A Study of PTC923 (CNSA-001) in Primary Tetrahydrobiopterin (BH4) Deficient Participants With Hyperphenylalaninemia

BH4 is an essential cofactor for phenylalanine hydroxylase, tyrosine hydroxylase, tryptophan hydroxylase, fatty acid glycerylether oxygenase, and nitric oxide (NO) synthase. The PBD is caused by deficiency of GTP cyclohydrolase I (GTP-CH), 6-pyruvoyl-tetrahydropterin synthase (PTPS), or sepiapterin reductase (SR) that impairs the biosynthesis of BH4 or by defects in BH4 recycling (pterin-4a-carbinolamine dehydratase \[PCD\] or dihydropteridine reductase \[DHPR\] deficiency). Participants will be randomized into one of 2 cohorts, with each cohort assessing 2 dose levels of PTC923 via intra-participant escalation.