This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
B12 deficiency causes - 
Select and explain. 
A. Demyelination, B. Dermatitis, C. Burning foot syndrome, D. Beriberi
A: Demyelination
Answer: A: Demyelination 
Explanation: Ans. is 'a' i.e., Demyelination* B12 in the form of Adenosyl B12 acts as a coenzyme for Methyl malonyl Co A mutase. Methyl Malonyl Co A mutase helps in the conversion of methyl malonyl Co A to Succinyl Co A. Hence, in B12 deficiency, methyl malonyl CoA accumulates. Methyl Malonyl CoA gets incorporated into fatty acids (instead of malonyl CoA). This results in abnormal fatty acids getting synthesized. When these fatty acids get incorporated in myelin, it results in rapid demyelination