CNR1 variation modulates risk for drug and alcohol dependence.

Human cannabinoid receptor 1 (CB1), which is encoded by the CNR1 gene, may play a role in the development of substance dependence (SD). Following initial reports of association of CNR1 with SD, we studied multiple markers at this locus in a large case-control sample. Ten CNR1 markers and 38 ancestry-informative markers were genotyped in 451 healthy control subjects and 550 SD (AD and/or DD) patients (including European Americans [EAs] and African Americans [AAs]). Common confounding effects on association analysis of population stratification and admixture, age, and sex were controlled for using regression analysis. Disease risk and protective alleles were fine-mapped using a linkage disequilibrium measure (delta). In EAs, risk for each SD subtype significantly increased with the number of "G" alleles at rs6454674 (single nucleotide polymorphisms [SNP]3). SNP3;G(+) (the genotypes containing a G allele) and SNP8;T/T genotypes had significant interaction effects (p = .0003 for comorbid DD and AD, .0002 for DD, and .007 for AD). SNP3 and SNP8 together exerted stronger genetic effects on SD than either did individually. The peak delta values among all the markers were seen for SNP3 and SNP8 (rs806368). We demonstrate that CNR1 variation and interactive effects play important roles in risk for both DD and AD.