<prompt> Which is seen more commonly in rheumatoid arthritis than in ankylosing spondylitis?An HLA-B27 haplotypeSacroiliitisIncreased incidence in menAutoantibody against IgG  <response>: An autoantibody against IgG usually IgM describes the rheumatoid factor RF, which is more likely to be seen in rheumatoid arthritis RA than in ankylosing spondylitis AS. Ankylosing spondylitis AS is a seronegative RF negative spondyloarthropathy that is either seen alone or in association with other disorders such as Reiter syndrome, psoriatic spondylitis, intestinal infections, and inflammatory bowel disease. AS most commonly involves young men between 15 and 30 years of age who are HLA-B27 positive 95 of cases. Approximately 20 of patients who are HLAB27 positive will develop AS or one of the other variants upon exposure to the environmental factors listed above. Characteristic features include an insidious onset of sacroiliitis, persistence for more than 3 months, and morning stiffness in the lower back that is relieved with exercise, as well as a diminished anterior flexion of the spine, which can be identified with the Schoeber test. The vertebral column is eventually involved with subsequent fusion of the vertebral column and production of the bamboo spine. Complications include 1 restricted chest movement with development of a restrictive type of lung disease; 2 iridocyclitis, with a potential for visual loss; and 3 aortic valve incompetence with regurgitation in a small percentage of cases. Indomethacin is the treatment of choice. 