Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy (CADASIL) is a brain disorder that can lead to problems with thinking and memory, called vascular cognitive impairment and dementia (VCID). This study aims to learn more about how CADASIL progresses and what factors affect it. 500 people will join the study, which lasts up to 5 years.

Participants with a family history of CADASIL and a positive genetic test result will complete various assessments during three in-person visits: a clinical interview, neurological exam, behavior tests, MRI scans, and blood tests. These visits occur at the start, after 18 months, and after 36 months. In between, there will be phone, email, or internet check-ins called "remote visits".

Key Points:

• Duration: Up to 5 years with 3 main visits (baseline, 18 months, 36 months).
• Participation: Requires a genetic test, willingness to complete visits, and a "study companion" for support.
• Exclusions: Severe learning disabilities or recent substance abuse may disqualify participation.