In alpha-thalassemia major (hydrops fetalis), which adult Hb type is absent on cord blood electrophoresis?

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Multiple Choice

In alpha-thalassemia major (hydrops fetalis), which adult Hb type is absent on cord blood electrophoresis?

In alpha-thalassemia major, there is a complete absence of alpha-globin chains. Without alpha chains, hemoglobins that require alpha to form cannot be produced. The fetus compensates by forming gamma-only tetramers (Hb Bart’s), which accumulate in the cord blood. Since HbA is made from alpha2 beta2, and HbA2 from alpha2 delta2, neither adult form can be produced when alpha is missing. That’s why adult hemoglobin types are not seen on cord blood electrophoresis in hydrops fetalis, with Hb Bart’s dominating. So the adult Hb type that is absent is HbA.

In alpha-thalassemia major, there is a complete absence of alpha-globin chains. Without alpha chains, hemoglobins that require alpha to form cannot be produced. The fetus compensates by forming gamma-only tetramers (Hb Bart’s), which accumulate in the cord blood. Since HbA is made from alpha2 beta2, and HbA2 from alpha2 delta2, neither adult form can be produced when alpha is missing. That’s why adult hemoglobin types are not seen on cord blood electrophoresis in hydrops fetalis, with Hb Bart’s dominating. So the adult Hb type that is absent is HbA.

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