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Thursday, May 3, 2007

Genetic link to heart disease found

By Colin Nickerson, Globe Staff

Scientists using powerful new genetics research methods have for the first time identified a snippet of DNA common to many people that dramatically increases the chances of developing heart disease.

The discovery, revealed in two large and independent studies in North America and Europe, indicates that 75 percent of Caucasians possess a previously unknown genetic defect that puts them at elevated risk of a heart attack regardless of bad habits -- smoking, for example -- or bad health, such as hypertension or high cholesterol levels. The increased risk is most substantial for the 25 percent of Caucasians who have two copies of this defective DNA, one on each set of chromosomes.

"This is one of the most significant genetic risk factors found to date for heart attack," said Dr. Kari Stefansson, chief executive of DeCode Genetics, an Iceland-based company famous for its gene-hunting prowess.

"The variant may account for one-fifth of heart attacks" among white Europeans and North Americans, he said in a telephone interview.

Heart disease is the deadliest affliction in the western world. In the United States alone, some 1.2 million people suffer a heart attack every year and at least 452,000 die from it, according to the American Heart Association.

Human DNA is mostly the same, with less than 1 percent of the "letters" that make up the genetic code varying among individuals. Those differences, called gene variants, can account for such distinguishing traits as green eyes or blonde hair. But gene variants can also translate into susceptibility to diseases.

The newly-identified genetic variant appears unrelated to other risk factors for heart attack, according to the studies, which were published online today by the journal Science.

"This is a very common genetic variant, which has a very strong effect on heart disease risk, that isn't related to any of the other factors we know of," said Dr. Ruth McPherson, an endocrinologist at Canada's University of Ottawa Heart Institute, leader of the other research team.

Scientists believe that they will ultimately find many genes that can contribute to heart disease, just as there might be genes that protect the heart. They also stress that environmental and lifestyle factors can cause heart disease in individuals without a genetic predisposition.

Intense medical interest was stirred by the genetic location of the heart disease variant. Both studies showed the morsel of DNA appears to be encoded on the same chromosome in almost exactly the same "neighborhood" as genes identified in papers published only last week as connected to the most common form of diabetes.

At the very least, that's extraordinary coincidence. It also raises the possibility of a lethal bunching of DNA responsible for multiple ailments.

"It's a stunner," said Dr. Francis S. Collins, director of the National Human Genome Research Institute, who was not involved in either heart study. "It seems like this place [possibly] carries all of that weight for two very common and very dangerous diseases."

No one knows why DNA variants associated with the two diseases might lie in such close genetic proximity.

"This may suggest a causal link between these two disorders that is much deeper than previously suspected," Dr. David Altshuler, director of medical and population genetics at the Broad Institute, a Cambridge research center affiliated with Harvard and the Massachusetts Institute of Technology, wrote in an e-mail.

"It is too early to say anything with certainty," he said, "but very exciting days, to be sure."

Altshuler led one of the diabetes research teams but was not involved with the hunt for the heart disease genes. Of the overall heart variant discovery, he said: "It is an extremely convincing and exciting finding, with great potential to influence our understanding of coronary artery disease."

The Canadian and Icelandic researchers compared people who had heart disease with healthy individuals, looking for common genetic variants that were far more prevalent among the heart patients. They found that an individual who possesses two copies of the newly-identified genetic variant has a 30- to 40 percent higher risk of suffering a heart attack than an individual of comparable age and health who does not. A person carrying a single copy of the defect has a 15- to 20 percent increase in risk.

Discovery of the genetic variant represents a potentially important tool for diagnosing people at risk of heart disease, one which might become available to hospitals and clinics as early as this year, according to DeCode's Stefansson. But researchers admit that the genetic research is still a long way from yielding new treatments.

"The hope is that by discovering genetic predisposition to heart attack, we can identify people who are at greater risk for genetic reasons alone," said McPherson, "and in the long run can develop custom-tailored treatments."

Other studies have linked heredity to heart disease, but previously identified "bad" genes have tended to be either rare or linked to other illnesses that cause or exacerbate coronary ailments.

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