Ankylosing spondylitis (AS) is the most important disease in the group of seronegative spondyloarthropathies, which includes ankylosing spondylitis (AS), reactive arthritis (ReA), reiter syndrome (RS), psoriatic arthritis (PsA), spondyloarthropathy associated with inflammatory bowel disease (IBD) and other undifferentiated spondyloarthropathies (USpA).