Updated May 2026 · ClinicalTrials.gov

RECRUITINGPhase 3INTERVENTIONAL

A Study of Sepiapterin in Participants With Phenylketonuria (PKU)

A Phase 3b Open-Label Study of Long-Term Neurocognitive Outcomes in Children With Phenylketonuria Treated With Sepiapterin

A Study of Sepiapterin in Participants With Phenylketonuria (PKU) (NCT06302348) is a Phase 3 interventional studying Phenylketonuria, sponsored by PTC Therapeutics. RECRUITING as of the most recent ClinicalTrials.gov update. Talk to your doctor before contacting the trial site.

About This Trial

The main purpose of this trial is to evaluate the long-term efficacy of sepiapterin on preserving neurocognitive functioning in children with PKU when treatment is initiated in early childhood.

What Stage of Research Is This?

Phase 3 trials confirm efficacy and safety in large patient groups (often 300–3,000+) and form the evidence base for an FDA approval submission. For Phenylketonuria, Phase 3 studies typically randomize participants between the investigational treatment and either a placebo or current standard of care. A successful Phase 3 result is the threshold most treatments need to clear before regulatory approval.

This trial is currently recruiting participants. The sponsor has registered the study with ClinicalTrials.gov as actively enrolling, which means new applicants who meet the eligibility criteria can be considered for screening. Trial status can change between updates — confirm current recruiting status with the study contact before traveling for a screening visit.

Target enrollment of 56 participants puts this in the typical range for a Phase 2-style efficacy study or a moderate Phase 3 trial in a focused Phenylketonuria subpopulation. At this scale, the study has enough statistical power to detect a clear treatment effect but is not the largest cohort in the field.

Who May Be Eligible (Plain English)

Key Who May Qualify: For all participants: - Women of childbearing potential must have a negative pregnancy test at Screening and agree to abstinence or the use of at least one highly effective form of contraception for the duration of the study, and for at least 90 days after the last dose of the study drug. - Willing to maintain prescribed daily protein/Phe during Screening and Part 1. For participants ≥1 month of age at Screening: - Established diagnosis of PKU with hyperphenylalaninemia (HPA) evidenced by at least 2 blood Phe measurement ≥600 micromoles (μmol)/liter (L) as documented in the medical history. - A minimum of 1 documented blood Phe measurement \<480 μmol/L within 1 month prior to Screening. - Two screening blood Phe concentration values must be in the range ≥120 to ≤480 μmol/L. For participants \<1 month of age at the time of willing to sign a consent form/assent only: - Blood Phe at newborn screening ≥600 μmol/L. For participants ≥30 months to \<10 years of age: - Baseline FSIQ score ≥80. Key Who Should NOT Join This Trial: - History of allergies or adverse reactions to any of the ingredients or excipients of synthetic tetrahydrobiopterin (BH4) or sepiapterin. - Serious neuropsychiatric illness (for example, major depression) not currently under medical control or other concurrent disease or condition that, in the opinion of the investigator or sponsor, would interfere with the participant's ability to participate in the study or increase the risk of participation for that participant. - Treatment with BH4 supplementation (sapropterin, KUVAN®) within 3 months prior to Screening. - Current participation in another investigational drug study or use of any investigational agent within 30 days prior to Screening. ...See full criteria on ClinicalTrials.gov Always talk to your doctor about whether this trial is right for you.

These are translations of the protocol\'s inclusion and exclusion criteria, simplified for patients and caregivers. The original clinical text appears below. Eligibility is ultimately confirmed by the trial site\'s screening process — this summary is a starting point for a conversation with your doctor, not a final determination.

Original Eligibility Criteria

View original clinical language

Key Inclusion Criteria: For all participants: * Women of childbearing potential must have a negative pregnancy test at Screening and agree to abstinence or the use of at least one highly effective form of contraception for the duration of the study, and for at least 90 days after the last dose of the study drug. * Willing to maintain prescribed daily protein/Phe during Screening and Part 1. For participants ≥1 month of age at Screening: * Established diagnosis of PKU with hyperphenylalaninemia (HPA) evidenced by at least 2 blood Phe measurement ≥600 micromoles (μmol)/liter (L) as documented in the medical history. * A minimum of 1 documented blood Phe measurement \<480 μmol/L within 1 month prior to Screening. * Two screening blood Phe concentration values must be in the range ≥120 to ≤480 μmol/L. For participants \<1 month of age at the time of informed consent/assent only: * Blood Phe at newborn screening ≥600 μmol/L. For participants ≥30 months to \<10 years of age: * Baseline FSIQ score ≥80. Key Exclusion Criteria: * History of allergies or adverse reactions to any of the ingredients or excipients of synthetic tetrahydrobiopterin (BH4) or sepiapterin. * Serious neuropsychiatric illness (for example, major depression) not currently under medical control or other concurrent disease or condition that, in the opinion of the investigator or sponsor, would interfere with the participant's ability to participate in the study or increase the risk of participation for that participant. * Treatment with BH4 supplementation (sapropterin, KUVAN®) within 3 months prior to Screening. * Current participation in another investigational drug study or use of any investigational agent within 30 days prior to Screening. * Confirmed diagnosis of a primary BH4 deficiency as evidenced by biallelic pathogenic mutations in 6-pyruvoyltetrahydropterin synthase, recessive Guanosine-5'-triphosphate (GTP) cyclohydrolase I, sepiapterin reductase, quinoid dihydropteridine reductase, or pterin 4-alphacarbinolamine dehydratase genes. * Any clinically significant laboratory abnormality as determined by the investigator. * Any past medical history of an abnormal physical examination and/or laboratory findings indicative of signs or symptoms of renal disease, including calculated (Bedside Schwartz Equation) glomerular filtration rate (GFR) \<60 milliliters (mL)/minute (min)/1.73 square meter (m\^2). * Major surgery within 90 days prior to Screening visit. * Previous treatment for \>6 weeks with sepiapterin (that is, Sephience). Note: Other protocol-defined inclusion and exclusion criteria may apply.

Treatments Being Tested

DRUG

Sepiapterin

Sepiapterin powder for oral use will be mixed in water or apple juice prior to administration.

Locations (8)

Trial sites listed on ClinicalTrials.gov for this study. Site activation status can vary — confirm with the specific site before traveling for a screening visit.

Indiana University School of Medicine

Indianapolis, Indiana, United States

Women and Children Hospital

North Adelaide, Australia

The Royal Children's Hospital

Parkville, Australia

Centre Hospitalier Régional Universitaire (CHRU) de Tours - Hôpital Clocheville

Tours, France

Children's Health Ireland (CHI)

Dublin, Ireland

Pomorski Uniwersytet Medyczny w Szczecinie

Szczecin, Poland

Instytut Matki i Dziecka

Warsaw, Poland

Birmingham Women's and Children's NHS Foundation Trust

Birmingham, United Kingdom

How to Talk to Your Doctor About This Trial

Bring the printable summary of this trial — including the NCT ID (NCT06302348), the sponsor (PTC Therapeutics), and the key eligibility criteria — to your next appointment. Your doctor can review the inclusion and exclusion criteria against your medical history, lab values, and current treatments to assess whether you are likely to qualify. They can also help you weigh whether trial participation makes sense alongside your existing care plan.

Useful questions to walk through together: What does the trial protocol require beyond standard care? How long is the active treatment phase, and how long is follow-up? Are there study visits at sites I can reach? Who pays for the trial-specific procedures, and who pays for standard-of-care portions? See our 25 questions to ask about clinical trials guide for a more complete checklist.

Authoritative Sources

The official record for this trial lives on ClinicalTrials.gov — the federal registry maintained by the National Library of Medicine at NIH. For background on how this trial fits into the FDA approval pathway, see the FDA drug approval process. For oncology-specific guidance for patients considering trials, the National Cancer Institute publishes patient-oriented overviews. International trial registries are aggregated by the WHO ICTRP.

Frequently Asked Questions

What is the NCT06302348 clinical trial studying?

The main purpose of this trial is to evaluate the long-term efficacy of sepiapterin on preserving neurocognitive functioning in children with PKU when treatment is initiated in early childhood. The full protocol is registered on ClinicalTrials.gov and includes the primary outcome measures, eligibility criteria, and study endpoints.

Who can participate in NCT06302348?

Eligibility for this trial depends on the specific inclusion and exclusion criteria set by the sponsor. The plain-English summary above translates the most important criteria into accessible language; the official clinical text is preserved in the collapsible section underneath. Whether you fit any specific trial is a medical decision your doctor needs to confirm — bring the trial information to your treating physician for a full review against your medical history.

How do I contact the trial site for NCT06302348?

Contact information registered with ClinicalTrials.gov is shown in the sidebar of this page. Before reaching out, confirm with your treating physician that this trial is appropriate for your situation. The trial site will then walk you through the screening process to determine final eligibility.

Is participating in a clinical trial safe?

Clinical trials in the United States are regulated by the FDA and overseen by Institutional Review Boards (IRBs) that review the protocol for safety. Risk varies by trial — Phase 1 studies test new treatments in humans for the first time, while Phase 3 trials use treatments that have already passed earlier safety screening. The informed consent document for any specific trial details the known risks and what to expect. Discuss those risks with your physician before deciding whether to participate.

Where can I verify the data on this page?

Every detail on this page comes directly from the ClinicalTrials.gov API. Click "View on ClinicalTrials.gov" in the sidebar to see the official, unmodified record. The federal record is always authoritative; this page is a structured presentation with a plain-English eligibility translation. For background on how clinical trials are regulated, see the FDA drug approval process documentation.

How This Page Is Built

Every field on this page is pulled directly from the ClinicalTrials.gov API v2 — no estimates, no proxies. The plain-English eligibility translation is generated from the original protocol text and reviewed for fidelity to the underlying clinical criteria. The original clinical text remains visible in the collapsible section above so users and clinicians can verify the translation. Read the full methodology for the data pipeline and known limitations.

Source: ClinicalTrials.gov API v2 record for NCT06302348. Maintained by the National Library of Medicine at NIH. Public domain. Cite as: "TrialFinderData. NCT06302348. Data: ClinicalTrials.gov."

Medical disclaimer: This page is informational, not medical advice. Talk to your doctor about whether a clinical trial is right for you.

Last updated 2026-05-08 · Data from ClinicalTrials.gov.