Thalassemia Easy Review Notes of Alpha and Beta Thalassemias

In the thalassemias, the synthesis of either the α- or the β-globin chain is defective.
Imbalance in α- and β-globin synthesis leads to precipitation of excess goblin chain e.g. α4-tetramers in β-thalassemias

β4-tetramers(HbH) and γ4-tetramers(Hb Barts) in α-thalassemias

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Clinical Features of Thalassemias

β-thalassemia minor and α-trait are often asymptomatic with mild microcytic and hypochromic anemia.

β-thalassemia major:
Decreased synthesis of goblin chain causes microcytic, hypochromic anemia, growth retardation and are sustained by repeated blood transfusions.

"Target Cells" (so called because hemoglobin collects in the center of the cell) are common.

Precipitation of α4-tetramers causes

Extravascular hemolysis of mature RBCs

Ineffective erythropoiesis- phenomenon of death of RBC precursors which in turn leads to :

Erythroid hyperplasia with left shift

Skeletal deformities; "crewcut" skull, chipmunk facies

Extramedullary hematopoiesis, splenomegaly, hepatomegaly

Cachexia

Iron overload and Hemosiderosis due to increased absorption from gut and repeated blood transfusions; leads to cardiac dysfunction and typically causes death between the ages of 15 and 25 years

HbH disease resembles β-Thalassemia intermedia and is not as severe as β-Thalassemia major.

Hydrops fetalis caused by deletions of all four α-genes is lethal in utero without transfusions.

(γ4, Hb Bart) or β tetramers (β4, Hb H) are fairly soluble, the subunits show no heme-heme interaction. These tetramers have very high oxygen affinities. This makes them essentially useless as oxygen deliverers to the tissues.

Diagnosis of thalassemias is by Hemoglobin-electrophoresis

β-Thalassemia major	HbA is absent; HbF, HbA2 are increased
β-Thalassemia minor	HbA is decreased; HbF, HbA2 are increased
HbH disease	β4 tetramers are seen
Hydrops fetalis	γ4-tetramers(Hb Barts) are seen

Links to:

Hereditary Spherocytosis	Sickle Cell Anemia
G-6-PD Deficiency	Immunohemolytic anemias
Hemolytic Anemias Introduction	Anemia

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