Background. Epigenetic polymorphisms are a potential source of human diversity, but their frequency and relationship to genetic polymorphisms are unclear. DNA methylation, an epigenetic mark that is a covalent modification of the DNA itself, plays an important role in the regulation of gene expression. Most studies of DNA methylation in mammalian cells have focused on CpG methylation present in CpG islands (areas of concentrated CpGs often found near promoters), but there are also interesting patterns of CpG methylation found outside of CpG islands. Results. We compared DNA methylation patterns on both alleles between many pairs (and larger groups) of related and unrelated individuals. Direct observation and simulation experiments revealed that around 10% of common single nucleotide polymorphisms (SNPs) reside in regions with differences in the propensity for local DNA methylation between the two alleles. We further showed that for the most common form of SNP, a polymorphism at a CpG dinucleotide, the presence of the CpG at the SNP positively affected local DNA methylation in cis. Conclusions. Taken together with the known effect of DNA methylation on mutation rate, our results suggest an interesting interdependence between genetics and epigenetics underlying diversity in the human genome.
Bibliographical noteFunding Information:
We are grateful to H. Cedar, M. Daly, J. Hutchinson, L. Merriam, T. Mitchison, V. Mootha and R. Mostoslavsky for discussions and comments, and to A. Kirby for discussions and analyses of polymorphisms. We thank J. Smoller for DNA samples. This work was supported by the National Institutes of Health (to A.C.), the Simons Foundation (to A.C.) and from the Israel Science Foundation (to A.H).