Folate deficiency: megaloblastic anemia
Dietary deficiency of folic acid is not uncommon and, as noted above, deficiency of vitamin B12 also leads to functional folic acid deficiency. In either case, it is cells that are dividing rapidly, and therefore have a large requirement for thymidine for DNA synthesis, that are most severely affected. These are the cells of the bone marrow that form red blood cells, the cells of the intestinal mucosa and the hair follicles. Clinically, folate deficiency leads to megaloblastic anemia, the release into the circulation of immature precursors of red blood cells.
Megaloblastic anemia is also seen in vitamin B12 deficiency, where it is due to functional folate defi-ciency as a result of trapping folate as methyl-tetra-hydrofolate. However, the neurological degeneration of pernicious anemia is rarely seen in folate deficiency, and indeed a high intake of folate can mask the devel-opment of megaloblastic anemia in vitamin B12 defi-ciency, so that the presenting sign is irreversible nerve damage.