The siblings of French-Canadian women seem to be at increased risk for the bizarre condition known as restless legs syndrome, which appears to have both genetic and environmental causes, new research suggests.

According to a large-scale study published in the Archives of Neurology, the brothers and sisters of people affected by restless legs syndrome are three-and-a-half times more likely to develop the disease than others.

Restless legs syndrome is a little understood condition that causes unpleasant sensations in the legs, particularly when a person is at rest, triggering an urge to move the legs to get relief. The cause is unknown, but research has suggested that iron deficiencies may play a role.

Previous studies have found the condition clusters in families, particularly among Caucasians, but until this study, there haven't been large-scale systematic family studies of the syndrome.

For this study, researchers led by Dr. Guy Rouleau, a professor at the University of Montreal faculty of medicine, director of the Sainte-Justine University Hospital Research Center and a scientist at the University of Montreal Hospital Research Centre, studied 671 people with restless legs syndrome.

They found that siblings of an individual with the condition were about 3.6 times more likely to develop the condition by the time they were 60 than those without an affected sibling. As well, the offspring of parents had 1.8 times the risk of developing the condition by the time they were 40.

"The cumulative total of family members affected by restless legs syndrome should be of interest to all concerned physicians, geneticists and epidemiologists," says Dr. Rouleau.

"We also recommend that scientists and clinicians further examine how environmental risk factors, combined with genetic predisposition, may contribute to the occurrence of restless legs syndrome in families."

The study's first author, Lan Xiong, a Université de Montréal researcher, noted that restless legs syndrome is prevalent in 10 to 15 per cent of French-Canadians, yet the neurological disorder is often misdiagnosed.

He adds that his team found that the syndrome usually begins before the age of 30 and results in an average of 24 years of suffering.

It's also more prominent among women, particularly those who also have anemia or iron deficiency conditions, and those who have had multiple pregnancies, which tends to deplete iron stores as well.

The researchers say they don't know why the condition appears to cluster in families. It could be because of a genetic cause, share environmental factors, such as similar diets, or a combination of both.

They say in order to get at the underlying genetic and non-genetic links, a larger prospective family study will be needed.

CTV.ca News Staff