![]() ![]() The degree to which these changes contribute to, or are the result of, other aspects of ageing remains unclear, but the rate of change at age-predictive sites varies slightly among individuals of the same chronological age and these deviations reflect individual acceleration or deceleration in biological ageing. At a subset of these CpG sites, change is so predictable across individuals that their methylation levels can be used to estimate chronological age using ‘epigenetic clock’ models (for a brief introduction, see ). In particular, levels of CpG methylation, an epigenetic modification involving the addition of a methyl group to the DNA base cytosine (C) when it occurs next to the base guanine (G), show pervasive age-related change. Widespread epigenetic changes with age have been characterized in humans, potentially implicating epigenetic mechanisms in senescence. This article is part of the theme issue ‘Evolution of the primate ageing process'. Although the use of a human microarray for profiling chimpanzees biases our results towards regions with shared genomic sequence between the species, nevertheless, our results indicate that there is considerable conservation in epigenetic ageing between chimpanzees and humans, but also substantial divergence in both rate and genomic distribution of ageing-associated sites. Methylation at CpGs comprising our chimpanzee clock showed moderate heritability. However, our chimpanzee clock showed little overlap with previously constructed human clocks. ![]() We also built a chimpanzee-specific epigenetic clock that predicted age in our test dataset with a median absolute deviation from known age of only 2.4 years. At over 80% of sites showing age-related change in both species, chimpanzees displayed a significantly faster rate of age-related change in methylation than humans. Many sites (greater than 65 000) showed significant change in methylation with age and around one-third (32%) of these overlap with sites showing significant age-related change in humans. We profiled genome-wide blood methylation levels by microarray for 113 samples from 83 chimpanzees aged 1–58 years (26 chimpanzees were sampled at multiple ages during their lifespan). Here, we examined how the pattern of epigenetic ageing in chimpanzees compares with humans. Change at some of these sites is so consistent across individuals that it can be used as an ‘epigenetic clock’ to predict an individual's chronological age to within a few years. Methylation levels have been shown to change with age at sites across the human genome. ![]()
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