Phenylalanine and Tyrosine Metabolism

A 3-year-old boy from rural Maharashtra is brought with developmental delay, light-colored skin, and a musty odor. Plasma phenylalanine is 28 mg/dL (normal <2). Urine shows no succinylacetone. Which finding would distinguish this child's condition from alkaptonuria?

A 3-day-old male neonate born to consanguineous parents presents with poor feeding, lethargy, and a distinctive musty or mousy odour on the breath and urine. Newborn screening shows elevated plasma phenylalanine (>20 mg/dL; normal <2 mg/dL) and elevated urinary phenylketones. Physical examination reveals fair skin and blonde hair. What is the most likely diagnosis?

A 28-year-old Indian woman with a history of classical phenylketonuria (PKU), well-controlled on a phenylalanine-restricted diet since infancy, presents to the antenatal clinic at 8 weeks of gestation. Her recent plasma phenylalanine level is 18 mg/dL (normal <2 mg/dL). Ultrasound shows a structurally normal fetus. Which of the following is the most appropriate next step in management?

Which single biochemical finding best distinguishes phenylketonuria (PKU) from tyrosinemia type I?

Regarding the metabolic pathways of phenylalanine and tyrosine, all of the following statements are correct EXCEPT: