To Evaluate the Safety of Long-term Use of HPN-100 in the Management of Urea Cycle Disorders (UCDs)

The duration of treatment in this study was open-ended. Participants were to return for
clinic visits as prescribed by the investigator, and were to be seen at a minimum of every 6
months. At each clinic visit, participants were queried about any adverse events (AEs) or
hyperammonemic crises (HACs) that occurred since the last visit. Physical and neurological
examinations were performed, and blood samples were collected for the analysis of ammonia,
amino acid panels, and routine clinical laboratory safety tests. Participants underwent
neuropsychological testing at baseline, every 12 months thereafter, and at the final study
visit.

Inclusion Criteria:

- Male and female subjects who completed Studies HPN-100-005SE, HPN-100-007, or
HPN-100-012SE

- Signed informed consent by participant and/or participant's legally authorized
representative

- Negative pregnancy test for all females of childbearing potential

Exclusion Criteria:

- Any clinical or laboratory abnormality or medical condition that, at the discretion of
the investigator, may have put the participant at increased risk when participating

- Known hypersensitivity to PAA (phenylacetate) or PBA (phenylbutyrate).

- Liver transplant, including hepatocellular transplant

- Pregnant, breastfeeding or lactating females