Indeed, the examination of SNPs across 19 circadian rhythm genes (including BMAL1, BHLHB2, BHLHB3, CLOCK, CRY1, CRY2, CSNK1E, DBP, NPAS2, NR1D1, PER1, PER2, PER3, RORA, TIMELESS, VIP, and VIPR2) revealed that the CRY1 and Neuronal PAS Domain Protein 2 (NPAS2) genes are linked to unipolar major depression, while the CLOCK and VIP genes are associated with bipolar disorder [25]. This evidence concerns the gene PER3 and bipolar disorder.