Sickle Cell Anemia | Anatomy2Medicine
Sickel Cell Anemia Causes

Sickle Cell Anemia

 

  • Hemoglobin S disorders
      • Conditions that confer resistance to falciparum malarial infection.(MCQ)
  • hemoglobin S gene
  • erythrocyte G6PD deficiency
  • absence of Duffy blood group antigens
  • Hemoglobin S
        • arises from a point mutation in codon 6 of the β-globin gene (MCQ)
  • results in a substitution of valine for glutamic acid(MCQ)
  • DNA defect is basis for prenatal diagnosis
        • At the DNA level, the mutation abolishes a recognition site for the restriction endonuclease Mst II.
        • It can be performed on amniotic cells or on chorionic villus samples.
      • Pathophysiology
        • Hemoglobin S polymerizes at low oxygen tension, forming tactoids that distort the shape of red cells to elongated, sickle shapes(MCQ)
        • repeated sickling episodes stiffen red cell membranes
        • affected cells are more subject to hemolysis
        • rigid, sickled cells are more likely to obstruct the microvasculature.
      • positive sickle cell preparation
        • in vitro sickling of red cells on exposure to reducing agents such as sodium metabisulfite(MCQ)
        • All hemoglobin S disorders are positive whenever hemoglobin S is present sickle cell anemia (MCQ)
          • sickle cell trait
          • sickle C disease
  • sickle cell thalassemia
      • Sickle cell anemia
        • The homozygous form of hemoglobin S leads to sickle cell anemia (sickle cell disease
        • characterized by:
  • Severe hemolyti anemia
  • Chronic leg ulcers(MCQ)
          • Vaso-occlusive painful crises (MCQ)
            • severe pain in the limbs, back, chest, and abdomen
            • often precipitated by infection or dehydration
          • Repeated infarctions in the lungs and spleen(MCQ)
            • spleen is characteristically congested and enlarged in childhood
            • becomes progressively smaller through repeated infarcts and fibrosis (autosplenectomy).
          • Aplastic crises (MCQ)
            • characterized by a precipitous fall in hemoglobin concentration
            • usually provoked by viral infection, such as human parvovirus(MCQ)
            • Infectious complications, such as Salmonella osteomyelitis(MCQ)
  • Sickle cell trait.
        • Hemoglobin S in the heterozygous form leads to sickle cell trait,
        • it is generally without clinical consequence
      • Hemoglobin C disorder
        • When homozygous, they are characterized by
          • mild hemolytic anemia accompanied by prominent splenomegaly
  • target cells (MCQ)
  • intraerythrocytic crystals. (MCQ)
    • When heterozygous, they result in disease only when coinherited with other abnormal hemoglobins, most often hemoglobin S. (MCQ)
    • Hemoglobin E disorders
      • prevalent in Southeast Asia.
      • Clinical manifestations are similar to those of hemoglobin C disorders.