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 à Calcitonine

Medullary thyroid cancer and pheochromocytoma in MEN2A: are there parent of origin effects on disease expression?

There are no data on the impact of parent-of-origin effects on the expression of multiple endocrine neoplasia type 2A (MEN2A). The present study aimed to explore effects of parent-of-origin and offspring gender in MEN2A. In total, 224 carriers harbored heterozygous RET (REarranged during Transfection) p.Cys634 missense variants, for 169 of whom information on parent-of-origin gender was available. Altogether, offspring from affected fathers harbored more often node metastases from medullary thyroid cancer (45 vs. 19%; P = 0.006) and bilateral pheochromocytoma (24 vs. 10%; P = 0.021) than offspring from affected mothers. The former also also tended to be older at most recent follow-up (medians of 21 vs. 14 years; P = 0.056) and tended to have more often pheochromocytoma (33 vs. 19 yrs.; P = 0.051) and primary hyperparathyroidism (13 vs. 4%; P = 0.090) than the latter. Daughters from affected fathers harbored more often node metastases (39 vs. 15%; P = 0.043) than daughters from affected mothers. This difference decreased in male offspring when sons from affected fathers were compared with sons from affected mothers (52 vs. 40%; P = 0.111). There was also a slight deficit of male offspring: 1.1 sons each per affected mother and father vs. 1.2 daughters per affected mother and 1.4 daughters per affected father. These data suggest a parent-of-origin effect in MEN2A, warranting international collaborative research.

Recurrent ipsilateral pheochromocytoma in carriers of RET p.Cys634 missense mutations

PURPOSE

The objective of this study was to provide RET genotype-specific data on recurrent ipsilateral pheochromocytoma in multiple endocrine neoplasia type 2A (MEN2A), which are sparse.

METHODS

Kaplan-Meier analyses were performed to determine the risk of recurrent ipsilateral adrenalectomy after subtotal and total adrenalectomy in 221 carriers of RET p.Cys634 missense mutations.

RESULTS

Altogether, pheochromocytoma emerged in 112 of 442 adrenals at risk, for which 63 adrenals underwent total adrenalectomy and 49 adrenals subtotal adrenalectomy. After a mean (median) of 99 (132.9) months, 10 recurrent ipsilateral pheochromocytomas arose in 10 (20.4%) of 49 adrenal remnants. Seven of these 10 adrenal remnants were subjected to total adrenalectomy and 3 to another subtotal adrenalectomy. After 23 and 250 (mean/median 136.5) more months, 2 of the 3 remaining adrenal remnants gave rise to 2 further recurrent ipsilateral pheochromocytomas, which were removed by total adrenalectomy. When the rare publications in which carriers of RET p.Cys634 mutations made up 81-84% of MEN2A patients were combined with the present RET p.Cys634-specific series, the risk of recurrent ipsilateral pheochromocytoma was 6.7% (25 recurrent ipsilateral pheochromocytomas in 375 adrenal remnants), with a mean time interval of 146 months after initial subtotal adrenalectomy.

CONCLUSION

Subtotal adrenalectomy is a viable treatment option for many carriers of RET p.Cys634 mutations who develop an initial pheochromocytoma. Although the adrenal remnant may give rise to recurrent ipsilateral pheochromocytoma after 8-11 years in up to 20% of patients, it is manageable very well in experienced hands, buying the patient valuable time off steroids.

Multiple Endocrine Neoplasia in Childhood: An Update on Diagnosis, Screening, Management and Treatment

Multiple endocrine neoplasia (MEN) is a group of heterogenous syndromes characterized by the occurrence of two or more endocrine gland tumors in a patient or related individuals in the same family. They are inherited in an autosomal dominant fashion and are highly penetrant. There are three types of MEN syndromes: MEN type 1 (MEN1), MEN type 2 (MEN2), and MEN type 4 (MEN4). MEN2 is further divided into MEN2A, MEN2B (formerly known MEN3), and familial medullary thyroid carcinoma (FMTC). Although MEN syndromes are rare, it is crucial to identify individuals at risk for potentially life-threatening neoplasias. This review article provides an update on each MEN syndrome, its genetics, diagnosis, and management in children.

Kidney malformations and Hirschsprung's disease in carriers of cysteine mutations in exon 10 of the RET proto-oncogene

PURPOSE

This investigation aimed at characterizing penetrance and interrelation of the loss-of-function phenotypes, Hirschsprung's disease and kidney malformations, in carriers of exon 10 REarranged during Transfection (RET) mutations.

METHODS

Comparative analysis of penetrance of and interdependencies between Hirschsprung's disease and kidney malformations among carriers of mutations in RET codons 609, 611, 618, and 620.

RESULTS

Hirschsprung's disease and kidney malformations (kidney agenesis, ureteropelvicalyceal dilatation, or polycystic kidney disease) each affected 3.6% (4 patients) of 112 carriers of RET mutations in exon 10. This percentage increased to 13% (4 patients) and 9% (3 patients) of 32 p.Cys620 carriers and 22% (4 patients) and 17% (3 patients) of 18 p.Cys620Arg carriers, respectively. Overall, Hirschsprung's disease (17%, 4 of 24 carriers; P = 0.002) and kidney malformations (13%, 3 of 24 carriers; P = 0.030) were associated with arginine-for-cysteine substitutions. Two of the six patients, originating from different p.Cys620Arg families, harbored both Hirschsprung's disease and kidney malformations.

CONCLUSION

Hirschsprung's disease and kidney malformations are the more penetrant, the closer the cysteine mutations are located to the transmembrane domain (codon 636-657) of the RET kinase receptor.

Functional impact of a germline RET mutation in alveolar rhabdomyosarcoma

Specific mutations in the RET proto-oncogene are associated with multiple endocrine neoplasia type 2A, a hereditary syndrome characterized by tumorigenesis in multiple glandular elements. In rare instances, MEN2A-associated germline RET mutations have also occurred with non-MEN2A associated cancers. One such germline mutant RET mutation occurred concomitantly in a young adult diagnosed with alveolar rhabdomyosarcoma, a pediatric and young adult soft-tissue cancer with a generally poor prognosis. Although tumor tissue samples were initially unable to provide a viable cell culture for study, tumor tissues were sequenced for molecular characteristics. Through a hierarchical clustering approach, the index case sample was matched to several genetically similar cell models, which were transformed to express the same mutant RET as the index case and used to explore potential therapeutic options for mutant RET-bearing alveolar rhabdomyosarcoma. We also determined whether the RET mutation associated with the index case caused synthetic lethality to select clinical agents. From our investigation, we did not identify synthetic lethality associated with the expression of that patient's RET variant, and overall we did not find experimental evidence for the role of RET in rhabdomyosarcoma progression.

Primary hyperparathyroidism as first manifestation in multiple endocrine neoplasia type 2A: an international multicenter study

OBJECTIVE

Multiple endocrine neoplasia type 2A (MEN 2A) is a rare syndrome caused by RET germline mutations and has been associated with primary hyperparathyroidism (PHPT) in up to 30% of cases. Recommendations on RET screening in patients with apparently sporadic PHPT are unclear. We aimed to estimate the prevalence of cases presenting with PHPT as first manifestation among MEN 2A index cases and to characterize the former cases.

DESIGN AND METHODS

An international retrospective multicenter study of 1085 MEN 2A index cases. Experts from MEN 2 centers all over the world were invited to participate. A total of 19 centers in 17 different countries provided registry data of index cases followed from 1974 to 2017.

RESULTS

Ten cases presented with PHPT as their first manifestation of MEN 2A, yielding a prevalence of 0.9% (95% CI: 0.4-1.6). 9/10 cases were diagnosed with medullary thyroid carcinoma (MTC) in relation to parathyroid surgery and 1/10 was diagnosed 15 years after parathyroid surgery. 7/9 cases with full TNM data were node-positive at MTC diagnosis.

CONCLUSIONS

Our data suggest that the prevalence of MEN 2A index cases that present with PHPT as their first manifestation is very low. The majority of index cases presenting with PHPT as first manifestation have synchronous MTC and are often node-positive. Thus, our observations suggest that not performing RET mutation analysis in patients with apparently sporadic PHPT would result in an extremely low false-negative rate, if no other MEN 2A component, specifically MTC, are found during work-up or resection of PHPT.

A primer on the genetics of medullary thyroid cancer

Medullary thyroid cancer is a rare type of neuroendocrine tumour that arises from the parafollicular cells (C cells) of the thyroid gland. It accounts for 3%-5% of thyroid cancer cases. Close to 25% of cases are familial, and 75% are considered sporadic. Familial cases are associated with a germline RET mutation; 43%-65% of sporadic cases harbour a somatic event in the gene. Germline RET mutations are associated with the autosomal-dominant inherited multiple endocrine neoplasia (men) 2a and 2b syndromes and the isolated familial medullary thyroid cancer syndrome. More than 100 RET codon mutations have been reported to date, with genotype-phenotype correlations that include the extent and aggressiveness of the medullary thyroid cancer and the presence of other features of the men2 syndromes. The latter include pheochromocytoma-paraganglioma, hyperparathyroidism, cutaneous lichen amyloidosis, and Hirschsprung disease. In this narrative review, we focus on RET proto-oncogene physiology and pathogenesis induced by germline and somatic RET mutations, the genotype-phenotype correlation, and the management and follow-up of patients with germline-mutated medullary thyroid cancer.

Evolution of Our Understanding of the Hyperparathyroid Syndromes: A Historical Perspective

We review advancing and overlapping stages for our understanding of the expressions of six hyperparathyroid (HPT) syndromes: multiple endocrine neoplasia type 1 (MEN1) or type 4, multiple endocrine neoplasia type 2A (MEN2A), hyperparathyroidism-jaw tumor syndrome, familial hypocalciuric hypercalcemia, neonatal severe primary hyperparathyroidism, and familial isolated hyperparathyroidism. During stage 1 (1903 to 1967), the introduction of robust measurement of serum calcium was a milestone that uncovered hypercalcemia as the first sign of dysfunction in many HPT subjects, and inheritability was reported in each syndrome. The earliest reports of HPT syndromes were biased toward severe or striking manifestations. During stage 2 (1959 to 1985), the early formulations of a syndrome were improved. Radioimmunoassays (parathyroid hormone [PTH], gastrin, insulin, prolactin, calcitonin) were breakthroughs. They could identify a syndrome carrier, indicate an emerging tumor, characterize a tumor, or monitor a tumor. During stage 3 (1981 to 2006), the assembly of many cases enabled recognition of further details. For example, hormone non-secreting skin lesions were discovered in MEN1 and MEN2A. During stage 4 (1985 to the present), new genomic tools were a revolution for gene identification. Four principal genes ("principal" implies mutated or deleted in 50% or more probands for its syndrome) (MEN1, RET, CASR, CDC73) were identified for five syndromes. During stage 5 (1993 to the present), seven syndromal genes other than a principal gene were identified (CDKN1B, CDKN2B, CDKN2C, CDKN1A, GNA11, AP2S1, GCM2). Identification of AP2S1 and GCM2 became possible because of whole-exome sequencing. During stages 4 and 5, the newly identified genes enabled many studies, including robust assignment of the carriers and non-carriers of a mutation. Furthermore, molecular pathways of RET and the calcium-sensing receptor were elaborated, thereby facilitating developments in pharmacotherapy. Current findings hold the promise that more genes for HPT syndromes will be identified and studied in the near future. © 2018 American Society for Bone and Mineral Research.

Probability of Positive Genetic Testing Results in Patients with Family History of Primary Hyperparathyroidism

BACKGROUND

Approximately 10% of patients with primary hyperparathyroidism (PHPT) have hereditary disease. Hereditary PHPT may be syndromic (MEN1, 2, and 4 and hyperparathyroidism-jaw tumor syndrome) or non-syndromic (familial isolated PHPT). There are limited data on the probability of testing positive for genetic mutation based on clinical presentation. The aim of this study was to determine potential associations between clinical and biochemical features and mutation in susceptibility genes for PHPT in patients with a family history of PHPT.

STUDY DESIGN

A retrospective analysis of 657 patients who had an initial parathyroidectomy for PHPT at a tertiary referral center. Logistic regression analyses were performed in 205 patients with a family history of PHPT to identify factors associated with a positive genetic test.

RESULTS

Of 657 patients, 205 (31.2%) had a family history of PHPT. Of those 205 patients, 123 (60%) had a germline mutation detected (91 MEN1, 14 CDC73, and 18 GCM2). In univariate analysis, younger age (45 years and younger), male sex, multigland disease, and parathyroid carcinoma were associated with positive germline mutation; biochemical cure after an initial parathyroidectomy was less frequent in patients with familial PHPT (96.2% vs 89.2%; p = 0.005). In multivariable analysis, age 45 years and younger, male sex, and multigland disease were independent factors associated with positive genetic testing.

CONCLUSIONS

In addition to a family history of PHPT, male sex, age 45 years and younger, and presence of multigland disease, should prompt physicians to offer the opportunity for genetic counseling and testing, as it could influence the management of patients with PHPT.

Familial isolated primary hyperparathyroidism associated with germline GCM2 mutations is more aggressive and has a lesser rate of biochemical cure

BACKGROUND

Hereditary primary hyperparathyroidism may be syndromic or nonsyndromic (familial isolated hyperparathyroidism). Recently, germline activating mutations in the GCM2 gene were identified in a subset of familial isolated hyperparathyroidism. This study examined the clinical and biochemical characteristics and the treatment outcomes of GCM2 mutation-positive familial isolated hyperparathyroidism as compared to sporadic primary hyperparathyroidism.

METHODS

We performed a retrospective analysis of clinical features, parathyroid pathology, and operative outcomes in 18 patients with GCM2 germline mutations and 457 patients with sporadic primary hyperparathyroidism.

RESULTS

Age at diagnosis, sex distribution, race/ethnicity, and preoperative serum calcium concentrations were similar between the 2 groups. The preoperative serum levels of intact parathyroid hormone was greater in patients with GCM2-associated primary hyperparathyroidism (239 ± 394 vs 136 ± 113, P = .005) as were rates of multigland disease and parathyroid carcinoma in the GCM2 group (78% vs 14.3%, P < .001 and 5% vs 0%, P = .04, respectively), but the biochemical cure rate was less in the GCM2 group (86% vs 99%, P < .001).

CONCLUSION

GCM2-associated primary hyperparathyroidism patients have greater preoperative parathyroid hormone levels, a greater rate of multigland disease, a lesser rate of biochemical cure, and a substantial risk of parathyroid carcinoma. Knowledge of these clinical characteristics could optimize the surgical management of GCM2-associated familial isolated hyperparathyroidism.

Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma

INTRODUCTION

The American Thyroid Association appointed a Task Force of experts to revise the original Medullary Thyroid Carcinoma: Management Guidelines of the American Thyroid Association.

METHODS

The Task Force identified relevant articles using a systematic PubMed search, supplemented with additional published materials, and then created evidence-based recommendations, which were set in categories using criteria adapted from the United States Preventive Services Task Force Agency for Healthcare Research and Quality. The original guidelines provided abundant source material and an excellent organizational structure that served as the basis for the current revised document.

RESULTS

The revised guidelines are focused primarily on the diagnosis and treatment of patients with sporadic medullary thyroid carcinoma (MTC) and hereditary MTC.

CONCLUSIONS

The Task Force developed 67 evidence-based recommendations to assist clinicians in the care of patients with MTC. The Task Force considers the recommendations to represent current, rational, and optimal medical practice.

Pheochromocytoma as the first manifestation of MEN2A with RET mutation S891A: report of a case

We report a rare case with pheochromocytoma as the first manifestation of multiple endocrine neoplasia type 2A with RET mutation S891A. Bilateral pheochromocytomas were identified in a 54-year-old woman. Screening for RET revealed a rare S891A mutation located in the intracellular tyrosine kinase domain. This mutation was previously recognized as one of the mutations only in cases manifesting solely medullary thyroid carcinomas (MTCs). Since calcitonin stimulation test indicated positive result, total thyroidectomy was performed 1 year after the bilateral adrenalectomy, and C-cell hyperplasia was diagnosed by histopathological examination. Our report suggests that cases with S891A mutation, akin to those with other RET mutations, require screening for pheochromocytoma. In addition, it is indicated that calcitonin stimulation test should be performed even in the unaffected elder cases with S891A mutation although the mutation is classified as lowest risk group on MTC in guidelines.

Management of hyperparathyroidism (PHP) in MEN2 syndromes in Europe

Hyperparathyroidism occurs in 20-30% of MEN2A syndrome patients. It is usually associated with mild disease and is frequently asymptomatic, especially in younger age. There is genotype/phenotype association and PHP is usually associated with codon 634 mutations; however association with more “rare” mutations has also been reported. The pathology of the parathyroid glands includes hyperplasia, adenoma or a combination of the two. The optimal surgical management of this entity has not been defined yet.

German Association of Endocrine Surgeons practice guideline for the surgical management of malignant thyroid tumors

INTRODUCTION

Over the past years, the incidence of thyroid cancer has surged not only in Germany but also in other countries of the Western hemisphere. This surge was first and foremost due to an increase of prognostically favorable ("low risk") papillary thyroid microcarcinomas, for which limited surgical procedures are often sufficient without loss of oncological benefit. These developments called for an update of the previous practice guideline to detail the surgical treatment options that are available for the various disease entities and tumor stages.

METHODS

The present German Association of Endocrine Surgeons practice guideline was developed on the basis of clinical evidence considering current national and international treatment recommendations through a formal expert consensus process in collaboration with the German Societies of General and Visceral Surgery, Endocrinology, Nuclear Medicine, Pathology, Radiooncology, Oncological Hematology, and a German thyroid cancer patient support organization.

RESULTS

The practice guideline for the surgical management of malignant thyroid tumors includes recommendations regarding preoperative workup; classification of locoregional nodes and terminology of surgical procedures; frequency, clinical, and histopathological features of occult and clinically apparent papillary, follicular, poorly differentiated, undifferentiated, and sporadic and hereditary medullary thyroid cancers, thyroid lymphoma and thyroid metastases from primaries outside the thyroid gland; extent of thyroidectomy; extent of lymph node dissection; aerodigestive tract resection; postoperative follow-up and surgery for recurrence and distant metastases.

CONCLUSION

These evidence-based recommendations for surgical therapy reflect various "treatment corridors" that are best discussed within multidisciplinary teams and the patient considering tumor type, stage, progression, and inherent surgical risk.

Genotype-phenotype correlation in multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 is an autosomal-dominant hereditary cancer syndrome caused by missense gain-of-function mutations of the rearranged during transfection proto-oncogene, which encodes the receptor tyrosine kinase, on chromosome 10. It has a strong penetrance of medullary thyroid carcinomas and can be associated with bilateral pheochromocytoma and primary hyperparathyroidism. Multiple endocrine neoplasia type 2 is divided into three varieties depending on its clinical features: multiple endocrine neoplasia type 2A, multiple endocrine neoplasia type 2B, and familial medullary thyroid carcinoma. The specific rearranged during transfection mutation may suggest a predilection toward a particular phenotype and clinical course of medullary thyroid carcinoma, with strong genotype-phenotype correlations. Offering rearranged during transfection testing is the best practice for the clinical management of patients at risk of developing multiple endocrine neoplasia type 2, and multiple endocrine neoplasia type 2 has become a classic model for the integration of molecular medicine into patient care. Recommendations on the timing of prophylactic thyroidectomy and extent of surgery are based on the classification of rearranged during transfection mutations into risk levels according to genotype-phenotype correlations. Earlier identification of patients with hereditary medullary thyroid carcinoma can change the presentation from clinical tumor to preclinical disease, resulting in a high cure rate of affected patients and a much better prognoses.

Management of medullary thyroid carcinoma and MEN2 syndromes in childhood

Medullary thyroid carcinoma (MTC) and the multiple endocrine neoplasia (MEN) type 2 syndromes are rare but important endocrine diseases that are increasingly managed by pediatric providers. MTC is generally associated with a favorable prognosis when diagnosed during childhood, where it frequently occurs secondary to activating mutations in the RET proto-oncogene and arises from pre-existing C-cell hyperplasia. MEN2A accounts for 90-95% of childhood MTC cases and is most commonly due to mutations in codon 634 of RET. MEN2B is associated with the most aggressive clinical presentation of MTC and is almost always due to the Met918Thr mutation of RET. Surgery is the primary treatment and only chance of cure, although the advent of targeted therapies seems to be improving progression-free survival in advanced cases. Since the discovery of the role of RET in MEN2A, considerable advances in the management of this syndrome have occurred, and most of the children with MEN2A who have undergone early thyroidectomy will now lead full, productive lives. Strong genotype-phenotype correlations have facilitated the development of guidelines for interventions. Contemporary approaches for deciding the appropriate age at which surgery should take place incorporate data from ultrasonography and calcitonin measurements in addition to the results of genotyping. To optimize care and to facilitate ongoing research, children with MTC and the MEN2 syndromes are optimally treated at tertiary centers with multidisciplinary expertise.

Predominant RET Germline Mutations in Exons 10, 11, and 16 in Iranian Patients with Hereditary Medullary Thyroid Carcinoma

Medullary thyroid carcinoma occurs in both sporadic (75%) and hereditary (25%) forms. The missense mutations of RET proto-oncogene in MTC development have been well demonstrated. To investigate the spectrum of predominant RET germline mutations in exons 10, 11, and 16 in hereditary MTC in Iranian population, 217 participants were included. Genomic DNAs were extracted from the leukocytes using the standard Salting Out/Proteinase K method. Mutation detection was performed through PCR-RFLP and DNA sequencing. In 217 participants, 43 missense mutations were identified in exons 10 (6%), 11 (13%), and 16 (0.9%). Moreover, a novel germline mutation was detected in exon 11 (S686N). Also four different polymorphisms were found in intron 16 in eight patients. The obtained data showed the frequency profile of RET mutations in Iranian individuals with MTC (19.8%). The most frequent mutation in our population was C634G whereas in most population it was C634R. Altogether, these results underline the importance of the genetic background of family members of any patient with MTC.

Pediatric ethics guidelines for hereditary medullary thyroid cancer

Hereditary medullary thyroid cancer is an aggressive cancer for which there is no standard effective systemic therapy, but which can be prevented through genetic screening and prophylactic thyroidectomy. Although this cancer accounts for roughly 17% of all pediatric thyroid cancers, a significant percentage of affected families do not "accept" screening, while many gene carriers delay or refuse prophylactic thyroid surgery for their children. Current genetic screening practices in medullary thyroid cancer are inadequate; more than 50% of index patients with hereditary medullary thyroid cancer present with a thyroid mass; up to 75% have distant metastasis. These proposed pediatric ethics guidelines focus on two ethical issues that affect at-risk children: (1) how do we identify at-risk children whose RET-positive relative refuses to disclose that they carry the mutation? (2) How do we protect RET-positive children whose parents refuse prophylactic thyroidectomy?

First description of parathyroid disease in multiple endocrine neoplasia 2A syndrome

Hyperparathyroidism and/or parathyroid hyperplasia, medullary thyroid carcinoma (MTC), and pheochromocytomas compose the hallmarks of the multiple endocrine neoplasia type 2A (MEN 2A) syndrome. Revisiting a report in 1939 of a patient with hyperparathyroidism and parathyroid hyperplasia led to a search for evidence of MEN 2A. From medical records and discussion with family members, longitudinal follow-up of the patient and her descendants was obtained. Molecular diagnostics were integrated in the care of subsequent generations. The literature on hyperparathyroidism and MEN 2A was reviewed. Children of the proband exhibited all components of MEN 2A and the RET mutation of 634 TGC>CGC. The pedigree was typical for this mutation. Papers on anthropologic studies demonstrate skeletal evidence of hyperparathyroidism in humans centuries ago. The initial report of the proband preceded the publications defining both MTC and MEN 2A. The values of in-depth family histories and genetic analyses are exemplified.

The HRPT2 tumor suppressor gene product parafibromin associates with human PAF1 and RNA polymerase II

Inactivation of the HRPT2 tumor suppressor gene is associated with the pathogenesis of the hereditary hyperparathyroidism-jaw tumor syndrome and malignancy in sporadic parathyroid tumors. The cellular function of the HPRT2 gene product, parafibromin, has not been defined yet. Here we show that parafibromin physically interacts with human orthologs of yeast Paf1 complex components, including PAF1, LEO1, and CTR9, that are involved in transcription elongation and 3' end processing. It also associates with modified forms of the large subunit of RNA polymerase II, in particular those phosphorylated on serine 5 or 2 within the carboxy-terminal domain, that are important for the coordinate recruitment of transcription elongation and RNA processing machineries during the transcription cycle. These interactions depend on a C-terminal domain of parafibromin, which is deleted in ca. 80% of clinically relevant mutations. Finally, RNAi-induced downregulation of parafibromin promotes entry into S phase, implying a role for parafibromin as an inhibitor of cell cycle progression. Taken together, these findings link the tumor suppressor parafibromin to the transcription elongation and RNA processing pathway as a PAF1 complex- and RNA polymerase II-bound protein. Dysfunction of this pathway may be a general phenomenon in the majority of cases of hereditary parathyroid cancer.

Novel germline mutation in the transmembrane region of RET gene close to Cys634Ser mutation associated with MEN 2A syndrome

Two mutations on the same allele of RET gene were revealed in a family with predisposition to multiple endocrine neoplasia (MEN) type 2A. The first mutation changes codon 634 from cysteine to serine. The second, a novel mutation in codon 641, changes alanine to serine in the transmembrane domain of the RET protein. Two mutations were present in close proximity in both the patients' germline and tumor DNA and were absent in DNA isolated from healthy family members and control blood donors. All MEN 2A affected family members suffered from medullary thyroid carcinoma and two of ten patients for pheochromocytoma. No parathyroid gland alterations were observed in patients with two RET gene mutations. Analysis of four genetic polymorphisms in the RET gene showed higher incidence of polymorphisms of exons 11 and 15. The observed allelic imbalance in favor of mutated allele in pheochromocytoma corresponded to higher expression of the RET gene. These observations confirm the multifactorial process leading to development of MEN 2A syndrome.

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.

Multiple endocrine neoplasia type 2 and RET: from neoplasia to neurogenesis

Multiple endocrine neoplasia type 2 (MEN 2) is an inherited cancer syndrome characterised by medullary thyroid carcinoma (MTC), with or without phaeochromocytoma and hyperparathyroidism. MEN 2 is unusual among cancer syndromes as it is caused by activation of a cellular oncogene, RET. Germline mutations in the gene encoding the RET receptor tyrosine kinase are found in the vast majority of MEN 2 patients and somatic RET mutations are found in a subset of sporadic MTC. Further, there are strong associations of RET mutation genotype and disease phenotype in MEN 2 which have led to predictions of tissue specific requirements and sensitivities to RET activity. Our ability to identify genetically, with high accuracy, subjects with MEN 2 has revolutionised our ability to diagnose, predict, and manage this disease. In the past few years, studies of RET and its normal ligand and downstream interactions and the signalling pathways it activates have clarified our understanding of the roles played by RET in normal cell survival, proliferation, and differentiation, as well as in disease. Here, we review the current knowledge of the normal functions of RET and the effects of mutations of this gene in tumorigenesis and in normal development.