MAPT and Alzheimer disease: The exact relationship between AD neuropathologic change (i.e., tau neurofibrillary pathology and Aβ1−42 extracellular plaques) and observed measurement of these analytes in CSF is unclear; however, the total tau level is thought to reflect underlying neurodegeneration and neuron loss, as elevations are also seen in other CNS insults (Otto et al., 1997; Hesse et al., 2000; Jin et al., 2006; Ost et al., 2006; Krut et al., 2013).