ISSN 1662-4009 (online)

ESPE Yearbook of Paediatric Endocrinology (2019) 16 1.1 | DOI: 10.1530/ey.16.1.1

Genetics of Complex Traits, University of Exeter Medical School, Royal Devon & Exeter Hospital, Exeter, UK M.N.Weedon@exeter.ac.uk


To read the full abstract: Nat Commun 2019;10:343

This paper reports many loci associated with chronotype (i.e. being a ‘morning person’ or ‘evening person’) in a genome-wide association study (GWAS) of 697, 828 participants from the UK Biobank and 23andMe cohorts. The link between chronotype and sleep timing and quality is well known. It was therefore interesting to assess whether these genes were also associated to sleep timing and/or quality.

Interestingly, the 351 loci identified for sleep timing were not also associated with sleep duration or quality. A detailed analysis of biological pathways enriched for genes at associated loci revealed a strong enrichment in circadian rhythm and circadian clock pathways. Interestingly, these genes also participate in pathways involved in neuronal connections and neurogenesis. For instance, among the genes that influence chronotype was vasoactive-intestinal peptide, a gene expressed in the suprachiasmatic nucleus which is a specific region of the hypothalamus involved in the control of the circadian rhythm. Also MADD, which regulates activation control of the Rab3 pathway, involved in the control of synaptic homeostasis, a fundamental neuronal process during sleep, which seems to be crucial for memory in mice.

In the last part of this complex study, the authors sought to define genetic loci which overlap between chronotype and other traits and diseases. The idea behind was to propose new hypothesis to understand the known association between alterations to circadian timing and disease development such as metabolic and psychiatric diseases. The strongest genetic correlation was observed with subjective well-being. Furthermore, the evening chronotype was positively correlated with schizophrenia, depressive symptoms, major depressive disorder and intelligence. There was no evidence for a direct effect of schizophrenia on chronotype, but rather the genetic correlation indicated that these two conditions share common biological pathways.

This GWAS approach represents one way to propose new hypotheses to understand the physiological control of circadian rhythm. In addition to confirming that clock genes are involved in being a ‘morning’ or an ‘evening’ person, as previously reported, it also defined many additional genes in the control of circadian rhythm. Finally, the association between certain chronotypes and psychiatric diseases was well known by epidemiological studies. This works brings new insights to understand this association at the molecular level.

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