Mitochondrial structural and functional stability: Administration of Aza or Dnmt1-siRNA, during the four months of good glycemic phase, which had followed the four months of poor glycemia (PC-GC/Aza or PC-GC/D-si), or soon after induction of diabetes (PC/Aza or D-si), reversed or prevented hypermethylation of Mfn2 promoter and decrease in its gene transcripts. This evidence concerns the gene DNMT1 and diabetes mellitus.