Definition:

Ankylosing spondylitis (AS), formerly also known as Bechterew's disease, is a rheumatic disease of the axial skeleton that mainly affects the spine and the sacroiliac joint in the pelvis. AS is one of a group of inflammatory diseases, called spondyloarthritides, which share features. This disease is characterized by erosion, sclerosis, and ossification, which may result in complete fusion and rigidity of the spine. Regarding extra-articular manifestations, the most frequent is anterior uveitis. The major functional losses occur during the first 10 years of disease. It usually begins in the second or third decade of life, preferentially in HLA-B27-positive Caucasian males. Its etiology and pathogenesis are not completely understood, but the most prevalent hypothesis involves immune mediation as its major mechanism, including several cytokines. To date, more than 40 genetic variants have been identified that influence the risk of developing AS, including HLA alleles such as HLA-B27.