BOSTON Two studies released on Wednesday offer new evidence that inheritance plays a role in restless leg syndrome, an uncomfortable and sometimes painful feeling in the legs that can wreak havoc with sleep.
Researchers reporting in the journal Nature Genetics say they have found three pieces of the human genetic code that are linked to RLS, giving more scientific backing to a condition sometimes derided as normal restlessness.
About 3 percent of the population is affected with RLS so badly that they have trouble sleeping. About 10 percent reportedly experience some degree of symptoms, which usually appear when a person is in bed or sitting quietly and can sometimes temporarily relieved by moving the legs or getting up and walking.
Julianne Winkelman of the Max Planck Institute of Psychiatry in Munich, and her colleagues, said three genes seem to account for up to 74 percent of the cases, based on studies of people in Germany and Canada.
In a related study, published online by the New England Journal of Medicine, a team led by Hreinn Stefansson of deCODE Genetics Inc. in Reykjavik, Iceland, found that the periodic leg movements that occur during the night in most patients with RLS seems to be linked one of the three identified in the Nature Genetics article.
Both research teams pinpointed the same gene independently.
The Stefansson team found from genetic testing of people in Iceland and North America that the gene accounts for about half of the cases of people whose legs move two or three times per minute during sleep and complain of RLS.
"And that's a conservative estimate," said David Rye of Emory University School of Medicine in Atlanta, who worked on the Stefansson study.
However many doctors believe that most people who experience periodic limb movements during sleep do not have RLS. Growing older, antidepressant medicines and other sleep disorders can cause the movements as well.
RLS has been the subject of skepticism from people who regard it as little more than a modern-day diagnosis for old fashioned "ants in the pants" restlessness. This attitude has gained some popularity after the condition was heavily promoted in "talk to your doctor" advertisements by GlaxoSmithKline, which is marketing the Parkinson's disease drug Requip as an RLS treatment.
"We now have concrete evidence that RLS is an authentic disorder with recognizable features and an underlying biological basis," said Rye.
He said the new finding was derived from genetic studies from French Canadians, Germans, Central Europeans, Icelanders and Americans. "So I don't think it's a frivolous result."
In a Journal commentary, Dr. John Winkelman of Brigham and Women's Hospital in Boston said the gene may not be one for RLS per se, but for its worst symptom -- the leg movements that disturb sleep. Winkelman said the findings offer hope for a durable treatment for the condition.
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