Methylation studies of conduct disorder-related outcomes to date have focused on cytokine genes and their regulators (Provencal et al., 2013), and the oxytocin receptor (OXTR) gene (Dadds et al., 2014), which show differential patterns of methylation as a function of physical aggression and callous-unemotional traits. In an effort to directly link environmental exposures with one of these methylation profiles, Cecil et al. (2014) found that prenatal risk factors such as maternal psychopathology, criminal behavior, and substance use predicted higher levels of methylation in/around the oxytocin receptor (OXTR) gene at birth in a subsample from the Avon Longitudinal Study of Parents and Children. In turn, methylation of OXTR was associated with higher levels of callous-unemotional traits in adolescence (Cecil et al., 2014), which define a subtype of conduct disorder (Blair et al., 2014; Frick and Ellis, 1999). The study of epigenetics for conduct disorder-related outcomes is an emerging area of research that is likely to expand, and these preliminary findings should be interpreted keeping in mind that many of the concerns related to testing cG × E (e.g., selection of the
