Systemic juvenile idiopathic arthritis (s-JIA) was suspected in P6 at the age of 3.6 years based on the presence of fever, rash, lymphadenectasis, hepatosplenomegaly, polyarthritis and a positive (1:100) titer of antinuclear antibody (ANA). Here, BTG3 is linked to systemic-onset juvenile idiopathic arthritis.