The diagnosis of HLH is established by fulfilling at least five of the eight HLH-2004 diagnostic criteria: fever, splenomegaly, bicytopenia, hypertriglyceridemia and/or hypofibrinogenemia, hemophagocytosis, hyperferritinemia (>500 mg/L), elevated soluble CD25 (>2400 U/mL), and decreased NK cell activity [1]. The gene discussed is IL2RA; the disease is hemophagocytic syndrome.