Thalassemia

Changed by Yuranga Weerakkody, 9 Jan 2017
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Thalassaemia is an autosomal recessive microcytic anaemia 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 haemoglobin molecules. The resultant anaemia is the characteristic presenting symptom of the thalassaemias.

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

Pathophysiology

Normal adult haemoglobin 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 δglobin chains. They are arranged into a heterotetramer. Thalassaemia 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 haemoglobin 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 thalassaemia trait may confer a degree of protection against malaria, which confers a selective survival advantage on carriers.

Radiographic features

Skeletal

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

Gastrointestinal: hepatobilliary
  • +<li>
  • +<a title="Osteoporosis" href="/articles/osteoporosis-3">osteoporosis</a><sup> 4</sup>
  • +</li>
  • -<li><a href="/articles/cholelithiasis">cholelithiasis</a></li>
  • +<li><a href="/articles/gallstones-1">cholelithiasis</a></li>

References changed:

  • 4. Toumba M & Skordis N. Osteoporosis Syndrome in Thalassaemia Major: An Overview. J Osteoporos. 2010;2010:537673. <a href="https://doi.org/10.4061/2010/537673">doi:10.4061/2010/537673</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/20976089">Pubmed</a>

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