Dr Henry Knipe and Radswiki et al.

Thalassaemia is an autosomal recessive haemoglobinopathy 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 microcytic anaemia is the characteristic presenting symptom of the thalassaemias.

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 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 δ globin 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.

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.

  • skull
    • hair-on-end appearance (classic)
    • widening of the diploic space
    • thinning of the inner & outer table
    • note: the occipital bone is spared, due to lack of hemopoietic bone marrow 6
  • facial bones
    • rodent facies
    • hypopneumatization of the frontal, maxillary & sphenoid sinuses, filled with marrow containing bone 6
    • note: the ethmoid sinuses are spared due to lack of red bone marrow  6
    • dental malocclusion
  • ribs: rib-within-a-rib appearance, noted particularly in the middle and anterior portions of the ribs
  • premature fusion of the epiphyses
  • osteoporosis 4
  • extramedullary haematopoiesis

Named for the Greek word for "sea" (θάλασσα - thálassa), Cooley and Lee described bone abnormalities and severe anaemia with associated splenomegaly in 1921 5.

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Article information

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

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Cases and figures

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    Case 1: chest wall deformity
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    Bulbous rib ends
    Case 2: thalassemia major
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    Case 3
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    Case 4: bone changes on MRI
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    Reversal of norma...
    Case 5: beta thalassemia major
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    Case 6: thalassaemia major
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    Case 7
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    Case 8
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    Case 9: beta thalassaemia
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    Case 10
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    Case 11 (skull manifestation)
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