Results from twin studies suggest that there may be two pathways for genetic influence on the development of AUDs: an early-onset pathway driven in part by genetic risk of externalizing disorders and a later, adult-onset pathway driven by genetic risk factors that are specific to AUDs [63, 64•]. Twin studies have also shown that environmental moderation (principally alcohol availability, peer deviance, and low prosocial behaviors and parental monitoring) of genetic effects on alcohol consumption is more pronounced in adolescence than in adulthood [64•]. Several twin and adoption studies have analyzed ways in which environmental factors interact with aggregate genetic effects to influence drinking behaviors. Most of these G×E studies have looked at moderating factors such as parental and peer influences and marital and religious status. Few studies have looked at early-life stressors. Exceptions include a large study of twin pairs aged 5 years that found that the effect of physical maltreatment increased the risk of conduct problems by 24% in children at high genetic risk, but by only 2% in children at low genetic risk [65]. The Minnesota Twin Family
