SNCA and Parkinson disease: α-synuclein (SNCA/PARK1), Parkin (PRKN/PARK2), PTEN-induced putative kinase 1 (PINK1/PARK6), leucine-rich repeat kinase 2 (LRRK2/PARK8), DJ-1 (PARK7), vacuolar protein sorting-associated protein 35 (VPS35/PARK17), ATP13A2 (PARK9) and glucocerebrosidase (GBA) are some of the extensively studied proteins for their association with PD [4].