THE β-thalassaemias are a heterogeneous group of hereditary haematological disorders in which there is absent or decreased synthesis of the β globin chain of normal human adult haemoglobin, HbA (α 2β2)1. When β chain synthesis is totally absent, the condition can be referred to as β°-thalassaemia, in contrast to β+-thalassaemia in which some β chain synthesis occurs. The genetics and manifestations of β°-thalassaemia are rather varied. In the heterozygote, there may be either increased levels of the minor haemoglobin, HbA2 (α2δ2) ('A2-thalassaemia'), or normal levels of HbA2 with elevated levels of foetal haemoglobin, HbF (α2γ 2), ('δβ-thalassaemia' or 'F-thalassaemia'). Homozygous β°-thalassaemia of the A2 variety is clinically severe, and has been described mainly in the Ferrara region of northen Italy and in Thailand, although it is found sporadically in other racial groups; the red cells of these individuals contain mainly HbF with variable amounts of HbA 2, but no HbA. Homozygous δβ-thalassaemia is extremely rare, having been described in only eight individuals from four different families1; it is associated with only mild symptoms; the red cells of these individuals contain 100% HbF, and there is total absence of both HbA and HbA2.
ASJC Scopus subject areas