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Study of Avalotcagene Ontaparvovec for Patients Aged 12 and Older with Late-onset Ornithine Transcarbamylase Deficiency

Fast replyRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying a condition known as late-onset Ornithine Transcarbamylase (OTC) deficiency. This is a genetic disorder that affects the body's ability to eliminate ammonia, a waste product that can be harmful if it builds up in the blood. The study is testing a new treatment called avalotcagene ontaparvovec, which is a type of gene therapy. Gene therapy involves using a virus to deliver a healthy copy of the OTC gene to the patient's cells, potentially improving the body's ability to process ammonia.

The purpose of the study is to evaluate how well this gene therapy works in improving the function of the OTC gene and maintaining safe levels of ammonia in the blood. Participants in the study will receive either the gene therapy or a placebo. The study will also involve the use of prednisolone, a medication that helps reduce inflammation, and [1-13C]sodium acetate, which is used as a tracer to help study the body's metabolism. The study will be conducted over a period of time, with regular check-ups and tests to monitor the participants' health and the effectiveness of the treatment.

Participants will be monitored for changes in their ammonia levels and overall health. The study aims to determine if the gene therapy can safely and effectively improve the condition of those with late-onset OTC deficiency. This research could potentially lead to new treatment options for individuals with this genetic disorder.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial assessment

    Upon joining the study, an initial assessment is conducted to confirm eligibility. This includes reviewing medical history and current treatments for late-onset ornithine transcarbamylase (OTC) deficiency.

    Blood and urine samples are collected to measure baseline ammonia levels and other relevant biomarkers.

  2. Step 2

    Randomization

    Participants are randomly assigned to receive either the gene therapy treatment or a placebo. This process is double-blind, meaning neither the participant nor the study team knows which treatment is being administered.

  3. Step 3

    Treatment administration

    The gene therapy, avalotcagene ontaparvovec, is administered through an intravenous infusion. This is a one-time procedure.

    Participants receiving the placebo will undergo a similar procedure without the active gene therapy.

  4. Step 4

    Prednisolone administration

    Following the infusion, participants take prednisolone orally to manage potential immune responses. The dosage is either 5 mg or 10 mg tablets, depending on the participant's specific needs.

    The duration and frequency of prednisolone administration are determined by the study protocol and adjusted based on individual response.

  5. Step 5

    Regular monitoring

    Participants attend regular follow-up visits to monitor ammonia levels and overall health. These visits include blood and urine tests, physical examinations, and questionnaires.

    Monitoring continues for up to 128 weeks to assess the long-term effects of the treatment.

  6. Step 6

    Final assessment

    At the end of the study period, a comprehensive assessment is conducted to evaluate the treatment's effectiveness in maintaining safe ammonia levels and improving OTC function.

    The results are compared between the gene therapy and placebo groups to determine the treatment's efficacy.

Who can join the trial?

10 criteria

  • Must be a male or female patient who is 12 years of age or older.
  • Must agree to use **highly effective contraception** if you are a female who can have children or a fertile male. This means using methods that are very reliable to prevent pregnancy.
  • Must provide **informed consent**, which means you agree to participate after understanding the study. If you are a minor, you need to agree as much as you can, and your legal guardian must also agree.
  • Must have a confirmed diagnosis of **late-onset OTC deficiency**. This can be shown through past medical tests like liver biopsy, blood tests, or genetic tests.
  • Must have a history of at least one episode of **symptomatic hyperammonemia**, which means having high ammonia levels in the blood, confirmed by a level of 100 micromoles per liter or more.
  • Must currently be on **ammonia scavenger therapy** or a **protein-restricted diet**, not have symptoms of high ammonia, and not have needed emergency treatment for high ammonia in the last 4 weeks.
  • Must have a **plasma 24-hour ammonia level** that is 4800 micromoles per hour per liter or less at screening. If the result doesn't match your health status, it can be checked again.
  • If taking daily ammonia scavenger therapy, the dose must be stable for at least 4 weeks before screening.
  • If on a protein-restricted diet, the amount of protein you eat daily should not change by more than 20% for at least 4 weeks before screening.
  • Must be willing and able to follow study procedures, which include hospital stays, frequent blood and urine tests, and completing questionnaires. If you are a minor, your caregiver must be willing and able to help with these requirements.

Who cannot join the trial?

4 criteria

  • Individuals who do not have a diagnosis of Late-onset Ornithine transcarbamylase (OTC) deficiency cannot participate. This is a specific genetic condition affecting the body's ability to process certain proteins.
  • Participants must be within certain age ranges, typically from children to adults. If you are outside these age ranges, you may not be eligible.
  • Both males and females can participate, but if you do not identify as either, you may not be eligible.
  • If you belong to a vulnerable population, such as those with certain health conditions or disabilities, you may not be eligible.
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Investigated drugs

DTX301 is a gene therapy that uses a virus called Adeno-associated Virus Serotype 8 (AAV8) to deliver a healthy copy of the human ornithine transcarbamylase (OTC) gene into the patient's liver cells. This therapy aims to improve the function of the OTC enzyme, which is important for breaking down ammonia in the body. The goal is to help patients with late-onset OTC deficiency maintain safe levels of ammonia in their blood.

What is already known about the treatment

DTX301 – This medication is administered through an intravenous infusion, delivering a gene therapy treatment using an adeno-associated virus serotype 8 (AAV8) vector. It is currently in Phase 3 clinical trials, focusing on its potential to treat late-onset Ornithine Transcarbamylase (OTC) deficiency. The main therapeutic indication is to improve OTC function, which is crucial for maintaining safe plasma ammonia levels in patients. At the molecular level, DTX301 works by transferring a functional copy of the human OTC gene into liver cells, aiming to restore normal enzyme activity. It is classified as a gene therapy product.

Investigated diseases

Late-onset Ornithine Transcarbamylase (OTC) Deficiency – This is a genetic disorder that affects the body's ability to eliminate ammonia, a waste product of protein metabolism. It occurs due to a deficiency of the enzyme ornithine transcarbamylase, which is crucial in the urea cycle. In late-onset cases, symptoms may appear later in life and can include episodes of vomiting, lethargy, and confusion due to elevated ammonia levels. The condition can lead to neurological issues if ammonia accumulates in the bloodstream. It is more common in males, but females can also be affected, often with milder symptoms. The severity and progression of symptoms can vary widely among individuals.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-514337-38-00Protocol codeDTX301-CL301Estimated enrolment54 patientsSponsorUltragenyx Pharmaceutical Inc.

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