The basis of juvenile idiopathic arthritis
Juvenile idiopathic arthritis (JIA) shares the feature of being a potentially disabling, chronic inflammation of the joint with rheumatoid arthritis (RA); however, it is a far more heterogeneous disease with different subtypes that are defined based on the number of joints affected from onset to 6 months, as well as the extra-articular involvement, according to the International League of Associations for Rheumatology (ILAR) classification [1]. The subtypes include oligoarthritis (<5 joints affected), polyarthritis (≥5 joints affected), systemic JIA (arthritis, fever, rash, and inflammation of other organs), enthesitis-related arthritis, and psoriatic arthritis (PsA). JIA is an example for a multi-faceted disease with certain genetic associations conferring overall susceptibility to the disease [2]. A variety of environmental triggers challenging a genetically susceptible person may ultimately cause the disease.