MAPT and Alzheimer disease: PET for Aβ and tau has been validated with neuropathology,5,6 but few studies have reported such validation for CSF AD biomarkers and mainly used older assays.7,8 CSF studies in FTLD focused on differentiation vs AD9, -, 12 or differences between FTLD variants.13, -, 17 Postmortem FTLD studies are rare, with some but not all15 finding reduced P-tau14,16 or P-tau/T-tau17,18 in FTLD-TDP compared to FTLD-tau.