The study aimed to: (1) characterize methylation levels in MAOA ROI CpGs by age, sex, and by the interaction of age and sex, adjusting for genotype and substance dependence; and (2) determine whether MAOA ROI methylation levels were associated with the interaction of MAOA-uVNTR genotype, sex, and sexual abuse among males and/or females. This evidence concerns the gene MAOA and substance dependence.