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DTX301

Phase 3

OTC Deficiency | Gene therapy | Other |Ultragenyx Pharmaceutical Inc.|Last Updated: Jun 2, 2026

Success Probability
Approval Probability 71%
TA Base Rate26%
Adjusted LOA41%
ML RiskLOW_RISK
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Market & Valuation
rNPV $3.2B
Market Size $9.4B
Revenue Basis $1.6B
Competitors 6
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Trial Design
RandomizedDouble-BlindCONTROLLEDDMCBiomarker
Total Trials1
Total Enrollment37
FDA Designations
No designations recorded
Clinical Trials (1)
NCT IDTitlePhaseStatusEnrollmentVelocityDesignStartCompletionLast UpdatedSitesCountries
NCT05345171Clinical Study of DTX301 AAV-Mediated Gene Transfer for Ornithine Transcarbamylase (OTC) DeficiencyPHASE3 ACTIVE NOT_RECRUITING 37Oct 18, 2022Mar 1, 2031Jun 2, 202616 United States, Argentina +8
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Study Endpoints
Primary Endpoints
Plasma Ammonia as Measured by 24-Hour Ammonia (AUC0-24)
Week 36
Complete Responder Rate at the Final Study Visit After DTX301 Exposure
Up to 64 Weeks Post DTX301 Infusion
Secondary Endpoints
Percentage of Complete Responders or Responders After DTX301 Exposure
Up to 64 Weeks Post DTX301 Infusion
Annualized Event Rate of Hyperammonemic Crises (HACs) Pre-DTX301 Exposure vs Post-DTX301 Exposure
Pre-enrollment, Baseline, Up to 64 Weeks Post DTX301 Infusion
Annualized Event Rate of Interim Clinical Events (ICEs) Pre-DTX301 Exposure vs Post-DTX301 Exposure
Pre-enrollment, Baseline, Up to 64 Weeks Post DTX301 Infusion
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Study Design & Arms
AllocationRANDOMIZED
MaskingQUADRUPLE
ModelCROSSOVER
PurposeTREATMENT
Treatment Arms
ArmTypeDescription
DTX301EXPERIMENTALParticipants receive single peripheral intravenous (IV) infusion of DTX301 in solution. Between Week 36 and Week 64, participants may receive single peripheral IV infusion of placebo.
Placebo, Then DTX301EXPERIMENTALParticipants receive single peripheral IV infusion of placebo. Between Week 36 and Week 64, participants receive single peripheral IV infusion of DTX301 in solution.
Interventions
NameTypeDescription
DTX301GENETICnon-replicating, self-complementary recombinant adeno-associated virus serotype 8 (AAV8) vector
PlaceboOTHERnormal saline infusion
Oral CorticosteroidsDRUGParticipants who receive DTX301 solution will receive oral corticosteroids.
Placebo for oral corticosteroidsDRUGParticipants who receive Placebo will receive placebo corticosteroids to maintain the study blind
Sodium AcetateDRUGA tracer for the Ureagenesis Rate Test (URT)
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Eligibility Criteria
Age Range12 Years — N/A
SexALL
Healthy VolunteersNo
Study Sites16

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...

Countries:United StatesArgentinaBrazilCanadaFranceGermanyJapanNetherlandsPortugalSpain
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Recent Changes (Last 90 Days)
LOWJun 2, 2026NCT05345171Enrollment: 32 → 37
LOWJun 2, 2026NCT05345171Enrollment: 32 → 37
LOWJun 2, 2026NCT05345171Enrollment: 32 → 37
LOWMay 26, 2026NCT05345171primaryCompletionDate: changed
LOWMay 24, 2026NCT05345171studyFirstPostDate: changed