The presence of α-synuclein (α-syn) aggregates in LBs [16], approximately 90% of which are phosphorylated on serine residue 129 [19], and the finding that mutations in the α-syn gene, SNCA, cause familial PD [20,21,22,23] and accelerate the pathogenic aggregation of α-syn [24,25], strongly suggested a role for α-syn in the pathogenesis of PD. This evidence concerns the gene SNCA and Parkinson disease.