MAPT and Alzheimer disease: Within the tau-first subtype we found an increased rate of Aβ accumulation in ε4 carriers compared to our normal ageing reference group, suggesting that this rare group may belong within the Alzheimer’s disease continuum (9 of 1338 participants in neuropathology dataset: 0.7%; 10 of 502 participants in ADNI: 2%; similarly infrequent in previous studies45,46).