MITOCHONDRIAL-DNA AND PARKINSONS-DISEASE

Two major lines of evidence support the hypothesis that an impairment of mitochondrial function may underlie neuronal death in Parkinson's disease. First, the neurotoxicity of the parkinsonism-inducing compound 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is due to the generation of its 1-methyl-4-phenylpyridinium (MPP +) metabolite in the central nervous system; the toxicity of MPP + is likely to result from its ability to block mitochondrial electron flow at the level of complex I. Second, recent studies have revealed a deficiency of mitochondrial complex I activity in the brain as well as other tissues of parkinsonian patients. This enzyme activity reduction might be explained by a defect in one or more of the genes coding for the subunits of complex I. Since seven of these genes are localized in the mitochondrial genome, it is conceivable that abnormal mitochondrial DNA (mtDNA) might play a role in the pathogenesis of Parkinson's disease. The entire sequence of the human mitochondrial genome is known, and human mtDNA can be isolated and rapidly analyzed using techniques such as the polymerase chain reaction. Therefore, identification of an easily detectable mtDNA alteration might ultimately be used as a marker for the diagnosis and screening of Parkinson's disease.