Alcohol use during adolescence is associated with sharp increases in the risk for myriad adverse outcomes, including alcohol dependence (Grant et al., 2006). Consequently, research efforts to identify factors that affect liability for developing an alcohol use disorder (AUD) during this key developmental period have grown considerably over the past decade. Early evidence from twin and adoption studies indicates that while initiation of alcohol use during adolescence is mainly influenced by environmental factors, genetics play a primary role in the development of alcohol-related problems (Hopfer et al., 2003, Lynskey et al., 2010). Emerging research, however, illustrates the importance of elucidating the interplay between genetic and environmental influences on alcohol-related problems and other forms of psychopathology (Dick 2011, Dick et al., 2011; Nilsson et al., 2005). Specifically, recent quantitative genetic research with twin data suggests that environmental factors moderate genetic liabilities for alcohol use in youth (Dick et al., 2007).The present study builds on twin studies, which provide estimates of the combined variance explained by multiple genes (i.e., heritability or estimates of additive genetic risk for a disorder), by conducting the
