Study of Phenoptin to Increase Phenylalanine Tolerance in Phenylketonuric Children on a Phenylalanine-restricted Diet

Inclusion Criteria:

- Clinical diagnosis of PKU with hyperphenylalaninemia (HPA) documented by at least one
blood Phe measurement >/=360 umol/L (6 mg/dL)

- Under dietary control with a Phe-restricted diet as evidenced by:· Estimated daily
Phe tolerance
- At least 6 months of blood Phe control (mean level of enrolling in the study

- Aged 4 to 12 years inclusive at screening

- A blood Phe level
- Female subjects of childbearing potential (as determined by the principal
investigator) must have a negative blood or urine pregnancy test at entry (prior to
the first dose). Note: All female subjects of childbearing potential and sexually
mature male subjects must be advised to use a medically accepted method of
contraception throughout the study. Female subjects of childbearing potential must be
willing to undergo periodic pregnancy tests during the course of the study

- Willing and able to comply with all study procedures

- Willing to provide written assent (if applicable) and written informed consent by a
parent or legal guardian after the nature of the study has been explained and prior
to any research-related procedures

Exclusion Criteria:

- Any condition that, in the view of the PI, renders the subject at high risk from
treatment compliance and/or completing the study

- Prior history of organ transplantation

- Perceived to be unreliable or unavailable for study participation or have parents or
legal guardians who are perceived to be unreliable or unavailable

- Use of any investigational agent within 30 days prior to screening, or requirement
for any investigational agent or vaccine prior to completion of all scheduled study
assessments

- ALT > 2 times the upper limit of normal (i.e., Grade 1 or higher based on World
Health Organization Toxicity Criteria) at screening

- Concurrent disease or condition that would interfere with study participation or
safety (e.g., seizure disorder, oral steroid-dependent asthma or other condition
requiring oral or parenteral corticosteroid administration, or insulin-dependent
diabetes)