Thalassemia

Dr Daniel J Bell and Radswiki et al.

Thalassemia is an autosomal recessive hemoglobinopathy that originated in the Mediterranean region. The genetic defect causes a reduction in the rate of globin chain synthesis which causes the formation of abnormal hemoglobin molecules. The resultant microcytic anemia is the characteristic presenting symptom of the thalassemias.

Thalassemia is a quantitative problem of globin synthesis, whereas sickle cell disease is a qualitative problem of synthesis of an incorrectly functioning globin.

Normal adult hemoglobin is composed of HbA (98%) and HbA2 (2%). HbA contains two α globin chains / two β globin chains, and HbA2 contains two α globin chains / two δ globin chains. They are arranged into a heterotetramer. Thalassemia patients produce a deficiency of either α or β globin, unlike sickle cell disease, which produces a specific mutant form of β globin.

The thalassemias are classified according to which chain of the hemoglobin molecule is affected. In α thalassemias, production of the α globin chain is reduced, while in β thalassemia production of the β globin chain is reduced.

The β globin chains are encoded by a single gene on chromosome 11; α globin chains are encoded by two closely linked genes on chromosome 16. Thus, in a normal person with two copies of each chromosome, there are two loci encoding the β chain, and four loci encoding the α chain. Deletion of one of the α loci has a high prevalence in people of African or Asian descent, making them more likely to develop α thalassemias. β thalassemias are common in Africans, but also in Greeks and Italians.

The thalassemia trait may confer a degree of protection against malaria, which confers a selective survival advantage on carriers.

Marrow proliferation consists of an expansion of the medulla, thinning of cortical bone, and resorption of cancellous bone resulting in a generalized loss of bone density.

Named for the Greek word for "sea" (θάλασσα - thálassa), as the condition is more prevalent in those living around the Mediterranean Sea e.g. Italians, Greeks, etc. Cooley and Lee described bone abnormalities and severe anemia with associated splenomegaly in 1921 5.

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Article information

rID: 15616
Tag: refs
Synonyms or Alternate Spellings:
  • Thalassemia
  • Thalassaemias

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Cases and figures

  • Case 1: chest wall deformity
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  • Case 2: thalassemia major
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  • Case 3
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  • Case 4: bone changes on MRI
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  • Case 5: beta thalassemia major
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  • Case 6: thalassemia major
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  • Case 7
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  • Case 8
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  • Case 9: beta thalassemia
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  • Case 10
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  • Case 11: skull manifestation
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