Liver Disease in Urea Cycle Disorders

Stage A Inclusion Criteria: * Age \> 6 years and \< 65 years * Weight ≥ 11 kg at time of screening * A molecular or biochemical diagnosis of OTCD, ASS1D, ASLD, or ARG1D. Exclusion Criteria: * Prior liver transplantation * Episode of acute hyperammonemia (≥100 umol/L) in the 30 days prior to enrollment * Confirmed diagnosis of chronic viral hepatitis, autoimmune liver disease, short gut, small bowel syndrome, alcohol liver disease, TPN requirement, or TPN-related cholestatic disease * Adults with BMI ≥ 45 kg/m2 * Current pregnancy * Open wound near expected Fibroscan® probe application site * Use of implantable active medical device such as cardiac pacemaker or implantable cardioverter-defibrillator Stage B Inclusion Criteria • Participation in Stage A of this study Exclusion Criteria * Individuals with claustrophobia or other inability to complete * Known diagnosis of hemochromatosis * Presence of implants or devices incompatible with MRI * Inability to breath-hold for 20 seconds for the elastography sequence * Current pregnancy * Confirmed diagnosis of chronic viral hepatitis, autoimmune liver disease, short gut, small bowel syndrome, alcohol liver disease, TPN requirement, or TPN-related cholestatic disease * Episode of documented acute hyperammonemia (ammonia ≥ 100 umol/L) in the 30 days prior to scheduled visit for Stage B