First, our best estimate for the heritability of AUDs, based on 13 twin and five adoption studies was 0.49 (95% CI 0.47–0.54). Importantly, while the diagnosis of AUD used in the various studies included in this meta-analysis may have substantial levels of clinical and etiological heterogeneity, the fact that we do not find statistical evidence of differential genetic or environmental heterogeneity as a function of ascertainment or diagnosis implies that the underlying construct of AUD is fairly robust to the specific measure of AUD that is used in any given study. Furthermore, the heterogeneity between AUD in twin and adoption studies was not statistically significant at conventional levels of significance (p = 0.06). While heterogeneity in the parameter estimate is trending towards significance, given that over 1 00 000 observations were included in the analysis, there is ample power to detect even relatively small differences across samples. Further, we found no evidence for genetic qualitative sex effects for AUD. That is, this result predicts that the same genetic factors increase risk for AUDs in males and females. As such, we find no evidence for any type of genetic sex limitation.
