Biomarkers are now widely available to establish evidence of preclinical AD and include amyloid and tau PET imaging, cerebrospinal fluid markers of amyloid-β peptide (Aβ), tau, and tau phosphorylated at position 181 (p-tau181), and more recently, plasma biomarkers of similar analytes including tau phosphorylated at position 217 (p-tau217) (10–11). This evidence concerns the gene MAPT and Alzheimer disease.