IMarkHD: in Vivo Longitudinal Imaging of HD Pathology

iMarkHD is an adaptive, longitudinal positron emission tomography (PET) and magnetic resonance (MR) imaging study in Huntington's disease (HD) that aims to assess abnormal molecular, functional, and structural changes in participants' brains, ranging from several years before symptom onset to the advanced symptom stage. The study will be conducted over a three (3) year period (Baseline, Year-1, and Year-2).

It is likely that, over time, multiple pathophysiological changes influence Huntington's disease (HD) progression. Rather than focusing on one element, the combined PET and multi-modal MRI assessments in this study will allow comprehensive examination of the molecular, functional, and structural framework of HD progression in the brain. The investigators will compare PET and MRI measurements at different disease stages with age- and sex-matched healthy control (HC) participants and monitor, over follow-up visits, to evaluate how specific or combinatorial changes may influence the development of symptoms and disease progression. Furthermore, disease progression markers may be identified that can characterize and predict events preceding symptom development, which could be used as outcome measures in future clinical trials. Study results could also lead to the development of new targeted therapies. The study has two main objectives. First, to use a series of PET scans to investigate four target receptors in specific areas of the brain that are affected by HD and are thought to be responsible for the motor, cognitive, and behavioral symptoms. Second, to investigate structural and functional changes, including alterations in brain connections, using a multi-modal MRI protocol. The investigators will combine MRI and PET findings with clinical measures to precisely characterize univariate and multivariate markers of disease progression. There will be two (2) cohorts in this study. Cohort 1 will consist of five (5) HC participants (who do not have the HD gene mutation) recruited and enrolled to enable optimization of MRI imaging techniques. Each participant in Cohort 1 will complete a minimum of 3 visits. Cohort 2 will consist of 72 people with HD (PwHD) and 36 HC participants; each participant will complete a minimum of 10 visits over three (3) years. The 72 PwHDs will be recruited into three (3) groups depending on disease stage: 24 PwHDs who do not have symptoms and are predicted to develop clinically relevant symptoms in a few years; 24 PwHDs with symptoms in early disease stages; and 24 PwHDs with symptoms in advanced disease stages. The investigators will conduct a preliminary analysis after all baseline visits are completed and a decision will be made whether to add an additional group of 24 PwHDs with no symptoms and who are several years away from developing symptoms, and an additional 12 HCs. After 50% of participants have completed Year 2 follow-up visits, preliminary analysis will be carried out to determine whether to extend the study to include a Year 3 follow-up visit which would be identical to the Year 1 and 2 follow-up visits.