Objective: HLA genes predict disease severity in psoriasis (HLA-Cw6) and rheumatoid arthritis (shared epitope (SE)), but the situation is unclear for psoriatic arthritis (PsA). The aim of this study was to determine the association of the HLA-Cw6 and HLA-DRB1 gene with disease severity in a large UK PsA cohort.
Methods: Genotyping of the HLA-Cw and HLA-DRB1 loci was undertaken in DNA samples from PsA patients (n=480). Stratification and regression analysis were used within the PsA cases to determine whether HLA-Cw6, HLA-DRB1 or the presence of the SE alleles predicted disease severity as measured by the health assessment questionnaire (HAQ) score, the total number of damaged or involved joints adjusted for disease duration and disease modifying antirheumatic treatments.
Results: HLA-Cw6 was found to be in linkage disequilibrium with HLA-DRB1*07 (r2 = 0.46). PsA patients who carried both HLA-Cw6 and HLA-DRB1*07 had fewer damaged or involved joints [41% fewer damaged (95% CI 23 to 55%, p=0.02) and 31% fewer involved joints (95% CI 16 to 44%, p<0.001)] compared to those who carried neither HLA-Cw6 nor HLA-DRB1*07 alleles. Those who carried either HLA-Cw6 or HLA-DRB1*07 alleles alone had no evidence of a reduction in joint involvement. The SE, HLA-DRB1*03 and HLA-DRB1*04 alleles did not predict severity using these outcome measures.
Conclusion: PsA patients carrying both HLA-Cw6 and HLA-DRB1*07 alleles have a less severe course of their arthritis. Thus suggests that a protective locus lies on a haplotype marked by these alleles. No association was detected with disease severity and SE status.
- psoriatic arthritis
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