The almost immediate degradation of GLP-1 in the body raised the question of the mechanisms involved, and inspired by early studies by the German enzymologist, Mentlein (99), Deacon and Holst identified the enzyme dipeptidyl peptidase 4 as the enzyme responsible for the degradation of GLP-1 in plasma (100) and demonstrated that this could be prevented with inhibitors of the enzyme; in analogy with the use of ACE inhibitors for hypertension, and based on clinical studies they proposed the use of DPP-4 inhibitors for the therapy of T2DM (101). The gene discussed is GCG; the disease is type 2 diabetes mellitus.