MAPT and Alzheimer disease: These explanations need not be mutually exclusive: Aβ-induced retrograde tau transmission should appear earlier in the disease course than retrograde spread caused by the breakdown of the axon-soma barrier, as amyloidopathy has been repeatedly shown to precede or co-occur with tauopathy in AD Bolmont et al. (2007); Götz et al. (2004); Ittner et al. (2010).