LOIS M. MULLIGAN Queen’s University
INTRODUCTION
The genomic revolution of the past 20 years has led to the identification of the genetic mechanisms that are responsible for a wide variety of human cancers, and has made a huge impact on our ability to recognize, diagnose and, more recently, treat patients with these diseases. Genetic diagnosis of heritable forms of cancer holds out the potential for presymptomatic detection in familial cases and raises the possibility of prophylactic treatments that would decrease morbidity and mortality and improve the quality of life for those affected. While the potential impact of these advances is huge, to date, our understanding of the underlying genetic events that contribute to the familial cancers has only allowed us to significantly modify our management of the disease in a few instances. The paradigm for such genetically based molecular management is the multiple endocrine neoplasia type 2 (MEN 2) syndromes.
Multiple endocrine neoplasia type 2 (MEN 2)
As described in previous chapters (1), MEN 2 is an inherited cancer syndrome char- acterized by medullary thyroid carcinoma (MTC) and its precursor lesion, C-cell hyperplasia. These phenotypes are clinically recognizable in >90% of all cases (2).
Traditionally, MEN 2 has been divided into three disease subtypes, based on the pres-
ence of other associated phenotypes. The most common subtype, MEN 2A accounts
for about 85% of MEN 2 cases. In addition to MTC, MEN 2A is characterized by
pheochromocytoma (PC), tumours of the adrenal chromaffin cells, in about 50% of
cases, and hyperparathyroidism (HPT) in 15–30% of individuals. The most aggressive of the MEN 2 subtypes, MEN 2B, occurs in about 5% of cases and has a median age of tumour onset that is 10 years earlier than other forms of MEN 2 (<10 years) (3, 4). Approximately 50% of MEN 2B are de novo cases with no previous family history (5). As in MEN 2A, PC occurs in about 50% of individuals with MEN 2B but HPT is rare and patients also have a variety of other developmental anomalies such as buc- cal neuromas, marfanoid habitus, ganglioneuromas of the gut, and thickened corneal nerves (3, 6). The final disease subtype, familial MTC (FMTC) is characterized only by thyroid tumors and has no other associated anomalies. This disease form is the least aggressive MEN 2 subtype and may have a lower penetrance and later disease onset (7). As a result, FMTC families are frequently small and may be phenotypically quite difficult to distinguish from MEN 2A families in which cases of PC or HPT have not yet manifested. Because of this, stringent definitions have been suggested in which the diagnosis of FMTC requires a minimum of 4 (8, 9) or even 10 (10) family members with MTC in the absence of other phenotypes.
RET and the genetics of MEN 2
MEN 2 is inherited as an autosomal dominant disease and, as a result, all first-degree relatives of an affected individual are at 50% risk of inheriting the disease causing mutation. Although they differ in phenotype and aggressiveness, all three MEN 2 subtypes are caused by mutations of the RET (Rearranged in Transfection) oncogene (8, 9). RET encodes a cell surface receptor tyrosine kinase normally required for development of neuroendocrine cell types, the peripheral nervous system, and kidney (1, 11). RET mutations are identified in more than 95% of all MEN 2 families and there is no evidence of families in which the MEN 2 phenotype is not linked to RET. In each case, RET mutations are single amino acid substitutions that result in inappropriate activation of the RET receptor (12, 13). Mutations are clustered in “hot spots” in the extracellular domain (exons 10 and 11) or in the tyrosine kinase domain (exons 13–16) of the receptor (8, 9) (Figure 1).
Because >99% of mutations occur in only 10 codons of RET, direct DNA testing in MEN 2 is simple, widely available, and very efficient and is recommended for all at-risk individuals (Discussed below).
Although all MEN 2 subtypes are associated with RET mutations, specific
mutations confer much higher risks for some phenotypes. For example, mutations of
RET codon 634 are strongly correlated with HPT and PC and thus, not surprisingly,
represent 85% of MEN 2A mutations (14, 15). In MEN 2A, mutations generally
alter specific cysteine residues in the extracellular domain of RET (residues 609, 611,
618, 620, 634), resulting in a ligand-independent constitutively activated molecule
(Figure 1). The mutations found in patients with FMTC have a broader range of
functional effects, and may include both the same type of mutations as those seen in
MEN 2A as well as mutations in the tyrosine kinase domain (residues 768, 804, 891)
that appear to alter ATP binding (16). More than 95% of MEN 2B patients share the
same amino acid substitution (Met918Thr) in the binding pocket of the RET kinase
Figure 1. Schematic diagram of the RET receptor showing the relative positions of the more common mutations found in MEN 2.
domain (8, 9), although rare mutations of codon 883 are also detected (17, 18). Both mutations appear to alter the substrates of RET, thereby changing the downstream signals it sends (16) (Figure 1). The strong associations of specific mutations with each of the disease phenotypes can provide us with an additional tool for predicting patient prognosis and guiding management strategies (Discussed below).
In contrast to the activating RET mutations found in MEN 2, inactivating mutations of RET are identified in patients with Hirschsprung disease (HSCR), a congenital abnormality of gut innervation
(19). HSCR mutations are found throughout the RET gene and result in reduced levels of functional RET protein (20, 21). In rare cases, both the MEN 2 and HSCR phenotypes are associated with a single RET mutation (22, 23). These are generally single amino acid substitutions found in cysteine residues in the extracellular domain of RET (exon 10) (22). These oncogenic mutations may be as frequent as 1% in the HSCR population (24).
Diagnosis and prediction of MEN 2 Diagnosis in the “pre-genotyping” era
Before the identification of disease causing mutations in RET, MEN 2 disease status in
at-risk individuals was established by biochemical screening. Generally, this involved
measurement of calcitonin peptide release by C-cells in response to a provocative agent, such as pentegastrin or calcium (25). Elevated levels of calcitonin indicated the presence of an increased number of C-cells (C-cell hyperplasia) or of MTC and these individuals would be offered prophylactic thyroidectomy. This strategy, while clinically important, had several drawbacks, not the least of which was that diagnosis was dependent on identification of early hyperplastic changes and frequently was not made until MTC or even metastatic disease was already present (26, 27). Further, a negative screen result did not indicate that a patient did not carry the MEN 2 disease mutation, only that they had no detectable disease at that time. Thus, repeated screening of all at-risk individuals was required annually, or at regular intervals, in order to detect all MEN 2 cases. As a result, 50% of at-risk individuals who had no MEN 2 mutation would be repeatedly and unnecessarily screened. Because every at-risk individual needed to be repeatedly tested, biochemical screening for MEN 2 was a relatively costly strategy. Further, after several negative tests compliance could be a significant issue. For those undergoing regular testing, borderline or difficult to interpret biochemical screening results occasionally resulted in unnecessary thyroidectomy in individuals who did not carry the MEN 2 mutation (28). The incidence of false positives may have been as high as 5–10% (10).
In individuals with a confirmed diagnosis of MEN 2 additional screening for other associated phenotypes such as PC and HPT was required. Patients would be screened for PC on a regular basis by measurement of plasma metanephrines or levels of cate- cholamines or metanephrines in 24 h urine collection (29). A positive screen would lead to unilateral or, if necessary bilateral adrenalectomy. In general, prophylactic adrenalec- tomy would not be recommended due to risks from adrenal insufficiency (30). HPT is rarely symptomatic in MEN 2 but can be detected by measurement of calcium or parathyroid hormone levels. Biochemical screening for PC and HPT is recommended annually for individuals diagnosed with MEN 2.
MEN 2 and RET mutation testing
The identification of RET mutations as the underlying cause of MEN 2 has changed
the management of the individual and family with MEN 2 significantly. Genetic
testing, scanning the RET codons known to be frequently mutated, is now the
preferred method for confirming the clinical diagnosis of MEN 2 and is considered the
standard of good practice (9, 10, 31). The rate of false negative (2–5%) (10) and false
positive (<0.1%) results in DNA testing is a dramatic improvement over biochemical
screening methods. Individuals at-risk for MEN 2 should now be screened at birth
or at the earliest possible time for RET mutations and the results should provide the
basis for recommending thyroidectomy. Prophylactic thyroidectomy for individuals
carrying a germline RET mutation has dramatically reduced morbidity and mortality
due to MTC, and perceived quality of life is much better in individuals at risk for MTC
than for those at risk of other cancers where diagnosis and management are less clear
cut (32).
Because the basis and expectations associated with genetic testing need to be clearly understood in order for at-risk individuals to understand the implications of a RET mutation test and for them to use that information to make informed decisions about disease management, it is essential that all DNA testing be accompanied by appro- priate genetic counseling. This would generally take the form of pretest counseling to explain the implications and risks of the test and one or more post-test coun- seling sessions involving delivery of results and discussion of their implications as necessary.
INDICATIONS FOR RET MUTATION TESTING . Screening for RET mutations is now the basis of all management strategies for MEN 2, replacing reliance on biochemical screening. In families where the disease causing mutation has already been estab- lished by previous screening of affected individuals, all at-risk individuals should be genetically screened for the familial mutation. Individuals who do not carry this mutation are not at risk of MEN 2 and can be excluded from further testing. Indi- viduals with the mutation are at high risk for MEN 2 phenotypes and should be managed accordingly. If diagnosis is made in a child, thyroidectomy should be per- formed before age 5 for MEN 2A and FMTC families and before age 6 months in individuals with MEN 2B mutations which are associated with earlier tumour development (10).
Early, genetically based identification of mutation carriers permits surgery before the usual onset of malignant disease and carries the optimal possibility of pre- venting metastatic disease. Older patients diagnosed with RET mutations will be offered thyroidectomy as soon as possible accompanied by biochemical monitoring for the presence of metastatic disease. Mutation positive individuals will be moni- tored throughout life for other tumour types or anomalies associated with their spe- cific MEN 2 subtype, as described above. The regime for these screening protocols may, in theory, be modified based on the occurrence and age of onset of these phe- notypes in other family members. However, variability in these, even within a sin- gle family, suggests that caution should be used when relaxing screening protocols (33, 34).
If an individual represents a new case/family diagnosed for MEN 2, RET mutation screening should be performed in a known affected family member. This also holds true for all individuals diagnosed with apparently sporadic MTC, as 1–7% of these have germline RET mutations and represent new MEN 2 families (35). Interestingly, early studies had suggested that germline RET mutations were very rare in sporadic PC but recent studies showing they may occur in up to 5% of cases (36) have suggested that all patients with these tumours should also be screened for RET mutations (10).
Initial screening must include RET exons in which mutations are most frequently
found, (exons 10, 11, 13–16) however these may be prioritized based on the patient
phenotype. For example, 85% of MEN 2A families have mutations in exon 11 and
almost 95% of MEN 2B cases have mutations of codon 918 in exon 16. If mutations
of these exons are not identified a broader screen, including all RET exons may be
necessary. Once a RETmutation is identified, all other at-risk family members may be
screened specifically for that change and individuals carrying the mutation are managed as described above.
In a few instances, a RET mutation may not be identified in a putative MEN 2 individual. These cases are rare and frequently, although not always, involve families that are quite small with few or a single affected individual. In the past, some of these families may have resulted from conservative diagnosis of FMTC in families that did not have clear features of MEN 2. For example, studies have shown that up to 5% of the population may have C-cell hyperplasia but do not have RET mutations nor a true MEN 2 phenotype (28). Recent studies suggest that at least some of these cases may be related to mutations of the succinate dehydrogenase subunit D gene (chromosome
11q23) and not to RET (37).
This highlights the necessity of accurate and unambiguous clinical diagnosis in cases where RET mutations have not been identified. If families with clearly defined MEN 2 but no RET mutation have sufficient confirmed affected family members available, linkage analysis using polymorphic sites in or near the RET gene (chro- mosome 10q11.2) may provide an alternative to direct mutation detection. In this method, a haplotype for a series of polymorphisms over the region of RET which presumably includes a disease mutation may be constructed based on the genotype of multiple affected family members (38–41). Inheritance of this “disease haplo- type” can be used to identify individuals who have also inherited the predicted RET mutation and are therefore assumed to be MEN 2 carriers. This method is less amenable to diagnosis than is direct mutation testing since it is dependent on the availability of a suitable family structure, the participation of multiple family mem- bers and relies on the assumption that the clinical diagnosis is correct in suggesting MEN 2.
Where suitable family members are not available, or a haplotype cannot be con- structed, MEN 2 families without RET mutations will be treated as they were before the advent of DNA mutation testing, using repeated biochemical screening of all at-risk individuals and offering surgery at the first sign of a positive test result.
WHO SHOULD BE OFFERED SCREENING ?RET mutation screening is consid- ered the standard of care for all individuals at-risk for MEN 2, irrespective of their age. Ideally, at-risk individuals in known MEN 2 families would be screened for RET mutations at birth or shortly thereafter. This is somewhat different from mutation test- ing in many other cancer syndromes where minors are not automatically screened.
In the case of MEN 2, the penetrance of the disease is very high (>90% have clini- cally detectable disease) and onset is very young, the earliest recognition of MEN 2B being reported in children under age 5 (24, 42, 43) necessitating very early detection to allow presymptomatic intervention. Further, unlike many other cancer syndromes of childhood, there are clear, well tolerated, prophylactic options available which are demonstrably valuable in decreasing the burden of the disease in affected individuals.
The advent of early childhood mutation detection has greatly reduced the incidence
of MTC in families with known MEN 2 and will, with time, virtually eliminate
the morbidity and mortality associated with metastatic disease in known MEN 2
families.
RET mutation screening is also recommended for individuals with sporadic MTC and also PC, although there has been no indications that RET mutations contribute to sporadic HPT (44). In each case, it is important to remember that RET mutations can occur somatically in these tumours (45–49) and that these should not be confused with germline MEN 2-RET mutations.
Approximately 1% of individuals with HSCR have a RET mutation in exon 10 which may also confer risk for MEN 2 phenotypes (24). While this may seem rare, RET mutations in HSCR are widely distributed throughout the gene and exon 10 mutations, primarily in codons 609, 618 and 620, represent one of the largest cluster- ings of mutations. Because of the oncogenic risk associated with these mutations, RET exon 10 mutation screening is recommended for all children diagnosed with HSCR.
Individuals identified with any of these mutations should be treated as a potential MEN 2 case and screening of at-risk family members and surgical intervention should be offered.
Diagnosis and management: The evolving genetic contribution
While the advent of genetic testing for RET mutations has significantly improved our ability to manage patients and families with MEN 2, the potential exists for additional refinement that may improve the prospects even further. Several exciting options for this refinement are currently being evaluated and the accumulating body of experience with RET genotype and phenotype are allowing us to improve the accuracy of disease prediction.
Genotype-phenotype associations in genetically based management
Our 10 year experience of RET mutation and MEN 2 disease phenotype correlation has shown us that not all RET mutations carry equal associated risk and that the traditional definitions of disease phenotype may in future not be as useful to us as genetically or mutation based disease risk estimates.
We have long known that some RET mutations conferred higher risk of PC (e.g.
Cys634Arg or Met918Thr) (8, 9) while others are associated with a less aggressive disease phenotype (e.g. Glu768Arg or Val804Met). Recent studies have begun to investigate the potential of using specific RET mutation data to guide management strategies. Three general categories of high, medium, and low risk RET mutations may be defined based on their relative penetrance, the specific disease phenotypes associated with them, and the aggressiveness of these phenotypes (Table 1) (10, 31).
Mutations in the highest disease risk group include those found in MEN 2B (Met 918Thr, Ala883Phe). The lowest risk mutations are those found most frequently in FMTC and those associated with later disease onset (Table 1) (50).
These risk groupings are an attractive tool to supplement clinical diagnosis for defin-
ing individuals with high risk who need early thyroidectomy and/or stringent bio-
chemical screening regimes. By defining a subgroup of higher risk patients genetically
predisposed to more, or more severe, disease phenotypes we may be able to focus
health care resources more effectively and reduce patient stress associated with disease
management. In future, the specific RET mutation found in a patient is likely, to act
as a guide to determine the frequency of screening required and the age at which surgery should be offered to mutation carriers. We may, for example, be able to reduce the frequency of screening for PC in individuals with mutations rarely associated with PC (e.g. Glu768Arg or Val804Met), or use a more relaxed age for thyroidectomy in patients with mutations and a family history consistent with later onset tumours. Such genotype-based management must be used with caution however, as there is still some variability in clinical presentation of MEN 2, even in families/individuals carrying the identical RET mutation. Aggressive, early onset cases can occur in families with mutations that have elsewhere been shown to be quite indolent (33, 34). It is clear that genotype-based management strategies will still rely heavily on the clinical diagnosis and the specific pattern of the disease within a family to optimize a program of surgery and biochemical screening appropriate to the specific genotype and phenotype of each patient.
Disease associated RET haplotypes in sporadic MTC and PC
The genotype at the RET locus may, in future, also provide us with some predictive information on the occurrence of sporadic tumours. The majority of MTC and PC (>75%) occur sporadically, without any associated family history (36, 51). However, recent studies have suggested that some haplotypes for polymorphic variants surround- ing the RET locus are associated with increased risk for these sporadic tumours (39, 52). These risk haplotypes may reflect a combination of variants that themselves confer risk or may be a simple marker for another risk contributing gene lying upstream of RET and not yet identified. In the future, this information may be useful in predicting individuals at risk for sporadic tumours or in establishing the risk of recurrence in family members of individuals with sporadic disease.
SUMMARY CONCLUSIONS
Diagnosis and management of MEN 2 has evolved considerably since the identifica- tion of the underlying disease mutations in the RET proto-oncogene. Presymptomatic detection and prophylactic surgical intervention are now the accepted standard of care.
The strong correlation of disease phenotype and mutation genotype has already also
allowed us to develop mutation-guided management strategies to optimize time of intervention and schedule follow-up and management. As our understanding of the depth of these correlations increases we look forward to better refining our manage- ment regimes to fit both the best care requirements and the quality of life needs of the MEN 2 patient.
REFERENCES
1. Pierotti, M. A. RET Activation in Medullary carcinomas. In: N. Farid (ed.), Molecular Basis of Thyroid Cancer: Kluwar Academic Publishers, In Press.
Easton, D. F., Ponder, M. A., Cummings, T., Gagel, R. F., Hansen, H. H., Reichlin, S., Tashjian, A.
H., Telenius-Berg, M., Ponder, B. A. J., and Cancer Research Campaign Medullary Thyroid Group The clinical and screening age-at-onset distribution for the MEN-2 syndrome. Am J Hum Genet, 44:
208–215, 1989.
Gorlin, R. J., Sedano, H. O., Vickers, R. A., and Cervenka, J. Multiple mucosal neuromas, pheochro- mocytoma and medullary carcinoma of the thyroid—a syndrome. Cancer, 22: 293–299, 1968.
Leboulleux, S., Travagli, J. P., Caillou, B., Laplanche, A., Bidart, J. M., Schlumberger, M., and Baudin, E. Medullary thyroid carcinoma as part of a multiple endocrine neoplasia type 2B syndrome: influence of the stage on the clinical course. Cancer, 94: 44–50, 2002.
Carlson, K., Bracamontes, J., Jackson, C., Clark, R., Lacroix, A., Wells, S., and Goodfellow, P. Parent- of-origin effects in multiple endocrine neoplasia type 2B. Am J Hum Genet, 55: 1076–1082, 1994.
Carney, J. A., Go, V. L., Sizemore, G. W., and Hayles, A. B. Alimentary-tract ganglioneuromatosis.
A major component of the syndrome of multiple endocrine neoplasia, type 2b. N Engl J Med, 295:
1287–1291, 1976.
Farndon.J. R., Leight, G. S., Dilley, W. G., Baylin, S. B., Smallridge, R. C., Harrison, T. S., and Wells, S.
A. Familial medullary thyroid carcinoma without associated endoerinopathies: a distinct clinical entity.
Br J Surg, 73: 278–281, 1986.
Mulligan, L. M., Marsh, D. J., Robinson, B. G., Schuffenecker, I., Zedenius, J., Lips, C. J. M., Gagel, R. F., Takai, S.-I., Noll, W. W., Fink, M., Raue, F., Lacroix, A., Thibodeau, S. N., Frilling, A., Ponder, B. A. J., Eng, C., and International RET Mutation Consortium Genotype-phenotype correlation in multiple endocrine neoplasia type 2: report of the International RET Mutation Consortium. J Intern Med, 238: 343–346, 1995.
Eng, C., Clayton, D., Schuffenecker, L, Lenoir, G., Cote, G., Gagel, R. F., Ploos van Amstel, H.-K., Lips, C. J. M., Nishisho, I., Takai, S.-I., Marsh, D. J., Robinson, B. G., Frank-Raue, K., Raue, F., Xu, F., Noll, W. W, Romei, C., Pacini, F., Fink, M., Niederle, B., Zedenius, J., Nordenskjöld, M., Komminoth, P., Hendy, G., Gharib, H., Thibodeau, S., Lacroix, A., Frilling, A., Ponder, B. A. J., and Mulligan, L. M. The relationship between spccificRET proto-oncogene mutations and disease phenotype in multiple endocrine neoplasia type 2: International RET Mutation Consortium. JAMA,
276: 1575–1579, 1996.Brandi, M. L., Gagel, R. F., Angeli, A., Bilezikian, J. P., Beck-Peccoz, P., Bordi, C., Conte-Devolx, B., Falchetti, A., Gheri, R. G., Libroia, A., Lips, C. J., Lombardi, G., Mannelli, M., Pacini, F., Ponder, B.
A., Raue, F., Skogseid, B., Tamburrano, G., Thakker, R. V., Thompson, N. W., Tomassetti, P., Tonelli, F., Wells, S. A., Jr., and Marx, S. J. Guidelines for diagnosis and therapy of MEN type 1 and type 2. J Clin Endocrinol Metab, 86: 5658–5671, 2001.
Schuchardt, A., D’Agati, V., Larsson-Blomberg, L., Costantini, F., and Pachnis, V. Defects in the kidney and enteric nervous system of mice lacking the tyrosine kinase receptor Ret. Nature, 367: 380–383, 1994.
Santoro, M., Carlomagno, F., Romano, A., Bottaro, D. P., Dathan, N. A., Grieco, M., Fusco, A., Vecchio, G., Matoskova, B., Kraus, M. H., and Di Fiore, P. P. Activation of RET as a dominant transforming gene by germline mutations of MEN2A and MEN2B. Science, 267: 381–383, 1995.
Asai, N., Iwashita, T, Matsuyama, M., and Takahashi, M. Mecahanism of activation of the ret proto- oncogene by multiple endocrine neoplasia 2A mutations. Mol Cell Biol, 15: 1613–1619, 1995.
Mulligan, L. M., Eng, C., Healey, C. S., Clayton, D., Kwok, J. B. J., Gardner, E., Ponder, M. A., Frilling, A., Jackson, C. E., Lehnert, H., Neumann, H. P. H., Thibodeau, S. N., and Ponder, B. A.
J. Specific mutations of the RET proto-oncogene are related to disease phenotype in MEN 2A and FMTC. Nature Genet, 6: 70–74, 1994.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15. Schuffenecker, I., Virally-Monod, M., Brohet, R., Goldgar, D., Conte-Devolx, B., Leclerc, L., Chabre, O., Boneu, A., Caron, J., Houdent, C., Modigliani, E., Rohmer, V., Schlumberger, M., Eng, C., Guillausseau, P. J., and Lenoir, G. M. Risk and penetrance of primary hyperparathyroidism in multiple endocrine neoplasia type 2A families with mutations at codon 634 of the RET proto–oncogene. Groupe D’etude des Tumeurs a Calcitonine. J Clin Endocrinol Metab, 83: 487–491, 1998.
Iwashita, T., Kato, M., Murakami, H., Asai, N., Ishiguro, Y., Ito, S., Iwata, Y, Kawai, K., Asai, M., Kurokawa, K., Kajita, H., and Takahashi, M. Biological and biochemical properties of Ret with kinase domain mutations identified in multiple endocrine neoplasia type 2B and familial medullary thyroid carcinoma. Oncogene, 18: 3919–3922, 1999.
Smith, D. P., Houghton, C., and Ponder, B. A. J. Germline mutation of RET codon 883 in two cases of de novo MEN 2B. Oncogene, 15: 1213–1217, 1997.
Gimm, O., Marsh, D. J., Andrew, S. D., Frilling, A., Dahia, P. L. M., Mulligan, L. M., Zajac, J. D., Robinson, B. G., and Eng, C. Germline dinucleotide mutation in codon 883 of the RET proto–
oncogene in multiple endocrine neoplasia type 2B without codon 918 mutation. J Clin Endocrinol Metab, 82: 3902–3904, 1997.
Edery, P., Lyonnet, S., Mulligan, L. M., Pelet, A., Dow, E., Abel, L., Holder, S., Nihoul–Fékété, C., Ponder, B. A. J., and Munnich, A. Mutations of the RET proto-oncogene in Hirschsprung’s disease.
Nature, 367: 378-380, 1994.
Pasini, B., Borrello, M. G., Greco, A., Bongarzone, I., Mondellini, P., Alberti, L., Miranda, C., Arighi, E., Bocciardi, R., Seri, M., Barone, V, Radice, M. T., Romeo, G., and Pierotti, M. A. Loss of function effect of RET mutations causing Hirschsprung disease. Nature Genet, 10: 35-40, 1995.
Iwashita, T., Murakami, H., Asai, N., and Takahashi, M. Mechanisms of Ret dysfunction by Hirschsprung mutations affecting its extracellular domain. Hum Molec Genet, 5: 1577–1580, 1996.
Mulligan, L. M., Eng, C., Attié, T., Lyonnet, S., Marsh, D. J., Hyland, V.J., Robinson, B. G., Frilling, A., Verellen–Dumoulin, C., Safar, A., Venter, D. J., Munnich, A., and Ponder, B. A. J. Diverse phenotypes associated with exon 10 mutations of the RET proto-oncogene. Hum Mol Genet, 3: 2163–2167, 1994.
Takahashi, M., Iwashita, T., Santoro, M., Lyonnet, S., Lenoir, G, M., and Billaud, M. Co-segregation of MEN2 and Hirschsprung’s disease: the same mutation of RET with both gain and loss-of-function?
Hum Mutat, 13: 331–336, 1999.
Torre, M., Martucciello, G., Ceccherini, I., Lerone, M., Aicardi, M., Gambini, C., and Jasonni, V.
Diagnostic and therapeutic approach to multiple endocrine neoplasia type 2B in pediatric patients.
Pediatr Surg Int, 18: 378–383, 2002.
Heshmati, H. M., Gharib, H., van Heerden, J. A., and Sizemore, G. W. Advances and controversies in the diagnosis and management of medullary thyroid carcinoma. Am J Med, 103: 60–69, 1997.
Wells, S., Chi, D., Toshima, K., Dehner, L., Coffin, C., Dowton, B., Ivanovich, J., DeBenedetti, M., Dilley, W., Moley, J., Norton, J., and Donis-Keller, H. Predictive DNA testing and prophylactic thyroidectomy in patients at risk for multiple endocrine neoplasia type 2A. Ann Surg, 220: 237–250, 1994.
Dralle, H., Gimm, O., Simon, D., Frank-Raue, K., Gortz, G., Niederle, B., Wahl, R. A., Koch, B., Walgenbach, S., Hampel, R., Ritter, M. M., Spelsberg, F., Heiss, A., Hinze, R., and Hoppner, W.
Prophylactic thyroidectomy in 75 children and adolescents with hereditary medullary thyroid carcinoma:
German and Austrian experience. World J Surg, 22: 744–750; discussion 750–741, 1998.
Lips, C. J. M., Landsvater, R. M., Höppener,J. W. M., Geerdink, R. A., Blijham, G., Jansen-Schillhorn van Veen, J. M., van Gils, A. P. G., de Wit, M.J., Zewald, R. A., Berends, M. J. H., Beemer, F. A., Brouwers-Smalbraak, J., Jansen, R. P. M., Ploos van Amstel, H. K., van Vroonhoven, T. J. M. V, and Vroom, T. M. Clinical screening as compared with DNA analysis in families with multiple endocrine neoplasia type 2A. N Engl J Med, 331: 828–835, 1994.
Frank-Raue, K., Kratt, T, Hoppner, W, Buhr, H., Ziegler, R., and Raue, F. Diagnosis and management of pheochromocytomas in patients with multiple endocrine neoplasia type 2-relevance of specific mutations in the RET proto-oncogene. Eur J Endocrinol, 135: 222–25, 1996.
Lee, J. E., Curley, S. A., Gagel, R. F., Evans, D. B., and Hickey, R. C. Cortical–sparing adrenalectomy for patients with bilateral pheochromocytoma. Surgery, 120: 1064–1070; discussion 1070–1061, 1996.
Yip, L., Cote, G. J., Shapiro, S. E., Ayers, G. D., Herzog, C. E., Sellin, R. V, Sherman, S. I., Gagel, R. F., Lee, J. E., and Evans, D. B. Multiple endocrine neoplasia type 2: evaluation of the genotype–phenotype relationship. Arch Surg, 138: 409–416, 2003.
Freyer, G., Ligneau, B., Schlumberger, M., Blandy, C., Contedevolx, B., Trillet-Lenoir, V, Lenoir, G. M., Chau, N., and Dazord, A. Quality of life in patients at risk of medullary thyroid carcinoma 16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
and followed by a comprehensive medical network: trends for future evaluations. Ann Oncol, 12:
1461–1465, 2001.
33. Feldman, G. L., Edmonds, M. W., Ainsworth, P. J., Schuffenecker, I., Lenoir, G. M., Saxe, A. W, Talpos, G. B., Roberson,J., Petrucelli, N., and Jackson, C. E. Variable expressivity of familial medullary thyroid carcinoma (FMTC) due to a RET V804M (GTG–>ATG) mutation. Surgery, 128: 93–98, 2000.
Lombardo, F., Baudin, E., Chiefari, E., Arturi, F., Bardet, S., Caillou, B., Conte, C., Dallapiccola, B., Giuffrida, D., Bidart, J. M., Schlumberger, M., and Filetti, S. Familial medullary thyroid carcinoma:
clinical variability and low aggressiveness associated with RET mutation at codon 804. J Clin Endocrinol Metab, 87: 1674–1680, 2002.
Eng, C., Mulligan, L. M., Smith, D. P., Healey, C. S., Frilling, A., Raue, F., Neumann, H. P. H., Ponder, M. A., and Ponder, B. A. J. Low frequency of germline mutations in the RET proto–oncogene in patients with apparently sporadic medullary thyroid carcinoma. Clin Endocrinol, 43: 123–127, 1995.
Neumann, H. P., Bausch, B., McWhinney, S. R., Bender, B. U., Gimm, O., Franke, G., Schipper, J., Klisch, J., Altehoefer, C., Zerres, K., Januszewicz, A., Eng, C., Smith, W. M., Munk, R., Manz, T., Glaesker, S., Apel, T. W., Treier, M., Reineke, M., Walz, M. K., Hoang-Vu, C., Brauckhoff, M., Klein-Franke, A., Klose, P., Schmidt, H., Maier-Woelfle, M., Peczkowska, M., and Szmigiel–
ski, C. Germ-line mutations in nonsyndromic pheochromocytoma. N Engl J Med, 346: 1459–1466, 2002.
Lima.J., Teixeira-Gomes,J., Soares, P., Maximo, V, Honavar, M., Williams, D., and Sobrinho–Simoes, M. Germline succinate dehydrogenase subunit D mutation segregating with familial non-RET C cell hyperplasia. J Clin Endocrinol Metab, 88: 4932–4937, 2003.
Sancandi, M., Griseri, P., Pesce, B., Patrone, G., Puppo, F., Lerone, M., Martucciello, G., Romeo, G., Ravazzolo, R., Devoto, M., and Ceccherini, I. Single nucleotide polymorphic alleles in the 5 ' region of the RET proto-oncogene define a risk haplotype in Hirschsprung’s disease. J Med Genet, 40: 714–718, 2003.
Borrego, S., Wright, F. A., Fernandez, R. M., Williams, N., Lopez-Alonso, M., Davuluri, R., Antinolo, G., and Eng, C. A Founding Locus within the RET Proto-Oncogene May Account for a Large Proportion of Apparently Sporadic Hirschsprung Disease and a Subset of Cases of Sporadic Medullary Thyroid Carcinoma. Am J Hum Genet, 72: 88–100, 2003.
Griseri, P., Pesce, B., Patrone, G., Osinga, J., Puppo, F., Sancandi, M., Hofstra, R., Romeo, G., Ravaz- zolo, R., Devoto, M., and Ceccherini, I. A rare haplotype of the RET proto-oncogene is a risk- modifying allele in hirschsprung disease. Am J Hum Genet, 71: 969–974, 2002.
Burzynski, G. M., Nolte, I. M., Osinga,J., Ceccherini, I., Twigt, B., Maas, S. M., Brooks, A. S., Verheij, J. B. G. M., Menacho, I. P., Buys, C. H. C. M., and Hofstra, R. M. W. Mapping a putative mutation as the major contributor to the development of sporadic Hirschsprung diseae to the RET genomic sequence between the promoter region and exon 2. Eur J Hum Genet, In press.
Skinner, M. A., DeBenedetti, M. K., Moley,J. F., Norton, J. A., and Wells, S. A., Jr. Medullary thyroid carcinoma in children with multiple endocrine neoplasia types 2A and 2B. J Pediatr Surg, 31: 177–181;
discussion 181–172, 1996.
Stjernholm, M. R., Freudenbourg, J. C., Mooney, H. S., Kinney, E J., and Deftos, L. J. Medullary carcinoma of the thyroid before age 2 years. J Clin Endocrinol Metab, 51: 252–253, 1980.
Padberg, B.-C., Schröder, S.,Jochum, W., Kastendieck, H., Roth, J., Heitz, P. U., and Komminoth, P. Absence of RET proto-oncogene point mutations in sporadic hyperplastic and neoplastic lesions of the parathyroid gland. Am J Pathol, 147: 1600–1607, 1995.
Eng, C., Crossey, P. A., Mulligan, L. M., Healey, C. S., Houghton, C., Prowse, A., Chew, S. L., Dahia, P. L. M., O’Riordan, J. L. H., Toledo, S. P. A., Smith, D. P., Maher, E. R., and Ponder, B. A. J.
Mutations in the RET proto-oncogene and the von Hippel-Lindau disease tumour suppressor gene in sporadic and syndromic phaeochromocytomas. J Med Genet, 32: 934–937, 1995.
Eng, C., Mulligan, L. M., Smith, D. P., Healey, C. S., Frilling, A., Raue, F., Neumann, H. P. H., Pfragner, R., Behmel, A., Lorenzo, M. J., Stonehouse, T. J., Ponder, M. A., and Ponder, B. A. J.
Mutation of the RET proto-oncogene in sporadic medullary thyroid carcinoma. Genes Chrom Canc,
12: 209–212, 1995.Hofstra, R. M. W., Landsvater, R. M., Ceccherini, I., Stulp, R. P., Stelwagen, T., Luo, Y, Pasini, B., Höppener, J. W. M., Ploos van Amstel, H. K., Romeo, G., Lips, C. J. M., and Buys, C. H. C. M.
A mutation in the RET proto-oncogene associated with multiple endocrine neoplasia type 2B and sporadic medullary thyroid carcinoma. Nature, 367: 375–376, 1994.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48. Blaugrund, J. E., Johns, M. M., Eby, Y. J., Ball, D. W., Baylin, S. B., Hruban, R. H., and Sidransky, D.
RET proto-oncogene mutations in inherited and sporadic medullary thyroid cancer. Hum Mol Genet, 3: 1895–1897, 1994.
