MAPT and Alzheimer disease: Although full length tau is found in cerebral spinal fluid (CSF) from both normal humans [6] and rodents [7, 8], a heterogeneous population of fragments of protein -including the NH2terminal and/or proline-rich domain- is for the most part detected in CSF from AD subjects [9, 10, 11, 12] and in conditioned media from AD patient-derived induced pluripotent stem cells (iPSC) cortical neurons [13].