MSH: Similar to MEN2A, it is also caused by mutations of the MEN2 gene, also known as the RET proto-oncogene. Its clinical symptoms include medullary carcinoma (CARCINOMA, MEDULLARY) of THYROID GLAND and PHEOCHROMOCYTOMA of ADRENAL MEDULLA (50%). Unlike MEN2a, MEN2b does not involve PARATHYROID NEOPLASMS. It can be distinguished from MEN2A by its neural abnormalities such as mucosal NEUROMAS on EYELIDS; LIP; and TONGUE, and ganglioneuromatosis of GASTROINTESTINAL TRACT leading to MEGACOLON. It is an autosomal dominant inherited disease.,NCI: Multiple endocrine neoplasia caused by mutation of the RET gene. Patients develop medullary thyroid carcinomas and numerous neural defects including neuromas.