We recently reported an association of the SPP1 rs9138 and rs11439060 functional variants with the risk of rheumatoid arthritis (RA), the association being greater in anti-citrullinated protein autoantibody (ACPA)-negative patients. We hypothesised that SPP1 may contribute to the severity of joint destruction in RA, specifically in the ACPA-negative population.
Patients with RA in the ESPOIR cohort underwent genotyping for SPP1 rs9138 and rs11439060. Radiographs of the hands and feet were obtained at the first visit and at 1- and 2-year follow-up. Association analyses were performed by ACPA status. A replication study of the relevant subset of the Leiden Early Arthritis Clinic (EAC) cohort was performed.
In the ESPOIR cohort (652 patients), rs9138 was significantly associated with radiological progression of joint destruction at 2 years, the association being restricted to 358 ACPA-negative patients (p=0.034). In the replication study with the Leiden EAC cohort (273 ACPA-negative patients), rs4754, which is in complete linkage disequilibrium with rs9138, was significantly associated with joint damage progression in ACPA-negative patients at 2- and 7-year follow-up (p=0.019 and p=0.005, respectively). Combined analysis of the two cohorts revealed a 0.95-fold rate of joint destruction per year per minor allele (p=0.022).
The SPP1 rs9138 variant contributes to joint damage progression in ACPA-negative RA.