Recently, a large longitudinal study of children followed for 26 years since birth showed that MAOA VNTR genotype moderates the association between childhood maltreatment and violent and antisocial behavior [14]. Although several studies have replicated this G×E effect [15]–[17], other studies have failed to replicate the original findings reported by Caspi and co-workers [18]–[20]. Explanations for these conflicting findings are manifold, including the use of different measures of the behavioral phenotype and of environmental risk factors. In this work, we studied a mixed population of psychiatric outpatients and healthy volunteers to test the hypothesis that the MAOA VNTR polymorphism moderates the association between early traumatic life events experienced during the first fifteen years of life and the display of physical aggression during adulthood. We found that the risk for displaying physical aggression during adulthood was significantly increased by the combination of low MAOA activity and exposure to early trauma.
