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The impact of human leukocyte antigen (HLA)-B27 on the age at disease onset in patients with ankylosing spondylitis (AS) has consistently been shown in several cohorts.1–⇓⇓4 A potential gender difference with respect to age at symptom onset remains, however, controversial5–⇓⇓8 as the distribution of HLA-B27 within these populations is not known in all studies. While no sex differences with regard to disease onset were found in several cohorts from Europe,5 ,6 a later disease onset in men was reported in a North American investigation.7 We analysed this issue within the ongoing Swiss Clinical Quality Management cohort of patients with axial spondyloarthritis (axSpA).9 Ethics approval was given by the regional review boards. Informed consent was obtained from all patients.
From a total of 3046 spondyloarthritis patients recruited until June 2014, 2098 (1294 men, 804 women) were included in this analysis, as they fulfilled the Assessment in SpondyloArthritis International Society (ASAS) classification criteria, with the following minor modifications, as the cohort was initiated before …