A newborn screen detects elevated phenylalanine (1200 μmol/L). The infant appears normal. Confirmatory testing shows classic PKU (PAH deficiency). What is the MOST CRITICAL principle in dietary management of PKU?
- A Restrict phenylalanine to the minimum required for growth while providing adequate tyrosine supplementation ✓
- B Eliminate all protein from the diet to prevent phenylalanine accumulation
- C Supplement with BH4 (sapropterin) as first-line therapy for all PKU patients
- D Restrict dietary fat and supplement with medium-chain triglycerides to improve brain energy metabolism
Explanation
PKU management requires restriction of phenylalanine (an essential amino acid) to the minimum needed for protein synthesis and growth, while providing adequate tyrosine, which becomes conditionally essential since the PAH enzyme that converts phenylalanine to tyrosine is deficient. Complete protein elimination would cause protein deficiency and growth failure. Sapropterin (BH4) is effective only in BH4-responsive PKU (a subset, not all patients), and in classic PAH deficiency it does not lower phenylalanine as dramatically as in mild/moderate forms. Dietary fat restriction is not indicated.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.