A 3-year-old boy is brought to the emergency department due to altered mental status with fever. He had multiple episodes of emesis this morning, and his mother was unable to wake him from his afternoon nap. The boy has had mild rhinorrhea and fever for the past 3 days. Since the newborn period, the parents say that the patient has had multiple illnesses characterized by vomiting and sleepiness. Prior laboratory testing revealed increased blood ammonia levels during these episodes and markedly increased orotic acid excretion in the urine. Physical examination shows a tachypneic boy who is unresponsive to all stimuli. Which of the following enzymes is most likely to be deficient in this patient?

Question

A 3-year-old boy is brought to the emergency department due to altered mental status with fever.  He had multiple episodes of emesis this morning, and his mother was unable to wake him from his afternoon nap.  The boy has had mild rhinorrhea and fever for the past 3 days.  Since the newborn period, the parents say that the patient has had multiple illnesses characterized by vomiting and sleepiness.  Prior laboratory testing revealed increased blood ammonia levels during these episodes and markedly increased orotic acid excretion in the urine.  Physical examination shows a tachypneic boy who is unresponsive to all stimuli.  Which of the following enzymes is most likely to be deficient in this patient?

Quizplus · Accepted Answer

Eductional Objective: Patients with urea cycle disorders typically have discrete episodes of vomiting, tachypnea, and confusion/coma secondary to hyperammonemia (a metabolic emergency).  Ornithine transcarbamylase deficiency is the most common disorder of the urea cycle and is characterized by hyperammonemia and elevated urinary orotic acid.

A 3-Year-Old Boy Is Brought to the Emergency Department Due