Project Summary This application is being submitted in response to NIH's INCLUDE (OT-OD-20-025) Notice of Special Interest. The purposed R01 provides the first longitudinal investigation of the time-ordered effect of four lifestyle factors - physical activity, sleep, cognitive stimulation, and social engagement - on early Alzheimer's disease (AD) neuropathology and the transition to clinical AD in adults with Down syndrome (DS). These lifestyle factors will be assessed at a total of three time points, each spaced 16 months apart, in 140 adults with DS enrolled in the NIH-funded Alzheimer's Biomarker Consortium in DS (ABC-DS; https://www.nia.nih.gov/ research/abc-ds). Adults with DS are at genetic risk for AD due to the triplication of chromosome 21, which contains the gene for the amyloid precursor protein and thus results in an overproduction of amyloid-bet (Aβ). Despite this genetic risk, there is variability in the age of onset of clinical AD in the DS population. Lifestyle factors may contribute to this variability, as has been found in non-DS populations including adults with early-onset familial forms of AD. Indeed, as a group, adults with DS have been found to engage in a relatively high rate of sedentary behavior, experience a high rate of sleep problems, and to have lifestyles marked by low levels of cognitive stimulation and social engagement. In the proposed study, we will collect information on physical health, sleep, cognitive stimulation, and social engagement across a 7-day/night period at three time points (spaced 16 months apart). Self/information report and objective measures (actigraph and WatchPAT) are used to assess these lifestyle factors. This data collection will correspond in time with ABC-DS data collection of AD biomarkers, cognitive functioning, and dementia symptoms and status. Time-ordered associations between lifestyle factors and AD biomarkers (PET Aβ, PET tau, PET FDG, structural and functional MRI, and CSF Aβ and tau, and blood) and cognitive functioning and dementia will be examined. The specific aims of the study are to: 1) Examine the association between lifestyle factors –physical activity, sleep, cognitive stimulation, and social engagement – and AD biomarkers longitudinally (T1 to T3; each spaced 16-months apart); 2) Determine the association between lifestyle factors and cognitive functioning and dementia symptoms and status longitudinally (T1 to T3); 3) Evaluate the moderating role of lifestyle factors on the relation between early AD neuropathology (indexed by biomarkers) and cognitive functioning and dementia symptoms and status longitudinally (T1 to T3). These lifestyle factors may be important modifiable resiliency mechanisms for delaying clinical AD in adults with DS despite their genetic risk.