Introduction. Ankylosing spondylitis (AS) affects only a minor portion of HLA B27+ individuals. Susceptibility to AS is determined by interactions of several genes and answers best to an oligogenic epistatic model. Aim. The aim was to find out if the gene encoding for IL-1 receptor antagonist (IL-1RN) has a role in the susceptibility to AS. Methods. Two hundred and fifteen patients with AS, as well as members of 38 families, were investigated and compared with 170 healthy controls. Patients were characterized by using the Bath system. Alleles of IL-1RN gene were detected by PCR. Results. IL-1RN*2 allele frequency (24.7% vs. 15.0%; p<0.001; OR=1.9) and carriage rate (39.1% vs. 25.3%; p=0.016; OR=1.7) were significantly higher in comparison with controls. Similarly, allele 2 frequency was increased in the mixed group of patients and their family members (30% vs. 15%; p<0.001; OR=2.4). Carriage rate for allele 2 was markedly increased in the subgroup of patients with more severe disease assessed collectively by BAS questionnaires (38.1% vs. 21.8%; p=0.0046; OR=2.2). Significant differences were found mainly for BASFI (Bath Ankylosing Spondylitis Functional Index), BASMI (Bath Ankylosing Spondylitis Metrology Index) and BASRI (Bath Ankylosing Spondylitis Radiology Index) as well as for patients with uveitis and with tendinitis. Conclusion. The results of the study suggest rather additive than purely predisposing role of this allele in the development of ankylosing spondylitis influencing clinical form and the severity of the disease.

        Key words: ankylosing spondylitis, polymorphism of IL-1RN gene, IL-1RN*2 allele