Hyperhemolysis syndrome (HHS), is a rare hemolytic transfusion reaction characterized by a lower hemoglobin (Hb) than pre-transfusion, fever and pain, decreased reticulocyte count, hyperbilirubinemia, raised lactate dehydrogenase, and hemoglobinuria generally occurring within two weeks of last transfusion.3,4 The cause of the precipitous drop in Hb remains a debate. The gene discussed is GSTM1; the disease is Hyperbilirubinemia.