Here we show that in substantia nigra neurons from both aged controls and individuals with Parkinson disease, there is a high level of deleted mitochondrial DNA (mtDNA) (controls, 43.3% +/- 9.3%; individuals with Parkinson disease, 52.3% +/- 9.3%). These mtDNA mutations are somatic, with different clonally expanded deletions in individual cells, and high levels of these mutations are associated with respiratory chain deficiency. Our studies suggest that somatic mtDNA deletions are important in the selective neuronal loss observed in brain aging and in Parkinson disease.

contributed equally to this work. Conflict of interest:The authors have declared that no conflict of interest exists. Nonstandard abbreviations used: mitochondrial DNA (mtDNA); ribosomal RNA (rRNA); transfer RNA (tRNA); succinate dehydrogenase (SDH).

contributed equally to this work. Conflict of interest:The authors have declared that no conflict of interest exists. Nonstandard abbreviations used: mitochondrial DNA (mtDNA); ribosomal RNA (rRNA); transfer RNA (tRNA); succinate dehydrogenase (SDH).

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