Megaloblasts result from the impaired synthesis

Megaloblasts result from the impaired synthesis of

A. DNA 
B. RNA
C. Glutathione 
D. β-globin chains

The answer is a. Deficiency of either vitamin B12 or folate results in megaloblastic anemia. Deficiency impairs DNA syn-thesis and delays mitotic division, which in turn causes the nuclei to be enlarged. The synthesis of RNA and cytoplasmic elements is not affected, however, so there is nuclear-cytoplasmic asynchrony. These cellular changes affect all rapidly proliferating cells in the body, but in the bone marrow they result in enlarged erythroid precursors, which are referred to as megaloblasts. These abnormal cells produce abnormally enlarged red cells, which are called macroovalocytes. These megaloblasts also undergo autohemolysis within the bone marrow, resulting in ineffective erythropoiesis. Granulocyte precursors are also enlarged and are called giant metamyelocytes. These abnormal cells produce enlarged hypersegmented neutrophils. The megakaryocytes are large and have nuclear abnormalities, but, although the platelet count is decreased, the platelets are not enlarged. Abnormalities of glutathione production are seen in patients with glucose-6-phosphate dehydrogenase deficiency, while decreased synthesis of β-globin chains is seen in patients with β thalassemia. Abnormalities of decay-accelerating factor are seen in patients with paroxysmal nocturnal hemoglobinuria.