DRD4 and major depressive disorder: In this study, we estimated the contribution of SLC6A4 (5HTT), HTR1A, HTR2A, HTR1B, SLC6A3 (DAT1), DRD4, DRD2, COMT, and BDNF genes to the suicidal behavior and severity of symptoms of depression and anxiety in the East-Slavic population of Russia.