Proinflammatory cytokines in SJIA-related MAS are excessively produced, including IFN-γ, TNF, IL-1, IL-2, IL-6, IL-10, IL-12, IL-18, and granulocyte macrophage-colony stimulating factor (GM-CSF). The gene discussed is CSF2; the disease is systemic-onset juvenile idiopathic arthritis.