our ability to compare across the AUDIT-C and AUDIT-P. Third, as the discovery GWAS was conducted on individuals of primarily European descent, these PRS could not be applied to other ancestral groups, reflecting a research gap in the dearth of large discovery GWAS of non-European populations (Martin et al., 2017). Results from the recent AUDIT-C GWAS by Kranzler et al (2019), which includes 57,340 African-Americans, for instance, will be instrumental in bridging this gap. Fourth, it is likely that the pattern of results reflects a complex interplay between developmental effects, ascertainment strategy, the psychometrics of the assessment instruments, and even population selection effects. For instance, distinctions between ALSPAC and COGA could be attributed to the higher median age of COGA participants, or even drinking patterns prevalent in earlier birth cohorts that are represented within COGA. Potential moderation of PRS by sex are also possible; however, power for such exploratory analyses is limited and beyond the scope of this study. Fifth, although this study examined a range of alcohol use phenotypes (from a measure of monthly alcohol use to dependence), the cross-sectional design cannot capture potential longitudinal changes in PRS association across the progression of stages of alcohol use. A sixth
