Vitamin B12

Neurology Board Preparation > Myelopathies, Multiple Sclerosis, & ALS > Nutritional Deficiencies

Q. A 65-year-old man presents with fatigue and pallor. Laboratory studies reveal macrocytic anemia with hypersegmented neutrophils. Serum testing shows elevated homocysteine and elevated methylmalonic acid. Which of the following best explains the elevated methylmalonic acid in this patient?

Defective thymidylate synthesis

Impaired conversion of methylmalonyl-CoA to succinyl-CoA

Inhibition of dihydrofolate reductase

Deficiency of cystathionine beta-synthase

Reduced intrinsic factor secretion

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