Motor control and learning in individuals with early-treated phenylketonuria.

OBJECTIVE Although past studies have documented motor control impairments in individuals with early-treated phenylketonuria (ETPKU), much less is known regarding motor learning in ETPKU. The goal of the present study was to advance our understanding on this front. METHOD We isolated and examined motor kinematics associated with the learning of a rapid aimed limb movement in a sample of 40 individuals (13-34 years of age) with ETPKU and a matched comparison group of 40 individuals without phenylketonuria (PKU). Indices of motor learning included overall movement duration as well as the relative proportion of movement time devoted to ballistic and corrective submovements. (Note that practice of motor movements in nonclinical populations is associated with, not only improvements in overall speed, but also reduction in the proportion of movement time devoted to corrective submovements relative to an initial ballistic submovement.) Results: A group-by-time interaction was found. With practice, the non-PKU group showed a significant reduction in the proportion of movement time devoted to the corrected (as compared to the ballistic) submovement. A similar change was not observed for the ETPKU group. In addition, within the ETPKU group, the rate of improvement in total movement duration was correlated with recent blood phenylalanine levels (an indicator of treatment adherence). CONCLUSIONS Motor learning is adversely affected in individuals with ETPKU. Further investigation into the behavioral and neural mechanisms of motor learning in ETPKU will advance our understanding of the etiologic basis for this disruption as well as how it relates to the broader neurocognitive profile of ETPKU. (PsycInfo Database Record (c) 2021 APA, all rights reserved).