Those fidgety legs that wake you up when sleep is sweetest have just received medical validation: scientists have linked leg twitching to a certain variation in genes.

This is the first time gene variants have been associated with restless legs syndrome. Two new studies, appearing in today's online editions of The New England Journal of Medicine and Nature Genetics, explored the problem.

The first study, published in the New England Journal of Medicine, involved people from Iceland and the US, whose blood was analyzed by the researchers. They found that a certain variation in the human genome was associated with restless legs syndrome.

That same variation was associated with lower iron levels, Kari Stefansson of Decode Genetics in Reykjavik, Iceland, and David Rye, an Emory University neurology professor, said.

“This discovery demonstrates the power of genetics not only for uncovering the biological causes of disease, but also for defining diseases such as RLS and establishing them as medical conditions,” said Dr. Kari Stefansson, in a statement.

The second study, published in Nature Genetics, took a different approach. Researchers, including Juliane Winkelmann, MD, of the Institute of Human Genetics in Munich, Germany, compared DNA in several thousand German and Canadian participants with or without a family history of restless leg syndrome.

Their analysis found variations in three genes, each responsible for a 50 percent increase in the risk for the syndrome.

Restless leg syndrome, sometimes called Jimmy Legs, is characterized by uncontrollable movement of the legs. The urge usually becomes stronger during rest, particularly at night, preventing the person from sleeping.

The neurological disorder affects thousands of people. Some find it very uncomfortable, as its intensity varies from person from person, as well as the time of day or circumstances when it appears.