MAPT and Parkinson disease: Our study does not provide the means to discover the underlying mechanism of these protein level differences; however, we speculate that at the very early stages of PD, i.e., at our baseline, there is an accumulation of toxic p-tau in form of neurofibrillary tangles (NFTs) in neurons, which causes absorption of more functional tau molecules from extracellular space as a compensatory mechanism in order to reverse back the function of neuronal trafficking.