Association of interleukin-4 gene polymorphism and rheumatoid arthritis in Egyptian patients

Introduction
Rheumatoid arthritis (RA) is a progressive disease characterized by chronic joint inflammation and subsequent structural damage. Interleukin (IL)-4-590 promoter polymorphism (rs2243250), a C-to-T base substitution, has been suggested to be associated with RA and has become of great interest to be investigated.
Aim
The aim of this study was to find the relationship between IL-4-590 promoter polymorphism and RA in Egyptians, and also to study the relationship of this gene with clinical and laboratory features of the disease.
Patients and methods
This study was carried on 180 subjects divided into two groups. The first group included 120 patients with RA and the second group were 60 apparently healthy individuals as controls. Genomic DNA was extracted from blood leukocytes of both groups and genotyped by PCR for amplification of IL-4 gene followed by restriction fragment length polymorphism.
Results
IL-4-590 (TT) genotype was significantly more frequent in patients with RA than controls (10 vs. 1.70%, =0.027, odd ratio (OR)=7.543 and Confidence interval (CI)=0.947–60.049). IL-4-590 (CT) genotype showed no significant difference between patients with RA and controls (31.70 vs. 25%, =0.195 OR=1.592 and CI=0.786–3.228), whereas IL-4-590 (CC) genotype was significantly less frequent in patients with RA than controls (58.30 vs. 73.30%, =0.048). Regarding the distribution of different alleles, the frequency of T allele was significantly more in patients with RA than controls (<0.01). In patients with RA, there were significant differences in some clinical and laboratory parameters of RA disease between different IL-4-590 genotypes (e.g. number of tender and swollen joints, duration of morning stiffness, disease activity score 28, serum rheumatoid factor, serum C-reactive protein, and serum anticyclic citrullinated peptide levels), all were higher in TT genotype, which means patients with RA with TT genotype may have more aggressive course of the disease.
Conclusion
The T allele and the TT genotype at position −590 of IL-4 gene may be related to development of RA in Egyptians and may be associated with the disease activity.