Most adults need seven to nine hours of sleep each night, but nearly 28% of U.S. adults report that they get six hours or less. Surprisingly, some of the sleep-deprived report no ill effects—no daytime sleepiness, no difficulties concentrating, no listlessness. What do these “short sleepers” have that the rest of us lack?
To answer this question, an international team of researchers started with the assumption that sleep is not merely a matter of personal preference. It is, rather, a biological requirement. In addition, the researchers decided to follow up on genetic clues uncovered in an earlier study. This study suggested that a mutation in a particular gene—DEC2, also known as BHLHE41—was prominent in a family of short sleepers.
If the BHLHE41 gene could be scrutinized more closely, the researchers reasoned, additional details about its role in sleep duration could be brought to light. The researchers decided to search for additional variants in the BHLHE41 gene in what they described as two “well-phenotyped cohorts.” The cohorts were populated by twins from twin pairs who were recruited at the University of Pennsylvania. All twin pairs were the same sex and were healthy with no chronic conditions.
Nightly sleep duration was measured at home by actigraphy for seven to eight nights. Response to 38 hours of sleep deprivation and length of recovery sleep were assessed in a sleep lab. During sleep deprivation, cognitive performance was measured every two hours using the Psychomotor Vigilance Test.
The results? The researchers identified new variants of the BHLHE41 gene in two cohorts who had either acute sleep deprivation (n = 200) or chronic partial sleep deprivation (n = 217). One variant, Y362H, at another location in the same exon occurred in one twin in a dizygotic twin pair and was associated with reduced sleep duration, less recovery sleep following sleep deprivation, and fewer performance lapses during sleep deprivation than the homozygous twin.
These findings appeared August 1 in the journal Sleep, where the researchers added that the genetic variant they found also appears to provide greater resistance to the effects of sleep deprivation.
“Mutations that affect sleep also modify the normal inhibition of BHLHE41 of CLOCK/BMAL1 transactivation,” the authors concluded. “Thus, clock mechanisms are likely involved in setting sleep length and the magnitude of sleep homeostasis.”
“This work provides an important second gene variant associated with sleep deprivation and for the first time shows the role of BHLHE41 in resistance to sleep deprivation in humans,” said lead author Renata Pellegrino, Ph.D., senior research associate in the Center for Applied Genomics at The Children’s Hospital of Philadelphia. “The mutation was associated with resistance to the neurobehavioral effects of sleep deprivation.”