Genetic and environmental influences on developmental trajectories of adolescent alcohol use.

Adolescent alcohol use demonstrates distinct developmental trajectories with different times of onset, levels, and rates of growth. Twin research on adolescent alcohol use has shown that genetic influences are consistent with a gradual growth of risks, whereas non-shared environmental influences are more consistent with an accumulation of risks over time. The current study investigated the relative contributions of genetic and environmental influences on shaping different developmental trajectories of alcohol use through adolescence. Self-reported past year alcohol use was collected from 877 Canadian twins (47.1% males) at age 13, 14, 15, and 17 years. Growth mixture models were fit to examine different developmental trajectories of alcohol use, and biometric liability threshold models were fit to investigate genetic and environmental influences on the liability of belonging to identified trajectories. Three trajectories were identified: low (15.1%), early onset (8.2%), and normative increasing (76.7%). Memberships in the low and early-onset group were under genetic (27.6% and 34.7%), shared (42.4% and 21.5%), and non-shared environment influences (30.0% and 43.8%). Membership in the normative increasing group was under genetic (37.7%) and non-shared environment influences (62.3%). Non-shared environmental influences were significantly larger for the normative increasing trajectory than for the low trajectory. These findings provide a more refined picture of genetic and environmental influences in the development of alcohol use in subgroups of adolescents. Genetic and environmental influences both matter, but to different degrees in different trajectories. Future research should identify specific shared and non-shared environmental experiences that distinguish different trajectories.