Brain monoamine oxidase activity predicts male aggression

Here is an edited version of the abstract from Alia-Klein et al.:

The genetic deletion of monoamine oxidase A (MAO A), an enzyme that breaks down the monoamine neurotransmitters norepinephrine, serotonin, and dopamine, produces aggressive phenotypes across species. In humans, studies provide evidence linking the MAOA genotypes and violent behavior but only through interaction with severe environmental stressors during childhood. The authors asked whether in healthy adult males the gene product of MAO A in the brain, rather than the gene per se, would be associated with regulating the concentration of brain amines involved in trait aggression. They measured brain MAO A activity was measured in vivo in healthy nonsmoking men with positron emission tomography using a radioligand specific for MAO A. Trait aggression was measured with the multidimensional personality questionnaire (MPQ). They show for the first time that brain MAO A correlates inversely with the MPQ trait measure of aggression (but not with other personality traits)...the lower the MAO A activity in cortical and subcortical brain regions, the higher the self-reported aggression (in both high and low MAO A genotype groups) contributing to more than one-third of the variability. Trait aggression is a measure used to predict antisocial behavior, and thus these results underscore the relevance of MAO A as a neurochemical substrate of aberrant aggression.