Previously, stronger association results were often obtained when the alcohol-dependent cases were limited to those with greater correlates of disease severity, such as earlier age of onset, comorbid drug dependence or higher likelihood of conduct disorder symptoms (Agrawal et al., 2006; Dick et al., 2007a; Edenberg et al., 2008b; Foroud et al., 2008). We performed secondary analyses to identify potential associations with early onset alcohol dependence. A median split of our sample (Table 1) was performed and those alcohol dependent cases with an onset of 22 years or younger (n=454) were classified as having earlier onset of alcohol dependence. Logistic regression using the additive model with sex as a covariate was employed to test for association between the genotyped SNPs and the phenotype of early onset alcohol dependence.
