The Obstetrician & Gynaecologist 2008;10:1:49-54
doi: 10.1576/toag.10.1.049.27378
Copyright © 2008 by the Royal College of Obstetricians and Gynaecologists.
The ethics of preimplantation genetic diagnosis
Tarek El-Toukhy, MD MRCOG, Subspecialty Registrar in Reproductive Medicine1,
Clare Williams, PhD, Professor of Social Science of Biomedicine2 and
Peter Braude, PhD FRCOG, Director of PGD Programme3
1. Centre for Preimplantation Genetic Diagnosis, Guy's and St Thomas' NHS Foundation Trust, London SE1 9RT, UK Email: tarekeltoukhy{at}hotmail.com (corresponding author)
2. Centre for Biomedicine and Society, School of Social Science and Public Policy, King's College London, London WC2R 2LS, UK
3. Centre for Preimplantation Genetic Diagnosis, Guy's and St Thomas' NHS Foundation Trust, London SE1 9RT; and Department of Women's Health, Division of Reproduction and Endocrinology, King's College London, London WC2R 2LS, UK
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Abstract
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Key content:- Preimplantation genetic diagnosis (PGD) is an alternative to prenatal diagnosis and termination of affected pregnancies.
- PGD for late-onset and susceptibility conditions requires careful consideration on a case-by-case basis.
- PGD for sex selection for nonmedical reasons is prohibited in the UK.
- The use of PGD is expanding and its ethical implications are likely to increase.
Learning objectives:
- To recognise the main ethical difficulties raised by the practice of PGD.
- To understand the role of regulation.
- To appreciate the potential ethical implications of new developments in reproductive genetics.
Ethical issues:
- Is PGD more acceptable than prenatal diagnosis and termination for all disorders?
- Should PGD be offered for Huntington disease on a nondisclosure basis?
- Should noncarrier embryos be replaced in preference to carrier embryos in recessive conditions?
- Is PGD for HLA typing a step too far?
Please cite this article as: El-Toukhy T, Williams C, Braude P. The ethics of preimplantation genetic diagnosis. The Obstetrician & Gynaecologist 2008;10:49–54.
Keywords ethics / HLA typing / Huntington disease / preimplantation genetic diagnosis / prenatal diagnosis
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Introduction
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Preimplantation genetic diagnosis (PGD) is an alternative to prenatal diagnosis; it is suitable for couples who are at substantial risk of conceiving a pregnancy affected by a known genetic disorder.1 One cell (occasionally two) is removed as a biopsy from a cleavage-stage embryo and a diagnostic genetic test is performed on the biopsied material. Only embryos believed to be unaffected are made available for transfer into the uterus.2
PGD became possible as a consequence of progress in three areas of groundbreaking biotechnology, each of which have stimulated their own ethical debates:
- in vitro fertilisation of human oocytes and culture of the zygotes to reach day 4 or 5 of preimplantation development
- embryo micromanipulation techniques to remove safely a single blastomere without substantially compromising further development3,4
- the ability to amplify miniscule quantities of DNA for genetic analysis using the polymerase chain reaction.5
The use of PGD is increasing and its indications are expanding.6 Box 1 shows some of the central ethical questions that are specifically related to PGD and which, therefore, deserve close scrutiny.
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Is PGD ethically more acceptable than prenatal diagnosis?
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PGD or prenatal diagnosis followed by termination of pregnancy can be used to prevent the birth of a child who would be affected by a serious disability. Both techniques are stressful and invasive and, importantly, both involve selection against disability. Prenatal diagnosis followed by termination of pregnancy has many critics and for those who propose and support that life starts at fertilisation and all forms of human life deserve respect, both procedures equally involve the intentional creation and subsequent destruction of an embryo. However, proponents of PGD argue that the difference in the timing of the test is significant. First, it is argued that, although they should be treated with respect because of their future potential,7 human embryos before implantation (‘potential life’) are rudimentary in development and thus have a relatively low moral status and limited rights compared with a fetus at 12 weeks of gestation (‘developing life’). In the same way, the fetus does not assume the highest moral (and legal) status until delivery or at least viability (‘developed life’).8 Some ethicists also argue that discarding embryos based on their genetic potential is not morally different from discarding embryos during in vitro fertilisation treatment based on their likely implantation potential, a process which is universally accepted as part of the assisted conception process.7
Secondly, PGD eliminates the anxiety experienced by prospective parents during the first few weeks of spontaneous pregnancy before prenatal diagnosis can be performed, even if the pregnancy later proves to be unaffected by the genetic condition. It has also been suggested that the decision during PGD to discard an affected embryo is made simultaneously with the decision to create a healthier fetus, therefore, the positive aspects balance the negative aspects. Prenatal diagnosis followed by termination of pregnancy does not offer this intrinsic balance.9
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The acceptability of genetic testing for late-onset and susceptibility conditions
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Few would argue with screening for serious or untreatable genetic conditions that manifest early in life, such as spinal muscular atrophy. However, it is ethically more challenging to accept the principle of creating and destroying embryos for the purpose of testing for late-onset conditions with high penetrance, such as Huntington disease or Alzheimer disease,10 which usually allow the affected person around four or five decades of normal and fulfilling life before the disease presents.11
Indeed, testing for adult-onset diseases has been viewed as a slippery slope towards testing for lower penetrance genes that merely increase risk (without a guarantee that the condition will develop later), such as cancer predisposition genes BRCA1 and BRCA2 and p53 tumour suppressor gene mutations.12 There could even be selection for desirable nonmedical traits unrelated to health, such as intelligence, beauty, height, hair or eye colour or athletic genotypes (so-called ‘designer babies’). In fact, this particular use of PGD – to select for nonmedical traits – has raised a host of ethical questions, such as whether parental reproductive interests justify creating and destroying human embryos and whether testing for such traits could possibly harm the resulting children, stigmatise existing persons or even create far-reaching social harm (by ultimately limiting biodiversity and uniqueness, leading to a decrease in creativity and increased susceptibility to disease).
Others argue that having a child with inherited susceptibility to a disease, such as cancer or a progressive neurological disorder leading to an early death, could be a considerable source of suffering for the child and parents. In this respect, it may be necessary to consider each case separately and take into account individual family circumstances.
Furthermore, screening to select for mentally and/or physically desirable characteristics (the ‘designer baby’ model) is unlikely to be available because of a number of factors. These include the complex, multifactorial genetic nature of these traits, the limited choice of genes available being restricted by the genetic pool of the parents, the limited number of embryos created during a PGD cycle and the burdens and stress of undergoing in vitro fertilisation in general.13,14
The application of PGD for late-onset disorders with high penetrance also raises concerns for the welfare of a child born to a person with the condition, who are themselves likely to become unwell or even die while the child is still dependent on their care. This concern is relevant and applicable to similar situations in assisted reproductive techniques where one or both partners is HIV-positive or where gamete or embryo cryopreservation is being provided before cancer therapy. However, it is generally accepted that, as long as another parent or competent care provider will be available to the child, the possibility of losing a parent does not justify withholding PGD.15
The use of PGD for Huntington disease presents specific ethical difficulties because of the implications of testing for one parent.16 Huntington disease is an autosomal dominant neurodegenerative disorder that occurs in adult life and the uptake of genetic testing and prenatal diagnosis in high-risk asymptomatic individuals is generally low.17 PGD provides an opportunity for preventing the birth of a carrier child to asymptomatic individuals who are at high (50%) risk of carrying Huntington disease without incurring the emotional, social and financial burdens that can result from presymptomatic testing. In this way, the prospective parents preserve their right not to know whether or not they carry, and in time will be affected by, the disease.
By knowing whether or not the embryos carry the mutation, the potentially affected parent could discover their own Huntington disease status. If the embryos are tested without disclosing the results (nondisclosure PGD), no information is given to the couple that may provide a basis for inferring whether or not any embryos with the affected gene were identified. However, assurance of absolute secrecy is difficult because of the large team required for PGD.18 In addition, changes in practice that may be required to maintain the deception could be viewed by some as unethical. For example, couples whose embryos are not found to be affected and whose first PGD cycle does not result in pregnancy may have to go through unnecessary in vitro fertilisation and PGD cycles, as they probably do not carry the mutation. Furthermore, a ‘mock’ embryo transfer would have to be performed if no unaffected embryos were available for transfer in case the patient believed that they were, indeed, a carrier.16 Finally, there is the psychological burden on the treating physician who knows the patient's carrier status but is unable to disclose it.18,19
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The fate of carrier embryos
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As the diagnostic spectrum of PGD expands to include more diseases, many embryos will be identified as unaffected carriers of a recessive disorder. Female carriers of some conditions, such as X-linked Duchenne muscular dystrophy, may themselves develop some symptoms of the disease. In these cases, selection against carrier embryos may be justified. However, in the majority of recessive disorders, carriers remain healthy throughout their lives.
The principal motive in selecting against ‘healthy’ carrier embryos is to protect the health of the grandchildren rather than the children. The magnitude of the risk to the grandchildren will depend on the mode of inheritance, prevalence and penetrance of the genetic condition. For example, in X-linked disorders all sons of female carriers will have a 50% chance of getting the disease, while 50% of daughters will be carriers. Conversely, carriers of rare autosomal recessive disorders would have a very low risk of facing a difficult reproductive decision unless their partner were to carry the same rare genetic mutation.20Thus, families undergoing PGD treatment and their physicians are faced with a number of choices. The first is whether or not to transfer all ‘unaffected’ embryos: noncarriers as well as carriers. In favour of this policy, it can be argued that carrier embryos are likely to grow into healthy individuals (which is the prime objective of PGD) and that selecting against carrier embryos stigmatises carriers and could be viewed as a form of positive eugenics.21 These arguments are less valid when carriers are at risk of developing some manifestations of the disorder.
The second choice is whether or not to transfer carrier embryos to prevent future reproductive conundrums. Although this option may be ethically acceptable to some, considering the limited number of embryos suitable for transfer after PGD, it may well compromise the chances of a successful cycle and predispose the couple to undergo more PGD cycles even though there are still ‘unaffected’ carrier embryos available. After careful consideration, our centre, at Guy's and St Thomas' NHS Foundation Trust, has opted for a more flexible approach to this dilemma. First, priority is given to embryo quality and transfer of those embryos most likely to result in a pregnancy, with no distinction made for carrier status of the embryos, since the main aim of the programme is to avoid the birth of an affected child. However, should good quality noncarrier and carrier embryos exist, a decision is usually reached with patients to give noncarrier embryos priority for transfer in the fresh cycle, while carrier embryos are cryopreserved to allow their later transfer in a cryothawed cycle. New PGD cycles are not started until all unaffected (noncarrier and carrier) embryos have been used. The use of mutation analysis with preimplantation genetic haplotyping22 has greatly helped with the management of such cases.
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Sex selection for nonmedical reasons
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Identification of the sex of preimplantation embryos to avoid X-linked diseases is the third most common indication for PGD after chromosomal abnormalities and monogenic diseases.6
Although sex selection for medical reasons is generally ethically acceptable, social sex selection to serve parental interests is contentious, especially as the embryos of the undesired sex are usually discarded.23 This request may be made either for the first child (where the overwhelming preference internationally is for a male child), or for a second or subsequent child of the opposite sex to the existing one(s), with no greater preference of males over females: so-called ‘family balancing’ or ‘gender variety’.24,25
By definition, social sex selection is not a therapeutic intervention as it does not prevent the ill health of any party and it confers no advantage to the selected child. Article 14 of the Convention on Human Rights and Biomedicine26 states that ‘the use of techniques of medically assisted procreation shall not be allowed for the purpose of choosing a future child’s sex, except when serious hereditary sex-related disease is to be avoided'. Social sex selection is prohibited in the UK and opposed by the American College of Obstetricians and Gynecologists.27,28 Opponents of social sex selection by PGD regard it as immoral and inherently sexist, particularly towards women, because it does not show respect for the 50% of healthy embryos that are destined to be discarded just because of their sex and because it sends a strong signal that social sex selection in pregnancy may be legitimate. Besides the possibility of imbalance in the sex ratio, already seen in China and India,29,30 it can appear to represent support of illegal practices of abortion after prenatal diagnosis or even infanticide in some countries. Furthermore, the future child may be subject to unreasonable parental pressure to conform to sexual stereotypes and some argue that this application of PGD can set a precedent for positive eugenics applications such as selection for desirable physical traits for those who can pay for them.27
Proponents of social sex selection, on the other hand, view it as an expression of parental reproductive freedom (autonomy) and argue that PGD is too expensive to be so widely used as to contribute to sex ratio disparities.31,32 Furthermore, it can also be argued that parents who seek family balancing are not sexist and are unlikely to devalue one or the other sex but simply wish to enjoy the different experiences that come with rearing children of opposite sexes.33 It is also feared that if PGD is not permitted, pregnancy and abortion may be practised instead.34 Indeed, the Ethics Committee of the American Society of Reproductive Medicine concluded in 200135 that sex selection for the purposes of sex variety, but not for the first child, was acceptable, thereby legitimising the desire to raise children of both sexes.
Conversely, the Human Fertilisation and Embryology Authority (HFEA) in the UK undertook a public consultation process in 2002–03,27 which demonstrated a negative public attitude towards PGD for nonmedical sex selection. This attitude was also reflected in a more recent study36 conducted in the northeast of England showing that 83% of participants were against the use of prenatal social sex selection. More evidence of the strength and prevalence of the desire for social sex selection in society at large would be needed before legitimising PGD for this purpose.
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PGD for HLA typing
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PGD has been used to enable families to have a child that is a tissue match for an existing sick sibling in need of an allogenic haematopoietic stem cell transplant because of a bone marrow disorder, such as leukaemia, Diamond–Blackfan anaemia, Fanconi anaemia, beta-thalassaemia major and severe combined immunodeficiency syndrome. The success of the transplant depends largely on the HLA match between the donor and recipient. In many situations the sooner the haematopoietic stem cell transplant is performed, the greater its success rate.37
PGD can be performed to ensure that only those embryos that are a tissue match (about 25% of all embryos) are transferred to the uterus. However, it should be remembered that leukaemia and Diamond– Blackfan anaemia in the sibling are often sporadic and the matched embryos (future children) are not at risk of developing the same disease.24
The fact that PGD is used solely for HLA typing has prompted critics to express their ethical disapproval of the use of PGD for this indication.20 The ethical argument advanced is that an embryo (and the child it will become) should not be exposed to the risks of PGD unless that embryo/child is likely to derive enough benefit to outweigh these risks. Opponents also argue that a child should be created, raised and valued in its own right, not used as a means to an end, for instance, to serve as a donor for an existing sick sibling. There is also the risk that the donor child may feel used and devalued, particularly if the tissue donation is unsuccessful,14 and there is the possibility of psychological damage to the donor child through the pressure of parental expectations.36
On the other hand, those who support its use argue that parents have children for all kinds of reasons, including to save a marriage and to achieve genetic ‘immortality’ of an individual or ‘continuity’ of the family, as well as for economic and psychological benefits to the parents. This is not considered unethical as long as the child is also valued in its own right, since people are judged on their attitudes towards children rather than on their motives for having them.38 The fact that these parents make so much physical, emotional and often financial effort to save their sick child could be seen to suggest that they are responsible, caring and loving parents and that children conceived to save an existing child are likely to be loved and valued for their own sake as well as for the added benefit they confer on the rest of the family by saving the sick sibling. It has also been argued that the donor child may feel proud to have saved the life of a sibling.39,40 Finally, people who support the use of PGD for HLA typing argue that the potential benefits for the sick child are so significant that they could well compensate for the theoretical risks to the future child.41The complexity of the ethical debate as to whether PGD for HLA typing should be allowed increases significantly when considering the limits that need be placed on how far the donor child (an incompetent minor) should be used to treat a sibling. For example, collecting umbilical cord blood at birth is noninvasive and, thus, widely seen as acceptable, while harvesting bone marrow stem cells or vital organs such as a kidney from the HLA-matched child constitutes a much more difficult ethical situation in view of the risks involved for the donor child.
As PGD is not an easy and guaranteed solution for the family involved, decisions about such complex cases should be made on a case-by-case basis after weighing carefully the potential risks and benefits to all those involved.42,43
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Regulation of PGD in the UK
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PGD is regulated in many countries through statutory legislation (as in Italy, Germany, Switzerland, France and Canada) or professionally binding guidelines published by scientific societies and ethics committees (as in Greece, Portugal, the Republic of Ireland and the USA).44,45
The UK has been a leader in pioneering as well as regulating reproductive technology. The HFEA, the statutory nongovernmental regulatory body in the UK, has legal authority over whether a clinic is licensed to practise PGD and for which indications. A clinic can use PGD for a particular disorder only if the HFEA is satisfied that the indication for treatment is within statutory guidelines and that the clinic staff are sufficiently qualified to perform the work. A centre wishing to do PGD may only perform tests for conditions specifically approved by the Licence Committee of the HFEA after submitting an application. Factors taken into consideration when making a decision concerning the medical and ethical acceptability of a particular use of PGD include:
- the welfare of the child who may be born as a result of treatment and of any other child who may be affected by the birth
- the seriousness of the condition being tested
- the perception of the level of risk by those seeking treatment and their previous reproductive history.
The advantages of public regulation in the area of PGD and assisted reproductive techniques in general include quality control, accountability and transparency of the process and the collection of data about use, safety and implications of PGD. It also promotes public debate on the ethical issues related to PGD technology46–48 and the HFEA has used public consultations to gauge public attitudes and help draw up guidelines for the use of PGD for new indications. As such, the HFEA has provided a regulatory model that other nations may emulate.47
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Conclusion
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With the completion of the Human Genome Project, PGD offers immense technological promise of increased reproductive choice and heralds a new era of predictive medicine. However, the application of PGD is replete with ethical problems and it can be envisaged that increasingly complicated cases will continue to present themselves as new technologies emerge. Even in the presence of an HFEA-style regulator, it is a moral duty of a healthy society to debate extensively and openly the ethical implications inherent to the use of PGD for various indications. This ethical debate will not halt technological advances but will help to ensure that such developments are only introduced with informed public support. More work addressing the safety, reliability and effectiveness of PGD is needed.
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Acknowledgement
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We thank Kathryn Ehrich, King's College London; and Yacoub Khalaf and Alison Lashwood, Guy's and St Thomas' NHS Foundation Trust, for their valuable contributions to the manuscript. Clare Williams acknowledges the support of the Wellcome Trust (grant no. 074935).
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Abstract
Introduction
