MEN2 is a hereditary disease resulting from mutations of the RET protooncogene subclassified into MEN2A (MTC, pheochromocytoma, and primary hyperparathyroidism) and MEN2B (MTC, pheochromocytoma, Marfanoid habitus, mucous neuromas, and intestinal ganglioneuromatosis). The gene discussed is RET; the disease is primary hyperparathyroidism.