The amplitude of circadian clock genes (CLOCK, BMAL1, PER, CRY, Rev-erba, and DPP) significantly decreased in T2D as compared to non-diabetic control (ND) islet cells, and levels of NFIL3 was slightly elevated, though BMAL1 and CRY1 remained the same [79]. This evidence concerns the gene PER1 and type 2 diabetes mellitus.