Scientists believe that they have identified the gene responsible for restless leg syndrome (RLS).
The international team of researchers hope that their findings will result in RLS being treated as a physical rather than psychological condition.
Dr David Rye, professor of neurology at Emory University School of Medicine in Iceland, said: "We now have concrete evidence that RLS is an authentic disorder with recognisable features and underlying biological basis.
"This is the most definitive link between genetics and RLS that has been reported to date.
"We have known for quite some time that the majority of RLS patients have a close family member with the disorder, and now we have found a gene which is clearly linked to RLS."
RLS affects millions of people worldwide. It produces an inexorable urge to move the legs and many blame it for disrupted sleep and insomnia.
The scientists estimate that 65 per cent of the population has at least one of the gene variants which can cause RLS, though not everyone develops the syndrome.