Genetic linkage studies map the multiple endocrine neoplasia type 2 loci to a small interval on chromosome 10q11.2

Medullary thyroid cancer: molecular factors, management and treatment

Medullary thyroid cancer (MTC) is an infrequent neuroendocrine tumor, which amounts to 3–5% of all thyroid malignancies. Approximately 75–80% of MTCs are sporadic neoplasms. The rest of 20–25% are familial cases that belong to multiple endocrine neoplasia (MEN) syndromes, specifically MEN2 and MEN3. These cases of familial MTC are attributed to an activating germline mutation of a tyrosine kinase receptor gene, the rearranged during transfection (RET) proto-oncogene, located on chromosome 10q11.21. These mutations are also found in some cases of sporadic MTC. This review sets forth in summary the accepted guidelines and approaches regarding diagnosis, management, and treatment of MTC. Surgical resection is the standard care, and an early, prophylactic intervention is performed in genetic cases. Further investigation and understanding of the molecular pathways involved in the growth and advancement of MTC is required in order to provide efficient therapy in cases of progressive disease.

Prophylactic thyroidectomy in children with multiple endocrine neoplasia type 2

BACKGROUND

In patients with multiple endocrine neoplasia type 2 (MEN2) syndrome, genetic testing offers early diagnosis, stratifies the risk of developing medullary thyroid cancer (MTC) and informs the timing of thyroidectomy. The efficacy of treatment, which depends on timely and safe surgery, is not well established.

METHODS

This was a retrospective review of diagnostic and clinicopathological outcomes of prophylactic thyroidectomy in children with MEN2 between 1995 and 2013 in the UK. American Thyroid Association (ATA) 2009 guidelines were used as a benchmark for adequate treatment.

RESULTS

Seventy-nine children from 16 centres underwent total thyroidectomy. Thirty-eight patients (48 per cent) underwent genetic testing and 36 (46 per cent) had an operation performed above the age recommended by the ATA 2009 guidelines; pathology showed MTC in 30 patients (38 per cent). Late surgery, above-normal preoperative calcitonin level and MTC on pathology correlated with late genetic testing. Twenty-five children had lymphadenectomy; these patients had more parathyroid glands excised (mean difference 0·61, 95 per cent c.i. 0·24 to 0·98; P = 0·001), and were more likely to have hypocalcaemia requiring medication (relative risk (RR) 3·12, 95 per cent c.i. 1·54 to 6·32; P = 0·002) and permanent hypoparathyroidism (RR 3·24, 1·29 to 8·11; P = 0·010) compared with those who underwent total thyroidectomy alone. Age did not influence the development of complications.

CONCLUSION

Late genetic testing may preclude age-appropriate surgery, increasing the risk of operating when MTC has already developed. Early genetic testing and age-appropriate surgery may help avoid unnecessary lymphadenectomy and improve outcomes.

Update on medullary thyroid cancer

Medullary thyroid carcinoma (MTC) is a rare type of thyroid cancer, demonstrating variable behavior from indolent disease to highly aggressive, progressive disease. There are distinguishing phenotypic features of sporadic and hereditary MTC. Activation or overexpression of cell surface receptors and up-regulation of intracellular signaling pathways in hereditary and sporadic MTC are involved in the disease pathogenesis. There has been an exponential rise in clinical trials with investigational agents, leading to approval of 2 medications for progressive, advanced MTC. Developments in understanding the pathogenesis of MTC will hopefully lead to more effective and less toxic treatments of this rare but difficult to treat cancer.

Identification of a lung adenocarcinoma cell line with CCDC6-RET fusion gene and the effect of RET inhibitors in vitro and in vivo

Rearrangements of the proto-oncogene RET are newly identified potential driver mutations in lung adenocarcinoma (LAD). However, the absence of cell lines harboring RET fusion genes has hampered the investigation of the biological relevance of RET and the development of RET-targeted therapy. Thus, we aimed to identify a RET fusion positive LAD cell line. Eleven LAD cell lines were screened for RET fusion transcripts by reverse transcription-polymerase chain reaction. The biological relevance of the CCDC6-RET gene products was assessed by cell growth, survival and phosphorylation of ERK1/2 and AKT with or without the suppression of RET expression using RNA interference. The efficacy of RET inhibitors was evaluated in vitro using a culture system and in an in vivo xenograft model. Expression of the CCDC6-RET fusion gene in LC-2/ad cells was demonstrated by the mRNA and protein levels, and the genomic break-point was confirmed by genomic DNA sequencing. Mutations in KRAS and EGFR were not observed in the LC-2/ad cells. CCDC6-RET was constitutively active, and the introduction of a siRNA targeting the RET 3' region decreased cell proliferation by downregulating RET and ERK1/2 phosphorylation. Moreover, treatment with RET-inhibitors, including vandetanib, reduced cell viability, which was accompanied by the downregulation of the AKT and ERK1/2 signaling pathways. Vandetanib exhibited anti-tumor effects in the xenograft model. Endogenously expressing CCDC6-RET contributed to cell growth. The inhibition of kinase activity could be an effective treatment strategy for LAD. LC-2/ad is a useful model for developing fusion RET-targeted therapy.

Animal models of hyperfunctioning parathyroid diseases for drug development

BACKGROUND

Disorders of mineral and bone metabolism have been implicated as a risk factor in the high mortality in patients with chronic kidney disease (CKD). Hyperphosphatemia, disorders of vitamin D metabolism and secondary hyperparathyroidism of uremia (SHPT) are therapeutic targets in these patients to improve the mortality. Animal models for CKD are indispensable and uremic rats produced by 5/6-nephrectomies are one of the most useful animal models for the development of new therapeutic agents. As there are limitations of uremic rats such as short lifespan and less severity of secondary hyperparathyroidism distinct from CKD patients on maintenance hemodialysis, the development of new model animals is expected.

OBJECTIVE

This review discusses the molecular pathogenesis of hyperfunctioning parathyroid diseases and the applications of animal models exhibiting hyperparathyroidisms in the aspect of the development of new therapeutics.

CONCLUSION

PTH-cyclin D1 transgenic mice, with parathyroid-targeted overexpression of cyclin D1 oncogene, not only developed abnormal parathyroid cell proliferation but, notably, also developed biochemical hyperparathyroidism with characteristic abnormalities in bone. The mice exhibit age-dependent development of biochemical hyperparathyroidism, which enables testing of the drug precisely. In addition, the mice develop parathyroid cell hyperplasia, followed by monoclonal expansion, which is observed in refractory SHPT patients.

Spontaneous adrenal pheochromocytoma rupture complicated by intraperitoneal hemorrhage and shock

MEN2A is a hereditary syndrome characterized by medullary thyroid carcinoma, hyperparathyroidism, and pheochromocytoma. Classically patients with a pheochromocytoma initially present with the triad of paroxysmal headaches, palpitations, and diaphoresis accompanied by marked hypertension. However, although reported as a rare presentation, spontaneous hemorrhage within a pheochromocytoma can present as an abdominal catastrophe. Unrecognized, this transformation can rapidly result in death. We report the only documented case of a thirty eight year old gentleman with MEN2A who presented to a community hospital with hemorrhagic shock and peritonitis secondary to an unrecognized hemorrhagic pheochromocytoma. The clinical course is notable for an inability to localize the source of hemorrhage during an initial damage control laparotomy that stabilized the patient sufficiently to allow emergent transfer to our facility, re-exploration for continued hemorrhage and abdominal compartment syndrome, and ultimately angiographic embolization of the left adrenal artery for control of the bleeding. Following recovery from his critical illness and appropriate medical management for pheochromocytoma, he returned for interval bilateral adrenal gland resection, from which his recovery was unremarkable. Our review of the literature highlights the high mortality associated with the undertaking of an operative intervention in the face of an unrecognized functional pheochromocytoma. This reinforces the need for maintaining a high index of suspicion for pheochromocytoma in similar cases. Our case also demonstrates the need for a mutimodal treatment approach that will often be required in these cases.

Medullary thyroid carcinoma: molecular signaling pathways and emerging therapies

Research on medullary thyroid carcinoma (MTC) over the last 55 years has led to a good understanding of the genetic defects and altered molecular pathways associated with its development. Currently, with the use of genetic testing, patients at high risk for MTC can be identified before the disease develops and offered prophylactic treatment. In cases of localized neck disease, surgery can be curative. However, once MTC has spread beyond the neck, systemic therapy may be necessary. Conventional chemotherapy has been shown to be ineffective; however, multikinase inhibitors have shown promise in stabilizing disease, and this year will probably see the approval of a drug (Vandetanib) for advanced unresectable or metastatic disease, which represents a new chapter in the history of MTC. In this paper, we explore newly understood molecular pathways and the most promising emerging therapies that may change the management of MTC.

Mendelian genetics of rare--and not so rare--cancers

Mendelian genetics forms the basis for gene-informed risk assessment and management for the patient and family, and should be at the very foundation of 21st century personalization of healthcare. Yet this is an underutilized commodity. Identification and characterization of germline mutations in the RET proto-oncogene, encoding a receptor tyrosine kinase, as causing >90% of multiple endocrine neoplasia type 2 (MEN 2), an autosomal dominant disorder characterized by medullary thyroid cancer, pheochromocytoma, and hyperparathyroidism, heralded the era of evidence-based molecular diagnosis, predictive testing, genetic counseling, gene-informed cancer risk assessment, and preventative medicine. Since then, many syndromic endocrine neoplasias have proven to fall under this clinically utile and actionable model, such as those caused by mutations in RET, VHL, or SDHB-D. The familial risk associated with epithelial (nonmedullary) thyroid carcinoma is among the highest of all solid tumors, yet only a few highly penetrant heritable epithelial thyroid cancer syndrome exist. This is illustrated by Cowden syndrome, a difficult-to-recognize autosomal dominant disorder characterized by breast, thyroid, and other cancers, caused by germline mutations in PTEN, encoding a phosphatase, and minorly, SDHB/SDHD variants.

Multiple endocrine neoplasia

MEN1 and MEN2 are autosomal dominant cancer syndromes with the potential for considerable morbidity and mortality. Better understanding of the molecular pathogenesis in MEN1 and MEN2 has fostered the development of specific DNA screening. Knowing the genetic status of patients is valuable for making decisions regarding surveillance and interventions, such as prophylactic thyroidectomy for medullary thyroid cancer. Identifying new RET pathways has provided molecular targets for therapies that currently are being tested in clinical trials for locally advanced, metastatic, and recurrent medullary thyroid cancer.

Molekularbiologie, Grundlagenforschung und Diagnose des Morbus Hirschsprung

The proto-oncogene RET is the major gene responsible for Hirschsprung's disease (HSCR), with RET mutations also implied in different pathologies. A variety of mutations of the RET proto-oncogene have been detected in HSCR patients. Special attention should be paid to rare patients who carry mutations of one of the critical cysteine residues of these exons, known to predispose to MEN2A. In these cases, HSCR can be associated with the development of neuroendocrine tumors such as medullary thyroid carcinoma (MTC) or MEN2A, for which a prophylactic thyroidectomy is advisable in the presence of a tumor causing RET mutation. In combined MEN2A/HSCR families, RET gene testing, tumor screening and prophylactic thyroidectomy are indicated as in MEN2A. The multigenic origin of HSCR and the absence of a "standard" RET mutation associated with HSCR currently make a routine molecular diagnosis impossible.

A rare extracellular D631Y germline mutation of the RET proto-oncogene in two Korean families with multiple endocrine neoplasia 2A

A mutation in codon 631 of exon 11 of the RET proto-oncogene is extremely rare in the patients with multiple endocrine neoplasia type 2A (MEN 2A). We report here on a rare extracellular mutation of the RET gene that led to the substitution of a tyrosine for an aspartate in codon 631 (D631Y, GAC to TAC) in two Korean families with MEN 2A. Eleven individuals from two unrelated families were found to have the D631Y germline mutation. Among them, medullary thyroid carcinoma (MTC) was identified in five patients: four of them had MEN 2A and one had familial MTC. They had tumors 2 cm or less in the greatest dimension that were limited to the thyroid, and they had a relatively old age above 30 at the time of diagnosis. Pheochromocytoma was detected in six patients including the four patients who had MEN 2A. All had adrenal tumors greater than 3 cm in the greatest dimension, and four of them had bilateral tumors. Two of six patients suffering with pheochromocytoma had no clinical evidence of MTC at the time of diagnosis. None had any evidence of hyperparathyroidism. This genetic profile might be related to the less vigorous clinical disease behavior and the late onset of MTC. In addition, pheochromocytoma might be the first manifestation prior to the development of MTC in some patients with the D631Y mutation. This report is the first description of the clinical characteristics of the D631Y germline mutation in the families with MEN 2A.

Hereditary cancer predisposition in children: Genetic basis and clinical implications

Although cancer predisposition syndromes are rare and malignancies arising in this context account for only 1-10% of childhood tumors, studies performed in affected patients and their families have been of unique value for the understanding of cancer development. Three classes of genes (tumor suppressor genes, oncogenes and stability genes) have been identified and shown to be involved in the pathogenesis of familial, as well as sporadic tumors. Cancer has long been recognized as a genetic disease of somatic cells. Despite improved understanding of the molecular basis of predisposition to cancer and better diagnostic tools, the care of these patients and their families remains a major challenge for the clinician. Medical, psychological, ethical and legal issues have to be considered. This review focuses on examples of each class of inherited cancer predisposition syndromes with special implications for patients in the pediatric age group, including retinoblastoma predisposition, Li-Fraumeni syndrome, multiple endocrine neoplasia disorders and Fanconi anemia. The genetic basis of cancer predisposition is discussed as well as the major concepts and controversies in the clinical management of these patients and their families.

Familial Multiple Endocrine Neoplasia

In 1903, Erdheim described the case of an acromegalic patient with a pituitary adenoma and three enlarged parathyroid glands. Fifty years later, Underdahl et al reported 8 patients with a syndrome of pituitary, parathyroid, and pancreatic islet adenomas. In 1954, Wermer found that the syndrome was transmitted as a dominant trait. In 1959, Hazard et al described medullary (solid) thyroid carcinoma (MTC), a tumor that later was found to be a component of two endocrine syndromes. The first of these described by Sipple in 1961 comprised pheochromocytoma, MTC, and parathyroid adenoma. The second, described by Williams et al in 1966, was the combination of mucosal neuromas, pheochromocytoma, and MTC. In 1968, Steiner et al introduced the term "multiple endocrine neoplasia" (MEN) to describe disorders featuring combinations of endocrine tumors; they designated the Wermer syndrome as MEN 1 and the Sipple syndrome as MEN 2. In 1974, Sizemore et al concluded that the MEN 2 category included two groups of patients with MTC and pheochromocytoma: one with parathyroid disease and a normal appearance (MEN 2A) and the other without parathyroid disease but with mucosal neuromas and mesodermal abnormalities (MEN 2B). Later, additional nonendocrine conditions (von Recklinghausen neurofibromatosis and von Hippel-Lindau disease) were found accompanying other more recently described familial MEN syndromes, indicating that these diseases are very complicated disorders.

Highly penetrant hereditary cancer syndromes

The past two decades have brought many important advances in our understanding of the hereditary susceptibility to cancer. Approximately 5-10% of all cancers are inherited, the majority in an autosomal dominant manner with incomplete penetrance. While this is a small fraction of the overall cancer burden worldwide, the molecular genetic discoveries that have resulted from the study of families with heritable cancer have not only changed the way these families are counselled and managed, but have shed light on molecular regulatory pathways important in sporadic tumour development as well. In this review, we consider 10 of the more highly penetrant cancer syndromes, with emphasis on those predisposing to breast, colon, and/or endocrine neoplasia. We discuss the prevalence, penetrance, and tumour spectrum associated with these syndromes, as well as their underlying genetic defects.

Immunohistochemical localisation of RET and p53 mutant protein of thyroid lesions in a North-Eastern Malaysian population and its prognostic implications

AIMS

To investigate RET and p53 expression in local thyroid lesions, in order to shed light on the pathogenesis of papillary carcinoma and explain the high prevalence of this condition among the nodular hyperplasia (multi-nodular goitre) cases.

METHODS

Archival thyroid tissue was retrieved from Hospital Universiti Sains Malaysia (HUSM) Pathology Department files and studied by immunohistochemistry for RET and p53 mutant protein. Normal tissues from 74 cases served as controls.

RESULTS

Fifty follicular adenoma, 66 nodular hyperplasia and 53 papillary carcinoma cases were studied. RET was expressed in 5.4% of normal thyroid tissue, 18% of follicular adenomas, 22.7% of nodular hyperplasia cases and 71.7% of papillary carcinomas. Its expression in papillary carcinoma was not associated with the coexistence of nodular hyperplasia lesions. p53 was expressed by 17% of papillary carcinomas. No association was found between p53 expression of nodular hyperplasia with or without co-existing papillary carcinoma. p53, rather than RET, was an excellent predictor of tumour lymph node metastasis and capsular invasion. p53 was also a significant prognosticator of survival outcome.

CONCLUSIONS

RET expression is highly prevalent in local papillary carcinoma, indicating a significant role in the pathogenesis of this tumour, with no apparent role in tumour behaviour and survival outcome. p53 on the other hand appears to be a significant factor in the latter events. The two genes appear to act in two different pathways: the former being an initiator, and the later a propagator of papillary carcinoma.

Limitations of stratifying sib-pair data in common disease linkage studies: an example using chromosome 10p14-10q11 in type 1 diabetes

IDDM10 on chromosome 10p11-q11 has been identified as a putative diabetes susceptibility locus through affected sib-pair (ASP) linkage analysis in UK nuclear families [Davies et al., 1994: Nature 371:130-136; Reed et al., 1997: Hum Mol Genet 6:1011-1016; Mein et al., 1998: Nat Genet 19:297-300]. We extended analysis of linkage to type 1 diabetes in this region by typing a total of 61 markers in a maximum of 418 UK sib-pairs (UK418; peak MLS = 3.84). We then stratified the dataset based on analyses performed previously by both our group [Mein et al., 1998: Nat Genet 19:297-300] and others [Paterson et al., 1999: Hum Hered 49:197-204; Paterson and Petronis, 1999a: Am J Med Genet 84:15-19; Paterson and Petronis, 2000a: J Med Genet 37:186-191; Paterson and Petronis, b: Eur J Hum Genet 8:145-148] and used a permutation procedure to assess the significance of the results. We conclude that the results obtained had a high probability of occurring by chance alone. These data highlight the limitations of stratifying small datasets (n < 500) by additional criteria and the recurrent problems of multiple testing in genetic analysis.

Novel Technique for Scanning of Codon 634 of the RET Protooncogene with Fluorescence Resonance Energy Transfer and Real-Time PCR in Patients with Medullary Thyroid Carcinoma

Background: The multiple endocrine neoplasia 2 (MEN 2) syndromes [MEN 2A, MEN 2B, and familial medullary thyroid carcinoma (FMTC)] are caused by germline mutations of the RET protooncogene. Because 85% of MEN 2A patients and 30% of FMTC patients have mutations at codon 634, the recommended molecular analyses begin at exon 11, where codon 634 is located.

Methods: We scanned codon 634 of the RET protooncogene with real-time PCR and fluorescence resonance energy transfer (FRET), using a unique pair of internal probes to detect mutations localized at codon 634. We compared results with sequencing results in 66 patients.

Results: The method detected all codon 634 mutations available in our laboratory (Cys634Tyr, Cys634Arg, Cys634Phe, Cys634Trp). Comparing this method with the direct sequencing of exon 11 in a cohort of 66 patients with MTC, the system identified all 14 MTC patients carrying germline mutations at codon 634. One apparent false-positive result occurred among 52 patients.

Conclusions: The simultaneous scanning of multiple mutations is possible with the FRET system. The method allows rapid characterization of germline mutations at codon 634 in MTC patients.

Genetic testing for cancer predisposition

Clinical cancer genetics is becoming an integral part of the care of cancer patients. This review describes the clinical aspects, genetics, and clinical genetic management of most of the major hereditary cancer susceptibility syndromes. Multiple endocrine neoplasia type 2, von Hippel-Lindau disease, and familial adenomatous polyposis are examples of syndromes for which genetic testing to identify at-risk family members is considered the standard of care. Genetic testing for these syndromes is sensitive and affordable, and it will change medical management. Cancer genetic counseling and testing is probably beneficial in other syndromes, such as the hereditary breast cancer syndromes, hereditary nonpolyposis colorectal cancer syndrome, Peutz-Jeghers syndrome, and juvenile polyposis. There are also hereditary cancer syndromes for which testing is not yet available and/or is unlikely to change medical management, including Li-Fraumeni syndrome and hereditary malignant melanoma. Thorough medical care requires the identification of families likely to have a hereditary cancer susceptibility syndrome for referral to cancer genetics professionals.

Psychosocial care in family cancer clinics in The Netherlands: a brief report

The present survey was undertaken to obtain a better understanding of the organisation of standard psychosocial services at the family cancer clinics in The Netherlands. Colleagues at the nine family cancer clinics in The Netherlands completed a brief questionnaire. It was found that all clinics offered professional psychosocial support for asymptomatic women from hereditary breast-ovarian cancer (HBOC) families. On average, one half-time psychosocial worker (usually a social worker and/or a psychologist) was involved in the genetic counselling. All clinics have developed education material about HBOC independently. As a result of the survey, an effort is made to coordinate the development of education material. Furthermore, it is concluded that more attention should be paid to symptomatic mutation carriers and those individuals, who receive inconclusive genetic test results. These subgroups are usually excluded from the protocols for psychosocial care in genetic counselling.

Multiple endocrine neoplasia type 2B — genetic basis and clinical expression

Multiple endocrine neoplasia (MEN) type 2B is a heritable endocrine disorder characterized by medullary thyroid carcinoma (MTC), pheochromocytoma, multiple mucosal neuromas, and a marfanoid habitus. Intestinal ganglioneuromatosis, corneal nerve thickening and skeletal abnormalities are also often present. The disease is inherited in an autosomal dominant fashion and is caused by a single mutation in the RET proto-oncogene, with a methionine to threonine substitution at codon 918. The MTC in MEN 2B presents at an earlier age and tends to be more aggressive than the MTC in MEN 2A. It is multicentric and bilateral and occurs as young as age 3, with early lymph node metastases. Pheochromocytoma is also often bilateral but is rarely malignant. If pheochromocytoma is detected, adrenalectomy should precede thyroidectomy to avoid intraoperative catecholamine crisis. Patients at risk for MEN 2B should undergo genetic screening in infancy. Total thyroidectomy should be performed on all patients positive for RET mutations even prior to the onset of clinical symptoms.

Pathogenesis of Hirschsprung's disease

Hirschsprung's disease is an inherited disorder showing incomplete penetrance and variable expressivity. Genetic mapping and mutation screening of candidate genes, together with the study of several natural and knockout animal models, clearly have shown the involvement of several different genes in the pathogenesis of Hirschsprung's disease. Among these genes, the RET proto-oncogene accounts for the highest proportion of both familial and sporadic cases, with a wide range of mutations scattered along its entire coding region. The low detection rate of RET mutations in Hirschsprung patients also led to different hypotheses, such as the existence of additional Hirschsprung genes. Different animal and human genetic studies have identified 6 Hirschsprung genes: RET proto-oncogene (RET), endothelin 3 (EDN3), endothelin B receptor gene (EDNRB), glial-cell-line-derived neurotrophic factor (GDNF), endothelin converting enzyme (ECE1), gene encoding the Sry-related transcription factor SOX10 (SOX10). Microenvironmental factors also can play a role in the pathogenesis of aganglionosis. The developmental process of the crest-derived progenitor cells is sensitive to the level of different molecules. The expression deficit of different factors (GDNF, NTN) in the hindgut, in the absence of genetic mutations, could determine a missed activation of the receptor system, causing enteric neuroblast migration arrest.

RET proto-oncogene in the development of human cancer

The RET proto-oncogene, located on chromosome subband 10q11.2, encodes a receptor tyrosine kinase expressed in tissues and tumors derived from neural crest. Germline (present in every cell of the body) mutations in RET cause multiple endocrine neoplasia type 2 (MEN 2), an inherited cancer syndrome characterized by medullary thyroid carcinoma (MTC), pheochromocytoma (PC), and hyperparathyroidism (HPT). This knowledge has allowed molecular diagnosis and presymptomatic DNA-based testing to become possible. RET testing is considered the standard of care in MEN 2 families because clinical decisions are made based on the results of such gene testing. There appears to be a correlation between specific RET mutation type and organ-specific tumor development. Such knowledge might be useful in tailoring targeted surveillance in the near future. Somatic (in the tumor only) RET mutations have been found in a proportion of sporadic MTCs and PCs. Whether the presence of somatic RET mutation is associated with a poor prognosis is currently being investigated as another tool for molecular medicine.

Absence of RET proto-oncogene mutations in a father and son with pheochromocytoma and pancreatic islet cell tumor

BACKGROUND

We describe a father and son with a combination of pheochromocytoma and pancreatic islet cell tumor. Although its familial occurrence is rare, this syndrome could be called overlapping-type multiple endocrine neoplasia (MEN), since it fulfills the criteria for both type 1 and type 2 MEN. Recently, germ line mutations of the RET proto-oncogene (RET) were found to be related to tumorigenesis and disease phenotypes in type 2 MEN.

METHODS

Using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis, we looked for germ line mutations of RET in 8 members of this family, including the 2 patients.

RESULTS

Analysis of RET exons 10, 11 and 16, which contain the hot-spot codons for MEN type 2, revealed no mutations in any individual examined.

CONCLUSION

These findings suggest that these 3 exons in RET are not related to tumorigenesis in overlapping-type MEN.

Mutation of RET codon 768 is associated with the FMTC phenotype

Multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC) are inherited cancer syndromes resulting from mutations in the RET proto-oncogene. Missense mutations of five codons in exons 10 and 11 are found in both MEN 2A and FMTC families, while mutations at codon 768 in exon 13 have been identified in three FMTC families. We report here the results of mutation analysis on a large multi-generation family with multiple cases of medullary thyroid carcinoma (MTC) or C-cell hyperplasia and two individuals with isolated adrenal medullary hyperplasia. A mutation in exon 13, which alters codon 768 from a GAG (Glu) to a GAC (Asp), was found to segregate with the FMTC phenotype in this family but not with the adrenal medullary hyperplasia. These findings suggest that the codon 768 mutation does not predispose to adrenal medullary hyperplasia, but is an accurate predictor of the MTC phenotype in this family.

The RET proto-oncogene: a challenge to our understanding of disease pathogenesis

RET gene alterations as disease-causative mutations have been demonstrated in five different disease entities: Hirschsprung's disease (HD); papillary thyroid carcinoma; and three types of inherited cancer syndromes: multiple endocrine neoplasia (MEN) 2A, MEN 2B, and familial medullary thyroid carcinoma. RET is expressed during embryogenesis in a temporally and spatially regulated manner, and plays an important role in the normal development of a variety of cell lineages, particularly in the establishment of the enteric nervous system. RET mutations observed in patients with HD are scattered along the gene without any hot spots, and possess a loss-of-function effect. RET mutations are detected with a higher incidence among familial cases (50%) than sporadic cases (15%-20%), and are more closely associated with long-segment HD than short-segment disease. In contrast to HD mutations, missense mutations observed in MEN 2 syndromes occur at specific codons, and gene rearrangements are characteristic in papillary thyroid carcinoma. Both missense mutations and gene rearrangements act in a dominant fashion, and cause constitutive phosphorylation on the tyrosine of RET and highly enhance RET kinase activity, leading to transforming or oncogenic activity.

Genetic testing and early thyroidectomy for inherited medullary thyroid carcinoma

The recent identification of mutations in the RET proto-oncogene that are associated with multiple endocrine neoplasia type 2 (MEN 2) syndromes has allowed therapeutic intervention in affected individuals on the basis of direct genetic testing. The principal endocrine neoplasm that occurs in patients with the MEN 2 syndromes is medullary thyroid carcinoma. This thyroid neoplasm is the only consistently malignant feature of the MEN 2 syndromes and it is the most common cause of death in affected patients. Kindred members at risk for one of the MEN 2 syndromes can be studied by direct DNA analysis to determine whether they have inherited a RET mutation. Those with a positive test can be treated by early thyroidectomy and cured when the disease is microscopic and localized to the thyroid gland. Total thyroidectomy is performed as early as 5 years of age and is associated with minimal morbidity and virtually no mortality. Residual or persistent medullary thyroid carcinoma following thyroidectomy can best be determined by detecting increased levels of calcitonin following the administration of intravenous calcium gluconate and pentagastrin.

Exclusion of linkage between RET and neuronal intestinal dysplasia type B

Neuronal Intestinal Dysplasia type B (NID B) is a complex alteration of the enteric nervous system belonging to the group of intestinal dysganglionoses which may involve rectum, colon, and small intestine. Second only to Hirschsprung disease (HSCR), NID B is one of the most frequent causes of chronic constipation and pseudo-obstructive intestinal dysmotility. Since NID B is often associated with HSCR and point mutations in the RET proto-oncogene have been identified in HSCR patients, we analyzed two NID B pedigrees to investigate if RET mutations might cause also the NID B phenotype. Linkage analysis demonstrated that the NID B locus is not linked to RET in the pedigrees analyzed. Further genetic analyses will possibly improve the understanding of the cause and facilitate diagnostic procedures in NID B.

Diagnosis of multiple endocrine neoplasia [MEN] 2A, 2B and familial medullary thyroid cancer [FMTC] by multiplex PCR and heteroduplex analyses of RET proto-oncogene mutations

Multiple endocrine neoplasia type 2 [MEN 2] is an autosomal dominant cancer syndrome with two subtypes, 2A and 2B. MEN 2A and medullary thyroid cancer [MTC] are caused by > 25 different point mutations in exons 10, 11, and 13 of the RET proto-oncogene, whereas MEN 2B is caused by a single exon 16-point mutation. Various molecular methods have been used to identify the different mutations, including DNA sequencing, restriction enzymatic analyses, chemical cleavage mismatch, Single Stranded Conformational Polymorphism [SSCP], and Denaturing Gradient Gel Electrophoresis [DGGE]. These techniques, although useful and accurate, are labor intensive and some involve the use of radioactivity. We have developed a multiplex PCR assay simultaneously to amplify exons 10, 11, and 13 of the RET proto-oncogene. The multiplex PCR product is then analyzed on a modified Mutation Detection Enhancement [MDE] matrix for heteroduplex identification and visualized with ethidium bromide. Distinct heteroduplexes were detected for each known RET proto-oncogene mutation available in our laboratory (nine in exon 10, five in exon 11, one in exon 13, and the single exon 16 mutation). Presymptomatic DNA diagnosis of MEN 2 is essential since pentagastrin-stimulated calcitonin studies can occasionally produce false positive results and lead to unnecessary thyroidectomies. Prophylactic thyroidectomy is recommended by age 5 or 6 once a mutation is identified in a patient, since penetrance is very high. MDE heteroduplex detection provides a quick, efficient, and inexpensive method of screening for RET mutations in MTC patients with unknown mutations, or for presymptomatic diagnosis in individuals at risk for inheriting a known RET mutation. Confirmation of the specific mutation can be achieved by restriction enzymatic digestion (if feasible) or by DNA sequencing.

Medullary thyroid carcinoma: recent advances and management update

Medullary thyroid carcinoma (MTC) is a malignancy of the thyroid C-cells that comprises 5-10% of all thyroid cancers. MTC occurs in both sporadic and familial forms, the latter making up 25% of all MTCs and being comprised of three distinct syndromes--multiple endocrine neoplasia type 2A (MEN 2A), multiple endocrine neoplasia type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC). To date, screening for MTC has been performed using the pentagastrin stimulation test, which is a provocative test for calcitonin release. Germline mutations in the RET protooncogene have been identified in families manifesting these syndromes and genetic screening of individuals at risk of one of these syndromes has become integral to their clinical management. The majority of the mutations associated with MEN 2A and FMTC are tightly clustered in a cysteine-rich region of the RET receptor. A single mutation associated with MEN 2B is in the the tyrosine kinase domain of the RET receptor. Somatic mutations have been identified in the tumor tissue of individuals with sporadic MTC and may prove to be helpful markers in discerning the hereditary or sporadic nature of the MTC. There is general agreement that the primary operation for MTC should include total thyroidectomy and central neck lymph node clearance. The role of microdissection for recurrent disease awaits longitudinal evaluation. External radiotherapy, radionuclide therapy, and chemotherapy may have a role in palliation, but have not been proven to have a curative value. Prognostic factors are discussed.

Simultaneous occurrence of medullary carcinoma and papillary carcinoma of the thyroid

We report a case of simultaneous occurrence of medullary carcinoma and papillary carcinoma of the thyroid in the same thyroid gland. Immunoreactivity of calcitonin, carcinoembryonic antigen, neuron specific enolase and thyroglobulin made a sharp distinction between both neoplasms of the thyroid. It appears reasonable to consider that simultaneous occurrence of medullary carcinoma and papillary carcinoma of the thyroid in this case does not have embryological or genetical significance.

Putting the bits and pieces of the RET proto-oncogene puzzle together

The RET proto-oncogene has been implicated in the causation of papillary thyroid carcinoma, multiple endocrine neoplasia types 2A (MEN 2A) and 2B (MEN 2B), and Hirschsprung's disease. The mutations in these syndromes can be categorized into activating or inactivating mutations. Activating mutations of a cysteine-rich extracellular region cause enhanced dimerization of the RET tyrosine kinase receptor and autophosphorylation, and are causative for MEN 2A and familial medullary thyroid carcinoma (FMTC). An activating mutation of the tyrosine kinase domain causes increased autophosphorylation but does not affect the state of dimerization. A variety of inactivating mutations of the RET proto-oncogene, which result in defective protein formation, are causative for Hirschsprung's disease.

Analysis of RET protooncogene point mutations distinguishes heritable from nonheritable medullary thyroid carcinomas

BACKGROUND

The distinction of sporadic from inherited medullary thyroid carcinomas (MTCs) is of clinical importance because of the differences in prognosis, and the need for family screening for genetic counseling required in the latter. Germline mutations in the RET protooncogene are associated with multiple endocrine neoplasia (MEN) type 2A, familial medullary thyroid carcinoma (FMTC), and MEN type 2B. Somatic point mutations in the same gene have been identified in a subset of sporadically occurring medullary thyroid carcinomas.

METHODS

A nonisotopic polymerase chain reaction-(PCR) based single strand conformation polymorphism (SSCP) analysis and heteroduplex gel electrophoresis method was used to screen DNA extracted from 32 formaldehyde fixed and paraffin embedded MTC specimens and normal tissue or blood of the same patient for point mutations in RET exons 10, 11, and 16. Point mutations were identified by nonisotopic cycle sequencing of PCR-products using an automated DNA-sequencer. Results were compared with the disease phenotype, clinical findings, and follow-up.

RESULTS

Six different missense germline mutations were identified at cysteine residues 618, 630, and 634 of the cysteine-rich extracellular RET domain encoded by exons 10 and 11 in all patients with FMTC and MEN 2A. The frequency of mutations at codon 634 was higher in patients with MEN 2A than with FMTC and a 634 Cys-->Arg mutation was associated with parathyroid disease in three patients. A germline Met-->Thr point mutation at codon 918 of the RET tyrosine kinase domain was identified in all three patients with MEN 2B. Two patients with clinically sporadic MTCs and negative family history exhibited a RET germline mutation at codon 634, indicating the presence of an nonpredicted inherited MTC. Furthermore, one patient had a 618 Cys-->Ser mutation in the tumor and nontumorous thyroid DNA but not in blood DNA, indicating a mosaic mutation affecting thyroid tissue but not blood cells. Tumor specific (somatic) Met-->Thr point mutations at codon 918 were identified in 5 of 13 sporadic MTCs. The remaining eight sporadic MTCs lacked mutations in all three RET exons tested.

CONCLUSIONS

This study demonstrates that (1) the molecular methods are not only suitable to identify asymptomatic individuals at risk for MEN 2A, FMTC, and MEN 2B but also to distinguish heritable from nonheritable MTCs using archival tissue specimens, and (2) that more MTCs than clinically expected are heritable, indicating the need for genetic analysis of all patients with MTC.

RET proto-oncogene mutations in multiple endocrine neoplasia type 2 and medullary thyroid carcinoma

The identification of RET proto-oncogene mutations in patients with MEN2 2 years ago was a watershed event in the management of this genetic cancer syndrome. The identification of a finite number of mutations that together causes more than 95% of hereditary and 15-25% of sporadic MTC has made it possible to develop simple and definitive tests to screen individuals at risk for this tumour syndrome. The impact of this technology is enormous. It is now possible to reassure 50% of family members at risk that they, and their children, do not have to worry about developing MTC. In the other 50% who are gene carriers, it is now possible to approach clinical management with greater certainty and plot strategies that are likely to result in a greater percentage of curative therapy. It seems likely that this technology will also have an impact on the management of sporadic MTC, although it is still too early to define a specific role for mutational analysis in these patients, except to exclude hereditary disease. The identification of specific mutations causative for MTC makes it possible to conceive future strategies for the treatment or prevention of MTC and to further extend the impact of these exciting findings.

Presymptomatic genetic screening in families with multiple endocrine neoplasia type 2

Medullary thyroid carcinoma occurs sporadically or as a part of the inherited cancer syndrome multiple endocrine neoplasia (MEN) type 2. The MEN 2 gene has been identified as the RET proto-oncogene on chromosome 10. In MEN 2A, RET mutations are detectable in one of five cysteine codons within exons 10 and 11 and in MEN 2B in codon 918 (exon 16). Direct DNA testing for RET proto-oncogene mutations is the method of first choice in presymptomatic screening of MEN 2 families. Gene carriers should be offered prophylactic thyroidectomy. The process of DNA analysis for RET proto-oncogene mutations is demonstrated in one family with hereditary medullary thyroid carcinoma. RET mutations were detectable in five of the nine family members at risk.

Molecular Diagnosis of Multiple Endocrine Neoplasia (MEN) in Paraffin-Embedded Specimens

In this article, we summarize our recent findings on rearranged during transfection (RE7) mutations in a series of 46 sporadic as well as multiple endocrine neoplasia (MEN) type 2- associated tumors and present results of our family screening efforts to identify MEN 2 and MEN 1 gene carriers. A nonisotopic polymerase chain reaction-based single-strand conformation polymorphism (PCR-SSCP) analysis and heteroduplex gel electrophoresis method was used to screen DNA extracted from archival specimens of 22 patients with MEN 2-associated and 24 patients with sporadic tumors for mutations in RETexons 1O, 11, 13, and 16. Point mutations were identified by nonisotopic cycle sequencing of PCR products using an automated DNA sequencer. We found six different missense germ line mutations at cysteine residues encoded by exons 10 and 11 in all patients with MEN 2A or familial medullary thyroid carcinoma (FMTC). The frequency of mutations at codon 634 was higher in patients with MEN 2A than with FMTC and a (63)Cys - Arg mutation was associated with parathyroid disease. A germline Met -* Thr point mutation at codon 918 of the RETtyrosine kinase domain encoded by exon 16 was identified in all MEN 2B patients. Nonpredicted inheritable medullary thyroid carcinomas (MTCs) were detected in two patients and a mosaic postzygotic mutation was found in one additional patient. Tumor-specific (somatic) Met - Thr point mutations at codon 918 were identified in 5 of 13 sporadic MTCs and 2 of 8 sporadic pheochromocytomas (PCCs). The remaining sporadic tumors lacked mutations in all four RET exons tested. In exon 13, a nucleic acid polymorphism (CTT/CTG; Leu) at codon 769 was identified, which is present in approx 40% of the examined population. Our study demonstrates that the molecular methods used are not only suitable to identify asymptomatic individuals at risk for MEN 2A, FMTC, and MEN 2B, but also to distinguish sporadic from inherited tumors using archival tissue specimens; and that more tumors than clinically expected are inheritable, indicating the need for genetic analysis of all MTC and PCC patients.

Germ line mutations of the ret proto-oncogene in Japanese patients with multiple endocrine neoplasia type 2A and type 2B

We investigated mutations of the ret proto-oncogene in Japanese patients with multiple endocrine neoplasia (MEN) type 2A and type 2B. DNAs from pheochromocytomas and/or medullary thyroid carcinomas (MTCs) of five MEN 2A and three MEN 2B patients were amplified by a polymerase chain reaction (PCR) and analyzed. Tumors of four MEN 2A patients had missense mutations in Cys 634 in the extracellular domain of the ret proto-oncogene. The same mutations were detected in normal tissues of the patients, indicating that the mutations had arisen in the germ line. Using a reverse transcriptase(RT)-PCR, both normal and mutant transcripts of the ret proto-oncogene were detected in a tumor of one patient with MEN 2A mutation. In addition, three MEN 2B patients examined had the same point mutation (ATG-->ACG) at codon 918 in the tyrosine kinase domain of the ret proto-oncogene. Since all mutations identified in this study generated new restriction enzyme sites or eliminated a restriction site, the mutant alleles of affected family members could be readily detected without sequencing.

Inherited cancers associated with the RET proto-oncogene

Mutations in the RET proto-oncogene have been identified in the constitutional DNA of patients with the inherited disorders multiple endocrine neoplasia type 2A and 2B and familial medullary thyroid carcinoma. This review focuses on the discoveries over the past year that pointed to RET as a candidate gene, and on the nature and spectrum of what appear to be dominant mutations associated with an inherited predisposition to tumor development.

The gene causing multiple endocrine neoplasia type 2 (MEN 2)

Multiple endocrine neoplasia (MEN) types 1 and 2 are distinct dominantly inherited syndromes of cancer predisposition in man. MEN 1 involves the parathyroids, pituitary, and pancreatic islets; MEN 2 involves the thyroid C-cells, adrenal medulla and parathyroids. In some varieties of MEN 2 there are also developmental abnormalities of the autonomic nervous system of the gut. The MEN 1 predisposing gene has been mapped by linkage to chromosome 11q13, and it is likely that the gene will shortly be identified by positional cloning. The predisposing gene for MEN 2 has been shown to be the receptor tyrosine kinase ret. Mutations in different domains of ret are responsible for the different combinations of phenotypes seen in distinct clinical varieties of MEN 2 and in Hirschsprung disease.