Though p-tau is a well-established AD biomarker, elevated levels of which in CSF, along with total tau and decreased Aβ42, are central to research criteria for AD diagnosis; CSF p-tau levels in some tauopathies like progressive supranuclear palsy (PSP) and Pick’s disease remain unchanged despite observable tau pathology [88]. This evidence concerns the gene MAPT and Classical progressive supranuclear palsy.