A Study of JNT-517 in Participants With Phenylketonuria (PKU)

• Male or female participants aged 4 years or older.
• Diagnosed with phenylketonuria.
• Have phenylalanine levels that meet study requirements.
• Meet study-specific requirements regarding current treatment for phenylketonuria.
• Willing and able to follow study dietary requirements.
• Weigh at least 12.5 kilograms.
• If able to become pregnant or father a child, willing to follow the study's contraception requirements.
• Any ongoing mental health condition must be stable before entering the study.
• Able to provide informed consent (or have consent provided by a parent or legal guardian, when applicable) and comply with study procedures.

Participants will be excluded from the study if any of the following criteria are met:

• Significant medical condition that, in the investigator's opinion, could make participation unsafe or interfere with study participation.
• Significant liver disease or impaired kidney function.
• Certain eye conditions, including significant cataracts.
• Active infection requiring medical evaluation.
• History of certain cancers within the past 5 years.
• Allergy or hypersensitivity to JNT-517 or its ingredients.
• Prior treatment with JNT-517.
• Recent participation in another investigational study or receipt of an investigational treatment that does not meet study requirements.
• Use of medications that are not permitted during the study.
• Abnormal laboratory or heart test results that would make study participation inappropriate.
• Conditions that could affect the absorption of oral study medication.
• History of recent substance or alcohol abuse.
• Unwillingness to follow study requirements, including restrictions on intentional weight loss.