MAPT and Alzheimer disease: Again, phosphorylated tau protein (p-Tau) is a key biomarker in diagnosing AD that is responsible for the degeneration of neurons and synaptic impairment [283], whereas due to glycogen synthase kinase-3β (GSK-3β), hyperphosphorylation of the tau protein occurs, resulting in the formation of abnormal clumps of tau protein called neurofibrillary tangles (NFTs) (Figure 5) [284].