In models where the measurement of childhood adversity was untransformed, significant G × E with weak effect (OR 0.77, p = 0.05) was detected. The direction of the interaction in females differed from that of males such that the high-activity MAOA allele conferred greater risk for CD at the highest level of childhood adversity in females. Among males, risk for CD increased with increasing exposure to childhood adversity in those with the low-activity MAOA genotype (Caspi et al. 2002; Foley et al. 2004; Nilsson et al. 2005; Kim-Cohen et al. 2006). The difference in direction of interaction along with the presence of a main effect of MAOA in females and its absence in males in this sample (Foley et al. 2004) is suggestive of genotype-sex interaction and has been detected in other studies of MAOA and aggression (Meyer-Lindenberg et al. 2006; Sjöberg et al. 2007). However, there was no significant G × E associated with CD in females after transformation of the measure of childhood adversity into modified ridit scores, lending little support for the inclusion of G × E.
