The recent development of several novel positron emission tomography (PET) tracers tailored to detect tau in the brain has opened the opportunity of using them to improve diagnostic accuracy in Alzheimer disease (AD) and related tauopathies, and to allow reliable quantification of brain tau burden and tracking of disease progression by in vivo neuroimaging [15, 35]. This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.