Phosphorylated tau aggregates have been reported in numerous synucleinopathy mouse models [20–25], suggesting a possible synergistic interaction between α-synuclein and tau in mediating neurodegeneration in PD, as α-synuclein may increase tau aggregation [23, 26–29] and tau may have a similar effect on α-synuclein. This evidence concerns the gene MAPT and Parkinson disease.