The phenotypic characteristics between the CADD clinical and GADD samples are comparable (Figure 1). Although the same subjects were used in the adolescent/young adult CD and AAD analyses, only phenotypic data from subjects that had used alcohol were included in the adolescent/young adult ADD analysis, accounting for the difference in sample size between the two adolescent/young adult analyses. This was done because most of the previous studies that found associations between GABRA2 and alcohol dependence used alcohol dependent cases and matched controls in their analyses (Edenberg et al. 2004; Covault et al. 2004; Lappalainen et al. 2005; Fehr et al. 2006; Drgon et al. 2006; Soyka et al. 2008; Covault et al. 2008; Enoch et al. 2009; Bierut et al. 2010; Olfson and Bierut 2012; Ittiwut et al. 2012), thus only subjects that had used alcohol were included in the present study in order to minimize sample differences between the current and past studies. Although our adolescent/young adult analyses include subjects of a substantially large age range, this is the approximate age range for probands in wave 1 of the CADD and GADD samples.
