Sleep duration

It is now clear that genetics plays a major role in sleep traits. Although environmental factors can influence sleep duration and intensity, certain genetic variants are known to affect these traits, and in some cases can even lead to familial sleep disorders.

Sleep is defined as a reversible natural state of unconsciousness in which there is a decreased responsiveness to external stimuli and relatively low activity.

Sufficient, high-quality sleep is essential for mental and physical well-being. The American Academy of Sleep Medicine recommends a daily sleep duration, in adults, of at least 7 hours per night on a regular basis.

Unlike other mammals, sleep duration in humans is thought to be regulated by two processes: the homeostatic S-process that increases during wakefulness and dissipates during sleep and the C-process, controlled by the circadian clock that is synchronized with the Earth's day-night cycles through the secretion of melatonin. In addition, sleep duration is a process that adjusts according to needs, so that when sleep is lost, compensatory mechanisms are activated that extend the duration of subsequent sleep.

Sleep is necessary for memory consolidation and involves the incorporation of memories acquired in the hippocampus into the neocortex brain network, where their long-term storage occurs.

Chronic sleep and circadian rhythm disturbances have been associated with an increased risk of mood disturbances, lower cognitive performance and cardiometabolic disturbances. Understanding the role of genetics and the underlying biological mechanisms that trigger sleep-associated disorders is still the subject of multiple studies.

Habitual sleep duration depends on multiple biological pathways and it has been assumed that the genetic component may determine up to 45% of sleep duration, making it a highly heritable trait.

Recently, a genome-wide association study or GWAS, which included 450,000 participants of European ancestry, has identified up to 52 markers related to sleep duration. These markers could explain up to 10% of the heritability of sleep duration. Among the markers detected, those located in the PAX8 gene showed the greatest effect. This result is consistent with the data obtained in three other previous GWAS studies.

The PAX8 gene is a transcription factor with a high expression in thyroid, although it is present in many tissues. The function of PAX8 is not well understood, but it is suggested that thyroid hormones may affect sleep and therefore it is possible that PAX8 may affect sleep regulation through this pathway.

Number of observed variants

13.5 million variants

Number of loci analyzed in the study

52 loci

Bibliography

Borbély AA, Daan S, Wirz-Justice A, Deboer T. The two-process model of sleep regulation: a reappraisal. J Sleep Res. 2016 Apr;25(2):131-43.

Dashti H.S., Jones S.E., et al. Genome-wide association study identifies genetic loci for self-reported habitual sleep duration supported by accelerometer-derived estimates. Nature Communications, 07 Mar 2019, 10(1):1100.

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