Gene mutations tied to increase heart attack risk

Canadian and international researchers have discovered genetic variations that may increase susceptibility to heart disease regardless of other risk factors.

The two studies used samples from 40,000 peoplein Canada, the U.S. and Iceland.

Caucasians who carried two mutated copies of a stretch of DNA known as 9q21 had a 30 to 40 per cent higher risk of coronary heart disease, compared with people without the mutated versions, Dr. Ruth McPherson of the University of Ottawa Heart Institute,Jonathan Cohen at the University of Texas Southwestern medical school, and their colleaguesreport in Thursday's online issue of the journal Science.

"To put this into perspective, of the groups studied in Ottawa, about 33 per cent of people with early onset heart disease had this genetic variant versus 24 per cent of healthy elderly people," McPherson said in a release.

Reducingrisk

The lifetime risk of developing heart disease is about one in two for men and one in three for women.

"If we can identify genetic factors which influence heart disease risk over and above known risk factors, we can do a better job of identifying those people who will benefit most from early intervention to reduce their risk."

Those early interventions include lifestyle changes such as quitting smoking and getting high blood pressure or high cholesterol levels under control through diet, exerciseand medication.

About one in four Caucasians are thought to carry the mutations. Africans did not appear to carry the mutations, and in African-Americans, the mutations were not linked with heart disease risk, McPherson's team said.

The findings may explain why heart disease iscommon among people who do not smoke, have high blood pressure or high cholesterol.

The tiny stretches of mutated DNA, called single nucleotide polymorphisms or SNPs, were not previously identified as a gene, which may make it more difficult to determine how they contribute to disease, the researchers said.

McPherson's team looked at two SNPs called rs10757274 and rs2383206.

'Soul of the genome'

In asecond study, appearing in the same issue, Anna Helgadottir and Kari Stefansson of the Iceland-based deCODE Genetics team and their colleagues in the U.S. found people carrying two copies of another SNP, called rs10757278, had about a 64 per cent elevated risk for heart attack, compared with people with no copies of the mutation.

The SNPs were found near two genes that last week were reported to increase the risk for diabetes. Although diabetes raises the risk for heart disease, researchers only scanned people without diabetes.

"How can one region of the genome, and it is not even containing a gene, contain risk factors for both diabetes and heart attack, when they don't seem to be heart attack on the basis of diabetes?" Dr. Frank Collins, director of the U.S. National Human Genome Research Institute, told reporters.

"I think this is a stunner. This is like the seat of the soul of the genome. It seems like this one place carries all of that weight for two very common and very dangerous diseases."

Test caution

The findings do not tell scientists about how the genetic variations work.

DeCODE said it plans to develop a test based on the findings that could be available before the end of the year.It would be aimed at people with known risk factors to help gauge their inherited risk for heart attack, the company said in a statement.

"If you have this particular marker, it appears as though you have an increased risk of coronary heart disease," saidDr. Sonia Anand of McMaster University in Hamilton, Ont., commentating on the research.

"But because not much is known about the marker, it would be very difficult from a clinical perspective to think about measuring it and advising people in any special way."

Rather, the McMaster-led INTERHEART study published two years ago showed nine modifiable risk factors predict most heart attacks in populations worldwide. So for now, the same risk factor advice would apply to everyone, Anand said.