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background the genetic basis of major depressive disorder (mdd) has been explored extensively, but the mode of transmission of the disease has yet to be established. to better understand the mechanism by which the monoamine oxidase a (maoa) gene may play a role in developing mdd, the present work examined the cis-phase interaction between genetic variants within the maoa gene for the pathogenesis of mdd. methods a variable number tandem repeat (vntr) and 19 single nucleotide polymorphisms (snps) within the gene were genotyped in 512 unrelated patients with mdd and 567 unrelated control subjects among a chinese population. quantitative real-time polymerase chain reaction analysis was applied to test the effect of genetic variants on expression of the maoa gene in mdd. results neither the vntr polymorphism nor seven informative snps showed allelic association with mdd, but the cis-acting interactions between the vntr polymorphism and four individual snps were strongly associated with mdd risk, of which the vntr-rs1465107 combination showed the strongest association (p = .000011). quantitative real-time polymerase chain reaction analysis showed that overall relative quantity of maoa messenger rna was significantly higher in patients with mdd than in control subjects (fold change = 5.28, p = 1.7 × 10−7) and that in the male subjects carrying the vntr-l, rs1465107-a, rs6323-g, rs2072743-a, or rs1137070-t alleles, expression of maoa messenger rna was significantly higher in the patient group than in the control group. conclusions the cis-phase interaction between the vntr polymorphism and functional snps may contribute to the etiology of mdd.