The primary objective of this study is to investigate the function of SC in response to visual stimulation using a funcional MRI(fMRI) in premanifest HD gene carriers (PMGC) compared to healthy subjects (HS). Our main hypothesis is the dysfunction of the SC at the pre-symptomatic stage of the disease (role of SC as an early biomarker of the disease). The superior colliculus (SC) is a midbrain structure involved in the integration of visual stimuli, in the generation of oriented eye movements and attention tasks.

Secondary objectives will be:

1. To study gait parameters using 3D virtual reality equipment in PMGC compared to HC, to demonstrate that they are abnormal at the pre-symptomatic stage of the disease.
2. To investigate the cognitive/emotional behavior in PMGC compared to HC, to demonstrate that it is abnormal at the pre-symptomatic stage of the disease.
3. To study the correlation between gait, neuroimaging, cognitive/emotional data and various clinical and neuropsychological variables.
4. To investigate potential pre-symptomatic subtypes profiles in HD carriers, based on neuroimaging, clinical, cognitive/emotional assessments correlation analysis.