s-JIA/AOSD patients with an IL-6–dominant pattern (s-JIA:IL-18/IL-6 <1000, AOSD IL-18/IL-6 <5000) had more severe joint disease, whereas those with an IL-18–dominant pattern (s-JIA:IL-18/IL-6 >1000) had a more severe systemic disease and developed MAS (20, 26). The gene discussed is IL18; the disease is macrophage activation syndrome.