RESEARCH
Sleep cycles
Why some sleep better than others
Last Updated: Friday, November 6, 2009 | 9:04 AM ET
By Rebecca Ruiz, Forbes.com
Sleep apnea, which affects an estimated 12 million Americans, causes arrested or shallow breathing during the night. (iStock)Out of more than 700 participants in a particular study, two people stood out. These individuals were blessed with a trait most of us can only envy: Just six hours of sleep was enough to propel them through a very active day. Unlike most people, who need about eight hours of shut-eye, the pair did not suffer debilitating effects of chronic sleep deprivation, such as impaired cognition and memory.
The two individuals also performed a great service to science: As participants in sleep research conducted by the University of California, San Francisco, the subjects' unusual sleep patterns led researchers to a specific gene for "short sleepers."
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The discovery of the gene, known as Dec2, was published in August in Science and became the first gene in humans known to control sleep quantity. The idea that a gene might determine sleep duration seemed improbable prior to this study, but the researchers also replicated the effect in mice and in fruit flies.
"Without that you could not convince anyone, not even myself," says Ying-Hui Fu, Ph.D, one of the UCSF researchers.
It's an important discovery, but not because it explains why so few Americans get the requisite eight hours of sleep; the fact that it was found in only two participants out of several hundred means that it's likely the gene is rare.
Instead, the finding gives researchers an essential clue about what role other genes might play in sleep regulation. It's becoming increasingly clear that the answer to improving sleep lies in identifying the vulnerabilities of our genetic makeup and understanding how our poor sleep habits can exacerbate them.
The Role of Genes
Though the discovery of the short-sleeper gene was the first of its kind, other researchers have connected sleep apnea to a gene variation and narcolepsy to a gene mutation. These disorders disrupt the normal sleep cycle in maddening and sometimes life-threatening ways.
Sleep apnea, which affects an estimated 12 million Americans, causes arrested or shallow breathing during the night. Carriers of this marker are twice as likely to suffer from the common disorder, which also predisposes sufferers to higher risk for stroke, cardiovascular disease and heart attacks.
Narcolepsy, a far less common disorder that affects only 135,000 Americans, is associated with a mutated gene that causes abnormal processing of neurotransmitters known to play a role in wakefulness. The brain of a narcolepsy sufferer fails to regulate the sleep-wake cycle normally, sending the person into sporadic fits of sleep, unwillingly, throughout the day.
Stanford professor and researcher Dr. Emmanuel Mignot, who is director of the university's Center for Narcolepsy, discovered the gene mutation and variation for narcolepsy and sleep apnea in 1999 and 2001, respectively.
Mignot's hunch — and it's just opinion until science proves him right — is that the spectrum of sleep disorders that also includes insomnia, nightmares and sleepwalking can also be traced back to genetic causes. Recent research has shown that even restless legs syndrome, long a punch line in pop culture that in fact keeps 12 million Americans awake at night, is strongly associated with gene variations.
What intrigues Mignot is how people respond to such sleep disruptions, particularly those that lead to chronic sleep deprivation.
"Some people will be extremely impaired and some people won't care at all," he says, noting that scientists control for factors like participant demographics and sleep hygiene and get the same resulst. "It's clear that some people have fundamentally different needs independent of the environment, and they're likely genetic."
The Black Box of Sleep
David F. Dinges, Ph.D., chief of the division of sleep and chronobiology at the University of Pennsylvania School of Medicine, knows this phenomenon well. Data gathered from his studies of several hundred participants has shown time and again that when sleep is chronically reduced, individuals have markedly different responses to handling that deprivation. Yet when they get the same amount of adequate sleep, behavior remains consistent.
40 million Americans suffer from chronic sleep disorders. Researchers have no scientific explanation for this — yet. Fu, Mignot and Dinges all strongly believe it has to do with gene variations, but for now the field remains — as Fu calls it — a black box.
In the meantime, the 40 million Americans who suffer from chronic sleep disorders will have to manage their conditions through medication, improved sleep hygiene and cognitive behavioral therapy.
The former is a common-sense approach to sleep that focuses on simple steps like maintaining a regular sleep schedule, eliminating distractions like noise and abstaining from caffeine and alcohol close to bedtime. The latter is a form of therapy that aims to help the sleepless cope with their condition by teaching them a variety of coping skills, including yoga and meditation.
Dinges hopes that research will lead to the discovery of key genes that determine and affect our sleep cycles, enabling medicine to provide personalized diagnoses and treatments for those who don't sleep well.
"It's not an issue of broken or bad genes," says Dinges. "We want to use that information in a personalized way to help people understand what environmental things will put them a risk because of their genetic variations."
