The frequent concurrence of neurodegenerative disorders is suggested to be due to complex interaction of αSyn, Aβ, tau and other pathological proteins like TDP-43 that clearly concur with aging [20,304], most probably affecting multiple separate pathways or interrelated molecular mechanisms that result in the complex interplay of disease progression and cognitive decline in PD (see Figure 2). This evidence concerns the gene MAPT and Parkinson disease.