Interleukin-1 receptor antagonist VNTR-polymorphism in inflammatory bowel disease

Both genetic and environmental factors have been implicated in the etiology of inflammatory bowel diseases (IBD) i.e., Crohn's disease (CD) and ulcerative colitis (UC). Polymorphisms in cytokine genes are likely to influence an individual's predisposition to IBD. In intron 2 of the interleukin-1 receptor antagonist (IL-1ra) gene, a variable number of an 86-bp tandem repeat (VNTR) polymorphism leads to the existence of five different alleles. In order to analyze the association between certain IL-1ra VNTR-alleles and IBD, we investigated the IL-1ra genotype and allele frequencies in 342 unrelated IBD patients and in 401 healthy control individuals. CD patients were also genotyped for the three main associated variants in the NOD2/CARD15 gene. In the IBD group, a significant decrease in the frequency of IL-1ra allele 1 (P=0.048) compared to controls was observed. The frequency of IL-1ra genotype 1/1 was significantly lower in the IBD population vs the control group (P=0.018). Analysis of the CD population without NOD2 homozygotes and compound heterozygotes revealed a more significant decrease in IL-1ra genotype 1/1 compared to controls (P=0.038). These results support the hypothesis that the IL-1ra VNTR-polymorphism could be among the genetic factors that are of importance in IBD susceptibility.