RT-QuIC selectivity is dependent on the recombinant protein substrate used, with AD detection relying on substrates encompassing the amino acid sequence found in the AD tau filament core structure (i.e. τ306-378 [31] or K12 [43]) and 4R tauopathy detection using 4R tau substrate (i.e. K18 [52]). This evidence concerns the gene KRT18 and Alzheimer disease.