Abstract
The number of de novo mutations (DNMs) found in an offspring’s genome increases with both paternal and maternal age. But does the rate of mutation accumulation in human gametes differ across families? Using sequencing data from 33 large, three-generation CEPH families, we observed significant variability in parental age effects on DNM counts across families, with estimates ranging from 0.19 to 3.24 DNMs per year. Additionally, we found that approximately 3% of DNMs originated following primordial germ cell specification (PGCS) in a parent, and differed from non-mosaic germline DNMs in their mutational spectra. We also discovered that nearly 10% of candidate DNMs in the second generation were post-zygotic, and present in both somatic and germ cells; these gonosomal mutations occurred at equivalent frequencies on both parental haplotypes. Our results demonstrate that the rate of germline mutation accumulation varies among families with similar ancestry, and confirm that post-zygotic mosaicism is a substantial source of de novo mutations in humans.
Data and code availability. Code used for statistical analysis and figure generation has been deposited on GitHub as a collection of annotated Jupyter Notebooks: https://github.com/quinlan-lab/ceph-dnm-manuscript. Data files containing high-confidence de novo mutations, as well as the gonosomal and post-primordial germ cell specification (PGCS) mosaic mutations, are included with these Notebooks. To mitigate compatibility issues, we have also made all notebooks available in a Binder environment, accessible at the above GitHub repository.
Footnotes
The manuscript has been revised to include improved methods for detecting post-zygotic mutations in the CEPH/Utah individuals, in addition to more minor textual changes and updates. The precise numbers of germline and post-zygotic mutations identified in both the second and third generations have been updated, though the major results of the manuscript remain very similar to those in the original version. Supplementary files (including IGV screenshots of representative mutations) have been updated accordingly.
