Finally, the relation between gut microbiota changes and methylation of the biomarker gene histone deacetylase HDAC is substantiated by several publications that show that this gene is implicated in mechanisms mediating the interaction between environmental factors and the genome, with particular importance in the pathogenesis of metabolic syndrome and type 2 diabetes.44 Large scale Genome-Wide Association Studies (GWAS) recently linked HDAC to insulin secretion.45 cg01395630 methylation was inversely correlated with plasma gamma-glutamylmethionine levels. This evidence concerns the gene HDAC9 and type 2 diabetes mellitus.