Observations on the ultrastructure of erythropoietic cells and reticulum cells in the bone marrow of patients with homozygous beta-thalassaemia.

An electron microscopic study of marrow fragments from patients with homozygous beta-thalassaemia has shown that 3% of early polychromatic erythroblast profiles and 20% of late polychromatic erythroblast profiles contain intracytoplasmic alpha-chain precipitates. Various nuclear abnormalities were found including the loss of parts of the nuclear membrane and the presence of intranuclear alpha-chain precipitates, and these abnormalities were virtually confined to the non-dividing, late polychromatic erythroblasts. As most profiles of the proliferating early polychromatic erythroblasts did not contain intracytoplasmic or intranuclear alpha-chain precipitates, it is suggested that the arrest of many of these cells in the G1 phase of the cell cycle may be related to the presence of an excess of free alpha-chains rather than to the presence of alpha-chain precipitates within them. The cytoplasm of the bone marrow reticulum cells contained early and late polychromatic erythroblasts at various stages of degradation, providing direct evidence of ineffective erythropoiesis.