much more quickly, but such

applications are not now envisioned.

Depletion of Diversity in the Gene Pool.-–

There is excellent evidence that some genetic diseases are common because of an advantage conferred to those individuals who carry one copy

of the aberrant gene. Those who carry one copy

of the sickle cell anemia gene, for example, are

better able to combat malarial infections. The

genetic disease is the price paid to preserve this

advantage for the population on average, mitigated only by the statistical rarity of having two

abnormal genes (and thus the disease) (Vogel,

1979).

ltrrhis examp]e is based on discussion of eliminating rare genes

for recessi~e disorders in several references (Li, 1961; Vogd, 1979).

These assume that those who carry two copies of a defective gene

would not reproduce. In considering the impact of human gene therapy for those who would otherwise die before reproducing, the

situation is reversed but the time scales would be comparable,

Genes causing other genetic diseases may also

serve a purpose that has not been discovered, and

so elimination of such genes might prove deleterious to the human population in the long run. In

somatic cell gene therapy, the patient own genes

would not be deleted, but new information would

be added in such a way that it would not be inherited. This would have no impact whatever on

the population’s reproductive gene pool. If gene

therapy permitted the survival of patients who

would otherwise die, however, then genes causing diseases might slowly become more widespread because they would not be eliminated.

Even if gene therapy did have an effect on

genetic diversity, this might not prevent its use,

The risk of slightly reducing diversity in the entire human population would likely seem insignificant to those patients for whom the potential

benefits loom large and immediate. Perpetuation

of genetic disease, particularly of the severe

childhood diseases that are now the targets for

gene therapy, would seem a cruel means to an

end of uncertain import.

The sickle cell example is instructive in this

sense, as well. While it is widely accepted that the

sickle cell gene conferred certain advantages in

combatting malaria among Mediterranean populations, it is also true that current antibiotics and

sanitation technologies have been much more effective in protecting the same populations. In the

era of modern medicine, sickle cell disease is no

longer a necessary price to pay for genetic protection from the ravages of malaria.

The arguments for refraining from gene therapy in order to maintain genetic diversity are also

weakened when raised in a population whose

main long term problem may be the very rapidity

of its growth. When a population is rapidly expanding, the diversity of genes generally increases

because there are more individuals who can carry

new genes.

Crossing Species Barriers. -Recombinant genetic technologies permit genes from one species

to be inserted into another. In the animal experiments cited, for example, rat growth hormone

genes were put into mice and rabbit globin genes
Social Implications of Gene Therapy 3 3

into rats. It is unlikely that an animal gene would

be used for human gene therapy, because if an

animal gene is available, then isolation and cloning of its human counterpart would be routine.

Human genes will be used in animals, however,

to test the safety and efficacy of gene therapy

before it is tried in humans. What would be the

significance of using human genes in animals?

Mythology and literature contain numerous examples of hybrid creatures that combine the characteristics of man and beast or involve engineering completely new organisms (Capron, 1984c;

Siegel, 1982). One need only think of the minotaur

(the apocryphal man-bull hybrid of Crete who

devoured fair youths from ancient Greece), the

golem (a creature of Jewish lore created to protect the residents of Prague; the golem eventually

turned against them and had to be destroyed),

or Frankenstein’s monster to note the horror associated with semi-human creatures, It is widely accepted in the religious and professional ethics

communities that attempting to create such creatures would be immoral (World Council of

Churches, 1982; National Council of Churches,

1984; Siegel, 1982,1983); it is also impossible to

create such creatures by attempting to alter single

gene defects. Some of the issues raised by interspecies transfer of genes are further discussed

in Technical Note 3,

FETAL RESEARCH

Research involving human fetuses is a topic of

controversy in the United States, and 25 States

have statutes that limit or prohibit it (Andrews,

1984b; Quigley, 1984). Fetal research bears on

gene therapy primarily if germ line gene therapy

is considered. If germ line gene therapy on human

embryos is to be undertaken, it must rest on a

foundation of knowledge about development and

genetic expression in very early human embryos.

Such knowledge can only be obtained using such

embryos.

Even if germ line therapy is not considered,

there may be instances in which fetal research

would be useful in establishing safety or efficacy

of somatic cell gene therapy. The history of research on Rubella during the 1960s may illuminate the utility of fetal investigation in several

respects.

Concern about Rubella infection, particularly

its proclivity for causing congenital malformations, intensified following the epidemic of 1964,

It was well known that Rubella infection during

pregnancy could cause malformations, but the

mechanisms were not clear. Investigation of the

epidemic was advanced by research on fetuses

that either spontaneously aborted or were

aborted because an infected woman chose to

avoid the risk of bearing a deformed child. Fetal

research showed that a majority of fetuses in

women known to be affected had been directly

infected by the Rubella virus, that the deformations were likely due to direct fetal infection, and

that fetal infection often persisted long after the

woman was no longer symptomatic (Horstmann,

1965).

Fetal investigation also led to the development

of Rubella vaccines. Many vaccines were developed during the mid-1960s, including the RA 27/3

vaccine derived from an infected human fetus

and propagated in tissue culture of human cells

(Plotkin, 1965; Plotkin, 1969). This strain is now

the only Rubella vaccine licensed for use in the

United States (Plotkin, 1981).

Finally, the guidelines for use of Rubella vaccines were influenced by human fetal research.

Animal experiments showed that Rubella could

infect fetuses of pregnant females (Parkman,

1965), as was expected from human studies. Preliminary experiments in monkeys, however, did

not show fetal infection by the weakened Rubella

used in vaccination (Parkman, 1966). The number of monkeys tested was necessarily small because of the expense and difficulty of animal experiments, and investigation of humans proved

necessary. Scandinavian workers showed that in

contrast to the monkey experiments, vaccine

strains might infect the human fetus (Vaheri,

1969). These experiments could only be done on

aborted fetuses. The findings were considered in

drafting the recommendations for use of vaccines

in pregnant women (Recommendations, 1969).

The strains of vaccine now in use are different

from those used in the Scandinavian experiments,

and further research on current strains (involving women who have inadvertently been vaccinated during pregnancy) has demonstrated that
34 • Human Gene Therapy—Background Paper

the risk of fetal infection from Rubella vaccination during pregnancy is quite low (Plotkin, 1981).

Fetal research thus played a role in better understanding the congenital Rubella syndrome, in

development of vaccines, and in establishing safe

practices for human vaccination. An analogous

role in establishing scientific background and

testing safety and efficacy of gene therapy might

also require fetal research for some future applications.

There is no reason to test human gene therapy

protocols in human fetuses now because neither

fetuses nor pregnant women are contemplated

for treatment. Should this change, then tests involving fetuses would be desirable. If a need for

application to fetuses or pregnant female patients

emerges, then it may depend on study abroad

(where fetal research is practiced), relaxation of

fetal research guidelines in the United States, or

repeal of statutes in those States that prohibit such

research (if the research is to be conducted in

such States). This issue will be especially difficult

to resolve if gene therapy is shown useful for

severe diseases of early childhood. This is because

gene therapy that is useful in infants is likely, in

some cases, to be potentially even more beneficial

during fetal development–before the metabolic

abnormalities caused by the genetic disease have

caused any deformities or irreversible effects on

the nervous system.

WHAT MIGHT BE THE EFFECTS ON

SOCIAL INSTITUTIONS?

Several religious leaders have noted that gene

therapy may be one more factor tending to reduce perceptions of humanity to mechanistic interpretations (Zaner, 1982; Siegel, 1982, 1983;

World Council of Churches, 1982; National Council of Churches, 1984). Focus on mechanism may

lead to diminished attention to social and moral

values, and may threaten attitudes about the sanctity of human life. The effects of the new technology on attitudes are not certain, however, and

the same commentators note that appreciation of

the complexity of life may increase our regard

for life more than it attenuates it. The attempt

to save lives by gene therapy is itself an attempt

to preserve or improve particular lives. The specific effect of gene therapy in changing perceptions is, in any case, likely to be one small part

in the general growth of science, complementing

other fields that also alter our self-perceptions

such as neuroscience, computer science, psychology, evolutionary biology, ecology, and other

parts of biology and medicine. If gene therapy is

found medically useful, it may prove difficult to

deny benefits to needy patients on the basis of

long-term shifts of human self-perceptions.

Gene therapy may play a larger role in indirectly altering parental expectations. If genetic

therapy is successful for extremely serious diseases, then it might be applied over time to progressively milder medical problems. This prospect

raises the possibility that parents may more and

more expect “perfect” children. So long as gene

therapy is confined to disorders that are recognized as significant burdens, then it will merely

bean addition to the medical armamentarium. If

it becomes possible to treat more and more disorders, especially if attempts are made to affect

intelligence or physical traits, then gene therapy

might indeed raise concern about parental expectations of their children. Again, however, the definition of appropriate application is one that must

be widely discussed because it is more a social

than a medical issue (although medical factors are

highly relevant). Discussion of such potential

dangers is, given present technology, mere speculation for now; as the technology develops, public discussion may need to be encouraged if it

appears that gene therapy is becoming widely

applicable.

The Federal role in gene therapy

The Federal Government performs several cal research is supported by the Federal Governfunctions that may affect the development and ment through the National Institutes of Health

application of human gene therapy. Most biomedi- (NIH) and other Executive agencies. Regulation of
The Federal Role in Gene Therapy 3 5

pharmaceutical products is the responsibility of

the Food and Drug Administration (FDA). Genetic

services including manpower training, basic and

applied research, genetic screening, and counseling, are partially supported through block grants

given to individual states under authority of the

National Sickle Cell Anemia, Cooley’s Anemia, TaySachs and Genetic Diseases Act (Reilly, 1977), and

administered under the Omnibus Budget and

Reconciliation Act. Finally, the Federal Government, through its legislative, judicial, and Executive branches, is often an effective instrument

for public discussion and education, through the

Department of Health and Human Services, congressional hearings and activities, and such agencies as the President’s Commission.

International interests in human

gene therapy

Human gene therapy is widely regarded to be

closer to clinical testing in the United States than

any other country. Other developed nations will

soon follow, however, and international interest

in its development has been noted, primarily in

Canada and Europe. Canadian research groups

have been involved in the design of viruses that

might be used in gene transfer (Merz, 1984), and

several European government groups have made

statements related to gene therapy. The Parliamentary Assembly of the Council of Europe, for

example, made a recommendation that ‘(the rights

to life and human dignity . . . imply the right to

inherit a genetic pattern which has not been artificially changed,” although this right was explicitly qualified so as to “not impede development

of the therapeutic applications of genetic engineering (gene therapy), which holds great promise . . . “ (Parliamentary Assembly, 1983). The

Parliamentary Assembly also called for the development of a list of diseases that could be treated

using gene therapy, based on several criteria:

seriousness of the disease,

simplicity of the technique and applicability

to only single gene disorders,

application to a well characterized disease,

supervision by scientific and ethical review .

commit tees,

A

restriction to centers of demonstrated expertise, and, interestingly,

exclusion of genes that are "the object of

commerce .“

recent report on reproductive technologies

was submitted to the Parliament of the United

Kingdom by a committee headed by Dame Mary

Warnock. The report recommended that a new

governmental licensing agency be created to oversee embryonic and fetal research and its applications. The committee also briefly commented on

potential germ line gene therapy, and recommended that the licensing authority give “guidance on what types of research, apart from those

precluded by law, would be unlikely to be considered ethically acceptable in any circumstances”

(Committee of Inquiry, 1984). The licensing authority would thus monitor gene therapy research and consider whether germ line therapy

should be permitted.

European political history in dealing with

genetic technologies differs from that in the

United States. The United Kingdom, for example,

has approached the regulation of novel biological

technologies from a different perspective (Wolstenholme, 1984). Fetal research is now performed in the United Kingdom and Australia, and

so questions regarding its regulation are more

prominent there than specific applications to gene

therapy. In the United States, fetal and embryonic

research has not been federally funded for almost

a decade (see below), and the scientific and medical focus of gene therapy has been on somatic

cell therapies whose development does not entail the use of fetuses or embryos.

Federal agencies potentially involved

in gene therapy

Several Federal agencies potentially have purview over some aspect of human gene therapy.

The National Institutes of Health, as the primary

sponsor of relevant research and the location of

the Recombinant DNA Advisory Commission, is

involved in approving both research grants to do

gene therapy research and in overseeing compliance with Federal research guidelines.
36 . Human Gene Therapy—Background Paper

The National Institutes of Health (NIH), through

its Recombinant DNA Advisory Committee (RAC),

is currently the most active Federal body involved

in monitoring human gene therapy. It was established in 1974 and is charged with recommending guidelines for safe conduct of research involving recombinant DNA (or, by extension, RNA)

(Milewski, 1984). The RAC has established a

Working Group on Human Gene Therapy, whose

members are listed in appendix C, to develop

guidelines for research on human applications of

gene therapy. The Working Group plans to have

guidelines published in 1985, in anticipation of

proposals for human gene therapy, The Working Group shall evaluate research proposals received by NIH, and shall report to RAC. RAC shall,

in turn, report the the Director of the NIH, who

will then approve the proposal or suggest needed

alterations. Another function of the Working

Group will be to educate the public and to review

some broader social implications of human gene

therapy that are not included in review by local

Institutional Review Boards (Working Group on

Human Gene Therapy, 1984).

The Food and Drug Administration (FDA) will

also play a role in regulating some aspects of

human gene therapy. The FDA has the authority to regulate drugs, including biological products intended for use in the diagnosis, treatment,

or prevention of diseases or injuries in humans.

The FDA will become involved in human gene

therapy if it involves products such as nucleic

acids or genetically modified viruses that are subject to agency regulations (under authority of the

Food Drug and Cosmetic Act and the Public

Health Service Act) (Miller, 1983a). The role of the

FDA generally includes review of applications submitted for products used in investigational studies

and encompasses the manufacture and quality

control procedures applied to such products. The

FDA review includes evaluation of the design of

clinical and preclinical studies, adequacy of procedures for assessing safety and efficacy, and

methods for obtaining informed consent from patient participants (Miller, 1983b).

The FDA authorizes (by approval of a New Drug

Application or granting of a license) the marketing of products when a review process has concluded that the data obtained during investigational trials support the safety and efficacy of the

product for its intended labeled claims (Miller,

1983b).

In addition to the NIH and FDA, which are

already monitoring human gene therapy, there

are several other Federal agencies or bodies that

might become involved in the future.

An Ethics Advisory Board (EAB) is an entity

composed of non- government experts in ethics,

law, medicine, and others with expertise related

to a particular topic under consideration. One

such board was formed in 1979 to advise the Secretary of Health and Human Services on several

topics, most notably fetal research. Federal regulations state that “One or more Ethical Advisory

Boards shall be established by the Secretary”

(Code of Federal Regulations, 1983) yet no such

board exists at present. An EAB was intended to

“render advice consistent with the policies and

requirements . . . as to ethical issues)” (Code of

Federal Regulations, 1983). Such a board, if it

were now reconstituted, might play a role in coordinating and overseeing the Federal Government’s activities regarding human gene therapy,

including public education, supervision of NIH,

FDA, and other agencies in the Department, and

advising the Secretary on other actions. Consideration of the broader questions related to progress in human gene therapy would fall within

the mandate established for EABs.

The Federal Interagency Advisory Committee

on Recombinant DNA Research, established in

1976, is another group that has not played a direct role in human gene therapy, but could theoretically do so. The Committee is composed of

members from several Federal agencies involved

in activities related to recombinant DNA research.

Members of the Committee agreed to comply with

the NIH Guidelines in 1976, thus in effect transferring authority to NIH for biomedical research

and clinical investigations. Recently, other agencies, including the Department of Agriculture and

the Environmental Protection Agency (both of

which have members on the Interagency Committee), have become involved in regulating agricultural and environmental applications of recombinant DNA research. The Committee may thus

play a more active role in agricultural, environ-
The Federal Role in Gene Therapy . 37

mental, and other new areas of research, but it

is likely that most authority to monitor and regulate human gene therapy will remain at NIH and

FDA because these agencies have the most extensive experience with biomedical and clinical applications.

The Office of Science and Technology Policy

(OSTP) is an Executive agency, headed by the

President Science Advisor, that reports directly

to the President. The OSTP has taken a lead in

Federal oversight of some areas of science and

technology, and has recently coordinated a group

of government officials in dealing with the questions surrounding deliberate release of genetically

altered organisms into the environment, and

other novel applications of biotechnology. The

OSTP could conceivably also serve a similar function for gene therapy, although the extensive experience of FDA and NIH in questions relating to

health and medical technologies makes OSTP less

likely to be involved in human gene therapy than

in more general questions such as environmental

release or new agricultural applications.

Determination of the Federal role in monitoring and public debate about questions relating to

bioethics, including human uses of recombinant

DNA technology, was a focus of considerable

legislative activity in the 98th Congress. Bills to

reauthorize the lapsed President’s Commission

were introduced in both houses, but no further

action on those bills was taken. Representative

Gore proposed a new President’s Commission on

Human Applications of Genetic Engineering that

eventually became part of the House version of

the NIH authorization bill. Senators Hatch and

Kennedy proposed creation of a bioethics commission at OTA as part of legislation creating a

new National Institute of Arthritis and Musculoskeletal and Skin Diseases at NIH. The Senate and

House bills were referred to conference. The conference report authorized a new Biomedical

Ethics Board, composed of 6 Senators and 6 Representatives, and a Biomedical Ethics Advisory

Committee, composed of 14 appointed individuals

and experts in relevant disciplines. The Committee would have performed studies related to

bioethics, including two mandated studies: one

on fetal research and another on human applications of genetic engineering (including human

gene therapy) (Conference Report, 1984). The legislation reported from conference was passed by

both houses, but vetoed by president Reagan on

October 30, 1984. The future of a Federal body

for investigation of bioethical questions is thus

uncertain.

Functions of the Federal Government

SUPPORT OF RESEARCH

The Federal Government, through the National

Institutes of Health (NIH), is the primary sponsor

of biomedical research in the United States. The

NIH budget for 1983 was $3.8 billion, accounting for 36 percent of all funds spent in the United

States on health-related research (NIH, 1984). In

those areas of biological science related to human

gene therapy, the NIH funds the bulk of research,

although a few companies with expertise in biotechnology are known to be sponsoring some research relevant to gene therapy.

The relative rarity, scientific difficulty, and long

term investment necessary to develop gene therapy for any one genetic disease suggest that research may not occur unless there is public funding. Individual genetic diseases are thus “orphan”

disorders when taken singly, yet relatively common as a group. The technology to identify or

treat one genetic disease often suggests means for

approaching biochemically similar disorders, and

many aspects of research on on one disorder may

be directly applied to others. A recent example

of this phenomenon is the discovery that the gene

for Huntington disease is located on human chromosome 4. This discovery was made by applying

a technique developed for general mapping of the

human chromosomes to large families in the

United States and Venezuela’s (Gusella, 1983;

Wexler, 1984; Rosenfeld, 1984; Kolata, 1984a).

The same technique, which may permit earlier

diagnosis and eventual identification of the specific gene responsible for the disease, promises

to apply to many other genetic diseases. The financial and scientific investments in discovering

lq-he te~hniqu~, called restriction fragment length polymorphism

linkage anal~sis, was de~’eloped to locate genes ei’en when the gene

had not been c]oneci or e~en identified IBotstein, 1980, 1984). This

method for identifJ’ing the chromosornal location of genes is desrrihed in app, A.
38 . Human Gene Therapy—Background Paper

and developing a technique used in locating the

Huntington disease gene may thus also pay off

for other disorders.

Research on genetic diseases is likely to continue to depend heavily on Federal funding, and

so long as gene therapy remains experimental,

Federal research policy will be influential in its

development. Seminal discoveries related to

human gene therapy will likely derive from both

clinical research and basic research on molecular

genetics and biochemistry. The technologies of

recombinant DNA and gene transfer now contemplated for use in human gene therapy are

themselves results of basic genetic inquiry, and

further practical applications of basic research

are likely to emerge. This has been the pattern

of development of molecular biology and other

biomedical sciences-research in one area leading

to breakthroughs in an unexpected and seemingly

unrelated discipline. The discovery of DNA’s relationship to inheritance was itself such a serendipitous discovery, resulting from Avery’s work

attempting to identify why certain bacteria caused

pneumonia (Thomas, 1984; Judson, 1980).

Research on developing animal models of human genetic diseases may be important in facilitating human gene therapy applications. Such

models provide methods for testing the efficacy

and safety of treatment methods.

In addition to basic research, some early experimental trials in humans will likely be supported

by Federal funds. Decisions about how Federal

research funds are expended for research on

basic molecular genetics, animal models of genetic

diseases, and preliminary human applications will

thus directly affect how rapidly gene therapy

develops and which diseases will be addressed.

REGULATION OF MEDICAL APPLICATIONS

A research proposal involving recombinant

DNA is generally originated by a scientist working at a university, industrial laboratory, or other

research center, A research proposal includes

general background, goals of the experiment,

methods to be used, evidence for efficacy, provisions for assuring safety and informed consent

of patient participants (and may also include information on compliance with standards for animal care). The proposal is sent to local review

committees that assess its compliance with safety

and human subjects protection guidelines. Certain classes of experiments are automatically referred to NIH for approval, and cases that cannot be decided locally are also referred to NIH.

These procedures are the ones followed by

scientists and clinicians using Federal funds who

act in good faith. Human investigations supported

by private firms must also meet human subjects

protections guidelines, usually to avoid problems

of liability and insurability. Clinical investigations

of pharmaceutical products, including genes or

modified viruses used in treatment, must also be

submitted for FDA review.

Ensuring Compliance with Human Subjects

Protections.—A process for protecting human

subjects in research already exists. In the context

of experiments involving human gene therapy,

a proposal for an experiment involving human

subjects should be sent to an institutional review

board (IRB), a local committee that would then

review the proposal for compliance with human

subjects protection standards, according to the

following criteria:

minimization of risk to the subjects,

reasonable risks in relation to anticipated

benefits,

equitable selection of subjects,

assurance of informed consent,

adequate provisions for monitoring data,

provisions for protecting patient privacy, and

assurance that decisions to participate in research will not be coerced (Code of Federal

Regulations, 1983).

Approval by a local IRB will be required before

proposals are forwarded to NIH for approval. IRB

approval may be contingent on approval by the

NIH. When received at NIH, the proposal will be

published in the Federal Register for public comment and will also be referred to the Working

Group on Human Gene Therapy, which will then

report to the RAC for review. If the proposed experiments meet the standards of the RAC, then

they are referred to the NIH director for approval

(Working Group on Human Gene Therapy, 1984).
The Federal Role in Gene Therapy . 39

Ensuring Safety and Efficacy.—Mechanisms for

reviewing research proposals to ensure safety potentially fall under the authority of several groups.

Assurance of safety is analogous to human subjects protection, including review by NIH and FDA

after approval by local safety and human subject

committees. Each investigator must submit his research proposal to his or her local Institutional

Biosafety Committee (IBC), which assesses compliance of the proposed experiments with NIH

safety guidelines for recombinant DNA research.

In the case of human gene therapy, the risks and

benefits of proposed experiments will also be reviewed, followed by approval by the NIH and FDA

before commencement (Krause, 1984, p. 17847).

There are several weaknesses in this regulatory

schema. Only research conducted at institutions

accepting federal funds for recombinant DNA experiments are obligated to conform to the NIH

Guidelines by law, although to date private research groups have voluntarily submitted to RAC

Guidelines. (Private corporations have complied

at least in part because of the risk of public censure, potential loss of insurance coverage, and

possible added legal liability in civil suits if they

do not.) The formal penalty for not conforming

to NIH guidelines is denial of Federal research

funds to the institution submitting the proposal.

This is quite powerful for universities and most

research centers, but is not a direct economic incentive for compliance in some privately sponsored research.

Another feature of the current review process

is the lack of evaluation of research goals. IRBs

are specifically precluded from assessing the

‘(long-range effects of applying knowledge gained

in the research” (Code of Federal Regulations,

1983). This is quite appropriate in the context of

a particular experiment involving patients with

specific defects, and IRBs cannot be expected to

do more than investigate specific protocols. The

lack of purview over goals, however, leaves a

vacuum for determining which experiments are

contrary to public policy. The NIH has formed the

Human Gene Therapy Working Group in part to

fill this vacuum, but there are potential questions

of conflict of interest because NIH is also the primary sponsor of biomedical research. Assessment

of public policy on goals for research, including

human gene therapy, could be performed by an

EAB, congressional commission or other Federal

body.

In addition to review of research proposals on

human gene therapy by the NIH, the Food and

Drug Administration (FDA) also has authority over

human experiments involving therapeutic products.

Genes introduced for gene therapy could constitute such a biological product under FDA jurisdiction and would thus involve FDA approval

before commencing (Miller, 1983b). FDA oversight

would follow regulator procedures used for

.

other products: submission of evidence for safety

and a rational basis for introduction of the product into humans (stemming from animal experiments, in vitro studies, and relevant previous clinical trials), Investigator submissions must include

data showing that the product is adequately pure

and sufficiently potent to justify clinical trials (Office of Biologics Research and Review, 1983). The

FDA then evaluates the evidence and determines

whether risk and benefit considerations support

clinical trials.

FDA authority may, in some circumstances,

overlap that of the NIH, whose Guidelines explicitly provide for oversight of human gene therapy and experiments that involve recombinant

DNA (or molecules derived from rDNA).

Whatever the mechanism or agency involved,

protocols and products will be evaluated case by

case. This will certainly involve local IRBs, NIH,

and FDA, and may eventually include other Federal agencies as well. If individual applications of

human gene therapy becomes standard medical

practice, or even widely available, they will then

be governed primarily by professional standards,

civil suits, or local authorities, like other medical

technologies.

For early experiments on human somatic cell

gene therapy, present oversight methods that involve local IRBs, RAC, NIH, and FDA appear adequate. For more controversial applications of gene

therapy involving germ line alterations, wider

public discussion, open goal setting, and greater

government oversight may prove necessary to

avoid undue controversy and assure prudent public policy.
40 • Human Gene Therapy—Background Paper

PAYMENT

If gene therapy were to become incorporated

into routine medical practice, the Federal government might become involved in paying for its use.

As long as gene therapy is experimental, most

costs will be borne by research funds. Typically,

as a therapy is used more widely, funding becomes much more complex. Many regulatory

decisions are made about reimbursement at the

Federal and State levels, and individual insurers

make reimbursement decisions that are subject

to State and Federal regulations.

Medicare reimbursement of gene therapy might

apply, for example, to those instances (probably

quite rare) involving people over age 65 or who

suffer from chronic kidney disease that could be

treated by gene therapy (polycystic kidney disease is a dominant trait that leads to kidney failure, but is not now a candidate for somatic cell

gene therapy because the gene has not been identified and its mechanism of causing disease is not

understood).

Medicaid is joint State and Federal health program that pays for medical services provided to

indigent individuals. Medicaid reimbursement

would involve both State and Federal policy, and

might be used to pay for gene therapy of pediatric

patients in indigent families.

Little has been written about how to pay for

gene therapy. If other medical technologies are

taken as examples, early costs are likely to be relatively high, and drop as clinical experience and

technical innovations accumulate. Decisions will

be made about applications to specific disease entities rather than for gene therapy in general, and

there will likely be regional and institutional variation among payers as to which applications are

reimbursable. Mechanisms of payment could

range from complete public subsidy to total payment from personal income at each stage of development. If gene therapy proves successful in

its early applications, more attention will need to

be devoted to sources of payment.

PUBLIC EDUCATION AND DISCUSSION

The high level of interest in topics relating to

genetics suggests that mechanisms need to be developed that permit discussion at all levels of

society. Several issues relating to genetics, such

as practices in a particular laboratory or individual patient-physician decisions, must be made

locally. Other issues of national importance, such

as research policy, health policy, and civil rights,

may require attention by the Government and international agencies.

Careful public policy decisions about novel technologies require an educated public. Federal agencies have been directly involved in educating the

public about gene therapy, through congressional

hearings such as Human Genetic Engineering held

by the Subcommittee on Investigations and Oversight of the House Committee on Science and

Technology in November 1982, symposia such as

the Public Forum on Gene Therapy sponsored by

NIH in October 1983, and publications such as

Splicing Life issued by the President’s Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research.

Several scientists have expressed concern that

the nuances of genetic technologies, such as the

distinctions between somatic and germ cell manipulations, may not be completely understood by

the public (Baltimore, D., in Friedmann, 1983, p.

59). One basis for such concern is the experience

with the early debates about the safety of recombinant DNA, when laboratory research involved

precautions and preservation of detailed records

on laboratory safety of recombinant DNA work

that were considered onerous by some scientists

(Weissmann, 1981). Rancorous public debates

occurred before the City Council of Cambridge,

Massachusetts, and other places about whether

certain recombinant DNA research should be permitted (Wade, 1984). While recognizing the need

for caution in research on recombinant DNA,

some believe that public concern led to overly

stringent regulation triggered by baseless fears.

One scientist noted, “It seemed that we had lost

track of the serious scientific and health considerations and were operating in a climate of

hysteria–some of which passed for responsibility” (Leder, 1984).

Public education is, many believe, the best solution to misapprehensions about genetic technologies (Beckwith, 1984; Capron, 1984a, b). Increased public education was designated a high

priority by President’s Commission, and was in-
The Federal Role in Gene Therapy . 41

eluded as the first of the major functions of any

Federal agency overseeing the development of

genetic technologies (President’s Commission,

1982, pp. 82-84). The consensus on a need for

public education does not, however, necessarily

imply agreement that public education is primarily a function of a Federal oversight body (H. I.

Miller, 1984).

Equitable social policy is another reason to foster public discussion. The governmental role in

developing, regulating, and applying gene therapy is crucial, as noted in other sections of this

Background Paper. Informed public decisions

presuppose not only adequate knowledge, but

also a process for ensuring that all views are fairly

represented.

The need for wide public discussion of human

uses of gene therapy and other genetic technologies has been noted by religious groups (World

Council of Churches, 1982; National Council of

Churches, 1984), by the President’s Commission

(President’s Commission, 1982), by ethicists and

scientists (Grobstein, 1984), and in congressional

hearings (Gore, 1982). Opinion on this issue appears to have converged from many quarters,

involving scientists, ethicists, politicians, and

religious leaders, and resulting in what one observer has called an “amazing consensus” about

the need for continued oversight and discussion

at the Federal level (Nightingale, 1984). The functions of such discussion include definition of goals,

identification of public policy issues, inclusion of

conflicting views held by different constituencies,

and consideration of short- and long-term consequences of genetic interventions of concern to

various scientific, medical, religious, and consumer groups.

There are some potential problems that even

an effective Federal forum for discussion may not

accomplish, however. It is doubtful that any commission can resolve the differences that emerge

from moral and social plurality in the United

States. For example, what conditions should be

treated by gene therapy? Disorders such as baldness or short stature that are considered minor

annoyances by one person might merit somatic

gene therapy as judged by another.16 No regula18Nelther of these conditions is sufficiently understood to be a

.

candidate for somatic cell gene therapy. They are mentioned only

to illustrate a point, not to indicate technical feasibility.

38-803 0 - 84 - 4 , ~L ~

tory apparatus is suited to resolving such dilemmas. Public debate can air differences, but

should not be expected to eliminate them.

In addition, there is a danger of gratuitous additional regulation that would impede the development of legitimate human applications of

genetics if new agencies are created, or overly

stringent regulations imposed 0-I. I. Miller, 1984).

Finally, public debate cannot and should not intervene in the decisions best made by individual

patients and the health professionals who provide

care. Personal choice is a value that should be constrained as little as possible in establishing public policy.

FAIR DISTRIBUTION OF BENEFITS AND COSTS

The costs and benefits of gene therapy are

uncertain because the technology is in its infancy.

If gene therapy becomes a part of routine medical practice, however, then many issues relating

to distribution of costs and benefits may arise.

In general, these would be similar to those raised

by other medical technologies: payment, informed

consent, and fair access. Fair distribution of costs

and benefits would be one of the considerations

in reimbursement decisions mentioned above. It

may fall to government to rectify reimbursement

decisions that do not provide equal access to all

social sectors and ethnic groups. Access to gene

therapy by the indigent or by minorities especially

prone to certain genetic diseases, for example,

might prove of special concern.

Decisions made now about research funding

will also influence the future distribution of

benefits from gene therapy. Because different

genetic diseases are more common in some racial

groups, decisions about which diseases to investigate can be expected to influence the later

availability of gene therapy or other treatments

among such groups. Neglect of hemoglobin disorders, for example, would be of more concern

to Blacks and those of Southern Mediterranean

extraction than to other Caucasians. Federal decisions about which diseases are addressed in

genetic research thus have potential distributional

consequences, and the large share of genetic research supported by the Federal Government

makes such decisions important in determining

which populations may eventually benefit from

available technologies.
42 . Human Gene Therapy—Background Paper

PROTECTION OF INDIVIDUAL RIGHTS

Some individual rights protected by the Federal

Government may be influenced by gene therapy,

as by any new medical technology. Any threat to

such rights is, however, more likely to derive

from new diagnostic techniques of genetic testing

than from gene therapy. Maintaining the privacy

of genetic diagnostic information about disease

risks is likely to be a much larger problem for

individuals’ rights than performing gene therapy

because: 1) more people will be affected, 2) more

information will be generated by diagnostic techniques than therapeutic interventions, 3) the diseases for which genetic risk factors might be

assessed are common and have large economic

consequences for employers and insurers, and 4)

problems in protecting individual rights for gene

therapy are quite similar to the problems arising

from other therapies, while genetic diagnostic

technologies may make much more information

available of a new type. These issues are briefly

addressed in appendix B.

Knowledge that a person has undergone gene

therapy should be accorded the same privacy

safeguards applied to other medical information.

In addition to ensuring the privacy of genetic information, including medical information about

gene therapy, the Federal Government has accepted a role in protecting the interests of research subjects. Such protections include IRB’s

and, in the case of gene therapy, the RAC at NIH.

FDA oversight also includes attention to informed

consent of participating patients.

A few weaknesses persist in the present methods of research subject protection. Children and

mentally incompetent patients cannot consent to

treatment because they cannot understand the

consequences of such consent. The process of informed consent requires different standards in

different court jurisdictions (see app. B and Andrews, 1984a), but all standards involve a competent patient or surrogate decisionmaker who

can rationally balance risks and potential benefits.

In cases of disagreement with physicians or other

health professionals, families often are involved

in making decisions in the best interests of the

patient. In some instances, especially when there

is disagreement between medical professionals

and families, it is not clear who can and who cannot give consent for treatment or participation

in experiments. The problem of surrogate informed consent is especially likely for gene therapy, because many genetic diseases primarily affeet children or cause mental incapacity in adults.

There are special guidelines for IRB’s to consider

in approving research protocols that involve

children (Code of Federal Regulations, 1983).

Uncertainty about informed consent can act as

an impediment to research on the one hand, and

may leave some patients insufficiently protected

on the other. Some states are drafting legislation

to deal with the problem (Andrews, 1984a). State

and local initiatives may eventually clarify the

legal status of surrogate informed consent, but,

in the interim, responsibility for monitoring the

informed consent process for research participation will fall to IRB’s and the courts.

Case histories

IN VITRO FERTILIZATION

Some lessons from Federal policy relating to research and clinical applications of in vitro fertilization (IVF) may be applicable to the development

of gene therapy technologies. In vitro fertilization

is the process of obtaining sperm and eggs from

donors, uniting the gametes in the laboratory, and

implanting the products of fertilization in a woman’s

womb. This technology was developed in the

1950s, and first successfully applied to humans

in 1969. Improvements in fertilizing eggs in the

laboratory led to the first human applications of

in vitro fertilization a decade later: Louise Brown,

a normal infant conceived using in vitro fertilization, was born on July 25, 1978. She has been followed by more than 700 pregnancies resulting

from in vitro fertilization and embryo transfer

(Hodgen, 1984).

The primary intent of those using in vitro fertilization in humans is to permit infertile couples

to have children (Hodgen, 1984) although other

applications are technically possible.

In vitro fertilization is related to gene therapy

because, for technical reasons, attempts at germ

line genetic alterations are most likely to be attempted on early embryos. Germ line gene therapy would involve either extraction of a fertilized

embryo from a woman (before the embryo had
The Federal Role in Gene Therapy 4 3

implanted in the uterine wall) or, more likely, in

vitro fertilization either immediately preceded or

followed by addition of genetic material. Availability of in vitro fertilization is thus a precondition for successful germ line gene therapy (Ryan,

1983) and so policy affecting in vitro fertilization

practices will also affect germ line gene therapy.

Even if in vitro fertilization were not directly

related to gene therapy, the history of Federal policy on it would still be of interest because it is

a controversial biological technology analogous

to gene therapy in some respects. A brief review

of decisions made about in vitro fertilization may

highlight potential pitfalls that could also occur

in connection with gene therapy.

There has been a de facto moratorium on Federally sponsored research on human in vitro fertilization in the United States since 1975. There

are nonetheless at least 60 centers and 200 programs offering it in the United States (Abramowitz, 1984; Hodgen, 1984). The research leading

to these early efforts was performed primarily

in the United Kingdom and Australia. American

centers have adopted the technology developed

in other nations, or have treated patients using

private moneys paid by patient fees.

Congress imposed a temporary moratorium on

Federally sponsored human in vitro fertilization

research in 1973, after NIH received its first request for a grant for fetal research. The 13 month

moratorium was technically lifted in 1975, when

guidelines proposed by the Ethics Advisory Board

(EAB) of the Department of Health and Human

Services (then the Department of Health, Education, and Welfare) were published. The guidelines

sanctioned carefully constrained research, provided that strict procedures were observed, including:

the intent of the research was to improve understanding of fertilization and assess risks,

the information could not be obtained by

other means,

informed consent, including disclosure of

risks, was obtained, and other regulations on

human subjects research were observed,

embryos beyond the fourteen-day stage of

development were excluded if embryos were

not to be implanted back into prospective

mothers,

measures were taken to ensure that possible risks to the public were disclosed,

only gametes from married couples were

employed if embryos were implanted in prospective mothers, and, most importantly,

approval was obtained from the EAB, in addition to IRB review, before commencing.

The findings of the EAB have never been accepted by a Secretary of HHS (or HEW), the EAB

has been disbanded, and no Federal grants have

been approved for research on in vitro fertilization. The NIH authorization bill from the 98th

Congress, as passed by both houses and vetoed

by the President, would have mandated a further

3 year moratorium on human fetal research, and

the new congressional bioethics board would

have undertaken a study of it (Conference Report,

1984). The moratorium on human fetal research

will continue, however, until an EAB that could

approve it is reconstituted by the Secretary of

Health and Human Services.

The Federal moratorium on research in the

United States did not prevent the development

of in vitro fertilization technology or its clinical

application, although its development has probably been somewhat slowed (Abramowitz, 1983).

There is some concern that the technology has

developed with less than usual Federal oversight,

and that some desirable steps, such as testing in

non-human primates, have been skipped in the

transition from experiments in lower mammals

to human clinical applications (Ryan, 1983). Experiments have not been subject to the NIH peer

review process, and may have “circumvented systematic accumulation of knowledge” (Ibid., p. 152).

The Federal Government may have lost some

ability to monitor and control the technology by

failing to sponsor research (Ibid., pp. 151-153) or

at least to provide a mechanism for Federal oversight. Furthermore, the technology developed in

spite of the lack of a consensus about its moral

acceptability (Ibid., p. 153).

The unusual development of in vitro fertilization research is exemplified by one technique of

in vivo fertilization of an egg in one woman fol-
44 . Human Gene Therapy—Background Paper

lowed by transfer of the embryo to another. The

technique permits obtaining the fertilized egg

without subjecting the donating woman to a major surgical procedure. This technique has been

developed with corporate funds in the United

States, and those who sponsored the research

have applied to patent some of the instruments

involved, as well as the process itself (Annas, 1984;

Chapman, 1984). A patent for a medical procedure is unusual, although not unprecedented

(Brotman, 1983); if granted, it would give the

sponsoring corporation the ability to limit the application of surrogate embryo transfer to those

who obtained a license. Such limitation might increase costs and diminish access to the technology, but might also permit enhanced quality and

controlled diffusion of the procedure. One of the

arguments used in favor of patenting the process is that the research was privately sponsored,

and so the investors merit a return on their investment (Chapman, 1984; Annas, 1984).

The example of in vitro fertilization technology

shows that techniques developed in other countries can be imported, and such applications made

available in the United States, even in the absence

of Federal research support. Widespread clinical

use of in vitro fertilization also shows that technologies whose appropriateness is seriously questioned may nevertheless enter clinical practice

without extensive Federal oversight or regulation,

and in the absence of pervasive public discussion.

Gene therapy is different from in vitro fertilization because there is no moratorium on gene therapy research, and so the bulk of research is

funded, like other biomedical research, through

the Federal government. Such research necessarily falls under the oversight purview of NIH,

and consequently the RAC and its Human Gene

Therapy Working Group. There are many agencies with jurisdiction over gene therapy, including

local IRBs, NIH, and the FDA (for specific products). These bodies are now preparing to deal

with the incremental medical advance embodied

in somatic gene therapy. Review by these bodies

may not be adequate for extension of gene therapy to reproductive cells. Several authors refer

to the need for national public discussion of the

greater ethical and social implications raised by

germ line alterations before commencing such research (although the authors do not uniformly

suggest that such discussion necessarily take place

through the Federal Government) (Fletcher,

1983b; Grobstein, 1984; Nightingale, 1984). The

lack of a forum for conducting public debate

holds also for fetal research and in vitro fertilization.

Human gene therapy may be less attractive to

corporate investors than in vitro fertilization research. The investment incentives for gene therapy are diminished by the relatively small number of individuals with any given genetic disease.

This restriction does not hold, however, for all

diseases and does not necessarily preclude the development of profitable products. Gene therapy

applicable to certain diseases such as sickle cell

anemia or cystic fibrosis might have a market

large enough to justify corporate interest. In addition, a general approach to gene therapy that

could apply to many genetic disorders might be

patented, analogous to the Cohen-Boyer patent

for recombinant DNA, or kept as a trade secret.

The incentives for private investment may thus

be weaker than for in vitro fertilization, but may

nonetheless be sufficient to induce corporate research and development.

There is a prominent regulatory difference between in vitro fertilization and human gene therapy: in vitro fertilization is not clearly under the

jurisdiction of FDA or NIH, but human gene therapy is subject to both. Gene therapy is likely to

involve new pharmaceutical products, and hence

be regulated by FDA, because experiments will

involve introduction of new genes or modified

viruses into human cells or into patients. In contrast, in vitro fertilization is more a process than

a product. Further, in vitro fertilization is applied

to correct infertility, a problem that is not necessarily considered a disease or injury, and thus

may not fall under FDA purview. In vitro fertilization has passed through the early phases of technological development to clinical application with

little regulation or Federal oversight, but human

gene therapy is receiving extensive public scrutiny and Federal oversight despite its technological infancy.

EARLY ATTEMPTS AT HUMAN GENE THERAPY

The Rogers Cases.—Between 1970 and 1973,

Dr. Stanfield Rogers, an American, assisted a German physician in treating three sisters with the
The Federal Role in Gene Therapy 4 5

genetic disease arginemia. The sisters were infected with the Shope papilloma virus, which had

activities that physicians believed might supplement an enzyme activity missing in the three girls.

The treatment was unsuccessful.

The Shope virus experiments were performed

before ethics review boards, IRB’s, or IBC’s existed. The experiments were discussed openly, although much of the debate about their propriety

did not take place until after the clinical trial. The

debate centered on whether there was sufficient

evidence to anticipate patient benefit, and

whether the intervention had been undertaken

at a time when it could best benefit the sisters

(Fletcher, 1983). The ethical debate about the

Shope virus experiments is thus unresolved, although it is clear that no institutional or legal

precepts were violated.

The Cline Cases.—Martin Cline, an American

scientist and physician primarily working at the

University of California at Los Angeles (UCLA),

became the first investigator to attempt gene therapy using recombinant DNA in 1980, when he attempted to treat two patients who had thalassemia.

One patient was treated in Italy, and the other

in Israel. Dr. Cline withdrew samples of bone marrow from each of the patients, treated them with

DNA containing a normal hemoglobin protein

gene, and restored the treated bone marrow cells

to the patients. The process for returning the

bone marrow involved killing a portion of the

native cells by radiation, so that the treated cells

would have a location in which to grow. The experiment was the first attempt at somatic gene

therapy using recombinant DNA techniques.

At the time the experiments were performed,

approval by the local review committees was

pending. The gene therapy experiments were attempted on July 10 and July 15, 1980, and Dr.

Cline’s proposal to the UCLA Human Subject Protection Committee was disapproved on July 16

(Talbot, 1982). Dr. Cline had prior approval for

a gene therapy experiment by the local board in

Israel, but not for the one, involving recombinant

DNA, that he actually performed.17

————

‘The Israeli board had approved insertion of genetic material that

included the normal hemoglobin protein genes. Dr. Cline contends

that the use of recombinant form was a technical detail that did

In contrast to the Shope virus experiments,

there was a consensus that Dr. Cline’s experiments were premature and unethical. Dr. Cline

resigned his division chairmanship, and the NIH

terminated two grants, To prevent future abuses,

NIH also added several requirements, including

the need to submit an assurance of compliance

with human subjects safeguards, prior review by

the local IBC and NIH of all recombinant DNA experiments, and inclusion of the NIH report of the

events to the review groups for his subsequent

new applications for NIH grants (Talbot, 1982).

The special sanctions were in effect until May

1984.

The issues raised by the Cline experiments are

likely to recur in any debate about the propriety

of human gene therapy, and so a summary of the

justifications and objections is instructive, followed by a review of Federal policy in the Cline

clinical trials.

There were several justifications for undertaking clinical trials of human gene therapy, as noted

in previous sections. Those used to justify the experiments involving the patients with thalassemia

included:

The condition was irreversible.

Alternative therapies were unpleasant, expensive, led to deleterious side effects, and

did not cure the cause of the disease, but

merely diminished its effects (Wade, 1980;

Cline, 1982).

The Human Subjects Protection and Institutional Biosafety Committees had been considering the proposals in the period between

May 1979 and July 1980 without approving

or disapproving them. There was also an

apparent logjam, with the Human Subjects

Committee requiring that the IBC approve the

protocol before it would assess it, and the IBC

awaiting the review of the Human Subjects

committee. Attempts to refer the matter to

the RAC were thwarted because NIH refused

to consider the proposals, reasoning that the

human subjects aspects were much more imnot add to the danger of the experiments, because the genes tend

to combine in the cell even if they are not in recombinant form

i~hcm first inserted (Cline, 1982),
46 . Human Gene Therapy—Background Paper

portant than the recombinant DNA technology itself (wade, 1981a).

The Israeli experiments were approved by

three committees in Israel, although not for

the protocol involving recombinant D N A

(Wade, 1981b).

Those who criticize the Cline experiments do

not disagree with these facts, but interpret them

differently, and add the following considerations:

The patients selected had an irreversible disease, but were not in a terminal state (as

called for in the protocol). They were alive

more than two years after the experiments

were undertaken, despite lack of any benefit deriving from the experiments (Cline,

1982).

The human experiments were never published and were based on other animal experiments that had not been peer-reviewed

at the time (and about which there are disagreements regarding interpretation) (Cline,

1982).

There were no data on the safety of the procedure, because directly analogous experiments had not been attempted in animals

(Williamson, 1982).

Dr. Cline personally decided to deviate from

his protocol, using a recombinant molecule

rather than separated genes. While this decision may have been scientifically valid, Dr.

Cline failed to notify the Israeli committees,

committees in the United States, and even the

patients and his collaborators, of his decision

to use recombinant DNA (Wade, 1981a; Cline,

1982).

The ambiguities about which committee

should first approve the protocol had been

resolved by the time the experiments took

place. The decision to refrain from using

recombinant DNA removed the need for IBC

approval, leaving only the local Human Subjects Protection Committees to approve the

protocol (Wade, 1980).

The Human Subjects Protection Committee

in the United States was not dallying, but

awaiting expert comments from four consultants to assess the scientific basis of the

experiments. The process took time, and the

comments were passed on to Dr. Cline and .

his collaborators as they were received; the

investigators knew that there were objections

to starting the experiments (Wade, 1980).

The issues raised by the controversial Cline experiments point out the importance of Federal research policy decisions. The research in question

was funded, in large part, through NIH, and the

review procedures for application to humans

were specified by the NIH. The sanctions rendered

against Dr. Cline were imposed by the Department of Health and Human Services, based on NIH

review; many believe that one reason that the

sanctions were relatively stringent was because

of congressional concern about previous laxity on

the part of NIH in punishing those who violated

research guidelines (Sun, 1981; Wade, 1981 b).

Some of the consequences of the Cline experiments are less tangible than receipt or denial of

grant applications. Many believe that the Cline experiments are one reason for the current prominence of gene therapy in the debate about recombinant DNA. Critics of the technology may cite

Dr. Cline’s experiment in arguing for tighter restraint on scientists because they cannot be

trusted to behave responsibly (Wade, 1980).

A de facto moratorium on somatic and germ

line gene therapy has reigned since 1980. The

Cline experiments may have catalyzed formation

of a consensus that the time was not ripe for such

experiments (Walters, 1982), and the opprobrium

directed at Dr. Cline may have made scientists

aware of the public sensitivity of the issue. The

case, above all, highlighted the changing milieu

for making decisions about human subjects in

clinical research, and the growth of research

oversight by the Federal Government. The results

have been summarized by John Fletcher, a specialist in bioethics at NIH:

Dr. Rogers treated the German sisters before

prior group review became institutionalized. Dr.

Cline, on the other hand, attempted to bypass that

safeguard by withholding information from those

who passed judgment on the wisdom of the experiment. The censure falling on Dr. Cline because of his deception indicates the strength of

prior group review as a structure to guide somatic

gene therapy when it becomes feasible (Fletcher,

1983b).
Conclusion 4 7

Conclusion

The first realistic applications of human gene

therapy will be closely scrutinized by both the

public and the Federal Government. Civic, religious, scientific, and medical groups have all accepted, in principle, the appropriateness of gene

therapy of somatic cells in humans for specific

genetic diseases. Somatic cell gene therapy is seen

as an extension of present methods of therapy

that might be preferable to other technologies.

Whether somatic cell gene therapy will become

a practical medical technology will thus depend

on its safety and efficacy, and the major question

is when to begin clinical trials, not whether to

begin them at all. The quality that distinguishes

somatic cell gene therapy most strongly from

other medical technologies is not technical, but

rather the public attention that is likely to attend

its commencement.

Federal oversight mechanisms for research and

clinical application of somatic cell therapy are

already in place, and enforcement of the mandated approval processes has already taken place

in one instance, the breach of NIH guidelines

perpetrated by Dr. Martin Cline. Committees exist at local institutions to monitor protocols for

human subject protection, and all proposals for

federally sponsored clinical trials should be referred to the RAC at NIH for approval, and may

also be reviewed by FDA.

The consensus about the propriety of somatic

cell therapy does not extend to treatment for

traits that do not constitute severe genetic diseases, and does not encompass germ line gene

therapy in humans. The question of whether

germ line gene therapy should ever begin is now

highly controversial. The risk to progeny, relative unreliability of the techniques for clinical use,

and ethical questions about when to apply it remain unresolved. The question of whether and

when to begin germ line gene therapy must therefore be decided in public debate informed by technological developments.

If gene therapy develops as a viable new medical technology, issues will emerge regarding who

is to pay for it, how to assure equitable access

to it, who is qualified to perform it, how to regulate its proper use, and which diseases merit its

application. Many Federal agencies, including NIH,

FDA, and health care payers, will be involved in

such issues if the technology becomes part of

standard medical practice.
48 . Human Gene Therapy—Background Paper

Technical note 1

DNA function

Deoxyribonucleic acid (DNA) is a long, double

stranded, helical molecule that contains building

blocks (nucleotide bases) in a sequence which encodes

instructions for all the metabolic processes in the

human body, These range from growth and development through specific biochemical interactions involved in the digestion of food and synthesis of new

molecules. DNA regulates its own expression and controls the production of proteins: structural proteins,

used to build the framework of cells, organs, and

tissues; and enzymes, used to perform biochemical

activity. There are two major processes involved in

putting this information to use in the body-transcription and translation.

Transcription is the simplest of these two processes. It consists of making an RNA (ribonucleic acid)

copy of the DNA. This copy is then used to transport

the instructions from the DNA to the protein building apparatus in the cell, outside the nucleus. This RNA

copy of the DNA is called ‘(messenger RNA” (mRNA)

because the message it carries from the gene allows

the construction of the specified protein.

The process by which the mRNA is formed is very

simple, taking advantage of the unique properties of

nucleic acids (DNA and RNA). The double stranded

DNA molecule separates, or unzips, at which point specific proteins present in the nucleus (enzymes) recognise precise signals present in the DNA (e.g., sequences

of nucleotide bases, such as TTAA) and attach to the

DNA at those sites. One enzyme (called an RNA polymerase) then moves along the DNA molecule, constructing an mRNA molecule that has a complementary sequence of nucleotide bases (i.e., where there

is an A in the DNA, the mRNA polymerase will add

a T to the growing polymer). The end result is an RNA

molecule that is a mirror image of the DNA region,

or gene, which can then direct the assembly of a specific product.

Before this mRNA molecule is used to assemble a

protein in the process of translation, however, it must

first be subtly modified; trimmed and tucked, as it

were, so as to more precisely fit its function. There

are several of these trimming processes and they are

known altogether as “mRNA processing” or “posttranscriptional modification”. Our understanding of

these processes is incomplete, but the two best known

are “excision/ligation” and “methylation. ”

Excision/ligation is most similar to an editing process, and it is necessary because many genes contain

more nucleotide bases than are necessary to code for

the number of amino acids the finished protein will

contain. Within a given gene there are two types of

regions: “exons,” or expressed regions, and ‘(in=

trons, ” or intervening regions. Exons contain the information that precisely directs the assembly of the

protein product, that is, the sequence of amino acids

added to the growing protein chain during translation.

Introns, on the other hand, are the regions found between expressed regions. Their function is unclear;

one hypothesis is that introns are involved in regulating gene expression (which includes turning genes on

and off and controlling the number of mRNA molecules produced, and therefore the amount of gene

product). The original mRNA transcript is thus

trimmed and spliced by specific enzymes and transported from the nucleus to the cytoplasm, where it

is decoded or translated into protein (see diagram).

Methylation refers to the process of attaching a small

molecule (a methyl group, or a carbon with three attached hydrogens, CH3) to the backside of one of the

nucleotide bases in the mRNA. The reason for this is

not completely understood, but it is thought that

methylation alters the mRNA in such a way that some

enzymes responsible for degrading it will not do so

as quickly as they otherwise might. Methylation provides a method for controlling the longevity of mRNA

molecules; it is desirable for some to be very short

lived (where only a small amount of the encoded protein is required, as for an enzyme briefly needed) and

for others to last longer (e.g., the mRNA coding for

hemoglobin production in red blood cells, which live

for about three months in the bloodstream).

The second major process involved in making use

of the information encoded in the DNA is translation,

This takes place after mRNA is transcribed from DNA

and then transported from the nucleus into the cytoplasm. In translation the information encoded in

mRNA is decoded (translated) into protein by ribosomes. Ribosomes are complex structures within the

cell that serve as the sites of protein synthesis, and

they are composed of a number of different proteins

combined with several different RNA molecules. On

ribosomes, amino acids are joined one at a time to

form a growing polypeptide chain. These individual

amino acids are brought to the ribosome by transfer

RNAs (tRNAs). Each different amino acid is brought
Technical Note 1 4 9

Gene Splicing

SOURCE: Office of Technology Assessment, adapted from Stanbury, et al., 1983,

to the ribosome by a specific tRNA, which has a recog- master DNA region (gene) in the nucleus. Proteins pronition site at one end specific for that amino acid, and duced by translation of messenger RNAs can begin

a recognition site at the other end specific for the their lives as enzymes involved in specific chemical

mRNA coding sequence that calls for the particular reactions in the cell, or the proteins can be moved

amino acid. These specific coding sequences in mRNA around or modified so that they become part of the

occur in a linear chain, and the amino acids added to surface of the cell, part of the cell’s skeleton, or perthe growing polypeptide as the mRNA moves along the form some other function.

ribosome reflect the linear sequence encoded in the
50 . Human Gene Therapy—Background Paper

met

met

I

a l a cys

mRNA—AUG GCA UGC CCU

Protein

Complete protein

AUG GCA UGC CCU AUG GCA UGC CCU

UAA AUG GCA UGC CCU AUG GCA UGC CCU AUG GCA UGC CCU

tRNA translates from mRNA into protein, with ribosomes acting as the conveyor belt to allow this process

SOURCE. Office of Technology Assessment.
Technical Note 2 5 1

Technical note 2

Genetic engineering techniques:

cloning and vectors

There are several techniques of genetic engineering that are fundamental to efforts at human gene

therapy. The most basic of these is cloning, or making multiple copies of a specific single gene. Once a

gene has been cloned, it may be made in as many

copies as desired (and thus easily studied), or moved

from place to place through the use of specialized

agents known as vectors. There are several types of

vectors; viruses (bacteriophages, or phages), plasmids, or transposable elements.

Cloning involves several different steps. First the

gene of interest must be identified; if it exists in only

one copy per haploid genome (as with single gene, or

Mendelian defects) then that one copy must be selected from perhaps as many as 100,000 other genes—

a formidable task. As daunting as this problem is, however, there are some elegantly simple solutions.

The most favored of these is to identify the messenger RNA used by ribosomes to assemble the protein

of interest. Although mRNA is short-lived and notoriously delicate, this can often be done. From this

mRNA a complementary DNA (cDNA) molecule can be

synthesised, labeled with a tracer (radioactivity or a

dye) and then used as a probe to identify the gene.

If an mRNA cannot be identified, then it is possible

to start with the protein product itself. This protein

can be analysed and its amino-acid sequence determined. The amino-acid sequence can be used to

deduce the nucleotide base sequence of the gene encoding the protein. A DNA molecule can then be synthesised and used as a probe to locate the relevant

gene with its associated control sequences.

Once identified and located, special enzymes (restriction endonucleases or restriction enzymes)

make it possible to isolate the entire intact gene and

insert it into the appropriate vector. Plasmid (circular

DNA molecules found in the cytoplasm of bacteria

such as E. coli) or virus (phage) vectors make it possible to produce enormous numbers of copies of the

gene of interest.

Plasmids.—In addition to the genetic information

required for the existence of a simple bacterium,

which is contained in its own genes, on its own

chromosome, many bacteria also carry in their cytoplasm small circular molecules of DNA that replicate

on their own. These are called plasmids and any number of them, from none to hundreds, can be found

in individual bacteria. They are transmitted to progeny

cells with the cytoplasm (hence the name) as the

parent cell divides. The genetic information encoded

in plasmid DNA often determines specialized characteristics of the bacteria, such as resistance to antibiotics. Their small size and simplicity have made

them handy tools for the precise duplication and delivery of genetic information.

Some plasmids can be injected into the cells of higher

animals where they replicate or integrate and pass

from cell to cell as the cells divide. They are widely

used in copying and multiplying genes because the

special characteristics (e.g., antibiotic resistance) are

easily engineered. These can he used to selectively promote the growth of cells that contain the plasmid, and

thus also the desired genes.

Phage.—Phage (or bacteriophage) are viruses that

infect bacteria, commandeer the bacterial machinery,

and use it to translate the genetic information contained in the phage into phage products. Normally this

leads to an infected bacterium producing phage offspring, but if the genes for building phage are replaced

with a gene of interest to researchers, then the infected bacterium will produce copies of that gene instead. Phage can thus be used in much the same way

that plasmids can, to make multiple copies of a given

gene. The choice between using phage or plasmids as

cloning vectors is based on the ease with which genes

of different sizes or composition can be cloned with

the different methods, and the advantages of different

screening methods that can be used with the different

vectors.

Transposable Elements.—Transposable elements

(transposons) are relatively small molecules of DNA

that can insert themselves into the genome of the host

organism and move from site to site within it. Their

origin is uncertain, but they seem closely related to

some viruses. They have been called infectious or

parasitic DNA and behave in some ways very much

like infectious agents.

Genes of interest can be inserted into a transposable

element, and thus be incorporated into the host

genome along with the transposable element at specific sites. Although there are no transposable elements presently in use in human cells, they have been .

successfully used to “treat” genetic defects in fruit flies

of the genus Drosophila (Rubin and Spradling, 1982;

Spradling and Rubin, 1983). A mammalian equivalent

to a transposable element would be a welcome discovery, as it could be used to control points of insertion into a human genome very precisely. Some viruses

being considered as vectors for human gene therapy

have similarities to transposable elements, including

precise insertion sites.
52 . Human Gene Therapy—Background Paper

Technical note 3

Violating species barriers

The majority of gene-therapy cases in humans would

involve transplanting human DNA from one individual to another. In the forseeable future, research on

and application of these techniques (or capabilities) is

unlikely to use genes from an animal species to treat

human genetic diseases. It is more likely that techniques involving the transplantation of genetic material from one animal species to another would be useful in agricultural or industrial applications; work of

this kind has already been performed (involving human genes being moved into certain agricultural animals). The most far- reaching experiments of this sort

are designed to increase understanding of mechanisms

of genetic control and gene regulation. * This research

will enhance scientists’ ability to work with the genes

of individuals within a species, and thus decrease the

need to transfer genetic material between species in

future therapeutic endeavors. The question has

arisen, though, as to whether such work should be

completely avoided or terminated because of an inherent danger or impropriety in “violating species

boundaries. ” A look at nature offers a useful

perspective.

A species is a community of organisms that is reproductively isolated from other such groups; that is,

within a species there is interbreeding (exchange of

genetic material) among individuals and their offspring, but none with individuals of other, different

species. The problems with this widely used definition are several, and many of them are quite technical and esoteric. The most significant of these involve

the existence and frequency of hybrids, or “crossbreeds” between species.

If species are to be defined on the basis of reproductive isolation, a sort of “genetic quarantine)” then violations of this quarantine, hybrids, should be rare and

IThe study of oncogenes (genes whose expression is linked to cancer) has

in~ol~ed hundreds of transfers of genes between species. From them we have

learned enormous amounts about the mechanisms of carcinogenesis and gene

regulation.

unusual. This is emphatically not the case in nature.

Hybrids are well known in higher organisms, where

admittedly many are sterile (e.g., mules, resulting from

a mating between a horse and a donkey). However in

some groups hybrids between species are so common

that distinct populations of these intermediate forms

may exist along the distribution boundaries of neighboring species (Endler, 1977; Mayr, 1963, 1970). In

these hybrid populations it is very difficult to assign

an individual to either of the parent populations,

which might themselves be quite easily distinguished

from one another. Hybrids are more common in less

advanced vertebrates, such as amphibians or fish, and

there are even cases known where new species have

been formed by hybridization between two previously

existing species (White, 1978). In other situations

species “boundaries” are so permeable that relatively

widespread movement of genetic material from one

species to another exists, a phenomenon called introgression. In plants, hybridization is so common that

one leading expert (Raven, 1980) has concluded that

it is almost useless to talk of “species” and that the most

important reproductive group is the local population,

or deme. To complicate matters further, some recent

research offers tantalizing hints that horizontal transmission (between individuals of the same generation)

very similar to the sort contemplated in some types

of gene therapy have probably taken place between

distantly related species (felids, or cat-like creatures,

and primates) in the past (Benveniste and Todaro,

1982; Lewin, 1984). Specialists today are therefore becoming increasingly interested in factors that keep a

species together rather than in mechanisms that may

serve to keep them apart (Paterson, 1981, 1982).

This is a useful approach in considering animal experiments relevant to human gene therapy. The question changes from “When can we justify violating

species barriers?” to ‘(How much transmission of

genetic material from one species to another can be

tolerated before the integrity or separateness of the

recipient species is threatened?” The answer is clear—

an enormous amount; far more than would ever be

involved in any case of gene therapy.
Technical Note 4 5 3

Technical note 4

Fertilization, implantation, and

development

FERTILIZATION

When a sperm and egg (or ovum) meet, the sperm

penetrates the wall of the egg. The genetic material

from the sperm and egg unite, and the process of unifying the genetic contents of sperm and egg is called

fertilization. The cell thus formed, containing DNA

from both sperm and egg, is called a zygote. The mass

of cells in the earliest stages after fertilization is also

called a conceptus.

The release of an unfertilized egg from a woman’s

ovary is triggered by a burst of luteinizing hormone,

or LH, from the pituitary gland (located near the base

of the brain). The released egg migrates from the

ovary a short distance through the abdominal cavity

and into the oviducts, or Fallopian tubes. The Fallopian tubes lead into the uterus, and are the usual site

of fertilization after the sperm have migrated into

them from the vagina through the uterus to meet the

descending egg. The developing conceptus then continues its descent through the Fallopian tubes into the

body of the uterus.

CELL DIVISION

The zygote begins to divide, first into two cells, then

into four, then eight, and so on. During the earliest

stages of development all the cells are more or less

equivalent. Once more than 16 cells are present, however, some distinctions between different types of cells

begin to appear. Quite small and difficult to detect at

first, these differences become more pronounced as

cell division and growth continue, and form the foundation for the later differentiation of tissues and

organs.

Different terms are applied to the developing organism as larger numbers of cells accumulate. The process of cell division is called cleavage. When enough

cells have accumulated (between 32 and about a hundred), the term morula is used. The following stage,

when the cells arrange themselves around a central

cavity, is called the blastocyst. About I week after

fertilization the blastocyst attaches to the uterine wall

to continue further development.

IMPLANTATION

Implantation is the term applied to the process by which the conceptus attaches to the wall

of the uterus and begins to send fingers of tissue

(chorionic villi) into the wall of the uterus as anchors. These fingers are made up of embryonic cells

that manufacture hormones to support pregnancy;

they also form the network of supporting tissues that

will eventually become the placenta, nourishing the

developing embryo, and later fetus.

DEVELOPMENT

At the same time the primitive placenta is forming,

the cells that will later become the embryo, and then

fetus, become more distinct from those embryonic

cells that develop into the supporting structures

(placenta and protective membranes). By 2 weeks postfertilization the process of implantation is almost complete, and differentiation of the embryo itself is becoming more pronounced: at least two distinct classes

of embryonic tissue can be identified. The third week

sees the emergence of a group of cells called the

primitive streak that will eventually lead to the development of the nervous system, which begins before

the end of the third week after fertilization. The

primitive streak is the first landmark that distinguishes

the “top” from the “bottom” of the embryo.

The embryo rapidly continues to develop more defined features, including limbs, organs, ears and eyes.

About 8 weeks after fertilization (7 weeks after implantation) most of the basic tissues have taken shape.

It is at this point that the embryo makes the transition to a fetus, with most subsequent development taking the form of growth and specialization of organ

function, rather than the formation of new organs.

Highly complex systems, like the brain and nervous

system, continue to develop long after the embryo has

become a fetus, and even after birth.

VIABILITY

Viability is the term used to indicate that the fetus

could survive outside the womb. The concept of viability played a central role in the Supreme Court decision in Roe v. Wade, in which maternal rights with

respect to abortion were decided. The point at which

viability begins has been considered to be about the

beginning of the third trimester of normal gestation.

This is subject to change, however, with innovation

and progress in postnatal care. New techniques are

proving to be efficient at preserving the lives of

younger and smaller premature infants, and the trend

promises to continue. The effect of these changes on

the medical determination of fetal viability and its relation to maternal legal rights is not at all clear.
54 • Human Gene Therapy—Background Paper

Sperm

nucleus

Egg

nucleus

Human Fertilization and Early Embryonic Development

Combined maternal &

paternal chromosomes

—

ZYGOTE

Nucleus of zygote

B

Fertilization F

2-cell stage

First mitotic

division

/

4 cell stage

terine

wall

I

Invading

trophoblast

Implantation starts

SOURCE: Office of Technology Assessment
Technical Note 4 5 5

Implantation of the Embryo in the Wall of the Uterus

Vertical section: Human embryo, on about the 10th day,

becomes embedded in the soft uterine

wall. After about 2 additional weeks, the

embryo wiII derive nourishment through

a new placenta which wiII develop at

the site of the attachment

Imbedded embryo forms site of placenta

Human Placenta

Maternal

blood vessels ~

Umbilical

cord
56 Human Gene Therapy—Background Paper

Head

Leg

Fetal Position in the Uterus

Umbilical cord

SOURCE: Office of Technology Assessment.

Human Embryonic and

Embryo

Fetal Stages

Jaws

15 weeks

SOURCE: Office of Technology Assessment.
—.—

Technical Note 5 5 7

Technical note 5

Hemoglobin disorders: a case study of

genetic disease

Inherited hemoglobin disorders are currently the

best studied and defined of all human genetic diseases.

They are probably the most common single-gene diseases in the world (Weatherall and Clegg, 1981). Because of that, and because the blood- manufacturing

cells in bone marrow are so accessible, hemoglobinopathies were presumed, until several years ago, to be

the first candidates for human gene therapy.

Although innovative recombinant DNA technology

has pinpointed the genetic defects responsible for different hemoglobin disorders, recent experiments revealing that the regulatory complexities in the manufacture of hemoglobin, and in gene regulation in

general, indicate that hemoglobinopathies will not be

effectively treated until these processes are better understood and can be controlled (Anderson, 1984).

NORMAL HUMAN HEMOGLOBIN

All normal human hemoglobins are composed of

two pairs of identical protein chains, forming a

"tetramer”. Hemoglobin differs between the embryo,

fetus and postnatal human because genes coding for

different protein chains are activated progressively

during development. Fetal hemoglobin (HbF), for example, is composed of two alpha and two gamma

chains while the adult version contains two alpha and

either two beta (95 percent) or, much less commonly

(3 percent), two delta chains (Orkin and Nathan, 1981).

These complex regulatory changes in hemoglobin synthesis aid in transporting oxygen across the placenta,

from mother to fetus. This is possible because embryonic and fetal hemoglobins have higher oxygen affinities than normal adult hemoglobins.

The two major types of single-gene hemoglobin diseases are sickle cell anemia and the thalassemias.

These genetic defects are not located on a sex chromosome and usually require two faulty copies of the gene

for the disease to manifest clinically. Hundreds of

thousands of people have only one faulty copy of the

gene out of the allotted two, and thus are labelled

heterozygous carriers of these diseases. An estimated

200,000 people with hemoglobinopathies are born annually, divided equally between sickle cell anemia and

thalassemia (WHO, 1982). The thalassemias are most

common in Asia, and sickle cell is most common in

Africa. Among American blacks, about 8 percent carry

sickle cell trait and one in 500 newborns have sickle

cell disease (Stern, 1973; McKusick, 1983; Bowman, in

personal communication, 1984).

Sickle cell anemia

Sickle cell anemia involves a variation in hemoglobin structure due to substitution of one nucleotide on

the beta globin gene, leading in turn to a substitution

of the amino acid glutamate for valine (the normal

sixth amino acid on the beta globin chain) when the

faulty gene is ‘(transcribed” and used to produce hemoglobin protein in the bone marrow cells. The hemoglobin containing the faulty beta globin chains (Hbs)

is less soluble than normal hemoglobin and, under

reduced-oxygen conditions, can form a crystal that

distorts the red blood cells into shapes resembling

Red blood cells–normal and sickle cell

SOURCE: Office of Technology Assessment.

38-803 0 - 84 - 5 , QL 3
58 Human Gene Therapy—Background Paper

sickles. These misshapen red blood cells are rapidly

destroyed and become lodged in capillaries, leading

to partial or total blockage of blood supply to parts

of the body. Pain and local-tissue damage results, especially in those organs with extensive capillary networks such as the lungs, heart, kidneys, brain, spleen

and hips.

The blood of a person with two copies of the “sickling” gene consists primarily of HbS; this person is said

to have “sickle cell disease” and generally has an abbreviated lifespan. The impaired circulation can lead

to anemia, pain in the joints, sporadic abdominal pain,

lung and spleen damage, ulcerations of the lower extremities and acute episodes such as stroke, kidney

failure, and heart failure (Bowman and Goldwasser,

1975). The clinical symptoms are extremely variable,

however, and some people may remain completely

free of serious illness. A person who possesses one

faulty and one normal copy of the beta globin gene

has “sickle cell trait” and has blood containing 20 to

40 percent HbS. Such “carriers” typically exhibit little

or no clinical symptoms of anemia and have a normal

life expectancy.

Thalassemias

The thalassemias are characterized by decreased

production of certain hemoglobin chains, There are

several types of thalassemia named according to which

globin chain is deficient. For example, in alpha thalassemia, little or no alpha globin is produced. The same

holds true for beta thalassemia, where little or no beta

globin is produced. These are the most common forms

of thalassemia.

The decrease in globin production by the affected

gene ranges from none at all (as in alphao

- or betaO-

thalassemias) to somewhat less than normal (as in

alpha +

- or beta+- thalassemia). The clinical signs and

symptoms are extremely variable, especially among

heterozygotes, ranging from none to serious anemia.

Generally, the symptoms afflicting an individual

heterozygous for thalassemia are exacerbated under

physical stress. Prolonged stress can exhaust the auxilliary blood production mechanisms that are already

being pushed to maintain normal hemoglobin levels.

The genetic defects underlying thalassemias are as

varied as the associated clinical symptoms. The impaired synthesis of globin chains could result from

mutations grossly affecting the structure of a globin

gene, decreased transcription of the gene, abnormal

RNA processing, or defects in the activity and translation of the mature RNA (Treisman, Orkin, Maniatis,

1983).

ALPHA THALASSEMIAS

Most alpha thalassemias involve gene deletion. “Silent carriers” (those showing no clinical symptoms)

have one of the four normal alpha globin genes per

cell deleted. Those with alpha thalassemia “trait” have

two genes deleted and usually show no anemia. “Hb H“

disease is associated with the deletion of three genes

(Kan, et al., 1975) and is characterized by mild to

moderate anemia. Homozygous alpha thalassemia involves deletions of all four gene copies and results in

severe anemia, accumulation of body fluid, and intrauterine death (Orkin, 1978).

BETA THALASSEMIAS

There are only two beta globin genes in the normal

human genome. If only one copy of the gene is affected, an individual is said to be heterozygous and

have beta thalassemia trait. Such heterozygotes are

usually asymptomatic, except for occasional mild anemia or slight spleen enlargement. If both genes are

affected, the individual is homozygous and has the disease beta thalassemia. Symptoms of the beta thalassemia disease include severe anemia, enlargement of

the spleen, liver and heart, skeletal deformation, abnormal facial features, and abbreviated life span.

Other less common forms of thalassemia involve persistence of fetal hemoglobin, however, and therefore

constitute models for the study of the mechanisms responsible for switching from fetal to adult hemoglobin synthesis during development. If better understood, this process might be exploited clinically as a

treatment for beta thalassemia in which fetal hemoglobin synthesis could be “turned on” to compensate

for deficient adult beta globin synthesis.

Other unstable hemoglobins

There are dozens of mutant types of globin protein

that replace either the alpha or, more commonly, the

beta chains in hemoglobin (Winslow, 1983). Many of

these form unstable hemoglobins that deteriorate

rapidly and cause anemia. Most are extremely rare,

with the exceptions of hemoglobin SC disease and hemoglobin S-thalassemia. These two disorders are

hemoglobinopathies that occur in patients who have

one sickle cell gene combined with another mutant

gene–for globin C in one case and for thalassemia in

the other.

The unusual hemoglobinopathies vary widely in clinical severity. Most are relatively well understood. Gene

therapy for most of them would involve the same steps

in replacing defective genes in bone marrow cells with

their normal globin gene counterpart.
Technical Note 5 • 5 9

Diagnosis of hemoglobinopathies

Because the symptoms of the hemoglobinopathies

are very heterogeneous, a definitive diagnosis usually

requires assays for abnormal hemoglobin or DNA analysis. The simplest and most common method of diagnosing sickle cell trait and anemia postnatally is

through protein electrophoresis of a blood sample (see

diagram). Because of the risk associated with fetal

blood sampling, however, this procedure may soon be

displaced in prenatal diagnosis by the less risky procedure of DNA analysis of cells obtained through amniocentesis or chorionic villus biopsy (see app. A).

Electrophoresis can also be used to detect most

forms of thalassemia postnatally, except for the “silent

carrier” form of alpha thalassemia which may now be

diagnosed using restriction endonuclease DNA analysis (Embury, et al., 1979). Prenatal detection of homozygous beta thalassemia has been possible since 1974

through quantitation of the amount of beta globin

manufactured by a fetal blood sample (Kan, 1977;

Alter, 1979). Prenatal diagnosis of certain forms of beta

thalassemia is also possible using DNA analysis (Alter,

1981; Antonarakis, 1982; Boehm, 1983; Connor, 1983;

Estein, 1983; Hodgkinson, 1984; Orkin, 1982, 1983;

Pirastu, 1983).

Treatment of Hemoglobinopathies

Currently, clinical treatment of hemoglobinopathies

is limited largely to treatment of infections, mitigation

of the associated symptoms (e.g., pain in the joints),

and organ-specific therapy (Dean and Schecter, 1978).

There is no effective long-term treatment for sickle

cell anemia, and the two treatments available for

thalassemia are only partially effective, with undesirable side effects (Adamson, 1984). The first treatment

involves repeated transfusions with normal red blood

cells can alleviate some of the symptoms, but eventually leads to toxic iron overload. The second treatment, bone marrow transplants, or the transfer of

healthy bone marrow from a relative into the patient,

has been used successfully to treat homozygous beta

thalassemia. This carries a high risk of failure, however, and the possibility of an immune reaction of the

patient against the transplanted marrow.

It could be argued that prenatal diagnosis obviates

the need for postnatal treatment. However, there will

always be children born with hemoglobinopathies and

other genetic diseases because: 1) parents often do not

realize that they are carriers until they have had an .

affected child; 2) parents who know they are carriers

may chose to take the risk of their child having a

genetic disease; 3) prenatal diagnosis is often unacceptable for moral, ethical, religious, or personal reasons;

and, 4) genetic mutation is constantly reintroducing

defective genes.

Several alternative treatments are currently being

developed experimentally that may be divided into

three categories: 1) drug therapy, 2) gene therapy, and

3) bone marrow transplant (Desnick, 1981). To date,

no form of gene therapy and only a handful of the

drug therapies have progressed to the point of clinical trials, and bone marrow transplant appears to be

of possible use for only a small percentage of patients.

DRUG THERAPY

Two types of drugs are currently being developed

to treat hemoglobinopathies. One type is designed

“turn on” the synthesis of fetal hemoglobins to compensate for the faulty or insufficiently produced adult

hemoglobins. Some of these drugs are already being

tested clinically (Dover, 1983, 1984). The second type

is meant to suppress the polymerization or gelling of

the sickle hemoglobin molecule that distorts the red

blood cells. Some of these drugs have also been tested

clinically (Bookchin, 1976; Dean, 1978; Lubin, 1975;

Nigen, 1974).

GENE THERAPY

Treatment of hemoglobinopathies through gene

therapy, or the insertion of normal globin genes into

the embryo (germ line) or into bone marrow (somatic)

that is then implanted, is still entirely in the experimental stage in animals. The success rate of in vitro

germ-line transplants is still disappointingly low (see

app. B). The lack of animal models for hemoglobinopathies has effectively hindered both germ-line and

somatic-cell experiments. Recently, however, a model

for beta thalassemia was developed in the mouse

(Skew’, et al., 1983). Even given such models, however,

the researcher is faced with the task of having the

gene express at all, at adequate levels, at the right time,

and in the right tissues in the whole animal.

BONE MARROW TRANSPLANT

Gene transplant for hemoglobinopathies attempts to

take advantage of the relative accessibility of human

bone marrow cells, where hemoglobin is produced.

Bone marrow is removed from a donor who produces

normal hemoglobin, who has been matched for tissue

compatibility with the recipient patient who suffers

from a disorder of hemoglobin. The donor patient then

receives radiation treatment sufficient to destroy the

cells of his own bone marrow. Once accomplished, the

patient receives the transplants of the donor’s bone

marrow. The recipient is then treated with drugs to
60 Human Gene Therapy—Background Paper

suppress his or her immune reaction against the do- procedure is quite stressful to the patient, relatively

nated cells (but this also affects general body defenses). risky, and not all patients can be matched with comIf not rejected by the host, the transplanted bone mar- patible donors.

row begins to manufacture normal hemoglobin. The
Appendixes

,
Appendix A

Diagnostic Technologies for

Genetic Diseases

Diagnosing genetic diseases requires

two types of technologies: those for

tissues and fluids, and those for

samples obtained before and after

a partnership of

sampling bodily

analyzing such

birth. Although

fetal imaging is not tissue analysis in the strict sense,

it will he discussed here as a technology useful both

in conjunction with prenatal tissue sampling and by

itself to view gross congenital malformations in utero.

This section reviews the major imaging, sampling, and

analysis techniques, and comments on their current

and potential use as clinical tools. It applies only to

prenatal and early postnatal diagnosis.

Often, the only ‘treatment” available for a fetus

diagnosed as having genetic disease is the elective termination of pregnancy. All the stigma, emotion, and

ethical controversy attached to this possible recourse

can be-and has been—transferred to the diagnostic

techniques themselves, and exacerbated by those techniques having been inapplicable until well into the 2nd

trimester of pregnancy. With the advent of techniques

minimizing risk to the fetus and allowing diagnosis

within the first trimester, prenatal diagnosis may become more accepted.

Controversy also attends the use of postnatal diagnostic techniques. Genetic testing for certain disorders

among high-risk populations—such as the screening

for sickle cell trait among American blacks in the

1960s--have been said to stigmatize and demean individuals in those populations. Recent advances in

diagnosing genetic disorders whose clinical symptoms

often do not surface until adulthood—such as Huntington disease or familial hypercholesterolemia (a predisposition for arterial hardening which causes early

heart attacks)-–have raised further questions: Would

a potential employer or insurance company have a

right to this information? (see app. B). Propelled by

rapidly advancing rDNA technologies, the expanding

use of these diagnostic techniques will soon necessitate an answer to these ethical and political questions.

Fetal imaging

Fetal imaging involves obtaining a visual image of the

fetus, either by means of special electronic techniques,

or by using fiberoptic. Ultrasound and fetoscopy are

the two major types of imaging. They can be used in

and of themselves, as well as being partnered with

techniques for tissue sampling (see below).

ULTRASOUND

Ultrasound is commonly used in determining fetal

age and defining large anatomic structures. It involves

high-frequency sound waves, undetectable to the

human ear, that are directed toward the uterus. A

fetal image is created from the differential reflection

of the sound waves bouncing off diverse fetal tissues.

Various gross congenital malformations may be detected using ultrasound, including hydrocephalus (excess fluid of the brain), anencephaly (absence of all

or most of the cerebral hemispheres), absent or

stunted limbs, and some defects of the heart and

kidney (Hobbins, Venus and Mahoney, 1981). For purposes of tissue sampling, it is generally used in conjunction with amniocentesis (see below). There is currently little evidence of risk to the fetus from the small

doses of ultrasound needed for in utero visualization.

However, cautioning against routine screening, the

NIH Consensus Development Conference on Diagnostic Ultrasound Imaging in Pregnancy stated in its findings, ‘(Lack of risk has been assumed because no

adverse effects have been demonstrated clearly in

humans. However, other evidence dictates that a hypothetical risk must be presumed with ultrasound. Likewise, the efficacy of many uses of ultrasound in improving the management and outcome of pregnancy

also has been assumed rather than demonstrated,

especially its value as a routine screening procedure . . . .Ultrasound examinations performed solely

to satisfy the family’s desire to know the fetal sex, to

view the fetus, or to obtain a picture of the fetus

should be discouraged. In addition, visualization of the

fetus solely for educational or commercial demonstrations without medical benefit to the patient should not

be performed” (Office of Medical Application of Research, 1984).

FETOSCOPY

Fetoscopy entails the insertion of a thin fiberoptic

scope through the abdomen into the uterus. The procedure usually is done around the 18th week of gestation. It permits a well-defined narrow-angle view of

63
64 Ž Human Gene Therapy—Background Paper

isolated parts of the fetus, and thus is used for fetal

surgery as well as imaging. Fetoscopy, however, primarily is used to obtain fetal tissue samples (see

below).

Technologies for fetal tissue sampling

The three major fetal tissue sampling technologies

in use today are: fetoscopy, amniocentesis, and chorionic villus biopsy. Fetoscopy is infrequently used because it is relatively risky and difficult to perform.

Amniocentesis is relatively safe for both the fetus and

mother, and is widely used today. Chorionic villus

biopsy still is largely in the developmental stage in the

United States, but has certain advantages that may

lead to its widespread use in the near future.

FETOSCOPY

Direct tissue sampling via fetoscopy makes use of

the fiberoptic scope—inserted into the uterus for fetal

imaging purposes—to remove blood and skin samples,

A needle or forceps, guided through the fetoscope by

ultrasound, accomplishes this purpose, Various hemoglobinopathies, muscular dystrophy, and hemophilia

can all be diagnosed using fetal blood samples (Hobbins, Venus and Mahoney, 1981). However, with the

advent of sensitive DNA analysis techniques in the late

1970s, diagnosis of hemoglobinopathies such as sickle

cell disease and thalassemia can now be obtained

through the less risky procedure of amniocentesis (see

below). Fetoscopy, never widely practiced, carries a

3-to-6 percent risk of fetal death over and above the

natural losses from spontaneous abortion and miscarriage (Alter, et al., 1981; Rocker and Laurence, 1981),

and is routinely performed at only a few medical

centers.

AMNIOCENTESIS

Amniocentesis involves sampling fetal cells and other

substances present in the amniotic fluid. This is accomplished via a needle inserted through the abdominal wall, through the wall of the uterus, and into the

fluid-filled space that surrounds the fetus. Amniocentesis normally is done using ultrasound to direct the

needle.

First used in the late 1960's amniocentesis is now

routinely employed with chromosome analysis techniques to detect abnormalities such as Down’s syndrome, neural tube defects (through testing of the amniotic fluid), enzyme deficiencies (as in Fabry disease

and Lesch-Nyhan syndrome), and hemoglobinopathies

(through testing of cultured fetal cells). Amniocentesis

is widely available, has a low associated risk of fetal

death (less than 0.5 percent), and is 99.4 percent accurate (NICHD, 1976).

Theoretically, amniocentesis could be performed

early in the pregnancy since DNA analysis allows detection of the defect in any cell, regardless of tissue

type or stage of fetal development. However, not

enough fetal cells are available in the amniotic fluid

early on, and thus, amniocentesis is usually performed

no earlier than between the 16th and 19th weeks of

pregnancy, Additionally, the cells from the fluid must

often be cultured for 1 to 5 weeks to yield a large

enough tissue sample for analysis, further delaying

diagnosis. Thus, with amniocentesis the abortion of

an affected fetus, if elected, must be performed well

into the second trimester when the results of the analysis become available. Such a delay increases the risk

of complications associated with abortion including

trauma, sepsis, and hemorrhaging (Brash, 1978). Abortion that late into a pregnancy also can carry a considerably increased risk of psychological and physical

stress to the parents, and is generally less acceptable

to parents and the community. The further development of methods to analyze uncultured amniotic fluid

cells continues to greatly speed diagnosis-e. g., a new

technique for examining uncultured cells with an electron microscope can diagnose a glycogen storage disease 3 to 6 days after amniocentesis (Hug, et al., 1984).

One of the consequences of this increasing effectiveness in neonatal and premature care is that the age

at which viability is reached (see Technical Note 4) is

constantly being pushed back, mandating earlier parental decisions vis a vis the course of the pregnancy.

CHORIONIC VILLUS BIOPSY

Chorionic villus biopsy (CVB) is a relatively new technique for the sampling of fetal tissue that can be performed as early as the 8th to 10th weeks of pregnancy.

It entails taking a sample of the fronds of tissue, or

villi, that root the fetal placenta to the uterus. Ultrasound is used to guide a catheter into the woman’s

uterus to the villi, a tiny bit of which is then suctioned

off using an attached syringe (see fig. A-l). The fetal

tissue is then separated from maternal tissue and subjected to biochemical or chromosomal analyses that

take an average of one week to yield a diagnosis. In

contrast to amniocentesis, extensive culturing of the

tissue is not necessary since a sufficient quantity of

DNA is obtained in the tissue sample. CVB can be performed weeks, even months, earlier than either amniocentesis or fetoscopy.

CVB was first used in China (Department of Obstetrics and Gynecology, Anshan, 1975), the U.S.S.R.

(Kazy, Rozovsky and Bakarev, 1982), and Norway. It
App. A—Diagnostic Technologies for Genetic Diseases 6 5

Figure A-1.—Chorionic Villus Biopsy

SOURCE: Product News, “Chorionic Villus Biopsy,” Out/ook, January 19S4, p. 8.

Carolyn Brooks, artist,

has been considered ethically acceptable in England

and used since mid-1981 for prenatal diagnosis of certain “high-risk” disorders such as hemoglobinopathies

(Old, et al., 1982), and fetal sexing of pregnancies at

risk of sex-linked diseases (Gosden, et al., 1982), mainly

Duchenne muscular dystrophy. It is used less often

there to diagnose the more common Down’s syndrome. Unlike amniocentesis, however, CVB cannot

be used to detect noncellular substances in the amniotic fluid, like alpha fetoprotein, whose presence indicates a high risk of neural tube defects.

According to the World Health Organization’s

registry, CVBs have been performed in the United

States since mid-1983. By November of that year, a

projected 12 percent associated fetal loss rate was

reported after only 240 CVBs had been performed in

the U.S. and Europe (Ward, as cited in Jackson newsletter, 1983). Because of this, several researchers (Lippman, 1984; Hecht, Hecht, Bixenman, 1984) contend

CVBs are risky and should be used with caution. Current clinical data from approximately 2900 CVBs performed to date in these same countries seems to indicate that the observed fetal loss is 4.2 percent

(Jackson, 1984 newsletter). This, however, includes an

unquantified number of spontaneous abortions and

miscarriages that are a danger to any normal pregnancy. In four similar series of ultrasound observations on ultrasound pregnancies and control groups,

the observed fetal loss rate is in the neighborhood of

2 percent. Extrapolating from that, it may be reasonable to assume that the risk of fetal loss that might

be associated with CVB is 2 to 3 percent. Any fetal loss

rate, however, is highly dependent on the expertise

of the laboratory involved, and there are laboratories

with a reported O percent observed fetal loss (Jackson,

1984 newsletter). Although generally higher than the

0.5 percent loss rate associated with amniocentesis,

much of the discrepancy may be due to the time when

the procedures are performed. There is a higher spontaneous abortion rate in the first trimester, when CVBs

are done, than in the second trimester, when amniocentesis is done. Some even predict that CVB will replace amniocentesis within a few years (Product News,

1984).

Current clinical applications of chorionic villus

biopsy include at least three groups in England, with

four or five more testing it for clinical use in that country (Dr. Robert Williamson, Ph. D., personal communication, 2-16-84). Other countries include Italy (over

200 cases of Down’s syndrome have been diagnosed

by a Milan group) and France (to diagnose hemoglobinopathies; Dr. Robert Williamson, Ph. D., personal

communication, 2-16-84).

Tissue and fluid analysis

Genetic diseases were first detected through their

characteristic behavioral or physical traits. This approach, combined with family histories, still is important to the diagnosis of many genetic diseases, especially those for which the underlying biochemical and

genetic defects are not known. However, behavioral

and physical examination is generally not applicable

to prenatal diagnosis, or on the cutting edge of diagnostic technologies, and will not be discussed here.

Many genetic diseases have surfaced in recent years

whose physical and behavioral manifestations are not

readily apparent, are progressive, or take several years

to emerge. Many such diseases are detectable through

biochemical assays for characteristic imbalances or abnormalities of certain body substances.

A small but growing number of diseases may now

be diagnosed through direct analysis of the genetic material. This was once only possible for gross chromosomal abnormalities involving the absence or duplication of entire chromosomes, but recent advances in

molecular genetic technology have made possible detection of minute defects within the chromosomes.

Such genetic analysis can allow diagnosis of the disease before the biochemical defect is detectable, especially prenatally, and before it becomes clinically

apparent, making possible early treatment and sometimes even prevention.

BIOCHEMICAL ASSAYS

Many genetic diseases are manifested as biochemical

imbalances caused by the reduced or absent activity

of certain enzymes that help manufacture a given

chemical, or convert it into another useful product.

Such enzyme deficiencies underlie a spectrum of dis-
66 Ž Human Gene Therapy—Background Paper

orders ranging from albinism to hemolytic anemia to

some immunodeficiency diseases. X-ray, urine analysis (for excretion of abnormal amounts of certain accumulating precursors) and physical or mental examinations are often used for preliminary detection.

However, enzyme assays of the blood or other tissues

are generally necessary to make a definitive diagnosis of such diseases. Tay-Sachs disease (TSD), for example, is a metabolic disorder primarily affecting Jews

of Eastern European descent (1:3,000 US.) (Stanbury,

et al., 1983) caused by the lack of an enzyme, Hexoseaminidase A, that results in the accumulation of

lipids in the brain. TSD is characterized by progressive

neurological degeneration including dementia, paralysis and blindness. Diagnosis routinely involves enzyme

assays of cultured amniotic fluid cells prenatally and

of the blood serum postnatally.

Lack of activity of an enzyme or other substance is

sometimes due not to a quantitative lack of the substance, but to a structural defect that prevents it from

functioning properly. Electrophoresis is a method of

distinguishing such variants through the different

speeds at which they migrate in an electrical field

according to their total net charge—a characteristic

that may vary with molecular structure. For example,

electrophoresis can reveal the absence of any one of

the three major classes of immunoglobulins—as well

as variations within any one class—that characterize

certain immune deficiency diseases. It also can detect

and distinguish between both heterozygotes (i.e., sickle

cell trait) and homozygotes (i.e., sickle cell disease) for

the sickle cell gene (see fig. A-2). Protein electrophoresis is a relatively inexpensive and expedient technique, and is commonly used for postnatal detection

of hemoglobinopathies. Because of the relatively high

risk involved in obtaining fetal blood samples (see

Technologies for Fetal Tissue Sampling, this appendix),

electrophoresis is less commonly used for prenatal

diagnosis. There are some cases in which electrophoresis is insufficient to distinguish particular genotypes, and therefore is frequently combined with a

volubility test. In most cases, these two tests will suffice to identify

+

a hemoglobin disorder.

Figure A-2

DIRECT ANALYSIS OF DNA

Cytogenetics: Visualization of Chromosomes.—

Cytogenetics is the examination of chromosomes

under a microscope in order to detect gross changes

in chromosomal structure. One of the first clinical applications of this technique was the detection of Down

syndrome (Lejeune, 1959), in which the cell carries an

entire extra chromosome 21. Although many reports

on other numerical chromosomal aberrations followed, researchers were often unable to identify

which chromosome was involved. Characterization of

banding patterns on particular chromosomes in the

late 1960s and early 1970s allowed the identification

of specific chromosome pairs as well as parts of each

chromosome (Hirschhorn, 1981). An array of chromosomal deletions, duplications and translocations, and

the corresponding syndromes, have since been identified (Borgoankar, 1980). Down syndrome and other

major numerical and structural chromosomal defects

afflict about 1 in 160 live-born infants (Hook and

Hamerton, 1977). Such chromosomal defects—including abnormalities of the sex chromosomes such as

Klinefelter syndrome in which the male possesses an

extra X chromosome, causing sterility and feminization—are now routinely diagnosed both before and

after birth using cytogenetics.

Genetic Markers.--The rapid progress in recombinant DNA techniques since the mid-1970s has made

possible detailed analysis of particular genes on the

chromosomes, and the characterization of minute

genetic defects that are not detectable through examination of gross chromosomal structure. In recent

years, the defective genes underlying various other

heritable diseases have been identified—including

Lesch-Nyhan syndrome (Jolly, et al., 1982, Brennand,

et al., 1982) familial hypercholesterolemia (Bishop,

1983), and phenylketonuria (Woo, et al., 1983). Within

the past 2 years, genetic “markers” (though not the

actual genetic defect) have been discovered for two

important genetic disorders: Duchenne muscular dystrophy (Murray, et al., 1982) and Huntington disease

(Gusella, et al., 1983).

The discovery of identifiable markers for genetic

defects opens up the possibility of using them to aid

in diagnosis. Such markers might be useful as prenatal

tests, for postnatal identification of risk, or perhaps

even for genetic screening. For example, phenylketonuria (PKU), an inherited enzyme deficiency that, if

untreated, can cause severe mental retardation, could

not be detected before birth until recently (although

biochemical tests were available for postnatal screening). The recent discovery of a genetic “probe)” or

SOURCE: Bowman, J. E. and Goldwasser, E. (1975) Sickle Cell Fundamentals,

The Unlverslty of Chicago.
App. A—Diagnostic Technologies for Genetic Diseases Ž 67

short stretch of DNA specific to the defective gene,

has made possible not only prenatal detection, but also

carrier identification (Woo, et al., 1983). This means

that parents at risk of having a child affected by PKU

can be identified. This opens up the technological prospect of parental carrier screening to supplement or

replace routine newborn screening.

Direct analysis of DNA is being used now in the diagnosis of several other diseases as well, including some

disorders of hemoglobin and one form of dwarfism

(Antonarakis, et al., 1982). Direct binding of DNA

probes to patient DNA could theoretically be developed for any disease caused by a single gene.

Genetic markers can be of several types. Some depend on the presence or absence of specific biochemical activities. Others depend on the differences

in how DNA is cut by enzymes specific to certain

nucleotide sequences in combination with DNA

probes—specific detectable stretches of DNA constructed in the laboratory that bind directly to either

the gene causing the disease or a piece of DNA so close

to the disease-causing gene that it can be used as an

indicator for the defective gene. The techniques are

briefly described below.

Restriction Enzymes. -Restriction enzymes are

proteins that are found in bacteria that cut DNA at

specific sequences. Human DNA is composed of roughly

3 billion pairs of nucleotides (see Technical Note 1);

restriction enzymes look for stretches of 4 to 12 nucleotides that are arranged in a particular order, and cut

the DNA at a site either in the middle of the sequence

or near to it. When the DNA from human cells is so

treated, DNA fragments of many lengths are generated. The DATA from any one individual will have a

specific pattern because-the sequence recognized by

a particular enzyme will occur in characteristic places

in that person’s DNA.

People generally have very similar patterns of DNA

fragmentation when their DNA is treated with restriction enzymes, and so most enzymes have not yet been

shown to be useful for diagnosis. Some enzymes, however, generate differences that correlate with disease.

The DNA coding for sickle cell disease, for example,

is cut by an enzyme that does not cut the normal gene.

Therefore, when this enzyme is used on DNA from

a patient, the one DNA fragment found in normal individuals is cut into two smaller pieces. These pieces

can be seen using standard laboratory methods, and

the technique has been used to detect both sickle cell

disease and sickle cell trait (Orkin, et al., 1982).

In most cases, the differences between the normal

and the abnormal gene will not be so easily identified:

the disease-causing mutation will not occur where restriction enzymes are known to cut. In this case, one

can sometimes identify people who might carry the

abnormal gene by identifying differences in a piece

of DNA close to the gene causing the disease. This technique depends on using restriction enzymes indirectly,

rather than directly, and is correspondingly less

precise.

People show characteristic variations in how their

DNA is cut by certain restriction enzymes, just as they

have specific blood groups. These variations usually

are not significant in and of themselves. The place

along the DNA that is responsible for the variations

can be located. The utility of such variations comes

when, by chance, a particular pattern is caused by differences close to a disease-causing gene. When this

occurs, it is often possible to track the abnormal gene

by following the restriction fragment pattern. This

technique of establishing “guilt by association” is called

linkage analysis (denoting a physical genetic linking

between a trait of interest and an identifiable marker)

and has permitted tracing of the Huntington disease

gene, (Gusella, et al., 1983) the Duchenne muscular

dystrophy gene, and genes underlying several hemoglobin disorders (Boehm, et al., 1983). Because the

technique does not require any special knowledge

about which gene causes a disease, or the biochemical

lesion responsible, restriction fragment analysis may

be used to diagnose diseases whose molecular mechanisms are not yet known, such as cystic fibrosis. A

major disadvantage of the technique is that the restriction enzyme pattern usually varies from family to

family, and many members of each family must be

tested before genetic detection within any one family

is practical.

The technique is analogous to searching for passengers of a downed plane. In thousands of miles of

mountainous territory, the wreckage of an aircraft is

found by tracing its radio distress signal. This does

not give much information about the condition of the

crew or the circumstances of the crash, but it does

permit restriction of the search to a smaller area, and

increases the probability of finding the passengers.

The crash site itself may provide some clues about the

cause of the mishap and where to look for survivors.

In this analogy, the radio signal is like a linked genetic

marker, while the defective gene is like the crash site.

DNA Probes.--Gene probes are short stretches of

DNA that bind to a specific DNA sequence. Through

cloning, many identical copies of a probe can be made.

Probes are usually made out of DNA that has been

specially labelled with either a radioactive or chemical tag that allows the probe to be used to detect specific DNA sequences, employing standard laboratory .

met hods.

Probes are often used in combination with restriction enzymes. First the DNA is chopped into manageable sizes by restriction enzymes, and then a probe
68 . Human Gene Therapy—Background Paper

is bound to the DNA. In the instance of the sickle cell

gene mentioned above, for example, the probe corresponds and binds to an abnormal variation of the hemoglobin gene that causes the disease, allowing its

detection.

Probes come in different sizes. Most sequences used

as probes are fairly long, composed of many copies

of a single ordered sequence of hundreds or thousands

of nucleotides. These are usually made using bacterial

clones of a gene or DNA fragment. Some short probes,

called oligonucleotide probes (“oligo-” means few), can

be chemically manufactured in the laboratory. These

small highly specific probes can, under carefully controlled conditions, detect the difference between genes

that differ only in a single nucleotide in their sequences. This property has been used to detect sickle

cell disease (Wallace, et al., 1981; Orkin, 1982; Conner, et al., 1983), and some thalassemias. (Orkin, et al.,

1983; Pirastu, et al., 1983) An oligonucleotide probe

has also been developed for another genetic disease,

alpha-1-antitrypsin deficiency (an inherited deficiency

of a blood protein that can lead to lung and liver disease), making prenatal diagnosis possible (Kidd, et al.,

1984).

The power of the new diagnostic techniques can be

imagined by noting that they can detect differences

of a single letter in a book composed of three billion

letters. If each gene is a paragraph, then only a few

paragraphs in a long monograph have been investigated using the new techniques; more of the text will

be tested over the next few decades, and the meaning of the book may thus slowly become clearer.
Appendix B

Privacy and Control of Genetic

Patient Data

introduction

Some of the same recombinant DNA technology that

makes human gene therapy possible will also facilitate the identification of many more individuals with

genetic diseases than earlier techniques allowed. This

new technology should result in a dramatic increase

in the amount of genetic patient data that can be collected, much of which has never been available before. ]

However, the ability to gather potentially large

amounts of new genetic data about individuals raises

questions about rights of privacy regarding that information, as well as the ability of others to have access to it.

WHAT ARE GENETIC PATIENT DATA?

Genetic patient data refer to information collected

about an individual relating to his or her genetic constitution. Information of this sort can include a large

number of individual traits, ranging from eye color

or blood type to predispositions to or presence of various diseases. Since genes determine many personal

characteristics, genetic data may reveal important

facts about an individual’s physical and intellectual

status or potential. One’s genetic complement is an involuntar y endowment, since the genes are passed on

from parents, and genetic characteristics are not generally subject to change.

Policies on access to genetic patient data must balance the benefits deriving from disclosure against the

need to preserve individual privacy. The benefits to

public health and other priorities often determine that

medical information be disclosed. Examples of situations in which medical information is used for public

good or prevention of harm include reporting child

abuse or other criminal conduct, notifying State officials about the presence of communicable disease that

might endanger public health, and use of disease statistics in planning priorities for biomedical research.

Patients might be harmed, however, as a consequence

of disclosing their genetic data. They might be socially

stigmatized, have difficulty finding a mate, encounter

barriers to obtaining life and health insurance, or be

discriminated against when seeking employment.

IThe number of cloned human genes is an index of this increase in poten.

tial genetic patient data The number of cloned human genes reported at

the Gene Mapping Meetings has risen from 22 in 1982 to 132 in 1984 (Skolnick,

et al., 1984)

Genetic patient data are different from other types

of disease- related medical information, in the following ways:

In contrast to communicable diseases, the public

at large is not at risk of contracting genetic disease, since it can be transmitted only to progeny.

Because of the genetic transmission of the disease,

information about close relatives may reveal information about oneself, and vice versa. Closely

related individuals can benefit from this information.

Because some genetic diseases, such as Huntington disease, colonic polyposis, or polycystic kidney

disease, may not be expressed until middle or old

age, genetic information in some cases provides

a look into the future health of an individual.

Because of the emotional concern of the patient

when learning about a genetic disease in their

family against which he/she has no defense.

Future generations may inherit the disease, and

therefore have an interest in it.

Those potentially interested in genetic patient data

include the patient, his or her family, insurance companies, employers, health care providers, and the Federal Government.

HOW ARE GENETIC PATIENT DATA COLLECTED?

Genetic patient data are collected about individuals

in many ways, but the bulk of specific information on

genetic traits derives from two main sources: family

histories and genetic tests.2

A family history can be relatively easy to collect, and

most genetic patient data available to physicians are

of this type. A family history is usually obtained by

asking the patient questions about the presence of diseases in his or her family that are known to be inherited. Histories can often be supplemented by inquiry among other family members. The importance

of genetic factors varies between diseases. Recent data

on Alzheimer disease indicate that a significant fraction, at least one-third of cases may be genetic (Breitner, 1984; Folstein, 1981; McKusick, 1983), while other

diseases, such as PKU, are always due to genetic defects. Variation in the genetic component among different diseases and even among diseases of the same

These include a varlet> of biochemical and genetic tests See app A for

further information on genetic testing techniques.

69
70 Ž Human Gene Therapy—Background Paper

type can be due to several factors, discussed in the

overview, such as:

incomplete penetrance,

variable expression,

environmental factors,

different patterns of inheritance: dominant,

recessive, or sex-linked,

multigene traits, and

multifactorial traits.

As a result of these factors, genetic patient data collected from family histories can alert individuals to

personal health risks and statistical likelihoods, but it

generally cannot predict with certainty whether an

individual with a family history of cardiovascular disease or cancer, for example, will actually develop those

disorders.

With reliable genetic tests, it is sometimes possible

to determine the presence of genes that can cause disease, permitting more accurate determination of the

probability of expressing symptoms. Genetic testing

may be performed as a result of information obtained

in the family history, or can, in some cases, be initiated to screen for diseases common in a more general population to which the patient belongs.

Genetic patient data are collected in several different

contexts. Family histories are recorded when an individual first visits a physician, and generally when a

person buys individual life insurance. Genetic testing

is often performed in the context of making personal,

medical, or reproductive decisions, and such tests are

performed at different times for different reasons

(Rowley, 1984). Carrier screening can identify individuals who carry one copy of a deleterious gene

so that they may be made aware of the risks of having a child with a genetic disease and make a clearly

informed decision about having children. Carrier

screening has been performed on groups at high risk

of carrying certain genes, such as Blacks and Mediterranean populations, who may have hemoglobin disorders, or Eastern European Jews who may carry TaySachs disease.3

Prenatal screening is performed to identify possible

genetic defects in the fetus and allow parents to decide

whether it should be brought to term or if it might

require special care when born (see app. A). Prenatal

screening is indicated in several situations, including

Screening for most genetic disorders is performed on a \ olun[arj, basis,

although most States require screening of newborns for PKLI and some other

disorders Fi\e States require such testing under all circumstances, 3(I per.

mit denial on the basis of religious convictions, and Y others permit some

other bases for refusal, PK[ I screening not required in three States (Aodrews,

IY&-ld) Some other mandatory screening laws, particularly those that im ol~e

srreenmg of adults for potential rarrier st~tus, hale been repealed beriiuse

of rl~iln]s made b! the affected groups that tht>y were being s]ngled out and

d!srrlminated against (Rowley, 1984)

when the mother is 35 years or older, if a previous

child were born with a genetic defect, or if both

parents are known carriers of a gene which can be

detected by such screening (Milunsky, 1980), Screening at birth can identify newborns who require special

care, such as PKU newborns who need a special diet,

low in phenylalanine. For this reason, newborn screening for PKU is required by most States.

Genetic screening raises many medical, ethical, legal,

and economic questions, such as: 1) Can family members crucial for testing be legally coerced to participate in linkage studies (see ch. 1), 2) Should a person

of any age have the right to be tested and informed

of test results?, 3) Should spouses or parents be permitted to know this information?, 4) Does a child have

the right to genetic information held by his parents?,

5) Should physicians inform at-risk individuals of the

availability of testing?, and 6) Can the release of information from genetic testing be withheld in employment and health insurance questionnaires? (Kurlan,

1983). One of the most difficult issues is the use of

abortion to prevent genetic disease. Other questions

include whether the benefits of genetic screening exceed the costs of the procedure, and if so, whether

newborn screening should be made mandatory (President’s Commission, 1983). The President’s Commission

for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research enunciated five principles for genetic screening with the following recommendations:

1. Confidentiality. “Genetic information should not

be given to unrelated third parties . . . ;“

2. Autonomy. “Mandatory genetic screening programs are only justified when voluntary testing proves

inadequate to prevent serious harm to the defenseless,

such as children, that could be avoided were screening performed;”

3. Knowledge. “Decisions regarding the release of

incidental findings (e.g., nonpaternity) or sensitive findings (e.g., diagnosis of an XY female) should begin with

the presumption in favor of disclosure . . . ;“

4. Well-being. “Screening programs should not be

undertaken until the test has first demonstrated its

value in well-conducted, large-scale pilot studies . . . .A

full range of prescreening and followup services for

the population to be screened should be available

before a program is introduced;” and

5. Equity. “Access to screening may take account

of the incidence of genetic disease in various racial or

ethnic groups within the population without violating

the principles of equity, justice, and fairness. ”

This paper will not discuss further the issues related

to the collection of genetic patient data; rather, it will

address issues which arise after the data is collected.
App. B—Privacy and Control of Genetic Patient Data . 71

WHY ARE GENETIC PATIENT DATA IMPORTANT?

Genetic patient data can play an important role in

the life of an individual, affecting such diverse areas as:

choice of spouse;

psychological health

reproductive decisions, such as

-decisions to have children

-decisions to undergo prenatal screening, and

-decisions to terminate pregnancy;

decisions about personal health risks affected by

diet, smoking, and health habits;

decisions about the personal health risks connected with certain jobs; and

decisions concerning financial, insurance, and

retirement plans.

These are among the most personal decisions that

an individual makes, and it is therefore important that

their privacy be ensured. However, as mentioned

above, there are others besides the individual who

have an interest in genetic patient data, and their interests must also be considered.

Genetic patient data may also be significant because

they have the potential for being misunderstood or

misinterpreted by the public. Earlier genetic screening programs to identify carriers of sickle cell disease

caused some individuals to be stigmatized because

they and others did not understand the difference between the carrier state and the disease state. Some

of these individuals were mistakenly treated as ‘sickly’

children or discriminated against in employment or

insurance coverage (Rowley, 1984; President’s Commission, 1983). This and other examples highlight the

need for greater understanding of genetic conditions

before using genetic patient data to direct social policy. As more is discovered about the genetic basis of

certain diseases, such as alcoholism, schizophrenia, or

complex traits such as intelligence, issues of individual privacy relating to genetic patient data may become even more important than they are today.

Privacy and access

In any discussion of the privacy of health records

it is important to consider the tradeoffs between an

individual’s right to privacy and others’ interests in

having access to the same information. Privacy and

access are two sides of the same coin, and to preserve

an individual’s right to privacy is to deny others that

access. If all genetic patient data were made completely private, society would forego the potential benefits

accruing from availability of that information, such

as planning national biomedical research priorities and

preventing potential harm to relatives, Equally unavailable would be data vital to the determination of paternity and the identification of criminals in court cases.

In addition, it would be impossible to conduct research

on genetic diseases. The benefits, however, must be

weighed against the fact that unrestricted access to

genetic patient data would violate the autonomy of individuals to reveal only the personal information of

their choice. Two models illustrate the ways in which

health records are treated: the physician-patient model

and the public health model.

THE PHYSICIAN-PATIENT MODEL

The precedent for confidentiality in the physicianpatient relationship was set many years before the

Hippocratic oath was written (Walters, 1983), and

since that time, physicians have held to an ethical code

of privacy in matters relating to patient’s records.

Utilitarian Justifications.--One way to consider

the privacy of the physician-patient relationship is

utilitarian: for the physician to effectively treat the individual there must be trust between them. A patient

can only be expected to reveal delicate health issues

to the physician if the information is to be held in strict

confidence. In daily life, a person can control whether

or not to disclose personal information to others. One’s

private thoughts may be represented by a set of concentric circles, with the outermost circles containing

information that a person is willing to give to anyone,

such as height or occupation, and the innermost circles

containing personal information that is reserved only

for those closest to him or her, if anyone. In the medical model, a patient allows a physician to enter an

inner circle in order to get help with a medical problem, and the physician therefore owes a duty to the

patient to keep the information confidential (Walters,

1983). Certain types of genetic patient data may be

considered so proprietary that, “Doctors in whose

records this information may reside should hold it extremely confidential and should not keep it in the person’s general medical file” (Wexler, 1983).

Patient Rights.-–Another approach to the

physician-patient relationship is centered on the rights

of the individual. These rights become particularly important in considering the difference between collecting a family history and performing genetic tests. A

patient has direct control over whether to provide a

family history to a physician, while genetic testing can

be performed on blood, body fluids, or tissues. This

technical ability to collect genetic patient data raises

two main concerns. First, the patient does not exercise the same discretionary control over information

garnered from biochemical testing as he or she does

in relating a family history: the patient merely assents

or dissents to undergoing the test. Second, blood or

tissue samples collected at other times for other rea-
72 . Human Gene Therapy—Background Paper

sons may be tested genetically, without the knowledge

of the patient.

Even following the guidelines for informed consent,

with the patient agreeing to genetic tests, their technical nature increases the risk that the patient does

not fully understand the possible significance of the

data. Patients may also fail to anticipate the potential

harm disclosure might cause him or her. The consent

of the patient is required to remove blood or tissue

from his or her body, and also to perform tests, but

it is important that the patient be informed of all the

tests which are done and that a concern for the privacy of the patient extends to the control of tissues

removed from his or her body.

Under normal circumstances, health records are not

released to third parties, except with the consent of

the patient, so that medical information which exists

in the record is still under the control of the patient.

Nevertheless, current practices involving information

release allow little or no control over withholding parts

of data. A patient with a genetic trait or disease is

rarely able to release only the parts of his or her record that do not contain that information once a waiver

is signed, as those waivers are considered as ‘blanket’

consent for release of their entire medical record.

However, even in instances when the physician-patient

relationship can be maintained, there are several cases

which supersede it and these can be grouped and

called the public health model

THE PUBLIC HEALTH MODEL

A physician’s duty to protect the privacy of his patient may be superseded by his duty to prevent harm

to others, such as the patient family or society in general. For example, a physician must report the occurrence of cases involving gunshot wounds, battered

children, and certain communicable diseases (Green

and Capron, 1974; Walters, 1983). Government interest in reporting communicable diseases centers on

identifying both the disease and those individuals who

are at risk of contracting it, and mobilizing efforts to

prevent or treat it. With certain communicable diseases, such as gonorrhea, there is a high risk of danger to significant numbers of people, and government

involvement may be a way to reduce the risk. With

gunshot wounds, it is possible that the injury occurred

as a result of an illegal act that may place others at

danger, and so government action may prevent harm

to others. This concern for the public well-being often

places the physician in a difficult ethical position, having to choose between the privacy interests of his patient and the interests of society. This is especially true

in the case of psychiatrists who may have reason to

believe a patient may become violent, and they must

decide whether their belief justifies reporting the patient to the police (Walters, 1983).

Since there are many different issues involved in the

disclosure of information, it is instructive to look at

several different cases of the disclosure of information,

beginning with the disclosure to the patient, himself.

DISCLOSURE TO THE PATIENT

The doctrine of informed consent, so called, was initially developed to assure a patient’s self-determination

and right to decide whether to undergo health care

procedures. One of the most important arguments for

an informed patient is that only with adequate information can an individual make informed decisions concerning his or her health or lifestyle, and genetic

information can play an important role in these decisions. Another, recently discovered, and perhaps more

compelling argument is that informed consent may actually provide numerous physical and psychological

benefits to the patient (Andrews, 1984a).

Studies of elective surgery patients have provided

the most notable evidence of the beneficial effects of

information disclosure. Patients ‘briefed’ on the nature

of surgical procedures and postoperative sensations

exhibited a greater capacity to adjust to postoperative

stress, needed less pain medication, and had fewer

recovery days in the hospital. In another study of hospital patients, one of the chief reasons for refusing

treatment seemed to be the occurrence of unexpected

procedures which exacerbated patient uncertainty

and aroused patient anger (Appelbaum, 1982).

However, the therapeutic effects of information disclosure are not limited to surgery patients. Patients

scheduled for endoscopic examination— where a fiberoptic tube for internal viewing is placed down the

esophagus and into the stomach—heard a taped

description of the sensations frequently experienced

during the procedure and subsequently needed less

medication to tolerate the examination than those who

did not hear the tape. Similar results indicating the

benefits of disclosure have been found in studies involving blood donors, burn treatment, and sigmoidoscopy examinations (Andrews, 1984a).

Disclosure also acts as an informal check and balance system whereby a patient may reject a procedure

that is being advocated more for the benefit of the

practitioner than the patient. Although generally acting in the patient’s best interest when they propose

diagnostic procedures and therapies, physicians may

be motivated by strong financial and professional considerations that place them in a conflict of interest

(Schneyer, 1976) .

Another potential benefit of informed consent is that

it may enhance the quality of physicians’ decisions. By
App. B—Privacy and Control of Genetic Patient Data . 73

requiring physicians to provide clear and factual information about the risks and alternatives to a given

procedure or therapy, they may recognize and account for their own judgment biases and suggest a

more thoroughly considered course of action. Additionally, in the course of the physician describing a

procedure, the patient may reveal information pertinent to the treatment choice— information which may

result in a different choice of action.

There is no consistent or prescribed amount of information due the patient on a national basis, but there

are three measures by which the legal system generally determines the patient’s right to decide. One is

the Reasonable Physician Standard, whereby the physician follows the standards of the community to determine how much, or whether to disclose anything

to the patient. The second is the Reasonable Patient

Standard, whereby the patient is informed of any and

all information necessary or helpful to a reasonable

patient. The third is the Individual Patient Standard,

whereby the physician must take into account what

he/she knows about the individual patient to determine what should be disclosed. Each of these standards carries different weight with different courts, and

despite the widespread acceptance of the doctrine and

its continued expansion, the patient’s right to informed

consent has always been and continues to be a qualified one (Andrews, 1984a).

Courts almost unanimously note several exceptions

to the general rule: an emergency situation where the

patient is unconscious or otherwise unable to authorize treatment, and serious damage will occur if treatment is not undertaken; where the patient is deemed

incompetent to make a decision; where a waiver to

informed consent is signed by the patient; and where

therapeutic privilege is invoked because disclosure

poses such a threat of psychological damage as to be

unwise from a medical viewpoint (Andrews, 1984a).

Third party access

Several groups besides the individual would have an

interest in genetic information gathered about an individual. For example, family members may wish to

be alerted to potential health risks revealed by the

genetic data about a close relative Also, insurance companies, employers, and the Federal Government have

an interest in access to genetic patient data for various

reasons which will be described below. In each case,

there is conflict between third party access to information and the individual’s right to privacy.

A physician’s duty to protect the confidentiality of

the patient data can be upheld if certain guidelines

are followed when disclosing information to third

parties:

there should be a high probability of harm to

others,

the potential for harm should be deemed serious,

such as being irreversible or fatal, and

there should be reason to believe that the information will prevent harm. (President’s Commission, 1983, p. 44).

Reasonable attempts for voluntary consent should

be made, since it would not be ethical and may not

be legal4 to disclose information without the consent

of the patient, and only the relevant information

should be disclosed. These guidelines will be considered in the following situations: disclosure to family

members, insurance companies, employers, and the

government.

DISCLOSURE TO FAMILY MEMBERS

There are many situations in which genetic data

about an individual may affect decisions made by close

relatives. Genetic data may be of greatest importance

to one’s spouse or prospective spouse because it may

directly affect the couple’s reproductive decisions. The

reason for disclosure is to prevent direct harm to the

unborn and indirect harm to one’s spouse. In many

cases, one partner would wish to inform the other

about possible genetic risks so that together they may

make an informed decision about having children. In

other situations, the affected partner may prefer not

to inform the other, in order to avoid being identified

as the cause of having deformed children or being the

reason for not having children at all.

Disclosure to a spouse may indeed prevent harm if

the couple decides not to have children at high risk

of genetic disease. The reasons supporting disclosure

of genetic patient data to a spouse increase with both

the severity of a potential genetic disease and the probability of the children inheriting it.

Another reason for disclosure goes beyond reproductive decisions to include the need for the spouse

and family to know the genetic condition of the affected person in order to make plans to care for them,

both physically and financially. For example, if it were

known that the provider of a household would develop

polycystic kidney disease or Huntington disease, the

family would have to plan for the debilitating effects

of the disease, significant medical expenses, and future

loss of income.

‘,A phjsician who discloses meciical data to relatiles or third parties ma}

he sued for damages resulting from \iolation of the patient’s prnacj;

38-803 0 - 84 - 6 , QL 3
74 • Human Gene Therapy—Background Paper

Since children receive half their genes from each

parent, they also have an interest in the genetic data

of their parents. The case for disclosure to children

is strong because there may be a significant probability of harm that could be reduced if the children were

to take health precautions. In families with colonic

polyposis, for example, those with the disease are at

high risk of developing colon cancer, and preventive

removal of the colon can thwart almost certain death

from cancer. Knowledge about colonic polyposis can,

therefore, be of extreme importance to those at risk.

Genetic patient data may also be relevant to health

care of other relatives. In families that carry the gene

for retinoblastoma, for example, children are at high

risk of developing potentially fatal eye cancer. Knowledge that a relative has the disease may precipitate

more careful scrutiny of cousins and siblings who are

also at risk, thus potentially saving lives.

The case for access to more distant relatives is generally not as strong as for the immediate family, since

the predictive value is lower, but here, too, genetic

patient data might alert the person to potential health

risks. If the severity of the disease and the degree of

risk is high and action can be taken to prevent harm,

then disclosure to more distant relatives maybe justified,

Finally, genetic patient data can be of use to children

and other relatives of parents affected with a genetic

disease when considering reproductive decisions.

Prospective parents may choose not to bear children

or may take special steps to monitor their children as

a consequence of information obtained about diseases

that are more likely in their children than in the general population.

DISCLOSURE TO INSURANCE COMPANIES

The insurance industry is the second largest user

of medical information in the United States, after the

Federal Government (Baskin, 1978). Both life and

health insurance companies use medical information

in order to assess the probability of health events for

those who are insured. There is a great deal of variation between individual firms in the amount of information required to accept an applicant.

Health Insurance Companies.—One hundred

ninety million people in this country had some form

of health insurance coverage in 1983 (Health Insurance Association of America, 1984), and many people

consider health insurance to be a necessity. The majority of health insurance policies are group policies,

received in conjunction with employment. These

group health policies do not consider the health risks

of the applicants to determine their insurability or

their premiums. However, claims made on preexisting

health conditions are exempted for a period usually

of 30 to 120 days (Health Insurance Association of

America, 1984). The access of insurance companies to

genetic patient data, therefore, does not seem to be

an issue for most group health insurance coverage .

Individual health insurance policies, however, are

similar to life insurance policies, since they both use

medical information to determine the premiums.

Group health insurance policies, generally used in

employee benefit packages, usually require applicants

to sign a blanket waiver permitting access to their entire health record, including family history and any

genetic patient data.

The people who purchase individual policies include

those over the age of 65, the self-employed, and workers in small businesses. The unemployed do not qualify for group insurance and usually cannot afford individual policies. For the remainder of this paper, the

term “insurance” will encompass both life and individual health insurance.

Life Insurance Companies.—Most life insurance

companies require an applicant to answer several

questions about his or her health on an application

form, and then if the answers warrant, and if the coverage sought exceeds a certain amount, they may require the applicant to release his or her medical

records, submit to a medical examination, or both. The

results of these medical findings and other data are

then used to determine the life insurance premiums

for an individual, or whether the person is insurable

at all. Some of the questions are related to conditions

with a genetic component, such as sickle cell disease,

and if an applicant reports or displays the symptoms

it is unlikely that he or she will be insured. Likewise,

an applicant may be asked about the presence of heart

disease, high blood pressure, or stroke in his or her

immediate family, and an affirmative answer would

increase the risk factors involved, even though the

genetic basis of these diseases is not clear. The use

of this genetic patient data raises several ethical questions that are not new, but the potential increase in

the amount of genetic patient data in the future may

increase the significance of these issues.

Risk Classification. -Insurance companies generally use several factors to determine an individual’s

insurance premium, such as gender, occupation,

weight, and blood pressure (Cummins, et al., 1983).

Recently, some insurance companies have begun using

lifestyle factors, such as one’s smoking or exercise

habits, in assessing insurance risk.

Controllable Risk Factors.—Smoking is considered

largely a voluntary activity, controllable by the individual, with strong actuarial evidence of significantly

reduced life spans. It is also generally accepted that

the primary health effects from smoking (e.g., cardiovascular disease, emphysema, and lung, esophageal,
App. B—Privacy and Control of Genetic Patient Data 7 5

and bladder cancers) can be caused by smoking. Perhaps the major drawback of using this type of lifestyle

information is that it is self-reported and, therefore,

not verifiable; since there is a price incentive to report that one is a non-smoker, an applicant may not

be truthful.

Diet is also a known risk factor for development of

certain types of diabetes, arthritis, and susceptibility

to colonic and breast cancers. Alcohol ingestion is

associated with liver cirrhosis, esophageal and stomach cancers, and more than a dozen neurological syndromes.

Uncontrollable Risk Factors.—Until a 1983 Supreme

Court Decision, it was common practice in the insurance industry to use the gender of the applicant to

determine the premium. While that practice continues

in the underwriting of individual policies, it is no

longer allowable in group health, or employee benefits, policies. (I. Katz Pinsler, ACLU, personal communication, 1984). In contrast to lifestyle factors, one’s

gender is genetically determined and is not under

one’s voluntary control, but there is strong actuarial

evidence that women tend to live longer than men.

Gender is verifiable, which makes it relatively easy to

use as a determinant. Some actuaries, however, question the use of gender, claiming that other factors such

as smoking, lifestyle, work habits, or competitive

behavior maybe the cause of the mortality differences

(Cummins, et al., 1983 p. 86), (Business Insurance,

1981).

The race of an applicant is not used to determine

the premium, although the criteria are similar to the

case of gender: one’s race is not under one’s own control, but although there is actuarial evidence for mortality differences between races, it is difficult in practice to identify distinct races because of the degree

of racial mixing. Insurance companies argue that the

actuarial differences between races are due to socioeconomic differences and not to race, per se, and that

these factors are already considered in the actuarial

process. Also, several States have prohibited the use

of race in insurance underwriting (Cummins, et al.,

1983 p. 90).

Some factors with genetic components are used

to determine the insurance premium, such as a family

history of heart disease. The criteria for using genetic

patient data are similar to those for race and market

since one’s genetic complement is not voluntary. At

present, however, most genetic diseases cannot be

verified before they are expressed.

Efficiency and Equality.—Insurance companies, as

profit-maximizing firms, have an incentive to use any

readily available genetic patient data because it will

allow them to function more efficiently in the free

market. By using this information, they will be better

able to identify high-risk applicants and thus be able

to charge them proportionately higher premiums.

The adverse selection model, described below,

provides one explanation for why insurance companies might wish to use genetic patient data in the

underwriting process. In an insurance market, when

there is no distinction made between the risks of the

applicants, there is a tendency for those who know

they are at risk to purchase the highest coverage they

can afford. With more of these high-risk clients, insurance company costs will increase, because the company will be paying more claims. The increase in costs

tend to drive up the insurance premiums, causing lowrisk clients to leave, this results in a pool of high-risk

clients, paying high premiums. If another type of insurance were available that differentiated applicants

on the basis of risk, insurance companies could make

a profit by offering it as an option (McGill, 1984). The

use of genetic patient data could help insurance companies counter this adverse selection phenomenon

which can lead to high rates.

The question of fairness remains, however, and the

crux of the issue is whether it is more fair for those

individuals with high risks to pay proportionately higher rates or for all individuals to pay the same rate,

regardless of risk. In the first case, market forces will

act to differentiate people on the basis of the risk they

present to the insurance company, and may lead to

groups of individuals unable to purchase insurance at

an affordable price. This type of situation may seem

fair when it concerns something over which an individual has some control, such as one’s smoking habits,

but the fairness issue becomes more difficult when

it involves something over which one has no control,

such as one’s genetic complement.

In the latter case, where everyone pays the same

rate, low-risk individuals would be subsidizing highrisk ones. In either case, one group will be harmed,

and society needs to determine whether the low-risk

or high- risk individuals will bear the burden. A compromise could be made using the U.S. Social Security

system as a model. In this system, contributions are

not actuarially equal to benefits, but the level of

benefits is related to the amount contributed (Cummins, et al., 1983).

Impacts of Using Improved Genetic Patient Data.—

Increased screening for genetic diseases could lead to

numerous groups of individuals that are substandard

risks, uninsurable, or who must pay prohibitively high

rates. At present, diseases or health conditions that

already exist carry more weight in the underwriting

formulae than those conditions which are just statistical probabilities. If reliable genetic patient data were
76 Human Gene Therapy—Background Paper

available at low cost to use in insurance underwriting,

however, more weight might be placed on them. For

example, if an applicant has expressed polycystic kidney disease, he or she is likely to be denied insurance.

However, since this disease is not expressed until later

in life, an individual can carry the gene for the disease and still obtain insurance, since there is no way

to detect the gene at present. If the gene could be

detected at an early age and one could say with high

certainty that a person would develop polycystic kidney disease, then such tests might be used to determine insurability. Further questions arise concerning

the use of tests that are under development, are not

perfectly accurate, or are prohibitively expensive. For

example, if a test were developed which indicated the

presence of a gene but not whether it would result

in disease,5 should the results of the test be used in

the underwriting process? Three States, Florida, Maryland, North Carolina, (Case, Health Insurance Association of America, personal communication, 1984)

already specifically prohibit health insurance companies from discriminating against sickle cell carriers.

The increased use of genetic patient data in the

underwriting process has significant legal implications.

Since several genetic diseases are linked closely with

race, (see table B-1) if an insurance company uses

genetic patient data to compute the health risks of applicants, it would have a disparate impact on the affected races. As genetic markers become more refined, it may become increasingly difficult to separate

the prevalence of specific genetic diseases from race.

Therein lies a potential conflict with current or future

civil rights laws.

The role of Federal and State Governments in constraining access to genetic patient data may increase

in proportion to the amount readily available. Patient

protection will be afforded by case law, but some

aspects of how genetic patient data are specifically

handled (in contrast to other personal or medical information) may depend on new Federal or State regulations. Public policy on genetic patient data turns,

in part, on whether it is classed as a basis, like race,

for civil rights protections. As the availability of genetic

patient data grows, pressures to use it and disclose

it to third parties will also likely increase. Legislatures

may wish to consider new laws to redress misapplications or to cover areas not clearly defined in case law.

DISCLOSURES TO EMPLOYERS

Because of the significant costs of occupational

illness— including the time lost from work, the cost

of training replacements, and increased health insur-

%ince most diseases at-e due to a combination of genetic and emrironmental

factors, genetic tests may eventually prove to be mostly of this type

ance rates—a profit-maximizing company has an incentive to reduce the incidence of work-related disease as long as the costs of the reduction are lower

than the costs of the disease (Murray, 1983).

Because the expression of a genetic disease is frequently thought to be determined by a combination

of genetic and environmental factors (Harsanyi, 1981),

companies may have the ability to change specific environmental factors which otherwise enhance the possibility of disease expression. Availability of genetic

data on employees could then lead to companies assisting those employees in remaining healthy.

But what if the cost of the disease is higher than that

of the reduction? Or if there is no known way to reduce incidence? Or if a company is disinclined to institute changes due to either inconvenience or cost?

The use of genetic patient data under these circumstances could lead companies to discriminatory hiring, promotion, or lay-off policies. In this light, the

question once again arises as to whether companies

should have general access to genetic patient data.

Title VII of the amended 1964 Civil Rights Act, and

sections 503 and 504 of the 1973 Rehabilitation Act

govern employment rights. The former prohibits employment discrimination on the basis of race, color,

religion, sex, or national origin. The latter prohibits

discrimination against otherwise qualified handicapped individuals by employers who are Government

contractors or recipients of Federal assistance.

Currently, the term ‘handicapped individual’ is defined in section 503 as “any person who: 1) has a physical or mental impairment which substantially limits

one or more of such person’s major life activities, 2)

has a record of such an impairment, or 3) is regarded

as having such an impairment.” Equally, in section 504,

an employer receiving Federal financial assistance may

not make preemployment inquiry about whether the

applicant is handicapped or about the nature and

severity of an existing handicap unless a preemployment medical examination is required of all applicants

and the information obtained from the examination

is relevant to the applicant’s ability to perform jobrelated functions. Both sections serve to limit the use

of discriminatory preemployment examinations and

tests, but it must nevertheless be determined whether

genetic trait is a handicap and whether screening procedures are job related.

These statutes indicate that individuals are not to

be discriminated against on the basis of some immutable characteristics and that their abilities are to

be judged on an individual basis. Since genetic screening could result in employment discrimination against

groups of individuals with particular inherited traits,

one question that arises is whether such discrimina-
App. B—Privacy and Control of Genetic Patient Data 7 7

Table B-1.—Genetic Diseases Found in Higher Prevalence Among Specific Racial or Ethnic Groups

Condition Prevalence

Amyloid nephropathy associated with familial

Mediterranean fever . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Aspartylglycosaminuria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cystic fibrosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diabetes mellitus, type 2 (insulin-dependent, ketosisresistant) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dubin-Johnson syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Essential fructosuria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Galactosylceramide Iipidosis (globoid cell

Ieukodystrophy; Krabbe’s disease).. . . . . . . . . . . . . . . . . .

Gaucher’s disease, type I . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Glucose-6-phosphate dehydrogenase (G6PD) deficiency;

multiple allelic disorders, including mild A-type and

severe Mediterranean type. . . . . . . . . . . . . . . . . . . . . . . . . .

Gyrate atropy of the choroid and retina . . . . . . . . . . . . . . . .

Hereditary fructose intolerance . . . . . . . . . . . . . . . . . . . . . . .

Hereditary spherocytosis, several types . . . . . . . . . . . . . . . .

Hermansky-Pudlak syndrome . . . . . . . . . . . . . . . . . . . . . . . . .

Intestinal Iactase deficiency . . . . . . . . . . . . . . . . . . . . . . . . . .

Niemann-Pick disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Nonketotic hyperglycinemia . . . . . . . . . . . . . . . . . . . . . . . . . .

Occulocutaneous albinism,

Occulocutaneous albinism,

Pentosuria . . . . . . . . . . . . . .

Primary gout: idiopathic . . .

Sickle cell anemia . . . . . . . .

Tay-Sachs disease. . . . . . . .

tyrosinase-negative type . . . . .

tyrosinase-positive type . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . .

Thalassemia, multiple allelic disorders . . . . . . . . . . . . . . . . .

Tyrosinemia, type I (hepatorenal tyrosinemia;

tyrosinosis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Variegate porphyria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Xeroderma pigmentosum, multiple types involving

multiple gene loci . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1:3,000Sephardic Jews

70-100 cases in Finland

1:2,000 Caucasians

1:130 Caucasians, uncertain in blacks

1:1,300 Iranian Jews

1:130,000; more common in Jews

1:50,000 in Sweden

1:2,000 U.S. Jews

A-type: 1:11 U.S. blacks (males)

Mediterranean type: common in Africa, Middle East and

other Mediterranean countries

1:50,000 in Finland

1:20,000 in Switzerland

1:5,000 Caucasians

1:60,000 Caucasians

1:5,000 Puerto Ricans

1:10 Caucasians, majority of Asians, Africans, and U.S.

blacks are affected

1:25,000 U.S. Jews

1:250,000 in United States

1:12,000 in Northern Finland

1:39,000 Caucasians

1:28,000 blacks

1:37,000 Caucasians

1:15,000 blacks

1:150 in certain American Indians

1:2,500 Eastern European Jews

1:500 in Western populations

1:50 in American males by age 50

1:10 in males in some Polynesian groups

1:25 in females in some Polynesian groups

1:500 U.S. blacks (newborns)

1:3,000 U.S. Jews

High frequency in Mediterranean, African, and Asian

populations

1:10,000 French Canadian isolate

Common in South Africa; rare in other parts of the world

1:25,000 in Egypt

SOURCE: Stanbury, 1983; as amended by Bowman, personal communication, 1984.

tion is prohibited by these two acts (OTA, 1983). If they

are judged not to prohibit genetically based discrimination, another question raised is whether additional federal legislation will be forthcoming.

The 1970 Occupational Safety and Health Act (OSHA),

which requires employers to maintain a workplace

free from recognized hazards, does not specify the

means by which that requirement can be met. For example, it neither supports the argument that genetic

testing is required nor that genetic testing is prohibited. Although the results of genetic testing could

have an adverse affect on particular employees, it certainly cannot be classified as a “hazard” (OTA, 1983).

Yet genetic testing might become the basis for employment discrimination, or harm to employees.

In this light, it is significant to note that it is common practice for employees to sign a blanket waiver

allowing the company to gain access to all medical

records it deems necessary. Employees generally “have

little genuine expectation of true confidentiality as to

employment medical records” (OTA, 1983). Any duty

to the confidentiality of the patient is based on a physician-patient relationship, and the traditional view is

that a physician-patient relationship does not exist be-
78 . Human Gene Therapy—Background Paper

tween an employee and an employer-provided physician. Some courts take a view that the existence of a

physician-patient relationship is dependent on the context of the health care provided. If the physician-patient relationship does not exist, neither does the duty

of confidentiality, and so the company generally may

have access to the medical records of its employees.

There are also few common law restrictions on the

disclosure of genetic patient data to parties outside of

the company, except for several State and Federal

restrictions. For example, California requires employers to establish procedures to protect the privacy of

medical records, and records may not be released

without the consent of the employee. Because of the

potential harm to the employee arising from disclosure, legislators may wish to anticipate the outcome

of the increased use of genetic information by employers.

Unauthorized Access.—Because of the use of computers to maintain health records, there has been a

growing concern for the security of the information,

especially in light of the reports of computer crime.

These concerns are not unique to the health care field,

since every major sector of the economy is relying

more on the computer for the maintenance of records.

Genetic patient data may not be as obvious a candidate for computer theft as would be valuable trade

secrets, but patient records at Memorial Sloan-Kettering Cancer Center have already been broken into (Marbach, 1983), and so the possibility of unauthorized or

inadvertent access should not be discounted as greater

amounts of genetic patient data become stored.

One solution to the problem of unauthorized access

is to remove any identifying data from the record and

keep it in a separate file. Then codes could be used

to match the individuals to their records. Another solution is to extend the concentric circle model of privacy

to include the genetic patient data stored in computer

files. The information could carry different access

codes, so that information could be accessed only by

those physicians who need to know. Different individuals would therefore have access to different levels

of private information, but this would not obviate the

need for patient control of disclosure of information

to third parties (Walters, 1983). These safeguards,

while protecting the privacy of individuals, might also

have the detrimental effect of making it more difficult for physicians to use the information in the medical record. The experience of research on Huntington

Disease suggests that it is possible, by careful attention to data entry and access restriction, to provide

aggregate data while protecting individual privacy

(Wexler, personal communication, 1984).

DISCLOSURE TO THE GOVERNMENT

The government will likely play an important role

in issues relating to genetic patient data both as a significant user of information and as a body acting to

control the access to that information.

The major objective of government in using medical information is the protection of the public health.

For example, by collecting statistics on the frequency

and incidence of various diseases, the government perhaps can take measures against those diseases in the

future, perhaps by mobilizing health care efforts in

particular areas. Other likely government uses of

genetic patient data include:

providing information about medical costs,

developing policies to better allocate health

resources, and

. identifying diseases which merit additional research.

For these purposes, the identity of the individual is

not important, and so all identifying pieces of information can be culled from the record. For other purposes,

such as tracking individuals with specific genetic diseases or doing epidemiological research, however, it

is important to know the identity of those at risk. In

the interests of privacy and security, the records may

be coded and the identifying information may be

stored in a separate file, but the identity of individuals

must still be accessible. In this instance, privacy can

be retained by authorizing only one, or a few, disease

centers to follow individual patients.

Because of the growing amount of information collected and used by the Federal Government, and because of improvements in information storage and retrieval technologies in the foreseeable future, Congress

passed the Privacy Act of 1974 to set a policy for the

appropriate use of personal information. The Act

states that “The right to privacy is a personal and fundamental right protected by the Constitution of the

United States, ” and that in order to “protect the

privacy of individuals identified in information systems

maintained by Federal agencies, it is necessary and

proper for the Congress to regulate the collection,

maintenance, use, and dissemination of information

by such agencies” (Privacy Protection Study Committee, 1977). The Act describes in detail the conditions

of disclosure and access, as well as agency requirements and rules. The Act forbids the disclosure of any

records to any person or agency, except with a written request by, or with the prior request of, the individual to whom the record pertains. Violations of the

Act can lead to a civil liability.
App. B—Privacy and Control of Genetic Patient Data 7 9

The Federal Government is involved in providing

funding for genetic testing and counseling, thus assisting in the process of collecting genetic patient data.

The government can also serve as an effective forum

to discuss the ethical, legal, economic, and social

aspects of genetic information. Since there are many

different groups involved in balancing the issues of

privacy and access, the Federal Government can ensure that these issues are included in the decisionmaking process.

The States also have the authority to compile and

store genetic patient data that is of potential benefit

to the public health (Reilly, 1977 pp. 250-252). Several

States have written laws that regulate the type of information that can be collected and the procedures

through which disclosure can be made (Reilly, 1977

pp. .252 -256) The States also have control over the

business practices of various industries including insurance companies, and they may determine the propriety of using genetic patient data in different

Conclusion

Public policy on genetic patient data is centered on

determining the rights of privacy and access, pitting individual autonomy against relatives’ or third parties’

needs for information. The legitimacy of others’ needs

are determined by the potential benefits to relatives,

health providers, insurers, employers, or the general

public compared to potential harm to the patient from

disclosure, Several factors are included in such assessments, including the seriousness of the genetic condition, the genetic relationship between interested parties, and the probability of preventing harm or

promoting good by disclosure. When no genetic relationship exists, as in the case of insurers and

employers, issues of fairness arise. Continuing public

scrutiny may be instrumental in the evolution of

deciding on a hierarchy of conditions and people for

whom disclosure of genetic patient data is important

(Rosenfeld, 1984).

employment and underwriting situations. Some States

have already forbidden the use of such data as gender, age, handicaps, or other impairments in the

underwriting process (Cummins, et al., 1973).

General education is an issue of Federal, State and

local interest, necessary so that all people can have

an understanding of genetics sufficient to understand

the complex issues of genetic patient data (President’s

Commission, 1983; Rowley, 1984). Some schools have

responded to this need by making genetics a major

focus of their biology courses. Genetic education is an

issue for health care providers, as well. The teaching

of genetics occurs primarily’ during the first 2 years

of medical school, with little integration of genetics

into the practical side of clinical training (Rowley,

1984). As the technology for identifying genetic disease improves, it is important that physicians become

aware of that technology and how to use it with patients.

Public policy on genetic patient data attempts to control access so that individual privacy is protected. This

effort may include support of data storage methods

that are coded so that epidemiologic research and research priority assessment may be performed without jeopardizing individual privacy. Legislation may

be required to guide genetic data collection agencies

in what constitutes appropriate disclosure of information and to act as a deterrent to unauthorized access.

Public policies may be required that would strengthen

individual’s control over access to their genetic data.

In contemplating new legislation, care must be taken

to ensure that controls are not so strict that the genetic

patient data cannot be used for legitimate and lifesaving purposes.
Appendix C

Working Group on Human Gene Therapy

Recombinant DNA Advisory Committee

National Institutes of Health

LeRoy Walters, Chairman

Director, Center for Bioethics

Kennedy Institute of Ethics, Georgetown University

W. French Anderson Robert F. Rich

Laboratory of Molecular Hematology School of Urban and Public Affairs

National Heart, Lung, and Blood Institute Carnegie-Mellon University

National Institutes of Health Harold Varmus

Judith Areen Department of Microbiology

Georgetown University Law Center University of California

Alexander Capron

The Law Center

University of Southern California

James F. Childress

The Wilson Center

Smithsonian Institution

Samuel Gorovitz

Department of Philosophy

University of Maryland

Anne R. Witherby

Public Representative

Executive Secretary

William J. Gartland, Jr.

Office of Recombinant DNA Activities

National Institute of Allergy and

Infectious Diseases

National Institutes of Health

Susan K. Gottesman

Laboratory of Molecular Biology Consultant

National Cancer Institute Howard M. Temin

Clifford Grobstein Department of Oncology

Department of Science, Technology, and University of Wisconsin

Public Affairs

University of California, San Diego Liaison Representatives

Maurice J. Mahoney Charles McCarthy

Department of Human Genetics Office of Protection From Research Risks

Yale University Office of the Director

Robert E. Mitchell (ex officio) National Institutes of Health

Attorney at Law Henry I. Miller

Norwalk, CA National Center for Drugs and Biologics

Arno G. Motulsky Food and Drug Administration

Department of Medicine

University of Maryland

Robert F. Murray

Division of Medical Genetics

Howard University

ao
Appendix D

Acknowledgements

Preparation of this background paper has been

greatly assisted by scientists, medical professionals,

journalists, members of the clergy, and other interested parties. Special thanks are extended to members

of the Human Gene Therapy Advisory Panel that convened at OTA on September 25, 1984, and others who

attended that meeting. Several other groups also deserve special mention. Many workers at the National

Institutes of Health, notably Elizabeth Milewski, Rachel

Levinson, and Bernard Talbot, critically reviewed

some sections of the report. Several members of the

Human Gene Therapy Working Group of the Recombinant DNA Advisory Committee at NIH were also

quite helpful, including Howard Temin (consultant to

the group), Judith Areen, Alexander Capron, James

Childress, Samuel Gorovitz, Anne Witherby, Harold

Varmus, Arno Motulsky, and Clifford Grobstein. Many

at the Food and Drug Administration, in addition to

the two representatives on the Advisory Panel, also

reviewed the report. Barbara Filner at the Institute

of Medicine of the National Academy of Sciences made

several helpful suggestions. Finally, many scientists,

health professionals, attorneys, ethicists, journalists,

and other interested parties assisted OTA in preparation of the document. These include David Martin,

Nancy Wexler, Zsolt Harsanyi, William Nyhan, Jeremy

Rifkin, Yale Bohn, Jeffrey Fox, Elena Nightingale, A.

L. Beaudet, Kenneth Ryan, Philip Leder, Thomas

Maniatis, Duane E. Jeffery, Monte Turner, Mark Skolnick, Leroy Hood, Leon Rosenberg, Leon Kass, and

Richard McCormick. Two Scandinavian reviewers also

submitted comments: Ole Johan Sandvan and Bertil

Wennergren. Those on the OTA staff thank all who

assisted us. Those who contributed should not, however, be construed to agree with our conclusions or

interpretations, and should not be held responsible for

mistakes or other errors.

81
———

Appendix E

List of Abbreviations and Glossary

Abbreviations

ADA — Adenosine deaminase, an enzyme whose

absence leads to metabolic errors that in

turn inhibit the bodies’ immune defenses.

ADA deficiency is a rare disorder caused by

genetic mutation that is inherited as an autosomal recessive trait. It is not the same disorder as PNP deficiency, although there are

some similarities.

cDNA — Complementary DNA, DNA made from a

messenger RNA template (see Technical

Notes).

DNA — Deoxyribonucleic Acid (see Technical Notes).

EAB — Ethics Advisory Board, established under the

Secretary of Health and Human Services to

advise the Secretary on ethical issues related

to public policy. There can be one or more

such boards (Code of Federal Regulations,

1983). None presently exist, despite Federal

regulations.

HPRT – Hypoxanthine-guanine phosphoribosyl

transferase (or hypoxanthine phosphoribosyl transferase), an enzyme whose complete deficiency leads to Lesch-Nyhan syndrome, and whose partial absence leads to

gout. HPRT deficiencies are inherited as Xlinked traits.

IBC — Institutional Biosafety Committee, established at a university hospital, private firm,

or other research center. IBCs supervise research protocols to ensure compliance with

Federal Guidelines for Research Involving

Recombinant DNA Molecules. In the case of

Human Gene Therapy, this will involve review also by the RAC and the NIH Director

before approval to commence experiments.

IRB — Institutional Review Board, established at a

university, hospital, private firm, or other research center. IRB’s must be composed of 5

members, at least one of whose primary interests are in nonscientific areas and one

member neither affiliated with the institution nor in the immediate family of anyone

who is so affiliated. IRBs supervise research

protocols to ensure compliance with Federal

Human Subjects Protections, and report noncompliance with the Protections to appropriate institutional officials and the Secretary

(Code of Federal Regulations, 1983).

mRNA — Messenger RNA (see Technical Notes).

NIH –

OCT –

OSTP –

OTA –

PKU –

PNP –

RAC –

RFLP –

RNA –

National Institutes of Health, Public Health

Service, U.S. Department of Health and

Human Services.

Ornithine carbamoyl transferase (or ornithine transcarbamylase), an enzyme that

mediates metabolism in the urea cycle, and

whose deficiency is inherited as an X-linked

trait.

Office of Science and Technology Policy,

reporting directly to the President.

Office of Technology Assessment, U.S.

Congress.

Phenylketonuria, a disorder caused by deficiency of an enzyme, phenylalanine hydroxylase, that metabolizes one amino acid

(phenylalanine) to another (tyrosine). It is inherited as an autosomal recessive trait.

Purine Nucleoside Phosphorylase, an enzyme whose absence leads to metabolic errors that in turn inhibit the bodies’ immune

defenses. PNP deficiency is caused by a rare

genetic mutation inherited as an autosomal

recessive trait different from ADA deficiency.

Recombinant DNA Advisory Committee, constituted at the National Institutes of Health

to advise the Director of NIH on experiments

involving recombinant DNA and molecules

derived from recombinant DNA.

Restriction fragment length polymorphism,

a phenomenon involving variation in the

length of DNA cut by specific enzymes that

permits location of genes of interest, including disease-related genes (see app. A).

Ribonucleic Acid (see Technical Notes).

tRNA — Transfer RNA (see Technical Notes).

TSD — Tay-Sachs disease, an autosomal recessive

disorder caused by deficiency of the enzyme

hexosaminidase A.

UCLA — The University of California at Los Angeles.

82
App. E—List of Abbreviations and Glossary • 83

Glossary

Achondroplasia—a defect in the formation of cartilage at the ends of long bones (femur, humerus)

that often produces a type of dwarfism. There are

a number of hereditary forms, the most common

of which is an autosomal dominant.

ADA deficiency—an autosomal dominant disorder

caused by deficiency of the enzyme adenosine deaminase, and resulting in inhibition of the bodies’

defenses.

Allele-one of several possible alternate forms of a

given gene.

Alpha fetoprotein—a fetal protein found in amniotic

fluid that indicates, by its presence and concentration, the presence of certain fetal defects (e.g.

anencephaly; spina bifida).

Alpha globin mRNA deficiency—an insufficiency

in the messenger RNA coding for the alpha chain

of hemoglobin.

Alpha-1-antitrypsin deficiency—a recessive

heritable disease due to the lack of a protein inhibiting enzyme, alpha-1-antitrypsin. Death is usually

due to degenerative lung and liver disease.

Alpha thalassemia—an hereditary disease due to an

insufficiency in the number of alpha hemoglobin

molecules in the blood. It is usually caused by the

deletion of a portion of the gene coding for the alpha

hemoglobin molecule.

Alzheimer disease—a progressive brain disease

marked by progressive dementia (loss of memory

and higher mental functions) and associated with

characteristic changes in and near nerve cells: senile

plaques and neurofibrillary tangles. The evidence

suggests the disease can be caused in several different ways: a hereditary form exists, but its prevalence is uncertain; slow acting infectious agents may

play a role; the body’s immune system may react

against the brain; specific populations of nerve cells

may die; and environmental toxins (ionic aluminum

or silicon) may be involved; or some combination

of factors.

Aminoaciduria (branched chain; and ketoaciduria)—any of a large class of diseases marked by

the accumulation of various amino acids (branched

chain or ketoacids) in the blood. Symptoms vary

with the specific compounds involved, each presumably the result of different defective enzymes in the

relevant metabolic pathways.

Amniocentesis—the process of withdrawing a sample of the amniotic fluid surrounding the fetus in

utero through a needle into a syringe. The fluid

taken (usually 2 to 8 milliliters, or cubic centimeters)

contains cells shed by the developing embryo. These

can be grown in cell culture and either analyzed

biochemically or cytogenetically to detect a variety

(over one hundred) of hereditary diseases.

Anencephaly-–a congenital defect characterized by

the absence or extreme reduction in size of the

brain and spinal cord. It is usually due to complex

developmental malformations rather than a simple

genetic defect.

Antibody molecule-protein molecules manufactured in the body that serve to recognize and

destroy cells identified as foreign. The antibody

molecule is a tetramer, composed of two large,

heavy chain molecules and two light (kappa or lambda) chain molecules. The ability to bind to different

antigens (molecules that stimulate the production

of antibodies) resides in antibodies.

Antigen—a molecule, usually a large protein or carbohydrate, which when introduced into the body

stimulates the production of an antibody that will

react specifically with the antigen to remove it.

Aneuploidy—a defect of chromosome number. Normal sexual organisms are diploid; that is, they have

two complete sets of chromosomes, one of paternal

origin and one of maternal origin. Defects of ploidy

can be either of individual chromosomes, where one

more or one less is present than normal (trisomy;

monosomy), or of entire chromosome sets (e.g.,

triploidy).

Argininemia—a recessive genetic defect marked by

severe mental retardation and various neurological

disorders. It is due to an excess of arginine in the

blood and spinal fluid, this being caused by decreased activity of the enzyme (arginase) that normally degrades this molecule. It was suggested a

decade ago that argininemia could be treated in

humans by deliberate infection with the Shope rabbit papilloma virus, which had been shown to restore arginase activity of deficient cells in tissue

culture.

Arginosuccinate synthetase deficiency—see Citrullinemia.

Arteriosclerosis (hardening of the arteries)--a

condition in which the walls of blood vessels become

thickened and hardened due to a number of different pathological conditions. The causes are multiple and complex, and often incompletely known.

There is good evidence that genetic factors are

sometimes involved.

Arylsulfatase B deficiency—an autosomal recessive

disorder of lipid metabolism caused by a deficiency

in the production of the enzyme arylsulfatase B. A

form of metachromatic leukodystrophy, the symptoms are severe physical changes including hydrocephalus, with death usual by the late teens.

Atherosclerosis—the most common form of arterio-
84 Human Gene Therapy—Background Paper

sclerosis in which there are localized deposits of

fatty material (lipids) in the walls or the chamber

(lumen) of blood vessels. It can be the result of

defects in lipid metabolism, many of which are

genetic in nature.

Auto-immune disease—a disease in which the

body’s defenses fail to distinguish its own tissue

from foreign matter (’(self” from “non-self”) and attack it. The causes are probably errors in gene regulation, and there are clearly hereditary forms of

this disease. A common form is lupus erythematosus, in which the connective tissues of the body

(collagen especially) are progressively destroyed.

Autosomal dominant—a genetic trait (or a gene) carried on one of the autosomes that produces an observable phenotype even if present in only one copy

(i.e., of the two alleles present for any given gene,

if only one of them is a dominant it will be expressed

regardless of whether the other is dominant or

recessive).

Autosomal recessive—a genetic trait (or gene) carried on one of the autosomes that must be present

in two copies (both of the alleles present must be

of the same type) in order for the gene to be expressed and the trait seen in the phenotype.

Autosome—any chromosome other than the sex

chromosome.

Azacytidine (5-azacytidine)-a drug used in cancer

therapy that has also been used experimentally to

promote expression of hemoglobin F genes (to replace defective Beta globin genes) in patients with

thalassemia and sickle cell disease.

Bacteriophage (phage)—a virus that infects a bacterial cell. Phage consist of a core of genetic material (DNA or RNA) carrying the particle’s genetic information which is surrounded by a protein coat

or capsule. When a phage infects a host cell, the cell

machinery that manufactures protein in response

to genetically encoded instructions is commandeered

by the phage and used to produce offspring phage.

These are released when the bacterium dies, liberating from 100 to 10,000 new phage particles per

infected bacterium.

Beta globin--one of the several types of hemoglobin

molecules. In normal adult humans hemoglobin is

a compound molecule formed of four protein subunits (globins) and a heme group. The four globins

consist of two alpha and two beta molecules.

Beta thalassemia—a hereditary genetic defect

caused by a deletion or alteration of a portion of

the gene coding for the beta globin molecule. The

result is an insufficiency in the number of beta

globin molecules, which leads to abnormal hemoglobin,

Blastocyst—the developmental stage (in a mammalian

embryo) immediately following the morula. It consists of an outer layer (the trophoblast) containing

a cell mass attached to the inner wall of the interior

cavity, or blastocoele. (See Technical Notes. )

Carcinogen—an agent or chemical that causes cancer.

Carrier (silent carrier)—an individual carrying a

genetic defect and capable of transmitting it to offspring, but who does not show the defect him/herself. Most often, a carrier is heterozygous for a

recessive allele, that is, carries only one of the two

copies of a gene necessary for the trait to be manifest. It is possible, however, for an individual to

carry a dominant allele that is not expressed and

thus to transmit the trait to offspring while never

showing it him/herself.

Chorionic villus biopsy—a technique of ante-natal

diagnosis by which a sample of tissue is taken from

the placenta (whose cells are of fetal origin) and

analysed to detect the presence or absence of certain hereditary defects in utero.

Chromosomal disorders-any of a great variety of

pathological conditions associated with abnormalities of the chromosomes, whether of number (aneuploidy) or structure (insertions, deletions, rearrangements).

Chromosome (colored body)–-so named by early

researchers because they stained very darkly when

colored with certain dyes, chromosomes are the

location of hereditary (genetic) material within the

cell. This hereditary material is packaged in the

form of a very long, double stranded molecule of

DNA surrounded by and complexed with several

different forms of protein. Genes are found arranged in a linear sequence along chromosomes, as

is also a large amount of DNA of unknown function,

but that may serve simply to help keep one gene

separated from its neighbors.

Citrullinemia--an autosomal recessive defect whose

clinical symptoms are associated with a deficiency

in the enzyme argininosuccinate synthestase. Symptoms include ammonia intoxication, severe vomiting,

and mental retardation.

Cleavage–the stage of cell multiplication immediately

after fertilization of the egg. It lasts until the cells

begin to segregate and differentiate, producing a

blastula and then gastrula.

Complementary DNA–- (cDNA)–DNA synthesised

from a messenger RNA template rather than the

usual DNA template. cDNA is often used as a DNA

probe to help locate a specific gene in an organism.

The advantage of cDNA over mRNA as a probe is

that the mRNA can be used to identify a specific

gene product (e.g., an enzyme important to the
App. E—List of Abbreviations and Glossary . 85

cause of a hereditary disease) and then to produce

a DNA probe (more stable and more easily handled

than RNA) to find the gene responsible for the hereditary disease.

Conceptus—a fertilized egg; an egg after conception.

Cystic fibrosis—an autosomal recessive disorder in

which the glands do not function normally. Most

often seen in children and young adults, it is usually lethal. Death is due to excess mucus in the lungs

and pancreatic insufficiency.

Cytogenetics—the study of chromosomes and their

behavior in the cell: what they look like, how many

there are, how they are replicated and distributed

to daughter cells (mitosis) or among gametes

(meiosis).

Cytotoxic agents-chemicals, compounds or other

agents that can cause cell death for any of a variety

of reasons.

Dementia—loss of higher mental functions: memory,

reasoning ability, speech, etc.

Diabetes mellitus—a disorder of carbohydrate metabolism marked by elevated blood sugar due to inadequate insulin production.

di-methyl adipimidate–an experimental compound

used to prevent sickling in the red blood cells of patients with sickle cell anemia.

DNA (deoxyribonucleic acid)—the molecule containing hereditary information in all but the most

primitive organisms (some viruses, that use RNA).

The molecule is double stranded, with an external

“backbone” formed by a chain of alternating phosphate and sugar (deoxyribose) units and an internal ladder-like structure formed by nucleotide basepairs held together by hydrogen bonds. The nucleotide base pairs consist of the bases adenine (A),

cytosine (C), guanine (G) and thymine (T) whose

structures are such that A can hydrogen bond only

with T, and C only with G. The sequence of each

individual strand can be deduced by knowing that

of its partner, This complementarily is the key to

the information transmitting capabilities of DNA.

(See Technical Notes.)

DNA probe–a molecule (usually a nucleic acid) of

known structure and/or function that has been

tagged with some tracer substance (a radioactive

isotope or specific dye-absorbing compound) that

is used to locate and identify a specific gene or region of a chromosome or portion of the genome.

Dominant--a gene that produces a visible effect even

when present in heterozygous condition; each diploid cell contains two copies (alleles) of the gene at

any specific locus. An allele that is expressed regardless of the nature of its companion allele is said to

be dominant.

Down syndrome—a chromosomal disorder caused

by the presence of all or part of an extra 21st chromosome. The symptoms are mental retardation,

congenital heart defects, immune system abnormalities, various morphological abnormalities and a reduced life expectancy. Down syndrome is one of

those diseases that has been most clearly shown to

increase in frequency with advancing maternal age.

(Down syndrome has been known by several equally inappropriate common names in different cultures, e.g. ‘(Mongolism” in the West and “round-eye”

syndrome in the Orient. )

Drosophila—a genus of diptera, or two-winged insects, that has been extremely useful in genetic

studies of nearly every sort. This is because of the

unique collection of advantages afforded those

working with the organism, which include a short

generation time (so that many generations can be

studied in a fairly short period of time) a high fecundity (thousands and even millions can be realistically

studied in a reasonable length of time) and the extremely favorable giant polytene chromosomes in

the salivary glands of the larvae, which make it possible to correlate genetic phenomena with morphological changes in the chromosomes, and follow

these characters through numerous generations

and experimental crosses. Also known as “fruit

flies, ” this genus is generally harmless, and not to

be confused with the ‘(true fruit-flies” or tephritids,

which are severe agricultural pests.

Duchenne Muscular Dystrophy—see Muscular

dsytrophy, Duchenne type.

Dwarfism-a pathological condition of abnormally

short stature. Some cases are known to be hereditary, while others result from disease or metabolic

dysfunction.

Electrophoresis--a technique for separating different molecules based on their differential movement

in an electric field. This differential movement is a

complex function of molecule size, shape, and net

electrical charge.

Embryogenesis—the process of cell growth that produces an embryo from the proper mixture of a zygote, nutrients, and time.

Expression—the process by which the blueprint contained in DNA is converted into the structures and

biochemical mechanisms present and operating in

a cell.

Expressivity—a term referring to the degree to

which a gene is manifest in an individual. Genes for

some traits (e.g., curliness of hair) may vary in the

extent or severity to which they are seen in different

individuals. Genes known to be manifest in different

degrees in different individuals are said to show differential or variable expressivity.

Fabry disease—an X-linked (the gene is located on
86 Human Gene Therapy—Background Paper

the X chromosome) hereditary disease of lipid metabolism. Symptoms are a particular type of skin lesion, kidney disease (the usual cause of death) and

a variety of neurological and biochemical abnormalities.

Fetoscopy--a procedure whereby the fetus is visually

examined with a fiber optic instrument while still

in utero.

Galactosemia--an inborn error of metabolism

(genetic defect of an enzyme system) marked by the

inability to digest galactose, a sugar produced (along

with glucose) in the digestion of lactose, the common sugar in milk and dairy products. The symptoms of galactosemia are an accumulation of galactose and byproducts which leads to liver damage,

cataracts, and mental retardation. Some relief can

be achieved by limiting the dietary intake of milk

and dairy products.

Gametes—mature male or female reproductive cells—

sperm or ova. Gametes of the opposite sex, when

fused, lead to the formation of a new, diploid

organism.

Gamma globulin—a large protein molecule found in

the blood that is very important to disease resistance. Individuals with a hereditary deficiency in

the production of this molecule (gamma globulinemia) experience a decreased ability to withstand

bacterial and viral infections.

Gaucher disease–an autosomal recessive defect of

lipid metabolism found with higher frequency

among Ashkenazic Jews of Eastern European origin

and their descendants. Symptoms include enlarged

spleen and liver and various neurological disorders.

There are several different types, the two most common being a chronic adult form and an acute juvenile form that often leads to early death.

Gene—the portion of a DNA molecule that comprises

the basic, functional hereditary unit; a sequence of

DNA that produces a specific product. The fruit fly,

Drosophila melanogaster probably has about 10,000

genes, whereas man may have as many as 100,000

genes.

Gene modification—a process of genetic therapy in

which genes are altered in the living organism. It

is not yet possible, but is expected in the future.

Gene supplementation—a technique of genetic therapy in which “new” or repaired genes are introduced into a cell by microinjection or a similar

process.

Gene surgery—a procedure whereby a defective

gene is excised and removed from a cell. A normal

gene may be substituted.

Gene transplantation—a technique of moving an entire gene from one organism into another.

Genetic marker-any character that acts as a

signpost or signal of the presence or location of a

gene, chromosome, or hereditary characteristic in

an individual, a population, chromosome or a DNA

molecule. For example, the phenotype of male sex

is a reliable indicator of the presence of the gene

for H-Y antigen, a cell surface protein found in all

genotypic males.

Genome—the total genetic information contained in

an organism’s genes. Also described as the total content of all the chromosomes in an organism.

Genotype—the total of the genetic information contained in the chromosomes of an organism. Compare to the phenotype, or external or morphological

appearance of an organism. For example, an individual may have a heterozygous genotype for eye

color consisting of an allele for brown eyes (which

is dominant) and an allele for blue eyes (which is

recessive) or a homozygous genotype, with two alleles (both dominant) for brown eyes. In either case,

the phenotype is the same: brown eyes.

Germ line—also known as “germinal tissue, ” it is the

tissue or cell lineage that produces gametes and is

used for reproductive purposes, as opposed to that

tissue or those cell lineages (somatic tissue, or soma)

producing the bodily structures and tissues used for

functions other than reproduction.

Globin–a class of proteins most often associated with

processes of oxygen or gas transport (e.g., hemoglobin or myoglobin).

Hemochromatosis—a pathological condition characterized by abnormal deposits of iron throughout the

body; signs and symptoms include defects of the

liver, glucose metabolism, and heart function.

Hemoglobin—a complex molecule that serves as the

primary oxygen transport vehicle in vertebrates. It

is composed of a single iron molecule surrounded

by four globin molecules, two each of two different

types (two alpha globins and two beta globins in normal adult humans).

Hemoglobinopathies—a collection of different, hereditary disorders of hemoglobin structure and/or

function (e.g., thalassemia, sickle cell anemia).

Hemophilia–a hereditary disease distinguished by

an abnormally long blood coagulation time. The important genes are recessive, and are found on the

X-chromosome, making it X-linked; this means that

it is most often seen in males, and most often transmitted to offspring by asymptomatic females.

Heterozygous--each normal cell in the body carries

two copies of any given gene; if these two copies

(alleles) are different one from another, or alternate

forms of the same gene (e.g., blue v. brown eyes),

then the individual is said to be heterozygous at that
App. E—List of Abbreviations and Glossary . 87

locus. If they are identical, the individual is homozygous.

Homozygous--each normal cell in the body carries

two copies of any given gene; if these two copies

(alleles) are identical to each other (e.g., both coding

for brown eyes) then the individual is said to be

homozygous at that locus.

Huntington disease—’’Huntington chorea”--a genetic disease that is not manifest until after birth

(usually between the ages of 30 and 50) resulting

in death due to progressive degeneration of specific

brain tissues. The primary signs and symptoms are

disorders of movement and dementia.

Hydrocephaly—a developmental defect marked by

an unusual accumulation of spinal fluid in the ventricles of the brain. The malformation caused by this

fluid buildup usually retards brain development,

often resulting in mental retardation and, in severe

cases, early death. The condition can now be treated

if diagnosed soon after birth.

Hydroxyurea--an experimental drug used to promote expression of hemoglobin F genes (to replace

defective Beta globin genes) in patients with

thalassemia or sickle cell disease.

Hypercholesterolemia (familial)—a pathological

condition of excess blood cholesterol that is inherited as an autosomal dominant trait,

Hyponatremia—a condition of low sodium concentrations in the blood.

Immune deficiencies—any of a number of conditions (e.g., adenosine deaminase deficiency, purine

nucleoside phosphorylase deficiency, or AIDS) resulting from a failure or malfunction of the bodily

defense mechanisms, or immune system.

Immunoglobins—a collection of complex protein

molecules that play a vital role in the body’s immune

system.

Implantation—the process by which the fertilized

egg (zygote) becomes attached to the wall of the

uterus (endometrium) which then serves to nourish

the embryo through growth and subsequent development.

in utero (in uterus) preferring to procedures that

are performed or events that take place within the

uterus .

in vitro (in glass) —meaning in the laboratory; in the

test tube.

in vivo (in life) —meaning in the living, intact

organism.

Klinefelter’s syndrome—a chromosomal abnormality in human males. In contrast to the usual complement of sex chromosomes, one X and one Y (XY),

Klinefelter males usually have two X’s and one Y

(XXY), although some have multiple Y’s or more than

two X’s. Clinical symptoms are abnormal height,

gonadal dysfunction (testicular atrophy; sterility),

below average intelligence, and possibly some behavioral abnormalities (although this is still disputed

by some).

Lesch-Nyhan syndrome-an X-linked recessive

disorder characterised by compulsive self mutilation

and other mental and behavioral symptoms. It is

caused by a defect in the gene that produces a particular enzyme (hypoxanthine-guanine phosphoribosyl transferase) important in metabolism. In the

absence of this enzyme large amounts of uric acid

accumulate in the blood, leading to gout. The causal

relationship to the behavioral disorder is not yet understood.

Linkage—the association, in inheritance, of different

genes due to their physical proximity on chromosomes.

Lipid metabolism–the process by which lipid (fatty)

molecules are broken down or synthesised in the

body.

Liposome—a structure with a lipid membrane like

that of a cell that can be filled with specific substances and then used as a delivery vehicle to transport those substances to the interior of a target cell

by fusion with the cell’s own membrane. It is one

of several potential delivery vehicles for use in gene

therapy.

Lysosomal storage diseases—lysosomes are intracellular organelles that contain enzymes capable of

digesting proteins and some carbohydrates. Lysosomal storage diseases result from an accumulation

of certain of these molecules caused by an insufficiency of a lysosomal enzyme. The symptoms and

prognosis vary with the specific enzyme involved.

Marfan syndrome—arachnodacytly (“spider fingeredness’’)--a single gene defect of which the symptoms are abnormally long fingers and toes, abnormalities of the eye lenses and heart. (Abraham

Lincoln is thought by some to have suffered from

this disease).

Membrane fusion—a process by which the membranes (outer walls) of two cells merge, thus creating one daughter cell from two parents. In contrast

to fertilization by gametes, membrane fusion describes the joining of somatic cells. One of the most

productive results of membrane fusion technologies

is the formation of hybridomas, wherein an antibody-producing white blood cell (leucocyte) is fused

with a tumor cell to produce a daughter cell that

can generate very large amounts of a specific antibody for use in diagnostic and therapeutic procedures (monoclinal antibodies).

Mendelian-–referring to a trait that is controlled by

a single gene, and which therefore shows a simple

pattern of inheritance (dominant or recessive). So
88 . Human Gene Therapy—Background Paper

named because traits of this sort were first recognized by Gregor Mendel, the Austrian monk whose

early researches laid the basis for modern genetics.

Messenger RNA (mRNA)—a ribonucleic acid molecule produced by transcribing a nucleotide base sequence from DNA into a complementary sequence

of RNA. Messenger RNA molecules carry the instructions for assembling enzymes (protein molecules) from the chromosomes in the nucleus to the

synthetic apparatus (ribosomes) in the cytoplasm,

or cellular tissue outside the nucleus.

Metachromatic leukodystrophy (MLD)—several

closely related disorders characterized by a degeneration of the protective sheath surrounding nerve

cells (myelin) and an accumulation of certain metabolic compounds as a result of insufficient activity

of the enzyme aryl sulfatase. Death is the result of

progressive central nervous system degeneration accompanied by abnormalities of the peripheral

nerves, kidney, and liver.

Metallothionein—a protein that binds metal ions.

The promoter sequence that controls the production of metallothionein has been spliced to other

genes and used to control their expression after

gene transfer, as in, for example, the rat growth

hormone transplanted into mice, resulting in

“mighty” mice of larger than normal size.

Microinjection—the technique of introducing very

small amounts of material (DNA or RNA molecules;

enzymes; cytotoxic agents) into an intact cell

through a microscopic needle penetrating the cell

membrane.

Morula—the solid mass of cells resembling a mulberry (“morula” in Latin) formed by the cleavage of

a zygote; the stage before blastocyst.

Mucopolysaccharidoses--a group of heritable diseases marked by defects in the metabolism of a class

of molecule, the glycosaminoglycans (formerly

called mucopolysaccharides). Symptoms usually include mental retardation (usually severe) and

various skeletal abnormalities all accompanied by

abnormal deposition of mucopolysaccharides in

tissues or excretion in urine.

Muscular dystrophy (Duchenne type)—an X-linked

recessive defect (therefore most affected individuals

are male) of muscle metabolism that usually causes

death by the age of twenty.

Multigenic disorder—(polygenic disorder)—a genetic

defect resulting from the interaction of alleles of

more than one gene. Although such disorders are

heritable they depend on the simultaneous presence

of several alleles and therefore the hereditary patterns are usually much more complicated than for

simple, single-gene (Mendelian) traits, making

prediction and diagnosis much more difficult.

Mutagen--any substance that can cause changes in

the structure of hereditary nucleic acids (DNA, RNA)

or the way the information they contain is transmitted to offspring.

Myopia (nearsightedness)--a defect in vision such

that objects can be accurately resolved only when

they are unusually close to the eyes. An autosomal

dominant form is known, but many (perhaps most)

cases are either non-Mendelian or complex in their

mode of inheritance (i.e., polygenic, or involving

variable expressivity or incomplete penetrance).

Neural tube defect-the neural tube is formed by the

fusion of the neural folds, which are ridges of tissue

that arise on either side of the primitive streak. The

brain and spinal cord develop from the neural tube,

and neural tube defects are any that affect their formation or development. Most such defects are developmental in origin; that is, though genetic factors may be involved these defects are more likely

to be polygenic or complex rather than single gene,

Mendelian traits.

Oligonucleotide–nucleic acid molecules formed by

the joining of a small number of nucleotide bases

(generally fewer than 10 or 20). A short sequence

of DNA or RNA.

Oncogene--a gene of which one or more mutant

forms is associated with cancer formation.

Ornithine carbamoyl transferase deficiency—

(transcarbamylase deficiency)–an X-linked defect

associated with a specific enzyme deficiency in the

nitrogen cycle (transcarbamylase). Symptoms include chronic ammonia intoxication, mental deterioration, and liver failure.

Papilloma virus (Shope)—a DNA virus found in rabbits that is associated with elevated arginase activity levels in epithelial cells. (See argininemia).

Penetrance--refers to the frequency with which the

effects of a gene (whether dominant or recessive)

known to be present are seen in the individuals carrying it.

Peptide—a class of compounds formed by joining

amino acids together by a chemical process that produces one molecule of water for each joining of one

amino acid to another. Peptides are intermediate in

size between amino acids and proteins.

Phage–see “bacteriophage.”

Phenylketonuria (PKU)—an inborn error of metabolism, or genetic disease, caused by the inability to

metabolize phenylalanine to tyrosine. The resulting

accumulation of phenylalanine and derived products causes mental retardation. The disease is due

to a defective enzyme (phenylalanine hydroxylase),

and the symptoms can be treated and the condition

ameliorated with a diet that eliminates phenylalanine. The disease can be diagnosed at birth by a sim-
App. E—List of Abbreviations and Glossary 8 9

ple test that detects the characteristic elevated levels

of phenylpyruvic acid (a phenylalanine derivative)

in the urine.

Plasmid—a circular piece of DNA found in the

cytoplasm, outside the nucleus. Replication and

segregation of plasmids to daughter cells is independent of the chromosomes, and plasmid transmission from parent to offspring is almost exclusively

matrilineal (from mother to offspring), because

while plasmids are common in ova they are generally absent from that portion of the sperm that fuses

with the ovum to form a zygote.

PNP deficiency—an autosomal recessive disorder of

immunity caused by deficiency of the enzyme

purine nucleoside phosphorylase.

Polycystic kidney disease—a hereditary disease

(single gene dominant) in which a progressive

deterioration of kidney function is associated with

the development of large numbers of cysts.

Polygenic—referring to a trait or characteristic that

is controlled not by one gene but rather by two or .

more acting in concert.

Polymerization—the process of joining molecular

subunits (e.g., nucleotide base pairs) together in sequence to form a larger molecule (e.g., a polynucleotide). primitive streak—the first visible sign of

differentiation in the developing embryo. It is a

darkened longitudinal stripe that forms at the

caudal (tailward) end of the embryo, and is composed of a layer of ectodermal cells (which develop

into skin and nervous tissue) and it marks the future

location of the longitudinal exis of the embryo.

probes—molecules that make it possible to seek out

and identify specific cellular features (see DNA

probes).

Promoter—a region of a DNA molecule found in

front of a gene (as the DNA molecule is “read” by

the proper enzymes) that controls the expression

of the gene.

Protoplasm (first formed)—a single cell or a mass of

protoplasm (the substance of which cells are

formed). The term usually refers to a bacterial cell

or to an individual plant cell from which the cell

wall has been removed preparatory to cell-fusion

experiments.

Pyridoxine responsive hemocystinuria—a condition of excess cystine in the blood that can be

treated with the drug pyridoxine.

Recessive—(contrast with Dominant) referring to an

allele of a gene that will not be seen in the phenotype of the organism carrying it unless it is present

in two copies (i.e., on both chromosomes), or homozygous. If present in only one copy, or heterozygous, its presence will be masked. (See Carrier). Xlinked traits generally act as if they were recessive

in females and dominant in males.

Recombinant DNA (rDNA)—referring to DNA molecules that have been assembled with the use of restriction enzymes, usually (but not always) by splicing together fragments from different species.

Restriction enzyme—an enzyme that has the ability

to recognize a specific nucleotide sequence in a nucleic acid (ranging from four to twelve base pairs

in length) and cut, or cleave, the nucleic acid at the

point. So called because, occurring naturally in bacteria, they recognize foreign nucleic acid (e.g. the

DNA of a bacterial virus as it begins to infect and

destroy its host) and destroy it, thus restricting the

ability of the virus to prey upon certain potential

host strains. Over four hundred different restriction

enzymes are known, recognizing a great variety of

different nucleotide base sequences. This has made

possible the cutting and splicing together of nucleic

acid within and between different organisms and

species.

Ribosome—a cellular organelle which is the site of

messenger RNA translation, the process of reading

the instructions in an mRNA molecule and using

them as the guide to constructing the specified protein. Ribosomes are composed of both RNA and protein, and they spontaneously assemble from the necessary constituents present in the cell.

RNA (Ribonucleic acid)—a polynucleotide consisting of a backbone of alternating phosphate and

sugar (ribose) molecules to which are attached the

nucleotide bases adenine (A), thymine (T), guanine

(G) and uracil (U, which replaces the cytosine, C, of

DNA). There are several classes of RNA that serve

different purposes, including messenger RNA (mRNA),

transfer RNA (tRNA), and ribosomal RNA (rRNA). (See

Technical Notes. )

Sickle cell disease (anemia)—a hereditary hemoglobinopathy caused by the presence of a defective

beta hemoglobin chain. Patients with sickle cell disease have red blood cells that tend to deform into

a sickle-like shape when the abnormal hemoglobin

crystallizes. The specific defect is caused by an abnormal gene resulting in the replacement of the

usual amino acid, glutamic acid, with valine, in the

sixth amino acid position in the beta-hemoglobin

molecule. This alters the resulting beta globin molecule in such a way as to increase its propensity to

crystallize, thus rupturing the red blood cell and

causing the cells to lodge in small blood vessels.

Sickle cell trait—refers to a person who is heterozygous for the gene producing the abnormal form

of the beta hemoglobin chain. People carrying the

sickle cell gene in heterozygous form (carriers) are

38-803 0 - 84 - 7 : QL 3
—

90 • Human Gene Therapy—Background Paper

usually asymptomatic, and thus not afflicted by the

disease. Under some conditions of extreme exertion

that reduce the concentration of oxygen in the blood

a small amount of sickling of red blood cells may

be detected, but usually not enough to bring on any

of the pathological conditions of the disease. The

mutation is found with high frequency in some populations subject to malarial infections, such as African blacks. The defective gene is thought to be maintained in the population because it confers increased

resistance to malaria upon heterozygotes.

Single gene disorder (Mendelian disorder)--a genetic disease caused by a single gene that shows a

simple pattern of inheritance (e.g., dominant or

recessive, autosomal, or X-linked).

Somatic—referring to body tissues apart from reproductive (germinal) tissues.

Tay-Sachs disease—an autosomal recessive genetic

defect resulting in developmental retardation, paralysis, dementia, and blindness followed by death,

usually before the end of the third year of life. The

defective gene codes for hexosaminidase A, an enzyme that degrades certain chemicals in the brain.

Symptoms are caused by an accumulation of cerebral gangliosides, fatty acid, and sugar molecules

found in the brain and nervous tissue. The gene is

found in highest frequency among Ashkenazic Jews

of Eastern European origin.

Tetramer--a complex molecule consisting of four major portions (moieties) joined together in some reversible, non-structural manner (e.g., hemoglobin,

in which two alpha chains and two beta chains are

joined by electromagnetic attractions).

Thalassemia--any of several heritable hemoglobinopathies resulting from defective genes causing

deletions or other alterations of different hemoglobin molecules.

Transcription—the process by which a complementary messenger RNA (mRNA) molecule is formed

from a single stranded DNA template. The result

of the process is that the information contained in

DNA is transferred to mRNA which is then used as

a template to direct the construction of protein

molecules that function in cellular metabolism.

Transferrin—a protein molecule that carries iron in

blood plasma. A number of different, genetically

coded molecules are known.

tRNA (transfer RNA)--specialized RNA molecules

that function to bring specific amino acids from the

cellular environment to ribosomes that are translating mRNA into proteins (constructing proteins

according to the information encoded in the parent

DNA template from which the mRNA was copied).

Translation—the process of decoding the information in an mRNA molecule and using it to direct the

construction of protein molecules specified in the

messenger RNA.

Transposable elements—a class of DNA molecules

capable of insertion into the chromosomes of the

host organism at any or several of numerous positions, and of moving from one position to another.

Speculation on the origin of these molecules suggests that they may be derived from virus-like

ancestors. They have been called “parasitic” DNA.

Ultrasound—high frequency sound waves that can

be focused and used to picture tissues, organs, structures, or tumors within the body. Ultrasound is particularly useful for in utero examinations of the

fetus. It is often used to locate the fetus and the

placenta prior to such procedures as amniocentesis

or chorionic villus biopsy.

Urea-cycle defects—the urea cycle is the metabolic

pathway in the body that moves nitrogen from one

source to another, and takes it out of and puts it

into the body chemistry when and where needed.

Each different step is mediated by one or more enzymes, all of which are genetically controlled and

which can, under the influence of abnormal genes,

lead to different genetic diseases (inborn errors of

metabolism) that are collectively known as ureacycle defects.

Wernicke-Korsakoff encephalopathy—a genetic

disease (probably autosomal recessive) of oxalate

metabolism caused by a defective transketolase enzyme. It seems to become clinically important only

when the diet is deficient in thiamine, can be exacerbated by alcohol and treated with vitamin B 1

supplements.

Wilson disease--an autosomal recessive disease of

copper metabolism in which various abnormalities

of the liver are accompanied by different neurological symptoms.

X-linked—referring to traits found on the X chromosome. X-linked recessive traits are seen far more

often in males, who have only one X chromosome,

than in females, who have two.

Zygote—a fertilised egg; a product of the fusion of

sperm and egg.
Appendix F

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