DRD2 and major depressive disorder: 2022). In SZ, DRD2 polymorphisms are associated with increased receptor expression and D2S/D2L splice variant imbalances, contributing to psychotic symptoms (Kaalund et al. 2014). In BD, increased D2L expression aligns with reward hypersensitivity during manic episodes (Kaalund et al. 2014). In PTSD and MDD, DRD2 variants also affect mood regulation and stress responsivity (Zhang et al. 2023).