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Sickle Cell Anemia

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By Ashesh

  1. Different types of hemoglobin
HbA
α2β2
HbA2
α2δ2
HbF   
Α2γ2
HbA1c
Α2β2-glucose
                  HbS             sickle hemoglobin, valine replaces glutamic acid
                  HbC             lysine replaces glutamic acid
  1. Sickle cell disease occurs primarily in individuals of African descent. HbS is protective against Plasmodium falciparum malaria.
  2. Sickle cell disease is caused by a point mutation in the sixth codon of β-globin that leads to the replacement of a glutamate residue with a valine residue. Sickle cell disease is a homozygous, recessive disorder.
  3. At low oxygen tension, deoxyhemoglobin S polymerizes inside the red blood cells, that stiffens and distorts the cell, producing rigid, spindled erythrocytes.
  4. The extent of sickling is enhanced by any variable that increases the proportion of HbS in the deoxy state
    • decreased oxygen tension as a result of high altitudes or flying in a nonpressurized plane
    • decreased pH
    • dehydration
    •  increased concentration of 2,3-BPG in erythrocytes
    •  increased pCO2
  5. Clinical Features of Sickle Cell Anemia
    1. Chronic Hemolytic Anemia that is associated with reticulocytosis, hyperbilirubinemia, and the presence of irreversibly sickled cells. Hemosiderosis and gallstones are common.
    2. Vaso-occlusive "pain" crises, are episodes of hypoxic injury and infarction that cause severe pain in the affected region, most commonly  bones, lungs, liver, brain, spleen, and penis. Bone pains can mimic osteomyelitis in children.
    3. Acute chest syndrome is a particularly dangerous type of vaso-occlusive crisis involving the lungs.
    4. Aplastic crises in infection by parvovirus B19
    5. Autosplenectomy splenic infarction, fibrosis, and progressive shrinkage results in increased susceptibility to infection with encapsulated organisms Pneumococcus pneumoniae and Haemophilus influenzae.  
             
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