DNA methylation is chemically simple: a methyl group is attached to cytosine bases, most often at cytosine-guanine dinucleotides known as CpG sites, catalysed by enzymes called DNA methyltransferases. Yet the consequences are profound. Methylated promoters can silence genes, methylation patterns define chromatin states, and the overall methylation landscape helps keep the genome structurally stable. As the editors of the Research Topic, Pietro Salvatore Carollo of the University of Enna Kore, Andrea Fuso of Sapienza University of Rome and Viviana Barra of the University of Palermo, frame it, DNA methylation acts as the critical software that executes precise cellular programs within the genome’s hardware. When that software is corrupted, the result can be inappropriate silencing or activation of genes, altered chromatin, genomic instability or the disruption of developmental programs, which is why methylation patterns are increasingly treated as predictors of health rather than mere byproducts of it.

Crucially, methylation is not a static feature of the genome. It responds to developmental environment and cellular cues, adapting dynamically and profoundly affecting cellular function and identity. That dynamism cuts both ways: depending on the biological context, a change in methylation may be the initiator of a pathological cascade or simply the consequence of a cell that has already gone awry. Disentangling cause from effect is one of the central challenges of modern epigenetics, and it is precisely the question that unites the six contributions gathered in this collection, which the editors organise into three strands: the enzymology of active demethylation, the methylation-based measurement of biological age, and methylation signatures in inflammatory and chronic disease.

The first strand centres on TET2, a member of the Ten-Eleven Translocation family of enzymes that mediate active DNA demethylation. While methyltransferases write the mark, TET enzymes erase it, and the process is far more intricate than simple reversal. TET2 catalyses the first step of the cascade, oxidising 5-methylcytosine, the canonical methylated base, into 5-hydroxymethylcytosine, an intermediate that carries its own regulatory meaning and can be further oxidised or passively diluted through cell division. In a review by Tang and colleagues, the authors survey how wild-type TET2 maintains cellular physiology and genetic stability, while somatic mutations in the gene are implicated in a striking range of pathologies, from inflammatory disorders to cancers. Because demethylation involves complex multi-step enzymatic cascades whose fine-tuning is still being worked out, understanding TET2’s behaviour in pathological contexts is viewed as a promising route to new therapeutic strategies, exploiting the fact that methylation, unlike the underlying DNA sequence, is chemically reversible.

The second strand turns to time. In 2013, Steve Horvath introduced the concept of the epigenetic clock, showing that variations in DNA methylation patterns across human tissues and cell types correlate with ageing phenotypes. Since then, a family of epigenetic clocks has been developed, and they can now be applied not only to individual tissues but to populations and to specific pathological contexts. Chen and colleagues review the mechanistic basis of these methylation-based age estimates and their expanding implications for ageing research, health monitoring and disease prediction. The idea that a blood sample can yield a molecular readout of biological age, one that may diverge from chronological age and predict disease risk, has moved epigenetics from the laboratory bench into preventive medicine, and the review charts both the technical progress and the open questions in the field.

The third strand delivers some of the collection’s most concrete clinical findings. In rheumatoid arthritis, an autoimmune disease characterised by chronic joint inflammation and erosion, Delgado-Cruzata and colleagues examined cell-free DNA, fragments of genetic material circulating in plasma, from 27 patients. Using pyrosequencing, a quantitative method that reads methylation levels at individual CpG sites, they found that patients displayed lower methylation of the DUSP22 gene promoter at one specific site compared with healthy controls. More strikingly, decreased methylation levels in circulating DNA were associated with increased joint space narrowing, a radiographic marker of disease progression. The result points toward cell-free DNA methylation as a new, non-invasive biomarker for rheumatoid arthritis, potentially allowing clinicians to track erosive disease from a simple blood draw.

Hypertension tells a similar story of methylation as a disease mirror. Zhu and colleagues used Illumina Infinium Methylation EPIC BeadChips, arrays capable of interrogating hundreds of thousands of CpG sites across the genome, to profile methylation in peripheral leukocytes from 179 patients with high blood pressure. Their epigenome-wide analysis uncovered associations between altered methylation patterns and inflammation biomarkers, reinforcing the emerging view that hypertension is not solely a vascular or haemodynamic disorder but one with a measurable inflammatory and epigenetic dimension. Patterns like these could eventually help stratify patients who respond differently to treatment, or flag individuals at risk before blood pressure becomes chronically elevated.

Inflammation also takes centre stage in neonatal medicine. Sankar and colleagues studied newborns with late-onset neonatal sepsis, a devastating bacterial infection that strikes after the first days of life. Infants with the condition displayed a distinctive methylation signature: pro-inflammatory genes were hypomethylated, a state generally permissive of gene expression, while anti-inflammatory genes were hypermethylated, relative to healthy newborns. The expression of key cytokines, including TNF-α, IFN-γ, IL-10 and TGF-β, was accordingly shaped by methylation status. Because neonatal sepsis is notoriously difficult to diagnose quickly, a methylation-based signature could improve both diagnostics and therapy, identifying which infants mount a runaway inflammatory response and guiding interventions before organ damage occurs.

The final study demonstrates how methylation profiles can capture the interplay of disease, sex and geography. Miranda-Morales and colleagues performed bisulfite pyrosequencing on leukocyte DNA from Parkinson’s disease patients and age- and sex-matched healthy individuals in the Mexican Mestizo population, targeting CpG sites within two genes central to the disease: MAPT, which encodes the tau protein, and SNCA, which encodes alpha-synuclein, the main component of the protein aggregates that define the disorder. Patients showed reduced methylation in the MAPT promoter region and in intron one of SNCA. Intriguingly, the methylation differences were sex-specific: men displayed significant differences in MAPT methylation, while women showed significant differences at SNCA. Patterns also varied with regional location within the population, establishing that sex- and geography-specific methylation signatures exist in Parkinson’s disease, with implications for how epigenetic risk is assessed across diverse populations.

Taken together, the six studies converge on a common theme that is reshaping biomedical research: DNA methylation is a dynamic, responsive layer of genome regulation whose disturbances both reflect and drive human disease. By combining multi-omic and clinical data, the field is evolving from the identification of individual methylation loci toward an integrated view of disease biology, one that clarifies the mechanisms underlying disease heterogeneity and uncovers molecular signatures with value for diagnostics, prognosis and therapy. And because methylation is reversible in a way that genetic mutations are not, aberrant patterns represent an inviting therapeutic target. From the demethylase activity of TET2 to the ticking of epigenetic clocks and the methylation signatures circulating in a drop of blood, the software of the genome is proving to be not just a record of disease, but a place where disease might be rewritten.

Subject of Research: The role of DNA methylation in human diseases, including TET2-mediated demethylation, epigenetic clocks, and methylation biomarkers in inflammatory and neurodegenerative conditions.

Article Title: Editorial: Discussing the implication of DNA methylation in human diseases

Article References: Carollo, P. S., Fuso, A., & Barra, V. (2026). Editorial: Discussing the implication of DNA methylation in human diseases. Frontiers in Molecular Biosciences, 13, Article 2015661. https://doi.org/10.3389/fmolb.2026.2015661

Image Credits: AI Generated

DOI: 10.3389/fmolb.2026.2015661

Keywords: DNA methylation, epigenetics, TET2, epigenetic clock, cell-free DNA, rheumatoid arthritis, hypertension, neonatal sepsis, Parkinson's disease, biomarkers, ageing, gene expression