This research study is looking at the safety and effects of an investigational medication for people with Huntington's Disease (HD). Huntington's Disease is a genetic disorder that affects the brain, causing movement, cognitive, and psychiatric problems. This study has two parts: Part 1 tests different doses, and Part 2 follows up on long-term effects. Participants must have a specific gene change linked to HD and be able to walk on their own. They should weigh over 40 kilograms (about 88 pounds) and have a healthy body mass index (BMI), which is a measure of body fat based on height and weight.

• The study includes MRI scans, which are pictures of the brain.
• It's important participants have not been in similar studies recently or used certain treatments.
• This study is not for pregnant or breastfeeding individuals.

The research involves regular visits to the study site. People who have had serious mental health issues recently or plan brain surgery cannot participate. If you meet these criteria and want to learn more, you can talk to the study team to see if this study is right for you.