for people ages 12 years and up (full criteria)
at Los Angeles, California and other locations
study started
completion around



The primary objective is to evaluate the efficacy of DTX301 on the improvement of ornithine transcarbamylase (OTC) function by maintaining safe plasma ammonia levels with removal of dietary protein restriction and alternative pathway medication.

Official Title

A Phase 3, Randomized, Double-blind, Placebo-controlled Study of Adeno-associated Virus (AAV) Serotype 8 (AAV8)-Mediated Gene Transfer of Human Ornithine Transcarbamylase (OTC) in Patients With Late-onset OTC Deficiency


This study is a Phase 3, randomized, double-blind, placebo-controlled study of DTX301 in patients with late-onset OTC deficiency 12 years of age and older.

Participants will be randomized 1:1 to DTX301 or placebo group and followed closely for 64 weeks. At week 64 eligible patients will crossover and receive DTX301 if they had previously received placebo or placebo if they had previously received DTX301.

The planned study duration is up to 324 weeks. Upon completion of this study or early withdrawal, all participants who received DTX301 are invited to enroll in the Disease Monitoring Program (DMP) for follow-up for up to an additional 5 years.


OTC Deficiency, Ornithine Carbamoyltransferase Deficiency Disease, Prednisolone, DTX301, Oral Corticosteroids, Sodium Acetate


You can join if…

Open to people ages 12 years and up

  • 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 Week 128, 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

You CAN'T join if...

  • 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


  • University of California accepting new patients
    Los Angeles California 90095 United States
  • University of Utah accepting new patients
    Salt Lake City Utah 84112 United States


accepting new patients
Start Date
Completion Date
Ultragenyx Pharmaceutical Inc
Ultragenyx Patient Advocacy/OTC Disease Information Sign up for this study
Phase 3 research study
Study Type
Expecting 50 study participants
Last Updated