Cassandra Willyard in Science:
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.