Vitamin B12 deficiency is likely to cause –
**Core Concept**
Vitamin B12 deficiency leads to a decrease in the production of methanol, a critical intermediate in the synthesis of myelin, the fatty substance surrounding nerve fibers. This impairment affects the normal functioning of the nervous system.
**Why the Correct Answer is Right**
Vitamin B12 plays a crucial role in the metabolism of fatty acids and amino acids. It serves as a cofactor for the enzyme methionine synthase, which converts homocysteine to methionine. Methionine is then converted to S-adenosylmethionine (SAMe), a key methyl donor for the synthesis of myelin. Without sufficient vitamin B12, this process is impaired, leading to demyelination and neurological symptoms.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is not directly related to the consequences of vitamin B12 deficiency. While anemia is a possible symptom, it is not the most likely consequence.
* **Option B:** This option is incorrect as vitamin B12 deficiency primarily affects the nervous system, not the cardiovascular system. However, it may contribute to an increased risk of cardiovascular disease due to its association with hyperhomocysteinemia.
* **Option C:** This option is incorrect as vitamin B12 deficiency is not directly linked to an increased risk of cancer.
**Clinical Pearl / High-Yield Fact**
Vitamin B12 deficiency can be caused by a variety of factors, including vegetarian or vegan diets, gastrointestinal disorders such as celiac disease or Crohn's disease, and the use of proton pump inhibitors.
**Correct Answer: A. Subacute combined degeneration of the spinal cord.**