In the present work a Simple Interdependent glucose/insulin MOdel, SIMO, is proposed and used to fit data from a cohort of subjects with different types and degrees of glucose metabolism impairment, ranging from normal (NGT) to impaired (IGT, IFG, IFG+IGT) glucose tolerance, to Type 2 Diabetes Mellitus (T2DM). This evidence concerns the gene INS and diabetes mellitus.