Three caveats are worth considering. First, only a small subset of individuals met DSM-IV criteria for opioid and cocaine dependence. Thus, it is possible that results pertain more closely to lower liabilities to these substances. Second, we did not include nicotine dependence criteria in this analysis. As we were interested in a confirmatory model of unidimensional genetic risk, we elected to exclude nicotine symptoms based on published evidence for a preponderance of non-overlapping genetic influences on these criteria. Finally, we elected not to utilize abuse criteria (nor craving), despite DSM-5 related changes. Previous findings in COGA families demonstrated that abuse did not aggregate in relatives of alcohol dependent probands (Nurnberger et al., 2004). In addition, the extant psychometric literature suggests that with the exception of hazardous use which is frequently endorsed to the exclusion of other abuse or dependence criteria, the remaining abuse criteria (failure to fulfill role obligations and social/interpersonal problems) and craving are infrequently endorsed in the absence of co-occurring dependence criteria. This is particularly true in samples ascertained for substance use disorders, such as SAGE and COGA.
