Having a parent with atrial fibrillation (AF) strongly increased an offspring's risk of developing this heart rhythm disorder, according to a study of participants in the National Heart, Lung, and Blood Institute's (NHLBI) Framingham Heart Study.

The risk doubled for offspring with at least one parent with AF compared to offspring whose parents did not have the condition. The study of 2,243 adults, published in the June 16 issue of The Journal of the American Medical Association, is the first to find a genetic connection for AF in a community sample.

"This important research finding will need to be confirmed but it opens up a new avenue of research on atrial fibrillation. Now scientists can start looking at genetic factors that might contribute to AF — searching for the genes involved in this increasingly common disorder," said Barbara Alving, M.D., acting director of the NHLBI, one of the components of the National Institutes of Health.

The study's findings strongly support the notion that AF has genetic underpinnings. Most cases of AF occur in older people. The disorder affects about 1 in every 10 persons aged 80 and over. In the new study, the risk of AF tripled when both parents and the offspring were under age 75. The risk also tripled when the analysis was limited to offspring who had no clinically apparent heart disease.

"Disorders with a genetic component often occur at a younger age or in the absence of major diseases like heart disease that trigger the condition," said the study's lead investigator Caroline Fox, M.D. M.P.H., of the Framingham Heart Study.

Atrial fibrillation is the most common heart rhythm disorder in the U.S., affecting more than 2 million adults. The prevalence of the condition is rising and scientists predict that about 5.6 million Americans will have the disorder by 2050. Known causes of AF include abnormalities in the heart's structure and long-term uncontrolled high blood pressure.

AF occurs when electrical signals in the heart's upper chambers (the atria) are fired in a very fast, uncontrolled manner. Electrical signals then arrive in the heart's lower chambers (the ventricles) in an erratic pattern, creating an irregular heartbeat and affecting the heart's ability to pump blood. Atrial fibrillation can produce symptoms including palpitations, an unexplained, rapid heartbeat, lightheadedness, or occasionally chest pain. It can also be asymptomatic. AF can lead to complications such as stroke and congestive heart failure. Treatment via drugs, surgery or devices, is designed to slow the heart rate and/or restore normal rhythm, and to prevent stroke. Blood-thinning medications (anticoagulants) are an important means of preventing stroke in AF patients.

The Framingham Offspring study of AF involved 1165 women and 1078 men whose parents were members of the "original" Framingham Heart Study. The offspring were at least 30 years of age and free of atrial fibrillation at the first exam. Offspring and original study participants had routine clinic exams, including physical examinations, interviews, lab tests, and electrocardiograms.

AF in both offspring and original "parental" participants was confirmed by an electrocardiogram. Parental cases occurred from 1949-2002 and offspring AF cases occurred from 1983-2002.

When the Framingham researchers analyzed the data, they found that 30 percent of participants had at least one parent with AF. Seventy offspring (23 women) developed AF during the study at a mean age of 62 years. When stated in terms of 1000 persons per year, the results indicate that the number of offspring developing AF would be 4.5 if a parent had AF and 3 if parents did not have AF.

Fox cautioned that the Framingham findings should not alarm people who have a parent with AF. "AF with or without a family history is a common condition in the elderly. Our findings indicate to the scientific community that we need more research on the genetic mechanisms of AF and how they interact with environmental influences," she said.

Fox added that Framingham scientists hope to conduct further research into the genetic basis of AF.

Study limitations, noted Fox, include the small number of offspring cases of AF and a predominantly Caucasian group of participants.

To interview Dr. Fox about this study, please call the NHLBI Communications Office at 301-496-4236 or e-mail NHLBInews@nhlbi.nih.gov.

NHLBI is part of the National Institutes of Health (NIH), the Federal Government's primary agency for biomedical and behavioral research. NIH is a component of the U.S. Department of Health and Human Services. NHLBI press releases and fact sheets, including a fact sheet on arrhythmias, can be found online at www.nhlbi.nih.gov.