GCG and type 2 diabetes mellitus: GIPR rs10423928, due to T/A exchange, is associated with increased fasting glucose and proinsulin levels, and reduced ß-cell function, thereby representing a risk factor in non-diabetic individuals [71], while in subjects with T2D it causes a reduced incretin effect (no effect on insulin secretion) and consequent postprandial hyperglycemia [72,73] (Table 1).