THURSDAY, Aug. 22, 2002 (HealthDayNews) -- Discovery of a gene variant that can increase the risk of irregular heartbeats opens a new window on the inherited factors involved in cardiac problems, researchers say.
"Subtle" is the word used repeatedly by Robert S. Kass, a Columbia University professor of pharmacology and a member of the research team reporting the finding, when he describes the effects of the genetic variant.
What the variant causes is a slight change in the chain of molecular events that sends an electric impulse through the heart muscle, causing it to contract. That change, detectable only after strenuous laboratory analysis, increases the chance that the heartbeat will be irregular. That arrhythmia could be life-threatening under certain circumstances.
What makes this genetic variant unusual is it is the first to be found in the general population, rather than only in families with a history of arrhythmia. For an unknown reason, it is common among people of African descent. It was found in 19.2 percent of people from West Africa and the Caribbean, and 13.2 percent of black Americans but not in any whites, says a report in tomorrow's issue of Science.
However, only specific individuals who carry the variant are in danger, says Igor Splawski, an instructor in medicine at Harvard Medical School and another member of the research team. "It is important for people who have other forms of heart disease, such as cardiomyopathy, or who take certain medications," he says. One such group of medications are diuretics, prescribed for high blood pressure.
The gene, designated SCN5A, codes for a protein that forms part of the channel that regulates the flow of sodium in and out of heart muscle cells. One variant of that gene, designated Y1002, was known to be common in families with inherited arrhythmias.
Splawski and his colleagues began looking for the variant in members of the general population. And they found it. Then they asked Kass to figure out how the variant worked.
"It changes the way the sodium channel operates," Kass says. "The change is so subtle that we thought it wouldn't do anything. In our laboratory, we put it into a computer model based on what we had learned about it and simulated what would happen if you took a medication that altered the sodium channel."
Under those circumstances, the variant keeps the sodium channel open slightly longer -- just enough to create the possibility of an arrhythmia.
The Harvard researchers estimate the variant can increase the risk of an arrhythmia eightfold, which sounds terrible. However, the risk generally is so low that the increase is not significant for most carriers of the variant, Splawski says.
"This could be significant for some people who are at risk of arrhythmias," Splawski says. "They would have to pay attention to the medications they are taking. For example, erythromycin is known to prolong the opening of the ion channel."
Now cardiologists have new knowledge that can help them reduce the risk of arrhythmias for some individuals, Kass says.
"It would be nice to know more not only about this but other variants," he adds.
What To Do
You can learn about arrhythmias and their treatment from the American Heart Association or the National Heart, Lung, and Blood Institute.
