When I was a destitute graduate student several years ago, I decided to earn a quick $75 by signing up for what sounded like a relatively innocuous clinical study. An I.V. in my left arm would feed precise amounts of glucose and insulin into my bloodstream, while from my right arm a nurse would periodically draw blood to test for glucose. The study would assess how effectively my body responded to sugar, a measure that predicts risk for developing type 2 diabetes.
As someone with a family history of the disease, I had long had a shapeless fear of it. A phone call from the nurse a few days later turned that vague anxiety into something much more concrete. The blood tests showed I was “insulin resistant,” meaning that my muscle, fat, and liver cells were not responding to insulin as efficiently as they should–significantly boosting my risk of diabetes.
About 20.8 million people in the United States have diabetes, and another 50 million or more are at risk. Although the onset of the disease can be delayed–sometimes even prevented–with diet and exercise, efforts by doctors and public-health agencies to encourage healthy habits are making marginal progress at best.
In the last several months, however, a potential new tool for diabetes prevention has come to market. A test developed by the Icelandic genomics company deCode Genetics and marketed to consumers by San Francisco-based DNA Direct determines whether people carry copies of a genetic variation that can greatly increase the risk of developing type 2 diabetes. It’s available for $500 through a website, and DNA Direct’s marketing material suggests that positive results will give people extra motivation to get fit. But critics say there is no evidence that this test will succeed where so many public-health efforts have failed.
Diabetes is the result of a complex mix of genetic and environmental factors. But recent genomic studies have identified several genetic variations that contribute heavily to the disease. The one that exerts by far the biggest influence occurs in a gene called TCF7L2, which was discovered by scientists at deCode in 2005; almost 20 percent of people with type 2 diabetes carry two copies of the high-risk version of the gene. These people are thought to secrete less insulin, a crucial hormone that signals cells to store glucose for energy. A single copy of the variation somewhat increases the risk of contracting the disease, and two copies double the risk, regardless of other risk factors.
The most likely customers for the new test are people with a family histories of the disease, like me, or early warning signs such as high blood sugar, says Ryan Phelan, founder and CEO of DNA Direct. And preliminary evidence suggests that people who already have diabetes might benefit as well: research presented at a conference this year found that people with the high-risk genetic variant are less likely to respond to a class of drugs that includes some of the most commonly prescribed treatments for type 2 diabetes.
But for people who don’t have diabetes, doctors’ advice would be the same whether the test came back positive or negative: maintain a healthy weight, and exercise. So what’s the point of testing? “If they know they’re at an increased risk, they will be motivated toward stronger interventions, be it losing weight or quitting smoking,” says Phelan.