A 13-year-old boy is brought to the emergency department with severe chest pain. He has had intermittent substernal chest pain for the past few months that typically occurs after heavy activity. The boy's activities have been limited due to the chest pain, and he is no longer able to play on the soccer team. The patient does not use tobacco or illicit drugs. His temperature is 36.7 C (98 F), blood pressure is 130/80 mm Hg, pulse is 132/min, respirations are 24/min, and pulse oximetry is 98% on room air. BMI is 17 kg/m². Physical examination shows an anxious-appearing boy with a rapid but regular pulse. No abnormalities are seen. Troponin is elevated, and ECG reveals ST segment elevations in leads II, III, and aVF. After acute stabilization and treatment, further laboratory workup shows an increased serum methionine level. Which of the following amino acids is most likely essential in this patient?

Question

Quizplus · Accepted Answer

Eductional Objective: Homocystinuria is most commonly caused by a defect in cystathionine synthase, resulting in an inability to form cysteine from homocysteine.  Cysteine becomes essential in affected patients, and homocysteine buildup leads to elevated methionine.  Homocysteine is prothrombotic, resulting in premature thromboembolic events (eg, atherosclerosis, acute coronary syndrome) in these patients.

A 13-Year-Old Boy Is Brought to the Emergency Department with Severe