Unraveling Your DNA's Secrets
Do-it-yourself genetic tests promise to reveal your risk of coming down with a disease. But do they really deliver?
Until now, most people who encountered genetic testing were expectant women, who are routinely offered screening to see if they're carriers of the genes for cystic fibrosis, sickle cell anemia, or Tay-Sachs. Amniocentesis and chorionic villi sampling tests can reveal genetic disorders in a fetus. Newborns are screened for dozens of genetic disorders like phenylketonuria, a metabolic disease, which are treatable if detected early. Preimplantation genetic diagnosis is increasingly being used to screen embryos for fatal disorders–and also to pick the child's sex.
So if embryos can have a molecular crystal ball, why not grownups? Alas, using genetic tests to predict eventual disease is a lot tougher than diagnosing if the person already has a disease. "It could account for the disease, or maybe it can't," says Georgia Wiesner, a geneticist at Case Western Reserve University. "There could be other genes or other factors." With only a few diseases caused by a single gene, like Huntington's disease, is it certain that a person who tests positive will succumb.
Future peek. Still, there's no question that many people find the chance to peek into the medical future irresistible. Unfortunately, three of the tests that we analyzed that are marketed as gauging the risk of major diseases relied on genes that don't provide a clear view. The Alzheimer's test, sold for $150 by Graceful Earth of Honolulu, examines the APOE gene. One version is associated with an increased risk of Alzheimer's. Our tester, a 41-year-old female, was told that she had APOEe3. Not having APOEe4, the test results said, offered "moderate protection" from Alzheimer's. But half of people with Alzheimer's don't have APOEe4, and many people with it will never get Alzheimer's. "It doesn't have a lot of value to the patient," says William Thies, vice president of medical and scientific affairs for the Alzheimer's Association, which recommends against using APOE for predictive testing. Kenneth Friedenberg, vice president of Graceful Earth, agrees that having APOEe4 doesn't mean that someone will get Alzheimer's. "We've gotten criticism from doctors," he says. "But I think people really want to know, especially if they'd had it in their family." Knowing a person is at increased risk, he says, could prompt him or her to eat healthier. "What is the harm if someone starts increasing their intake of antioxidants? Or fish oils? How is that going to hurt them?"
Depression is another serious disease, estimated to affect 1 in 10 Americans. A depression risk test, sold by NeuroMark of Boulder, Colo., for $125, says it tests for variations in a serotonin transporter gene, 5-HTTLPR. In 2003, researchers found that people with one version of the gene were more likely to become clinically depressed after stressful events. Our tester, a woman in her 50s with a family history of depression, was told she had a variant that makes her less susceptible. But 5-HTTLPR is only one of dozens of genes that may play a role in depression. And five years from now, the genes linked to depression will probably be totally different from those on the list now, says Douglas Levinson, a professor of psychiatry at Stanford University who is leading a huge national hunt for depression genes. Knowing those genes may also make it easier to identify nongenetic factors. Studies on twins, for example, suggest that about half of depression is caused by genes, the other half by the environment. "Are there some people for whom it's almost entirely genes? And others it's not genes?" asks Levinson. "We just don't know."
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