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Multiple endocrine neoplasia type 2B (MEN2B) is an autosomal dominant disorder characterized by medullary thyroid cancer (MTC) and pheochromocytoma. The disorder can also include mucosal neuromas, which are often located on the lips and tongue. Patients with MEN2B frequently suffer from disturbances of colonic motility, including intestinal pseudo-obstruction. The underlying defect in patients with MEN2B is a germline mutation in the RET proto-oncogene.
The most common clinical features of MEN2B are:
Variations in the RET proto-oncogene cause MEN2B. In recent decades no case of MEN2B has been reported that lacks such a variation. The M918T variant alone is responsible for approximately 95% of cases. All DNA variants that cause MEN2B are thought to enhance signaling through the RET protein, which is a receptor molecule found on cell membranes, whose ligands are part of the transforming growth factor beta signaling system.
About half of cases are inherited from a parent as an autosomal dominant trait. The other half appear to be spontaneous mutations, usually arising in the paternal allele, particularly from older fathers. The sex ratio in de novo cases is also uneven: sons are twice as likely to develop MEN 2B as daughters.
Multiple endocrine neoplasia type 2 (MEN 2) occurs in 1:200000 live births; it is a neuroendocrine neoplasia with an autosomal dominant predisposition and has variable penetration.
The neoplasia MEN 2B includes only 5% of all MEN 2 cases. However, its clinical course is the most aggressive of the MEN 2. It is a rare disease caused by mutations in the germline in the RET proto-oncogene and codifies tyrosine for a kinase receptor that is expressed in neuroendocrine cells.
Gastroenterologists should consider the diagnosis of MEN2B when evaluating patients with pseudo-obstruction of unknown etiology. Elevated calcitonin levels suggest the presence of MTG. Because the MTG associated with MEN2B can be life-threatening, thyroidectomy is advised at the time of diagnosis. First-degree relatives of patients with MEN2B should undergo genetic testing for identical RET mutations. Any relative carrying such a mutation can be diagnosed with the disease.
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