By Diane Allingham-Hawkins, PhD, FCCMG, FACMG, Senior Director, Genetic Test Evaluation Program and Technical Editing
Last month, CBS News’ 60 Minutes aired Breeding out Disease, a segment about a controversial procedure known as preimplantation genetic diagnosis (PGD). PGD involves fertilizing ova with sperm in the laboratory, then testing the resulting embryos for specific genetic disorders before implanting into a woman’s womb only those that are free of the disorder. The aim of PGD is to prevent genetic variants linked to potentially serious and life-threatening diseases such as breast cancer, Tay-Sachs disease, cystic fibrosis, and others from being passed on to future generations. This is a noble aim, to be sure.
Predictive genetic testing looks for variants of a particular gene that are passed from one generation to the next and are found in every cell in the body. With regard to cancer, we know that certain gene variants do cause cancer and that they may be inherited from a parent. BRCA1 and BRCA2 are examples. However, what the 60 Minutes piece failed to mention is that only a small percentage of cancers, about 5% to 10%, are actually caused by an inherited genetic variant that increases the person’s risk for developing a certain type of cancer. The majority of cancers occur as a result of an acquired genetic variant that develops during a person’s lifetime. Some acquired variants may develop, for example, from tobacco use or exposure to too much sunlight. Others are simply random events that occur within a cell without an obvious cause. So, even though prospective parents choose PGD because they want to ensure they will not pass on a known genetic variant for a certain type of cancer, PGD does not guarantee that the offspring will never develop that cancer during his or her lifetime. Similarly, the presence in an embryo of a gene variant known to cause cancer does not mean that the offspring actually will develop that type of cancer. It means that the risk is greater, but it is not an absolute. And, of course, testing for 1 or a few genetic conditions does not guarantee that a child will not have another, previously unanticipated condition.
PGD has been available since 1989; however, there is mounting concern that PGD may be used for less noble purposes, as was highlighted in the 60 Minutes segment. For example, in addition to testing for serious, life-threatening conditions, PGD can be used to create siblings who can be used as bone marrow or other donors for sick older siblings, to test for adult-onset or less serious genetic conditions, or even testing for purely cosmetic traits such as eye or hair color.
It should be noted that the experts interviewed were adamant that they are using PGD exclusively to eliminate serious genetic disease, but as journalist Norah O’Donnell asked, “Who is the gatekeeper?” At present, there is none. The genetic testing industry has advanced so rapidly that we’ve been unable to control it. It’s become big business and that comes with big concerns about how to ensure the technology is not misused. Let’s take steps now to ensure that the genetic tests being used to detect variants linked to inherited diseases are accurate. Let’s take the time to educate prospective parents about what the results really mean. Finally, let’s consider the ethics of testing for purely cosmetic traits desired by future parents. There is nothing inherently wrong with stopping the spread of life-threatening, heritable diseases. But let’s not open Pandora’s Box in the process.