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.
A Phase 3 substudy to evaluate executive function in adults with phenylketonuria who are participating in the phase 3 Study, 165-302. Approximately 100 subjects, aged ≥ 18 to ≤ 70 years old, with PKU will be enrolled.