The interactive effect of MAOA ‐ LPR genotype and childhood physical neglect on aggressive behaviors in Italian male prisoners

Aggressive disorders are moderately heritable; therefore, identification of genetic influences is important. The X‐linked MAOA gene, encoding the MAOA enzyme, has a functional 30 bp repeat polymorphism in the promoter region ( MAOA ‐LPR) that has been shown to influence aggression. Childhood trauma is a known risk factor for numerous psychopathologies in adulthood including aggressive behaviors. We investigated the interactive effect of MAOA ‐LPR genotype and a history of childhood trauma in predicting aggressive behaviors in a prisoner population. A total of 692 male prisoners were genotyped for MAOA ‐LPR with genotypes grouped into high and low transcriptional activity. Participant evaluations included measures of aggression (Brown‐Goodwin Lifetime History of Aggression, BGHA), hostility (Buss–Durkee Hostility Inventory), impulsivity (Barratt Impulsiveness Scale), violence directed toward self and others, and childhood trauma [Childhood Trauma Questionnaire (CTQ)]. MAOA ‐LPR interacted with CTQ physical neglect (PN), the most common (47%) form of childhood trauma in this sample, to predict BGHA aggression ( P  = 0.002). Within the group not exposed to PN, carriers of the MAOA ‐LPR high‐activity variant were more aggressive: ( t R  = 2.47, P  < 0.014). We observed a crossover effect in that the increase in aggression scores with PN was greater in low‐activity individuals ( t R  = 5.55, P  < 0.0001) than in high‐activity individuals ( t R  = 4.18, P  < 0.0001). These findings suggest that childhood trauma and the functional MAOA ‐LPR polymorphism may interact to specifically increase risk for over aggressive behavior but not impulsivity or hostility. The MAOA ‐LPR low‐activity variant may be protective against the development of aggressive behavior under low stress conditions, at least in this prisoner population.