In examining the possible mechanisms underlying the association between early initiation of alcohol use and AD, the current study raised questions that are critical to address in future research efforts. First, the generalizability of our findings to populations with different attitudes toward alcohol use is not known. To what extent might cross-cultural differences in norms for drinking behaviors (including distinctions by gender in those norms) translate into differences in heritability and common genetic risk in other populations? Second, to what degree do genetic factors account for variance in other stages of alcohol use, such as cessation of problem drinking, and do they overlap with those that influence timing of initiation and AD? Furthermore, are these associations explained by inherited vulnerability to disinhibitory behaviors more generally9 rather than - or perhaps in addition to - genetic liability specific to alcohol-related behaviors? Another important consideration for future work in this area is the potential bias posed by retrospective reporting, most notably, forward telescoping. We attempted to minimize the influence of this bias by adjusting for age at which participants were interviewed, but
