SNCA and Parkinson disease: Although PD in most patients is idiopathic, approximately 5–10% of patients suffer from familial PD with Mendelian inheritance, and to date, more than 20 genes that cause familial PD have been identified; these genes are referred to as “PARK” genes, including PARK1 (encoding α-syn), PARK2 (encoding Parkin), PARK6 (encoding PTEN-induced putative kinase 1, PINK1), PARK8 (encoding leucine-rich repeat kinase 2, LRKK2), PARK9 (encoding ATPase 13A2, ATP13A2), etc. [10,11].