E3 PreliminaryPreliminaryPEM ?Case-ControlPeer-reviewedMachine draft
Comparing DNA Methylation Landscapes in Peripheral Blood from Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Long COVID Patients.
Peppercorn, Katie, Sharma, Sayan, Edgar, Christina D et al. · International journal of molecular sciences · 2025 · DOI
Quick Summary
This study examined chemical markers called DNA methylation in blood cells from people with ME/CFS, Long COVID, and healthy individuals. Researchers found that while the overall patterns were similar between ME/CFS and Long COVID patients, there were specific differences in which genes were chemically marked, suggesting these two conditions may have related but distinct biological changes. The findings lay groundwork for understanding what makes these post-viral conditions work at a molecular level.
Why It Matters
This is the first direct epigenetic comparison between ME/CFS and Long COVID, two conditions that share >95% of symptoms but may have different underlying mechanisms. Understanding these molecular differences could help explain why patients respond differently to treatments and may guide development of condition-specific therapies. These findings open new avenues for biomarker research in post-viral illnesses.
Observed Findings
- Patients with ME/CFS and Long COVID showed distinct separation from healthy controls in methylation profiles, with 214 DMFs in ME/CFS and 429 in Long COVID versus controls.
- 118 Differentially Methylated Fragments were shared between both disease cohorts, indicating overlapping epigenetic changes.
- DMFs located in promoters and exons were predominantly hypermethylated in disease cohorts, with rarer hypomethylated regions.
- Long COVID patients showed significantly greater differential methylation magnitude in some fragments compared to ME/CFS patients.
- Some methylation changes occurred in only one disease cohort or in opposite directions between cohorts, suggesting condition-specific epigenetic alterations.
Inferred Conclusions
- ME/CFS and Long COVID share a largely similar epigenetic architecture but with specific, distinct differences that may reflect disease-specific pathways or different disease stages.
- Differences between cohorts likely reflect both the distinct disease duration (LC ~1 year vs. ME/CFS ~12 years) and potential SARS-CoV-2-specific effects in Long COVID.
- Epigenetic changes provide a foundation for identifying molecular mechanisms and potential biomarkers in post-viral conditions.
- Functional studies are needed to establish whether these methylation patterns have clinical relevance to symptom expression or disease progression.
What This Study Does Not Prove
This study does not establish whether methylation changes cause the symptoms of ME/CFS or Long COVID, nor does it prove the conditions are the same or fundamentally different—it only reveals that some epigenetic patterns differ. The small sample size and cross-sectional design cannot determine whether methylation changes precede symptoms, result from the disease process, or correlate with disease severity. The confounding effect of disease duration (12 years vs. 1 year) makes it unclear whether observed differences reflect disease stage or inherent differences between conditions.
Tags
Biomarker:Gene ExpressionBlood Biomarker
Phenotype:Infection-TriggeredLong COVID Overlap
Method Flag:PEM Not DefinedWeak Case DefinitionSmall SampleExploratory Only
Metadata
- DOI
- 10.3390/ijms26146631
- PMID
- 40724879
- Review status
- Machine draft
- Evidence level
- Early hypothesis, preprint, editorial, or weak support
- Last updated
- 8 April 2026