Clinical features and molecular analysis of acquired hemoglobin H disease.

The presence of hemoglobin H (beta 4), resulting from a deficiency of alpha-globin chain synthesis, was observed as an acquired characteristic in the red cells of five elderly patients with myeloproliferative disorders or preleukemia. The variability in amount of hemoglobin H and in the alpha/beta globin synthesis ratios in these patients is most likely explained by the relative proportions of normal and abnormal cell populations in the peripheral blood, since some reticulocyte fractions with balanced alpha/beta globin synthesis ratios and others with almost no detectable alpha-chain production could be obtained from these patients. In one patient, the hemoglobin H virtually disappeared despite continuing disease. The amount of cytoplasmic alpha-mRNA matched the proportion of alpha-chain synthesis and, in one patient, this was also true for nuclear RNA. However, extensive analysis of the alpha-globin gene complex by restriction endonuclease mapping revealed no detectable rearrangements of the normal gene organization in any of these patients, suggesting that transcription of each pair of alpha-globin genes on each chromosome 16 is defective. These observations have important implications for both the normal regulation of alpha-globin gene expression and the molecular basis of the underlying defect that is associated with the neoplastic transformation of these cells.