Longitudinal Biomarker of Alzheimer's Disease

Eligibility Details: Inclusion Criteria: 1. Persons with age-related MCI or AD according to clinical diagnosis, consistent with NIA-AA diagnostic criteria 2. Individuals with DS according to clinical diagnosis, with cognitive ability sufficient to follow directions, Age > 30 years 3. Non-DS community-dwelling controls, Age > 60 years 4. Non-pregnant mothers and fathers of DS individuals (controls) 5. Ability to complete baseline assessments 6. Has an informant (study partner) available to complete functional interviews/survey measures annually Exclusion Criteria: - Presence of concomitant medical, neurological, or psychiatric illness or condition that in the opinion of the investigators would confound interpretation of study results. These include: Korsakoff encephalopathy; active substance abuse; hepatitis C; opportunistic brain infection; brain tumor; active neoplastic disease (skin tumors other than melanoma are not exclusionary; participants with stable prostate cancer may be included at the discretion of the project director); multiple sclerosis; history of clinically significant stroke; current evidence or history in the past 2 years of focal brain lesion, head injury with loss of consciousness, or DSM-V criteria for any major psychiatric disorder, including psychosis, major depression, bipolar disorder, alcohol or substance abuse; blindness, deafness or any other disability which may prevent the participant from participating or cooperating in the protocol. - Presence of contraindication for MRI scan for Non-Down Syndrome participants