a greater number of older friends who may provide access to drinking opportunities. Earlier access to alcohol and earlier evidence of heritability in drinking frequency may also be related to the earlier influence of alcohol specific risk for intoxication frequency in early adolescence. In addition, risk for alcohol dependence symptoms at age 22 for females is largely influenced by AUD-GR, with EXT-GR playing a minor role. Conversely, both AUD-GR and EXT-GR appear to substantively influence age 22 alcohol problems for males, with AUD-GR playing the larger role. Past studies have reported sex differences in alcoholic subtypes, including an excess of women in internalizing subtypes and an excess of men in externalizing subtypes (Carpenter and Hasin, 2001; Epstein et al., 2002; Moss et al., 2007). Findings from the present study support these sex differences given that alcohol dependence criteria are influenced more by EXT-GR for males than females.
