DRD2 and major depressive disorder: Individual genes that commonly emerge among these studies include those with existing links to depression, such as DRD2 [4, 159, 162, 163] and FADS1 [4, 164, 165], as well as novel genes such as NEGR1 [4, 158, 162, 166] and RPL31P12 [160, 166] without existing links to depression.