Studies addressing genetic risk during adolescence, which have made use of data from sibling, twin and adopted pairs (Rhee et al., 2003), as well as multiple longitudinal twin samples (Pagan et al., 2006) have found that although the initiation of alcohol use and social drinking were only minimally related to genetic risk, problematic use in this age range appears highly heritable. Rose and colleagues’ (2001) work further signifies the importance of investigating the impact of age on heritability. The authors report that the genetic contribution to problem drinking in youth is only modest in mid-adolescence, but this biological risk actually increases as teens mature into late adolescence. A recent study has demonstrated that the genetic risk for alcohol use is highly correlated with friends’ alcohol use, highlighting the complicated interaction of genetic and environmental variables in explaining teen alcohol use (Fowler et al., 2007). Although twin and adoption studies offer some of the most compelling evidence for genetic risk, interpretation of findings should always consider that an assumption of equal environments is being made in terms of the influence of
