Three main biomarkers have been identified for AD, namely: (i) the Aβ42 peptide, which is the main component of the toxic Aβ plaques; (ii) the coupled units of hyperphosphorylated tau protein (P-tau) and total-tau monomers (T-tau) which are the key bricks of the neurofibrillary tangles (NFTs). The gene discussed is MAPT; the disease is Alzheimer disease.