An old man, Om Prakash presented with anorexia, weakness, and paraesthesia. On further investigation, his hemoglobin came out to be 5.8 g% and the peripheral smear showed the presence of macrocytes and neutrophils having hypersegmented nuclei. His tendon reflexes also were sluggish. Endoscopy revealed atrophic gastritis. Deficiency of which of the following factors can lead to such a clinical situation?

**Core Concept**
The clinical presentation of anorexia, weakness, paraesthesia, macrocytic anemia, hypersegmented neutrophils, and sluggish tendon reflexes in the context of atrophic gastritis suggests a deficiency of a vitamin that is crucial for DNA synthesis and myelination.

**Why the Correct Answer is Right**
The presence of macrocytic anemia, characterized by large red blood cells, and hypersegmented neutrophils, which have more than five nuclear lobes, indicates a defect in DNA synthesis. Atrophic gastritis leads to a reduction in the production of intrinsic factor, a protein required for the absorption of vitamin B12. Vitamin B12 is essential for the synthesis of DNA, fatty acid, and myelin. A deficiency in vitamin B12 can lead to megaloblastic anemia, neurological symptoms such as paraesthesia and weakness, and impaired myelination, resulting in sluggish tendon reflexes.

**Why Each Wrong Option is Incorrect**
**Option A:** Folate deficiency also leads to megaloblastic anemia, but it is less likely in this scenario since the patient has atrophic gastritis, which primarily affects vitamin B12 absorption.
**Option B:** Iron deficiency typically presents with microcytic anemia, which is characterized by small red blood cells, not macrocytic anemia.
**Option C:** Vitamin C deficiency leads to scurvy, which is characterized by collagen synthesis defects, not macrocytic anemia or atrophic gastritis.

**Clinical Pearl / High-Yield Fact**
A mnemonic to remember the clinical presentation of vitamin B12 deficiency is "B12 - Brain, Blood, Bones, and Balance": neurological symptoms (brain), megaloblastic anemia (blood), osteoporosis (bones), and impaired balance (balance).

**Correct Answer:** C. Vitamin B12.

✓ Correct Answer: B. Vitamin B12