EVIDENCE FOR GENETIC-HETEROGENEITY IN IBD .1. THE INTERLEUKIN-2 RECEPTOR ANTAGONIST IN THE PREDISPOSITION TO SUFFER FROM ULCERATIVE-COLITIS

Objective: To investigate a polymorphism within intron 2 of the interl eukin-1 receptor antagonist (IL-1ra) gene in a Dutch white population of patients with ulcerative colitis and Crohn's disease. Design: Genot ype and allele frequencies of the polymorphic region in the IL-1ra gen e were determined in 111 unrelated patients with ulcerative colitis, 9 2 patients with Crohn's disease, and 86 healthy controls. Methods: The polymorphic region of the IL-1ra gene was amplified by the polymerase chain reaction (PCR). The resultant products were analyzed by electro phoresis on 2% agarose gels and stained with ethidium bromide. Amplifi cation of the second exon of HLA-DRB1, HLA-DQA1, and HLA-DQB1 genes wa s performed by PCR, and Dot-blot analysis with biotin-labelled sequenc e-specific oligonucleotide probes was used for HLA typing. The standar d perinuclear antineutrophil cytoplasmic antibodies (pANCA) indirect i mmunofluorescence assay was performed according to the protocol descri bed by the First International Workshop on ANCA. Results: The frequenc y of allele 2 of the IL-1ra gene in ulcerative colitis (27.0%) and Cro hn's disease patients (25.5%) did not differ significantly from health y controls (23.8%). However, the estimate of the relative risk for car riers of allele 2 for ulcerative colitis [odds ratio (OR): 1.35, 95%-c onfidence interval (CI) from 0.73 to 2.49] was in agreement with a pre vious British study. The exact test for homogeneity of odds ratios pro vided no evidence for heterogeneity between both populations (P=0.35) and therefore confirmed the genetic association between ulcerative col itis and the IL-1ra allele 2 in a different population. Our data confi rm that, in ulcerative colitis, the presence of this allele is a genet ic marker for severity of the disease. A significant association was d emonstrated between the carriership of allele 2 of the IL-1ra gene and the trend over the three localizations in ulcerative colitis (P=0.023 ). The same approach for Crohn's disease when compared with healthy co ntrols did not provide evidence for a similar association. The meta-an alysis, based on the British data and our data, yielded: OR=1.06, 95%- Cl from 0.71 to 1.59, and P=0.767. No association between IL-1ra gene polymorphism, and pANCA and the HLA-DR2 allele was found in ulcerative colitis. Conclusion: The observations confirm that the allele 2 of th e IL-1ra gene is a marker for genetic susceptibility and severity in u lcerative colitis and contributes to the definition of the immunogenet ic heterogeneity of the disease.