Numerous physiological processes and behaviors in mammals exhibit an inherent circadian oscillation that is vital for normal function. Disruption in the diurnal cycle is a common feature of different types of psychiatric illnesses including stress and anxiety disorders, bipolar disorder and depression.1 The circadian rhythm is under the coordinated regulation of clock genes such as Arntl, Dbp and Csnk1d, and the period homologs Per1, Per2 and Per3.2, 3 There is now growing evidence that implicates allelic variants in these genes in the development of neuropsychiatric diseases.4, 5 Additionally, clock genes have also been linked to responses to neuropharmacological agents in model organisms, as well as alcoholism and addiction in humans.2, 6 In mice, inactivation of Per1 and Per2 leads to changes in sensitivity to cocaine and ethanol,7 and in humans, gene variants in PER2 have been linked to alcoholism.8
