Association between the catechol-O-methyltransferase Val158Met polymorphism and cocaine dependence

Dopaminergic brain systems have been documented to have a major role in drug reward, thus making genes involved in these circuits plausible candidates for susceptibility to substance use disorders. The catechol-O-methyltransferase (COMT) is involved in the degradation of catecholamines and a functional polymorphism (Val158Met) has been suggested to influence enzyme activity. In this study we hypothesize that genetic variation in the COMT gene contributes to increased risk for cocaine dependence. Cocaine-dependent individuals (n=330) and screened unaffected normal controls (n=255) were genotyped for three SNPs in the COMT gene (rs737865, rs4680 (Val158Met), rs165599). All cases and controls were of African descent. Genotype and allele frequencies differed significantly for the Val158Met polymorphism between cases (f(Met)=35%) and controls (f(Met)=27%) (p=0.004; corrected p=0.014; OR 1.44; 95% CI 1.12-1.86). Haplotype analysis showed a significant association for a two-marker haplotype rs737865-Val158Met (p=0.005). Results suggest that variation in COMT increases risk for cocaine dependence. The low enzyme activity 158Met allele or haplotypes containing this variant might have functional effects on dopamine-derived reward processes and cortical functions resulting in increased susceptibility for cocaine dependence. Additional studies are required to elucidate the role of COMT in the pathophysiology of substance use disorders.