Genetic polymorphisms in the IL-18 gene and ulcerative colitis risk: a meta-analysis

This meta-analysis was performed to evaluate the relationships between genetic polymorphisms in the IL-18 gene and ulcerative colitis (UC) risk. The PubMed, CISCOM, CINAHL, Web of Science, Google Scholar, EBSCO, Cochrane Library, and CBM databases were searched for relevant articles published before November 1st, 2013 without any language restrictions. Meta-analysis was conducted using the STATA 12.0 software. Crude odds ratios (ORs) with their 95% confidence intervals (95% CI) were calculated. Eight case-control studies with a total of 1000 UC cases and 1392 healthy subjects met the inclusion criteria. Six common polymorphisms in the IL-18 gene were evaluated, including rs1946518 A>C, rs187238 G>C, rs917997 G>A, Codon35, rs1946519 C>A, and rs360718 A>C. The results of our meta-analysis suggest that the IL-18 rs1946518 (allele model: OR=1.22, 95% CI: 1.01-1.48, p=0.039; dominant model: OR=1.44, 95% CI: 1.01-2.06, p=0.045; respectively), rs187238 (allele model: OR=1.38, 95% CI: 1.19-1.61, p<0.001; dominant model: OR=1.50, 95% CI: 1.03-2.19, p=0.034; respectively), and rs360718 (allele model: OR=2.18, 95% CI: 1.22-3.90, p=0.008) polymorphisms might be strongly correlated with an increased risk of UC. A subgroup analysis was conducted to investigate the effect of ethnicity on an individual's risk of UC. Our results revealed positive significant correlations between IL-18 genetic polymorphisms and an increased risk of UC among Asians (allele model: OR=1.36, 95% CI: 1.16-1.60, p<0.001; dominant model: OR=1.50, 95% CI: 1.14-1.98, p=0.004; respectively) and Africans (allele model: OR=1.45, 95% CI: 1.03-2.05, p=0.034), but not among Caucasians (all p>0.05). Our findings provide convincing evidence that IL-18 genetic polymorphisms may contribute to susceptibility to UC, especially the rs1946518, rs187238, and rs360718 polymorphisms among Asians and Africans.