The Food and Drug Administration (FDA) has granted Orphan Drug designation to PTC923 for the treatment of patients with hyperphenylalaninemia.

Hyperphenylalaninemia, a rare metabolic condition, is caused by mutations in the phenylalanine hydroxylase (PAH) gene leading to the toxic accumulation of phenylalanine in the brain, resulting in cognitive disabilities and seizures. Phenylketonuria (PKU) accounts for 98% of all hyperphenylalaninemia cases.   

PTC923 is an oral formulation of synthetic sepiapterin, a precursor to intracellular tetrahydrobiopterin, which is an enzymatic cofactor involved in the metabolism and synthesis of numerous metabolic products. The Company expects to initiate the global, placebo-controlled phase 3 APHENITY trial in mid-2021 to evaluate PTC923 in patients with PKU.

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“PKU is a devastating disease that can have severe and irreversible outcomes, including seizures, intellectual disability, behavioral problems and psychiatric disorders,” said Stuart W. Peltz, PhD, CEO PTC Therapeutics. “There still remains a high unmet need for more effective and safe treatment options for patients living with PKU.”

The FDA’s Orphan Drug designation is granted to medicines intended to treat or prevent rare diseases or disorders that affect fewer than 200,000 individuals.


PTC Therapeutics announces Orphan Drug designations of PTC923 for the treatment of hyperphenylalaninemia. [press release]. South Plainfield, NJ: PTC Therapeutics, Inc.; May 26, 2021.

This article originally appeared on MPR