Spondyloarthropathies are inflammatory joint diseases associated with the MHC class I molecule HLA-B27. The major histocompatibility complex ( MHC) is a large genomic region or Gene family found in most Vertebrates It is the most gene-dense region Serotype Disease associations Spondylarthropathies The relationship between HLA-B27 and many diseases has not yet been fully elucidated The term seronegative spondylarthropathy is used by medical practitioners because this set of conditions may mimic rheumatoid diseases such as rheumatoid arthritis, but serological (blood) tests are typically negative for rheumatoid factor (RhF). Rheumatoid arthritis ( RA) is a chronic systemic autoimmune disorder that causes the Immune system to attack the Joints, where Serology is the scientific study of blood serum. In practice the term usually refers to the Diagnostic identification of antibodies in the serum Rheumatoid factor (RF or RhF is an Autoantibody ( Antibody direct against an organism's own tissues most relevant in Rheumatoid arthritis.

Subgroups (with increased HLA-B27 frequency) are:

• ankylosing spondylitis Caucasians (AS, 92%),
• ankylosing spondylitis African-Americans (AS, 50%),
• reactive arthritis (Reiter's syndrome) (RS, 60-80%),
• enteropathic arthritis associated with inflammatory bowel disease (IBD, 60%),
• Psoriatic arthritis (60%),
• isolated acute anterior uveitis (AAU, iritis or iridocyclitis, 50%), and
• undifferentiated SpA (USpA, 20-25%). Ankylosing spondylitis ( AS; previously known as Bechterew's disease, Bechterew syndrome, Marie Strümpell disease and a form of Spondyloarthritis Ankylosing spondylitis ( AS; previously known as Bechterew's disease, Bechterew syndrome, Marie Strümpell disease and a form of Spondyloarthritis Reactive arthritis (ReA is an Autoimmune condition that develops in response to an infection in another part of the body Enteropathy refers to any Pathology of the Intestine. Types Specific types of enteropathy include Gluten-sensitive enteropathy In Medicine, inflammatory bowel disease ( IBD) is a group of inflammatory conditions of the large intestine and Small intestine Psoriatic arthritis (also arthritis psoriatica, arthropathic psoriasis or psoriatic arthropathy) is a type of Inflammatory Arthritis

Whipple disease and Behçet disease may also be linked to HLA-B27, as may undifferentiated spondyloarthropathy. Whipple's disease is a rare, Systemic infectious disease caused by the Bacterium Tropheryma whipplei. Behçet disease (Behçet's syndrome Morbus Behçet, silk road disease (bɛˈtʃɛt (enPR bĕCHĔT is a chronic condition due to disturbances in the body’s Immune