A genetic mutation that allows people to feel fully rested with fewer than six hours sleep a night has been identified by studying a family who get by on less than average. It is the second such finding in recent months.
Ying-Hui Fu at the University of California, San Francisco, and her colleagues have been seeking out and studying families in which some people seem to need less sleep than normal. They have been looking for the gene variants that might be responsible, and genetically engineering these variants into mice to confirm their effect.
Her team has found several mutations make people need less sleep. In August, Fu's team reported that a mutation in a gene called ADRB1 allows 12 members of a family to sleep as little as 4.5 hours per night without feeling tired. This gene codes for a receptor protein common 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 some people report feeling fully rested after much less sleep than average. Of the two members of this family whose sleep habits they studied, one averaged 5.5 hours a night and the other just 4.3 hours.
NPSR1 codes for a protein receptor in the brain known to be involved in arousal and sleep behaviour. When the team engineered the mutation into mice, they slept less without any obvious effect on health or memory.
Another variation in NPSR1 has previously been linked to people requiring 20 minutes less sleep 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 a night results in a marked decline in cognitive abilities within days. Over long periods, sleep deprivation can contribute to many disorders, including obesity, heart disease, high blood pressure, diabetes and depression.
As far as Fu's team has been able to tell, however, people who sleep less because they have one of these gene variants are healthy and don't appear to suffer any ill effects. However, to be absolutely sure would require long-term studies involving large numbers of people, which isn't feasible.
"Right now, we cannot say for sure," says Fu.
In theory, if these gene variants provided a big advantage, evolution should have made them common – yet they appear to be rare. It might be, say, that sleeping less only became an advantage after the development of lights. But other advantageous gene variants that appeared only recently in human history, such as those allowing adults to digest milk, became widespread very rapidly.
It might be possible to develop drugs that mimic the effects of these mutations. However, as NPSR1 is also involved in processes such as stress, anxiety and fear, there is a risk of nasty side effects.
Expect more reports soon. Fu say her team has already discovered more sleep-shortening mutations.