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

Study 165-303, is a Phase 3 substudy enrolling approximately 100 subjects, aged ≥ 18 to ≤ 70 years old, with PKU who are participating in the Phase 3 study, 165-302. Per the 165-303 protocol, the investigator does not assign a specific intervention to the study participants. In accordance with the protocol for Study 165-303, subjects were asked to perform selected set of three tasks from the CANTAB tool (Rapid Visual Processing \[RVP\], Spatial Working Memory \[SWM\], and Stop Signal Task \[SST\]) to assess executive function and each subject's self perception of their current state was measured using a subject global assessment questionnaire that contains seven questions about current state perception of attention, energy level, tiredness, confusion, sadness, anger and tension. The time points for administering the above tools are as follows, which coincide with time points in part 2 and part 4 of Study 165-302: screening (entry into Part 2 165-302 Day 1 of Week 1), baseline visit (Part 2 Week 8), and 3 additional study visits at different time points in the Part 4 of 165-302 study.