As with other forms of chronic inflammatory disease, autoimmune or otherwise, patients with juvenile idiopathic arthritis (JIA) may have only a limited family history of the JIA phenotype but a more evident family history of autoimmune disease in general (1). Based on this family history and reports of HLA associations in JIA, the generation of risk of developing the disease is likely based on complex trait genetics (for review, see ref. 2).

Our understanding of the genetic contribution has not progressed as quickly for JIA as compared with other autoimmune arthropathies, including rheumatoid arthritis and ankylosing spondylitis. A major hindrance to progress has been the change in nomenclature, from 3 subtypes in the familiar juvenile rheumatoid arthritis system to 7 subtypes in the JIA system (3). This new nomenclature, while now commonly used, has not been adopted by the American College of Rheumatology. Consistent with observations in the clinic, the JIA criteria provide increases in phenotype homogeneity that can be translated to a corresponding need for studies to consider 7 subtypes as separate entities. This splitting of the patient population into smaller groups provides challenges for recruiting patient cohorts of adequate size