This study is looking at the long-term safety of a medicine called pegvaliase for treating a condition known as PKU (phenylketonuria). PKU is a genetic disorder where the body can't break down a certain protein building block called phenylalanine (Phe), leading to health problems. Pegvaliase is a treatment that helps reduce Phe levels in the blood. This study will observe patients over 10 years to see how the medicine affects them, especially in terms of any allergic reactions or other side effects.

• This study lasts for 10 years and involves no extra procedures; regular doctor visits are needed.
• Participants must be currently receiving or planning to receive pegvaliase for PKU.
• There is no experimental treatment involved; it's just observation.

Note: Participants should have a diagnosis of PKU and be able to provide consent to join the study. This is not for those in other experimental studies. If you meet the criteria and want to learn about the safety of pegvaliase, this study might be for you!