Results from this study converge with previous epidemiological (Kendler et al. 2011) and twin studies that indicate that in early adolescence, genetic influences on alcohol use behaviors are largely non-specific and may reflect largely adolescent-limited externalizing behaviors (Moffitt, 1993; Moffitt et al. 2002). Further, alcohol-specific genetic risk factors become more important than non-specific (externalizing) genetic influences in early adulthood (Rose et al. 2003). Moreover, this shift in genetic influences maps onto typical developmental timing for the onset of serious alcohol problems (Schuckit et al., 1995). In this study, prospective reports from a population based, longitudinal sample of Finnish twins permitted several important comparisons to extend previous findings. The first is the age at which alcohol-specific genetic risk factors and externalizing genetic risk factors shift in their relative importance. The most dramatic shift in genetic influence on drinking frequency occurred at approximately age 21 in the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders (VATSPSUD;(Kendler et al. 2011)). However, this shift occurred earlier at an average age of 17.5 in the FinnTwin12. There are differences both in the legal
