Replication of individual variants/genes other than those involved in alcohol metabolism can be challenging and notably influenced by heterogeneity across samples, ascertainment approach, definitions of affected and unaffected, and even nuanced differences in interview instruments 17. For instance, although families ascertained for AD were included in the replication samples, OZALC had samples ascertained for heavy smoking and drinking (as well as sibships ascertained merely for large pedigree size), and SAGE included two subsamples recruited for nicotine and cocaine dependence. In addition, unlike the prior large AD GWAS by Gelernter and colleagues 19, we excluded individuals with ≥2 abuse or dependence criteria for alcohol or any illicit drug from our unaffected group 19. This may have led to a greater degree of genetic separation between affecteds and unaffecteds in the current analysis and contributed to the lack of replication. Despite these potential differences, for 2 of the 5 loci (rs1229984 and rs188227250), meta-analyses across samples yielded more significant associations. In addition, the PRS analyses found that the aggregated effect of variants in regions other than the ADH cluster and the ALDH2
