MAPT and Alzheimer disease: The tau-FRET signal (samples diluted to the same total protein concentration) was strongest in the AD group, being ~300-fold higher than controls (P < 0.0001) and 15–43 times higher than the primary tauopathies (P = 0.0003 versus PSP and P = 0.0048 versus PiD; Fig. 1d).