CSF Aβ42/Aβ40 is an indicator of amyloid burden, with lower levels in the CSF reflecting greater amyloid deposition in the brain; p-tau is a marker of neurofibrillary tangles, with higher levels reflecting greater tangle pathology in the brain; the ratio of p-tau/Aβ42 incorporates both aspects of pathology, with higher values implying greater AD pathology19. Here, MAPT is linked to Alzheimer disease.