Thalassemia
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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 thalassemias.
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 haemoglobin is composed of four protein chains, two α globin chains and two β globin chains 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 thalassemia 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.
- skull: classic "hair-on-end" appearance
- facial bones: rodent facies
- ribs: "rib-within-a-rib" appearance, noted particularly in the middle and anterior portions of the ribs
- extramedullary hematopoiesis
- premature fusion of the epiphyses
Gastrointestinal: hepatobilliary
-<p><strong>Thalassaemia</strong> is an <a href="/articles/autosomal-recessive">autosomal recessive</a> <a href="/articles/microcytic-anaemia">microcytic anaemia</a> that originated in the Mediterranean region. The genetic defect causes a reduction in the rate of <a href="/articles/globin-chain">globin chain</a> synthesis which causes the formation of abnormal <a href="/articles/haemoglobin">haemoglobin </a>molecules. The resultant anaemia is the characteristic presenting symptom of the thalassemias.</p><p>Thalassemia is a quantitative problem of globin synthesis, whereas <a href="/articles/sickle-cell-disease">sickle-cell disease</a> (a <a href="/articles/haemoglobinopathy">haemoglobinopathy</a>) is a qualitative problem of synthesis of an incorrectly functioning globin. </p><h4>Pathophysiology</h4><p>Normal haemoglobin is composed of four protein chains, two <a href="/articles/a-globin-chains">α globin chains</a> and two <a href="/articles/b-globin-chains">β globin chains</a> 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.</p><p>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.</p><p>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.</p><p>The <a href="/articles/thalassemia-trait">thalassemia trait</a> may confer a degree of protection against malaria, which confers a selective survival advantage on carriers.</p><h4>Radiographic features</h4><h5>Skeletal</h5><p>Marrow proliferation consists of expansion of the medulla, thinning of <a href="/articles/cortical-bone">cortical bone</a>, and resorption of <a href="/articles/cancellous-bone">cancellous bone</a> resulting in a generalized loss of bone density.</p><ul>-<li>skull: classic "<a href="/articles/hair-on-end-sign">hair-on-end</a>" appearance</li>-<li>facial bones: <a href="/articles/rodent-facies">rodent facies</a>-</li>-<li>ribs: "<a href="/articles/rib-within-a-rib">rib-within-a-rib</a>" appearance, noted particularly in the middle and anterior portions of the ribs</li>-<li><a href="/articles/extramedullary-haematopoiesis">extramedullary hematopoiesis</a></li>-<li>premature fusion of the epiphyses</li>-</ul><h5>Gastrointestinal: hepatobilliary </h5><ul>-<li><a href="/articles/cholelithiasis">cholelithiasis</a></li>-<li><a href="/articles/haemosiderosis">hemosiderosis</a></li>- +<p><strong>Thalassaemia</strong> is an <a href="/articles/autosomal-recessive">autosomal recessive</a> <a href="/articles/microcytic-anaemia">microcytic anaemia</a> that originated in the Mediterranean region. The genetic defect causes a reduction in the rate of <a href="/articles/globin-chain">globin chain</a> synthesis which causes the formation of abnormal <a href="/articles/haemoglobin">haemoglobin </a>molecules. The resultant anaemia is the characteristic presenting symptom of the thalassemias.</p><p>Thalassemia is a quantitative problem of globin synthesis, whereas <a href="/articles/sickle-cell-disease">sickle-cell disease</a> (a <a href="/articles/haemoglobinopathy">haemoglobinopathy</a>) is a qualitative problem of synthesis of an incorrectly functioning globin. </p><h4>Pathophysiology</h4><p>Normal haemoglobin is composed of four protein chains, two <a href="/articles/a-globin-chains">α globin chains</a> and two <a href="/articles/b-globin-chains">β globin chains</a> 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.</p><p>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.</p><p>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.</p><p>The <a href="/articles/thalassemia-trait">thalassemia trait</a> may confer a degree of protection against malaria, which confers a selective survival advantage on carriers.</p><h4>Radiographic features</h4><h5>Skeletal</h5><p>Marrow proliferation consists of expansion of the medulla, thinning of <a href="/articles/cortical-bone">cortical bone</a>, and resorption of <a href="/articles/cancellous-bone">cancellous bone</a> resulting in a generalized loss of bone density.</p><ul>
- +<li>skull: classic "<a href="/articles/hair-on-end-sign">hair-on-end</a>" appearance</li>
- +<li>facial bones: <a href="/articles/rodent-facies">rodent facies</a>
- +</li>
- +<li>ribs: "<a href="/articles/rib-within-a-rib">rib-within-a-rib</a>" appearance, noted particularly in the middle and anterior portions of the ribs</li>
- +<li><a href="/articles/extramedullary-haematopoiesis">extramedullary hematopoiesis</a></li>
- +<li>premature fusion of the epiphyses</li>
- +</ul><h5>Gastrointestinal: hepatobilliary </h5><ul>
- +<li><a href="/articles/cholelithiasis">cholelithiasis</a></li>
- +<li><a href="/articles/haemosiderosis">hemosiderosis</a></li>
References changed:
- 1. Cohen A, Galanello R, Pennell D, Cunningham M, Vichinsky E. Thalassemia. Hematology Am Soc Hematol Educ Program. 2004;2004(1):14-34. <a href="https://doi.org/10.1182/asheducation-2004.1.14">doi:10.1182/asheducation-2004.1.14</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/15561674">Pubmed</a>
- 2. Galanello R & Origa R. Beta-Thalassemia. Orphanet J Rare Dis. 2010;5(1):11. <a href="https://doi.org/10.1186/1750-1172-5-11">doi:10.1186/1750-1172-5-11</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/20492708">Pubmed</a>
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Case 72: thalassemia major
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