Lecture 6-Thalassemia 2015.ppt - Thalassemias Thalassemias...

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Thalassemias Thalassemias are a diverse group of inherited disorders caused by gene mutations These gene mutations reduce or completely eliminate the synthesis of one or more of the globin chains of the Hgb tetramer The homozygous state for the abnormal autosomal gene for beta- globin chain synthesis (Cooley’s anemia) has become known as thalassemia major 03/30/18
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Thalassemias The heterozygous state for the abnormal gene for beta-globin chain synthesis is called thalassemia minor The heterozygous, milder forms of thalassemia are the most frequent genetic defect in humans The homozygous, more sever forms are capable of causing significant morbidity and mortality 03/30/18
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Thalassemias Thalassemia is a group of disorders defined as a condition in which a reduction in the rate of production of one or more of the globin chains leads to 1. Imbalanced globin chain production 2. Defective Hgb production 3. Damage to the RBCs or their precursors by the buildup of the globin chain that is produced in excess 03/30/18
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Thalassemias Usually it is the synthesis of either the alpha or beta chains of hemoglobin A (HbA; α 2 β 2 ) that is impaired Thalassemias are named according to the chain with reduced or absent globin synthesis 03/30/18
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Thalassemias – Genetic Control of Hgb Synthesis The normal Hgb molecule is a tetramer (double dimer) of two alpha-like chains (either α or ζ) with two beta-like chains (either β, γ, δ or ε) Combinations of these chains produce six normal hemoglobins Three of the normal Hgbs are embryonic Gower-1 (ζ 2 ε 2 ) Gower-2 (α 2 ε 2 ) Portland (ζ 2 γ 2 ) 03/30/18
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Thalassemias – Genetic Control of Hgb Synthesis The other three normal Hgbs are Fetal (α 2 γ 2 ) A (α 2 β 2 ) A2 (α 2 δ 2 ) 1. By the 10 th week of gestation, zeta and epsilon chain production ceases and gamma chain synthesis begins 2. The gamma chains combine with alpha chains to make HbF, which predominates during fetal life 03/30/18
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Thalassemias – Genetic Control of Hgb Synthesis After birth, gamma chain production decreases and beta chains are the predominant chains produced The transition from gamma chain to beta chain globin production is called the gamma-to-beta switch HbA is 95-97% of normal adult Hgb, HbA2 is 2-3% and HbF is 2% 03/30/18
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Thalassemias – Genetic Control of Hgb Synthesis The alpha and zeta genes are located on the short arm of chromosome 16 The cluster of beta-like genes is distributed on the short arm of chromosome 11
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