What mechanism leads to vitamin B12 deficiency in pernicious anemia?

What mechanism leads to vitamin B12 deficiency in pernicious anemia?

• A. Autoimmune destruction of gastric parietal cells causing intrinsic factor deficiency
• B. Dietary deficiency of vitamin B12
• C. Pancreatic insufficiency causing poor B12 absorption
• D. Malabsorption due to celiac disease

Answer: (A)

Autoimmune destruction of gastric parietal cells leading to intrinsic factor deficiency. Parietal cells produce intrinsic factor, which binds vitamin B12 in the gut. In pernicious anemia, autoimmune damage or antibodies against intrinsic factor or parietal cells reduce or abolish intrinsic factor production, so the B12–intrinsic factor complex cannot form. Without this complex, absorption of vitamin B12 in the terminal ileum is markedly impaired, causing deficiency despite adequate dietary intake. Over time, B12 stores are depleted, leading to the megaloblastic anemia characteristic of this condition and sometimes neurologic symptoms. Other scenarios can cause low B12, but the defining mechanism in pernicious anemia is the autoimmune loss of intrinsic factor due to parietal cell dysfunction.

Autoimmune destruction of gastric parietal cells leading to intrinsic factor deficiency. Parietal cells produce intrinsic factor, which binds vitamin B12 in the gut. In pernicious anemia, autoimmune damage or antibodies against intrinsic factor or parietal cells reduce or abolish intrinsic factor production, so the B12–intrinsic factor complex cannot form. Without this complex, absorption of vitamin B12 in the terminal ileum is markedly impaired, causing deficiency despite adequate dietary intake. Over time, B12 stores are depleted, leading to the megaloblastic anemia characteristic of this condition and sometimes neurologic symptoms. Other scenarios can cause low B12, but the defining mechanism in pernicious anemia is the autoimmune loss of intrinsic factor due to parietal cell dysfunction.