To investigate the associations of the HLA-DRB1 rheumatoid arthritis shared epitope (SE) with clinical characteristics and radiological outcome in patients with psoriatic arthritis (PsA).
One hundred fifty-eight patients with well documented PsA and 250 controls were typed for HLA-DRB1 alleles including the SE by polymerase chain reaction. Clinical data collected on the patient group included disease subset, swollen and tender joint counts, the psoriasis area severity index (PASI), and the presence of radiological erosions. Clinical and radiological associations with HLA-DRB1 and SE alleles were determined.
There was an increased frequency of HLA-DR7 (41 vs 25%; puncorr = 0.001, OR 2.02, pcorr = 0.01) and a decreased frequency of HLA-DR2 (19 vs 28%; puncorr = 0.03, OR 0.59, pcorr = 0.3) in the patient population compared with controls. There was no significant difference in the frequency of HLA-DR1 and HLA-DR4 between patient and control populations. There was no significant difference in the prevalence of SE alleles between the patient and control populations (48 vs 54%). There was no increase in the prevalence of the SE in the polyarthritis subgroup, but there was a marginal decrease in those who remained in the oligoarthritis subgroup. There were no differences with respect to sex, age of onset of disease, family history, Health Assessment Questionnaire score, joint score, skin score, or nail score between those patients who were SE positive and those who were SE negative. However, significantly more patients who were SE positive developed radiological erosions (60 vs 43%; p = 0.03, OR 2.11).
Overall, the prevalence of the SE in patients with PsA did not differ from our control population. However, it was overrepresented in those who developed radiological erosions. It is possible that the SE does have a role in the clinical severity of PsA.