MAPT and Alzheimer disease: The diagnosis of AD is based on biological tests following lumbar puncture and measurement of cerebrospinal fluid (CSF) biomarkers: phosphorylated-tau (p-tau) or total-tau (t-tau), amyloid-β42 (Aβ42), and amyloid-β42-to-amyloid-β40 ratio (Aβ42/Aβ40).