Fibrils formed in vitro from 2N4R and K18 tau have unique amyloid cores, as shown by their unique limited-proteolysis signatures53 and differences in backbone mobility.51 Furthermore, the amyloid cores from AD and PiD fibrils also extend beyond 4th repeat so it would not be possible for K18 to form these disease conformations in vitro. Here, KRT18 is linked to Alzheimer disease.