Impairments of postural control in patient's with Huntington's disease while sitting – a new motor phenotype biomarker?

Background: Patients with Huntington's Disease (HD) develop a progressive impairment of stability of stance and walking (Rumpf et al. 2007 [abstract]), frequently resulting in falls and injuries. Objective assessment of postural control in HD may be helpful to assess the risk of injury and may serve as a surrogate for motor phenotype dysfunction.

Objective: To investigate whether patients with HD (1) exhibit impairments in the control of postural stability while sitting with or without availability of visual feedback (2) assess whether these measures correlate to the severity of disease as assessed clinically by the „UHDRS“ (Unified Huntingtons Disease Rating Scale) „total motor score“ (TMS).

Subjects and methods: Symptomatic HD patients (n=15) and age-and-sex-matched controls (n=13) were seated on a force plate (Satel, France) with eyes open and closed for 25 seconds. Subjects were instructed to sit still without moving. Stability of center of mass (COM) location was assessed by the variables „SURFACE“ and „DISTANCE“ reflecting COM mobility. Data was stored and analyzed using a data acquisition system. All subjects were assessed clinically using the UHDRS-TMS. Non-parametric statistics were performed to compare patients and controls (Mann-Whitney-Test) and to assess dependent variables (Wilcoxon-Test) using SPSS 15.0. Correlation analysis was performed using non-parametric Spearman correlations.

Results: Both measures SURFACE and DISTANCE were significantly increased in HD compared to controls (p<0.001 for all conditions except DISTANCE for eyes closed with p=0.002). In HD SURFACE (r=0.74, p=0.004 „eyes-open“; r=0.64, p=0.018 „eyes-closed“) and DISTANCE (r=0.78, p=0.001 „eyes-open“; r=0.63, p=0.019 „eyes-closed“) were correlated to the severity of the disease as assessed in the UHDRS-TMS.

Conclusion: Assessment of stability of sitting using a force plate provides objective and quantitative readouts of motor phenotype dysfunction in HD. The measures SURFACE and DISTANCE of COM dislocation were correlated to the severity of the motor phenotype (UHDRS-TMS). A possible use of these measures as surrogate markers for treatment trials in HD warrants further exploration, e.g., in a blinded follow-up study.

Acknowledgment: RR was supported by a grant from the High-Q-Foundation and IMF-RE-120225 from the „Innovative Medizinische Forschung“, Faculty of Medicine, University of Münster