Natural History Study in Huntington Disease Gene Expansion Carriers (HDGECs) - SHIELD HD

Key Inclusion Criteria Patients who meet all of the following criteria will be eligible to participate in the study: 1. Capacity to comprehend the study objectives and procedures 2. Documentation of genetically confirmed disease by direct DNA testing, defined as a CAG repeat length ≥39 in the HTT gene 3. Ability to undergo and tolerate MRI scans 4. Ability to tolerate blood draws and lumbar punctures Key Exclusion Criteria Patients who meet any of the following criteria will be excluded from participation in the study: 1. Any conditions, including severe chorea and dementia, that would prevent either writing or performing pen and paper, tablet, or computer based tasks as determined by the Investigator 2. Treatment with an investigational drug within 30 days prior to screening or within 5 half lives of the investigational drug, whichever is longer 3. History of gene therapy or cell transplantation or any other experimental brain surgery