The Risks of Peering into Your Medical Future

Despite an explosion in the discovery of SNPs, most experts say it's too early to make strong links between these tiny genetic variants and the development of genetic diseases. That's because the role played by a single mutation is believed to be modest. Rather, it's the interaction between multiple SNPs and factors like diet, exercise, and weight that predispose you to disease--indeed, studies show that lifestyle accounts for about 70% of our susceptibility to health problems such as diabetes, heart disease, and some types of cancer. As a result, "these tests can't accurately predict the risk of developing these complex diseases at the moment," says David Hunter, MD, ScD, professor of epidemiology and nutrition at the Harvard School of Public Health. Likewise, some tests that claim to gauge your risk of diseases such as depression examine single genes that explain only a small part of the predisposition to those illnesses.

Critics also note that DNA testing results can be tough to interpret, making it difficult to know when and if you should take action. A Navigenics test told Robert C. Green, MD, PhD, MPH, a professor of neurology, genetics, and epidemiology at Boston University Schools of Medicine and Public Health, that he had a 20% above-average risk of developing multiple sclerosis. But the average risk is 0.3%, and his was just 0.5%. These are both very low risks (3 out of every 1,000 versus 5 out of every 1,000, respectively), yet the results were highlighted in orange, indicating an elevated risk. Green, a geneticist, understood his real risk, but the average person might not, causing needless worry.

And consider the flip side: that someone who tests negative for a gene or is told she's at low risk for developing a dreaded disease becomes less motivated to lead a healthy lifestyle. David Katz, MD, MPH, director of the Prevention Research Center at Yale University School of Medicine, points to a study on premenopausal women given a range of tests to determine their risks of developing heart disease. Half saw scans of their coronary arteries, which were surprisingly healthy. But despite other risks revealed from triglyceride and blood glucose levels, the group that saw its healthy scans did less to follow recommendations to prevent heart disease. "We don't want a single test talking people out of taking care of themselves, and this study suggests that can happen," says Katz.