This study will use PET imaging to designate A/T groups based on cortical Aβ and a meta-temporal tau region, with a particular focus on the A−/T+ or ‘PART’ group as it relates to the A+/T− and A+/T+ groups who are traditionally considered to be on the Alzheimer’s disease continuum. Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.