Platform presentation—Impairments in Precision Grip Control in Pre-symptomatic Huntington's Disease

Abstract

Background Precision grip control is important for accurate object manipulation and requires coordination between horizontal (grip) and vertical (load) fingertip forces. Manifest Huntington's disease (HD) subjects demonstrate excessive and highly variable grip force, and delayed coordination between grip and load forces. Because the onset of these impairments is unknown, we examined precision grip control in presymptomatic HD (pre-HD) subjects. Methods Fifteen pre-HD and 15 age- and gender-matched controls performed the precision grip task in a seated position. Subjects grasped and lifted an object instrumented with a force transducer that measured horizontal grip and vertical load forces. Outcomes were preload time, loading time, maximum grip force, average grip force during the hold phase, and variability for all measures, and were computed from pre-defined events, such as onset of grip force (>0.1 N), onset of load force (>0.1 N), and maximum grip force during the trial. We measured static grip force in a 3-second window during the hold phase. Pre-HD subjects were administered the UHDRS, and predicted years to onset was calculated using a probabilistic model (Langbehn DR, et al., Clin Genet 2004;65:267–277). Results Preload time and loading time was slower for pre-HD subjects (158.97 ms, 123.0 ms), compared with controls (64.97 ms, 57.2 ms). Variability (SD) of preload and loading time was higher in pre-HD subjects (61, 55.15) than in controls (35.74, 22.08). Variability in maximum and static grip force was higher in pre-HD subjects (0.22, 0.66) than in controls (0.08, 0.03). Pearson correlation with predicted years to disease onset in pre-HD was 0.65 for loading time and 0.69 for loading time variability. Conclusions Temporal delay in coordination between grip and load force, and increased motor variability are seen well before diagnosis of HD and may serve as good biomarkers of disease onset and progression.