Genes Only Slightly Helpful For Predicting Diabetes



By Anne Harding
WEDNESDAY, Nov. 19, 2008 ( — About 11 to 18 genes can help predict a person's likelihood of developing type 2 diabetes, two new studies say. However, those genes don’t add much more to a patient’s diabetes-risk profile than information that’s easily available, such as body mass index, family history, and lifestyle, according to the studies in the New England Journal of Medicine.

The studies included more than 20,000 men and women who were followed for 20 to 30 years to see if they developed diabetes. In both studies, the gene variants’ predictive effect was more powerful for younger people.

However, experts say that genetic testing is probably not very useful in young adults, and probably not in children either. (The studies did not include kids.)

It's not clear how much genetic testing of children would cost, says Richard Hellman, MD, an endocrinologist in North Kansas City, Mo., who was not involved in the new research. Plus, diabetes is a complex disorder and even testing for a dozen or so genetic variants may not be all that helpful.

"As many as 500 genotypic variants are at play in the development of type 2 diabetes; it's usually not a single one," he says. "Lots of factors are playing a role."

Although more research is needed about type 2 diabetes and children, the disease is still relatively rare in kids, says John Buse, MD, director of the Diabetes Care Center at the University of North Carolina in Chapel Hill. "It would be hard to justify massive screening without a specific trial in that regard."

Next: What the studies found

In the first study, Valeriya Lyssenko, MD, of Lund University, in Sweden, and her colleagues tested 16,061 Swedes and 2,770 Finns for 16 gene variants. They found that 11 of them were linked to an increased risk of type 2 diabetes.

In the second study, James B. Meigs, MD, of Massachusetts General Hospital, in Boston, and his team looked at 18 gene variants in 2,377 men and women. The chances of developing type 2 diabetes rose with the number of these variants.

But the data gleaned from the genes provides little new information about risk. In Dr. Meigs's study, in which participants were classified into three risk groups, the addition of genetic risk to the equation would, at most, have resulted in 4% of patients being reclassified as being at higher risk.

For the Scandinavian research team, adding genetic risk factors to the mix moved 9% of the Swedish group and 20% of the Finnish group into a higher-risk category. The researchers did take a closer look at what the genetic variants were doing in the body, and found that "all of them influence the capacity of insulin-producing beta-cells to increase insulin secretion when needed, for example, during pregnancy or when getting obese or old," Dr. Lyssenko says.

For now, the studies seem to have little application in the real world. The findings are "too premature" to help individual people figure out their own risk, according to Dr. Lyssenko.

However, Dr. Hellman still sees it as good news for patients. "It says that there's much more that we can do to change the course,” he says. “It isn't just, ‘This is your genotype and this is your destiny.'"

Dr. Lyssenko agrees. "We may not be able to change our genes, but genes only work in concert with the environment, and we can change the environment; we can still improve our future by healthy diet and exercise."