Variation at interleukin-6 receptor gene is associated to joint damage in rheumatoid arthritis.

Journal Article; Multicenter Study; Research Support, Non-U.S. Gov't;INTRODUCTION Interleukin-6 (IL-6) cytokine signaling is key in Rheumatoid Arthritis (RA) pathophysiology. Blocking IL-6 receptor (IL6R) has proven to be a highly effective treatment to prevent joint damage. This study was performed to investigate the association between the genetic variation at IL6R gene and the severity of joint damage in RA. METHODS IL6R gene tagging SNPs (n = 5) were genotyped in a discovery group of 527 RA patients from 5 different university hospitals from Spain. For each marker, a linear regression analysis was performed using an additive model and adjusting for the years of evolution of the disease, autoantibody status, gender and age. Haplotypes combining the SNPs were also estimated and tested for association with the level of joint destruction. Using an independent cohort of 705 RA patients from 6 university hospitals we performed a validation study of the SNPs associated in the discovery phase. RESULTS In the discovery group we found a highly significant association between IL6R SNP rs4845618 and the level of joint destruction in RA (P = 0.0058, P corrected = 0.026), and a moderate association with SNP rs4453032 (P = 0.02, P corrected = 0.05). The resulting haplotype from both SNPs was more significantly associated with joint damage (P = 0.0037, P corrected = 0.011). Using the validation cohort, we replicated the association between the two IL-6R SNPs with the degree of joint destruction in RA (P = 0.007 and P = 0.04, meta-analysis P = 0.00011 and P = 0.0021, respectively), and the haplotype association (P = 0.0058, meta-analysis P = 6.64 e-5). CONCLUSIONS Genetic variation at IL6R gene is associated with joint damage in RA.This study was funded by the Spanish Ministry of Economy and Competitiveness (grant numbers PSE-010000-2006-6 and IPT-010000-2010-36).Ye

Identification of IRX1 as a Risk Locus for Rheumatoid Factor Positivity in Rheumatoid Arthritis in a Genome-Wide Association Study.

Rheumatoid factor (RF) is a well-established diagnostic and prognostic biomarker in rheumatoid arthritis (RA). However, ∼20% of RA patients are negative for this anti-IgG antibody. To date, only variation at the HLA-DRB1 gene has been associated with the presence of RF. This study was undertaken to identify additional genetic variants associated with RF positivity. A genome-wide association study (GWAS) for RF positivity was performed using an Illumina Quad610 genotyping platform. A total of 937 RF-positive and 323 RF-negative RA patients were genotyped for >550,000 single-nucleotide polymorphisms (SNPs). Association testing was performed using an allelic chi-square test implemented in Plink software. An independent cohort of 472 RF-positive and 190 RF-negative RA patients was used to validate the most significant findings. In the discovery stage, a SNP in the IRX1 locus on chromosome 5p15.3 (SNP rs1502644) showed a genome-wide significant association with RF positivity (P = 4.13 × 10(-8) , odds ratio [OR] 0.37 [95% confidence interval (95% CI) 0.26-0.53]). In the validation stage, the association of IRX1 with RF was replicated in an independent group of RA patients (P = 0.034, OR 0.58 [95% CI 0.35-0.97] and combined P = 1.14 × 10(-8) , OR 0.43 [95% CI 0.32-0.58]). To our knowledge, this is the first GWAS of RF positivity in RA. Variation at the IRX1 locus on chromosome 5p15.3 is associated with the presence of RF. Our findings indicate that IRX1 and HLA-DRB1 are the strongest genetic factors for RF production in RA

Additional file 1: Table S1. of Variation at interleukin-6 receptor gene is associated to joint damage in rheumatoid arthritis

Presenting the association of IL6R locus SNPs with joint damage in the discovery stage under alternative genetic models, Table S2. Presenting the association of IL6R locus SNPs with joint damage in the discovery stage according to ACPA or RF status, and Table S3. Presenting the enhancer histone marks associated with the IL6R rs4845618 SNP identified in 111 reference epigenomes from the Epigenome Roadmap Project