A large germline deletion of the MEN1 gene in a family with multiple endocrine neoplasia type 1

Mutational and large deletion study of genes implicated in hereditary forms of primary hyperparathyroidism and correlation with clinical features

The aim of this study was to carry out genetic screening of the MEN1, CDKN1B and AIP genes, both by direct sequencing of the coding region and multiplex ligation-dependent probe amplification (MLPA) assay in the largest monocentric series of Italian patients with Multiple Endocrine Neoplasia type 1 syndrome (MEN1) and Familial Isolated Hyperparathyroidism (FIHP). The study also aimed to describe and compare the clinical features of MEN1 mutation-negative and mutation-positive patients during long-term follow-up and to correlate the specific types and locations of MEN1 gene mutations with onset and aggressiveness of the main MEN1 manifestations. A total of 69 index cases followed at the Endocrinology Unit in Pisa over a period of 19 years, including 54 MEN1 and 15 FIHP kindreds were enrolled. Seven index cases with MEN1 but MEN1 mutation-negative, followed at the University Hospital of Cagliari, were also investigated. FIHP were also tested for CDC73 and CaSR gene alterations. MEN1 germline mutations were identified in 90% of the index cases of familial MEN1 (F-MEN1) and in 23% of sporadic cases (S-MEN1). MEN1 and CDC73 mutations accounted for 13% and 7% of the FIHP cohort, respectively. A CDKN1B mutation was identified in one F-MEN1. Two AIP variants of unknown significance were detected in two MEN1-negative S-MEN1. A MEN1 positive test best predicted the onset of all three major MEN1-related manifestations or parathyroid and gastro-entero-pancreatic tumors during follow-up. A comparison between the clinical characteristics of F and S-MEN1 showed a higher prevalence of a single parathyroid disease and pituitary tumors in sporadic compared to familial MEN1 patients. No significant correlation was found between the type and location of MEN1 mutations and the clinical phenotype. Since all MEN1 mutation-positive sporadic patients had a phenotype resembling that of familial MEN1 (multiglandular parathyroid hyperplasia, a prevalence of gastro-entero-pancreatic tumors and/or the classic triad) we might hypothesize that a subset of the sporadic MEN1 mutation-negative patients could represent an incidental coexistence of sporadic primary hyperparathyroidism and pituitary tumors or a MEN1 phenocopy, in our cohort, as in most cases described in the literature.

Deletion of exons 1-3 of the MEN1 gene in a large Italian family causes the loss of menin expression

Multiple endocrine neoplasia type 1 (MEN1) syndrome is an autosomal dominant disease, characterized by parathyroid adenomas, endocrine gastroenteropancreatic tumors and pituitary adenomas, due to inactivating mutations of the MEN1 gene (chromosome 11q13). MEN1 mutations are mainly represented by nonsense, deletions/insertions, splice site or missense mutations that can be detected by direct sequencing of genomic DNA. However, MEN1 patients with large heterozygous deletions may escape classical genetic screening and may be misidentified as phenocopies, thereby hindering proper clinical surveillance. We employed a real-time polymerase chain reaction application, the TaqMan copy number variation assay, to evaluate a family in which we failed to identify an MEN1 mutation by direct sequencing, despite a clear clinical diagnosis of MEN1 syndrome. Using the TaqMan copy number variation assay we identified a large deletion of the MEN1 gene involving exons 1 and 2, in three affected family members, but not in the other nine family members that were to date clinically unaffected. The same genetic alteration was not found in a group of ten unaffected subjects, without family history of endocrine tumors. The MEN1 deletion was further confirmed by multiplex ligation-dependent probe amplification, which showed the deletion extended from exon 1 to exon 3. This new approach allowed us to correctly genetically diagnose three clinical MEN1 patients that were previously considered as MEN1 phenocopies. More importantly, we excluded the presence of genetic alterations in the unaffected family members. These results underline the importance of using a variety of available biotechnology approaches when pursuing a genetic diagnosis in a clinically suggestive setting of inherited endocrine cancer.

Copy number variations and cancer susceptibility

PURPOSE OF REVIEW

DNA copy number variations (CNVs) comprise a recently discovered element of genetic variation that affects a greater cumulative fraction of the genome than single-nucleotide polymorphisms (SNPs). This review discusses current understanding of the characteristics of CNVs in the human genome and explores the emerging discoveries of both constitutional and somatic CNVs in an ever-expanding variety of human cancers.

RECENT FINDINGS

The advent of high-resolution SNP arrays has made it possible to identify CNVs. Characterization of widespread constitutional CNVs offers insight into their role in disease susceptibility, whereas somatic CNVs identify regions of the genome involved in disease phenotype. The role of CNVs in cancer has only emerged in the last 2 years, with constitutional CNVs originally being observed in the Li-Fraumeni cancer susceptibility syndrome, and more recently in neuroblastoma.

SUMMARY

It is not yet known how common or how functionally relevant CNVs will be to the process of carcinogenesis. Nonetheless, the inherent instability and structural variability that characterize cancer cell genomes make this form of genetic variation particularly intriguing to the study of cancer.

Caspase 8 and menin expressions are not correlated in human parathyroid tumors

Menin is lost by the sequential inactivation of both MEN1 alleles in subsets of non-hereditary endocrine tumors as well as those associated with multiple endocrine neoplasia type 1 (MEN1), an autosomal dominant hereditary cancer syndrome characterized by multiple tumors including parathyroid, pituitary and enteropancreatic endocrine tumors. Loss of menin has been reported to be associated with lowered caspase 8 expression and resistance to apoptosis in murine fibroblasts and in pancreatic islet tumors arising in heterozygous MEN1 gene knockout mice, the animal model of the human MEN1 syndrome. We confirmed by menin-knockdown experiments with specific siRNA that menin is crucial for caspase 8 expression in human culture cells while overexpression of menin did not increase caspase 8 protein over basal levels. We then examined expression of menin, caspase 8 and cyclin-dependent kinase inhibitors p27(Kip1) and p15(Ink4b) by Western blotting in human parathyroid tumors surgically resected from patients with MEN1 and those with non-hereditary primary hyperparathyroidism. The menin and p27(Kip1) expression levels were correlated with MEN1 mutation status that was confirmed by DNA analysis. The caspase 8 and p15(Ink4b) protein levels were variable among tumors, and were not correlated with menin protein levels. These findings suggest that human endocrine tumors lacking menin may not always exhibit lowered caspase 8 expression and hence may not be resistant to apoptosis-inducing therapy.

DNA-based test: when and why to apply it to primary hyperparathyroidism clinical phenotypes

Several cancer-related genes have been discovered and molecular test for the cancer genetic risk assessment has been widely increasing. Disorders such as Multiple Endocrine Neoplasia syndromes have received benefits from the identification of the responsible genes whose mutations account for the genetic susceptibility to develop endocrine tumours. Primary hyperparathyroidism (PHPT)is a clinical phenotype frequently associated to Multiple Endocrine Neoplasia syndromes, but it can also represent the unique endocrinopathy recurring as a familial cluster. In recent years, care options have been made available to patients and families with hereditary PHPT, and the process of systematically assessing the genetic risk has been becoming increasingly important. This review aims to help health providers not frequently dealing with genetic testing use and it will introduce some general concepts concerning genetic diagnosis issues. As an example the role and the practical usefulness of DNA-based diagnosis in patients affected by different forms of congenital PHPT is described, with a close look on why, when and how genetic testing should be performed in these subjects and their relatives. Some practical recommendations and suggestions concerning on how to deal when a suspect or known case of familial PHPT has to be faced conclude this manuscript.

Copy number variations and cancer

DNA copy number variations (CNVs) are an important component of genetic variation, affecting a greater fraction of the genome than single nucleotide polymorphisms (SNPs). The advent of high-resolution SNP arrays has made it possible to identify CNVs. Characterization of widespread constitutional (germline) CNVs has provided insight into their role in susceptibility to a wide spectrum of diseases, and somatic CNVs can be used to identify regions of the genome involved in disease phenotypes. The role of CNVs as risk factors for cancer is currently underappreciated. However, the genomic instability and structural dynamism that characterize cancer cells would seem to make this form of genetic variation particularly intriguing to study in cancer. Here, we provide a detailed overview of the current understanding of the CNVs that arise in the human genome and explore the emerging literature that reveals associations of both constitutional and somatic CNVs with a wide variety of human cancers.

Copy number variations and cancer

DNA copy number variations (CNVs) are an important component of genetic variation, affecting a greater fraction of the genome than single nucleotide polymorphisms (SNPs). The advent of high-resolution SNP arrays has made it possible to identify CNVs. Characterization of widespread constitutional (germline) CNVs has provided insight into their role in susceptibility to a wide spectrum of diseases, and somatic CNVs can be used to identify regions of the genome involved in disease phenotypes. The role of CNVs as risk factors for cancer is currently underappreciated. However, the genomic instability and structural dynamism that characterize cancer cells would seem to make this form of genetic variation particularly intriguing to study in cancer. Here, we provide a detailed overview of the current understanding of the CNVs that arise in the human genome and explore the emerging literature that reveals associations of both constitutional and somatic CNVs with a wide variety of human cancers.

MEN1 gene and its mutations: basic and clinical implications

Heterozygous germline mutations of the tumor-suppressor gene MEN1 are responsible for multiple endocrine neoplasia type 1 (MEN1), a dominantly inherited familial cancer syndrome characterized by pituitary, parathyroid, and enteropancreatic tumors. Various mutations have been identified throughout the entire gene region in patients with MEN1 and related disorders. Neither mutation hot spot nor phenotype–genotype correlation has been established in MEN1 although some missense mutations may be specifically associated with a phenotype of familial isolated hyperparathyroidism. The gene product menin has been implicated in multiple roles, including gene transcription, maintenance of genomic integrity, and control of cell division and differentiation. These multiple functions are likely to be conferred by association with multiple protein factors. Occurrence of MEN1-causing missense mutations throughout menin also suggests the requirement of multiple binding factors for its full tumor-suppressive activity. The effect of menin depletion is highly tissue specific, but its underlying mechanism remains to be elucidated. A DNA test for MEN1 germline mutations is a useful tool for diagnosis of MEN1 although it needs further improvements

Multiple endocrine neoplasms

Multiple endocrine neoplasia type 1 (MEN1) and type 2 (MEN2) are rare autosomal-dominant disorders characterized by primary tumours in at least two different endocrine tissues. Both syndromes present as sporadic (a single case with two of the characteristic endocrine tumours) or familial form (an MEN case plus at least one first-degree relative showing one of the characteristic endocrine tumours). MEN1 is characterized by the occurrence of parathyroid, gastro-entero-pancreatic and anterior pituitary tumours, but it can include various combinations of more than 20 endocrine and non-endocrine tumours. Generally, tumours in MEN1 are benign, although gastrinomas and foregut carcinoids may exhibit a malignant course. MEN2 is characterized by medullary thyroid carcinoma (MTC), uni- or bi-lateral pheochromocytoma, and other tumours of different endocrine tissues. If not diagnosed precociously, MTC can be fatal. MEN1 develops after tissue inactivation of both MEN1 gene copies. Activating mutations of c-RET proto-oncogene causes MEN2.

Analysis of gross deletions in the MEN1 gene in patients with multiple endocrine neoplasia type 1

BACKGROUND

Mutation analysis with direct DNA sequencing is commonly used for the molecular diagnosis of multiple endocrine neoplasia type 1 (MEN1). However, a significant number of patients, despite clinical features of MEN1, do not show MEN1 mutations on direct DNA sequencing. Some of these patients may have gross gene deletions not detected by direct DNA sequencing or mutations in the noncoding regions of the gene not examined routinely.

OBJECTIVE

To determine the prevalence of gross deletions in MEN1 in a large cohort of MEN1 patients.

PATIENTS AND METHODS

During 1997-2006, we screened MEN1 mutations by direct DNA sequencing in 368 probands referred to our diagnostic molecular genetic laboratory. Of these, 101 probands (23 familial, 78 sporadic) fulfilled the clinical criteria for MEN1 (presence of at least two of the parathyroid, pancreatic or pituitary tumours) but were negative for mutations on DNA sequencing. Their DNA samples were examined for gross deletions of one or more exons of MEN1 by using multiple ligation-dependent probe amplification (MLPA) and long-range polymerase chain reaction (PCR) amplification. We also sequenced the minimal promoter region of MEN1 for mutations in the familial cases.

RESULTS

We identified a gross deletion involving exons 5 and 6 of MEN1 in one proband (prevalence rate 1%). The sequencing of the minimal promoter region in the familial cases revealed no mutations.

CONCLUSION

Gross deletion in the MEN1 gene is an uncommon cause of MEN1 and should be tested for in patients with a high clinical suspicion but without mutations on direct DNA sequencing.

A whole MEN1 gene deletion flanked by Alu repeats in a family with multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 is an autosomal dominant cancer syndrome characterized by pituitary, parathyroid and enteropancreatic endocrine tumors, which is caused by germline mutations of the tumor suppressor gene MEN1. In the case reported here, the patient had family with this disease whose germline MEN1 mutation was undetectable by conventional sequencing analysis. Further investigations involving polymorphism analyses, gene dose assay and nucleotide sequencing identified a large germline deletion of approximately 29 kilobase pairs spanning the whole MEN1 gene. The deletion was flanked by Alu repetitive sequences, suggesting unequal homologous recombination as the deletion mechanism. The polymorphism linkage data suggested that an asymptomatic son of the proband did not carry the family mutation. More direct evidence was obtained by gene dose assay and deletion-specific polymerase chain reaction, which demonstrated the normal MEN1 gene dosage and the absence of the deletion breakpoints in this asymptomatic subject and thus definitely excluded the possibility of disease predisposition.

Genetic analyses in patients with familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumour syndrome

BACKGROUND

A subset of familial isolated primary hyperparathyroidism (FIHP) is a variant of hyperparathyroidism-jaw tumour syndrome (HPT-JT). AIM/PATIENTS AND METHODS: We investigated the involvement of the HRPT2, MEN1 and CASR genes in 11 provisional FIHP families and two HPT-JT families.

RESULTS

Germline mutations of HRPT2 were found in two of the 11 FIHP families and one of the two HPT-JT families. One FIHP family with parathyroid carcinoma and atypical adenomas and another FIHP family with cystic parathyroid adenoma had novel frameshift mutations of 518-521del and 62-66del, respectively. In a patient with HPT-JT, a de novo germline mutation of 39delC was detected. Novel somatic HRPT2 mutations of 70-73del and 95-102del were found in two of five parathyroid tumours in a family with a 518-521del mutation. Biallelic inactivation of HRPT2 by a combination of germline and somatic mutation was confirmed in the parathyroid tumours. The finding that two families diagnosed with FIHP carried HRPT2 mutations suggests that they have occult HPT-JT. In the remaining 10 families, one family had a missense MEN1 mutation. No mutations of CASR were detected.

CONCLUSION

Our results confirm the need to test for HRPT2 in FIHP families, especially those with parathyroid carcinomas, atypical adenomas or adenomas with cystic change.

Expression and functional analysis of menin in a multiple endocrine neoplasia type 1 (MEN1) patient with somatic loss of heterozygosity in chromosome 11q13 and unidentified germline mutation of the MEN1 gene

In some patients with multiple endocrine neoplasia type 1 (MEN1) it is not possible to identify a germline mutation in the MEN1 gene. We sought to document the loss of expression and function of the MEN1 gene product, menin, in the tumors of such a patient. The proband is an elderly female patient with primary hyperparathyroidism, pancreatic islet tumor, and breast cancer. Her son has primary hyperparathyroidism. No germline MEN1 mutation was identified in the proband or her son. However, loss of heterozygosity at the MEN1 locus and complete lack of menin expression were demonstrated in the proband's tumor tissue. The proband's cultured parathyroid cells lacked the normal reduction in proliferation and parathyroid hormone secretion in response to transforming growth factor- beta. This assessment provided insight into the molecular pathogenesis of the patient and provides evidence for a critical requirement for menin in the antiproliferative action of transforming growth factor-beta.

Effect of tetrahydrocurcumin on blood glucose, plasma insulin and hepatic key enzymes in streptozotocin induced diabetic rats

The enzymes of glucose and lipid metabolism are markedly altered in experimental diabetes. In the present study, we investigated the effect of tetrahydrocurcumin (THC), one of the active metabolites in curcumin, on the key hepatic metabolic enzymes involved in carbohydrate metabolism in streptozotocin-induced diabetic rats. Different doses of THC (20, 40, and 80 mg\kg body weight) were orally administered to diabetic rats for 45 days. The activities of hexokinase, glucose-6-phosphate dehydrogenase (G6PD), glucose-6-phosphatase, fructose-1,6-bisphosphatase, and sorbitol dehydrogenase in liver, and glycogen content in liver and muscle were assayed. In untreated diabetic control rats, the activities of the gluconeogenic enzymes were significantly increased, whereas hexokinase and G6PD activity and glycogen levels were significantly decreased. Both THC and curcumin were able to restore the altered enzyme activities to near normal levels. Tetrahydrocurcumin was more effective than curcumin. Our results indicate that the administration of THC to diabetic animals normalizes blood glucose and causes a marked improvement of altered carbohydrate metabolic enzymes.

Detection of an MEN1 gene mutation depends on clinical features and supports current referral criteria for diagnostic molecular genetic testing

OBJECTIVE

Diagnostic molecular genetic testing for multiple endocrine neoplasia type 1 (MEN1) has been available since the identification of the MEN1 gene in 1997. Mutation screening of the MEN1 gene has been recommended for patients who meet clinical criteria for MEN1 (at least two of the following: parathyroid hyperplasia, pancreatic endocrine tumour or pituitary adenoma) and those in whom a diagnosis of MEN1 is suspected. We examined the appropriateness of these clinical criteria.

PATIENTS AND METHODS

A total of 292 patients were referred for diagnostic testing. The coding region of the MEN1 gene was sequenced in 186 index cases and mutation testing was requested for 106 subjects, including 83 asymptomatic relatives.

RESULTS

MEN1 gene mutations were identified in 68/186 index cases (37%). Twenty-nine of the 60 MEN1 mutations reported are novel. The likelihood of finding a mutation was correlated with the number of MEN1-related tumours (mutation detection rate of 79%, 37% and 15% in patients with three, two and one main MEN1-related tumours; P < or = 0.00001) and increased in the presence of a family history (mutation detection rate of 91%, 69% and 29%vs. 69%, 23% and 0% in sporadic cases with three, two or one main MEN1-related tumours, respectively; P < or = 0.00001). The pick-up rate in the 83% of subjects who met proposed criteria for diagnostic testing was 42%, but in those who did not meet these criteria this fell to 0%.

CONCLUSIONS

The likelihood of finding an MEN1 mutation depends on the clinical features of the patient and their family. This large series supports present referral criteria for diagnostic mutation screening, but suggests that patients with sporadic isolated tumours rarely have MEN1 mutations.

Multiple endocrine neoplasia type 1 with unusual concomitance of various neoplastic disorders

A patient with multiple endocrine neoplasia type 1 (MEN1) who manifested various MEN1-unrelated tumors was reported. The patient was a 43-year-old woman who manifested typical features of MEN1 including primary hyperparathyroidism, prolactinoma, adrenal adenoma and visceral lipomas. During the course, she also manifested chondrosarcoma, B cell lymphoma and mesothelioma. The patient had no apparent family history of MEN1 or any other neoplastic diseases. Genetic analysis of DNA from peripheral mononuclear cells of the patient revealed no germline mutations in MEN1 gene. Genetic instability due to yet unidentified cause is the possible explanation of occurrence of multiple tumors. Careful periodic screening of endocrine and other disorders for her siblings and children as well as for the patient is warranted.

Clinical and genetic features of patients with multiple endocrine tumors who have neither family history nor MEN1 germline mutations

Multiple endocrine neoplasia type 1 (MEN1) is an hereditary tumor syndrome that involves specific endocrine organs such as parathyroids, anterior pituitary gland, and endocrine pancreas. The responsible gene for this syndrome, MEN1, has been isolated and that enabled genetic diagnosis for patients with endocrine tumors and early detection of asymptomatic gene carriers in affected families. Nevertheless, there are a considerable number of patients with MEN1 who have neither family history nor germline MEN1 mutations. In this article, clinical features of such patients are described. Among 53 MEN1 patients we have seen during the last 20 yr, five patients who did not have either MEN1 germline mutation or family history were categorized as MEN1 phenocopy. During the same period, we have also experienced three patients who had primary hyperparathyroidism and adrenocortical tumor but had no apparent family history of endocrine tumors. These patients were considered as MEN1 phenocopy variants and included in the study. The mean age of MEN1 phenocopy patients (including variants) at diagnosis was 48 yr, which was not significantly different from that of probands of familial MEN1 (46 yr) who carry heterozygous MEN1 gene mutations. In the majority of MEN1 phenocopy patients, primary hyperparathyroidism was due to a single parathyroid adenoma. In contrast to a previous report, we found that MEN1 phenocopy patients are not necessarily older than probands of familial MEN1. Phenotypic expression of such patients is variable, thus differentiation of familial MEN1 and MEN1 phenocopy cannot be made based on age and clinical phenotype alone.

Germline mutation profile of MEN1 in multiple endocrine neoplasia type 1: search for correlation between phenotype and the functional domains of the MEN1 protein

Multiple Endocrine Neoplasia type 1 (MEN1) is an autosomal dominant disease characterized by endocrine tumors of the parathyroids, the pancreatic islets, and the anterior pituitary. The MEN1 gene encodes menin, a nuclear protein interacting with JunD/AP1, Smad3, NFkappaB, and other proteins involved in transcription and cell growth regulation. Here, by exhaustive sequence analysis of 170 probands/families collected through a French clinical network, we identified 165 mutations located in coding parts of the MEN1 gene, which represent 114 distinct MEN1 germline alterations. These mutations have been included in a MEN1-locus specific database available on the world wide web together with approximately 240 germline and somatic MEN1 mutations listed from international published data. Our mutation series included 56 frameshifts, 23 nonsense, 27 missense, and eight deletion or insertion in-frame mutations. Mutations were spread over the entire coding sequence. Taken together, most missense and in-frame MEN1 genomic alterations affect one or all domains of menin interacting with JunD [codons 1-40; 139-242; 323-428], Smad3 [distal to codon 478], and NFkappaB [codons 276-479], three major effectors in transcription and cell growth regulation. No correlation has been observed between genotype and MEN1 phenotype. We suggest that the knowledge of structure and location of a specific mutation has not been useful in clinical practice for the follow-up of affected patients and asymptomatic gene carriers. Our results provide the largest series of MEN1 mutations published to date. They will be a useful tool for further studies focusing on the functional effects of missense mutations and understanding which mechanisms or pathways related to multiple menin interactions might be involved in tumorigenesis of endocrine cells.

Mutational analysis of Portuguese families with multiple endocrine neoplasia type 1 reveals large germline deletions

OBJECTIVE

To determine the spectrum of MEN1 mutations in Portuguese kindreds, and identify mutation-carriers.

PATIENTS, DESIGN AND RESULTS

Six unrelated MEN1 families were studied for MEN1 gene mutations by single-strand conformational polymorphism (SSCP) and DNA sequence analysis of the coding region and exon-intron boundaries of the MEN1 gene. These methods identified 4 different heterozygous mutations in four families: two mutations are novel (mt 1539 delG and mt 655 ims 11 bp) and two have been previously observed (mt 735 del 46p and mt 1656 del C) all resulting in a premature stop codon. In the remaining two families, in whom no mutations or abnormal MEN1 transcripts were detected, segregation studies of the 5' intragenic marker D11S4946 and codon 418 polymorphism in exon 9 revealed two large germline deletions of the MEN1 gene. Southern blot and tumour loss of heterozygosity analysis confirmed and refined the limits of these deletions, which spanned the MEN1 gene at least from: exon 7 to the 3' untranslated region, in one family, and the 5' polymorphic site D11S4946 to exon 9 (obliterating the initiation codon), in the other family. Twenty-six mutant-gene carriers were identified, 6 of which were asymptomatic.

CONCLUSIONS

These results emphasize the importance of the detection of MEN1 germline deletions in patients who do not have mutations of the coding region. Important clues indicating the presence of such deletions may be obtained by segregation studies using the intragenic polymorphisms D11S4946 and at codon 418. The detection of these mutations will help in the genetic counselling of clinical management of the MEN1 families in Portugal.

Deregulation of genetic pathways in neuroendocrine tumors

Complexity and redundancy of functional pathways controlled by the human genome explain that a single type of tumor can be induced by independant defective mutations in various genes that encode proteins acting in different parts of the cell physiology. Neuroendocrine tumors represent a powerful model for understanding such a complexity from the fact that at least six unrelated genetic syndromes have been characterized in the last decade which predispose to endocrine cell proliferation with variable penetrance and expressivity. Multiple Endocrine Neoplasia, von Hippel-Lindau. Carney and uncommonly Recklinghausen and Tuberous Sclerosis syndromes represent almost the whole panel of genetic diseases for which genes have been cloned and most of the functional knowledge has been collected. All the endocrine glands are concerned in these diseases, but the cellular pathways that are deregulated downstream from the deleterious mutations occurring in the genes of these autosomal dominant syndromes. might be related to each step of the cell life, from mitosis to DNA transcription, membrane receptor signalling and growth factor production, protein catabolism and extracellular matrix synthesis, and from transcription regulation to apoptosis and response to hypoxia and cellular stress. Here, we present an overview of genes involved in genetic predisposition to neuroendocrine tumors and highlight the complexity of pathways involved and the need of further studies focussing on genes involved in tumoral progression, most neuroendocrine tumors being benign at initial diagnosis but able to produce highly malignant cellular clones related to secondary genetic alterations or deregulation of growth factor production or cell cell adhesion processes.

The MEN1 gene and associated diseases: an update

Heterozygous germline mutations of the tumor suppressor gene MEN1 are responsible for multiple endocrine neoplasia type 1 (MEN1), a dominantly inherited familial cancer syndrome characterized by the combined occurrence of pituitary, parathyroid, and enteropancreatic tumors. Various types of mutations likely causing loss of the gene function have been identified throughout the entire gene region in patients with MEN1 and related disorders including a small fraction of familial isolated hyperparathyroidism (FIHP). Neither mutation hot spot nor phenotype-genotype correlation has been established in classical MEN1, although some missense mutations may be specifically associated with a phenotype of FIHP. Familial isolated pituitary tumor and atypical familial MEN1 consisting of only pituitary tumor and hyperparathyroidism usually lack germline MEN1 mutations, suggesting that these familial endocrine tumor syndromes are genetic entities distinct from MEN1. DNA test for MEN1 germline mutations is a robust tool for diagnosis of predisposition to MEN1, and will be useful for the counseling and management of patients and their families. In this review, we will summarize the most recent findings on the MEN1 gene, focusing primarily on germline mutations and associated diseases.

Identification of MEN1 gene mutations in families with MEN 1 and related disorders

Following identification of the MEN1 gene, we analysed patients from 12 MEN 1 families, 8 sporadic cases of MEN 1, and 13 patients with MEN 1-like symptoms (e.g. cases of familial isolated hyperparathyroidism (FIHPT), familial acromegaly, or atypical MEN 1 cases) for the presence of germline MEN1 mutations. The entire coding region of the MEN1 gene was sequenced, and mutations were detected in 11 MEN 1 families; one sporadic MEN 1 patient, one case of FIHPT and one MEN 1-like case. Constitutional DNA samples from individuals without MEN1 mutations were digested with several restriction enzymes, Southern blotted and probed with MEN1 cDNA to analyse for the presence of larger deletions of the MEN1 gene unable to be detected by PCR. One MEN 1 patient was found to carry such a deletion. This patient was heterozygous for the D418D polymorphism, however sequence analysis of RT-PCR products showed that only the variant allele was transcribed, thus confirming the result obtained by Southern analysis, which indicated loss of a region containing the initiation codon of one allele.

Multiple endocrine neoplasia type 1

Combined clinical and laboratory investigations of MEN-1 have resulted in an increased understanding of this disorder, which may be inherited as an autosomal dominant condition. Defining the features of each disease manifestation in MEN-1 has improved patient management and treatment and has facilitated a screening protocol. Application of the techniques of molecular biology has enabled the identification of the gene causing MEN-1 and the detection of mutations in patients. The protein encoded by the MEN1 gene has been shown to be involved in the regulation of JunD-mediated transcription, but much still remains to be elucidated. Recent advances permit the identification of mutant MEN1 gene carriers who are at a high risk for this disorder and who require regular and biochemical screening to detect the development of endocrine tumors.

Novel deletional mutation of the MEN 1 gene in a kindred with multiple endocrine neoplasia type 1

MEN1 gene mutation in a Japanese kindred with multiple endocrine neoplasia type 1 was examined. A heterozygous deletion involving 29 base pairs in exon 10 (1606del29) was identified in the proband, and the same deletion was found in the affected family members. Most previously reported germline MEN1 gene mutations are nucleotide substitutions and small insertions/deletions, and a large deletion is rare. The hairpin structure mediated by an incomplete palindromic sequence at deletion termini is the most likely mechanism to be associated with the deletion in the present family.

Germline mutations in the multiple endocrine neoplasia type 1 gene: evidence for frequent splicing defects

Multiple endocrine neoplasia type 1 (MEN 1) is a familial cancer syndrome characterized by parathyroid hyperplasia, pituitary adenomas, and neuroendocrine tumors of the pancreas and duodenum. In 1997, the MEN1 tumor suppressor gene was identified, and numerous germline mutations have been reported to be distributed throughout the gene. We used single strand conformational variant (SSCV) analysis to search for germline mutations in the members of 33 kindreds with a confirmed diagnosis of MEN 1. SSCV analysis revealed 25 conformational variants representing germline mutations that are predicted to result in loss of normal menin function. Twenty different disease-associated mutations were identified: five resulting in potential abnormal RNA splicing, two missense mutations, seven nonsense mutations, and six frameshift mutations. The aberrant splice products were identified and confirmed by RT-PCR and direct sequence analysis for two of the five splice mutations. Sixteen of the 20 (80%) mutations identified have not been previously reported. Mutations were not identified in eight kindreds with signs and symptoms consistent with MEN 1. The SSCV analysis revealed mutations in 76% (25 of 33) of the kindreds investigated, thus showing SSCV analysis to be a reliable mutation detection strategy. One-fifth of the mutations identified in this study involve intron sequences, therefore, highlighting the importance of including intron sequences in the search for germline mutations in the MEN1 gene. The need to investigate the entire gene when characterizing new MEN 1 families presents challenges in the translation of genetic studies to efficient clinical diagnostic tests.

Gene diagnosis and clinical management of multiple endocrine neoplasia type 1 (MEN1)

Identification of the MEN1 gene as a disease gene for multiple endocrine neoplasia type 1 (MEN1) has made it possible to predict whether a family member of an MEN1 patient will suffer from the same disease. MEN1 mutations have been found in almost all cases with familial MEN 1, but in fewer cases with sporadic MEN1. We analyzed MEN1 mutations in the largest number of Japanese MEN1 patients, 17 families and 21 sporadic cases, and found 54 MEN1 mutant carriers and 30 non-carriers. Furthermore, we identified a MEN1 phenocopy: GH-secreting pituitary tumor and primary hyperparathyroidism, which develops at older ages. In this article, we discuss how to utilize MEN1 gene diagnostics for the clinical management of MEN 1 patients and MEN1 mutation carriers.

Criteria for mutation analysis in MEN 1-suspected patients: MEN 1 case-finding

BACKGROUND

Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal, dominantly inherited cancer syndrome, with tumours in various endocrine glands. In 1997 the responsible tumour suppressor gene was identified. MEN1 gene germ-line mutations are detected in the vast majority of MEN 1 patients, however, with regard to case-finding, unfortunately only at a very low frequency in patients with apparently sporadic MEN 1-related tumours. In order to increase the detection rate of disease gene carriers among patients with apparently sporadic MEN 1-related tumours, clinical criteria were needed.

DESIGN AND RESULTS

In this study MEN1 gene germ-line mutations were revealed in 16/16 MEN 1 patients/families (100%). Based on our clinical experience with MEN 1 patients/families we formulated clinical criteria to identify disease gene carriers among patients with apparently sporadic MEN 1-related tumours. The criteria for MEN 1-suspected patients are: young age at onset (< 35 years) and/or multiple MEN 1-related lesions in a single organ or two distinct organs affected. Application of these criteria yielded MEN1 gene germ-line mutations in nine of 15 MEN 1-suspected patients (60%), thus identifying novel MEN 1 families. Follow up was also guaranteed for patients not fulfilling these criteria.

CONCLUSIONS

The clinical criteria for MEN 1-suspected patients increase the detection rate of germ-line MEN1 gene mutations among patients with apparently sporadic MEN 1-related tumours. These criteria may be used for (presymptomatic) identification of MEN 1 disease gene-carriers, thus enabling early detection of tumour development and timely treatment, as well as genetic counselling.

Clinical features of multiple endocrine neoplasia type 1 (MEN1) phenocopy without germline MEN1 gene mutations: analysis of 20 Japanese sporadic cases with MEN1

OBJECTIVE

Multiple endocrine neoplasia type 1 (MEN1) is a familial tumour syndrome of endocrine tumours involving parathyroids, anterior pituitary and enteropancreatic neuroendocrine tissues, and is inherited in an autosomal dominant manner with high penetrance. Recently, the gene responsible for this syndrome, MEN1, was positionally cloned from chromosome 11q13.

PATIENTS

To characterize sporadic MEN1 patients, we analysed the MEN1 gene by direct sequencing of the entire open reading frame from 20 individuals.

RESULTS

We identified heterozygous germline mutations of the MEN1 gene in 8 of 20 (40%) cases. Seven were novel MEN1 germline mutations. Three mutations were splicing abnormalities, and all were confirmed to be splicing defects by RT-PCR. The clinical significance of detecting germline MEN1 mutations, not only in familial MEN1 but also in sporadic MEN1, was confirmed by the finding of asymptomatic mutant carriers among family members of the sporadic MEN1 patients. Seven of 8 cases with MEN1 mutations had enteropancreatic lesions in contrast to 4 of 12 (P < 0.018) in those cases with no mutation. Ten of the 12 cases without MEN1 mutation were more than 50-year-old. Six of these 10 cases had the same clinical features; primary hyperparathyroidism and a GH-secreting pituitary tumour.

CONCLUSIONS

It is likely that the six cases without mutations were MEN1 phenocopies due to (i) two kinds of tumours with high natural incidence in older subjects developed by chance (ii) another familial tumour syndrome with low penetrance, e. g. familial acromegaly with primary hyperparathyroidism by mutation of another gene, or (iii) somatic mutation during early embryonic stages.

Characterization of the MEN1 gene product, menin, by site-specific polyclonal antibodies

The gene associated with multiple endocrine neoplasia type 1 (MEN 1), designated MEN1, has recently been identified. This gene shows no homology to other known genes, and its expression is not restricted to endocrine organs as estimated by northern blotting. Expression of the MEN1 gene product, menin, has been studied only in a few tissues. In this report, expression of menin in various cells and mouse tissues was studied using two polyclonal antibodies against menin. Expression of menin as a 76 kDa single protein was observed in all cell lines examined, regardless of origin. Two nuclear localization signals of the menin have been reported, but through the study of mutant menin in lymphocytes from subjects with MEN 1, impaired nuclear localization of the mutant menin was observed even though the mutant retained one of the two nuclear localization signals (NLSs). Menin was stable in vitro with a half-life of over 24 h at 37 degrees C. In the cell, the half-life of wild-type menin was about 10 h, while that of the mutant was about 2 h. The mutant rapidly disappeared from the nucleus.

Analysis of the MEN1 gene in sporadic pituitary adenomas from Japanese patients

An autosomal-dominant syndrome known as multiple endocrine neoplasia type 1 (MEN1) is characterized by tumors in parathyroid glands, pancreatic endocrine tissues and the anterior pituitary gland. The predisposing gene was identified at 11q13 when germline mutations in the MEN1 gene were detected in affected pedigrees. To investigate a possible role of this gene in tumorigenesis of non-familial pituitary adenomas, we examined 24 sporadic tumors from Japanese patients for loss of heterozygosity (LOH) at the 11q13 region and for somatic mutations in the entire coding region and exon-intron boundaries of MEN1. Although three common sequence variants were detected, none of the tumors exhibited either LOH or somatic mutations of this gene. Our results indicate that inherited and sporadic forms of pituitary adenomas are different in terms of the genetic events that contribute to their development, and that other loci associated with pituitary neoplasia must still be sought.

Review: multiple endocrine neoplasia type 1, sporadic neuroendocrine tumors, and MENIN

Since the identification and cloning of the gene responsible for the inherited syndrome multiple endocrine neoplasia type 1 (MEN1) in 1997, important advances in the understanding of the disease, the encoded protein (MENIN) and its role in the development of sporadic neuroendocrine and other neoplasms have been made. In this review, the most important recently published data on the pathology of the MEN1 syndrome, alterations of the MEN1 gene in affected families, and sporadic neuroendocrine tumors and the possible function of MENIN will be summarized.

A novel splicing mutation (894-9 G --> A) of the MEN1 gene responsible for multiple endocrine neoplasia type 1

Germline MEN1 gene mutations are responsible for multiple endocrine neoplasia type 1 (MEN1), a dominantly inherited cancer syndrome. We identified a MEN1 germline mutation 894-9 G --> A in three MEN1 patients from two unrelated families. This mutation was not present in any of the 100 blood samples from normal volunteers. The wild type MEN1 sequence was lost in the patient's pancreatic tumor. Abnormal mRNA was identified in the tumor, which retained an intronic sequence indicating aberrant mRNA splicing at a newly created splicing acceptor site. These findings indicate that this nucleotide substitution is, though previously reported to be a polymorphism, a causative splicing mutation.

Type 1 multiple endocrine neoplasia (MEN1): contribution of genetic analysis to the screening and follow-up of a large French kindred

OBJECTIVE

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal genetic disorder, the clinical phenotype of which includes tumours of the parathyroids and/or anterior pituitary and/or endocrine pancreas. The genetic defect has been mapped to the chromosome 11q13 and the MEN1 gene has been recently identified, thus allowing genetic screening in affected kindreds. The aim of this study was to establish the usefulness of genetic screening in the follow-up of a large MEN1 kindred.

PATIENTS

We describe a large kindred of 91 members, of whom 56 had clinical, biochemical and genetic screening. Twenty eight of them have been tested annually for the last 5 years.

RESULTS

Although the precise mutation is still undetermined in this kindred, genotypic determination confirmed linkage with the MEN1 gene in affected members and excluded 28 members from annual testing. By drawing our attention to susceptible subjects, genetic screening improved the evaluation of age-related penetrance of the disease in the 3 generations from this kindred. For instance, annual screening showed conversion from unaffected to affected phenotype in 4 subjects aged 14, 14, 15, and 17 years. Moreover, genetics helped us to evaluate the specificity of clinical or biochemical markers, and thus to discard useless investigations. So far however, the genetics have not helped to explain the phenotypic heterogeneity and particularly low incidence of pancreatic tumours in this kindred.

CONCLUSION

Genetic screening is very useful in detecting high risk individuals for MEN 1, since it avoids time-consuming and expensive investigations in non-affected subjects. By providing better understanding of the age-related penetrance of this syndrome, it improves the efficiency of screening. Genetic studies allow differentiation between clinical and biochemical features that are useful in follow-up and other confusing or unhelpful parameters.

Germ-line mutation analysis in patients with multiple endocrine neoplasia type 1 and related disorders

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant syndrome predisposing to tumors of the parathyroid, endocrine pancreas, anterior pituitary, adrenal glands, and diffuse neuroendocrine tissues. The MEN1 gene has been assigned, by linkage analysis and loss of heterozygosity, to chromosome 11q13 and recently has been identified by positional cloning. In this study, a total of 84 families and/or isolated patients with either MEN1 or MEN1-related inherited endocrine tumors were screened for MEN1 germ-line mutations, by heteroduplex and sequence analysis of the MEN1 gene-coding region and untranslated exon 1. Germ-line MEN1 alterations were identified in 47/54 (87%) MEN1 families, in 9/11 (82%) isolated MEN1 patients, and in only 6/19 (31.5%) atypical MEN1-related inherited cases. We characterized 52 distinct mutations in a total of 62 MEN1 germ-line alterations. Thirty-five of the 52 mutations were frameshifts and nonsense mutations predicted to encode for a truncated MEN1 protein. We identified eight missense mutations and five in-frame deletions over the entire coding sequence. Six mutations were observed more than once in familial MEN1. Haplotype analysis in families with identical mutations indicate that these occurrences reflected mainly independent mutational events. No MEN1 germ-line mutations were found in 7/54 (13%) MEN1 families, in 2/11 (18%) isolated MEN1 cases, in 13/19 (68. 5%) MEN1-related cases, and in a kindred with familial isolated hyperparathyroidism. Two hundred twenty gene carriers (167 affected and 53 unaffected) were identified. No evidence of genotype-phenotype correlation was found. Age-related penetrance was estimated to be >95% at age >30 years. Our results add to the diversity of MEN1 germ-line mutations and provide new tools in genetic screening of MEN1 and clinically related cases.