Because the clinical features of AOSD are similar to sJIA [7], and severe MAS in both sJIA or AOSD is treated with repeated GC pulse therapy together with high-dose oral GC, immunosuppressive drugs, TNF inhibitors, or tocilizumab [8–10], the experience with sJIA suggests that high serum ferritin and cytopenia due to MAS might be associated with poor treatment response to initial GC therapy also in AOSD. The gene discussed is TNF; the disease is adult-onset Still disease.