In thalassaemia the main defect is in hemoglobin polypeptide chain synthesis. Specific pairs of genes are responsible for synthesis of alpha, beta, gamma and delta chains of the hemoglobin molecules and deficiency of synthesis of one of these chains will lead to thalassaemia.
Beta-thalassaemia is most common type in which there is quantitative reduction in the rate of chain synthesis. When abnormal genes are inherited from both parents, thalassaemia major results. Heterozygous patients show mild anemia and termed thalassaemia minor.
In thalassaemia major, reduction in the rate of beta chain synthesis produces marked decrease in the amount of normal adult hemoglobin and compensatory increase in foetal hemoglobin. Homozygous alpha thalassaemia is incompatible with life and these infants are either stillborn or die shortly after birth.
In thalassaemia major, deficiency of beta-chain synthesis results in relative over production of alpha chains, which form insoluble inclusions in bone marrow erythroid precursors. These inclusion bearing red cells are detained in the spleen and are ultimately destroyed.
Thalassaemia major is usually manifested in the first year of life. There is pallor, retarded body growth and enlargement of the head. There is usually spelnomegalyand hepatomegaly. Intractable leg ulcers, intercurrent infections and gallstones may be seen in certain cases. Intense erythroid hyperplasia in the bone marrow results in expansion of the medullary cavities and attenuation of the cortex producing bony abnormalities, which may predispose fractures.
Thalassaemia minor patients lead normal lives, though a few show severe expression of the disease. These cases may present with mild jaundice and moderate splenomegaly.
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