MADD and pancreatic insulinoma: MAPK-activating death domain-containing protein (MADD), also known as Rab3aGTP-GDP exchange factor (RAB3GEP) or differentially expressed in normal and neoplastic cells (DENN) or insulinoma-glucagonoma clone 20 (IG20), is a ubiquitously expressed protein10 that regulates Rab3/Rab27 functions11–16, which in turn play critical roles in cell survival, vesicular trafficking and secretion13,17–31.