Effects of the MAOA gene and levels of exposure to violence on antisocial outcomes.

Background: The monoamine oxidase A (MAOA) gene has been shown to moderate the impact of maltreatment on antisocial behaviour. Replication efforts have, however, yielded inconsistent results.

Aims: To investigate whether the interaction between the MAOA gene and violence is present across the full distribution of violence or emerges at higher levels of exposure.

Method: Participants were 327 male members of the Québec Longitudinal Study of Kindergarten Children. Exposure to violence comprised retrospective reports of mother's and father's maltreatment, sexual and physical abuse. Conduct disorder and antisocial personality symptoms were assessed in semi-structured interviews and partner violence, property-violent crimes and arrest were self-reported.

Results: Non-linear interactions between the MAOA gene and violence were detected, suggesting that the genetic moderation may come about once a certain level of violence is experienced.

Conclusions: Future studies should investigate the mechanisms translating substantial violence exposure, which could, subsequently, trigger the expression of genetically based differences in antisocial behaviour.