Twenty additional UCD subjects ≥ 6 years of age were enrolled. These subjects included those who did not qualify for HPN-100-006 [e.g., subjects between the ages of 6-17; 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. See the inclusion criteria for examples of clinical evidence of potential benefit.