Health Science Reviews

By Angela Mutugi
Genetic testing is more often viewed as a device to trace your family’s ancestry to know where you came from or if you are secretly a royal, but your genes can help you understand why you’re ready to go to bed at 9 pm, why you sleep in and why you lie awake at night. Your genes guard the code to your ideal sleep-wake cycle, and this could greatly impact your day-to-day productivity and your health in the long term.

A chronotype is your body’s natural preference in the sleep-wake cycle. It governs whether we are more ‘morning larks’ or ‘night owls’, and this is driven by an internal master clock, the suprachiasmatic nucleus of the brain, stitched together by our genetic code. Though it is important to note that external factors like age, lifestyle, and light exposure can still affect our sleep-wake cycle.

In this study, three major genome-wide association studies (GWAS) were conducted using data from 23andMe and the UK Biobank. The aim was to review and synthesise findings in this genetic data that investigated the genetic underpinnings of human chronotypes. Our chronotype is a polygenic trait, influenced predominantly by the PER1, PER2, PER3, CRY1, CRY2, CLOCK and BMAL1 genes. These genes regulate the circadian rhythms of nearly every cell, managing sleep timing, hormone release and metabolism, through feedback loops all controlled and synchronised by the suprachiasmatic nucleus.

The results affirmed the known genes of circadian rhythm and identified novel loci. Nine key genes were further confirmed and associated with specific chronotypes. Variations amongst these genes were noted to affect the longevity of sleep, the onset of melatonin and the length of your circadian rhythm.

Furthering these studies would benefit the understanding of common and rare genetic variations affecting one’s chronotype and provide greater insight into the foundation of our circadian system. Individual sleep profiles could lead to personalised sleep recommendations, greatly impact the treatment of sleep disorders and optimise work scheduling. There is still more to uncover in this field as studies with conflicting findings regarding gene-specific polymorphism have yielded inconsistent results, suggesting that this complexity will require broader genetic approaches.