MAPT and frontotemporal dementia: Despite this major gap in knowledge, there are few autopsy studies directly comparing FTLD-Tau and FTLD-TDP, and most of these were performed prior to the discovery of TDP-43 as the pathological substrate for FTD and amyotrophic lateral sclerosis (ALS) [1, 54], did not account for clinical phenotype or did not include the full spectrum of tauopathies [29, 79].