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.