We sought to examine the relationship between age at 1st drink and DSM-IV AD symptomatology. Our analyses revealed that even after controlling for the main effects of age at 1st drink on AD symptomatology (i.e. more symptoms in those with earlier age at 1st drink) and for gene-environment correlation (i.e. common genetic influences on age at 1st drink and AD symptoms), heritable influences on AD symptoms decreased with increasing age at 1st drink. In contrast, in individuals who initiated alcohol use after the age of 18 years, nearly all variance on AD symptoms could be attributed to unique environmental factors and/or measurement error.
