MAPT and early-onset autosomal dominant Alzheimer disease: Plasma t-tau has also been shown to be increased in Alzheimer’s disease when compared to controls and Aβ+ MCI, however, high overlap between the diagnostic groups and lack of correlation with CSF t-tau has hindered its usability.28,29 This could be due to the interference caused by peripheral expression of tau and/or rapid metabolism and fragmentation of tau in plasma, resulting in fragments that might not be recognized by the commercial t-tau assays.