Caspi et al. (2002) have also reported findings consistent with the presence of a G × E that is associated with an increased risk for CD in females. However, heterozygous females, comprising 46% of the sample, were not included because of concerns surrounding the perceived inability to estimate genotypic effects as a result of X-inactivation. The loss of such a large portion of the sample is anticipated to result in a loss of power to detect a significant genetic effect on CD diagnosis as well as an incomplete understanding of the etiology of CD in females. Thus, the inclusion and appropriate treatment of data from heterozygous females is necessary in the analysis of the effect of MAOA and G × E on risk for CD. Another study reported evidence of a significant G × E where females with the high-activity MAOA allele were at increased risk for criminal behavior when exposed to psychosocial risk, as defined by the type of housing (multi-family versus owned single family) and experiencing childhood sexual abuse (Sjöberg et al. 2007).
