Pigmented neurons in aged human substantia nigra -- the main site of neurodegeneration in Parkinson disease -- contain very high levels of mitochondrial DNA (mtDNA) deletions, according to two papers published online this week in Nature Genetics. Neurons with the most mtDNA deletions showed defects in cellular respiration, which the authors say may lead to common symptoms of aging, such as the mild Parkinson-like symptoms often observed in older people."I think our result in nigra is the most convincing case so far" for the mtDNA mutational theory of aging, Konstantin Khrapko of Harvard Medical School, senior author of one of the papers, told The Scientist. Some evidence has hinted that the substantia nigra might be a good place to look at the effects of mtDNA mutations: Researchers had found that pigmented cells contain high levels of one type of mtDNA deletion, and many of these cells suffer...

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