Vitamin B 12 deficiency is likely to cause –
**Core Concept**
Vitamin B12 deficiency can lead to various clinical manifestations due to its crucial role in the synthesis of DNA, fatty acids, and energy production. The underlying principle being tested involves the understanding of **methylmalonic acid** and **homocysteine** metabolism, where **Vitamin B12** acts as a co-factor.
**Why the Correct Answer is Right**
The correct answer choice is related to the neurological and hematological effects of **Vitamin B12** deficiency. A deficiency in **Vitamin B12** leads to impaired synthesis of **myelin**, resulting in neurological symptoms, and affects the production of red blood cells, leading to **megaloblastic anemia**.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect as it does not directly relate to the primary effects of **Vitamin B12** deficiency.
**Option B:** Similarly, this option is not a direct consequence of **Vitamin B12** deficiency.
**Option C:** This choice is also incorrect as it is not a primary manifestation of **Vitamin B12** deficiency.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **Vitamin B12** deficiency can present with **pernicious anemia**, characterized by **megaloblastic anemia** and **neurological symptoms** such as numbness and weakness in the legs.
**Correct Answer:** D. Megaloblastic anemia