Normative Values for Cognitive Testing and Alzheimer's Imaging Biomarkers in Young Adults

Biomarkers of Alzheimer's disease (AD) occupy an essential place in recently formulated diagnostic criteria for AD where their role is to identify the pathophysiological processes underlying cognitive impairment or to predict time to dementia. Three of these biomarkers are brain imaging tests (amyloid PET, fludeoxyglucose (FDG) PET, and structural MRI). In order to effectively use AD biomarkers for diagnostic and prognostic purposes, continuous values much be divided into normal and abnormal ranges. This requires that a cut point(s) be established in the continuous distribution of values for each biomarker.

The investigators objective in this proposal is to obtain imaging biomarker data in a group of individuals who are appropriate for establishing normative values for AD biomarkers. The investigators believe the most valid approach to establishing biomarker cut points is to base them on the upper bound of the range observed in young to early-middle-age subjects in whom the presence of occult AD pathology is extremely unlikely. Based on a large volume of community-based autopsy data, that upper age limit would be about 50 years old. The lower age bound for a group of subjects used to establish normative AD biomarker values would have to be based on considerations of brain maturation, which may continue into the middle- to late-20s. Thus, taking the above into consideration, the ideal age range for establishing normative AD imaging biomarker data (amyloid PET, FDG PET, and structural MRI) may be ages 30-49 years old.