Macrocytic anaemia is due to deficiency of:
**Core Concept**
Macrocytic anaemia is characterized by larger-than-normal red blood cells (RBCs) with a mean corpuscular volume (MCV) of > 100 fl. This type of anaemia is often caused by a deficiency in either vitamin B12 or folate, leading to impaired DNA synthesis and subsequent RBC production.
**Why the Correct Answer is Right**
The correct answer is related to the role of these two essential nutrients in the synthesis of DNA and RNA. Vitamin B12 and folate are crucial for the production of thymidine and purines, which are necessary for DNA replication and cell division. A deficiency in either of these nutrients can lead to megaloblastic anaemia, characterized by large, immature RBCs. This is because the cells are unable to progress through the normal cell cycle due to impaired DNA synthesis.
**Why Each Wrong Option is Incorrect**
**Option A:** While iron deficiency can cause microcytic anaemia, it is not associated with macrocytic anaemia.
**Option B:** Vitamin C deficiency can cause scurvy, but it is not directly related to the development of macrocytic anaemia.
**Option C:** While a deficiency in vitamin B6 can cause various neurological symptoms, it is not a primary cause of macrocytic anaemia.
**Clinical Pearl / High-Yield Fact**
Remember the "MAD" acronym to associate with macrocytic anaemia: "Megaloblastic Anaemia Due to" deficiencies in either vitamin B12 or folate.
**Correct Answer:** D.