Gene therapy aims to tame rare metabolic disorder
NCT ID NCT05345171
First seen Jun 27, 2026 · Last updated Sep 10, 2026 · Updated 2 times
Summary
This Phase 3 trial tests a gene therapy called DTX301 for people with late-onset OTC deficiency, a rare genetic disorder that causes dangerous ammonia buildup. The study involves 37 participants and compares the gene therapy to a placebo. The goal is to see if the treatment can help control ammonia levels and reduce the number of metabolic crises.
What this could mean
Our plain-language read of the trial. This is informational only, not medical advice or a prediction.
- Active substance
- DTX301 (avalotcagene ontaparvovec) gene therapy
- What this could lead to
- If successful, this gene therapy could help people with OTC deficiency maintain safe ammonia levels and reduce the risk of dangerous metabolic crises.
- What could go wrong
- This is an early-stage Phase 3 trial with only 37 participants. The therapy may not work for everyone, and side effects from the gene vector or required steroids are possible.
Why investors are watching
Ultragenyx is running a phase 3 trial of DTX301, a gene therapy for late-onset OTC deficiency, a rare liver enzyme disorder. The trial tests whether the therapy keeps ammonia levels safe in 37 patients. For a small company, this readout could define the value of its gene therapy pipeline.
If it works: A positive result could support approval of DTX301 and give Ultragenyx a new commercial product for a rare disease with few options. That would broaden the company's portfolio beyond its existing treatments.
If it fails: A failed or delayed trial could set back the program and hurt the company's prospects. Gene therapy trials often fail, and a small company has limited resources to absorb a major setback.
AI-written from the trial record. Speculative, and not investment advice.
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
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Phase 3
Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.
- Participants
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37 people
The number who actually took part.
- Started
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Oct 2022
- Expected to finish
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Mar 2031
An estimate. End dates often move.
- Lead sponsor
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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
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12 years and older
- Sex
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Anyone
- Healthy volunteers
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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 Hide 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.
Key Inclusion Criteria: * Confirmed clinical diagnosis of late-onset OTC deficiency with historical documentation by enzymatic (ie, liver biopsy), biochemical (ie, hyperammonemia in the presence of elevated plasma glutamine, low citrulline, and elevated spot urine orotic acid), or molecular testing (ie, OTC analysis) * Free from symptomatic hyperammonemia and has not required emergent active intervention for hyperammonemia within 4 weeks before screening/baseline * If on ongoing daily ammonia scavenger therapy, must be at stable daily dose(s) for ≥ 4 weeks prior to screening * If on a protein-restricted diet, must be on a stable total daily protein intake that does not vary more than 20% for ≥ 4 weeks prior to screening * From the time written informed consent through Visit 28, females of childbearing potential and fertile males must consent to use highly effective contraception. If female, agree not to become pregnant. If male, agree not father a child or donate sperm Key Exclusion Criteria: * Significant hepatic inflammation or cirrhosis * Estimated glomerular filtration rate \< 60 mL/min/1.73 m2 at screening by the 2021 CKD-EPI creatinine-based formula (Inker et al., 2021) for patients ≥ 18 years of age or the Schwartz bedside formula (Schwartz and Work, 2009) for patients \< 18 years of age * Evidence of active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection, documented by current use of antiviral therapy for HBV or HCV or by hepatitis B surface antigen (HBsAg) or HCV RNA positivity * Active infection (viral or bacterial) * Detectable pre-existing antibodies to the AAV8 capsid * Presence or history of any condition that, in the view of the Investigator, would interfere with participation, pose undue risk, or would confound interpretation of results * Participation (current or previous) in another gene transfer study Note: Additional inclusion/exclusion criteria may apply, per protocol
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Conditions
The condition(s) this trial relates to.
As listed by the trial registrant
The condition terms exactly as the trial's registrant entered them.
Contacts and locations
Locations
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Ann & Robert H. Lurie Children's Hospital of Chicago
Chicago, Illinois, 60611, United States
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Centro Hospitalar Universitario de Sao Joao
Porto, 4200-319, Portugal
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Clinica Universitaria Reina Fabiola
Córdoba, X5004, Argentina
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Erasmus Universitair Medisch Centrum Rotterrdam
Rotterdam, 3015, Netherlands
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Fujita Health University Hospital
Toyoake, 470-1192, Japan
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Fundacio Hospital Universitari Vall D'Hebron-Institute de Recerca
Barcelona, 08035, Spain
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Hopital Femme Mere Enfant
Bron, 69500, France
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Hospital Italiano de Buenos Aires
Buenos Aires, C1199, Argentina
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Hospital de Clinicas de Porto Alegre
Porto Alegre, 90035-903, Brazil
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Kumamoto University Hospital
Kumamoto, 860-8556, Japan
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Necker-Enfants Maladas Hospital
Paris, 75015, France
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The Hospital for Sick Children
Toronto, Ontario, M5G 1X8, Canada
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Universitatsklinikum Heidelberg
Heidelberg, 69120, Germany
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University Hospitals Cleveland Medical Center
Cleveland, Ohio, 44106, United States
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University of California
Los Angeles, California, 90095, United States
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University of Colorado
Aurora, Colorado, 80045, United States
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