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The thalassemias are a group of inherited hematological disorders caused by defects in the synthesis of one or more of the hemoglobin (Hb) chains.1 β-Thalassemia is caused by reduced or absent synthesis of ß-globin chains. α-Thalassemia is caused by reduced or absent synthesis of α-globin chains. Globin-chain imbalances cause hemolysis and impair erythropoiesis.

Thalassemia is generally classified along a spectrum according to severity.2,3

Thalassemia: Severity Spectrum

The least serious group is thalassemia trait, an asymptomatic condition requiring no blood transfusions. A more severe form is non–transfusion-dependent thalassemia (NTDT), which has clinically relevant symptoms and may require only occasional transfusions or none. The most serious group is β-thalassemia major, or transfusion-dependent thalassemia (TDT). With severe clinical manifestations, TDT is usually diagnosed early in life, and patients require regular blood transfusions to survive.2,3

Patients wih abnormal synthesis within these hemoglobin chains may have NTDT: HbE/β-thalassemia, HbH/α-thalassemia, or thalassemia intermedia.4,5

Globally, an estimated 15 million people have thalassemia.6 Emigration of populations from South and Southeast Asia has increased the worldwide prevalence of the disease (Figure).7-10

For patients suspected of having thalassemia, physicians should enquire about their ethnic background, family history of hematological disorders, and dietary history.

Figure. Immigration Trends Impacting Thalassemia.8

Thalassemia: Global Emigration

Learn more about the epidemiology of thalassemia >


  1. Yaish HM. Available from: Accessed May 2011.
  2. Cappellini M-D, Cohen A, Eleftheriou A, et al. Guidelines for the Clinical Management of Thalassaemia. 2nd rev ed. Nicosia, Cyprus: Thalassaemia International Federation; 2008.
  3. Taher AT, Musallam KM, Cappellini MD, Weatherall DJ. Optimal management of β thalassaemia intermedia. Br J Haematol. 2011;152(5):512-523.
  4. Taher AT, Porter J, Viprakasit V, et al. Deferasirox reduces iron overload significantly in nontransfusion-dependent thalassemia: 1-year results from a prospective, randomized, double-blind, placebo-controlled study. Blood. 2012;120(5):970-977.
  5. United Kingdom Thalassaemia Society. Standards for the clinical care of children and adults with thalassaemia in the UK. 2nd ed. 2008. Accessed February 5, 2013.
  6. Weatherall D, et al. In: Jamison DT, et al., editors. Disease control priorities in developing countries. 2nd ed. New York: Oxford University Press; 2006. p. 663-80. Available from: Accessed May 2011.
  7. Weatherall DJ. Keynote address: the challenge of thalassemia for the developing countries. Ann NY Acad Sci. 2005;1054:11-17.
  8. Weatherall DJ. The definition and epidemiology of non-transfusion-dependent thalassemia. Blood Rev. 2012;26(suppl 1):S3-S6.
  9. Michlitsch J, Azimi M, Hoppe C, et al. Newborn screening for hemoglobinopathies in California. Pediatr Blood Cancer. 2009;52(4):486-490.
  10. Pew Research Center. The rise of Asian Americans. Available at: Accessed February 11, 2013.

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