A 2-week-old male presents with poor feeding and hypotonia. Newborn screening revealed markedly elevated serum phenylalanine (28 mg/dL; normal <2). Despite strict low-phenylalanine diet initiated at 5 days of life, he develops progressive developmental delay and seizures at 3 weeks. Vital signs show HR 145, RR 32, temp 37.2°C. CSF analysis demonstrates low dopamine and serotonin metabolites. Serum tyrosine remains low despite adequate protein intake. Which of the following best explains his neurologic deterioration despite dietary phenylalanine restriction?

1. A)Cystathionine beta synthase deficiency
2. B)Dihydrofolate reductase deficiency
3. C)Tetrahydrobiopterin deficiencyGABARITO
4. D)Phenylalanine hydroxylase deficiency only
5. E)Branched chain alpha ketoacid dehydrogenase deficiency