Juvenile idiopathic arthritis, or JIA, is the most common form of childhood arthritis. It appears to be an autoimmune disease, caused by antibodies attacking certain proteins in a person’s own tissue. But no ‘autoantigens’– the proteins triggering an immune attack — have been linked to JIA to date. Now, a new study offers evidence that a human protein called transthyretin (TTR) causes an autoimmune reaction in the joints of JIA patients.