Hence, the available data related to MAOA expression in mood disorders in other ethnicities are very limited, whereas the role of MAOA-30 bp μVNTR in common psychiatric conditions, including MDD, BD, and SHZ, in individuals of Pakistani descent has not been established yet; therefore, the current study aimed to investigate the genetic association of promoter region functional polymorphism (MAOA-30 bp μVNTR) with MDD, BD, and SHZ, and the effect of different repeat alleles on MAOA serum levels in cases compared to controls in the Pakistani population. The gene discussed is MAOA; the disease is major depressive disorder.