It is not clear why the G × E results were weaker in boys than in girls. The influence of adversity on behavior was the same in both sexes. Boys tended to be slightly more hyperactive. Conduct problem scores differed little between the sexes unlike in adulthood when the prevalence of antisocial behavior is much higher in men than women (Rutter et al, 2003). Indeed, a recent study has shown that MAOA-LPR interacts with CSF testosterone to predict antisocial behaviors in men (Sjoberg et al, 2008). Thus there may be hormonal or age-related effects that complicate the relationship between MAOA-LPR genotype and early life stress, and therefore the G × E interaction may be hard to detect in pre-pubertal boys. Only one study has detected a G × E effect in boys aged 7 years but in this case the MAOA-LPR interaction was with severe maltreatment (Kim-Cohen et al, 2006).
