- 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
- aa/—thalassemia trait is most common in Asians. (MCQ)
- a–/a–thalassemia trait is most common in Africans.
- 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
- Blood smear: Microcytic anemia, hypochromia, target cells, Heinz bodies(MCQ)
- HbH precipitates on staining with brilliant cresyl blue(MCQ)
- Gene defects including deletions, abnormalities of transcription and translation, and instability of mRNA in b globin hemoglobin
- 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
- Elevated HbF and HbA2 measurements on hemoglobin electrophoresis
- 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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