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

Open to people ages 18 years and up

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 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

1. Screening or Baseline (Day 0) ammonia level ≥100 µmol/L or signs and symptoms indicative of hyperammonemia during the 4-week period preceding Day 0
2. Liver transplant, including hepatocyte cell therapy/transplant.
3. History of liver disease
4. Serum creatinine >2.0 mg/dL.
5. Participation in another investigational medicine study (including another gene transfer trial) within 3 months of Screening
6. History of a malignancy for which the subject has received treatment in the past 2 years except for prostate cancer treated with watchful waiting or surgically removed non-melanoma skin cancer.