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Sickle Cell Disease

By Levi Clancy for Student Reader on

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Sickle cell hemoglobin (HbS) results from a single nucleotide substitution which changes the codon of the sixth β-globin amino acid from glutamic acid to valine (GAG→GTG: Glu6Val) and is the causative agent of sickle cell disease when homozygous. Homozygotes have α2Aβ2S hemoglobin. Heterozygotes (said to have sickle cell trait) have α2Aβ2S (HbS), α2Aβ2A (HbA) and α2Aβ2Sβ2A (HbS/HbA hybrid) hemoglobin, and are clinically normal despite mild symptoms under low oxygen pressure. In Sickle Cell Disease, the HbS β chains form chains, aggregating into long fibers which deform the cell, impair its function and result in hemolysis for homozygotes.