The pathogenesis of PD comprises multiple mechanisms and can be generally classified into several categories: increased a-syn production, decreased a-syn clearance (owing to lysosome-autophagosome impairment), mitochondrial dysfunction, enhanced neuroinflammation, reduced neuronal survival, and dysregulated PD-related genes such as SNCA, PTEN-induced putative kinase 1 (PINK1), leucine-rich repeat kinase 2 (LRRK2), glucosylceramidase beta (GBA), or Parkin RBR E3 ubiquitin protein ligase (PRKN). Here, SNCA is linked to Parkinson disease.