Our findings add to the growing knowledge implicating genotypic variation in the moderation of the individual’s response to stress exposure [10], [37]–[39]. In particular, they parallel evidence from our study demonstrating a moderating effect of the CRHR1 genotype on the relationship between stressful life events and drinking behavior in adolescents [40]. In 15-year-olds, the number of negative life events during the past three years was found to be related to increasing rates of heavy drinking only among individuals carrying a specific genotype of a haplotype tagging SNP of this gene. While activation of brain circuits involved in stress regulation is considered as the biological basis of the latter gene-environment interaction, a different physiological mechanism has been suggested to underlie the PER2 x stress interaction. The PER genes (PER1, PER2 and PER3) in general, together with other clock genes, are part of the central circadian rhythm organization system in the suprachiasmatic nucleus (SCN). PER1 has recently been shown to be associated with alcohol use, indicating that variation in PER1 gene mediated stress-induced drinking in animals and humans [41]. Molecular experiments in
