MAPT and Alzheimer disease: We found that, whilst p-tau Ser356 is almost undetectable in control brain synapses, there is a small but significant proportion (~ 1 to 3%) of pre- and post-synapses that co-localise with p-tau Ser356 in AD brain with positive FRET signals indicating co-localisation of p-tau356 with either synaptophysin or PSD95 within the synaptic compartments.