LRRK2 and Parkinson disease: The genes implicated in the onset of PD (PARK genes) currently comprise 20 genes including SNCA (encoding α-synuclein), LRRK2 (encoding leucine-rich repeat kinase 2, LRRK2), and VPS35 (encoding vacuolar protein sorting 35).208,209 In addition to genetic abnormalities, toxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), paraquat, rotenone, and dieldrin caused the loss of dopaminergic neurons and increased the expression and aggregation of α-synuclein, which are also used to investigate PD pathogenesis.204,210,211