or different genes. In view of the challenges associated with gene identification, and the massive sample sizes that would be required for sex-specific gene identification, twin studies of latent genetic influence provide much of the field’s current knowledge on whether the pathway from genotype–phenotype is the same across males and females. For example, the most comprehensive test of genetic differences in the heritability of alcohol use disorder (AUD) to date comes from the Verhulst et al. (2015) meta-analysis of twin and adoption studies of AUD across clinically-ascertained and registry-based samples. They found that genetic factors account for roughly 50% of the variance in AUD, and this estimate applies to both males and females. Furthermore, there was no evidence of qualitative sex differences in the Verhulst et al.’s (2015) meta-analysis. This suggests that the source and magnitude of genetic influences on AUD are likely to be the same across sexes. Recent sex-specific analyses in a sizeable (N = 112,117) GWAS of alcohol consumption in the UKBioBank sample (Clarke et al., 2017) largely replicated this conclusion from the twin and adoption studies: The genetic correlation for alcohol consumption in males and females was +0.90 (indicating overlapping genetic influences), and there was no
