Fourth, genetically informed data can be leveraged to test causal hypotheses about purported risk factors for conduct disorder. Although our review has primarily focused on how genetic and environmental risk factors come together to predict conduct disorder, it is also important to note that genetically informed designs can also be used to test competing hypotheses about causation versus correlation due to confounding familial factors (D’Onofrio et al., 2013). Testing causal hypotheses about risk factors is central to identifying the appropriate targets for conduct disorder intervention and prevention efforts, and ultimately reducing the burden of these behaviors on individuals and societies. For example, if the association between OXTR methylation at birth and callous-unemotional traits in adolescence (Cecil et al., 2014) is causal, environmental interventions aimed at changing methylation patterns (e.g., through exercise, pharmaceutical intervention, or other manipulations) may be reasonable. The power of quasi-causal designs comes from comparison of sibling pairs who are discordant on a factor of interest. Under a causal model, if the risk factor has a causal impact on the phenotype, the exposed sibling would have a higher
