MAPT and Alzheimer disease: In the initial biological stage, only amyloid PET is positive (A), whereas in the early (B), intermediate (C), and advanced (D) stages, tau-PET is also positive, but involving only the medial temporal lobe in B, then also moderate neocortical uptake in C, and high neocortical uptake in D. With the clinical and biological stages is possible to classify AD cases as 3B or 4C or 6D.