The CSF Aβ1‐42, Aβ1‐42/Aβ1‐40 ratio, and tau (especially phosphorylated tau) serve as biomarkers for AD (Blennow, Mattsson, Scholl, Hansson, & Zetterberg, 2015), whereas in FTD, only a nonspecific increase in tau is involved because of neurodegeneration. Here, MAPT is linked to Alzheimer disease.