The primary phenotype analyzed was max drinks, a phenotype related to alcohol metabolism capacity. Although max drinks may reflect an acute event unrepresentative of chronic alcohol consumption, studies have demonstrated max drinks to be an indicator of alcoholism that differs significantly between alcohol dependent subjects with and without a physiological component (Schuckit et al., 1998; Schuckit et al., 1995). In addition, adult twin studies have shown max drinks to have heritability on the order of 50% [A. Heath, unpublished data], making it an attractive phenotype for genetic analysis. We also tested the number of DSM-IV alcohol dependence symptoms endorsed as a dimensional linear predictor, a model shown to best describe the association between dependence criteria and validating variables (Hasin et al., 2006).
