Pernicious anemia results from which underlying problem?

1. Vitamin B12 and folate act as co-enzymes for DNA synthesis, so both are needed for new cells. 2. Pernicious anemia is caused specifically by poor absorption of vitamin B12, not by a shortage in the diet. 3. It is therefore seen after intestinal or gastric surgery, in Crohn disease, with intestinal parasites and in AIDS. 4. Dietary lack of folate produces megaloblastic anemia instead, which is the trap in the first option. 5. Deficient red cell stem cells define aplastic anemia. 6. Abnormal maturation of the red cells defines thalassemia, so that option names a third distinct disorder. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.3 Erythrocytes_