The impact of gene mapping techniques on the management of multiple endocrine neoplasia type 2

[Genetic screening of multiple endocrine neoplasia type 2: experience of the USP Endocrine Genetics Unit]

Multiple endocrine neoplasia type 2 (MEN-2) is an inherited tumor syndrome that includes medullary thyroid carcinoma (MTC), primary hyperparathyroidism, pheochromocytoma and other non-endocrine diseases. Since the first RET missense mutations in association with MEN-2 were identified, RET mutation analysis had a great impact in the clinical management of MEN-2, such as in early diagnosis and treatment of MTC. Presently, early total thyroidectomy provides real cure of MTC for cases in which molecular diagnosis has been performed at early ages. After RET mutation identification, family members should be screened for this mutation by using methods as DGGE, SSCP, restriction enzyme, genetic sequencing or mini-sequencing. In this paper, we briefly review our experience with the direct RET gene sequencing and DGGE approaches. In 50 typical MEN-2 patients analyzed using both methods, we found no false results suggesting that DGGE is a reliable screening method for RET proto-oncogene mutation analysis.

Multigenerational familial medullary thyroid cancer (FMTC): evidence for FMTC phenocopies and association with papillary thyroid cancer

BACKGROUND

Occurrence in a familial setting is well established for medullary thyroid carcinoma (MTC) and has been more recently reported for papillary thyroid cancer (PTC). Germline mutations or rearrangements of the RET proto-oncogene are the genetic background of the majority of hereditary MTCs and of about 25-40% of PTCs.

PATIENTS

A large multigenerational familial medullary thyroid cancer (FMTC) family, comprised of four generations and a total of 60 subjects, has been fully evaluated. Studies on germline RET mutations and polymorphisms, on somatic RET activation and on haplotyping with RET-linked markers, were performed.

RESULTS

RET mutational analysis revealed a rare missense point mutation in exon 15 of RET (A891S), associated with FMTC. Haplotype analysis showed a co-segregation between the allelic variant 5 of D10S578 marker (which is tightly linked to the RET locus) and the RET mutation. Two patients, from different branches of the family, did not harbour the point mutation A891S despite histological confirmation of MTC. In these cases, haplotype analysis excluded the involvement of the RET gene itself in the pathogenesis of the MTC. In three patients, the coexistence, in different foci, of medullary and papillary thyroid cancer was documented. The genetic studies did not show ret/PTC rearrangements. The microsatellite analysis excluded co-segregation of RET locus with the MTC/PTC phenotype.

CONCLUSIONS

We report a full clinical and molecular analysis of a large FMTC kindred with an uncommon RET mutation. In two family members, phenotype and genotype were not concordant, representing the first evidence of FMTC phenocopies. Furthermore, the association of familial forms of medullary and papillary thyroid cancers has been found in 30% of patients undergoing thyroidectomy for MTC. In these situations, genetic analyses excluded the possible germline involvement of RET. Though FMTC phenocopies are likely to represent an exceptional finding, such a possibility should be taken into account in the genetic counselling for MEN 2 syndromes.

Application of genetic screening information to the management of medullary thyroid carcinoma and multiple endocrine neoplasia type 2

Application of RET proto-oncogene mutation analysis to the clinical management of MEN 2 and FMTC has simplified and enhanced the power of earlier used screening and treatment efforts for hereditary MTC. The approaches outlined herein are cost-effective, have improved diagnostic accuracy, and hold the promise of improved cure rates for this neoplasm. Further studies to elucidate the mechanism by which these activating mutations cause transformation may lead to other strategies for prevention or treatment of this neoplasm.

The practical management of multiple endocrine neoplasia

Adbances in the identification and localization of the abnormal genes in the multiple endocrine neoplasia syndromes have provided new methods of identifying "at risk" individuals in these families. Genetic testing using linkage analysis in multiple endocrine neoplasia (MEN) 1 and direct mutation analysis of the RET protooncogene in MEN 2 is now available for these disorders. New management issues for these disorders have resulted, and a practical approach to these issues is discussed.