Systemic juvenile idiopathic arthritis (sJIA) is characterized by arthritis, spiking fever, evanescent erythematous rash, lymphadenopathy, hepatomegaly, splenomegaly and/or serositis, in combination with a substantial increase in the inflammatory parameters, such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, ferritin level and so on. This evidence concerns the gene CRP and systemic-onset juvenile idiopathic arthritis.