Announcement • Aug 24

Ptc Therapeutics Announces New Sephience Data Reinforcing Broad Patient Benefits Including Sustained Metabolic Control and Diet Liberalization as Well as Consistent Favorable Safety Profile

PTC Therapeutics, Inc. announced that multiple Sephience (sepiapterin) scientific data presentations will be featured at the 2026 Society for the Study of Inborn Errors of Metabolism (SSIEM) Annual Symposium, taking place in Helsinki, Finland, from August 25-28. The presentations include new data from clinical trials and real-world evidence which reinforce the clinically meaningful benefits of Sephience on lowering phenylalanine (Phe), significant diet liberalization and sustained metabolic control for the full spectrum of individuals living with phenylketonuria (PKU) including those with classical PKU. In addition, Sephience studies continue to show a consistent and favorable safety profile. Highlights of the data to be presented at SSIEM 2026 include: New analyses from the AMPLIPHY study demonstrate that Sephience treatment resulted in a 100% greater reduction in blood Phe for participants on sapropterin at screening after switching to Sephience. In an analysis of participants in Sephience studies with high baseline Phe levels (=900 µmol/L), Sephience treatment resulted in clinically meaningful reductions in blood Phe levels within 14 days, with response rates comparable to the overall study population, and a safety profile consistent with prior studies. These findings support a trial of Sephience treatment in individuals with PKU regardless of severity or baseline Phe. An analysis of real-world data performed by a global key opinion leader shows that Sephience enabled significant dietary liberalization in adolescents, supporting greater independence, reduced dietary burden, and maintained metabolic control within recommended targets. These results were observed in individuals with both BH4-responsive and classical/non-BH4 responsive PKU mutations. Sephience is indicated for the treatment of adult and pediatric patients with phenylketonuria (PKU). Sephience is a natural precursor of the enzymatic co-factor BH4, a critical co-factor for phenylalanine hydroxylase (PAH). Through its unique dual mechanism of action, Sephience is able to effectively reduce blood phenylalanine (Phe) levels and has the potential to treat a broad range of PKU patients. Sephience is approved in the United States, the European Union/European Economic Area region, Japan and other countries. SEPHIENCE is indicated for the treatment of hyperphenylalaninemia (HPA) in adult and pediatric patients 1 month of age and older with sepiapterin-responsive phenylketonuria (PKU). SEPHIENCE is to be used in conjunction with a phenylalanine (Phe)-restricted diet. Treatment with SEPHIENCE should be directed by physicians knowledgeable in the management of PKU. Biochemical response to SEPHIENCE can only be determined by a therapeutic trial with careful monitoring of ongoing dietary and nutritional balance to ensure adequate Phe control. SEPHIENCE may increase the risk of bleeding. Bleeding events, including superficial hematomas, prolonged bleeding, and heavy menstrual bleeding have occurred in patients treated with SEPHIENCE. Consider treatment interruption with SEPHIENCE in patients with active bleeding. Some pediatric patients receiving SEPHIENCE experienced hypophenylalaninemia. Monitor blood Phe levels during treatment and modify the dosage of SEPHIENCE and/or dietary protein and Phe intake as needed to ensure adequate blood Phe level control. Frequent blood monitoring is recommended in the pediatric population. In a 10-year post-marketing safety surveillance program for a non-PKU indication using another drug that is a phenylalanine hydroxylase (PAH) activator, three patients with underlying neurological disorders experienced seizures, exacerbation of seizures, over-stimulation, and irritability during co-administration with levodopa. Monitor patients who are receiving levodopa for changes in neurological status during treatment with SEPHIENCE. Most common adverse reactions with SEPHIENCE (=2% and > placebo) were diarrhea, headache, abdominal pain, hypophenylalaninemia, feces discoloration and oropharyngeal pain. Avoid concomitant use of drugs known to inhibit folate synthesis dihydrofolate reductase (DHFR) (e.g., trimethoprim, methotrexate, trimetrexate, pemetrexed, pralatrexate, raltitrexed, and piritrexim) while taking SEPHIENCE. Concomitant administration of such drugs may reduce sepiapterin metabolism to BH4. If concomitant use is not avoidable, monitor blood Phe levels. SEPHIENCE and PDE-5 inhibitors (e.g., sildenafil, vardenafil, or tadalafil) induce vasorelaxation and may reduce blood pressure. Monitor for signs and symptoms of hypotension. Phenylketonuria (PKU) is a rare, inherited metabolic disease, characterized by the body's inability to break down an essential amino acid called phenylalanine (Phe) and which can result in neurological and other symptoms. If left untreated or poorly managed, Phe can build up to harmful levels in the body. This causes severe and irreversible disabilities, such as permanent intellectual disability, seizures, delayed development, memory loss, and behavioral and emotional problems. Newborns with PKU initially do not have any symptoms, but symptoms are usually progressive, and damage caused by toxic levels of Phe in the first few years of life is irreversible. Diagnosis of PKU usually takes place during newborn screening programs. There are an estimated 58,000 people living with PKU globally.

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