The best-fitting genetic models both for initiation and alcohol dependence equated A, C, and E across males and females, indicating that the nature and strength of the influences on timing of first alcohol use and AD did not vary by sex - an interesting parallel to our finding that the relationship between the two outcomes was the same for men and women. The absence of distinctions by sex in the relative contributions of genetic and environmental influences on AD is consistent with the highly similar heritability estimates for males and females reported in the larger literature12,13,25,26. In studies of alcohol use initiation, comparisons between sex-specific and non sex-specific genetic models have only rarely been made and findings across the few that have reported on these comparisons are inconsistent. Higher heritability estimates for males, non-significant trends for a greater influence of shared environment for females, and the absence of significant differences between females and males4,18,19 have all been reported. Thus, our findings contribute to an as-yet inconclusive literature on an aspect of alcohol use that, given its important implications for understanding the etiology of drinking behaviors, merits further investigation.
