Although developmental patterns of alcohol use vary between individuals (Brown et al., 2008), on average, alcohol use increases in accelerating fashion over the course of adolescence (Walden, et al., 2007), typically reaching a maximum during early adulthood (Sher, Grekin, & Williams, 2005), and declining thereafter (Moore et al., 2005). Twin studies, and studies using other genetically informative family designs, indicate that genetic factors account for a substantial proportion of variance in alcohol use (McGue, 1999), but the magnitude of genetic effects upon alcohol use may change over the course of development. Some studies have shown that shared environmental influences are important to the initiation and establishment of alcohol use during adolescence, but give way to increasing genetic influences upon alcohol use phenotypes through adolescence and into adulthood (Kendler, et al., 2008; Rose and Dick, 2005). The pattern of increasing genetic relationship to alcohol use-related phenotypes with age has also been observed in association with measured genetic polymorphisms in candidate genes. For example, the strength of the association observed between a polymorphism in the GABA-A receptor alpha 2 subunit gene GABRA2 and alcohol dependence was shown to increase with age (Dick et al., 2006).
