The role of monoamine oxidase A, MAOA, in the aetiology of antisocial behaviour: the importance of gene-environment interactions.

Reports from both human studies and animal models suggest that MAOA may have a key role in aggression. Differences in the copy number of a repeat motif in the promoter of MAOA appear to regulate its activity. We review the evidence that suggests activity levels of this enzyme may play a key role in modulating antisocial/aggressive behavioural outcomes. Two common alleles in the human population have been identified which confer either high or low transcriptional functionality. The gene is X-linked and males can, therefore, be typed as 'low' or 'high' types. A key feature that has emerged from both our own studies and replicated recently by others, is that high activity variants of the gene appear to confer a protective influence against maltreatment, such that maltreated males with a high-MAOA activity genotype were less likely to develop antisocial problems, an observation that may explain part of the variability in developmental outcomes associated with maltreatment.