PLOS Genetics study quantifies how DNA sequence context and methylation jointly shape germline mutation rates at CpG sites

A study by Sheel Chandra and Ziyue Gao, published in PLOS Genetics, examines the factors that govern germline mutation rates at CpG dinucleotides — positions in the genome that are both highly mutable and important in epigenetic regulation.

It has long been established that the elevated mutation rate at CpG sites is largely driven by cytosine methylation: methylated cytosines can spontaneously deaminate to thymine, producing C-to-T transitions. However, CpG sites embedded in different flanking sequences mutate at substantially different rates, and previous work had shown that this variation is only partly explained by differences in methylation levels.

Using human polymorphism data from the gnomAD dataset, Chandra and Gao apply a regression framework that accounts for recurrent mutations — a known source of bias in such analyses — to quantify the CpG mutation rate and the mutagenic contribution of methylation across diverse sequence contexts. The analysis aims to disentangle the independent contributions of sequence context and methylation to observed mutation rate variation.

The findings add resolution to population-genetic models of de novo mutation and germline mutagenesis, with implications for variant interpretation, demographic inference, and the understanding of heritable disease risk at the molecular level. The work is primarily of interest to population geneticists, statistical geneticists, and researchers working on variant pathogenicity assessment.