- Thalassemias are a set of inherited disorders of hemoglobin synthesis that result in anemias with a range of possible severity, depending on the nature of the genetic defect.
- Thalassemias result from mutations that yield reduced synthesis of either the alpha- or beta-globin chains that compose the traditional α2β2 hemoglobin tetramer. The reduced synthesis of any one chain not only results in reduced total hemoglobin production, but also yields a relative excess of the unaffected chain. These excess chains aggregate and precipitate within developing or peripheral erythrocytes, resulting in either ineffective erythropoiesis or hemolysis.
- The thalassemias are divided into two basic categories based on the affected chain. Therefore, alpha-thalassemias are due to defects in alpha-globin synthesis while beta-thalassemias are due to defects in beta-globin synthesis. Because the genetics and clinical consequences of these diseases are somewhat distinct, they will be discussed on their own pages.
- Thalassemia traits are more common in certain demographic groups. The alpha-thalassemia trait is more common among Asians and Middle Easterners whereas the beta-thalassemia trait is more common among African Americans
- Thalassemias all result in a microcytic anemia; however, the degree of anemia depends on how many of the alpha- or beta-alleles are affected. Mild thalassemias may be asymptomatic and detectable only on laboratory tests whereas severe types may require constant transfusions or are incompatible with life. These variations are discussed in more detail under the individual thalasemia pages.