Phenylketonuria (PKU) is a genetic disorder where the body can't properly break down an amino acid called phenylalanine (Phe). If not controlled, Phe builds up and can cause serious brain problems. Traditionally, people with PKU follow a strict diet to keep Phe levels safe. However, a new medicine called Palynziq helps lower Phe levels, allowing for a more flexible diet. This study is exploring how Palynziq affects diet quality, brain health, and overall nutrition in PKU patients.

This is a three-year study for PKU patients who are 16 or older and have a prescription for Palynziq. Participants can choose to join an extended five-year study after completing the main one. They must also be part of the Palynziq Risk Evaluation and Mitigation Strategy (REMS) program, which helps ensure safe use of the medicine. People who can't consent or have other mental health disorders can't participate.

• Study Duration: Main study lasts 3 years, with an option to join a 5-year follow-up.
• Eligibility: Must be 16+, diagnosed with PKU, and have a Palynziq prescription.
• Exclusions: Those unable to give consent or with other mental health issues.