Eligible participants are:~Feeder participants: those who have completed a Phase 3 PTC Therapeutics (PTC) sponsored feeder study (including Study PTC923-MD-003-PKU).~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.
The main purpose of this study is to evaluate the long-term safety of PTC923 in participants with phenylketonuria, and to evaluate the changes from baseline in dietary phenylalanine (Phe)/protein consumption.