The Boomerang Effect
What is the real utility of a predictive test? It depends, geneticists say. A test is useful when it warns about a serious and clear risk of disease and, most of all, when there is a real possibility of preventing it, as in Marina's case. But the same information can boomerang when no countermeasure is at hand. Learning simply that a disease may or may not occur can lead to undue anxiety and limitations in our lives. Even worse, the results of such a test might give employers or insurance companies new grounds for discrimination.
BOOMERANG EFFECT: The results of genetic testing can boomerang, producing more worry than useful information.
But not all susceptibility tests are so successful. Take, for instance, a test for Alzheimer¿s disease. In 1993, after years of difficult work, researchers discovered that people with a variant of the gene for the fat-transporter apolipoprotein E, ApoE(4), face a 10-fold risk of Alzheimer¿s. Excitement for the discovery waned, however, when it became clear that up to 70 percent of all people with the ApoE variant would never develop the disease. Again, it is the boomerang effect: about 15 percent of all Caucasians carry the "bad" ApoE(4) version, but they hardly need to know that before an effective prevention becomes available. For this reason, guidelines from expert groups in Europe and in the U.S. recommend that the ApoE exam be used to confirm the disease in affected individuals but not as a predictive test in healthy people.
More generally, experts agree that the utility of a predictive test depends on the possibility of an effective prevention. Most likely, a growing number of diseases will be preventable in the future with drugs, vaccines, or gene therapies and stem cell transplants. When that happens, many predictive tests, which now are useless and even dangerous, will become powerful tools for helping us to secure our health.
IN PART II OF THIS STORY:
Available at www.sciam.com beginning next Monday, February 25, 2002
The complexities of predictive genetic testing, Evans, J.P. et al., British Medical Journal, 2001; 322:1052-6
Epidemiology and prevention of coronary heart disease in families. Higgins, M., American Journal of Medicine, 2000 Apr 1;108(5):387-395
Your Genetic Destiny, A. Milunsky, Perseus Publishing, Cambridge, Mass., 2001