Extremely high total IL-18 was first observed in Adult-Onset Still’s Disease (AOSD) in 2001 [5], and soon thereafter in Systemic Juvenile Idiopathic Arthritis (SJIA) where the highest levels were observed in patients with Macrophage Activation Syndrome (MAS) [6]. The gene discussed is IL18; the disease is systemic-onset juvenile idiopathic arthritis.