In terms of pathologic protein accumulation, another molecule called nerve growth factor (NGF) has been found to inhibit the hyperphosphorylation of tau protein in both in vitro and in vivo investigations, whereas glial cell line-derived neurotrophic factor (GDNF) is suspected to provide a therapeutic impact in PD patients, based on animal trials [73,88,89]. Here, MAPT is linked to Parkinson disease.