Designing Our Descendants: The Promises and Perils of Genetic Modifications

11 Ethical Differences between Inheritable Genetic Modification and Embryo Selection

c h a p t e r e l e v e n Ethical Differences between Inheritable Genetic Modification and Embryo Selection Bonnie Steinbock, Ph.D. Germ-line gene therapy, or inheritable genetic modification (IGM), offers the possibility of preventing serious genetic disorders by replacing defective genes in an embryo with functioning genes. Thus, IGM might be able to treat genetic disease in the embryo, instead of the current method of prenatal diagnosis and selective abortion. In avoiding the need for abortion, IGM resembles preimplantation genetic diagnosis (PGD). PGD is a technique to determine genetic defects in embryos created by in vitro fertilization (IVF) before implantation in a uterus for gestation.The diagnosis occurs at the six- to ten-cell stage of embryonic development, when one or two cells can be removed without harming the embryo or affecting its potential to implant.The cellular DNA is then tested for chromosomal abnormalities or genetic mutations, using polymerase chain reaction (PCR) for monogenic diseases and fluorescent in-situ hybridization (FISH) for chromosomal aberrations.1 Embryos carrying serious genetic diseases are discarded (or frozen indefinitely); embryos free of disease can be implanted for gestation. Because embryos are discarded before implantation, PGD obviates the need for prenatal testing and abortion. Whether this makes PGD morally superior to abortion depends on one’s view of the moral status of the embryo and fetus . Those who regard fetuses as having greater moral value or status than preimplantation embryos will regard PGD as morally superior to abortion. Those who regard even early embryos as human persons will not. Indeed, from the perspective of loss of prenatal life, PGD is worse than traditional prenatal diagnosis and selective abortion, because PGD requires the creation of numerous embryos for each live birth produced.2 IGM differs from PGD (and obviously abortion) in that it does not involve embryo selection or discard (much less, killing a fetus). Thus, IGM avoids the entire issue of the moral status of the embryo. In addition, many find the idea of IGM attractive because it “fixes” rather than discards embryos. Walters and Palmer argue that gene therapy is preferable to embryo selection because it “best accords with the health professions’ healing role.” They write: “prenatal diagnosis followed by selective abortion and preimplantation diagnosis followed by selective discard seem to us to be uncomfortable and probably discriminatory halfway technologies that should eventually be replaced by effective modes of treatment.”3 A problem with both IGM and PGD is that they require the creation of extracorporeal embryos, embryos created through IVF. This means subjecting the woman to drugs which cause her to superovulate, and which have significant side effects, including bloating, weight gain, fatigue, hot flashes, depression and mood swings, and possibly an increased risk of ovarian cancer.4 IVF not only poses significant health risks to the woman, but also is less likely to result in a successful pregnancy and is of course more expensive (and less fun) than making babies the old-fashioned way. For these reasons, PGD might be appropriate for infertile couples already undergoing IVF who are at risk of passing on a genetic disease, but it is not clear that it would be advisable for fertile couples. This would depend on how strongly they were opposed to selective abortion and how strongly they wished to avoid having a child with a genetic disease. The alleged advantage of IGM is that it cures the disease instead of discarding the embryo. However, in virtually all genetic diseases, the risk of transmission is not 100 percent. This means that both affected and unaffected embryos will be created using IVF, and PGD would be needed to discover which of the embryos had the genetic defect in question. But as one critic of germ-line gene therapy has asked, why would it make sense to attempt to correct an embryo with a genetic defect? “Surely one should discard the affected and reimplant 180 Bonnie Steinbock one of the unaffected.”5 IGM would make sense only if the number of embryos created by IVF were limited to the number that would be transferred. In that case, there would be a point to fixing a defective embryo so that it could be transplanted. However, it would obviously be simpler and less expensive to follow the standard practice of creating more embryos than...