Gastroenterology
Intrinsic factor
Intrinsic factor is a human gastric glycoprotein secreted by parietal cells that binds vitamin B12 and enables its receptor‑mediated uptake in the terminal ileum. Deficiency of intrinsic factor—most commonly from autoimmune gastritis—impairs vitamin B12 absorption and can cause pernicious anemia and neurologic dysfunction.
Pernicious anemia
Pernicious anemia is an autoimmune cause of vitamin B12 deficiency resulting from loss of intrinsic factor due to autoimmune gastritis, leading to megaloblastic anemia and neurological dysfunction. It predominantly affects older adults and is associated with other autoimmune diseases and an elevated risk of gastric neoplasia. Lifelong vitamin B12 replacement is required once diagnosed.