Brutes or Angels: Human Possibility in the Age of Biotechnology

3. Embryo Selection: Preimplantation Genetic Diagnosis

3 Embryo Selection Preimplantation Genetic Diagnosis She’s a typical teenage girl, she loves to dance. . . . We never thought she would live to see 15. . . . Adam knows he helped his sister, that’s all. They’re normal kids. —Lisa Nash, interview by Dan Vergano for USA Today Prospective parenthood can be anxiety ridden when one or both partners carry a genetic disorder in their DNA or advancing age puts children at risk for genetic abnormalities. If possible, most persons would choose not to bring a child into the world who has little or no chance of living to adulthood or whose life will be filled with suffering. Genetic counselors examine parents’ ancestries and assess the risk for concerned parents. With enough information, some parents opt to use donor eggs or sperm to avoid inherited abnormalities. This chapter is not about that option. Rather, it is about a rather new option for genetically at-­ risk parents who embark upon parenthood with their own eggs and sperm, preimplantation genetic diagnosis (PGD). PGD is technology that allows parents to assess the genetic health of embryos generated by in vitro fertilization (IVF) (see fig. 2.3). A major advantage of PGD over traditional diagnostic procedures like amniocentesis is that genetic diagnosis occurs before embryos are ever in the womb. By selecting only genetically healthy embryos for implantation, prospective parents greatly increase the odds of having a healthy baby. But PGD carries with it several ethical issues. This chapter addresses the following questions about PGD and the challenges it raises for human values: 82 / Chapter 3 1. What are traditional prenatal screening/diagnostic tests for at-­ risk parents and how does PGD differ from these? 2. How is PGD currently used? 3. Will PGD usher in a new era of human eugenics? 4. Will PGD sometimes bring personal values of parents and physicians into conflict? 5. What is a savior sibling, and is it ethical to use PGD to create savior siblings? 6. Do IVF and PGD pose risks to women, fetuses, or children? 7. How might PGD affect families and society? 8. Should the use of PGD be regulated? Preimplantation Genetic Diagnosis: The Biology An array of prenatal tests is available to assess the genetic health of developing embryos and fetuses in utero. Noninvasive ultrasound and blood screening tests performed between ten and eighteen weeks of pregnancy assess the baby’s risk of having congenital heart defects and chromosomal abnormalities, in­ clud­ ing the one that causes Down syndrome. But these tests are not diagnostic. For a diagnosis, couples need to use invasive tests: chorionic villus sampling (CVS) near the end of the first trimester or amniocentesis midway through the sec­ond trimester.1 Results from these tests help couples to prepare for a child with special needs and to weigh the good and ill of terminating a pregnancy. When conception is by IVF, PGD offers another option. Since the early 1990s PGD has made it possible for couples to obtain genetic information about their embryos while they are still small clumps of cells growing in a laboratory dish. PGD and embryo selection raise ethical issues for parents , doctors, and society that are different from those raised by prenatal screening and intrauterine diagnostic tests. Preimplantation Genetic Diagnosis: What Is It? Why or Why Not Do It? Available since 1990, PGD allows genetic diagnosis of IVF-­ conceived embryos when they are a small ball of six to ten cells growing in the laboratory . The procedure allows parents to cull defective embryos and to se- Embryo Selection / 83 lect only embryos with or without certain genetic traits for transfer to the uterus. The PGD technologist starts with a dozen or so embryos obtained by IVF from a couple at risk for passing genetic abnormalities to their children . Two to three days after fertilization, a single cell is removed from each embryo without injuring the remaining portion of the embryo. DNA is extracted from each single-­ cell biopsy and subjected to specific genetic tests from among the hundreds now available for known genetic diseases and conditions (figs. 3.1 and 3.2). Meanwhile, each biopsied embryo continues to grow and retain the potential to develop into a fetus if transferred to the woman’s uterus. Depending on the results of DNA testing, certain embryos are selected for uterine transfer or stored frozen for future pregnancies. As for the genetically abnormal embryos, parents decide whether to...