- For subjects who did not participate in PAL-001, evidence that the subject is a non-responder to Kuvan® treatment (ie, 4 weeks of treatment with 20 mg/kg/day of Kuvan®, insufficient response per investigator determination, and treatment end date ≥ 14 days prior to Day 1 [ie, first dose]). Subjects who have had a previous response to Kuvan® treatment but are not currently taking Kuvan® because of noncompliance and have been off treatment for ≥ 6 months prior to Screening are eligible for participation.