The misfolded and aggregated forms of α-synuclein protein (denoted hereafter as α-Syn), which is encoded by the SNCA gene, have been implicated in the development of several neurodegenerative diseases, including PD, Parkinson disease dementia (PDD), dementia with Lewy bodies (DLB), incidental Lewy bodies disease (ILBD), and multiple system atrophy (MSA) [5–7]. This evidence concerns the gene SNCA and Parkinson disease.