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

The RVP task measures sustained attention. In this task, a series of random digits continuously appears in the middle of the screen. Subjects are asked to recognize a specific sequence of digits and are asked to press a button on the screen whenever this specific sequence of digits appears within this series of continuous digits. RVP mean latency is the mean response latency during assessment sequence blocks where the subject responded correctly (Latency units are milliseconds). Lower scores represent better performance. Observed range for Pooled Active: -103.1 to 65.5 (change from baseline) Observed range for Pooled Placebo: -10.4 to 39.0 (change from baseline)

Time frame: Baseline to Part 2 Week 8

Population: Pooled Results: This is a sub-study of 165-302, with a randomized, placebo-control discontinuation design in Part 2. 9 subjects were enrolled in 165-303: 3 in 20mg/day and 3 in 40mg/day Active arm, 2 in 20mg/day and 1 in 40mg/day Placebo arm. Data interpretability was extremely limited, hence planned analysis was using the pooled treatment groups.

The SWM task measures visuospatial working memory. During this task, a number of boxes appears on a screen. The objective of the task is to find a token under a box and to place this token in a designated area. There is only one token under one box during each round and the location of the token rotates in each round to a different box, other than a box within which the token was found in previous rounds. The subject is therefore asked to remember which boxes previously contained tokens so as to better the chances and speed of finding tokens under boxes which did not previously contain tokens. SWM between errors measures the total number of times the subject revisits a box in which a token has previously been found in the same problem (calculated for assessed problems only). Observed range for Pooled Active: -8 to 1 (change from baseline) Observed range for Pooled Placebo: -5 to 12 (change from baseline) Lower scores represent better performance.

Time frame: Baseline to Part 2 Week 8

Population: Pooled Results: This is a sub-study of 165-302, with a randomized, placebo-control discontinuation design in Part 2. 9 subjects were enrolled in 165-303: 3 in 20mg/day and 3 in 40mg/day Active arm, 2 in 20mg/day and 1 in 40mg/day Placebo arm. Data interpretability was extremely limited, hence planned analysis was using the pooled treatment groups.

The SST task measures inhibitory control and cognitive flexibility. The SST is a 2-part task. During part 1, an arrow appears on the screen and subjects are asked to press an arrow button on the screen corresponding with the direction of the arrow displayed. During part 2 of the task, subjects follow the same instructions as in part 1; however, they are asked to withhold their response (do not press an arrow button) if they hear an auditory signal (beep) when the arrow is displayed. SST stop signal delay is the length of time between the go stimulus and the stop stimulus at which the subject is able to successfully inhibit their response on 50% of trials. Lower time represents better performance. Observed range for Pooled Active: -31.6 to 48.7 (change from baseline) Observed range for Pooled Placebo: 47.8 to 72.5 (change from baseline)

Time frame: Baseline to Part 2 Week 8

Population: Pooled Results: This is a sub-study of 165-302, with a randomized, placebo-control discontinuation design in Part 2. 9 subjects were enrolled in 165-303: 3 in 20mg/day and 3 in 40mg/day Active arm, 2 in 20mg/day and 1 in 40mg/day Placebo arm. Data interpretability was extremely limited, hence planned analysis was using the pooled treatment groups.

The RVP task measures sustained attention. In this task, a series of random digits continuously appears in the middle of the screen. Subjects are asked to recognize a specific sequence of digits and are asked to press a button on the screen whenever this specific sequence of digits appears within this series of continuous digits. RVP A prime represents the signal detection measure of sensitivity to the target, regardless of response tendency. In essence, measure of how good the subject is at detecting target sequences. Observed range for Pooled Active: -0.004 to 0.030 (change from baseline) Observed range for Pooled Placebo: -0.057 to -0.001 (change from baseline) A higher score on the test represents a better performance.

Time frame: Baseline to Part 2 Week 8

Population: Pooled Results: This is a sub-study of 165-302, with a randomized, placebo-control discontinuation design in Part 2. 9 subjects were enrolled in 165-303: 3 in 20mg/day and 3 in 40mg/day Active arm, 2 in 20mg/day and 1 in 40mg/day Placebo arm. Data interpretability was extremely limited, hence planned analysis was using the pooled treatment groups.

The SST task measures inhibitory control and cognitive flexibility. The SST is a 2-part task. During part 1, an arrow appears on the screen and subjects are asked to press an arrow button on the screen corresponding with the direction of the arrow displayed. During part 2 of the task, subjects follow the same instructions as in part 1; however, they are asked to withhold their response (do not press an arrow button) if they hear an auditory signal (beep) when the arrow is displayed. SST stop signal delay is the length of time between the go stimulus and the stop stimulus at which the subject is able to successfully inhibit their response on 50% of trials. SST proportion of successful stops measures the proportion of completed stop trials that were successful stops. A higher score on the test represents a better performance. Observed range for Pooled Active: -0.1 to 0.05 (change from baseline) Observed range for Pooled Placebo: 0.0 to 0.0 (change from baseline)

Time frame: Baseline to Part 2 Week 8

Population: Pooled Results: This is a sub-study of 165-302, with a randomized, placebo-control discontinuation design in Part 2. 9 subjects were enrolled in 165-303: 3 in 20mg/day and 3 in 40mg/day Active arm, 2 in 20mg/day and 1 in 40mg/day Placebo arm. Data interpretability was extremely limited, hence planned analysis was using the pooled treatment groups.

The SWM task measures visuospatial working memory. During this task, a number of boxes appears on a screen. The objective of the task is to find a token under a box and to place this token in a designated area. There is only one token under one box during each round and the location of the token rotates in each round to a different box, other than a box within which the token was found in previous rounds. The subject is therefore asked to remember which boxes previously contained tokens so as to better the chances and speed of finding tokens under boxes which did not previously contain tokens. For assessed problems with six boxes or more, SWM strategy is the number of distinct boxes used by the subject to begin a new search for a token (within the same problem). A high score represents poor use of this strategy and a low score equates to effective use. Observed range for Pooled Active: -3 to 3 (change from baseline) Observed range for Pooled Placebo: -3 to 1(change from baseline)

Time frame: Baseline to Part 2 Week 8

Population: Pooled Results: This is a sub-study of 165-302, with a randomized, placebo-control discontinuation design in Part 2. 9 subjects were enrolled in 165-303: 3 in 20mg/day and 3 in 40mg/day Active arm, 2 in 20mg/day and 1 in 40mg/day Placebo arm. Data interpretability was extremely limited, hence planned analysis was using the pooled treatment groups.