GENE LINKED TO IRREGULAR HEARTBEAT FOUND.

Byline: Angela La Voie Medical Tribune News Service

Researchers have identified the location of a gene that they believe can cause the most common type of irregular heartbeat.

Atrial fibrillation (AF) is an electrical disturbance of the heart that affects more than 2 million Americans and accounts for one-third of strokes in people ages 65 and over. AF can prevent blood from being pumped completely out of the two upper chambers of the heart, allowing the blood to pool and clot. These clots can travel to an artery leading to or in the brain, blocking blood flow and causing a stroke.

While AF often occurs in patients with heart conditions or other disorders such as an overactive thyroid gland, the condition sometimes is unexplained, occurring in otherwise healthy individuals.

In a new study of three Spanish families, in which 19 living people had AF from an unknown cause, researchers led by Dr. Ramon Brugada, a cardiology fellow at the Baylor College of Medicine in Houston, identified the location of a genetic abnormality on the long arm of chromosome 10.

While the researchers believe that the inherited form of AF probably is rare, they hope that identifying the gene will lead to a better understanding of the condition and to better treatments.

The findings were published in Thursday's issue of the New England Journal of Medicine.

``Although familial atrial fibrillation is extremely rare, the important question raised by this study is to what extent genetic defects may be risk factors for the development of atrial fibrillation,'' Dr. Maurits Allessie, a researcher at Maastricht University in Maastricht, the Netherlands, wrote in an accompanying editorial.

The study ``may represent a first step toward elucidating a possible molecular basis for atrial fibrillation,'' he wrote.

``I think it's a very interesting paper,'' said Dr. Michael Ezekowitz, a professor of medicine at Yale University School of Medicine in New Haven, Conn.

``It is possible that the gene interferes with the insulation of the wiring of the heart, but this is just speculation,'' he said.

Identifying an actual gene that causes AF may provide a clue for determining a more effective mechanism of treatment, Ezekowitz said.

Current AF treatment includes the use of electrical shocks administered to the heart - known as electrical cardioversion - and medications that restore the heart's normal rhythm, but none of the treatments has a success rate greater than 50 percent after 18 months, he explained.

``There also may be several genes that predispose a patient to atrial fibrillation,'' Ezekowitz said.

The researchers since have identified other families with inherited AF who did not have the genetic abnormality in chromosome 10, leading the researchers to speculate that more than one gene may be involved in causing the condition, according to Brugada.

The researchers are seeking other families in which AF is common to further study what role genetics play in the disorder. Families with a history of AF wishing to contact the researchers may call Baylor College of Medicine toll-free at [phone].