related genes of dopamine system (DRD2, COMT) (Vaske et al., 2009; Nyman et al., 2011), HPA axis system (CRHR1) (Roy et al., 2018), and immune system (IL-1β SNP) (McQuaid et al., 2019), can also interact with the environment to affect the occurrence of depression in a gender-specific manner (Table 4). This evidence concerns the gene DRD2 and major depressive disorder.