Objective: To analyse the relative role of HLA-DR antigens in the susceptibility to, and clinical expression of psoriatic arthritis (PsA).
Patients and methods: A retrospective cohort study of 120 patients with PsA who were assessed according to a standard protocol. Patients were classified in accordance with the predominant pattern observed in the last 5 years of disease evolution: polyarthritis (n = 33), oligoarthritis (n = 45), and spondylitis (n = 42). HLA-Cw gene typing was done by the polymerase chain reaction (PCR) sequence-specific oligonucleotide probes (PCR-SSOP) method, while HLA-DR and B27 typing were performed by serological methods. The distribution of HLA-DR and Cw antigens was also analysed in 50 patients with psoriasis alone. One hundred and seventy subjects from our general population served as controls.
Results: No definite association was found between HLA-DR alleles and the risk of psoriasis or PsA. HLA-DR4 was found to be under-represented in arthritic patients [probability (p) = 0.03]. HLA-DR7 showed association with oligoarthritis [odds ratio (OR) 6, 95% confidence interval (CI): 2-16, corrected probability (Pc) = 0.01], whereas HLA-DR8 appeared to be related to the risk of polyarthritis (OR 9.5, 95% CI: 2-42, Pc = 0.02). HLA-Cw*0602 conferred risk for psoriasis (Pc < 0.00001), but not for PsA. As expected, HLA-B27 appeared to be over-represented in patients with spondylitis (p = 0.03).
Conclusions: This is the first report that associates HLA-DR8 with psoriatic polyarthritis. Although HLA-DR antigens have a marginal role in PsA or psoriasis susceptibility, they may be relevant to the modulation of the clinical expression of PsA. These HLA data add support to the classification of PsA into three disease subsets.