March 30, 2009

Gene Variants Tied to Abnormal Heart Rhythm Risk

Illustration of an EKG graph showing the QT interval. The QT interval is easily measured in an EKG, which shows the electrical activity of the heart.Dr. Christopher Newton-Cheh, Massachusetts General Hospital.

Two international research teams, working independently, have linked variations in 10 gene regions with potentially harmful modifications in the heart's electrical rhythm. The discoveries may lead to new approaches for treating and preventing irregular heart rhythms and sudden cardiac death.

Irregular heart rhythms, or arrhythmias, are a common cause of sudden cardiac death, a condition in which the heart suddenly and unexpectedly stops beating. It leads to about 450,000 deaths nationwide each year.

One risk factor for arrhythmias and sudden cardiac death is an unusually long or short QT interval. The QT interval appears on electrocardiograms, which measure the heart's electrical activity, as the time from the major spike to the end of the follow-up wave. It represents the time it takes for the heart's lower chambers to contract and then reset for the next heartbeat.

Several rare genetic mutations are already known to cause some long-QT disorders. But in the 2 new studies, scientists searched for common rather than rare gene variants that may have subtle effects on QT duration. Both studies were supported in part by NIH's National Heart, Lung and Blood Institute (NHLBI) and several other NIH components. The results were published as separate papers in the online edition of Nature Genetics on March 22, 2009.

Both research teams compiled and analyzed data from several genome-wide association studies, which involved scanning the genomes of large numbers of people to find variations associated the QT interval. One team compiled and analyzed data on nearly 16,000 people from Germany, Italy and the United States. The other looked at more than 13,000 individuals of European ancestry.

Both teams identified 10 gene regions that contained common variants related to QT duration. Five of these regions were already known to include genes linked to long-QT syndrome. But the other regions contained common gene variants that had never before been tied to the function of the heart's electrical system. These new variants could help lead to a better understanding of the causes and prevention of arrhythmias.

The scientists note that the newly identified variants alone may not significantly boost a person's risk for dangerous arrhythmias. It is likely that several genetic variants and other risk factors must combine to significantly increase susceptibility to heart abnormalities and sudden cardiac death.

"It's likely that many more genes will be found to contribute to changes in QT interval," says Dr. Christopher Newton-Cheh of the Massachusetts General Hospital and lead author on one of the new papers. "The real challenge will be understanding the mechanism behind their effects."

—by Vicki Contie

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