Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is a type of genetic disease that affects the brain's blood vessels and can lead to problems like memory loss and difficulty thinking clearly, a condition known as vascular cognitive impairment and dementia (VCID). This study is looking at 500 people from families with a history of CADASIL to understand how it develops and what could make it worse. Participants will take part in 3 visits over about 3 years: the first visit, one at 18 months, and another at 36 months, with some contact by phone, mail, or email in between.

• Study Length: Lasts up to 5 years with 3 main visits.
• Tests: Includes interviews, brain scans (MRI), and blood tests.
• Requirements: Must be 18+, have a CADASIL family history, and a "study companion" for support.