Genetic markers of the endocannabinoid system have been linked to a variety of addiction-related behaviors that extend beyond cannabis use. In the current study we investigate the relationship between endocannabinoid (eCB) genetic markers and alcohol use disorder (AUD) in European adolescents (14-18 years old) followed in the IMAGEN study ( = 2,051) and explore replication in a cohort of North American adolescents from Canadian Saguenay Youth Study (SYS) ( = 772). Case-control status is represented by a score of more than 7 on the Alcohol Use Disorder Identification Test (AUDIT). First a set-based test method was used to examine if a relationship between the eCB system and AUDIT case/control status exists at the gene level. Using only SNPs that are both independent and significantly associated to case-control status, we perform Fisher's exact test to determine SNP level odds ratios in relation to case-control status and then perform logistic regressions as analysis, while considering various covariates. Generalized multifactor dimensionality reduction (GMDR) was used to analyze the most robust SNP×SNP interaction of the five eCB genes with positive AUDIT screen. While no gene-sets were significantly associated to AUDIT scores after correction for multiple tests, in the case/control analysis, 7 SNPs were significantly associated with AUDIT scores of > 7 ( < 0.05; OR<1). Two SNPs remain significant after correction by false discovery rate (FDR): rs9343525 in (p =0.042, OR = 0.73) and rs507961 in (p = 0.043, OR = 0.78).

Logistic regression showed that both rs9353525 () and rs507961 () remained significantly associated with positive AUDIT screens ( < 0.01; OR < 1) after correction for multiple covariables and interaction of covariable × SNP. This result was not replicated in the SYS cohort. The GMDR model revealed a significant three-SNP interaction ( = 0.006) involving rs484061 (), rs4963307 (), and rs7766029 () predicted case-control status, after correcting for multiple covariables in the IMAGEN sample. A binomial logistic regression of the combination of these three SNPs by phenotype in the SYS cohort showed a result in the same direction as seen in the IMAGEN cohort (BETA = 0.501, = 0.06). While preliminary, the present study suggests that the eCB system may play a role in the development of AUD in adolescents.