Study of the Safety of HPN (Hyperion)-100 for the Long-Term Treatment of Urea Cycle Disorders (Treat UCD)

Inclusion Criteria: * Male and female subjects who completed HPN-100-006: \*Additionally, approximately 20 UCD subjects ≥ 6 years of age may be enrolled who have not participated in HPN-100-006. These subjects may include those who did not qualify HPN-100-006 (e.g., subjects between the ages of 6-17 years, subjects with other UCD subtypes, or adult subjects who have not taken sodium phenylbutyrate (NaPBA) in the past 6 months, etc.). For adult subjects not receiving NaPBA in the past 6 months, subjects must, in the judgment of the investigator, be anticipated to benefit from the addition of a nitrogen-scavenging agent to their current treatment. Clinical evidence of potential benefit from introduction of an ammonia-scavenging agent might include a recent history (in the past year) of clinically overt hyperammonemia accompanied by a venous ammonia ≥ 100 μmol/L, a recent history (within the past year) of protein intolerance, or a history of abnormally high venous ammonia levels accompanied by symptoms (e.g., headache) that might reasonably be attributed to hyperammonemia. * Signed informed consent by subject and/or subject's legally acceptable representative. * Diagnosis of urea cycle disorder (enzyme or transporter deficiency) confirmed via enzymatic, biochemical, or genetic testing. * Able to perform and comply with study activities, including blood draws. * Negative pregnancy test for all females of childbearing potential. * All females of childbearing potential and all …