Motor markers of congenital cerebellar hypoplasia.

The Reach-to-Grasp (RtG) movement is a fundamental feature of human competence and a widely adopted model for the study of functional movements in both healthy and disease-affected individuals. In particular, 3-D kinematic analysis of RtG allows the study of fine hand movements and submovements, described as secondary fluctuations of the main movement. The aim of this study was to use a RtG movement to test upper limb motor performance in a patient with ataxic syndrome due to cerebellar hypoplasia. 3-D kinematical recording and MRI-based structural measures were combined to provide a comprehensive characterization of the movement and its neural underpinnings at the baseline and after a 2 years follow-up. In terms of kinematics, a dissociation between reaching and grasping performance was observed over time: while grasping appeared to be characterized by an improvement at the 2 years follow-up, reaching showed a significant increase of jerk submovements, suggesting a loss of functionality in feedback mechanisms allowing for smoothness of the movement. At the neural level, an increase of gray matter volume of the anterior right cerebellar hemisphere, alongside with an increased structural connectivity within the sensorimotor network were observed at the 2 years follow up, presumably mirroring the improvement observed for the grasping component. These results highlight the potential of the jerk submovements as a motor biomarker in contexts where feedback mechanisms may be compromised, such as in the case of cerebellar dysfunctions, contributing to the development of new methods for the motor assessment of patients in clinical settings.