Background: In the present study, we aimed to evaluate whether polymorphisms within the RORc2 gene are involved in the risk and severity of rheumatoid arthritis (RA).

Methods: 591 RA patients and 341 healthy individuals were examined for RORc2 gene polymorphisms. Serum retinoic acid receptor-related orphan receptor C (RORc) levels were measured by enzyme-linked immunosorbent assay (ELISA).

Results: The rs9826 A/G, rs12045886 T/C and rs9017 G/A RORc2 gene SNPs show no significant differences in the proportion of cases and control. Overall, rs9826 and rs9017 were in high linkage disequilibrium (LD) with D= 0.952 and r² = 0.874, except rs9826 and rs12045886; and rs12045886 and rs9017 in weak LD. The genotype-phenotype analysis showed a significant association between RORc2 rs9826 A/G and rs9017 G/A single nucleotide polymorphisms (SNPs) and median of C-reactive protein (CRP). Serum RORc levels was higher in RA patients with rs9826AA, rs12045886TT and -TC, and rs9017AA genotypes compared to healthy subjects with the same genotypes (p = 0.02, p = 0.04 and p = 0.01, respectively). Moreover, the median of RORc protein level was higher in RA patients with number of swollen joints bigger then 3 (p = 0.04) and with Health Assessment Questionnaires (HAQ) score bigger then 1.5 (0.049).

Conclusions: Current findings indicated that the RORc2 genetic polymorphism and the RORc2 protein level may be associated with severity of RA in the Polish population.