Growing older often means packing on a few extra pounds, which increases the risk for Type 2 diabetes. But if you’re diabetic — despite leading a healthy lifestyle — it could be your genes are to blame.

That’s the upshot of new research out of Duke University School of Medicine that shows two different mutations in a gene called ankyrin-B cause cells to suck up blood glucose faster than normal — fattening them up and eventually triggering diabetes.

Nearly one million Americans have the more severe of the two mutations, called R1788W. The milder mutation, known as L1622I, is shared by seven percent of the African-American population, making it as common as the trait for sickle cell anemia.

The findings, based on studies involving mice, could help identify at-risk individuals who might counteract their genetic deficits by eating better and exercising more.

"This is one of the first examples of a susceptibility gene that would only be manifested through a modern lifestyle," said Vann Bennett, M.D., professor of biochemistry and biology at Duke. "The obesity epidemic really took off in the 1980's, when sugary sodas and French fries became popular.

"It's not like we suddenly changed genetically in 1980, but rather we have carried susceptibility genes that were exacerbated by this new diet. We think our findings are just the beginning, and that there are going to be many genes like this."

The findings were published in the Journal of Clinical Investigation.