(Enoch, 2013; Melroy-Greif, et al., 2017; Polimanti, Yang, Zhao, & Gelernter, 2015; Verweij, et al., 2012) and (6) phenotypic comorbidity where the SUD diagnosis, itself, may have multiple subtypes (i.e., single-drug versus poly-drug dependence, rate of time from initiation to the development of dependence, or comorbidity between substance dependence and psychiatric conditions) with shared genetic and environmental architecture (Bi, et al., 2014; Palmer et al., 2014). Consequently, there remains discrepancies in the convergence of results from different genetic epidemiology study designs (Vrieze, McGue, Miller, Hicks, & Iacono, 2013).
