The influence of genes on alcohol dependence and related symptomatology is well established. Results from twin studies indicate that approximately half of the variance in AD (50-60%) is accounted for by genetic factors and heritability does not vary significantly by gender (Heath et al., 1997; Knopik et al., 2004; Reed et al., 1996; True et al., 1996; van den Bree et al., 1998). Twin studies have also produced evidence for genetic contributions to alcohol consumption (Grant et al., in press; Heath et al., 1991; King et al., 2005; Whitfield et al., 2004), but the literature on consumption phenotypes is more limited than the AD literature and heritability estimates appear to vary by both age and sex. An early study by Heath et al. (1991) found that in females 57% of variance in quantity consumed was attributable to genetic factors, but results were less clear in males: an equally good fit was found for models in which 24% and 61% of variance was accounted for by genetic factors. In a longitudinal study by King et al. (2005), heavy drinking was assessed
