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Gene variant linked to arrhythmia in African Americans


Scientists have identified a gene variant that slightly increases the risk for developing an irregular heartbeat, known as arrhythmia. The variant is primarily found in African Americans and persons of African descent. Most individuals with the variant will not develop arrhythmia, but the researchers say the gene warrants further study in a larger group of individuals.

Detail from diagram of SCN5A gene. View full

Forms of cardiac arrhythmias are a relatively common cause of death, and risk factors include structural heart problems and medication such as diuretics, which are taken to reduce blood pressure. Strenuous exercise can also trigger an irregular heartbeat in individuals at risk.

Mark T. Keating, of Harvard Medical School and Children's Hospital in Boston, Massachusetts, led the study. His team estimates that about 13.2 percent of African Americans carry the Y1102 variant of the gene. Most of these individuals will never have arrhythmia because the effect of Y1102 is subtle.

Nonetheless, prevention is the key to avoiding heart problems, and the researchers say that individuals with a history of arrhythmia or related heart conditions can now be screened for the variant.

The variant occurs in the cardiac sodium channel gene SCN5A. This gene, when mutated, has caused arrhythmia in families with a history of heart disease.

The gene encodes part of a channel that regulates the flow of sodium in and out of heart muscle cells. The variant has a subtle effect on how the channel functions, the researchers report in Science. But this is a potentially serious health risk, because imbalances in these cells can result in heart failure.

"The SCN5A gene has been implicated in several types of arrhythmias," says Igor Splawski, also of Harvard Medical School and Children's Hospital. It was simply by chance that the variant they were studying turned out to be present mostly in African Americans.

Splawski expects additional variants associated with arrhythmia will be reported in the coming months, some of which may be more common in other ethnic groups.

Studies in human genetics until now have largely concentrated on rare conditions that give researchers the opportunity to investigate the molecular mechanisms of disease, he notes. Many genes for rare, inherited disorders have been identified in large families with many affected members.

"Now we see that variants in these genes may be responsible for more common forms of arrhythmias," says Splawski.

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Splawski, I. et al. Variant of SCN5A sodium channel implicated in risk of cardiac arrhythmia. Science 297, 1333-1336 (August 23, 2002).

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