Are SMAD2/4/7 genetic variants associated with rheumatoid arthritis susceptibility and severity?

Objectives: SMADs play one of the key roles in the TGFβ signalling pathway. Therefore, through their involvement in the immune response as well as in the fibrosis process, these proteins appear to take on one of the essential functions in the pathogenesis of autoimmune connective tissue diseases such as RA. This study aimed to investigate the association of selected SNPs in SMAD2/4/7 with RA risk in the Caucasian population and disease course in RA patients.

Methods: The study was conducted on 647 patients with established RA and 496 unrelated healthy controls (HCs). All patients fulfilled the American College of Rheumatology Diagnostic classification criteria for RA (ACR 1987). The analysis has been conducted using TaqMan genotyping assay. Transcript-inferred pathogenicity score (TraP-score) has been evaluated by TrapScore. PredictSNP.2 has been used to predict the effect of amino acid substitutions.

Results: The present study revealed in SMAD4 a significantly higher frequency of AG rs12456284 (under codominant model OR=0.62 p=0.027 and overdominant model OR=0.59 p=0.016) and GA rs10502913 (under codominant model OR=0.65 p=0.050 and overdominant OR=0.64 p=0.033) genotypes in healthy subjects in comparison to RA patients. Additionally, very strong LD has been noted between these two genetic variants (D'=0.95 r2=0.90). Moreover, bioinformatic analysis classified rs12456284 as deleterious change with 94% prediction accuracy. SMAD2 rs1792666 and SMAD7 rs3736242 showed to have the highest association with disease course. SMAD4 rs10502913, SMAD7 rs3736242, and SMAD7 rs4464148 were associated with the concentration of creatinine.

Conclusions: Our results suggested that rs12456284 and rs10502913 in SMAD4 may have a potential protective effect against RA. Particularly, SMAD2 rs1792666 and SMAD7 rs3736242 seem to be significantly associated with diseases course in RA patients in the Caucasian population.