He was switched to the anti-IL-6R monoclonal antibody tocilizumab aged 5 years (162 mg subcutaneously [8.1 mg/kg] every 3 weeks based on a modified Still’s disease dosing protocol for children) which resulted in an immediate, complete, and sustained clinical and serological resolution of systemic inflammation (cessation of fevers and complete normalization of inflammatory markers), and complete resolution of anemia (Supplementary Figure 1A and Supplementary Table 2). Here, IL6R is linked to systemic-onset juvenile idiopathic arthritis.