Sickle Cell Anemia

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Sickle cell disease is a hereditary hemoglobin defect that occurs in people of African and Mediterranean decent. “First identified in 1904 by a hospital intern, sickle cell disease became, more than forty years later, the first disease found to be a genetic disease” (Harris 83). This disorder is caused by a recessive allele that changes the structure of hemoglobin. Sickle cell hemoglobin (HbS) differs from normal hemoglobin (HbA) in that of all the 574 amino acids it is made of, just one is different. In the sixth amino acid of the beta chain, HbA has glutamic acid and HbS has valine.

Normal red blood cells have a biconcave shape that transports hemoglobin which is responsible for most oxygen transport. The shape of the RBC is what allows it to move easily through narrow capillaries. The change in just the one amino acid has far reaching consequences on hemoglobin interactions. “The HbS B chain, with valine at the sixth position, has an unusual propensity to bind with other HbS chains (contained in other hemoglobin molecules within the RBC) when deoxygenated” (Abbondanzo, Cline and Lonegran 1) creating large polymers. These chains lose their elasticity and when trying to move through tiny capillaries clogging vessels causing painful vaso-occlusion.

Not everyone with the HbS gene will have sickle cell anemia. “People that have a sickle cell beta globin gene and a normal beta globin gene” (Jones, 47) are said to be heterozygous. They have sickle cell trait but rarely have severe symptoms if any. However, if a child inherits HbS from both the mother and father (HbSS) they are said to be homozygous and will have sickle cell disease. If both parents have sickle cell trait there is a 25% chance that each o...

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