DPP-4 has a wide substrate specificity and acts on various regulatory peptides, chiefly cleaving small peptides with proline or alanine as the penultimate N-terminal residue.56 As such, although DPP-4 inhibitor drugs are now clinically approved for the treatment of type 2 diabetes with an excellent adverse effect profile, lack of substrate specificity was an initial concern.56 In this respect, the first clinically approved GLP-1 peptide mimetic with inherent stability against DPP-4 was derived from the saliva of the venomous Gila monster lizard, Heloderma suspectum. This evidence concerns the gene DPP4 and type 2 diabetes mellitus.