Association studies suggest that the low activity variant of the monoamine 
oxidase A (MAOA)-uVNTR polymorphism confers risk for emotional disturbances 
associated with antisocial traits, particularly in males. Here, we assessed the 
low (MAOA-L) activity variant in relation to both brain function and a 
behavioral index of antisocial traits. From an initial sample of 290 healthy 
participants, 210 had low (MAOA-L) or high (MAOA-H) activity variants. 
Participants underwent a brief assessment of personality traits and 
event-related potential (ERP) recording during an emotion-processing task. 
Genotype differences in ERPs were localized using LORETA. The MAOA-L genotype 
was distinguished by elevated scores on the index of antisocial traits. These 
traits were related to altered ERPs elicited 120-280ms post-stimulus, 
particularly for negative emotion. Altered neural processing of anger in MAOA-L 
genotypes was localized to medial frontal, parietal, and superior 
temporo-occipital regions in males, but only to the superior occipital cortex in 
females. The MAOA low activity variant may increase susceptibility to antisocial 
traits through alterations to the neural systems for processing threat-related 
emotion, especially for males. Monoamines such as noradrenalin and serotonin may 
modulate these relationships, given that their metabolism varies according to 
MAOA variants, and that they modulate both emotional brain systems and 
antisocial aggression.