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Early riser. Genes may explain why some people sleep less than others.

Early Risers Are Mutants

Don't hate those people who are perky and efficient after only a few hours of sleep. They can't help it. New research suggests that a genetic mutation may explain why some people sleep less.

Researchers don't know exactly why some people do fine with as little as 4 hours of sleep a night, while others need 12. "We've believed for a long time that there's a genetic basis," says Paul Shaw, a neurobiologist at Washington University in St. Louis, Missouri. But scientists have only recently begun to ferret out which genes are responsible.

In 2001, geneticist Ying-Hui Fu and colleagues identified a mutation in a gene called Per2 that appeared to cause familial advanced sleep-phase syndrome (FASPS). People who have this condition sleep a normal 8 hours, but they go to bed earlier than most people, retiring at 6 or 7 in the evening and waking at 3 or 4 in the morning. "After that was published, a lot of these people [with unusual sleep schedules] came to us," says Fu, who is now at the University of California, San Francisco. "So we started to collect DNA samples." The team now has genetic information from more than 60 families.

Fu and her colleagues have spent the past several years mining this vast genetic storehouse for more mutations that might affect sleep patterns. In 2005, they uncovered another mutation associated with FASPS. And now they say they have found the first genetic mutation in humans that appears to affect sleep duration rather than sleep timing. The mutation lies in DEC2, a gene that codes for a protein that helps turn off expression of other genes, including some that control circadian rhythm, the internal clock that regulates a person's sleep-wake cycle. The mutation occurred in just two people, a mother and her daughter. The women sleep an average of only 6.25 hours, whereas the rest of the family members sleep a more typical 8 hours.

To confirm that this mutation shortens sleep, Fu and colleagues engineered mice to carry the mutant form of DEC2. The mutant mice slept about an hour less than normal mice, the team reports today in Science. The finding also held for fruit flies: Mutant flies slept about 2 hours less than normal flies.

DEC2 likely isn't the whole story when it comes to short sleep. "Genetic control of sleep is going to be complex and is going to include multiple types of genes," says Shaw, who was not affiliated with the study. But that doesn't diminish the importance of this paper, he notes. "It's really an amazing piece of work."

The findings, says Fu, could lead to better treatments for sleep disorders. If the mutated form of DEC2 were available in a pill, Fu says she'd take it, noting that she needs about 8 hours of shuteye a night to feel rested. "All my life I've wanted to be able to sleep less."

Posted in Biology, Brain & Behavior