The role of global and regional DNA methylation and histone modifications in glycemic traits and type 2 diabetes: A systematic review

• We identified 53 studies focusing on candidate-gene approaches and nine epigenome-wide association relevant to diabetes.
• There was no consistent association between global DNA-methylation and type 2 diabetes and glycemic traits.
• Histone modification processes in the mechanism of type 2 diabetes are understudied.
• The drawbacks of current research include the lack of replication, establishing causality, controlling for confounders.

BackgroundNew evidence suggests the potential involvement of epigenetic mechanisms in type 2 diabetes (T2D) as a crucial interface between the effects of genetic predisposition and environmental influences.AimTo systematically review studies investigating the association between epigenetic marks (DNA methylation and histone modifications) with T2D and glycemic traits (glucose and insulin levels, insulin resistance measured by HOMA-IR).Method and ResultsSix bibliographic databases (Embase.com, Medline (Ovid), Web-of-Science, PubMed, Cochrane Central and Google Scholar) were screened until 28th August 2015. We included randomized controlled trials, cohort, case-control and cross-sectional studies in humans that examined the association between epigenetic marks (global, candidate or genome-wide methylation of DNA and histone modifications) with T2D, glucose and insulin levels and insulin metabolism.Of the initially identified 3879 references, 53 articles, based on 47 unique studies met our inclusion criteria. Overall, data were available on 10,823 participants, with a total of 3358 T2D cases. There was no consistent evidence for an association between global DNA-methylation with T2D, glucose, insulin and insulin resistance. The studies reported epigenetic regulation of several candidate genes for diabetes susceptibility in blood cells, muscle, adipose tissue and placenta to be related with T2D without any general overlap between them. Histone modifications in relation to T2D were reported only in 3 observational studies.Conclusions and relevanceCurrent evidence supports an association between epigenetic marks and T2D. However, overall evidence is limited, highlighting the need for further larger-scale and prospective investigations to establish whether epigenetic marks may influence the risk of developing T2D.