The fate of excess beta-globin chains within erythropoietic cells in alpha-thalassaemia 2 trait, alpha-thalassaemia 1 trait, haemoglobin H disease and haemoglobin Q-H disease: an electron microscope study.

Electron microscope studies have been performed on bone marrow cells from individuals with various alpha-thalassaemia syndromes. Globin chain precipitates were rarely found in the erythropoietic cells of a subject with alpha-thalassaemia 2 trait. By contrast, such precipitates were found in 0.6 - 1.3% of the erythroblast and marrow reticulocyte profiles in two cases of alpha-thalassaemia 1 trait, 2.1 - 13.7% of profiles in five patients with haemoglobin H (HbH) disease and 6.2% of profiles in one patient with haemoglobin Q-H (HbQ-H) disease. In the patient with HbQ-H disease, but not in the others, the nuclei of some erythroblasts displayed the 'Swiss cheese' appearance which has been reported in some forms of congenital dyserythropoietic anaemia. It is proposed that in alpha-thalassaemia 2 trait, where the degree of excess of beta-chains is slight, most of the excess chains are degraded by proteolysis. In alpha-thalassaemia 1 trait, where there is a greater excess of beta-chains, the excess chains can undergo either proteolysis or precipitation, but there is little or no tetramerization to form soluble HbH. Finally, in HbH disease, where the degree of excess is considerable, the excess beta-chains may be subject to proteolysis, precipitation and tetramerization.