GSTM1 and anemia (phenotype): Indeed, anaemia (Hb < 11 g/dl blood) was more often found in patients with sickle cell phenotypes HbAS, HbSC and HbSS, than in HbAA (11.28 ± 2.10 g/L) and was more severe for HbSS phenotypes (6.51 ± 2.24 g/L) (Mann Whitney test, p < 0.001).