While some studies found no difference between individuals with T2DM and matched non-diabetic controls (67–69), others found plasma DPP-4 activity to be reduced in the patients, and suggested this might reflect a compensatory response to the reduced insulin sensitivity and hyperglycaemia, in an attempt to increase intact incretin hormone concentrations and improve insulin secretion (70, 71). Here, INS is linked to type 2 diabetes mellitus.