Research criteria for the diagnosis of Alzheimer’s Disease (AD), in the Mild Cognitive Impairment (MCI) or dementia stages [1–3], incorporate biomarkers in the diagnostic process, converging on the recommendations about the use of the so-called pathophysiological biomarkers, namely Positron Emission Tomography with ligands for cerebral amyloid deposits (amy-PET) and Aβ, Tau and phospho-Tau in cerebrospinal fluid (CSF), but diverging on the role of brain 18-fluorodeoxy-glucose PET (FDG-PET). The gene discussed is MAPT; the disease is Cognitive impairment.