Concomitant pathologies (i.e., Alzheimer and Lewy bodies pathologies) resulting from the mutual interaction between Aβ42, tau and α-syn during the course of the disease have major role in the neuropathological processes underlying dementia in PD (Tsigelny et al., 2008; Ciaccioli et al., 2013). This evidence concerns the gene MAPT and dementia.