RET and Aganglionic megacolon: In MEN2 (previously MEN2A), medullary thyroid carcinoma (MTC) occurs with phaeochromocytoma and parathyroid tumours, while in MEN3 (previously MEN2B) parathyroid tumours are rare, and the occurrence of MTC and phaeochromocytoma is found in association with a marfanoid habitus, mucosal neuromas, medullated corneal fibers, and intestinal autonomic ganglion dysfunction leading to megacolon (9).