- 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
3.
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- Clinical Features of Thalassemias
β-thalassemia major:
Decreased synthesis of goblin chain causes microcytic, hypochromic anemia, growth retardation and are sustained by repeated blood transfusions.
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
|
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