MAPT and early-onset autosomal dominant Alzheimer disease: Across studies, classic CSF biomarkers (amyloid β [A β]1–42, total tau, and phosphorylated tau181) consistently differentiated individuals with Alzheimer’s disease from controls.35-38 Individuals with Alzheimer’s disease generally had lower levels of Aβ1–42 and higher levels of total tau and phosphorylated tau181 than did the healthy controls35,39-41 and individuals presenting with MCI;35,39,41-43 in addition, combined biomarker ratios (eg, Aβ1–42 to phosphorylated tau181) showed potential as diagnostic tools.