The role of mitochondrial dysfunction in the pathomechanism of PD was initially observed through the findings of induced parkinsonism following the administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP), an inhibitor of the mitochondrial respiratory chain (MRC) complex I (139, 140). This evidence concerns the gene CD200 and Parkinson disease.