Hepatic Histopathology in Urea Cycle Disorders

Inclusion Criteria: * Diagnosis of primary urea cycle disorder based on clinical suspicion confirmed by enzyme activity, DNA testing or metabolite analysis. * History of liver transplantation and/or liver biopsy OR * Planned liver transplantation and/or liver biopsy Exclusion Criteria: * Unavailability of histopathology report from the liver biopsy or explant, or unavailability of liver tissue or slides from the biopsy or explant OR * Anticipated inability to obtain pathology report, liver disease, tissue blocks, or pathology slides after liver biopsy or transplantation * Known history of a secondary cause for liver disease such as chronic viral hepatitis, autoimmune liver disease, short gut, small bowel syndrome, alcohol liver disease, or TPN-related cholestatic disease