The MAOA-uVNTR has been suggested to play a role regarding aggression, however, results are inconsistent. We aimed at further elucidating potential effects of the MAOA-uVNTR on aggressiveness with respect to potential modulators: sex, experimental vs. trait aggressiveness and type of aggressiveness (proactive vs. reactive aggressiveness). We tested 239 healthy young adults (88 men/151 women). Participants were genotyped for the MAOA-uVNTR and performed a modified version of a competitive reaction time task - a commonly used and well established tool to elicit and measure aggressiveness. Furthermore, they completed a self-report scale measuring trait aggressiveness. We found a main effect of MAOA-uVNTR on a measure of reactive aggressiveness for both men and women, whereby the low-activity alleles of the MAOA-uVNTR were associated with substantially increased aggressive reactions (p<.05). This effect was unique for reactive aggressiveness. Measures of proactive aggressiveness or self reports were not associated with the MAOA-uVNTR-genotype. Our data are in line with earlier studies and indicate the MAOA-uVNTR-genotype to be specifically associated with measures of reactive impulsive experimental aggressiveness in healthy men and women. Furthermore the association between the MAOA-uVNTR genotype and aggressive responses increases in a fashion linear to the degree of provocation. This indicates that the low-functional alleles of the MAOA-uVNTR are not associated with increased aggressive behavior per se, but rather with an increased aggressive reactivity to provocation.
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