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.
Inclusion Criteria: - Participants will be positive for the CAGn expansion in the Huntingtin gene (>36 repeats) and be pre-manifest by virtue of scoring 3 or less on diagnostic confidence level (Question 17 of the UHDRS) - Participants will have received genetic testing prior to enrollment through a standard pre-manifest testing protocol. - 18 years of age or older. - Concomitant medications are permitted with the exception of CoQ10, creatine > 5g/day and warfarin. Exclusion Criteria: - History of intolerability to CoQ10. - CoQ10 use within 60 days prior to randomization. - Unstable medical or psychiatric illness; - Substance abuse within one year of the baseline visit. - Pregnancy, breastfeeding or lack of reliable contraception in women of childbearing age. - Subjects with known allergy to FD&C #6 yellow food coloring.