Age predicts Alzheimer's in Down syndrome better than MRI, plasma, or cognition

Alzheimer's disease (AD) dementia in Down syndrome (DS) occurs at predictable ages. It is unclear whether age can differentiate across AD stages (amyloid positivity, tau positivity, mild cognitive impairment [MCI], dementia).

Using data from the Alzheimer's Biomarker Consortium-Down Syndrome, we analyzed how well age differentiated stage using receiver operating characteristic curves. We compared areas under the curve (AUC) for age to AUCs for imaging, biofluid, cognitive, motor, and behavioral variables.

Sample varied by stage and variable. Up to 148 variables and 461 participants were analyzed. Age effectively differentiated amyloid positivity, tau positivity, and MCI (AUCs > 0.85) but poorly discriminated MCI from dementia (0.588). No variable was better than age in distinguishing stages, except for MCI/dementia.

Our results show that age alone is effective at staging DS AD. Age is the most reliable correlate of amyloid, tau status, and cognitive impairment in DS and could screen for future clinical trials.