MAPT and Alzheimer disease: Blood biomarkers are currently reasonably advanced in their development, with plasma P-tau 217 (particularly the P-T217/T217 ratio [35,36]) proving to be a strong predictive marker of amyloid burden and tau deposition, in real life populations [37,38] and plasma Aβ42/40 ratio allowing for reasonable separation of AD from non-AD individuals [39].