Occurs when there is a reduction in the synthesis of the α-globin chains of adult hemoglobin (HbA, α2β2) relative to beta-globin synthesis. Underproduction of α globin chains gives rise to excess β-like globin chains which form γ4 tetramers, called Hb Bart’s (in fetal life) and β4 tetramers, called HbH (in adult life).
- α thalassemia trait:
- Mutations affecting the α globin genes on one chromosome
- Associated with minimal anaemia
- Compound heterozygotes and some homozygotes for α thalassemia (HbH disease):
- Moderately severe anemia
- Presence of HbH in the peripheral blood
- Hb Bart’s hydrops fetalis syndrome:
- Little or no α globin chains have a very severe form of anaemia
- May cause death in the neonatal period if left untreated
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