A recent study, which included 413 patients with mood disorders and compared them to 1294 patients without these conditions, investigated the relationship between mood disorders and various clock genes, such as BHLHB2, CLOCK, CSNK1E, NR1D1, PER2, PER3, and TIMELESS, through allele, genotype, and haplotype analyses. The gene discussed is PER2; the disease is mood disorder.