Among females, the persistence of a modest main genetic effect (OR 1.59) of the low/low MAOA genotype while controlling for all other risk factors is striking because there was no significant effect of MAOA on CD in males of the same sample. The observation of a main genetic effect in females rather than males has been reported in twin studies of antisocial behavior. Significant additive genetic effects have been reported to account for a greater amount of variation of ASP in females as compared with males (Eley et al. 1999; Jacobson et al. 2002). However, Gelhorn et al. (2005) demonstrated equal contributions of unmeasured environmental and genetic effects across gender after controlling for prevalence differences in CD symptoms between males and females and such an approach to these data may alter these results. Ultimately, low/low MAOA genotype does not predispose a female to CD, but suggests an increased risk for CD at lower levels of childhood adversity compared with the heterozygous and high/high genotypes.
