Childhood adversity, monoamine oxidase a genotype, and risk for conduct disorder.

Very little is known about how different sets of risk factors interact to influence risk for psychiatric disorder. To replicate a recent report of a genotype-environment interaction that predicts risk for antisocial behavior in boys. Characterizing risk for conduct disorder in boys in association with monoamine oxidase A genotype and exposure to familial adversity, defined by interparental violence, parental neglect, and inconsistent discipline. A community-based sample of twin boys. Five hundred fourteen male twins aged 8 to 17 years. Conduct disorder. There was a main effect of adversity but not of monoamine oxidase A on risk for conduct disorder. Low monoamine oxidase A activity increased risk for conduct disorder only in the presence of an adverse childhood environment. Neither a passive nor an evocative genotype-environment correlation accounted for the interaction. This study replicates a recent report of a genotype-environment interaction that predicts individual variation in risk for antisocial behavior in boys.