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zoom RSS 眠気の原因は遺伝子にある

<<   作成日時 : 2010/10/28 22:27   >>

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 ほとんど眠らなくても元気な人がいる一方、いつもあくびがでて睡魔と戦っている人もいる。ペンシルバニア大の新たな研究によれば、その原因は遺伝子にあるという。
 DQB1 *0602 と呼ばれる遺伝子変異を約25%の人が持っているが、実際に睡眠障害で苦しむ人は少数である。
 43才のロバート・ギブソンはこの遺伝子変異をおそらく持っていると思われ、寝入りばなや覚醒する時に数秒から数分の間、睡眠麻痺という麻痺した感覚に襲われる。その影響は1日中に及ぶ。薬を飲んで体が重くなるような感覚が翌日中続く。
 睡眠の比較研究で、遺伝子変異を持つ人は、深睡眠時間が短く、中途覚醒が多く、睡眠が粉々にされていた。健康な人なのに、ナルコレプシー患者のようにも見えた、と研究者はいう。
 遺伝子変異のない92人の健常者と、遺伝子変異があるが睡眠障害のない37人の健康な成人とを睡眠特性検査を施行し、疲労を自己評価した。記憶や注意、日中睡眠に抵抗する能力を検査した。睡眠研究所で7日間生活した。最初の2日間は夜間10時間ベッドの中で過ごし、その後の5日間は4時間睡眠した。覚醒時は照明を付け、ゲームや映画鑑賞ができた。睡眠に影響するカフェイン、七面鳥、バナナ、アルコールなどの飲食は許可されなかった。記憶や認知機能検査では差はなかった。
 社会的には眠さを怠惰や抑鬱のように人格障害と見られてしまうが、実際に眠い人がおり、昼寝やうたた寝をしやすい。睡眠時間が遺伝的に決定されていて欠陥ではないという事実を受け入れる必要がある。

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Sleepiness Might Be in the Genes, Study Finds
A new study finds that a genetic marker associated with narcolepsy may determine sleepiness
http://abcnews.go.com/Health/Sleep/genes-people-react-differently-lack-sleep-study/story?id=11965827
By MIKAELA CONLEY
Oct. 26, 2010

画像No matter how little they sleep, some people can keep a skip in their step while others will yawn and struggle through the day. A new study from the University of Pennsylvania School of Medicine found that the reason could be in our genes.
Researchers found that healthy people with one particular genetic variant were generally sleepier than those without the gene. About 25 percent of the general public has the genetic variant, called DQB1 *0602, but only a small percentage of them actually suffer from sleep problems.

One person who has been told by his doctor that he may have this genetic variation is Robert Gibson, a 43-year-old machine shop supervisor in Milan, Illinois. Sleep is supposed to rejuvenate the body, but for Gibson, it can be anything but invigorating.

It would not be the only gene-linked sleep condition Gibson experiences; he already suffers from bouts of sleep paralysis, a disorder in which sufferers feel paralyzed as they fall asleep or as they wake up. Episodes can last a few seconds to a couple of minutes, but Gibson said the effects of the temporary paralysis seem to bog him down all day.

"It feels like I am drugged down, like there's a heavy weight on me the whole next day," said Gibson.

Gibson's sleep problems are more than just the garden-variety; years ago, doctor's did find a genetic biomarker that may have to do with his sleep disorders, and, because many genes probably contribute to sleep habits, doctors say Gibson probably has DQB1 *0602 as well.

"He hasn't been tested for this gene yet, but it could be part of the spectrum of genes that contribute to his sleep habits," said Dr. Mark Dyken, a professor of neurology at University of Iowa College of Medicine who treated Gibson.

Genes and Heavy-Eyes

For the study, researchers compared healthy people with the gene variant to healthy people without it to see if they suffered from any other sleep-related problems.

The research, published in the journal Neurology, found that people with the gene variant reported feeling sleepier and more fatigued compared to the people without the variant, whether they slept four hours or 10 hours. People with the gene variant also spent less time in deep sleep, and woke up more times during their sleep compared to the non-gene participants.

"When the genetic variant people were fully rested, they still rated themselves sleepy," said Dr. Namni Goel, lead author of the study and assistant professor of psychiatry at the University of Pennsylvania School of Medicine. "They had a lower drive to sleep when challenged by sleep loss, and overall they had a more fragmented sleep with more arousals in comparison to those who didn't carry the gene. We found it very interesting that they were healthy people, but when challenged, they looked like narcoleptics."

Could Some Sleepiness Be Genetic?

In the study, 92 healthy adults without the gene were compared to 37 healthy adults who had the gene but did not have a sleep disorder. Researchers tested each participants' sleep quality and self-rated tiredness. They also tested memory, attention, and the ability to resist sleep during the day.

The participants spent seven days in the sleep laboratory. For the first two nights, everyone spent 10 hours in bed. For the following five nights, participants only spent four hours in bed per night. During waking hours, the lights were kept on, and they were allowed to play games, read, and watch movies. They were not allowed to consume foods and drinks that could affect their sleep, such as caffeine, turkey, bananas, or alcohol.

Despite the inconsistent sleep patterns throughout the seven-day trial, results for the memory and cognitive skills were similar in both groups.

Dr. Mark Mahowald, medical director of the Minnesota Regional Sleep Disorders Center, said that the study results are important because people tend to make sweeping statements about sleep deprivation -- when sleep is different for everyone because there are huge genetic components that contribute to our slumber.

"The medical profession has been guilty for decades of sleep deprivation in its trainees, so they made recommendations of the number of hours someone should work, but they made across-the-board, sweeping recommendations," said Mahowald. "The implication is that everyone is sleep-deprived and sleep-deprivation does the same thing to everyone, but the tolerance and range of sleep is so different for different people."

"A one-size-fits-all policy is probably not a very wise idea when it comes to sleep," said Mahowald. "Our society has equated sleepiness with defects of character, like laziness and depression, but really, some people are generally sleepier during the day. They're more prone to naps, and to sleeping in. We have to accept the fact that sleep duration is genetically determined and not a sign of defect."

No Rest for the Weary

So what's a tired person to do? Not much, said doctors, but Dr. Goel said she hopes to continue her research with genetic biomarkers. She said they might help to predict a person's response to sleep deprivation, especially for those who work a night shift, travel often through many time zones, or those who lose sleep due to personal or family obligations. At any rate, doctors said that tiredness is certainly a manageable condition.

"Down the line, if someone is carrying this gene, maybe they can employ a countermeasure," said Goel. "Maybe they could have caffeine to counteract some of these symptoms."

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NEUROLOGY 2010;75:1509-1519
(c) 2010 American Academy of Neurology

DQB1*0602 predicts interindividual differences in physiologic sleep, sleepiness, and fatigue
Namni Goel, PhD, Siobhan Banks, PhD, Emmanuel Mignot, MD,, PhD and David F. Dinges, PhD

From the Division of Sleep and Chronobiology (N.G., S.B., D.F.D.), Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia; and Center for Narcolepsy (E.M.), Department of Psychiatry and Behavioral Sciences, and Howard Hughes Medical Institute, Stanford University, Palo Alto, CA. S.B. is currently affiliated with the Centre for Sleep Research, University of South Australia, Adelaide, Australia.

Address correspondence and reprint requests to Dr. Namni Goel, Division of Sleep and Chronobiology, Unit for Experimental Psychiatry, Department of Psychiatry, University of Pennsylvania School of Medicine, 1013 Blockley Hall, 423 Guardian Drive, Philadelphia, PA 19104-6021 goel@mail.med.upenn.edu

Objective: The human leukocyte antigen (HLA) DQB1*0602 allele is closely associated with narcolepsy, a neurologic disorder characterized by excessive daytime sleepiness, fragmented sleep, and shortened REM sleep latency. We evaluated whether DQB1*0602 was a novel marker of interindividual differences by determining its relationship to sleep homeostatic, sleepiness, and cognitive responses to baseline and chronic partial sleep deprivation (PSD) conditions.

Methods: Ninety-two DQB1*0602-negative and 37 DQB1*0602-positive healthy adults participated in a protocol of 2 baseline 10 hours time in bed (TIB) nights followed by 5 consecutive 4 hours TIB nights. DQB1*0602 allelic frequencies did not differ significantly between Caucasians and African Americans.

Results: During baseline, although DQB1*0602-positive subjects were subjectively sleepier and more fatigued, they showed greater sleep fragmentation, and decreased sleep homeostatic pressure and differentially sharper declines during the night (measured by non-REM EEG slow-wave energy [SWE]). During PSD, DQB1*0602-positive subjects were sleepier and showed more fragmented sleep, despite SWE elevation comparable to negative subjects. Moreover, they showed differentially greater REM sleep latency reductions and smaller stage 2 reductions, along with differentially greater increases in fatigue. Both groups demonstrated comparable cumulative decreases in cognitive performance.

Conclusions: DQB1*0602 positivity in a healthy population may represent a continuum of some sleep--wake features of narcolepsy. DQB1*0602 was associated with interindividual differences in sleep homeostasis, physiologic sleep, sleepiness, and fatigue―but not in cognitive measures―during baseline and chronic PSD. Thus, DQB1*0602 may represent a genetic biomarker for predicting such individual differences in basal and sleep loss conditions.


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