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New PKU drug could loosen strict diet restrictions

NCT ID NCT05166161

Disease control Sponsor: PTC Therapeutics Source: ClinicalTrials.gov ↗

What the study statuses mean

This study's is highlighted.

Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed This study
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jun 26, 2026 · Last updated Sep 10, 2026 · Updated 3 times

Summary

This phase 3 study tests a drug called PTC923 (sepiapterin) in 200 people with phenylketonuria (PKU), a genetic condition that requires a strict low-protein diet. The main goal is to see if the drug is safe over the long term and whether it allows people to eat more protein without harmful side effects. Participants take the drug daily as a powder mixed in water or apple juice.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance
PTC923 (sepiapterin), a powder taken by mouth mixed with water or apple juice
What this could lead to
If successful, this could provide a new treatment option that helps people with PKU tolerate more protein in their diet, potentially easing dietary restrictions.
What could go wrong
This is an open-label study without a placebo group, so results may be less reliable. The main focus is safety, and it is not designed to prove the drug works better than existing treatments.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 3

Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.

Participants

247 people

The number who actually took part.

Started

Feb 2022

Finished

Jul 2026

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

Children (under 18), adults (18 to 64) and older adults (65 and over)

Sex

Anyone

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Clinical diagnosis of PKU with hyperphenylalaninemia (HPA) documented by past medical history of at least 2 blood Phe measurements ≥600 μmol/L. * 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 up to 90 days after the last dose of the study drug. * Males who are sexually active with women of childbearing potential who have not had a vasectomy must agree to use a barrier method of birth control during the study and for up to 90 days after the last dose of study drug. Males must also refrain from sperm donations during this time period. * Willing to continue current diet unchanged while participating in the study (unless specifically instructed to change diet during the study by the investigator). Exclusion Criteria: * Inability to tolerate oral medication. * A female who is pregnant or breastfeeding, or considering pregnancy. * Serious neuropsychiatric illness (for example, major depression) not currently under medical control, that in the opinion of the investigator or PTC, would interfere with the participant's ability to participate in the study or increase the risk of participation for that participant. * Past medical history and/or evidence of renal impairment and/or condition including moderate/severe renal insufficiency (glomerular filtration rate \[GFR\] \<60 milliliters \[mL\]/minute \[min\] min as estimated most recently during qualifying participation in a feeder study) and/or under care of a nephrologist. * Any other condition that in the opinion of the investigator or PTC, would interfere with the participant's ability to participate in the study or increase the risk of participation for that participant. * Requirement for concomitant treatment with any drug known to inhibit folate synthesis (for example, methotrexate). * Concomitant treatment with tetrahydrobiopterin (BH4) supplementation (for example, sapropterin dihydrochloride, KUVAN) or pegvaliase-pqpz (PALYNZIQ). Additional criteria for non-feeder participants who did not participate in a feeder study: * Gastrointestinal disease (such as irritable bowel syndrome, inflammatory bowel disease, chronic gastritis, and peptic ulcer disease, etc) that could affect the absorption of study drug. * History of gastric surgery, including Roux-en-Y gastric bypass surgery or an antrectomy with vagotomy, or gastrectomy. * History of allergies or adverse reactions to synthetic BH4 or sepiapterin. * Any clinically significant laboratory abnormality as determined by the investigator. * Any abnormal physical examination and/or laboratory findings indicative of signs or symptoms of renal disease, including calculated GFR \<60 milliliters (mL)/minute/1.73 square meter (m\^2). Confirmed diagnosis of a primary BH4 deficiency as evidenced by biallelic pathogenic mutations in 6-pyruvoyltetrahydropterin synthase, recessive GTP cyclohydrolase I, sepiapterin reductase, quinoid dihydropteridine reductase, or pterin-4-alphacarbinolamine dehydratase genes.

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Conditions

The condition(s) this trial relates to.

phenylketonuria

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Phenylketonuria

Contacts and locations

Locations

  • Azienda Ospedaliera-Universita Padova

    Padua, Veneto, 35129, Italy

  • Birmingham Children's Hospital NHS Foundation Trust

    Birmingham, B4 6NH, United Kingdom

  • Boston Children's Hospital

    Boston, Massachusetts, 02115, United States

  • CENTRO HOSPITALAR UNIVERSITÁRIO LISBOA NORTE Hospital de Santa Maria

    Lisbon, Estremadura, 1649-035, Portugal

  • CENTRO HOSPITALAR UNIVERSITÁRIO LISBOA NORTE Hospital de Santa Maria,

    Lisbon, Estremadura, 1649-035, Portugal

  • Centro Hospitalar Universitário Do Porto, Epe

    Porto, 4099-001, Portugal

  • Children's Hospital Colorado

    Aurora, Colorado, 80045, United States

  • Copenhagen University Hospital, Rigshospitalet

    Copenhagen, DK-2100, Denmark

  • Department of Human Neuroscience, Child and Adolescent Neuropsychiatry, Policlinico Umberto I

    Rome, 00185, Italy

  • Ege University Faculty of Medicine Children Hospital

    Bornova, İzmir, 35100, Turkey (Türkiye)

  • Fakultní nemocnice Královské Vinohrady Klinika dětí a dorostu Ambulance pro léčbu PKU a HPA

    Prague, 100 34, Czechia

  • Gazi Üniversitesi Tıp Fakültesi

    Yenimahalle, Ankara, 06500, Turkey (Türkiye)

  • Great Ormond Street Hospital

    London, WC1N 3JH, United Kingdom

  • Hacettepe University Medical Faculty

    Altındağ, Ankara, 06230, Turkey (Türkiye)

  • Hospital Sant Joan de Déu

    Barcelona, Esplugues de Llobregat, 08950, Spain

  • Hospital Universitario Ramón y Cajal

    Madrid, 28034, Spain

  • Hospital Universitario Virgen del Rocío

    Seville, 41013, Spain

  • Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo

    Ribeirão Preto, São Paulo, 14051-140, Brazil

  • Hospital de clinicas de Porto Alegre

    Porto Alegre, Rio Grande do Sul, 90035-903, Brazil

  • Hôpital Necker-Enfants Malades - Centre de Référence des Maladies Héréditaires du Métabolisme

    Paris, 75015, France

  • Icahn School of Medicine at Mount Sinai (ISMMS)

    New York, New York, 10009, United States

  • Indiana University School of Medicine Department of Medical and Molecular Genetics

    Indianapolis, Indiana, 46202, United States

  • McMaster Children's Hospital Hamilton Health Sciences

    Hamilton, Ontario, L8N 3Z5, Canada

  • Medical Genetics and Laboratory Diagnostics Center

    Tbilisi, 0159, Georgia

  • Metabolics and Genetics in Calgary (MAGIC) Clinic, Ltd.

    Calgary, Alberta, T2E 7Z4, Canada

  • PARC Clinical Research

    Adelaide, South Australia, SA 5000, Australia

  • PTC Clinical Site 1

    Multiple Locations, Japan

  • PTC Clinical Site 2

    Multiple Locations, Japan

  • PTC Clinical Site 3

    Multiple Locations, Japan

  • PanAmerican Clinical Research

    Guadalajara, Jalisco, 44670, Mexico

  • Pomorski Uniwersytet Medyczny w Szczecinie Centrum Wsparcia Badań Klinicznych

    Szczecin, 71-252, Poland

  • Royal Children's Hospital

    Parkville, Victoria, 3052, Australia

  • The Hospital for Sick Children University of Toronto Adult Clinic: The Fred A Litwin Family Centre in Genetic Medicine University Health Network & Mt. Sinai Hospital

    Toronto, Ontario, M5G 1X8, Canada

  • The Queensland Children's Hospital

    South Brisbane, Brisbane, Australia

  • UF College of Medicine, Department of Pediatrics Division of Genetics and Metabolism

    Gainesville, Florida, 32610, United States

  • UMCG Beatrix Children's Hospital

    Groningen, 9713 GZ, Netherlands

  • UNIVERSITY HOSPITALS BIRMINGHAM NHS Foundation Trust

    Birmingham, United Kingdom

  • UPMC Children's Hospital of Pittsburgh

    Pittsburgh, Pennsylvania, 15224, United States

  • University Children's Hospital Hamburg Eppendorf (Kinder-UKE) Klinik für Kinder- und Jugendmedizin (Kinder-UKE)

    Hamburg, 20246, Germany

  • University of Utah

    Salt Lake City, Utah, 84108, United States

  • Universitätsklinikum Heidelberg / Zentrum für Kinder- und Jugendmedizin / Sektion für Neuropädiatrie & Stoffwechselmedizin

    Heidelberg, 69120, Germany

  • Universitätsklinikum Münster

    Münster, 48149, Germany

  • Univerzitetni klinicni center Ljubljana

    Ljubljana, 1000, Slovenia

  • Westmead Hospital

    Westmead, New South Wales, 2145, Australia

  • Çukurova Üniversitesi Tıp Fakültesi Balcalı Hastanesi

    Adana, 01330, Turkey (Türkiye)

  • İstanbul Üniversitesi Cerrahpaşa Tıp Fakültesi

    Fatih, Istanbul, 34098, Turkey (Türkiye)

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