The megaloblastic anemias are a group of disorders characterized by the presence of distinctive morphologic appearances of the developing red cells in the bone marrow. The cause is usually deficiency of either cobalamin (vitamin B12) or folate, but megaloblastic anemia may arise because of genetic or acquired abnormalities affecting the metabolism of these vitamins or because of defects in DNA synthesis not related to cobalamin or folate (Table 100-1). Cobalamin and folate absorption and metabolism are described next and then the biochemical basis, clinical and laboratory features, causes, and treatment of megaloblastic anemia. The marrow is usually cellular, and.
