Abstract
The thalassaemias are genetic disorders in which there is decreased production of one or more of the globin chains of haemoglobin. They are commonly encountered among the Mediterranean people. Asians and Africans. In the α-thalassaemia (α-thal.) syndromes, α-globin chain synthesis is defective and as a result, Hb Bart's (γ<sub>4</sub>) or Hb H (<i>β</i><sub>4</sub>) may form. Four types have been defined: (a) α-thal.2 or the ‘silent carrier" state in which there are no symptoms and minimal or no anaemia and red cell changes, (b) α-thal. 1 in which there is mild hypochromic anaemia but no symptoms, (c) Haemoglobin H disease in which there is a moderate hypochromic, haemolytic anaemia, varying splenomegaly but a normal life expectancy and (d) Haemoglobin Bart's hydrops foetalis in which infants are stillborn with severe erythroblastic anaemia and the haemoglobin comprises Bart's and Portland-I (ζ<sub>2</sub> γ<sub>2</sub>)-Molecular hybridization and restriction endonuclease mapping have revealed that these disorders usually result from deletion of, respectively. 1,2, 3 or all 4 of the genes which code for the α-globin chain, α-thalassaemia may also arise from mechanisms other than gene deletion. Subjects homozygous for α-thal.2 are phenotypically similar to those with α-thal. 1 trait. The imbalance in globin chain synthesis results in precipitation of the excess <i>γ</i>- or <i>β</i>-chains which damages the red blood cell membrane leading to ineffective erythropoiesis or haemolytic anaemia. Subjects doubly heterozygous for α-thal. 1 and <i>β</i>-thal. are less anaemic. Certain α-globin chain variants e.g. Hb Constant Spring, Hb Icaria may behave genetically like α-thal.2. Clinically, α-thalassaemia is less severe in Africans and Hb Bart's hydrops foetalis is rare in Italians and Greeks. The reason for this will be discussed as well as the diagnosis, clinical features and management of these disorders. Pre-natal diagnosis is possible in Hb Bart's hydrops foetalis while the other 3 types of α-thalassaemia arc compatible with normal or near normal life.
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