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PTC Therapeutics Presents New Sepiapterin Data from Ongoing Studies

On March 20, 2025, PTC Therapeutics, Inc. (NASDAQ: PTCT) unveiled promising findings from their Phase 3 APHENITY trial, along with its open-label extension study, during the 2025 American College of Medical Genetics and Genomics (ACMG) Annual Clinical Genetics Meeting. These results highlight the meaningful positive impact of sepiapterin treatment for a wide range of patients suffering from phenylketonuria (PKU), notably allowing for greater diet flexibility.

Key Findings from the Study

The data revealed that an impressive 97% of participants who followed the Phe tolerance protocol in the APHENITY open-label extension were capable of broadening their dietary intake while undergoing sepiapterin treatment, achieving a mean increase of 126% in protein consumption. Notably, 66% of these individuals met or surpassed the recommended daily allowance of protein for someone without PKU, all while maintaining controlled blood Phe levels. This underlines not only the effectiveness of sepiapterin but its potential to allow patients a more normal dietary routine, contributing to improved quality of life.

The genetic analysis conducted during the APHENITY trial indicated that over 70% of subjects had genotype-phenotype values consistent with classical PKU, affirming the relevance of sepiapterin treatment for this specific group. Matthew B. Klein, M.D., the CEO of PTC Therapeutics, expressed optimism regarding these findings, stating, "These new data provide further evidence of the meaningful benefit sepiapterin can provide for children and adults with PKU, including those with the most severe form of the disease."

What is Sepiapterin?

Sepiapterin, previously known as PTC923, is an oral formulation that operates through a dual mechanism to boost the activity of the phenylalanine hydroxylase (PAH) enzyme. Initially, sepiapterin acts as a precursor that swiftly absorbs and converts to tetrahydrobiopterin (BH4), an essential cofactor for PAH function. Additionally, sepiapterin showcases a unique pharmacological chaperone effect, rectifying misfolded PAH to enhance its functionality. This dual-action approach enables sepiapterin to effectively reduce blood phenylalanine levels while catering to a broad patient demographic.

Understanding Phenylketonuria (PKU)

PKU is a rare genetic metabolic disorder that affects cerebral function, stemming from a gene defect essential for producing an enzyme responsible for breaking down phenylalanine—a crucial amino acid abundant in proteins. If improperly managed, excess phenylalanine can lead to serious disabilities including intellectual disability, seizures, and developmental delays. Infants with PKU may initially appear healthy, but symptoms progressively worsen, necessitating early screening for effective management.Globally, it is estimated that around 58,000 individuals are diagnosed with PKU.

About PTC Therapeutics, Inc.

PTC Therapeutics is a global biopharmaceutical firm committed to discovering, developing, and commercializing innovative medicines tailored for patients with rare diseases. The company’s strategy hinges on leveraging its extensive scientific expertise to deliver transformative treatments and maximize patient value. More about PTC and its ongoing projects can be found on their official website and social media channels.

This recent data presented at the ACMG meeting offers vital insights into the advantages associated with sepiapterin for PKU patients, paving the way for future developments in treatment strategies. As PTC Therapeutics continues to push the boundaries in addressing rare conditions, it solidifies its position at the forefront of the biopharmaceutical landscape.