Background ACPA-negative and ACPA-positive Rheumatoid Arthritis (RA) are increasingly regarded as separate clinical entities. Although ACPA-negative patients have a less severe disease course at group level, considerable inter-individual differences in the amount of joint destruction occur.
Objectives As no studies focusing on genetic risk factors underlying the differences in joint destruction in ACPA-negative patients have been performed thus far, we performed the present study.
Methods A Genome-Wide Association Study was performed using Illumina Human CytoSNP-12v2 in relation to radiographic joint destruction in 276 ACPA-negative early RA-patients included in the Leiden Early Arthritis Clinic (EAC). According to the Bonferroni correction on the number of tested SNPs, the threshold for genome wide significance was p<2x10-7. Subsequently, the significant SNPs were evaluated for association with the progression of radiographic joint destruction in 253 ACPA-negative early RA-patients included in the BARFOT-study. As 11 uncorrelated SNPs were tested, the Bonferroni threshold for significance was 0.0045. In all patients, joint destruction was measured by Sharp-van der Heijde Score with good reproducibility.
Results 33 SNPs associated significantly to the severity of joint damage (p<2x10-7) in phase-1. In phase-2, two SNPs showed a trend towards a significant association with joint damage, rs2833522 (p=0.0049) and rs17763915 (p=0.047). A combined analysis of both the Leiden and BARFOT datasets of rs2833522 showed a highly significant association with joint destruction (p=3.57x10-9), the presence of the minor allele associated with more severe damage.
Conclusions Rs2833522 might be associated with the severity of joint damage in ACPA-negative RA. Larger, longitudinal, studies are needed for confirmation.
Acknowledgements This work is supported by the Masterswitch project and BtheCure project. The work of Annette van der Helm-van Mil is supported by the Dutch organization for scientific research (ZonMW). The Dutch Arthritis Foundation (Reumafonds) provided financial support for the genotyping.
Disclosure of Interest None Declared