Review Question - QID 109670

A 7-month-old boy is brought to the pediatrician for a change in his behavior. The patient has been breastfeeding up until this point and has been meeting his developmental milestones. He is in the 90th percentile for weight and 89th percentile for height. This past week, the patient has been lethargic, vomiting, and has been refusing to eat. The patient's parents state that he had an episode this morning where he was not responsive and was moving his extremities abnormally followed by a period of somnolence. The patient's past medical history is notable for shoulder dystocia and poorly managed maternal diabetes during the pregnancy. His temperature is 99.5°F (37.5°C), blood pressure is 60/30 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. On physical exam, you note a lethargic infant with a sweet smell to his breath. Which of the following is most likely deficient in this patient?