Our findings also complement other studies that have tested for genetic effects across adolescents/young adults of different ages. In at least two independent studies examining other genes thought to be involved in alcohol related outcomes, genetic effects that were present at later ages were not evident earlier in adolescence. Using data from the Add Health study on individuals ages 13–26, genetic effects associated with five monoamine genes and patterns of alcohol consumption were only evident among individuals age 19 or older, not among younger individuals (Guo, Wilhelmsen et al. 2007). Similarly, associations between ALDH2 and alcohol consumption among Asian-Americans also showed a parallel pattern with genetic effects becoming evident late in adolescence/young adulthood (Irons, Iacono et al. 2012). These studies together point toward a more global picture of genetic effects on alcohol related outcomes emerging in young adulthood. However we note that the increase in drunkenness observed at the transition to adulthood in our sample is not sustained. There are no significant differences in rate of change in drunkenness after age 19, and mean levels of drunkenness do not differ
