In clinical practice, the disease activity of JIA is measured with a combination of patient- and physician-reported outcomes, clinical examination and laboratory markers, which include the patient/parent global assessment of well-being visual analogue score (PtGA), Childhood Health Assessment Questionnaire (CHAQ), physician’s global assessment of disease activity visual analogue score (PhGA), active joint count (AJC), limited joint count (LJC), ESR and/or CRP, and the composite outcome Juvenile Arthritis Disease Activity Score (JADAS) [5]. The gene discussed is CRP; the disease is juvenile idiopathic arthritis.