In this study, we utilized data from 2,322 subjects from 118 families of European-American descent ascertained for alcohol dependence liability to conduct genomewide association analysis of a binary and a continuous index of general substance dependence liability. While some prior genomewide efforts (McGue et al., 2013) have utilized similar phenotypes in population samples of related individuals, the ascertainment strategy and extended family-based design in our study should increase our ability to detect genetic variation in this phenotype. First, there is substantial evidence that alcohol use disorders that co-aggregate with other substance use disorders (Khan et al., 2013) may represent a more heritable form of addiction (Pickens et al., 1991). Secondly, by modeling the strength of the phenotypic correlation across different degrees of genetic relatedness (i.e. kinship), we utilize data on all related individuals, even those not meeting criteria for diagnoses, allowing us to better explore the extent of co-aggregation of genetic risk across alcohol, cannabis, cocaine and opioid dependence.
