The epigenetic landscape of AD is not one landscape
In the 2023 study, CSF biomarker–associated methylation was analysed separately in CN and AD subjects. The overlap of significant CpGs between the two groups was minimal, arguing against a single universal "AD methylation signature" that simply changes in magnitude over the disease course. Instead, the preclinical phase looks like a regulated, possibly compensatory response, while the symptomatic phase looks like the breakdown of that response.
Figure 1. Stacked composition of significant CSF-biomarker-associated CpGs across biomarker categories. Bars decompose into CN-specific, AD-specific, and shared CpGs. The shared fraction is small, consistent with stage-specific epigenetic regulation.
A 44-CpG / 44-DMR signature for incident dementia
Using longitudinal data from the Framingham Heart Study and ADNI, the 2025 Alzheimer's & Dementia paper derived a blood methylation signature that predicts dementia onset years before clinical diagnosis. The signature consists of 44 individual CpG sites plus 44 differentially methylated regions (DMRs). DMRs (clusters of co-regulated CpGs) are preferred over single sites because they are more biologically functional and more statistically robust against site-level noise.
Pathway enrichment — systemic, not just neural
The 44-CpG signature is enriched in peripheral immune, metabolic, and vascular pathways as strongly as in CNS pathways. Three biological axes stand out:
- Peripheral immune dysregulation. Enrichment of immune-gene methylation challenges the "immune-privileged" view of the brain. Leukocyte DNAm changes reflect "inflammaging" — a low-grade chronic inflammatory state that communicates with the CNS via cytokine signalling.
- Metabolic dysfunction ("type-3 diabetes"). Dysregulation of glucose and lipid metabolism genes mirrors brain insulin resistance. Peripheral energy deficits disproportionately affect the brain, which consumes ~20% of systemic glucose.
- DMR-level regulation. Coordinated regional methylation (DMRs) captures joint regulation of gene neighbourhoods that single CpGs miss.
Why some people with pathology remain cognitively intact
The 2025 Alzheimer's Research & Therapy paper studied the Healthy Brain Initiative and ADNI cohorts to ask why some individuals maintain cognition despite accumulated pathology. We operationalised a methylation-based Resilience Index (mRI) from a lifestyle-based resilience score, and identified a blood DNAm signature that mediates the association between lifestyle and cognitive trajectory, independent of known risk factors.
The widget below is a schematic illustration — adjust lifestyle inputs to see how the model weights three canonical resilience genes (APOC2, UBAP1, GSTCD) and an inferred heart–brain axis term.
Lifestyle inputs
Epigenetic targets — modulation
Note. The simulator is for illustration only; weights are schematic. Actual analyses estimate mediation on the methylation-based Resilience Index in HBI and ADNI participants, adjusting for age, sex, APOE, and standard risk factors.
Peripheral methylation as a proxy for central biomarkers
A central question for liquid-biopsy biomarkers is whether blood methylation meaningfully reflects central-nervous-system biology. Across the Zhang et al. studies we report that:
- Several HOX-family and immune-regulatory loci show coordinated methylation in blood and brain tissue.
- Blood methylation at these loci correlates with CSF pTau181 in matched participants, supporting a blood–brain epigenetic axis.
- Concordance is loci-specific, not genome-wide — caution is warranted when extrapolating from whole-blood DNAm to brain epigenetics.
This concordance is what makes a peripheral assay worth pursuing, provided the signature is anchored on loci where blood–brain agreement is empirically demonstrated rather than assumed.
Probe reliability on the Illumina EPIC v1.0 BeadChip
The 2024 Epigenetics paper performs a systematic evaluation of probe reliability on the EPIC v1.0 BeadChip. Not every probe is equally trustworthy — reliability varies with beta-value range, probe chemistry, and intra-array characteristics. We recommend a filtering workflow to retain probes with reproducible measurement properties before downstream inference.
| Tier | Probe class | Recommended action |
|---|---|---|
| I. | High reliability | Reproducible ICC > 0.75 across technical replicates. Suitable for discovery and clinical use. |
| II. | Moderate reliability | ICC 0.4–0.75; retain for discovery with sensitivity analyses. |
| III. | Low reliability | ICC < 0.4. Exclude from candidate biomarker lists. |
| IV. | Cross-reactive / ambiguous | Known problematic probes; exclude by default. |
Table 1. Probe reliability tiering. Applied before downstream biomarker discovery, this filter reduces false-positive rates and improves reproducibility across cohorts.
Underlying studies
Zhang, W., et al. (2023). Distinct CSF biomarker-associated DNA methylation in Alzheimer's disease and cognitively normal subjects. Alzheimer's Research & Therapy.
Zhang, W., et al. (2024). Critical evaluation of the reliability of DNA methylation probes on the Illumina MethylationEPIC v1.0 BeadChip. Epigenetics.
Zhang, W., et al. (2025). Blood DNA methylation signature for incident dementia: evidence from longitudinal cohorts. Alzheimer's & Dementia.
Zhang, W., et al. (2025). DNA methylation signature of a lifestyle-based resilience index for cognitive health. Alzheimer's Research & Therapy.
See the full list on Google Scholar.