Sleep Paralysis Linked to Stress and Genetics

"Sleep Paralysis" is a disorder in which people may feel like they can't move their body when they're falling asleep or waking up, and often report hallucinations of "a malevolent presence" pressing down on them. A new study suggests the phenomenon may have a genetic cause.

In the study prepared by the University of Sheffield in England and published online Feb. 9 in the Journal of Sleep Research, researchers asked a group of more than 800 twins and siblings whether they had experienced sleep paralysis. The results showed that genetics were partially to blame for the strange phenomenon. In addition, the people in the study who had anxiety, slept poorly or had experienced stress in their lives were more likely to have these nighttime bouts of paralysis, the researchers found. The findings shed some light on what is still quite a mysterious condition.

 Sleep paralysis often occurs during the rapid eye movement (REM) stage of sleep, when people are usually dreaming. In REM sleep the muscles are nearly paralyzed, possibly to prevent people from acting out their dreams. Some people who suffer from sleep paralysis experience hallucinations of a "terrifying figure" pressing down on them and preventing them from moving. Estimates of how many people experience the phenomenon vary widely; some studies report that app. 7 percent of people will experience the feeling at some point in their lives, while other studies suggest that it affects as many as 60 percent. Yet scientists don't really know what causes the phenomenon.

Researchers used data from 862 twins (identical and nonidentical) and other (non-twin) siblings between ages 22 and 32 in England and Wales. The participants indicated on the survey whether they agreed with the statement, "Sometimes, when falling asleep or waking up from sleep, I experience a brief period during which I feel I am unable to move, even though I think I am awake and conscious of my surroundings."

By comparing the responses of identical twins who share almost all of their DNA with those of nonidentical siblings who only share about half of their DNA, the researchers found that genes accounted for more than 50 percent of the incidence of sleep paralysis. They also found that sleep paralysis was more common in people with anxiety, those who weren't getting good sleep and those who had had traumatic experiences, such as an illness or death in the family.

The researchers then studied the participant's PER2 genes, which are linked to the circadian rhythms. They found that the people who had certain versions of this gene were more likely to have sleep paralysis, intimating that something to do with the control of circadian rhythms is probably involved in sleep paralysis.

The study has a number of limitations; it was based on a relatively small number of participants, and was limited to young adults. In addition, the findings don't prove that genetics or stressful factors cause the paralyzing experience, only that the two are linked; Researches still aren't sure whether anxiety could cause a person to experience sleep paralysis, or if experiencing sleep paralysis can make a person more anxious. However their conclusions indicate that sleep paralysis appears to be heritable, and there seem to be some genes influencing sleep and wake patterns involved.

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References:
 livescience.com