There is currently a strong push from the National Institutes of Health to more carefully examine the extent to which pathways of risk may vary across males and females. Genetically informed designs can be used to examine the extent to which there are sex differences in the genetic influences on psychiatric outcomes (Powers et al., 2017; Salvatore et al., 2017). There are two forms of sex-specific genetic differences identified in twin studies (Neale & Cardon, 1992). Quantitative sex differences refer to differences in the degree to which additive genetic factors account for variation in an outcome in males and females. Qualitative sex differences refer to differences in the source of genetic variation across males and females. In other words, researchers can study whether the relative importance of genetic effects varies between males and females, and whether it is the same 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
