A Classroom Activity Debating the Ethical Issues of Preimplantation Genetic Diagnosis: A Role-Playing Exercise

Abstract

Almost three decades ago, the birth of Louise Brown England marked the beginning of the vitro fertilization (IVF) era. IVF is done to overcome infertility problems that some couples experience. Sperm and eggs are collected and fertilized the lab. (In vitro means in glass and is used to refer to laboratory conditions.) Fertilized eggs are allowed to divide to form an embryo which is then implanted the mother. IVF begins by stimulating the ovaries with the hormone gonadotropin. Ultrasound is used to monitor the number and size of the follicles. When the follicles are suitable, hormones are used to mature the oocytes (cells from which the egg develops) which are collected after 34 to 38 hours. Oocytes are either inseminated and left to fertilize or have sperm injected directly (Braude et. al., 2002). The fertilized egg begins to divide, forming an embryo. Embryos divide until two to eight cells have formed and are then implanted the mother. IVF has allowed many couples to overcome infertility problems. During the 1980s scientists began developing procedures for characterizing the genetic makeup of embryos created by IVF a process known as preimplantation genetic diagnosis (PDG). Detection of chromosomal abnormalities that may lead to miscarriage and single gene disorders for certain diseases are among the reasons for performing this procedure. Once the genetic makeup of the embryo has been determined, the parents can then decide if they want it to be implanted. Those that are not implanted can be discarded or frozen. PGD is recommended for the following couples: * those who have family histories of inherited genetic disease * those which the female is over 35 and, therefore, has an increased likelihood of producing eggs with an abnormal chromosome number * those which the woman has experienced numerous miscarriages, suggesting an abnormal chromosome set coming from either the mother or father * those which either the mother or father has chromosomal translocations (see below) * those who have experienced repeated IVF failure * those which the male's infertility necessitates sperm injection (Marick, 2005) The first successful PGD procedure was reported 1989 (Marick, 2005). As of 2003, more than 1,000 babies had been born following PGD (Verlinsky et. al, 2004). For PGD, once the embryos have reached the eight-to-ten cell stage (typically after three days), one or two of the cells are removed for genetic testing. The removal of these cells does not adversely affect the embryo. Alternatively, polar bodies (meiotic products that do not become an egg) may be examined prior to fertilization. There are two basic approaches for genetic testing PGD: polymerase chain reaction (PCR) and fluorescent situ hybridization (FISH). With PCR, a small section of the DNA is repeatedly copied (called amplification). This creates billions of copies of a specific section of DNA that can be used for further testing. For PGD, genes associated with different diseases are amplified. PCR is performed by repeating a series of temperature-dependent steps. First, the double-stranded DNA is heated to a temperature where the two strands separate (95[degrees] C). The DNA is then cooled (50[degrees] C) the presence of primers, short pieces of DNA that bind to specific sequences the genomic DNA (i.e., those associated with a specific trait). The temperature is again raised (75[degrees] C), allowing a special DNA polymerase (isolated from a thermophilic bacteria found growing hot springs) to begin synthesizing new DNA from the primers. After a short period, the temperature is again raised, causing the DNA strands to separate, beginning the cycle over again. With each cycle, the desired region of DNA is doubled. After 30 to 35 cycles, billions of copies of specific DNA sequences (i.e., genes that may code for abnormalities) are created for further analysis. …