PRS predicted a higher initial status and a greater rate of change in heavy episodic drinking during the transition from adolescence to young adulthood (age 15.5 to 21.5) for males, but not for females. Furthermore, there was no main effect for PRS on heavy episodic drinking trajectories from young adulthood to later young adulthood (age 23.5 to 27.5). First, research on sex differences in genetic influences for alcohol-related phenotypes have been mixed, as some studies have reported no differences in the degree of genetic influences (Prescott et al., 1999; Agrawal et al., 2008) or stronger genetic effects for one sex over the other (Perry et al., 2013; Dick et al., 2007). Crucially, earlier patterns of drinking (i.e., age-of-onset) are not typically accounted for in these studies, and some evidence suggests that genetic influences are stronger among earlier onset male drinkers than female drinkers (McGue et al., 1992, although see Dick et al., 2007 for an exception). It is speculated that the more robust association between PRS for alcohol dependence and early patterns of heavy episodic drinking in males may be
