majority of studies addressing heritability of alcohol use have defined initiation in terms of “ever use” without reference to the timing of first drink, which, given the variability in prevalence of AD by age at first drink, is a key aspect of initiation to consider. The few known studies to do so found that, like “ever use,” shared environmental factors accounted for the most variance in age at initiation, but additive genetic factors played a modest role as well23,24. Importantly, although initiation is influenced to a lesser degree by genetics than AD, evidence from the small number of investigations in this area indicates that the genetic factors that contribute to the timing of first drink overlap significantly with those that influence onset of AD10,24, suggesting that at least some component of the observed association is non-causal.
