Juvenile Idiopathic Arthritis (JIA) is a broad disease which comprises a set of clinically heterogeneous chronic arthropathies of unknown aetiology which develop before the age of 16. It was previously called Juvenile Chronic Arthritis in Europe and Juvenile Rheumatoid Arthritis in the USA. Several subtypes of Juvenile Idiopathic Arthritis have been defined, including Systemic Juvenile Arthritis, Oligoarthritis, Polyarthritis, Enthesitis-related arthritis and Psoriatic arthritis. Each of these conditions has distinct methods of presentation and clinical symptoms and in some cases, different genetic background.
Systemic Juvenile Arthritis is a form of JIA which affects more than 5 joints and is typically accompanied by or preceded by fever and rash. Oligoarthritis affects 4 or fewer joints during the first 6 months of disease. Polyarthritis affects 5 or more joints. Patients may be rheumatoid factor pos or neg. Enthesitis related arthritis most commonly affects sites such as cranial insertion points and the Achilles tendon. Psoriatic arthritis is diagnosed by the presence of arthritis and a psoriatic rash as well as swelling of one or more fingers.
Both genetics and non genetic factors are believed to play a role in susceptibility to JIA. HLA class I and II genes are the most commonly linked genes in association studies, though non HLA genes have also been implicated. Systemic Juvenile Arthritis has been associated with a single nucleotide polymorphism in the regulatory region of the interleukin-6 gene. Oligoarthritis has been associated most frequently with HLA-A2, DRB1*08 and DRB1*11. HLA-DRB1*04 and HLA-DRB1*07 are thought to be protective for Oligoarthritis. Polyarthritis is associated in most studies with HLA-DRB1*04. Enthesitis related arthritis is associated with HLA-B*27 and Psoriatic arthritis is associated with HLA-C*06:02 and with polymorphisms in the IL-23 receptor gene.
There is no cure for JIA and treatment is based mainly on early diagnosis and a combination of drug and physical therapy aimed at relieving symptoms. In this regard genetic testing is clinically relevant as a contributor to early diagnosis.
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