MAPT and Alzheimer disease: Reasons for the limited data on the molecular organization of Tau fibers are the size of the protein, the necessity to use an exogenous poly-anion to obtain large quantities of fibers, the different isoforms of Tau that do not necessarily adopt the same organization, and evidently the ever-present doubt of whether the synthetic fibers one can make on a bench represent the intraneuronal fibers present in AD patients.