The histocompatibility antigen W27 has been found to have a high incidence in ankylosing spondylitis (96%), Reiter syndrome (74%), and other forms of arthritis that may involve the axial skeleton.
In patients with Reiter syndrome, there was no correlation between the presence of W27 antigen and the extent or duration of the symptoms. Sacroiliitis was predominantly found in those patients with W27 antigen in all the axial arthropathies. Tissue-typing techniques may be of value in detecting early or atypical disease.
(JAMA 231:268-270, 1975)
Mills DM, Arai Y, Gupta RC. HL-A Antigens and Sacroiliitis. JAMA. 1975;231(3):268-270. doi:10.1001/jama.1975.03240150030017