The role of clock genes in the etiology of Major Depressive Disorder

•Clock genes are thought to be involved in circadian abnormalities of Major Depressive Disorder.•Abnormalities in the expression of clock genes have been reported in depressed subjects.•SNP rs2287161 of CRY1 might confer a higher susceptibility to circadian dysregulation in Major Depression.•Lifestyles, hormones or pollution are hypothesized to regulate the expression of clock genes of depressed patients.