A Long-Term Safety Study of PTC923 in Participants With Phenylketonuria

Eligible participants are: Feeder participants: those who have completed a Phase 3 PTC Therapeutics (PTC) sponsored feeder study. Non-feeder controlled participants: those who have not completed a feeder study and have blood Phe levels \<360 μmol/L at study entry. Non-feeder uncontrolled participants: those who have not completed a feeder study and have blood Phe levels ≥360 μmol/L at study entry.