The alpha-globin gene adjacent to the gene for HbQ-alpha 74 Asp replaced by His is deleted, but not that adjacent to the gene for HbG-alpha 30 Glu replaced by Gln; three-fourths of the alpha-globin genes are deleted in HbQ-alpha-thalassemia.

Two Chinese patients with HbQ-alpha 2 74 Asp replaced by His beta 2-alpha-thalassemia, one HbQ-alpha 2 74 or 75 Asp replaced by His beta 2 carrier, and one HbG-alpha 2 30 Glu replaced by Gln beta 2 carrier were studied to determine the number of alpha-globin genes in their chromosomes. DNA was isolated from white blood cells and bone marrow cells and studied by liquid hybridization and by hybridization of DNA fragments obtained by restriction enzyme endonuclease digestion (Ecr to nitrocellulose filters. The liquid hybridization analysis showed that in HbQ-alpha 2 74 Asp replaced by His beta 2-alpha-thalassemia, as in HbH disease, only one-fourth of the usual number of alpha-globin genes is present. Hybridization patterns of DNA restriction enzyme fragments showed that in HbQ-alpha 2 74 Asp replaced by His beta 2-alpha-thalassemia one chromosome has both alpha-globin genes deleted and the other chromosome, which carries the alpha-mutant gene, has one alpha-globin gene deleted. Our results show that the HbQ-alpha 74 Asp replaced by His structural gene is located adjacent to a deleted alpha-globin gene, whereas the alpha-globin gene adjacent to HbG-alpha 30 Glu replaced by Gln gene is not deleted.