A 4-day old infant (patient A) is being followed in your clinic. Her birth weight was 5.9 pounds and the pregnancy and birth (vaginal delivery) were normal. Results from newborn screening demonstrated a phenylalanine (Phe) level of 6.6 mg/dl (normal range: 1-2 mg/dL). A presumptive diagnosis of phenylketonuria was made and additional samples were obtained for further analysis. The parents deny a family history of PKU. Phe dietary restriction therapy was initiated at 14 days of age with good response of plasma phenylalanine levels that dropped to within the normal range (1.65 mg/dL, 100 uM). *BH4 loading test: Tablets of synthetic cofactor are dissolved in 20 ml of water in dim light and administered to the patients at least 30 min before a meal. Blood was drawn before, and 4 and 8 hours after BH4 loading: Phe levels are determined. 1. Is phenylalanine glucogenic, ketogenic, or both? Explain 2. Tyrosine is not an essential amino acid in normal persons, but it is essential in persons with PKU. Explain why 3. What are the potential cause(s) of the presentation of phenylketonuria? 4. What happens during PKU to cause brain damage? 5. What is one lifestyle change that can be used to treat PKU