USMLE Step 1 Question 357

Question:

A pair of new parents bring in their one-month-old son saying he has been acting strangely since being brought home from the hospital. They report that the child has been not eating well and seems lethargic. The physical exam is normal except for mild hypotonia. Blood tests taken the week before show a significantly elevated lactate level. Due to a high suspicion for pyruvate dehydrogenase deficiency, a functional enzyme assay is ordered. The diagnosis is confirmed. Which one of these amino acids will the doctor recommend increasing in the child’s diet?

Correct Answer: D.  Lysine

In pyruvate dehydrogenase deficiency, there is a backup of pyruvate and alanine resulting in lactic acidosis. This can be caused from a congenital enzyme deficiency or can be acquired due to vitamin B1 deficiency (in alcoholics for example). The treatment for this is to increase the intake of ketogenic nutrients. The two ketogenic amino acids are leucine and lysine (choice D). The other amino acids listed here are not ketogenic.

Histamine (choice C) is not an amino acid and is unlikely to be an option on well-edited exam.