In order to treat individuals with Down syndrome (DS) better and more efficiently and to gain more insights on its relation to Alzheimer's disease (AD), a comprehensive understanding is needed for its progression in the early or preclinical phase using various biomarkers. DS is a significant risk factor for the early development of AD, with plaques and tangles typically developing by age 35. A better understanding is needed of early markers of the disease in DS patients. Additionally the DS population represents a unique group - due to this elevated risk for AD - to examine biomarkers that may translate in general outside of the DS population to individuals at risk for developing late onset AD. In this proposal, the researchers will assess the longitudinal changes of various biomarkers in a cohort of individuals similar in design to the cross-sectional sectional study in the preliminary data.