• HLA
• spondyloarthropathy
• ankylosing spondylitis
• transmission disequilibrium test

Ankylosing spondylitis (AS) was first described as a pathological entity in the 1690s by a medical student who found, in a French graveyard, a skeleton in which the ilium, sacrum, and 15 lowest vertebrae were completely fused.¹ Several similar descriptions were reported during the 18th century. A number of isolated clinical descriptions were reported throughout the 19th century, culminating in the detailed classical descriptions by Bechterew, Strümpell, and Marie in the late 19th century. By the mid-1930s, the classical pathological and radiographic features of AS had been described. Nevertheless, rheumatologists, particularly in America, tended to view AS a variant of rheumatoid arthritis (RA) and referred to the disorder as “rheumatoid spondylitis”.² This view was partly based on the similarity between the two diseases of the early inflammatory histology in the peripheral joints and in the cervical spine.³ It even prevailed for several decades after the discovery of rheumatoid factor and the observation that patients with “rheumatoid spondylitis” were almost uniformly seronegative.⁴ Other entities with both axial and peripheral arthritis, including Reiter's …