Of note, over the course, our patient had fevers, splenomegaly, hemoglobin (Hb) <9 g/dL, platelets (Plts) < 100,000/μL, hypofibrinogenemia, hemophagocytosis on biopsy, absent NK cell activity, >500 μg/L serum ferritin level, and >2400 U/mL soluble CD25 (sIL-2 receptor) suggestive of primary HLH. The gene discussed is GSTM1; the disease is Splenomegaly.