MAPT and Alzheimer disease: While repeated measurements of CSF Aβ as well as PIB PET Aβ plaque burden in AD patients have not been shown to change further with the progression of AD [99], [100], [101], [102], t-tau CSF levels have been reported to increase as AD progresses over time [99], [102] thereby suggesting that the CSF T-tau/Aβ42 ratio could increase with the progression of AD and serve as a biomarker of increasing disease severity.