We have demonstrated that the inclusion of females heterozygous for the low- and high-activity MAOA alleles is reasonable and yields meaningful results despite the ambiguity around the issue of X-inactivation by defining both the homozygous (additive) and heterozygous (dominance) effects of MAOA. Additionally, the risk for CD associated with the heterozygous MAOA genotype is between that of the homozygous groups and resembles that of the highactivity genotype (Meyer-Lindenberg et al. 2006).
