To investigate the association between PK2 and PKR2 and mood disorders, Kishi et al. [29] conducted a case–control study in Japanese patients with mood disorders (151 BP patients, 319 patients with severe MDD and 340 control subjects) and found a single nucleotide polymorphism (SNP) in PKR2 that was significantly associated with female BP and MDD [29]. Here, PROK2 is linked to major depressive disorder.