Genetic testing in multiple endocrine neoplasia and related syndromes.

Multiple Endocrine Neoplasia (MEN) syndromes are inherited diseases characterised by endocrine tumours occuring as autosomal dominant genetic diseases with high penetrance. In MEN1, most tumours affect the parathyroids, endocrine pancreas, anterior pituitary, and adrenal glands. The MEN1 gene has been cloned recently and encodes a nuclear protein without known function so far. More than 200 germline mutations have been identified in MEN1 patients throughout the entire coding sequence and no genotype-phenotype correlation has been found. Now, MEN1 gene screening is a powerful tool in pre-symptomatic diagnosis for MEN1 patients and those with inherited MEN1 related syndromes. MEN2 refers to the inherited forms of medullary thyroid carcinoma (MTC) which is associated with phaechromocytoma and parathyroid tumours in MEN2A, phaechromocytoma and mucosal neuromas in MEN2B. Familial isolated MTC is characterised by MTC only, and the three variants of MEN2 are related to germline missense mutations of the RET proto-oncogene, which encodes a tyrosine-kinase receptor. Germline RET mutations in MEN2 patients are related to the two main functionnal domains in the RET protein, the extracellular ligand binding domain (MEN2A and FMTC) and the intracellular catalytic domain (MEN2A, MEN2B and FMTC). Genotype-phenotype correlations have been established but must be used carefully in clinical practice. RET mutation analysis is now available for patients and prophylactic thyroidectomy in gene-carriers could be the most reliable way to cure the patients. Mechanisms of tumourigenesis induced by MEN2-related RET germline mutations have been analysed by in vitro studies and the generation of transgenic mice which develop true bilateral MTC. Recent insights on MEN syndrome pathogenesis and related inherited endocrine disorders have a major clinical impact and fundamental studies are now in progress in order to identify all genetic events leading from a normal endocrine tissue towards a fully malignant phenotype.