SNCA and Parkinson disease: Cell damage could be further exacerbated by environmental factors such as exposure to mitochondrial toxins [i.e., MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), rotenone, 6-hydroxy dopamine (6-OHDA), paraquat (1,1′-dimethyl-4,4′-bipyridine)] or upon loss of function of specific proteins such as alpha-synuclein, Parkin, PINK1 and DJ-1, whose mutations are linked to genetic forms of PD.