Despite limited SNP-level findings, there is significant evidence for polygenic effects of common variants in both EU and AA cohorts. The estimated h2g = 0.09 for AD in EU is only modestly lower than those recently reported for alcohol consumption (h2g = 0.13)17 and AUDIT scores (h2g = 0.12)18, and comparable to estimates derived for cigarettes-per-day25. Our h2g estimate is lower than a prior report7, likely reflecting a combination of differences in estimation method (GREML vs. LDSR) and greater heterogeneity in ascertainment strategy across samples in the current study (see26–28). The latter is especially relevant in comparing h2g from that prior single cohort to our meta-analysis that included cohorts with a wide range of ages at ascertainment, cultural environments, and ascertainment strategies, including enrichment for other substance use disorders. Similar to other psychiatric disorders (e.g. schizophrenia), a much larger sample size will potentially aid in overcoming across-sample heterogeneity and capture a greater proportion of genetic variance.
