The classification of a MCI subject as “MCI-AD” requires the positivity of at least one biomarker of in vivo AD pathology, either CSF amyloid-β 1–42 (Aβ42), total tau (T-tau) and 181-phopshoprylated tau (P-tau) assay or amyloid tracer PET. This evidence concerns the gene MAPT and Alzheimer disease.