]> 2026-07-31T09:41:33+00:00 WBR0302 0 en Arginine Arginine is not usually supplemented in patients with PKU. Arginine is a nonessential amino acid, which serves as a precursor for nitric oxide synthesis. Cysteine Phenylalanine Phenylalanine supplementation would be disastrous for a patient with phenylketonuria. The deleterious effects of phenylketonuria are caused by the accumulation of phenylalanine, leading to toxic concentrations in the body. Tryptophan Tryptophan is not supplemented in PKU. Tryptophan is required for the synthesis of niacin (vitamin B3). Tryptophan can be deficient in patients with Hartnup disease, malabsorption syndromes, or carcinoid syndrome (resulting from the excessive conversion of tryptophan into serotonin). Tyrosine Tyrosine supplementation is essential for patients with phenylketonuria. Biochemistry A 4-month-old girl is brought to the emergency department following a seizure. Her mother had an uncomplicated pregnancy and had regular follow-ups with her obstetrician. The patient was delivered abroad and had a normal neonatal course. The family immigrated to USA only 3 weeks ago. Ever since the family moved, her mother has noticed that the girl has not been the same anymore. She does not seem to develop like her 2 sisters did before her; she appears lethargic all the time and feeds poorly. Upon further questioning, the mother adds that the patient's urine has an unusual musty odor. On physical examination, the patient has a pale skin with blonde hair and blue eyes. Her skin appears dry with eczematous lesions. Administration of which amino acid is required to relieve this patient's symptoms? E General Principles 2020-10-28T00:07:13Z 2459150.5050116 WBR0302