Objective: To investigate differences between HLA-B27(-) and HLA-B27(+) patients with ankylosing spondylitis (AS).
Methods: A total of 1080 patients with AS responded to a questionnaire containing 30 questions; 945 (87.5%) knew their HLA-B27 status, 10% of them being B27(-).
Results: The average age at disease onset was 27.7 years in B27(-) and 24.8 years in B27(+) AS (P < 0.01). The average age at diagnosis was 39.1 and 33.2 years and the average diagnosis delay 11.4 and 8.5 years, respectively. The distribution in age at disease onset was significantly wider in B27(-) (standard deviation 10.0 years) than in B27(+) AS (8.3 years). The percentages with childhood (age < 16 years) disease onset did not differ significantly (7.6% vs. 6.2%, respectively), whereas the percentage of late onset (age > 40 years) was significantly greater among B27(-) (13%) than among B27(+) (5%) patients with AS. There is a difference in average age at disease onset between male (25.7 years) and female (24.2 years) AS patients, and no difference between patients with primary AS and AS associated with psoriasis, inflammatory bowel disease, or reactive arthritis. Acute anterior uveitis was significantly less frequent in B27(-) (26%) than in B27(+) (41%) patients with AS. CONCLUSIONS. This study of a much larger number of B27(-) AS patients than have been studied previously confirms earlier reports indicating a significantly older average age at disease onset and a less frequent prevalence of acute anterior uveitis in B27(-) than in B27(+) AS. The frequency of late disease onset (after 40 years of age) is significantly higher in B27(-) AS. We provide the first report on significant differences in the distribution curves for the age at disease onset and for the age at diagnosis between B27(-)and B27(+) patients with AS. The average delay between the first spondyloarthritic symptoms and the diagnosis is significantly longer in B27(-) than in B27(+) AS. The frequency of juvenile disease onset (before age 16 years) is nearly the same, irrespective of the B27 status.