Genetic vulnerability is also an important influence on the development of behavioral disinhibition (Jaffe et al, 2005). One gene that has been implicated is monoamine oxidase A (MAOA) (Xp11.23) that encodes an enzyme that plays an important role in the degradation of central nervous system (CNS) serotonin and norepinephrine. Variation in serotonergic activity is implicated in impulsivity and anxiety. MAOA deficient mice have increased CNS serotonin and norepinephrine levels; pups show increased fearfulness and adult males show increased aggression (Cases et al, 1995). In healthy men, MAOA activity in cortical regions correlates inversely with measures of aggression (Alia-Klein et al, 2008). The MAOA gene has a 30 base pair repeat in the promoter region (MAOA-LPR) that affects transcriptional efficiency (Sabol et al, 1998). In healthy humans, MAOA-LPR genotype predicts limbic circuitry variation for emotional regulation, including inhibitory control, and also brain response differences in tests for impulsivity (Meyer-Lindenberg et al, 2006; Passamonti et al, 2006).
