HBA2 and thalassemia: The α–thalassaemia trait (α+–thalassaemia or −α/−α), is known to protect against severe malaria and like HBB-βS (Fig. 3A), is thus highly prevalent in malaria endemic areas, particularly the 3·7 kb alpha-globin gene (HBA1/HBA2) deletion in Africa (Fig. 3B).