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MELISSA BLOCK, host:

Modern life can get pretty hectic and often it's our sleep that suffers. Some of us cope better than others. There are those people who famously and maddeningly can get by on just a few hours of sleep. Well, now a study in the journal "Science" finds that how much you sleep may be written in your genes, as Geoff Brumfiel reports.

GEOFF BRUMFIEL: Meet my friend Ann Marie Williams(ph). She's a graduate student and she doesn't sleep much.

Ms. ANN MARIE WILLIAMS: I went to bed at midnight.

BRUMFIEL: People like her really bug me. I need a solid eight hours just to function and that's pretty normal. Studies show that most people who get less can have difficulty with everyday tasks like driving. Ann Marie is in the more elite class. Thomas Edison, for example, claimed to sleep just four or five hours a night with no problem.

It turns out that the reason for these differences may be genetic. Researchers have now found a mutation that appears to let some people get by on less sleep than others.

Dr. YING-HUI FU (Neurologist, University of California at San Francisco): I wish I had the mutation but I don't.

(Soundbite of laughter)

BRUMFIEL: Ying-Hui Fu is a neurologist at the University of California at San Francisco. She and her colleagues were doing a large-scale sleep study when they came across a mother and daughter who had an unusual change to their genetic code. Both had the same mutation of a gene known to help regulate the body clocks of animals.

Dr. FU: When these people have this mutation, their sleep amount is less. Normal people need eight to eight-and-a-half hours of sleep. These people sleep five-and-a-half to six.

BRUMFIEL: Even though the pair weren't sleeping as much, they seem fine.

Dr. FU: It's not like they have sleep problem. They just don't sleep as much.

BRUMFIEL: Do they feel tired?

Dr. FU: Not more than most regular people.

BRUMFIEL: Fu's group wanted to study the effect of the mutation in a more controlled way. So they created a strain of mice with the same genetic change. Sure enough, they found that these mice slept less than the average mouse. What's more, they seemed to recover more quickly from periods of sleep deprivation. The work is an important step forward, says Charles Czeisler, a sleep expert at Harvard Medical School.

Professor CHARLES CZEISLER (Sleep Medicine, Harvard Medical School): This study really shows that the amount of sleep that we need each night is genetically hardwired. This tiny genetic change is making a huge change in the behavior of both the people and the animals.

BRUMFIEL: In some ways this study raises as many questions as it answers about sleep. Czeisler says that it doesn't prove that people with the mutation function as well as the rest of us. It's possible that they're just unable to get the sleep they need. He says it's hard to tell because we really don't understand the process of sleep at all.

Prof. CZEISLER: No one really knows what the function of sleep is, although the leading hypothesis is that sleep's core function relates to the repair and reorganization of brain cells.

BRUMFIEL: Still, studying this gene could help give clues about how and why we sleep. As for those of us who don't have the mutation, Ying-Hui Fu says that we shouldn't try and beat our genetic code.

Dr. FU: When I was younger, I was one of those people that tried every method to not sleep as much, you know. And now that I study sleep, I really realize sleep is so important for our health. So I say forget this. I'm just going to sleep as much as I need.

(Soundbite of laughter)

BRUMFIEL: So if you're feeling sleepy right now, turn down your radio and take a nap.

Geoff Brumfiel, NPR News.

BLOCK: What's he talking about? Don't touch that dial, we've got a lot more great radio coming up to keep you awake.

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