GSTM1 and beta thalassemia: The mean age at sickle cell anemia diagnosis was 21 months (SD = 20) and 55% (n = 15) had sickle cell anemia with high HbF levels, 26% (n = 7) had HbSS disease, 15% (n = 4) had sickle beta thalassemia, and 3% (n = 1) had HbSC based on hemoglobin electrophoresis prior to starting HU.The mean Hb, WBC, neutrophil, and platelet counts before starting HU were 8.7 g/dl (SD = 1), 11.5 × 109/L (SD = 3.3), 5.5 × 109/L (SD = 6.8) and 471 × 109/L (SD = 193), respectively.