The SNP-heritability of DSM-5 AUD diagnosis (h2SNP=0.14) was not significant but approximates the estimate of 0.09 from a recent GWAS meta-analysis of DSM-IV alcohol dependence (Sanchez-Roige et al., 2018). In contrast, SNP-heritability for the AUD factor score (0.36) and for the AUD severity score (0.22) were significant and higher. The use of a quantitative index of liability likely increased sensitivity to capture genetic effects and supports the transition from a binary (DSM-IV) to categorical (DSM-5) definition of AUD. However, the modest reduction in heritability when using the AUD severity score, which represents DSM-5 categories implies some compression of meaningful variability that the full spectrum of scores affords. Indeed, a symptom count was used amongst the few successful GWAS of alcohol dependence (Gelernter et al., 2014). As a symptom count is similar to a unidimensional factor score, our analyses support the use of such symptom counts, potentially augmented to even include indices of alcohol consumption (Saha et al., 2007), as well as other comorbid internalizing and externalizing type disorders that have evidenced genetic overlap (Cerda et al., 2010).
