The capacity for peptide measurements to serve as a diagnostic biomarker distinguishing individuals with AD and even asymptomatic disease from individuals not on a trajectory to develop AD is well-established, with secreted amyloid and tau peptide measurements in CSF being the current gold standard for interrogation of patients’ AD stage from their CSF41 where CSF Aβ(1–42) concentration inversely correlates to plaque deposition in the living brain42. This evidence concerns the gene MAPT and Alzheimer disease.