It is unlikely that a single hypothesis adequately explains the relationship between age at 1st drink and AD symptomatology. For instance, we find evidence, both for common vulnerabilities (i.e. common genetic factors) and for moderation (i.e. increased role of genetic influences on AD symptoms in those with early age at 1st drink). Therefore, the current study also tested whether after accounting for the common vulnerability underlying the timing of 1st drink and AD symptomatology, earlier age at 1st drink had a moderating influence on individual differences in AD symptomatology. We found that the relationship between age at 1st drink and AD symptoms could be attributed to (a) shared genetic and familial environmental factors and also to (b) moderation of these shared and specific genetic influences by age at 1st drink.
