A list of 15 known clock genes from the primary (Arntl, Clock, Npas2, Per1, Per2, Per3, Cry1, Cry2), secondary (Nrd1d1, Nr1d2, Rora, Rorb, Rorc), and accessory TTFL loops (Nfil3, Dbp) (Fig. 1A) were selected to investigate the effect of diabetes on their rhythmic expression. This evidence concerns the gene PER2 and diabetes mellitus.