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Multiple endocrine neoplasia type 2B
Multiple endocrine neoplasia 2B (MEN2B) syndrome is a rare aggressive form of MEN2 (see this term) characterized by medullary thyroid carcinoma (MTC, see this term), pheochromocytoma (see this term), mucosal ganglioneuroma, and marfanoid habitus.
The exact prevalence of MEN2B is unknown but it accounts for 5 to 10% of all cases of MEN2 syndrome, providing estimated prevalence of 1/700,000 to 1/350,000.
Onset usually occurs earlier than MEN2A (see this term) and most frequently in infants and young children. Chronic constipation, abdominal distension, diarrhea, or megacolon at birth are often the initial manifestations of the disease due to ganglioneuromatosis of the gastrointestinal tract. Patients also exhibit mucosal neuromas of the lips, eyelids, and tongue, bumpy lips, and marfanoid habitus (with skeletal abnormalities and joint laxity). MEN2B has a higher mortality rate than MEN2A. Unlike MEN2A, MEN2B follows a more severe course and hyperparathyroidism is not found. Pheochromocytoma occurs in 50% of patients.
A single mutation at codon 918 in the tyrosine kinase domain of the RET proto-oncogene (10q11.2) has been associated with the MEN2B phenotype.
Transmission is autosomal dominant.