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a homotetramer of Hb (all four polypeptides identical) of molecular formula β4, found only when α chain synthesis is depressed and not effective in oxygen transport. Hb H disease (α-thalassemia intermedia) is a thalassemialike syndrome in people heterozygous for both severe and mild genes for α-thalassemia; moderate anemia and red blood cell abnormalities with 25-35% Hb Bart at birth, but with Hb Bart later replaced by Hb H and with Hb A2 decreased. Hb H shows no cooperativity with O2 binding and does not exhibit a Bohr effect.
hemoglobin composed of four beta chains, found in alpha thalassemia. Infants may be born with a mixture of hemoglobin H and hemoglobin Bart's.