GSTM1 and hereditary spherocytosis: HLH: hemophagocytic lymphohistiocytosis; PVB19: parvovirus B19; HS: hereditary spherocytosis; Hb: hemoglobin; F: female; PLT: platelets; sIL2-R: soluble IL-2 receptor; N.D.: not determined; WBC: white blood cells.