The aim of the study is to assess the efficacy of HepaStem treatment in paediatric patients suffering from urea cycle disorders.

Main Inclusion Criteria:

• Paediatric patients < 12 years prior to infusion
• Patient presents with UCD
• Patient shows patency of the portal vein and branches, with normal flow velocity as confirmed by Doppler US and accessibility of the portal vein and /or affluants.

Main Exclusion Criteria:

• Patient has mild disease severity, easily controlled under standard of care therapy, with no recurrent metabolic crises.
• Patient is registered on a liver transplant waiting list or is scheduled for living donor liver transplantation before the end of the study.
• Patient presents acute liver failure.
• Patient presents clinical or radiological evidence of liver cirrhosis.
• Patient presents or has a history of hepatic or extrahepatic malignancy.
• Patient has a known clinically significant cardiac malformation.
• Patient has a personal history of venous thrombosis, or has a clinically significant abnormal value for protein S, protein C, anti-thrombin III, and /or activated Protein C Resistance (aPCR) at screening. In case of known family history, a complete coagulation work-up should be performed. In all above described cases, results need to be discussed with PB before enrolling the patient in the study.
• Patient had or has a renal insufficiency treated by dialysis.