Study in PRE-manifest Huntington's Disease of Coenzyme Q10 (UbiquinonE) Leading to Preventive Trials (PREQUEL)

secondary objectives: 1. To assess the change from baseline to 20 weeks on biomarkers of oxidative stress (8OHdG and 8OHrG) and DNA repair mechanisms (OGG1) in pre-manifest participants treated with 600, 1200 or 2400 mg per day of CoQ10. 2. To assess the dose-response relationship between CoQ10 at dosages of 600, 1200 or 2400 mg per day and 8OHdG/8OHrG and OGG1. 3. To assess the serum levels of CoQ10 at 600, 1200 or 2400 mg in pre-manifest participants and their relationship to 8OHdG/8OHrG and OGG1. 4. To assess the feasibility of implementing a preventive therapeutic trial in a pre-manifest population. 5. To assess the utility and stability of clinical measures of HD, social relations, behavior and employment in a pre-manifest sample enrolled in a treatment trial.