Ethnicity-stratified analysis of the association between IL-18 polymorphisms and systemic lupus erythematosus in a European population: a meta-analysis

We performed a meta-analysis to identify the association between polymorphisms in the promoter of interleukin-18 (IL-18) and susceptibility for systemic lupus erythematosus (SLE) . Genotype data for three single-nucleotide polymorphisms (SNPs rs360719, rs1946518, and rs187238) in the IL-18 promoter were extracted from 20 studies of three different ethnicities (European, Asian, and South American). Data from each ethnicity group and their combinations were analyzed. We found distinct evidence of an association between rs360719 and SLE (P = 0.001) in the European/South American group [odds ratio (OR) 1.31 per C allele, 95 % confidence interval (CI) 1.11–1.53]. Stratification analysis by ethnicity showed a significant association between rs360719 and SLE in the European population (OR 1.33 per C allele, 95 % CI 1.11–1.61, P = 0.003) and a lesser effect in the same direction in the South American population (OR 1.18). A significant association was also identified between rs1946518 and SLE in the European population (OR 1.16 per A allele, 95 % CI 1.03–1.30, P = 0.017), although there was no association in the Asian or the combined European/Asian population. We also examined genome-wide association study (GWAS) data from an Asian subpopulation (Chinese) for the association between rs1946518 and SLE, but found no association (P = 0.83). The third SNP, rs187238, was not significantly associated with SLE in any of the populations examined. In summary, this study identified a significant association between SLE and two SNPs within the IL-18 gene promoter region (rs360719 and rs1946518) in a European population, but not in populations of Asian origin.