Participants came from the Collaborative Study on the Genetics of Alcoholism (COGA) (Begleiter et al., 1995), whose objective is to identify genes involved in alcohol dependence and related disorders. Probands were identified through alcohol treatment programs at six U.S. sites and were invited to participate if they had a sufficiently large family (usually sibships > 3 with parents available) with two or more members in the COGA catchment area. The Institutional Review Boards at all sites approved this study and written consent was obtained from all participants. As shown in Figure 1, the present analyses included a subset of 118 European-American COGA families densely affected with alcohol dependence (at least 3+ affected members) and for whom genome-wide association data were available (Kang et al., 2013; Wang et al., 2013). By design, this sample was limited to European-American individuals in order to avoid false positives in the GWAS driven by population stratification (i.e., differences in allele frequencies between populations) (for a review see Cardon & Palmer, 2003). We focused on the adolescent (Adolescent subsample; ages 12-17) and young adult (Young Adult
