Not everyone agrees. David Altshuler, a geneticist at Harvard and MIT’s Broad Institute for genomic medicine in Cambridge, MA, and a physician who treats diabetes patients at Massachusetts General Hospital in Boston, was one of the researchers who reported in the New England Journal of Medicine last year that among people considered prediabetic–meaning their blood sugar was high but not within the diabetic range–those with the high-risk variant of TCF7L2 were more likely to develop diabetes than those with the normal version. The researchers also found that exercise and diet could slow or prevent onset of the disease, regardless of a person’s genetic status. Yet Altshuler says he would not recommend the test to his patients. He says that although it appears to be accurate–the variation has been linked to type 2 diabetes in multiple populations–“there is no evidence that this genetic test does result in an improved health outcome.” Highlighting patients’ other risk factors, such as body mass index, often fails to inspire lifestyle changes, he points out, and it’s not clear that a piece of genetic information will be any different.
Altshuler also worries that the test could have unintended consequences. Someone who turns out to lack the high-risk variation might slip into unhealthy habits, he says. Other critics have suggested that positive results might instill in their bearers a sort of genetic fatalism, giving them an excuse not to diet and exercise because diabetes is already written into their genes.
Given the uncertainty about the test’s impact, Altshuler argues that it’s too soon to market it to consumers. He suggests that, like drugs, genetic diagnostics should undergo clinical trials to prove their effectiveness. “If it turns out that people given this information reduce their risk of diabetes in a cost-effective way, I’m all for it,” he says. “On the other hand, $500 is a lot to spend if no good comes of it.”
But deCode CEO Kári Stefánsson, thinks it’s time to make the test available. “Once you have discovered a sequence variant [linked to disease],” he says, “you could make the moral argument that people who want to know have the right to do so.”
While many genetic tests are already commercially available or in the works, deCode’s is the first to assess risk for a common disease that many people can relatively easily prevent or delay. People with family histories of certain cancers can undergo tests that detect mutations linked to those diseases, but the recommended interventions can be as drastic as preëmptive mastectomy. Scientists have also identified a genetic variant linked to increased risk of Alzheimer’s disease, but in that case, there are no recommended interventions at all.
The deCode diabetes test could be a bellwether for diagnostics that predict risk of heart disease, hypertension, and other problems that can be ameliorated by lifestyle changes. “This test is an example of the direction we’re headed over time,” says Benjamin Wilfond, an ethicist who studies genetic testing at the University of Washington School of Medicine in Seattle. “This is potentially the sort of information that would be relevant to everyone.”
But as Altshuler points out, we have little information on whether people really do make lifestyle changes in response to genetic tests. And the few studies that have been done are not encouraging.