MC3R and major depressive disorder: In humans, polymorphisms in the melanocortin receptor genes have been previously reported in patients with major depressive disorder (MDD) (MC1R [29], MC2R [30], and MC5R [31]), emotional eating and food craving (MC4R [32]), obesity (MC1R [33], MC3R [34], MC4R [12], and MC5R [12] via linkage studies in Quebec families [12]), and T2D (MC4R) [35], but never in the MDD-T2D comorbidity.