This research will have two components. In one the investigators will use statistical methods to compare numbers or percentages of survival, illness, psychological testing for IQ, executive function, memory, behaviors, and quality of life among patients that choose conservative management and those who have chosen liver transplantation. Some of this information is already being collected by the Urea Cycle Disorders Consortium (UCDC) in 14 metabolic clinics (11 of them in the US) as part of its long-term follow-up study. To ensure that the information the investigators analyze is representative of the UCD patient population in the US, the investigators will also obtain data from the Studies of Pediatric Liver Transplantation (SPLIT) registry, which collects information about children who undergo liver transplantation for many different diseases (including UCD).