While our study is limited by our sample size, particularly of discordant siblings and longitudinal analyses, a major strength of our results is the convergent evidence provided by the different study designs (75). We note that our cross-sectional analyses of alcohol consumption and longitudinal analyses of adolescent use initiation are the largest to date that we know of. A primary limitation of our gene-expression analyses is that both of the gene-expression datasets included alcohol-exposed donors. Given the wide prevalence of alcohol use across the world (76), it will likely be impossible to ever definitively confirm in human adults that alcohol use is not confounding these results. Notably, none of the identified genes have been found to be differentially expressed in the frontal cortex of donors with alcoholism (77,78). Our analyses are also limited by the omission of the insula from the gene-expression data, precluding a comparison of the gene-expression correlates between the insula and frontal cortex.
