Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 111, Issue 43, Pages 15474-15479Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1409328111
Keywords
mitochondria; heteroplasmy
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Funding
- Pennsylvania Department of Health using Tobacco Settlement Funds
- Battelle Memorial Institute
- Huck Institutes of Life Sciences at Pennsylvania State University
- Penn State Clinical and Translational Science Institute
- Eberly College of Sciences at Pennsylvania State University
- Direct For Biological Sciences
- Div Of Biological Infrastructure [0850103] Funding Source: National Science Foundation
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The manifestation of mitochondrial DNA (mtDNA) diseases depends on the frequency of heteroplasmy (the presence of several alleles in an individual), yet its transmission across generations cannot be readily predicted owing to a lack of data on the size of the mtDNA bottleneck during oogenesis. For deleterious heteroplasmies, a severe bottleneck may abruptly transform a benign (low) frequency in a mother into a disease-causing (high) frequency in her child. Here we present a high-resolution study of heteroplasmy transmission conducted on blood and buccal mtDNA of 39 healthy mother-child pairs of European ancestry (a total of 156 samples, each sequenced at similar to 20,000x per site). On average, each individual carried one heteroplasmy, and one in eight individuals carried a disease- associated heteroplasmy, with minor allele frequency >= 1%. We observed frequent drastic heteroplasmy frequency shifts between generations and estimated the effective size of the germline mtDNA bottleneck at only similar to 30-35 (interquartile range from 9 to 141). Accounting for heteroplasmies, we estimated the mtDNA germ-line mutation rate at 1.3 x 10(-8) (interquartile range from 4.2 x 10(-9) to 4.1 x 10(-8)) mutations per site per year, an order of magnitude higher than for nuclear DNA. Notably, we found a positive association between the number of heteroplasmies in a child and maternal age at fertilization, likely attributable to oocyte aging. This study also took advantage of droplet digital PCR (ddPCR) to validate heteroplasmies and confirm a de novo mutation. Our results can be used to predict the transmission of disease-causing mtDNA variants and illuminate evolutionary dynamics of the mitochondrial genome.
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