HBA2 and thalassemia: In addition, α+–thalassaemia is independently associated with favourable SCD clinical outcomes in Africa, whereby an increase in the frequency of the common 3·7 kb alpha-globin gene (HBA1/HBA2) deletion leads to low intracellular Hb concentration, reduced haemolytic anaemia, and ultimately delayed onset of clinical manifestations and improved survival (53,59,60).