The major hemoglobin in adults is hemoglobin A, a tetramer consisting of one pair of alpha globin chains and one pair of beta globin chains. In normal subjects, globin chain synthesis is very tightly controlled, such that the ratio of production of alpha to non-alpha chains is 1.00 ± 0.05. Thalassemia refers to a spectrum of diseases characterized by reduced or absent production of one or more globin chains, thus disrupting this closely regulated ratio. (See "Molecular pathology of the thalassemic syndromes".)
●The vast majority of adult patients with alpha or beta thalassemia minor are asymptomatic and may be diagnosed because of the presence of microcytic, hypochromic red cells, with or without minor degrees of anemia.
●Thalassemias of intermediate degrees of severity (thalassemia intermedia) are common throughout the world, and may be due to the presence of more than one hemoglobin mutation in the same patient (eg, sickle cell thalassemia, hemoglobin E/beta thalassemia) or to the presence of an abnormal hemoglobin with a reduced (ie, thalassemic) production rate (eg, hemoglobin Lepore, hemoglobin Constant Spring).
●Beta thalassemia major and alpha thalassemia major are on the other end of this spectrum. The former is associated with life-long transfusion-dependent anemia, while the latter is incompatible with extra-uterine life.
The clinical manifestations and diagnosis of the thalassemias will be reviewed here . The management of beta thalassemia is discussed separately. (See "Treatment of beta thalassemia" and "Efficacy of hematopoietic cell transplantation in beta thalassemia major".)