MAPT and Alzheimer disease: Based on the current data showing little to no binding of [18F]-AV-1451 in the majority of DM1 participants in this sample, and only strong binding in the patient with possible concomitant AD, we conjecture that [18F]-AV-1451 either does not bind to DM1-specific Tau conformations, or that it is not sufficiently sensitive to detect the low levels of Tau pathology that are present in many or most DM1 participants.