Around 5 % of PD cases are familial and caused by known disease mutations in one of several genes, including alpha-synuclein (SNCA), parkin (PRKN), leucine-rich repeat kinase 2 (LRRK2 or dardarin), and PTEN-induced putative kinase 1 (PINK1) [134–136]. This evidence concerns the gene SNCA and Parkinson disease.