Evaluation of Phe Fluctuation in PKU Pts Treated With PKU GOLIKE Versus Standard Amino Acid Protein Substitute.

This is a 2 arm, randomised, controlled, cross-over study in 16 children with PKU. Subjects who are currently taking a Phe free/low Phe protein substitute will be recruited for a 31-day trial. Patients will be randomised to receive: 1. The study product for 7 days as their last dose of protein substitute for the day (at least one sachet with 15g PE) in an amount equivalent to their usual protein substitute PE; or 2. An amino acid protein substitute for all daily doses for 7 days; followed by a 2-week washout period on their usual protein substitute, and then 7 days of the other study arm. During this time, patients/caregivers will be asked to: * Collect 3 finger prick blood spots on days -1, 0, 6, 7, 20, 21, 27 and 28. * Collect urine sample, second void of the day on days 0, 7, 21 and 28. * Complete a questionnaire on sleep quality on day 0, 7, 21 and 28. * Complete a 24 hour food diary on days -1, 0, 6, 7, 20, 21, 27 and 28. APR will supply the study product for participants free of charge.