MAPT and Alzheimer disease: Thus, it is reasonable to speculate that the characteristic increase in CSF p-tau species (i.e., p181, p217, p231, and p235) and total-tau in AD [25, 53, 74, 75] are the result of N-terminal and mid-region truncations [76] on the highly abundant tau pool present in AD brain, and their subsequent migration into CSF.