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.

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.

"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, acting director of the NHLBI, one of the components of the National Institutes of Health.

"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 of the Framingham Heart Study.

Atrial fibrillation is the most common heart rhythm disorder in the US, 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.

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.

When the Framingham researchers analyzed the data, they found that 30 per cent 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.