Accumulation of wild-type α-synuclein has also been found with synaptic loss in the substantia nigra of monkey models of PD treated with the neurotoxic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which selectively kills dopaminergic cells of the brain and the retina [19,20]. This evidence concerns the gene SNCA and Parkinson disease.