This is a Phase 1/2, multinational, open-label, study to evaluate the safety and efficacy of an intravenous infusion of GNT0003 in patients with Crigler-Najjar aged ≥10 years and requiring phototherapy. Patients will received a single administration of GNT0003 and will be followed for safety and efficacy of approximately 60 months (5 years): * a follow-up of approximately 12 months (48 weeks) * a long term follow-up of approximately 48 months (4 years), in order to be in line with the latest EMEA Guideline on follow-up of patients administered with gene therapy medicinal products, released on 22 Oct.2009 by the Committee for medicinal products for human use.