IAPP and type 1 diabetes mellitus: Other bioactive polypeptides, which have been localized to the pancreatic islets, include glutamic acid decarboxylase (GAD), which is expressed by the β cells and is thought to be one of the auto-antigens responsible for inciting the autoimmune damage leading to type 1 diabetes, and the islet amyloid polypeptide (IAP), which has been found to contribute to the pathogenesis of type 2 DM [61].