BMP4 and juvenile idiopathic arthritis: We examined changes to the chondrocyte-like phenotype of FLS from three JIA subtypes: persistent, FLS isolated from synovial fluid of patients prior to extension to a polyarticular course or what we termed extended-to-be (ETB), and polyarticular in response to BMP4 inhibitors and methotrexate, the mainstay of JIA treatment.