Absence of Messenger RNA for Beta Globin Chain in β°-Thalassaemia

Abstract

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 (α₂β₂)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 (α₂γ₂), (‘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 HbA₂, 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.