Conversely, serum insulin concentration was significantly lower in T2DM rats compared to healthy, age-matched controls during the early onset stage (T2DM: n = 9; healthy: n = 8; p = 0.03) and the chronic stage (T2DM: n = 9; healthy: n = 7; p = 0.001), but not the established stage (T2DM: n = 10; healthy: n = 10; p = 0.11). This evidence concerns the gene INS and type 2 diabetes mellitus.