HLA - B27 is positive in 90-95% of cases. Uveitis occurs in 40% of patients (Harrison 17th /e 2111) Ankylosing spondylitis is more common in males. Radiological changes do not occur before clinical symptoms :-"One of the drawback to radiography is that the disease may be present for 7-10 years before changes are significance enough to be visualized with conventional X-rays. Thus patients presenting with early - stage ankylosing spondylitis will most likely have a negative X-ray". — Medifocus Guidebook on ankylosing spondylitis