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Background DNA methylation (DNAm) has been linked with the pathophysiology of brain aging, cognitive impairment and dementia. Methods The present study investigated the association between blood genome-wide DNAm profiles, cognitive dysfunction and brain magnetic resonance imaging (MRI) measures in 48 participants of the Whitehall II imaging sub-study. Results We identified eight differentially methylated regions (DMRs) associated with cognitive impairment. Accelerated aging based on the Hannum epigenetic clock was associated with mean diffusivity and global fractional anisotropy. We also identified modules of co-methylated loci associated with white matter hyperintensities. These co-methylation modules were enriched among pathways relevant to beta-amyloid processing and glutamatergic signalling Conclusion Our data support the notion that blood DNAm changes may have utility as a biomarker for cognitive dysfunction and brain aging.

Epigenetic processes play a key role in the central nervous system and altered levels of 5-methylcytosine have been associated with a number of neurologic phenotypes, including Alzheimer's disease (AD). Recently, 3 additional cytosine modifications have been identified (5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxylcytosine), which are thought to be intermediate steps in the demethylation of 5-methylcytosine to unmodified cytosine. Little is known about the frequency of these modifications in the human brain during health or disease. In this study, we used immunofluorescence to confirm the presence of each modification in human brain and investigate their cross-tissue abundance in AD patients and elderly control samples. We identify a significant AD-associated decrease in global 5-hydroxymethylcytosine in entorhinal cortex and cerebellum, and differences in 5-formylcytosine levels between brain regions. Our study further implicates a role for epigenetic alterations in AD. © 2014 Elsevier Inc.