THE amount of deep sleep you get each night is at least partly down to your genes, according to a study of 14 students. The seven students with the 鈥渟lumber gene鈥� averaged 50 per cent more deep sleep per night than the others. The finding could lead to new ways of treating sleep disorders.
According to Hans-Peter Landolt, head of the team at the University of Zurich, Switzerland, this is the first research to show a direct link between people鈥檚 different deep-sleep patterns and variation in their genes.
The slumber gene is one variant of the gene for the enzyme adenosine deaminase (ADA). About 10 per cent of the population have this variant. While we are awake, adenosine builds up in the brain as a breakdown product of the energy-containing molecules adenosine triphosphate and adenosine monophosphate. While we sleep, ADA gradually clears away the adenosine. People with the sleepy variant of the ADA gene make a less efficient version of the enzyme so the adenosine lingers longer in their brains at night, which may be why they sleep so deeply (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0505414102).
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For some time adenosine has been suspected of playing a role in sleep regulation because caffeine stops it binding to the receptors in the brain (快猫短视频, 24 September, p 38). 鈥淚f adenosine can鈥檛 bind to its receptors, it stops people from sleeping,鈥� says Malcolm von Schwantz of the Surrey Sleep Research Centre at the University of Surrey, UK.
So thanks to their inefficient ADA, people with the slumber gene typically spend 50 per cent longer clearing the adenosine. This happens during slow-wave sleep, the deepest phase, although people with the gene don鈥檛 spend longer overall sleeping. 鈥淪low-wave sleep is beyond dreaming. You鈥檙e completely knocked out, and it takes noise greater than 65 decibels to waken you,鈥� says von Schwantz. However, it is not clear whether extra slow-wave sleep is beneficial.
Jason Ellis, also at the Surrey Sleep Research Centre, says that there might be a link between deep sleep and the immune system, because other common defects in the ADA gene cause the immune system to malfunction. The immune system is thought to re-prime itself during deep sleep, he says, so perhaps the process takes longer in people with the slumber gene, although the effect this would have on people is unknown.
鈥淭he gene is also linked to the immune system, which might take longer to re-prime during sleep in people with the variant鈥�
Landolt says that now we know that ADA and adenosine affect our sleep quality, it may be possible to devise new approaches to treating insomnia. Simply administering adenosine would not work however, because it also has receptors in several other organs and so would cause major side effects.
