Decreased alpha globine mRNA in nucleated red cell precursors in alpha thalassemia

Abstract

The alpha thalassemias are associated with a decrease in alpha chain synthesis. Hemoglobin H (HbH) disease is a moderately severe form of alpha thalassemia characterized by the production of 5%--20% of HbH, while alpha thalassemia trait is a milder form of alpha thalassemia. In two patients with HbH disease, the ratio of alpha chain synthesis to beta chain synthesis (alpha/beta ratio) was decreased in both bone marrow cells and reticulocytes. When isolated mRNA from bone marrow cells and reticulocytes was translated in a heterologous cell-free system, the alpha/beta ratios were lower than the intact cell ratios. These findings were confirmed by hybridization of the mRNA of both marrow cells and reticulocytes using purified alpha and beta cDNA probes. In the intact cells of two patients with alpha thalassemia trait, the alpha/beta ratios were also decreased and were similar in marrow cells and reticulocytes. Cell-free studies of translatable mRNA also demonstrated decreased alpha/beta ratios, but, unlike the HbH studies, the cell-free alpha/beta ratios were similar to the intact cell ratios. One hybridization study utilizing peripheral blood mRNA had an alpha/beta ratio consistent with the cell-free ratios. These results indicated that, in both HbH disease and alpha thalassemia trait, there was decreased alpha globin mRNA present in both nucleated red cell precursors and reticulocytes. In addition, the data suggested that there may be translational mechanisms that operate in intact HbH cells which attempt to balance globin chain production. In alpha thalassemia trait cells, no such controls appeared to be active and globin chain synthesis was directly proportional to the amount of alpha and beta globin mRNA in the cells.