For something so essential and basic, sleep has turned out to be a complicated biological nightmare for scientists. Certain genes, such as CLOCK and BMAL1, have been pegged for their roles in the body's circadian rhythm, but the full cast of characters involved in moderating the process of sleep remains fuzzy.



But thanks to a mother and daughter who share a rare genetic mutation—and who routinely need just six hours of sleep a night—researchers have recently taken a step forward in the journey to unravel the tangled genetic web of sleep.



The new study, published online today in Science, reports the discovery of a genetic mutation on the gene DEC2 that appears to allow the mother–daughter pair of "short sleepers"—and a handful of transgenic mice—to truly need less sleep.



"We know sleep is necessary for survival," says co-author Ying-Hui Fu, a professor of neurology at the University of California, San Francisco. But, "we don't know anything about how it's regulated," she adds.



Sleep requirements seem to follow a typical curve in the general population, with most people needing between seven and eight hours nightly. Only about 5 percent of the population can get by just fine on six hours of sleep, notes Fu.



"In normal sleepers, if you reduce their duration to six hours, after a few days you will see some negative impact," explains Mehdi Tafti, an associate professor at the Center for Integrative Genomics at the University of Lausanne in Switzerland, who wrote the accompanying perspectives piece and wasn't involved in the study. "And no one should sleep-deprive him or herself."



Despite only getting an average of 6.25 hours of sleep a night in the study, both the 17-year-old daughter and the mother in her late 40s seemed to be perfectly healthy and well-rested, Fu notes. "They feel just fine," she says. Unlike the rest of their family members (who needed an average of about eight hours of slumber), they had a mutation on the DEC2 transcription facilitator, which is involved in the circadian clock, among other functions. But was this the sole cause of the curtailed sleep needs?



To further investigate the gene and its impact on the body, the researchers studied transgenic mice with the introduced mutation. These experimental animals experienced a daily activity period about 1.2 hours longer than their nonmutant compatriots. Removing Dec2 in mice, however, did not generate the same wakefulness, and instead the genetic knockout mice actually slept a little bit more.



The underlying question, Tafti says, is how much sleep do people really need? Could most people do just fine on seven hours or do some really need to slumber for a full nine? In order to sleep less, people would need to sleep better—that is, more efficiently, with more intense REM states, Tafti explains, which appears to be happening in those with the DEC2 mutation. "We believe that short-sleepers have more efficient sleep," he says.



Even though this mutation is exceedingly rare, even in short-sleepers (Tafti estimates the total at less than 1 percent of short-sleepers), and it didn't turn up in any of the 250 control individuals tested), Fu is still hopeful that the discovery will pay off in the future. She says the find is "an opportunity to start looking into the pathways and whether we can modify that in the future." Indeed, she and her colleagues are already investigating other genes.



Tafti expects a long road still ahead before scientists solidly understand sleep. "It's a complex phenotype," he says, which is "probably the result of many, many genes—and the environment."



In the future discoveries like this one may play a role in developing treatments for those who have sleep disorders, or just help regular people get by with less sleep. "Decades from now, we can act on that pathway and make sleep more efficient," Tafti notes.



Fu says helping people sleep a little less while maintaining their health and well-being is her ultimate dream.