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). This evidence concerns the gene GIP and type 2 diabetes mellitus.