In order to find an appropriate tau substrate for SAA of skin tau (sTau-SAA) with RT-QuIC, based on our recent finding with autopsy brain tissues from cadavers with AD and other non-AD tauopathies [20], we first examined 4 types of tau substrates including 2 full-length tau isoforms (2N3R/2N4R) and 2 truncated tau fragments consisting of 4RCF (cysteine-free, equivalent to K18CFh)/3RCF (equivalent to K19CFh) using autopsy skin samples from AD cadavers diagnosed neuropathologically. This evidence concerns the gene MAPT and Alzheimer disease.