Early comparative studies of parasite rates and density in children with the sickle cell trait and controls, together with the discovery of the relative rarity of Hb S in patients with severe malaria in Africa, provided convincing evidence that the sickle cell trait provides at least some degree of protection against severe malarial infection.7 More recent studies in East Africa suggest that the major impact of Hb S seems to be on protection against either death or severe disease, that is profound anemia or cerebral malaria, while having less effect on infection rates per se. Here, GSTM1 is linked to anemia (phenotype).