Fig. 2.

Working memory performance (as reflected as reflected by the difference score of error rate in the 2-back condition minus that in the 0-back condition) shown separately for timepoint (baseline, week 4, and 6 month) and BH₄ responsiveness as determined independently at the 4-week timepoint by each participant's treating physician. [Patients deemed “non-responders” were discontinued on BH4 treatment after the 4-week trial period. “Responders” were continued on BH₄ treatment and remained in the present study through the 6-month timepoint.] For comparison purposes, the mean and standard error of the behavioral performance observed for the non-PKU group are represented by a dashed line and gray shaded area, respectively.