Interleukin-18 -137 G/C and -607 C/A polymorphisms and Alzheimer's disease risk: a meta-analysis

The -137 G/C and -607 C/A polymorphisms in interleukin-18 (IL-18) gene have been reported to be associated with Alzheimer's disease (AD) risk, but the results are inconclusive. Considering a single study may lack the power to provide reliable conclusion, we performed a meta-analysis to investigate the association between the IL-18 -137 G/C and -607 C/A polymorphisms and AD susceptibility. A comprehensive literature search of PubMed, Embase, China National Knowledge Infrastructure (CNKI) and Wanfang databases were conducted before September 1, 2015. The pooled odds ratio (OR) with 95 % confidence intervals (CIs) were calculated. Five eligible studies with a total of 1536 subjects were finally included in this meta-analysis. For the IL-18 -137 G/C polymorphism, a significantly decreased risk was detected in patients carrying the C allele of -137 G/C in all study subjects in allele model (C vs. G: OR = 0.816, 95 % CI = 0.680-0.980, p = 0.029). Moreover, stratification by ethnicity indicated markedly association between the -137 G/C C allele and AD risk in Asians. For the IL-18 -607 C/A polymorphism, a significantly decreased risk was found in patients carrying the A allele of -607 C/A in all study subjects in dominant model (AA + CA vs. CC: OR = 0.696, 95 % CI = 0.529-0.915, p = 0.010). However, the results suggested no significant association between the -607 C/A polymorphism and AD susceptibility when stratified by ethnicity. Our present meta-analysis suggests that the C allele carrier of IL-18 -137 G/C was associated with decreased risk for AD in Asians. Further well-designed case-control studies with larger sample size and more ethnic groups are needed to confirm these conclusions.