The landscape of complex trait genetics is changing rapidly, and we are optimistic that over the next few years there will be further gains in the field’s understanding of the genes implicated in conduct disorder, as well as how environmental factors interface with this risk through G × E, rGE, and epigenetic processes. We offer a few suggestions on potential ways forward for this area of research. First, the Diagnostic and Statistical Manual was developed as a clinical tool, and accordingly, separates externalizing disorders into distinct clinical diagnoses. However, the results from multiple twin studies indicate that there is a common genetic etiology across externalizing spectrum disorders (Kendler et al., 2003; Krueger et al., 2002; Slutske et al., 1998; Young et al., 2000). This suggests that there remains a great deal of leverage to be gained through gene identification efforts that combine phenotypes across the externalizing spectrum, as illustrated in Dick et al. (2008). Relatedly, forthcoming results from the substance use workgroup of the Psychiatric Genomics Consortium’s analyses of nicotine, cannabis, cocaine, opioid, alcohol, and other substances will likely produce several candidates worth following up for association with conduct disorder.
