MAPT and early-onset autosomal dominant Alzheimer disease: Some factors, such as excitotoxicity, oxidative stress, cholinergic dysfunctions, tau protein hyperphosphorylation, changes in amyloid-beta peptide metabolism, apolipoprotein E, herpes viruses, insulin resistance, glycogen synthase kinase 3 and the endocannabinoid system seem to be related to pathophysiology of Alzheimer’s disease.