β-Thalassemia

beta-Thalassemia is caused by reduced (beta(+)) or absent (beta(0)) synthesis of the beta-globin chains of hemoglobin. Three clinical and hematological conditions of increasing severity are recognized: the beta-thalassemia carrier state, thalassemia intermedia, and thalassemia major, a severe transfusion-dependent anemia. The severity of disease expression is related mainly to the degree of alpha-globin chain excess, which precipitates in the red blood cell precursors, causing both mechanic and oxidative damage (ineffective erythropoiesis). Any mechanism that reduces the number of unbound alpha-globin chains in the red cells may ameliorate the detrimental effects of excess alpha-globin chains. Factors include the inheritance of mild/silent beta-thalassemia mutations, the coinheritance of alpha-thalassemia alleles, and increased gamma-globin chain production. The clinical severity of beta-thalassemia syndromes is also influenced by genetic factors unlinked to globin genes as well as environmental conditions and management. Transfusions and oral iron chelation therapy have dramatically improved the quality of life for patients with thalassemia major. Previously a rapidly fatal disease in early childhood, beta-thalassemia is now a chronic disease with a greater life expectancy. At present, the only definitive cure is bone marrow transplantation. Therapies undergoing investigation are modulators of erythropoiesis and stem cell gene therapy.