Objectives:
Rheumatoid arthritis (RA) is the most common systemic inflammatory disease and is of unknown etiology. The altered balance between immunosuppressive and inflammatory T cell subpopulations exerts a huge impact on RA pathogenesis. The STAT3 protein regulates genes involved in the immune responses. It regulates maturation of T and B cells. Its abnormal activity is significantly associated with autoimmune diseases and cancer development. We aimed to evaluate the contribution of three potentially functional single nucleotide polymorphisms (SNPs) within the STAT3 gene to susceptibility and severity of RA in the Polish population.

Material and methods:
A total of 595 patients with RA and 330 healthy individuals were included in the study. DNA from patients and healthy subjects was obtained from peripheral blood using standard DNA isolating methods. The STAT3 rs1053005, rs1026916 and rs2293152 polymorphisms were genotyped using the TaqMan SNP genotyping assay. The accuracy of SNP genotyping was confirmed using direct DNA sequence analysis.

Results:
The distribution of STAT3 polymorphisms did not differ significantly between cases and controls. Our results revealed a tendency only, where rs1026916 AA genotype occurred more frequently in RA patients compared to healthy controls, in codominant (p = 0.09), dominant (p = 0.06) and recessive (p = 0.09) models. STAT3 rs2293152 polymorphism was associated with higher DAS28 (p = 0.014 codominant model; p = 0.003 dominant model), increased number of swollen joints (p = 0.02), higher VAS (p = 0.01) and higher HAQ score (p = 0.05).

Conclusions:
We did not observe a significant association between the three studied STAT3 genetic variants and increased susceptibility to or severity of RA. Only the STAT3 rs2293152 polymorphism was associated with parameters that indicate a more severe course of the disease. However, its distribution did not differ between RA and control groups. According to our observations these 3 studied STAT3 SNPs may not be used as risk factors for developing RA.