MAPT and Alzheimer disease: CSF Aβ42 levels can increase and then begin to decline 25 years before the onset of AD symptoms, according to a FAD cohort study from the Dominantly Inherited Alzheimer Network, while amyloid deposition measured with PET and Pittsburgh compound B, as well as an increased concentration of T-tau in the CSF, can be detected 15 years before expected symptom onset (Bateman et al., 2012).