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Association between interleukin-6 −174G/C polymorphism and the risk of Alzheimer's disease: a meta-analysis

Background: The −174G/C polymorphism in interleukin 6 (IL-6) gene has been extensively investigated for association to Alzheimer's disease (AD); however, results of different studies have been inconsistent. The objective of this study is to assess the relationship of IL-6 −174G/C polymorphism and Alzheimer's disease (AD) risk by using meta-analysis. Methods: All eligible case–control studies were searched in PubMed and EMBASE. Odds ratios (ORs) with the 95% confidence intervals (CIs) were used to assess the association. Results: A total of 5316 cases and 10 757 controls in 21 case–control studies were included. Obvious heterogeneity among studies was detected, and no significant association was observed between the IL-6 −174G/C polymorphism and AD risk. After exclusion of three studies, the heterogeneity disappeared and significant association was observed between the polymorphism and AD risk in Asians (CC vs. CG+GG: OR = 0.5; 95%CI, 0.33–0.75) but not in Caucasians. Conclusion: This meta-analysis suggested that the −174G/C polymorphism of IL-6 gene would be a protective risk factor for AD in Asians. To further evaluate gene-to-gene and gene-to-environmental interactions between polymorphisms of IL-10 gene and AD risk, more studies with large groups of patients are required.