A genetic mutation that allows people to feel fully rested with fewer than six hours sleep anight has been identified by studying a family who get by on less than average. It is thesecond such finding in recent months.
Ying-Hui Fu at the University of California, San Francisco, and her colleagues have been seekingout and studying families in which some people seem to need less sleep than normal. Theyhave been looking for the gene variants that might be responsible, and geneticallyengineering these variants into mice to confirm their effect.
Her team has found several mutations make people need less sleep. In August, Fu's teamreported that a mutation in a gene called ADRB1 allows 12 members of a family to sleep aslittle as 4.5 hours per night without feeling tired. This gene codes for a receptor proteincommon in a brain region called the dorsal pons, known to regulate sleep.
Now the team has found a mutation in a gene called NPSR1 in another family in which somepeople report feeling fully rested after much less sleep than average. Of the two members ofthis family whose sleep habits they studied, one averaged 5.5 hours a night and the other just4.3 hours.
NPSR1 codes for a protein receptor in the brain known to be involved in arousal and sleepbehaviour. When the team engineered the mutation into mice, they slept less without anyobvious effect on health or memory.
Another variation in NPSR1 has previously been linked to people requiring 20 minutes lesssleep than average, based on studies of tens of thousands of people.
On average, people need 8 hours sleep a night. In most people, sleeping less than 6 hours anight results in a marked decline in cognitive abilities within days. Over long periods, sleepdeprivation can contribute to many disorders, including obesity, heart disease, high bloodpressure, diabetes and depression.
As far as Fu's team has been able to tell, however, people who sleep less because they haveone of these gene variants are healthy and don't appear to suffer any ill effects. However, to beabsolutely sure would require long-term studies involving large numbers of people, which isn'tfeasible.
"Right now, we cannot say for sure," says Fu.
In theory, if these gene variants provided a big advantage, evolution should have madethem common – yet they appear to be rare. It might be, say, that sleeping less only becamean advantage after the development of lights. But other advantageous gene variants thatappeared only recently in human history, such as those allowing adults to digest milk, becamewidespread very rapidly.
It might be possible to develop drugs that mimic the effects of these mutations. However, asNPSR1 is also involved in processes such as stress, anxiety and fear, there is a risk of nastyside effects.
Expect more reports soon. Fu say her team has already discovered more sleep-shorteningmutations.