A Study of the Safety, Efficacy and Pharmacokinetics of Glycerol Phenylbutyrate in Pediatric Subjects Under 2 Years of Age With Urea Cycle Disorders

Inclusion Criteria: * Male and female subjects up to 2 years of age * Signed informed consent by subject's parent/legal guardian * UCD diagnosis or suspected diagnosis of any subtype, except N-acetyl glutamate synthetase deficiency. If UCD has not been previously confirmed by genetic testing, consent must be obtained from parent/legal guardian prior to perform genetic testing. If genetic testing is inconsistent with or excludes a UCD diagnosis, the subject will be withdrawn from the study. Exclusion Criteria: * Use of any investigational drug within 30 days of Day 1 * Uncontrolled infection (viral or bacterial) or any other condition known to precipitate hyperammonemic crises. Once these precipitating factors are medically controlled, patients presenting in crisis are eligible. * Any clinical or laboratory abnormality of Grade 3 or greater severity according to the Common Terminology Criteria for Adverse Events (CTCAE) v4.03, except Grade 3 elevations in ammonia and liver enzymes, defined as levels 5-20 times the upper limit of normal in alanine aminotransferase (ALT), aspartate aminotransferase (AST), or gamma glutamyl transpeptidase (GGT) in a clinically stable subject * Any clinical or laboratory abnormality or medical condition that, at the discretion of the Investigator, may put the subject at increased risk by participating in this study * Known hypersensitivity to phenylacetate (PAA) or phenylbutyrate (PBA) * Liver transplantation, including hepatocellular transplan…