We all need shut-eye, but some of us sleep much more soundly than others. Now, researchers have found a gene that appears to determine how intensely we sleep.
When it comes to getting a good night's rest, not all sleep is the same. The most important stage of the sleep cycle is deep sleep--also known as slow wave sleep--the slumber where the brain's electrical activity is at its slowest. Even after only a few nights deprived of these roughly hour-long plunges into nothingness, body temperature and immune functions become unstable.
In spite of its importance, not everyone gets the same amount of deep sleep, and studies of twins indicate that some of this variation is genetic. In mice, differences in sleep quality have been linked to a collection of genes regulating the neurotransmitter adenosine. (Adenosine is part of the pathway that caffeine inhibits to keep us awake.) Researchers studying rats found that the amount of deep sleep could be increased by chemically interfering with one of these adenosine-regulating genes, called adenosine deaminase (ADA). To see whether ADA plays a role in human sleep quality, a team led by Hans-Peter Landolt, a sleep physiologist at the University of Zurich, Switzerland, sequenced the gene in 119 student volunteers and hosted them for three nights of sleep in the lab.
A tiny difference in DNA translates to a big improvement in sleep quality. Ten percent of the volunteers, who had a mutation in ADA, enjoyed about half an hour more deep sleep, as measured by electrical activity in the brain, than volunteers without the mutation, the team reports online this week in Proceedings of the National Academies of Science. Those with the mutation also reported waking up far less often during the night. The team now plans to see if other mutations in the adenosine pathway might account for insomnia or other sleep disorders, says Landolt.
"It's a very encouraging advance," says Mehdi Tafti, a geneticist at the University of Lausanne, Switzerland. The next step, he says, will be to see if the deep sleepers are also more resistant to the ill effects of sleep deprivation.