GSTM1 and sickle cell disease and related diseases: The mean Hb for those with sickle cell disorders 9.1 ± 2.4 g/dL, was significantly lower than normal (Hb:11.2 ± 1.6 g/dL, sickle cell trait:10.9 ± 1.5 g/dL and other Hb disorders: 11.4 ± 1.7 g/dL).