Refining the scope of genetic influences on alcohol misuse through environmental stratification and gene-environment interaction

Background Gene-environment interaction (G×E) is likely an important influence shaping individual differences in alcohol misuse (AM), yet it has not been extensively studied in molecular genetic research. In this study, we utilize a series of genome-wide gene-environment interaction (GWEIS) and in silico annotation methods with the aim of improving gene identification and biological understanding of AM. Methods We carried out GWEIS for four AM phenotypes in the large UK Biobank sample ( N = 360,314), with trauma exposure and socioeconomic status (SES) as moderators of the genetic effects. Exploratory analyses compared stratified GWAS and GWEIS modelling approaches. We applied functional annotation, gene- and gene-set enrichment, and polygenic score analyses to interpret the GWEIS results. Results GWEIS models showed few genetic variants with significant interaction effects across all gene-environment pairs. Enrichment analyses identified moderation by SES of the genes NOXA1 , DLGAP1 , and UBE2L3, on drinking quantity and the gene IFIT1B on drinking frequency. Except for DLGAP1 , these genes have not previously been linked to AM. The most robust results (GWEIS interaction p = 4.59e-09) were seen for SES moderating the effects of variants linked to immune-related genes on a pattern of drinking with versus without meals. Conclusions Even in large samples, G×E effects are difficult to detect at the molecular level. Our results highlight several genes and a potential mechanism of immune system functioning behind the moderating effect of SES on the genetic influences on AM. While GWEIS seems to be a preferred approach over stratified GWAS, modelling molecular G×E effects remains a challenge that will require larger consortia and more in-depth phenotypic measurement.