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A blood test to identify the gene should not be hard to develop, said Dr. Jussi Mikkelsson, a senior research fellow and resident in internal medicine at the University of Tampere Medical School in Finland who led the study.

External Defibrillator Could Come in Handy

That could translate into better prevention and treatment, said Vinay Nadkarni, chairman of the Emergency Cardiovascular Care Committee for the American Heart Association.

"If down the road we could develop a test based on this genetic marker, gentlemen in their 40s who have this risk factor might alert your family doctor, could be started on medications like aspirin or a clot buster or it might make you pay attention to other risk factors," Nadkarni said.

Also, Nadkarni said, relatives of patients who have been found to carry the gene could keep an external defibrillator nearby and be trained to use it.

In a study of 700 white men who suffered violent or sudden out-of-hospital deaths, the HPA-2 Met gene was found 2.2 times more often among men under the age of 55 who died of sudden cardiac death, according to the study in today's issue of the journal Circulation.

The genetic trait also may be a major risk factor for fatal heart attacks and blood clots in the heart in early middle age, the study found.

"I believe that this will lead to better drugs being developed in the near future that can block clotting in these individuals," Mikkelsson said. "It needs to be studied further because the knowledge we have right now is quite limited, but we have opened a gate."

Dr. Valentin Fuster, director of the Cardiovascular Institute at Mount Sinai Hospital in New York, said the findings should be approached with caution.

"I think that this is a very positive discovery, but what I think is even more questionable is that many of the patients that die suddenly had many other risk factors like high cholesterol and smoking," Fuster said.