Association of A118G polymorphism in the μ-opioid receptor gene with smoking behaviors: a meta-analysis.

Many studies have investigated the association between the A118G polymorphism in the μ-opioid receptor gene and smoking behaviors, but the results remain controversial. This meta-analysis aimed to derive a more reliable estimate of the effect of the A118G polymorphism on smoking behaviors. We systematically searched the PubMed/Medline, Embase and Web of Science databases for eligible articles published up to October 23, 2014. A total of six studies were selected. Odds ratios (ORs) as well as their corresponding 95% confidence intervals (CIs) were used to estimate the association between A118G polymorphism and smoking behaviors in four genetic models. Heterogeneity analysis and publication bias were also performed. Subgroup analysis was conducted according to different ethnicities. The meta-analysis was performed using either a fixed- or random-effects model as deemed appropriate. In the result of the meta-analysis, a significant association was detected in the dominant model in the Caucasian subgroup (OR = 3.26, 95% CI = 2.65-4.05). This result indicated that Caucasians carrying the G allele (AG + GG) of the A118G polymorphism in the μ-opioid receptor gene were more likely to be addicted to smoking compared with those with the AA homozygote. However, no significant association was found in other genetic models.