Although a small percentage of PD cases are inheritable as a result of mutations in genes including α-synuclein, Parkin, LRRK2, PINK1, and DJ-1, exposure to environmental toxins and pesticides, such as paraquat and rotenone, and synthetic toxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), can also lead to PD (Goldman 2014). Here, LRRK2 is linked to Parkinson disease.