December 25, 2008

New Cause of Heart Arrhythmia Found

Scientists have long believed that atrial fibrillation, the most common form of sustained heart arrhythmia, is an electrical problem of the heart. However, a new study has uncovered a surprising genetic cause for the rare and particularly severe form of heart disease.

A team of researchers at the Cleveland Clinic has found that defects in a gene known as NUP155, a key component of the nuclear pore complex that is involved in shuttling molecules in and out of the cell nucleus, also leads to arrhythmia in patients with two abnormal copies of the gene.

"It's unexpected," the Cleveland Clinic's Qing Kenneth Wang was quoted as saying. "We never thought a gene like this could lead to atrial fibrillation."

In most people, the heart disease is the result of a combination of genetic and environmental causes. But in about 30 percent of cases, the disease is tied directly to single inherited genes, spurring disease in some cases, according to the study.

In some families, those with two copies of the offending variant can develop symptoms of the disease and can suffer sudden death in early childhood. Wang's team has now identified NUP155 as the root cause of those deaths.

In lab studies, mice with two defective copies of NUP155 died very early, but those with only one copy lived and showed signed of atrial fibrillation. The researchers found that the mutated gene sets off a chain reaction.

They said a gene known as heat shock protein 70 (Hsp70) plays an important role in protecting the heart from stress damage.

"We think when NUP155 is mutated it leads to a decline in expression of Hsp70 and the heart is unprotected from damages. That may be why people develop atrial fibrillation," Wang was quoted as saying.

Researchers said they hope this discovery helps facilitate the development of new diagnostic tools for catching the disease early and even preventing it. It eventually could also help scientists identify good targets for drugs designed to combat atrial fibrillation.


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