An Open-label Study to Investigate ECUR-506 in Male Babies Less Than 9 Months of Age With Neonatal Onset OTC Deficiency

Key Inclusion Criteria:

1. Male sex

2. Gestational or adjusted (corrected) gestational age ≥ 37 weeks

3. Age at screening is 24 hours to 7 months

4. Weight ≥ 3.5 kg and ≤ 13.5 kg at screening

5. Has received age-appropriate vaccinations

6. Genetically confirmed OTCD defined by genetic confirmation of an OTC variant (pathogenic or likely pathogenic) associated with severe neonatal OTCD defined belowin Inclusion Criteria #7 or has the same OTC variant as a family member who hadsevere neonatal OTCD within first week of life.

7. Severe neonatal OTCD defined by hyperammonemic crisis with elevated ammonia level of >560 μmol/L and clinical symptoms within first week of life, and currently receivingtreatment with both dietary protein restriction and nitrogen scavenger therapy.

8. Current or historical biochemical profile consistent with OTCD

9. Participant's parent(s)/LAR must be able to comprehend and be willing to provide asigned IRB/IEC-approved ICF.

Key Exclusion Criteria:

1. Neonatal diagnosis of severe to profound Hypoxic Ischemic Encephalopathy due tobirth injury

2. Requiring urgent liver transplant due to liver failure as assessed by the PI.

3. Contiguous gene deletion involving the OTC gene and including at least the CYBB geneon the telomeric side or the TSPAN7 gene on the centromeric side.

4. Known or suspected major organ injury/dysfunction/anomalies.

5. Vital sign and laboratory abnormalities outside of reference ranges.

6. Treatment with any other gene therapy or gene editing therapy

7. Co-enrollment in any other study unless approved by the sponsor.

8. Any condition, that in the opinion of the Investigator, would compromise the safetyof the participant or study data

9. Documented vertical transmission of HepA/HepB/HepC

10. Documented in-utero teratogen, substance, and/or alcohol exposure, which in theopinion of the Investigator may increase the participant's risk of developmentaldelays, congenital anomalies, and/or significant medical complications