MAPT and early-onset autosomal dominant Alzheimer disease: Though these numbers are relatively small, the finding is in line with a recent longitudinal study where 45% of clinically diagnosed Alzheimer’s disease dementia cases did not show pathological levels of CSF p-tau or t-tau, and did not differ in cognitive or functional decline as compared to cases with pathological tau levels (i.e. A+/T+/N+).62 Moreover, it has been shown that up to 30% of autopsy-confirmed Alzheimer’s disease patients have normal CSF t-tau levels.63