Safety and Dose-Finding Study of DTX301 (scAAV8OTC) in Adults With Late-Onset Ornithine Transcarbamylase (OTC) Deficiency

Key Inclusion Criteria: 1. Males and females ≥18 years of age with documented diagnosis of late onset (defined as first manifestation of signs and symptoms at ≥1 month of age) OTC deficiency, confirmed via enzymatic, biochemical, or molecular testing 2. Documented history of ≥1 symptomatic hyperammonemia event with ammonia ≥100 µmol/L. 3. Subject's OTC deficiency is stable as evidenced by either a) no clinical symptoms of hyperammonemia OR b) an ammonia level \<100 µmol/L within the 4 week period preceding the Screening visit. 4. On ongoing daily stable dose of ammonia scavenger therapy for ≥4 weeks. 5. Males and all females of childbearing potential must be willing to use effective contraception at the time of administration of gene transfer and for the 52 weeks following administration of DTX301 Key Exclusion Criteria: 1. At Screening or Baseline (Day 0), plasma ammonia level ≥ 100 μmol/L for patients who historically maintain normal ammonia levels; OR plasma ammonia level ≥ 200 μmol/L for patients who historically are not able to fully control ammonia levels with baseline management; OR signs and symptoms of hyperammonemia. 2. Liver transplant, including hepatocyte cell therapy/transplant. 3. History of liver disease 4. Significant hepatic inflammation or cirrhosis 5. Serum creatinine \>2.0 mg/dL. 6. Participation in another investigational medicine study (including another gene transfer trial) within 3 months of Screening 7. Pregnant or nursing Note additional inclusion/exclusion criteria may apply, per protocol.