A 23-year-old man comes to the clinic with progressive fatigue and difficulty walking over the past several months. He also reports numbness and tingling in his feet, along with occasional problems with balance. His appetite is normal, but he has noticed an unintentional weight loss of 4 kg in the last six months. He denies alcohol use and has no significant surgical history. On examination, he appears pale, with a smooth, shiny tongue and decreased vibratory sensation in the lower extremities. Reflexes in the ankles are diminished, and he demonstrates a positive Romberg sign. His blood pressure and heart rate are within normal limits. He has no hepatosplenomegaly or lymphadenopathy. MCV is 104 fL. Which of the following is the most likely explanation for this patient’s findings?
A) Antibodies against gastric chief cells
B) Deficiency of cofactor for dehydrogenase enzymes
C) Dietary deficiency
D) Dry beriberi
E) Hartnup disease
