A Phase 3 Study of PTC923 in Subjects with Phenylketonuria

This is a Phase 3 open-label extension study for subjects with PKU who complete a Phase 3 PTC Therapeutics (PTC)-sponsored feeder study (including Study PTC923-MD-003-PKU). The study consists consists of open-label treatment with PTC923 administered orally once a day for a minimum of 12 months or until subject experiences lack of efficacy, adverse events AEs) that lead to discontinuation, withdraws from treatment, or PTC923 receives regulatory approval.