November 25 (HealthDay News) -- Adding to earlier research, a new study has identified a genetic variation that increases the risk of coronary artery disease (CAD) in type 2 diabetes patients with poor sugar glucose (glycemic) control.

Previous research has found that genetic variations on a genetic chromosome known as chromosome 9p21 are associated with increased risk of CAD in the general population.

The team at the Joslin Diabetes Center at Harvard Medical School studied more than 1,500 people with type 2 diabetes (including 322 diagnosed with CAD) who were tested for a gene variation of chromosome 9p21 and checked for long-term glycemic control.

The findings were published in the Nov. 26 issue of the Journal of the American Medical Association.

Compared to patients with good glycemic control and no 9p21 gene risk variant, those subjects with two risk gene variants and good glycemic control were twice as likely to have CAD, while those with two risk gene variants and poor glycemic control were four times more likely to have CAD.

This association was strongest when long-term (seven years) glycemic control was measured in patients with two risk gene variants and a history of poor glycemia, and for patients with the same genotype but not long-term poor glycemia. The researchers also noted a similar interaction between the 9p21 variant and poor glycemia was associated with the death rate after 10 years.

"In conclusion, 9p21 (variant) and poor glycemic control interact in determining the odds of CAD in type 2 diabetes," Dr. Alessandro Doria and colleagues are quoted in a medical association news release. "This finding may have implications for our understanding of atherogenesis (the process of plaque forming in arteries) in diabetes and for the design of more effective prevention strategies. More broadly, it illustrates the complex etiology of multifactorial disorders and highlights the importance of accounting for gene-environment and gene-gene interactions in the quest for genetic factors contributing to these conditions."

Type 2 diabetes is one of the most significant risk factors for cardiovascular disease, and people with type 2 diabetes are two to four times more likely to suffer a major cardiac event than those without diabetes, according to background information in the article. According to the U.S. Centers for Disease Control and Prevention, more than 22 million Americans have type 2 diabetes.

SOURCE: Journal of the American Medical Association, news release, Nov. 25, 2008