MAPT and Alzheimer disease: Although there are many markers for AD pathology including the soluble cerebrospinal fluid (CSF) concentration of Aβ42 [4], the CSF and plasma Aβ42/40 ratio [5, 6], the levels of CSF and plasma p-tau species [7, 8], and radiotracers that bind to Aβ and tau via positron emission tomography [9–11], a major goal of the field is to develop AD biomarkers of brain function to identify individuals who are at risk for cognitive impairment before symptom onset.