• Types of hemoglobin (MCQ)
    • Hemoglobin A: a 2/b2 globin chains (normal hemoglobin)
    • Hemoglobin F: a2/g2 globin chains (fetal hemoglobin)
    • Hemoglobin A2: a2/d2
  • Normal distribution of Hb in adults is: 96%- HbA 3%- HbF 1%- HbA2
  • There are two a and one b gene on each chromosome, making a total of four a genes and two b genes in each chromosome pair.
  • a Thalassemia
    • Genetic defects causing gene deletions of a chains
    • Epidemiology
      • aa/—thalassemia trait is most common in Asians. (MCQ)
      • a–/a–thalassemia trait is most common in Africans.
    • Pathophysiology
      • Ineffective production of a globin chains causes b globin chains to accumulate. (MCQ)
    • Signs and symptoms
      • Depends on how many of the four foci are deleted or mutated: (MCQ)
        • 1/4 foci involved = silent thalassemia ,Asymptomatic
        • 2/4 foci involved = thalassemia trait ,Mild anemia
        • 3/4 foci involved
          • Hemoglobin H disease
          • Microcytic, hypochromic, hemolytic anemia with marked splenomegaly.
          • Patient may need occasional transfusions.
        • 4/4 foci involved =
          • Hemoglobin Barts
          • hydrops fetalis
          • Incompatible with life
    • Diagnosis
      • Blood smear: Microcytic anemia, hypochromia, target cells, Heinz bodies(MCQ)
      • HbH precipitates on staining with brilliant cresyl blue(MCQ)
  • Beta-thalassemia
    • Gene defects including deletions, abnormalities of transcription and translation, and instability of mRNA in b globin hemoglobin
    • Pathophysiology
      • Ineffective production of b globin chains causes a globin chains to accumulate in the cell.
      • The accumulation of a chains form insoluble aggregates that damage cell membranes.
      • A partial compensatory increase of the d and g chains yields elevated levels of HbA2 (a2d2) or HbF (a2g2). (MCQ)
    • Signs and symptoms
      • b-Thalassemia major (Cooley’s anemia): Associated with jaundice, hep- atosplenomegaly, and jaundice
      • b-Thalassemia minor: Mild or no anemia
    • Diagnosis
      • Elevated HbF and HbA2 measurements on hemoglobin electrophoresis
    • Treatment
      • b-Thalassemia major: (MCQ)
        • Aggressive transfusions
        • Splenectomy to enhance survival of RBCs, bone marrow transplant
      • b-Thalassemia minor: No treatment indicated.
  • Clinical Pearls :
    • Abnormal red blood cell morphology with microcytes, acanthocytes, and target cells. (MCQ)
    • In -thalassemia, elevated levels of hemoglobin A2 or F. (MCQ)
    • The thalassemias are hereditary disorders characterized by reduction in the synthesis of globin chains ( or ).
    • Two copies of the -globin gene are located on chromosome 16, (MCQ)
    • The -globin gene resides on chromosome 11 adjacent to genes encoding the -like globin chains,  and .(MCQ)
    • In cases of severe thalassemia, the marked expansion of the erythroid element in the bone marrow may cause severe bony deformities, osteopenia, and pathologic fractures.
    • Hemoglobin electrophoresis will show the presence of a fast migrating hemoglobin (hemoglobin H), which comprises 10–40% of the hemoglobin. (MCQ)
    • A peripheral blood smear can be stained with supravital dyes to demonstrate the presence of hemoglobin H. (MCQ)
    • Compared to iron deficiency anemia, patients with thalassemia have a(MCQ)
      • lower MCV
      • a more normal red blood count
      • a more abnormal peripheral blood smear at modest levels of anemia.
      • Iron studies are normal.
    • Patients with hemoglobin H disease (MCQ)
      • should take folate supplementation
      • avoid medicinal iron and oxidative drugs such as sulfonamides.
    • Patients with severe thalassemia are maintained on a regular transfusion schedule and receive folate supplementation.
    • Splenectomy is performed if hypersplenism causes a marked increase in the transfusion requirement.
    • Patients with regular transfusion requirements should be treated with iron chelation
    • Subcutaneous infusion of deferoxamine has largely been replaced by the oral agent deferasirox. (MCQ)
    • Allogeneic bone marrow transplantation is the treatment of choice for -thalassemia major(MCQ)

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