Several studies have demonstrated that promoters of genes important for beta cell identity and function such as INS, PDX1, PPARGC1A and GLP1R are hypermethylated in human islets from donors with T2D compared to islets from non-diabetic donors (134, 155, 156, 158), resulting in their decreased expression and the consequent impairment of beta cell identity and insulin secretion. This evidence concerns the gene GLP1R and type 2 diabetes mellitus.