MAPT and Alzheimer disease: Although, for diagnosing MCI subjects entering clinical trials, the core AD biomarkers (amyloid β1–40, amyloid β1–42, total tau and tau phosphorylated at serine 181 amino acid residue) are being measured—however, they can only be measured from a cerebrospinal fluid (CSF) sample, which is obtained from a patient by an invasive procedure—lumbar puncture.