Interleukin-1 receptor antagonist gene polymorphism in patients with rheumatoid arthritis in India

Interleukin-1 receptor antagonist (IL-1Ra) is a naturally occurring anti-inflammatory molecule that blocks action of IL-1. Polymorphism in IL-1Ra gene intron 2 results in differences in production of IL-1Ra. These polymorphisms are reportedly associated with autoimmune disease susceptibility in different studies. However, such data are lacking from India. We undertook this study to examine the IL-1Ra polymorphism as a susceptibility marker in patients with rheumatoid arthritis (RA).

DNA samples from 107 patients with RA and 111 healthy controls were used to study genotypes of the IL-1RA gene by PCR. Allelic frequencies and carriage rates were calculated and compared in both the groups.

Among the 107 patients with RA, 93 were females and 75 per cent were seropositive for rheumatoid factor. The frequencies of IL-1RA alleles in controls were as follows: Allele 1 (IL- 1RN*1) was 83.33 per cent, IL-1RA allele 2 (IL-1RN*2) was 16.21 per cent and allele 3 (0.46%). In RA patients the allele frequencies were 84.11 per cent for IL-1RN*1, 14.95 per cent for IL- 1RN*2, 0.47 per cent each for IL-1RN*3 and IL-1RN*4. There was no difference in frequency of different alleles between the two groups. However, homozygosity for allele 2 was more frequent in controls (9.91%) as compared to patients (4.67%).

Our findings indicated that IL-1RA polymorphism was not a susceptibility marker in RA nor did it show any association with seropositivity, Sjögren's syndrome or subcutaneous nodules. Further studies with large sample need to be done to confirm these findings.