Clinical and genetic characteristics of ankylosing spondylitis patients with peripheral arthritis at disease onset.

Objectives: The aim of this study was to assess the clinical and genetic characteristics associated with the presence of peripheral arthritis (PA) at disease onset in patients with ankylosing spondylitis (AS).

Methods: 456 Spanish AS patients, diagnosed according to the modified New York Criteria, who had at least ten years of follow-up since initial disease onset were selected from the National Spondyloarthropathies Registry (REGISPONSER). 18.9% of AS patients initially presented PA. Clinical variables and 384 single nucleotide polymorphisms (SNPs) distributed in 190 genes were analysed. SNP genotyping was performed using the Illumina GoldenGate genotyping platform. Association tests for allele frequencies and for categorical clinical variables were performed by the χ2 test and with the unpaired t-test for continuous variables. p-values of <0.05 were considered statistically significant.

Results: AS patients with PA showed an earlier age of disease onset (p=0.021), longer disease duration (p=0.020) and longer duration of AS symptoms from onset (p=0.034) than AS patients without PA. We found significant associations with the presence of PA at disease onset in 14 SNPs located in 10 genes: HLA-DQB2 (rs2857210 and rs9276615), HLA-DOB (rs2857151, rs2621332 and rs1383261), JAK2 (rs7857730), IL-23R (rs11209008 and rs10489630), CYP1B1 (rs1056836), NELL1 (rs8176786), KL (rs564481), and MEFV (rs224204), IL-2RB (rs743777) and IL-1A (rs1800587).

Conclusions: Both clinical and genetic factors are associated with the presence of PA at disease onset in Spanish AS patients. The results suggest that this subset of AS patients with PA at disease onset might have differentiation factors involved in disease pathogenesis.