Genes that increase the risk of heart disease in the general population carry an even greater risk of heart trouble in diabetics, U.S. researchers said on Tuesday.

The findings may help better identify which diabetics are at risk for heart disease and could lead to new treatments, they said.

"Coronary artery disease is one of the leading causes of death in this country and diabetes is a major risk factor for coronary artery disease," Dr. Alessandro Doria of Harvard Medical School in Boston, whose study appeared in the Journal of the American Medical Association, said in a statement.

"But not everybody with diabetes is at the same risk."

In the general population, people who have a common genetic flaw in a gene on chromosome 9p21 are at higher risk of developing coronary artery disease, which can lead to heart attacks and strokes.

Doria's team studied whether this heart disease-causing gene might play a role in type 2 diabetes, a disease marked by high levels of glucose in the blood. In particular, they looked for a link in people with poor control of their blood sugar.

In one study, researchers looked at 734 people with type 2 diabetes between 2001 and 2006, 322 with coronary artery disease and 412 without. In another, they looked at 475 people with type 2 diabetes who were followed between 1993 and 2004.

Both groups were tested for the 9p21 gene variation and had their blood sugar control checked through a measurement known as hemoglobin A1c.

The researchers found that people who had two copies of this gene variation but normal blood sugar had twice the risk of developing coronary artery disease, compared with people who did not carry the genetic variation.

The finding was stronger for diabetics who struggled to keep their blood sugar at normal levels. People in this group who also had two copies of this gene variant had a four times higher risk of developing coronary artery disease.

"Further studies are necessary, but the two factors -- poor glycemic control and genetic variant on chromosome 9 -- appear to enhance each other," Doria said.

He said while good glucose control is important for all diabetics, testing for this genetic predisposition may help doctors find patients who are at greatest risk for heart problems and in need of aggressive treatment.

Type 2 diabetes is the form closely linked to obesity and it is becoming increasingly common worldwide.