The biochemical defect in thalassemia is thought to consist of a diminished capacity of the erythropoietic cells to synthesize one of the polypeptide chains of hemoglobin. Thus, the common variants of this disease have been designated as αand β-thalassemia. β-Thalassemia is usually associated with a twofold increased proportion of hemoglobin A2 and a slight elevation of fetal hemoglobin (hemoglobin F) in hemolysates, but many families have been described in which the hemoglobin abnormality is characterized by low or normal levels of hemoglobin A2 and high concentrations of hemoglobin F (10% to 30%). This variant of the disease has been designated as F-thalassemia or βδ-thalassemia since the synthesis of both β- and δ-chains appears to be impaired. The distribution of hemoglobin F in the erythrocyte population is uneven in contrast to the hereditary persistence of fetal hemoglobin (HPFH) in which all erythrocytes appear to have the same concentration of hemoglobin
Zelkowitz L, Torres C, Bhoopalam N, Yakulis VJ, Heller P. Double Heterozygous ßd-Thalassemia in Negroes. Arch Intern Med. 1972;129(6):975–979. doi:10.1001/archinte.1972.00320060123017
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