A Phase 3 Substudy to Evaluate Executive Function in Adults With PKU Who Are Participating in the Phase 3 Study, 165-302

This is a Phase 3 substudy enrolling approximately 100 subjects, aged ≥ 18 to ≤ 70 years old,
with PKU who are concurrently treated with BMN 165 or placebo in Part 2 and BMN 165 in Part 4
of Study 165-302. No study drug is administered as part of this study. For this study,
subjects will be asked to perform computer-based assessments (CANTAB) that assess executive
function (specifically, attention, working memory, cognitive flexibility) and to answer
questions about their current state of self perception (subject global assessment comprised
of seven questions). The study visits are as follows: screening, baseline visit, and 3
additional study visits at different time points in the study.

Inclusion Criteria:

- Are currently participating in Part 1 of Study 165-302 and meet the criteria for
participation in Part 2 of 165-302

- Are willing and able to provide written, signed informed consent after the nature of
the study has been explained and prior to any research-related procedures.

- Have the ability to complete the CANTAB and subject global assessment.

- Are willing and able to comply with all study procedures.

Exclusion Criteria:

- Any condition that, in the view of the investigator, places the subject at high risk
of poor compliance or terminating early from the study