Safety Study of HepaStem for the Treatment of Urea Cycle Disorders (UCD) and Crigler-Najjar Syndrome (CN)

GENERAL: 1. Subject shows patency of the portal vein and branches, with normal flow velocity in the main portal vein as confirmed by Doppler ultrasound and accessibility of the portal vein, or respectively, accessibility of the umbilical vein. 2. Subject (if capable of signing) and parents or legal representative have provided a written informed assent/consent. 3. Female subjects of childbearing potential need to have a negative pregnancy test and must agree to use an acceptable method of contraception throughout the study. MAIN INCLUSION CRITERIA Crigler-Najjar Syndrome specific: * Patient presents with Crigler-Najjar syndrome type 1. * Patient presents with Crigler-Najjar syndrome type 2, poorly controlled under phenobarbital treatment, or experiencing serious impairment in quality of life. Diagnosis must be confirmed by genetic mutation analysis if not available. Urea Cycle Disorders specific: * Diagnosis of one of the urea cycle disorders of which the disease is of such severity to warrant liver transplantation or alternatives despite full conservative therapy, * subject experiencing serious impairment in quality of life despite full conservative therapy. MAIN EXCLUSION CRITERIA * The subject is 18 years or older at time of screening. * The subject presents acute liver failure, clinical or radiological evidence of liver fibrosis or cirrhosis, presents or has a history of hepatic or extrahepatic malignancy * The patient has a non-corrected cardiac malformation, has a known medical or family history of coagulopathy, had or has a renal insufficiency treated by dialysis. * The subject requires valproate therapy. * The subject has a thrombosis of the portal vein or persisting impairment of anterograde portal blood flow. * The subject has a porto systemic shunt or fistula assessed by Doppler US. * Patients with disease of such severity that liver transplantation is an absolute indication.