Rare mutations in a handful of genes are known to directly cause PD (Table 1), including α-synuclein (SNCA), leucine-rich repeat kinase 2 (LRRK2), PTEN-induced kinase 1 (PINK1), parkin (PRKN), parkinsonism-associated deglycase (DJ-1) and ATPase cation transporting 13A2 (ATP13A2) [20]. Here, SNCA is linked to Parkinson disease.