RET and multiple endocrine neoplasia type 2A: RET loss of function mutations are associated with the development of Hirschsprung’s disease [22] while gain of function mutations or translocations are associated with the development of a variety of human cancers, including medullary thyroid carcinoma, multiple endocrine neoplasias (MEN) type 2A and 2B, pheochromocytoma, and parathyroid hyperplasia [23], [24].