Aim: To assess whether DNA methylation of monocytes play a role in the development of acute diabetic Charcot foot (CF). Patients & methods: We studied the whole methylome (WM) of circulating monocytes in 18 patients with Type 2 diabetes (T2D) and acute CF, 18 T2D patients with equivalent neuropathy and 18 T2D patients without neuropathy, using the enhanced reduced representation bisulfite sequencing technique. Results & conclusion: WM analysis demonstrated that CF monocytes are differentially methylated compared with non-CF monocytes, in both CpG-site and gene-mapped analysis approaches. Among the methylated genes, several are involved in the migration process during monocyte differentiation into osteoclasts or are indirectly involved through the regulation of inflammatory pathways. Finally, we demonstrated an association between methylation and gene expression in cis- and trans-association.

One-carbon metabolism provides a direct link among dietary folate/vitamin B12 exposure, the activity of the enzyme methylenetetrahydrofolate reductase (MTHFR), and epigenetic regulation of the genome via DNA methylation. Previously, it has been shown that the common c.677C > T polymorphism in MTHFRinfluences global DNA methylation status through a direct interaction with folate status and (indirectly) with total homocysteine (tHcy) levels. To build on that and other more-recent observations that have further highlighted associations among MTHFR c.677C > T, tHcy, and aberrations in DNA methylation, we investigated whether the interaction between mildly elevated plasma tHcy and the c.677C > T polymorphism is associated with site-specific changes in DNA methylation in humans. We used data on plasma tHcy levels, c.677C > T polymorphism, and site-specific DNA methylation levels for a total of 915 white women and 335 men from the TwinsUK registry (n = 610) and the Rotterdam study (n = 670). We performed methylome-wide association analyses in each cohort to model the interaction between levels of tHcy and c.677C > T genotypes on DNA methylation β values. Our meta-analysis identified 13 probes significantly associated with rs1801133 × tHcy levels [false-discovery rate (FDR) < 0.05]. The most significant associations were with a cluster of probes at the AGTRAP–MTHFR–NPPA/B gene locus on chromosome 1 (FDR = 1.3E−04), with additional probes on chromosomes 2, 3, 4, 7, 12, 16, and 19. Our top 2 hits on chromosome 1 were functionally associated with variability in expression of the TNF receptor superfamily member 8 (TNFRSF8) gene/locus on that chromosome. This is the first study, to our knowledge, to provide a direct link between perturbations in 1-carbon metabolism, through an interaction of tHcy and the activity of MTHFR enzyme on epigenetic regulation of the genome via DNA methylation.—Nash, A. J., Mandaviya, P. R., Dib, M.-J., Uitterlinden, A. G., van Meurs, J., Heil, S. G., Andrew, T., Ahmadi, K. R. Interaction between plasma homocysteine and the MTHFR c.677C>T polymorphism is associated with site-specific changes in DNA methylation in humans.

Vitamin B12 deficiency is common among older adults. However, the most commonly used marker of deficiency, total serum vitamin B12 (B12), is not sensitive enough to diagnose true deficiency in a significant proportion of the population. The combined indicator of B12 status (cB12), formulated as a composite score of various biomarkers of vitamin B12 status which also accounts for folate status and age, has been shown to offer a more robust and powerful test to diagnose B12 deficiency. There are no epidemiological studies of cB12 variability in older adults. We carried out a twin study to characterise the relative contribution of heritable (h2) and environmental factors to the observed variability in cB12 score in an older adult population (n = 378). Furthermore, we tested for association between variability in cB12 and candidate polymorphisms and genes previously associated with serum B12 levels characterized in-silico the mechanism linking the genetic variants and cB12 variability. We found the variability in cB12 and its constituents to be highly heritable (h2= 55%-64%). The SNP rs291466 in HIBCH, previously associated with variation in MMA, was significantly associated with cB12 (R2= 5%|P= 5E-04). Furthermore, variants in MTRR, MMAB, and MUT, underlying inborn errors of B12 metabolism, were nominally associated with variation in cB12. Pathway accompanied by expression quantitative trait loci (eQTL) analysis revealed that HIBCH rs291466 influences the concentration of MMA via the valine degradation pathway. Our study provides etiological insight into how B12 deficiency can manifest into impaired mitochondrial function through perturbations in mitochondrial “fuel” usage.