The mysterious condition restless leg syndrome may have a genetic cause, a new study in fruit flies suggests.
Researchers messed with a gene called BTBD9, and found they disrupted the flies' normally sound sleep. The human version of the gene has been linked to sleep disorders in people.
"The major significance of our study is to highlight the fact that there might be a genetic basis for RLS [restless leg syndrome]," study researcher Subhabrata Sanyal, of Emory University in Georgia, said in a statement.
Better ways to diagnose and treat restless leg syndrome could come from further study of the gene, Sanyal said.
People with restless leg syndrome have an irresistible urge to move, to rid themselves of unpleasant leg sensations, that gets worse when they try to rest. Previous studies have shown the condition runs in families, and human genetic studies have suggested that BTBD9 may be involved.
It's unclear what the gene's normal role is, so Sanyal and colleagues decided to see what would happen to the flies if they snipped the gene out of the flies' DNA.
They found that flies without BTBD9 moved more often than normal flies, and lost sleep because of this movement. Fly sleep is defined as five minutes without movement, and on average, the mutant flies woke up 50 percent more often than normal flies.
"Flies don't have restless legs, but we find that mutant flies walk more and pause less. This is similar to the general restlessness that is seen in RLS patients," Sanyal told LiveScience in an email. "This is difficult to model in flies, but the overall restlessness seems to be conserved."
The mutant flies also had changes to their brain chemistry: Their dopamine levels were half those of normal flies. They also had low levels of iron, a symptom also seen in people with restless leg syndrome. Their lifespan was also about 25 percent shorter than normal — they died after 30 days, instead of 40.
When given a restless leg syndrome drug, which influences dopamine levels, the flies' nighttime jitteriness and other symptoms improved.
When asked how low dopamine levels could cause such a specific physical movement, Sanyal said: "The easiest way to understand this is to realize that dopamine is a neuromodulator and it will influence most nervous system functions, including locomotion."
But, he said, "We don't quite understand the precise connection between iron and dopamine yet, and this will be the topic of future research."
The study was published today (May 31) in the journal Current Biology.