Clinical Assessment Study in Crigler-Najjar Syndrome

Key Inclusion Criteria: * Subject has a diagnosis of Crigler-Najjar syndrome resulting from a confirmed mutation in the UGT1A1 gene * Subject is aged equal or greater than 1 year of age * Subject receives daily phototherapy for a minimum of 6 hours within a 24-hour period (daily illumination time) Exclusion Criteria: * Subject is currently participating in an interventional study or has received gene or cell therapy * Subject has received a whole liver, partial liver, or hepatocyte transplant; or subject has a liver transplant scheduled within the planned participation period of this study * Subject has significant cholestatic disease, in the opinion of the investigator * Subject is receiving phenobarbital or other known inducer of UGT1A1 within 30 days of screening * Subject has any clinically significant underlying liver disease (other than Crigler-Najjar syndrome), in the opinion of the investigator * Subject has a history of, or currently has, a clinically important condition other than Crigler-Najjar syndrome, in the opinion of the investigator