PTPRN and type 1 diabetes mellitus: PTPRN and PTPRN2 are both expressed in neuro-endocrine cells and proteolytic processing of their products (Trajkovski et al., 2004) yields protein fragments that represent major autoantigens in type 1 diabetes and are critical regulators of endocrine secretion in adrenal, pancreatic and brain tissue (Cai and Notkins, 2016).