Monoamine oxidase A gene promoter variation and rearing experience influences aggressive behavior in rhesus monkeys

Background: Allelic variation of the monoamine oxidase A (MAOA) gene has been implicated in conduct disorder and antisocial, aggressive behavior in humans when associated with early adverse experiences. We tested the hypothesis that a repeat polymorphism in the rhesus macaque MAOA gene promoter region influences aggressive behavior in male subjects. Methods: Forty-five unrelated male monkeys raised with or without their mothers were tested for competitive and social group aggression. Functional activity of the MAOA gene promoter polymorphism was determined and genotypes scored for assessing genetic and environmental influences on aggression. Results: Transcription of the MAOA gene in rhesus monkeys is modulated by an orthologous polymorphism (rhMAOA-LPR) in its upstream regulatory region. High- and low-activity alleles of the rhMAOA-LPR show a genotype X environment interaction of aggressive behavior, such that mother reared male monkeys with the low-activity-associated allele had higher aggression scores. Conclusions: These results suggest that the behavioral expression of allelic variation in MAOA activity is sensitive to social experiences early in development and that its functional outcome might depend on social context.