The Association between Interleukin-6 Gene Polymorphisms and Risk of Systemic Lupus Erythematosus: A Meta-analysis with Trial Sequential Analysis

Background: Molecular epidemiological studies have sought associations between interleukin-6 (IL-6) polymorphisms and the risk of systemic lupus erythematosus (SLE); however, the results are controversial. Therefore, we conducted a meta-analysis with trial sequential analysis to evaluate a more accurate estimation of the associations.

Methods: Published literatures reporting the relationships of two IL-6 polymorphisms (G-174C and G-572C) and SLE risk were retrieved from electronic databases such as PubMed and EMBASE. The most appropriate genetic model was chosen for each polymorphism. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Trial sequential analysis (TSA) was introduced to assess the information size and the positive results.

Results: With 17 studies (2780 cases and 3100 controls) included, a dominant association (CC+GC vs. GG) was suggested for G-174C polymorphism, and compared with the GG genotype, the CC+GC genotype of G-174C was associated with a decreased SLE risk (OR = 0.71; 95% CI = 0.56-0.88, P =.02). No association was found for G-572C under all genetic models (e.g. OR and 95%CI for CC+GC vs. GG: 0.89, 0.73-1.08, P =.22). Subgroup analyses indicated that SLE risk decreased in G-174C polymorphism by subgroups of Caucasian population, publications after 2010, studies with high quality, and studies complied with Hardy-Weinberg equilibrium (HWE). TSA suggested that the sample sizes used for G-572C were insufficient.

Conclusion: We found that the minor allele C of IL6G-174C polymorphism is a protective factor in SLE. Further studies with a larger sample size are needed to confirm the null association for G-572C.