PRF1 and hemophagocytic syndrome: The diagnostic guidelines of HLH include a molecular diagnosis consistent with mutations in the perforin gene (PRF1), fever, splenomegaly, cytopenia, hypertriglyceridemia and/or hypofibrinogenemia (fibrinogen ≤150 mg/dL), hemophagocytosis in BM, spleen, or lymph nodes, low or absent NK-cell activity, ferritin ≥500 μg/L, and elevated serum soluble CD25 that is soluble interleukin 2 (sIL2r) receptor [11, 13].