OPRD1 and diabetes mellitus: Furthermore, it is important to recognise the potential of this technology if it were applied to commonly methylated gene promoters from a larger scope of age-related disease; such as the INS gene promoter in type 2 diabetes mellitus (T2DM) [49], the OPRD1 gene promoter in AD [50], the SLC6A4 gene promoter in obesity [51], or the ABCA1 gene promoter in coronary artery disease (CAD) [52], which have all been shown to be hypermethylated during disease.