Genetic diagnosis of embryos: clear explanation, not rhetoric, is needed.

1 E mbryonic research and genetic testing continue to raise concerns. 1 With controversy comes debate and, sometimes, distortion of facts through the use of loaded terms and concepts that call to mind both historical events and science fiction. Achieving greater public understanding of genetic diagnosis of embryos, known generally as preimplantation genetic diagnosis (see definitions of terms in Appendix 1, available at www .cmaj .ca /cgi /content /full /cmaj .080658 /DC1), has implications for the development of regulations and health policies for a broad field that includes genomics, reproductive genetics and embryonic research. 2 We examine the debate about genetic testing and embryonic research with particular reference to the use of words and concepts that have distorted public and scientific discourse in ways that could have a negative influence on laws and regulations for new reproductive technologies generally. Genetic diagnostic testing of embryos is the first reproductive genetic service combining genetic testing and in vitro fertilization that is widely available and offered in a clinical setting. Like prenatal diagnosis, it can allow for the selection of embryos that are free of single-gene defects (e.g., cystic fibrosis and Huntington chorea) and frequently occurring chromosomal abnormalities including aneuploidy (e.g., Down syndrome) before the embryos are implanted in the uterus. (See other examples of genetic abnormalities in Appendix 2, available at www .cmaj .ca /cgi /content /full /cmaj .080658 /DC1). It can also be used specifically to screen for aneu-ploidy and to determine the sex of an embryo. Unlike prenatal diagnosis, preimplantation genetic diagnosis is not performed when a woman is pregnant. Rather, it is performed on embry-onic cells that have been conceived in vitro. Two diagnostic approaches can be used. One is known as polymerase chain reaction and the other as chromosome visualization by fluorescence in situ hybridization (FISH). Polymerase chain reaction allows for the amplification of target DNA sequences to facilitate the diagnosis of single-gene defects and the identification of sex in X-linked diseases. Chromosome visualization by fluorescence in situ hybridiza-tion is used to screen for aneuploidy, to identify chromoso-mal abnormalities and to determine sex in X-linked diseases (Figure 1). Quite apart from questions of the availability of these techniques is the issue of their rates of success. From the very first step of a procedure to the birth of a child, the process of genetic diagnostic testing of embryos is not without the risk of failure (Figure 2). Nevertheless, …