Homozygous α-thalassemia has the beneficial effect in sickle cell anemia of reducing the hemolytic severity while changing several other hematological parameters. We examined in detail the cellular basis of some of these hematologic alterations. We find that the broad distribution in erythrocyte density and the large proportion of dense cells associated with sickle cell anemia are both reduced with coexisting α-thalassemia. Measurements of glycosylated hemoglobin levels as a function of cell density indicate that the accelerated increase in cell density, beyond normal cell aging, in sickel cell anemia is also reduced with α-thalassemia. The patients with homozygous α-thalassemia and sickle cell disease have slightly lower levels of hemoglobin F than the nonthalassemic sickle cell patients. Examination of hemoglobin F production revealed that the proportion of hemoglobin F containing reticulocytes remained unchanged, as did the proportion of hemoglobin F in cells containing hemoglobin F (F cells). Preferential survival of F cells occurs in sickle cell anemia, with or without α- thalassemia, and the slight difference in hemoglobin F levels appears to reflect differences in numbers of circulating F cells. Thus, in sickle cell disease with coexisting α-thalassemia, the change in the erythrocyte density profile, possibly due to inhibition of polymerization-related increases in cell density, explains the hematological improvement.
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