Furthermore, in their cross-sectional study looking at biomarker trajectories with increasing Aβ burden, Palmqvist et al. (2019) showed that in AD plasma p-tau changes significantly before CSF and plasma Aβ1–42/1–40, and CSF p-tau, all of which exhibit changes before Aβ PET positivity is detected. This evidence concerns the gene MAPT and Alzheimer disease.