Among the rarer causes of arthritis were toxic synovitis in 12 patients, CNO in 12 patients, Blau syndrome in two patients, and type 1 interferonopathies in two patients (one with Aicardi–Goutières syndrome and the other with STING-associated vasculopathy with onset in infancy). Here, STING1 is linked to type 1 interferonopathy.