Two independent groups of scientists have discovered genes linked to Restless Leg Syndrome (RLS), a disorder affecting millions that causes sometimes violent leg movements during sleep.

“We now have concrete evidence that RLS is an authentic disorder with recognizable features and underlying biological basis,” said David Rye, MD, PhD, professor of neurology at Emory University School of Medicine, director of the Emory Healthcare Program in Sleep and one of the lead authors of the study which was published in the New England Journal of Medicine.

Rye said that although RLS is very common, because it is not covered in medical training, many health professionals remain skeptical about its authenticity and prevalence.

They focused on patients who exhibited limb movements while sleeping. One group also found a link between iron deficiency and a gene associated with RLS.

They discovered a significant link between a common gene variant, BTBD9, located on chromosome 6p21.2 and RLS and periodic limb movements in sleep. This was found in one Icelandic sample and replicated in two further samples: another in Iceland and one in the United States.

According to Rye the variant is very common and at least one copy is carried by 65% of the population. Having both copies more than doubles a person’s risk of getting RLS.

A separate study in Nature Genetics led by Juliane Winkelmann, PhD, of the Institute of Human Genetics in Munich also links the BTBD9 gene to RLS and two other variants. Winkelmann’s team  concluded that each genetic variant was linked to more than 50% increase in the risk of getting RLS suggesting that “RLS has components of a developmental disorder.”