Multiple endocrine neoplasia type 1 (MEN1): analysis of 1336 mutations reported in the first decade following identification of the gene

Molecular profiling of pancreatic neuroendocrine tumors (pNETS) and the clinical potential

Pancreatic neuroendocrine tumors (pNETs) represent a small part of pancreatic neoplasms, and the knowledge about their indolent clinical course remains a subject of investigation. They occur sporadically or as part of familial cancer syndromes and are classified by WHO in 3 categories. There is ongoing research to understand their molecular profiling and leading mutations. Areas covered: The aim of this review is to clarify the overall aspects of tumorigenesis, to expose the latest developments in understanding the course of the disease and the possible therapeutic implications of these. The review also discusses functional and non-functional pNETs and associated inherited syndromes as well as pNET molecular profiling and its possible guidance in the use of targeted therapy. Expert commentary: In the next decade, a more extensive application of new technologies will help improve quality of life and survival, individualizing treatment protocols and identifying which therapeutic strategy is more suitable for each kind of NET.

An update on the genetics of benign pituitary adenomas in children and adolescents

Pituitary adenomas in children and adolescents are rare tumors that often result from a tumor predisposition syndrome. Several inherited causes for pituitary adenomas have been identified in the last few years, including multiple endocrine neoplasia type 1 and 4, Carney's complex, Tuberous sclerosis, DICER1 syndrome, neurofibromatosis type 1, McCune Albright syndrome, familial isolated pituitary adenoma, and pituitary adenoma association due to defects in succinate dehydrogenase genes. Recently, our group discovered X-linked acrogigantism (X-LAG), a new pediatric disorder that is caused by an Xq26.3 genomic duplication (involving the GPR101 gene). Genes that predispose to pediatric Cushing disease, including CABLES1 and USP8, were also recently identified. Genetic screening and counseling of affected or at risk individuals is a key component of their comprehensive care. In this review, we provide an up-to-date discussion on the latest pediatric genetic discoveries associated with pituitary adenomas with a focus on familial syndromes.

Current and emerging therapies for PNETs in patients with or without MEN1

Pancreatic neuroendocrine tumours (PNETs) might occur as a non-familial isolated endocrinopathy or as part of a complex hereditary syndrome, such as multiple endocrine neoplasia type 1 (MEN1). MEN1 is an autosomal dominant disorder characterized by the combined occurrence of PNETs with tumours of the parathyroids and anterior pituitary. Treatments for primary PNETs include surgery. Treatments for non-resectable PNETs and metastases include biotherapy (for example, somatostatin analogues, inhibitors of receptors and monoclonal antibodies), chemotherapy and radiological therapy. All these treatments are effective for PNETs in patients without MEN1; however, there is a scarcity of clinical trials reporting the efficacy of the same treatments of PNETs in patients with MEN1. Treatment of PNETs in patients with MEN1 is challenging owing to the concomitant development of other tumours, which might have metastasized. In recent years, preclinical studies have identified potential new therapeutic targets for treating MEN1-associated neuroendocrine tumours (including PNETs), and these include epigenetic modification, the β-catenin-wingless (WNT) pathway, Hedgehog signalling, somatostatin receptors and MEN1 gene replacement therapy. This Review discusses these advances.

Diagnosis, management, histology and genetics of sporadic primary hyperparathyroidism: old knowledge with new tricks

Primary hyperparathyroidism (pHPT) is a common endocrinopathy resulting from inappropriately high PTH secretion. It usually results from the presence of a single gland adenoma, multiple gland hyperplasia or rarely parathyroid carcinoma. All these conditions require different management, and it is important to be able to differentiate the underlined pathology, in order for the clinicians to provide the best therapeutic approach. Elucidation of the genetic background of each of these clinical entities would be of great interest. However, the molecular factors that control parathyroid tumorigenesis are poorly understood. There are data implicating the existence of specific genetic pathways involved in the emergence of parathyroid tumorigenesis. The main focus of the present study is to present the current optimal diagnostic and management protocols for pHPT as well as to review the literature regarding all molecular and genetic pathways that are to be involved in the pathophysiology of sporadic pHPT.

6. MEN syndromes

MEN1 and MEN2 are rare inherited cancer syndromes which express a variety of endocrine and nonendocrine tumors. The improved knowledge of molecular and clinical physiopathology of MEN syndromes, together with the availability of genetic testing, have led to earlier detection and intervention, with consequent reduction of mortality and morbidity for MEN-associated tumors. Genetic testing has gained a key role in the detection of asymptomatic patients harbouring mutations responsible for these syndrome, and allows institution of early and tailored intervention with a positive impact on the course of disease. Free full text available at www.tumorionline.it

Long-term follow-up and novel splice donor mutation in MEN1 in a Chinese family

Heterozygous germline mutation of the MEN1 tumor suppressor gene is responsible for multiple endocrine neoplasia type 1. Parathyroid and thoracic neuroendocrine tumor specimens and DNA from two Han Chinese MEN1 family patients were analyzed using whole exome and Sanger sequencing. The proband (II-3) was sequentially diagnosed with pituitary adenoma, pancreatic tumor, adrenal cortical tumor, abdominal lipoma, and parathyroid adenoma during the 6-year follow-up. The son of the proband (III-6) was also diagnosed with a thoracic neuroendocrine tumor and a parathyroid adenoma during this period. Splice alterations were studied by RT-PCR and sequencing. The mutation impact was evaluated using bioinformatics. Sequence analysis revealed a novel splice donor mutation, MEN1 IVS9 + 1G > C, that changed the splicing mode of MEN1 to halt translation before two nuclear localization signals in the menin protein. Novel somatic mutations, MEN1 c.1402_1405delGAGG and c.286 C > T, were identified in the parathyroid adenoma of II-3 and thoracic neuroendocrine tumor of III-6, respectively, indicating a two-hit etiology of MEN1 syndrome. Our study revealed the clinical and genetic basis of MEN1 in this Han Chinese family and provides insight into MEN1 mechanisms, diagnosis, and management.

The Importance of an Early and Accurate MEN1 Diagnosis

Multiple Endocrine Neoplasia type 1 (MEN1) is a rare autosomal dominant inherited condition, causing significant morbidity, and a reduction of life expectancy. A timely and accurate diagnosis of MEN1 is paramount to improve disease outcomes. This enables early identification of tumor manifestations allowing timely treatment for reducing morbidity and improving survival. Current management of MEN1 poses two challenges regarding the MEN1 diagnosis: diagnostic delay and the issue of phenocopies. A delay in diagnosis can be caused by a delay in identifying the index case, and by a delay in identifying affected family members of an index case. At present, lag time between diagnosis of MEN1 in index cases and genetic testing of family members was estimated to be 3.5 years. A subsequent delay in diagnosing affected family members was demonstrated to cause potential harm. Non-index cases have been found to develop clinically relevant tumor manifestations during the lag times. Centralized care, monitoring of patients outcomes on a national level and thereby improving awareness of physicians treating MEN1 patients, will contribute to improved care. The second challenge relates to "phenocopies." Phenocopies refers to the 5-25% of clinically diagnosed patients with MEN1in whom no mutation can be found. Up to now, the clinical diagnosis of MEN1 is defined as the simultaneous presence of at least two of the three characteristic tumors (pituitary, parathyroids, or pancreatic islets). These clinically diagnosed patients undergo intensive follow up. Recent insights, however, challenge the validity of this clinical criterion. The most common mutation-negative MEN1 phenotype is the combination of primary hyperparathyroidism and a pituitary adenoma. This phenotype might also be caused by mutations in the CDKN1B gene, causing the recently described MEN4 syndrome. Moreover, primary hyperparathyroidism and pituitary adenoma are relatively common in the general population. Limiting follow-up in patients with a sporadic co-occurrence of pHPT and PIT could reduce exposure to radiation from imaging, healthcare costs and anxiety.

Molecular genetics of syndromic and non-syndromic forms of parathyroid carcinoma

Parathyroid carcinoma (PC) may occur as part of a complex hereditary syndrome or an isolated (i.e., non-syndromic) non-hereditary (i.e., sporadic) endocrinopathy. Studies of hereditary and syndromic forms of PC, which include the hyperparathyroidism-jaw tumor syndrome (HPT-JT), multiple endocrine neoplasia types 1 and 2 (MEN1 and MEN2), and familial isolated primary hyperparathyroidism (FIHP), have revealed some genetic mechanisms underlying PC. Thus, cell division cycle 73 (CDC73) germline mutations cause HPT-JT, and CDC73 mutations occur in 70% of sporadic PC, but in only ∼2% of parathyroid adenomas. Moreover, CDC73 germline mutations occur in 20%-40% of patients with sporadic PC and may reveal unrecognized HPT-JT. This indicates that CDC73 mutations are major driver mutations in the etiology of PCs. However, there is no genotype-phenotype correlation and some CDC73 mutations (e.g., c.679_680insAG) have been reported in patients with sporadic PC, HPT-JT, or FIHP. Other genes involved in sporadic PC include germline MEN1 and rearranged during transfection (RET) mutations and somatic alterations of the retinoblastoma 1 (RB1) and tumor protein P53 (TP53) genes, as well as epigenetic modifications including DNA methylation and histone modifications, and microRNA misregulation. This review summarizes the genetics and epigenetics of the familial syndromic and non-syndromic (sporadic) forms of PC.

Frequency of familial pituitary adenoma syndromes among patients with functioning pituitary adenomas in a reference outpatient clinic

INTRODUCTION

Pituitary adenomas (PA) occur mainly as sporadic disease, but familial syndromes are found in approximately 5% of cases. Identification of these syndromes is important in order to diagnose individuals at risk at an earlier stage.

AIMS

To evaluate the frequency of familial PA in a reference outpatient clinic devoted to PA treatment and to identify family members suspected to have pituitary disease.

METHODS

Patients with PA were interviewed with respect to the presence of family members with diagnosis of PA or with signs or symptoms suggestive of them. The family members who had a clinical picture suggestive of pituitary disease were further evaluated in an attempt to identify new PA cases. In families with familial disease, the AIP gene was sequenced.

RESULTS

262 patients were evaluated and familial syndrome was found in 13 (5%). Ten (3.8%) patients had familial isolated PA (FIPA) and three (1.2%) had multiple endocrine neoplasia type 1. After evaluation of family members' symptomatology, 110 were considered suspected of having pituitary disease, but only 24 participated in the study. Of these 24, 1 was diagnosed with a corticotropinoma. AIP mutations were found in 20% of FIPA families.

CONCLUSION

We found a frequency of familial PA similar to that previously described, as well as a similar frequency of AIP mutations among FIPA families. An active search of the affected family members was able to identify one case of Cushing´s disease. Patients should be aware of pituitary disease's clinical picture to identify possibly affected family members.

Gastrin Induces Nuclear Export and Proteasome Degradation of Menin in Enteric Glial Cells

BACKGROUND & AIMS

The multiple endocrine neoplasia, type 1 (MEN1) locus encodes the nuclear protein and tumor suppressor menin. MEN1 mutations frequently cause neuroendocrine tumors such as gastrinomas, characterized by their predominant duodenal location and local metastasis at time of diagnosis. Diffuse gastrin cell hyperplasia precedes the appearance of MEN1 gastrinomas, which develop within submucosal Brunner's glands. We investigated how menin regulates expression of the gastrin gene and induces generation of submucosal gastrin-expressing cell hyperplasia.

METHODS

Primary enteric glial cultures were generated from the VillinCre:Men1FL/FL:Sst-/- mice or C57BL/6 mice (controls), with or without inhibition of gastric acid by omeprazole. Primary enteric glial cells from C57BL/6 mice were incubated with gastrin and separated into nuclear and cytoplasmic fractions. Cells were incubated with forskolin and H89 to activate or inhibit protein kinase A (a family of enzymes whose activity depends on cellular levels of cyclic AMP). Gastrin was measured in blood, tissue, and cell cultures using an ELISA. Immunoprecipitation with menin or ubiquitin was used to demonstrate post-translational modification of menin. Primary glial cells were incubated with leptomycin b and MG132 to block nuclear export and proteasome activity, respectively. We obtained human duodenal, lymph node, and pancreatic gastrinoma samples, collected from patients who underwent surgery from 1996 through 2007 in the United States or the United Kingdom.

RESULTS

Enteric glial cells that stained positive for glial fibrillary acidic protein (GFAP+) expressed gastrin de novo through a mechanism that required PKA. Gastrin-induced nuclear export of menin via cholecystokinin B receptor (CCKBR)-mediated activation of PKA. Once exported from the nucleus, menin was ubiquitinated and degraded by the proteasome. GFAP and other markers of enteric glial cells (eg, p75 and S100B), colocalized with gastrin in human duodenal gastrinomas.

CONCLUSIONS

MEN1-associated gastrinomas, which develop in the submucosa, might arise from enteric glial cells through hormone-dependent PKA signaling. This pathway disrupts nuclear menin function, leading to hypergastrinemia and associated sequelae.

MEN1 gene mutation with parathyroid carcinoma: first report of a familial case

BACKGROUND

The occurrence of parathyroid carcinoma in multiple endocrine neoplasia type I (MENI) is rare and the 15 cases of malignant parathyroid tumor reported so far have been associated with MENI in individuals and not with multiple members within a family.

METHODS

We report on a 61-year-old male, operated for a 7.3 cm parathyroid carcinoma infiltrating the esophagus. In his brother, a 4.6 cm parathyroid carcinoma was diagnosed histologically, while in the daughter, neck ultrasonography revealed 2 extrathyroidal nodules, yet to be excised.

RESULTS

Screening of the MEN1 gene identified a known germline heterozygous missense mutation (c.1252G>A; p.D418N) in exon 9, in all affected subjects.

CONCLUSIONS

The occurrence of parathyroid carcinoma in more than one affected member of a single MEN1 family represents the first reported familial case. This suggests that additional constitutional genetic mutations may contribute to the variation in malignant potential and clinical behavior of parathyroid tumors in MEN1.

Multiple endocrine neoplasia syndrome type 1: institution, management, and data analysis of a nationwide multicenter patient database

OBJECTIVE

The aim of this study was to integrate European epidemiological data on patients with multiple endocrine neoplasia type 1 by creating an Italian registry of this syndrome, including clinical and genetic characteristics and therapeutic management.

METHODS

Clinical, familial and genetic data of patients with multiple endocrine neoplasia type 1, diagnosed, treated, and followed-up for a mean time of 11.3 years, in 14 Italian referral endocrinological centers, were collected, over a 3-year course (2011-2013), to build a national electronic database.

RESULTS

The Italian multiple endocrine neoplasia type 1 database includes 475 patients (271 women and 204 men), of whom 383 patients (80.6%) were classified as familial cases (from 136 different pedigrees), and 92 (19.4%) patients were sporadic cases. A MEN1 mutation was identified in 92.6% of familial cases and in 48.9% of sporadic cases. Four hundred thirty-six patients were symptomatic, presenting primary hyperparathyroidism, gastroenteropancreatic neuroendocrine tumors and pituitary tumors in 93, 53, and 41% of cases, respectively. Thirty-nine subjects, belonging to affected pedigrees positive for a MEN1 mutation, were asymptomatic at clinical and biochemical screening. Age at diagnosis of multiple endocrine neoplasia type 1 probands was similar for both familial and simplex cases (mean age 47.2 ± 15.3 years). In familial cases, diagnosis of multiple endocrine neoplasia type 1 in relatives of affected probands was made more than 10 years in advance (mean age at diagnosis 36.5 ± 17.6 years).

CONCLUSIONS

The analysis of Italian registry of multiple endocrine neoplasia type 1 patients revealed that clinical features of Italian multiple endocrine neoplasia type 1 patients are similar to those of other western countries, and confirmed that the genetic test allowed multiple endocrine neoplasia type 1 diagnosis 10 years earlier than biochemical or clinical diagnosis.

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.

Analysis of MEN1 c.482G>A (p.Gly161Asp) mutation in a pedigree with familial multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by the development of neuroendocrine tumors, which in turn are caused by mutations in the MEN1 gene. In the present study, a case of a 46‑year‑old woman who was clinically diagnosed with MEN1 based on the presence of prolactinoma and bilateral parathyroid adenoma was reported. The patient's serum prolactin (PRL) levels were successfully controlled via bromocriptine therapy, and the serum levels of calcium and intact parathyroid hormone (PTH) reduced one day following parathyroidectomy. Genetic testing revealed a missense mutation c.482G>A (p.Gly161Asp) in exon 3 of the MEN1 gene, and it led to the identification of two carriers in the pedigree (patient's elder sister and brother). Both of the carriers revealed to have high blood calcium, PTH and PRL. The mutation identified in this pedigree has never been reported in China. The sequence alignments and tertiary structure of menin protein were made by Polyphen2, SNPs3D, and SIFT, which were used to predict the function of mutant menin. Since the mutant menin may interfere with the menin‑JunD or menin‑Smad3 interactions, further investigations are necessary to explore the function of mutant protein. In view of that, identification of mutations and longtime follow‑up are important for patients with a pedigree clearly indicating MEN1.

Insights into beta cell regeneration for diabetes via integration of molecular landscapes in human insulinomas

Although diabetes results in part from a deficiency of normal pancreatic beta cells, inducing human beta cells to regenerate is difficult. Reasoning that insulinomas hold the “genomic recipe” for beta cell expansion, we surveyed 38 human insulinomas to obtain insights into therapeutic pathways for beta cell regeneration. An integrative analysis of whole-exome and RNA-sequencing data was employed to extensively characterize the genomic and molecular landscape of insulinomas relative to normal beta cells. Here, we show at the pathway level that the majority of the insulinomas display mutations, copy number variants and/or dysregulation of epigenetic modifying genes, most prominently in the polycomb and trithorax families. Importantly, these processes are coupled to co-expression network modules associated with cell proliferation, revealing candidates for inducing beta cell regeneration. Validation of key computational predictions supports the concept that understanding the molecular complexity of insulinoma may be a valuable approach to diabetes drug discovery.

Diabetes results in part from a deficiency of functional pancreatic beta cells. Here, the authors study the genomic and epigenetic landscapes of human insulinomas to gain insight into possible pathways for therapeutic beta cell regeneration, highlighting epigenetic genes and pathways.

The future: diagnostic and imaging advances in MEN1 therapeutic approaches and management strategies

Prospective randomized data are lacking, but current clinical expert guidelines recommend annual screening examinations, including laboratory assessments and various imaging modalities (e.g. CT, MRI, scintigraphy and EUS) for patients with multiple endocrine neoplasia type 1 (MEN1). Routine screening is proposed to detect and localize neuroendocrine manifestations as early as possible. The goal is timely intervention to improve quality of life and to increase life expectancy by preventing the development of life-threatening hormonal syndromes and/or metastatic disease. In recent years, some studies compared different and new imaging methods regarding their sensitivity and utility in MEN1 patients. This present article reviews the proposed diagnostic tools for MEN1 screening as well as potential future perspectives.

Management impact: effects on quality of life and prognosis in MEN1

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant endocrine tumor syndrome, caused by inactivating mutations of the MEN1 tumor suppressor gene at 11q13 locus, which predisposes to develop tumors in target neuroendocrine tissues. As the positional cloning and identification of the causative gene in 1997, genetic diagnosis, by the sequencing-based research of gene mutations, has become an important tool in the early and differential diagnosis of the disease. Application of the genetic test, in MEN1 index cases and in first-degree relatives of mutated patients, has been constantly increasing during the last two decades, also thanks to the establishment of multidisciplinary referral centers and specific genetic counseling, and thanks to the wide availability of high throughput instruments for gene sequencing and gene mutation identification. The MEN1 genetic test helps the specific diagnosis of probands, and allows the early identification of asymptomatic carriers, strongly contributing, together with progressions in tumor diagnostic techniques and in pharmacological and surgical therapeutic approaches, to the reduction of morbidity and mortality associated with the syndrome. International clinical guidelines for MEN1 have been drafted by panels of specialists in the field, with the main goal to improve the management of the disease and grant patients a better quality of life. Here, we review main recommendations and suggestions derived by the last published general guidelines in 2012, and by most recent published studies about MEN1 syndrome diagnosis, clinical management, therapeutic approaches and patients' quality of life.

Twenty years of menin: emerging opportunities for restoration of transcriptional regulation in MEN1

Since the discovery of the multiple endocrine neoplasia type 1 (MEN1) gene in 1997, elucidation of the molecular function of its protein product, menin, has been a challenge. Biochemical, proteomics, genetics and genomics approaches have identified various potential roles, which converge on gene expression regulation. The most consistent findings show that menin connects transcription factors and chromatin-modifying enzymes, in particular, the histone H3K4 methyltransferase complexes MLL1 and MLL2. Chromatin immunoprecipitation combined with next-generation sequencing has enabled studying genome-wide dynamics of chromatin binding by menin. We propose that menin regulates cell type-specific transcriptional programs by linking chromatin regulatory complexes to specific transcription factors. In this fashion, the MEN1 gene is a tumor suppressor gene in the endocrine tissues that are affected in MEN1. Recent studies have hinted at possibilities to pharmacologically restore the epigenetic changes caused by loss of menin function as therapeutic strategies for MEN1, for example, by inhibition of histone demethylases. The current lack of appropriate cellular model systems for MEN1-associated tumors is a limitation for compound testing, which needs to be addressed in the near future. In this review, we look back at the past twenty years of research on menin and the mechanism of disease of MEN1. In addition, we discuss how the current understanding of the molecular function of menin offers future directions to develop novel treatments for MEN1-associated endocrine tumors.

The future: genetics advances in MEN1 therapeutic approaches and management strategies

The identification of the multiple endocrine neoplasia type 1 (MEN1) gene in 1997 has shown that germline heterozygous mutations in the MEN1 gene located on chromosome 11q13 predisposes to the development of tumors in the MEN1 syndrome. Tumor development occurs upon loss of the remaining normal copy of the MEN1 gene in MEN1-target tissues. Therefore, MEN1 is a classic tumor suppressor gene in the context of MEN1. This tumor suppressor role of the protein encoded by the MEN1 gene, menin, holds true in mouse models with germline heterozygous Men1 loss, wherein MEN1-associated tumors develop in adult mice after spontaneous loss of the remaining non-targeted copy of the Men1 gene. The availability of genetic testing for mutations in the MEN1 gene has become an essential part of the diagnosis and management of MEN1. Genetic testing is also helping to exclude mutation-negative cases in MEN1 families from the burden of lifelong clinical screening. In the past 20 years, efforts of various groups world-wide have been directed at mutation analysis, molecular genetic studies, mouse models, gene expression studies, epigenetic regulation analysis, biochemical studies and anti-tumor effects of candidate therapies in mouse models. This review will focus on the findings and advances from these studies to identify MEN1 germline and somatic mutations, the genetics of MEN1-related states, several protein partners of menin, the three-dimensional structure of menin and menin-dependent target genes. The ongoing impact of all these studies on disease prediction, management and outcomes will continue in the years to come.

Animal models of MEN1

Animal models of cancer have been instrumental in advancing our understanding of the biology of tumor initiation and progression, in studying gene function and in performing preclinical studies aimed at testing novel therapies. Several animal models of the MEN1 syndrome have been generated in different organisms by introducing loss-of-function mutations in the orthologues of the human MEN1 gene. In this review, we will discuss MEN1 and MEN1-like models in Drosophila, mice and rats. These model systems with their specific advantages and limitations have contributed to elucidate the function of Menin in tumorigenesis, which turned out to be remarkably conserved from flies to mammals, as well as the biology of the disease. Mouse models of MEN1 closely resemble the human disease in terms of tumor spectrum and associated hormonal changes, although individual tumor frequencies are variable. Rats affected by the MENX (MEN1-like) syndrome share some features with MEN1 patients albeit they bear a germline mutation in Cdkn1b (p27) and not in Men1 Both Men1-knockout mice and MENX rats have been exploited for therapy-response studies testing novel drugs for efficacy against neuroendocrine tumors (NETs) and have provided promising leads for novel therapies. In addition to presenting well-established models of MEN1, we also discuss potential models which, if implemented, might broaden even further our knowledge of neuroendocrine tumorigenesis. In the future, patient-derived xenografts in zebrafish or mice might allow us to expand the tool-box currently available for preclinical studies of MEN1-associated tumors.

The future: medical advances in MEN1 therapeutic approaches and management strategies

Multiple endocrine neoplasia type 1 is a rare autosomal inherited disorder associated with a high risk for patients to simultaneously develop tumors of the parathyroid glands, duodenopancreatic neuroendocrine tumors and tumors of the anterior pituitary gland. Early identification of MEN1 in patients enables presymptomatic screening of manifestations, which makes timely interventions possible with the intention to prevent morbidity and mortality. Causes of death nowadays have shifted toward local or metastatic progression of malignant neuroendocrine tumors. In early cohorts, complications like peptic ulcers in gastrinoma, renal failure in hyperparathyroidism, hypoglycemia and acute hypercalcemia were the primary causes of early mortality. Improved medical treatments of these complications led to a significantly improved life expectancy. The MEN1 landscape is still evolving, considering the finding of breast cancer as a new MEN1-related manifestation and ongoing publications on follow-up and medical care for patients with MEN1. This review aims at summarizing the most recent insights into the follow-up and medical care for patients with MEN1 and identifying the gaps for future research.

Atypical pituitary adenoma with MEN1 somatic mutation associated with abnormalities of DNA mismatch repair genes; MLH1 germline mutation and MSH6 somatic mutation

The mechanism of pituitary tumorigenesis remains largely unknown. Lynch syndrome is an autosomal, dominantly inherited syndrome caused by a defective mismatch repair (MMR) mechanism involved in the development of various tumors at an early age. In this case study, we showed the occurrence of pituitary tumors associated with Lynch syndrome for the first time and performed genetic and immunohistochemical analysis to evaluate the genetic aberrations that might be related to the tumorigenesis and proliferation. A 68-year-old female patient with Lynch syndrome due to mutL homolog 1 (MLH1) gene mutation suffered from hypersecretion of adrenocorticotrophic hormone (ACTH), hypercortisolism and a rapidly progressive pituitary tumor. We performed genetic analysis by whole genome sequencing with genomic DNA of the pituitary tumor and peripheral blood leukocytes, as well as immunohistochemical analysis of MMR proteins. Genetic analysis revealed that the tumor had homozygous gene mutation of MEN1 associated with pituitary tumorigenesis and mutS homolog 6 (MSH6) gene. Furthermore, immunohistochemical analysis showed that MLH1 and MSH6 immunoexpression were negative. We reveal for the first time that MMR abnormality could cause somatic mutation of MEN1 and pituitary tumor occurrence is associated with Lynch syndrome. We suggest that the identified gene mutations, especially those of MSH6 and MLH1 genes, may be involved in the pathogenesis and proliferation of pituitary tumor. The knowledge obtained from our case study is important to elucidate the pathogenesis and proliferation mechanisms of pituitary tumors.

Genetic and epigenetic drivers of neuroendocrine tumours (NET)

Neuroendocrine tumours (NET) of the gastrointestinal tract and the lung are a rare and heterogeneous group of tumours. The molecular characterization and the clinical classification of these tumours have been evolving slowly and show differences according to organs of origin. Novel technologies such as next-generation sequencing revealed new molecular aspects of NET over the last years. Notably, whole-exome/genome sequencing (WES/WGS) approaches underlined the very low mutation rate of well-differentiated NET of all organs compared to other malignancies, while the engagement of epigenetic changes in driving NET evolution is emerging. Indeed, mutations in genes encoding for proteins directly involved in chromatin remodelling, such as DAXX and ATRX are a frequent event in NET. Epigenetic changes are reversible and targetable; therefore, an attractive target for treatment. The discovery of the mechanisms underlying the epigenetic changes and the implication on gene and miRNA expression in the different subgroups of NET may represent a crucial change in the diagnosis of this disease, reveal new therapy targets and identify predictive markers. Molecular profiles derived from omics data including DNA mutation, methylation, gene and miRNA expression have already shown promising results in distinguishing clinically and molecularly different subtypes of NET. In this review, we recapitulate the major genetic and epigenetic characteristics of pancreatic, lung and small intestinal NET and the affected pathways. We also discuss potential epigenetic mechanisms leading to NET development.

Late onset asymptomatic pancreatic neuroendocrine tumor - A case report on the phenotypic expansion for MEN1

Background

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary cancer syndrome associated with several endocrine as well as non-endocrine tumors and is caused by mutations in the MEN1 gene. Primary hyperparathyroidism affects the majority of MEN1 individuals by age 50 years. Additionally, MEN1 mutations trigger familial isolated hyperparathyroidism. We describe a seemingly unaffected 76-year-old female who presented to our Genetics Clinic with a family history of primary hyperparathyroidism and the identification of a pathogenic MEN1 variant.

Case Presentation

The patient was a 76 year-old woman who appeared to be unaffected. She had a family history of a known MEN1 pathogenic variant. Molecular testing for the known MEN1 mutation c.1A > G, as well as, biochemical testing, MRI of the brain and abdomen were all performed using standard methods. Molecular testing revealed our patient possessed the MEN1 pathogenic variant previously identified in her two offspring. Physical exam revealed red facial papules with onset in her seventies, involving her cheeks, nose and upper lip. Formerly, she was diagnosed with rosacea by a dermatologist and noted no improvement with treatment. Clinically, these lesions appeared to be facial angiofibromas. Brain MRI was normal. However, an MRI of her abdomen revealed a 1.5 cm lesion at the tail of the pancreas with normal adrenal glands. Glucagon was mildly elevated and pancreatic polypeptide was nearly seven times the upper limit of the normal range. The patient underwent spleen sparing distal pancreatectomy and subsequent pathology was consistent with a well-differentiated pancreatic neuroendocrine tumor (pNET).

Conclusions

Age-related penetrance and variable expressivity are well documented in families with MEN1. It is thought that nearly all individuals with MEN1 manifest disease by age 40. We present a case of late-onset MEN1 in the absence of the most common feature, primary hyperparathyroidism, but with the presence of a pNET and cutaneous findings. This family expands the phenotype associated with the c.1A > G pathogenic variant and highlights the importance of providing comprehensive assessment of MEN1 mutation carriers in families that at first blush may appear to have isolated hyperparathyroidism.

A Review of the Scaffold Protein Menin and its Role in Hepatobiliary Pathology

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome with neuroendocrine tumorigenesis of the parathyroid glands, pituitary gland, and pancreatic islet cells. The MEN1 gene codes for the canonical tumor suppressor protein, menin. Its protein structure has recently been crystallized, and it has been investigated in a multitude of other tissues. In this review, we summarize recent advancements in understanding the structure of the menin protein and its function as a scaffold protein in histone modification and epigenetic gene regulation. Furthermore, we explore its role in hepatobiliary autoimmune diseases, cancers, and metabolic diseases. In particular, we discuss how menin expression and function are regulated by extracellular signaling factors and nuclear receptor activation in various hepatic cell types. How the many signaling pathways and tissue types affect menin's diverse functions is not fully understood. We show that small-molecule inhibitors affecting menin function can shed light on menin's broad role in pathophysiology and elucidate distinct menin-dependent processes. This review reveals menin's often dichotomous function through analysis of its role in multiple disease processes and could potentially lead to novel small-molecule therapies in the treatment of cholangiocarcinoma or biliary autoimmune diseases.

Clinical Identification of Oncogenic Drivers and Copy-Number Alterations in Pituitary Tumors

Pituitary tumors are the second most common adult primary brain tumor, with a variable clinical course. Recent work has identified a number of genetic determinants of pituitary tumor subtypes, which may augment traditional histopathologic classification schemes. We sought to determine whether pituitary tumors could be stratified based on objective molecular characteristics using a clinical genomics assay. We performed a retrospective analysis of patients operated on at the Brigham and Women's Hospital from 2012 to 2016 whose pituitary tumors were profiled using multiplexed next-generation sequencing. We analyzed 127 pituitary tumors, including 114 adenomas, 5 craniopharyngiomas, and 8 tumors of other histologies. We observed recurrent BRAFV600E mutations in papillary craniopharyngiomas, CTNNB1 mutations in adamantinomatous craniopharyngiomas, and activating GNAS mutations in growth hormone-secreting adenomas. Furthermore, we validated the presence of two distinct genomic subclasses in adenomas (i.e., those with disrupted or quiet copy-number profiles) and the significant association of disruption with functional hormone status (P < 0.05). We report the clinical implementation of next-generation sequencing of pituitary tumors. We confirmed previously identified molecular subclasses for these tumors and show that routine screening as part of clinical practice is both feasible and informative. This large-scale proof-of-principle study may help to guide future institutional efforts for pituitary tumor classification as well as the incorporation of such techniques into prospective analysis as part of clinical trials.

Genetics of Multiple Endocrine Neoplasia Type 1/Multiple Endocrine Neoplasia Type 2 Syndromes

Multiple endocrine neoplasia syndromes types 1 and 2 represent well-characterized yet clinically heterogeneous hereditary conditions for which diagnostic and management recommendations exist; genetic testing for these inherited endocrinopathies is included in these guidelines and is an important part of identifying affected patients and their family members. Understanding of these mature syndromes is challenged as more individuals undergo genetic testing and genetic data are amassed, with the potential to create clinical conundrums that may have an impact on individualized approaches to management and counseling. Clinicians who diagnose and treat patients with MEN syndromes should be aware of these possibilities.

Genetics of Hyperparathyroidism, Including Parathyroid Cancer

Primary hyperparathyroidism (HPT) is a metabolic disease caused by the excessive secretion of parathyroid hormone from 1 or more neoplastic parathyroid glands. HPT is largely sporadic, but it can be associated with a familial syndrome. The study of such families led to the discovery of tumor suppressor genes whose loss of function is now recognized to underlie the development of many sporadic parathyroid tumors. Heritable and acquired oncogenes causing parathyroid neoplasia are also known. Studies of somatic changes in parathyroid tumor DNA and investigation of kindreds with unexplained familial HPT promise to unmask more genes relevant to parathyroid neoplasia.

Genetic Aspects of Pituitary Adenomas

Although most of pituitary adenomas are benign, they may cause significant burden to patients. Sporadic adenomas represent the vast majority of the cases, where recognized somatic mutations (eg, GNAS or USP8), as well as altered gene-expression profile often affecting cell cycle proteins have been identified. More rarely, germline mutations predisposing to pituitary adenomas -as part of a syndrome (eg, MEN1 or Carney complex), or isolated to the pituitary (AIP or GPR101) can be identified. These alterations influence the biological behavior, clinical presentations and therapeutic responses, and their full understanding helps to provide appropriate care for these patients.

Molecular genetics in primary hyperparathyroidism: the role of genetic tests in differential diagnosis, disease prevention strategy, and therapeutic planning. A 2017 update

Primary hyperparathyroidism (PHPT) is one of the most frequent endocrine disease in developed countries. It mainly occurs as sporadic cases (about 90-95% of cases), while only the remaining 5-10% is represented by familial inherited parathyroid disorders due to causative mutations in specific target genes. Clinical variability among the different familial parathyroid syndromes is generally linked to the specific mutated gene and it can predispose subjects to different manifestations of parathyroid pathology, various degrees of PHPT severity, persistence and/or after-surgery recurrences. Genetic tests is helpful in differential diagnosis favouring the recognition of the specific familial PHPT syndrome and, subsequently, in planning the most suitable surgical procedures and/or pharmacological interventions. Moreover, genetic test is important to recognise mutation carriers, within PHPT familial forms, even before the appearance of biochemical and/or clinical symptoms. This review resumes general concepts about genetic diagnosis of PHPT in familial hereditary syndromes, specifically describing why, when, and which genetic screenings should be performed in every specific PHPT-associated parathyroid disease.

Neuroendocrine Tumors in the Stomach, Duodenum, and Pancreas Accompanied by Novel MEN1 Gene Mutation

Multiple endocrine neoplasia type 1 (MEN1) syndrome is a relatively rare disease, characterized by the occurrence of multiple endocrine tumors in the parathyroid and pituitary glands as well as the pancreas. Here, we report a case of MEN1 with neuroendocrine tumors (NETs) in the stomach, duodenum, and pancreas. A 53-year-old man visited our hospital to manage gastric NET. Five years prior to his visit, he had undergone surgery for incidental meningioma. His brother had pancreatic nodules and a history of surgery for adrenal adenoma. His brother's daughter also had pancreatic nodules, but had not undergone surgery. The lesion was treated by endoscopic submucosal dissection and diagnosed as a grade 1 NET. Another small NET was detected in the second duodenal portion, resected by endoscopic submucosal dissection, which was also diagnosed as a grade 1 NET. During evaluation, three nodules were detected in the pancreas, and no evidence of pituitary, parathyroid tumors, or metastasis was observed. After surgery, the pancreatic lesions were diagnosed as NETs, with the same immunohistochemical patterns as those of the stomach and duodenum. Genetic testing was performed, and a heterozygous mutation was detected in the MEN1 gene, which is located on 11q13.

Epigenetic pathway inhibitors represent potential drugs for treating pancreatic and bronchial neuroendocrine tumors

Cancer is associated with alterations in epigenetic mechanisms such as histone modifications and methylation of DNA, and inhibitors targeting epigenetic mechanisms represent a novel class of anti-cancer drugs. Neuroendocrine tumors (NETs) of the pancreas (PNETs) and bronchus (BNETs), which may have 5-year survivals of <50% and as low as 5%, respectively, represent targets for such drugs, as >40% of PNETs and ~35% of BNETs have mutations of the multiple endocrine neoplasia type 1 (MEN1) gene, which encodes menin that modifies histones by interacting with histone methyltransferases. We assessed 9 inhibitors of epigenetic pathways, for their effects on proliferation, by CellTiter Blue assay, and apoptosis, by CaspaseGlo assay, using 1 PNET and 2 BNET cell lines. Two inhibitors, referred to as (+)-JQ1 (JQ1) and PFI-1, targeting the bromo and extra terminal (BET) protein family which bind acetylated histone residues, were most effective in decreasing proliferation (by 40-85%, P<0.001) and increasing apoptosis (by 2-3.6 fold, P<0.001) in all 3 NET cell lines. The anti-proliferative effects of JQ1 and PFI-1 remained present for at least 48 hours after removal of the compound. JQ1, but not PFI-1, had cell cycle effects, assessed by propidium iodide staining and flow cytometry, resulting in increased and decreased proportions of NET cells in G1, and S and G2 phases, respectively. RNA Sequencing analysis revealed that these JQ1 effects were associated with increased histone 2B expression, and likely mediated through altered activity of bromodomain-containing (Brd) proteins. Assessment of JQ1 in vivo, using a pancreatic beta cell-specific conditional Men1 knockout mouse model that develops PNETs, revealed that JQ1 significantly reduced proliferation (by ~50%, P<0.0005), assessed by bromodeoxyuridine incorporation, and increased apoptosis (by ~3 fold, P<0.0005), assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling, of PNETs. Thus, our studies demonstrate that BET protein inhibitors may provide new treatments for NETs.

Novel association of MEN1 gene mutations with parathyroid carcinoma

Inactivating mutations of the multiple endocrine neoplasia 1 (MEN1) gene cause MEN1 syndrome, characterized by primary hyperparathyroidism (pHPT), and parathyroid and gastro-entero-pancreatic pituitary tumors. At present, only 14 cases of malignant parathyroid tumor have been associated with the syndrome, with 6 cases carrying an inactivating mutation of the MEN1 gene. The present study presents the case of a 48-year-old female who presented with multigland pHPT and multiple pancreatic lesions. The patient underwent surgery several times for the excision of parathyroid hyperplasia, carcinoma and adenoma. The MEN1 gene was screened, revealing three variants (in cis) at the intron/exon 3 boundary (IVS2-3G>C, c.497A>T and c.499G>T) detected on the DNA of the proband, not shared by her relatives. RNA sequencing revealed that the IVS2-3C>G variant caused the skipping of the exon 3. Therefore, the present study reports on a novel rare association of MEN1 syndrome and parathyroid carcinoma. The reported splicing mutation was previously identified in subjects who always developed malignant lesions; thus, a possible genotype-phenotype association may be considered.

A MEN1 pancreatic neuroendocrine tumour mouse model under temporal control

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by occurrence of parathyroid tumours and neuroendocrine tumours (NETs) of the pancreatic islets and anterior pituitary. The MEN1 gene, encoding menin, is a tumour suppressor, but its precise role in initiating in vivo tumourigenesis remains to be elucidated. The availability of a temporally controlled conditional MEN1 mouse model would greatly facilitate the study of such early tumourigenic events, and overcome the limitations of other MEN1 knockout models, in which menin is lost from conception or tumour development occurs asynchronously. To generate a temporally controlled conditional mouse model, we crossbred mice with the MEN1 gene floxed by LoxP sites (Men1L/L ), and mice expressing tamoxifen-inducible Cre recombinase under the control of the rat insulin promoter (RIP2-CreER), to establish a pancreatic β-cell-specific NET model under temporal control (Men1L/L /RIP2-CreER). Men1L/L /RIP2-CreER mice aged ~3 months were given tamoxifen in the diet for 5 days, and pancreata harvested 2-2.5, 2.9-3.5 and 4.5-5.5 months later. Control mice did not express Cre and did not receive tamoxifen. Immunostaining of pancreata from tamoxifen-treated Men1L/L /RIP2-CreER mice, compared to control mice, showed at all ages: loss of menin in all islets; increased islet area (>4.2-fold); increased proliferation of insulin immunostaining β-cells (>2.3-fold) and decreased proliferation of glucagon immunostaining α-cells (>1.7-fold). There were no gender and apoptotic or proliferation differences, and extra-pancreatic tumours were not detected. Thus, we have established a mouse model (Men1L/L /RIP2-CreER) to study early events in the development of pancreatic β-cell NETs.

Surgical approaches in hereditary endocrine tumors

Endocrine tumors of thyroid, adrenal and parathyroid glands may be due to germline and inheritable mutations in 5-30% of patients. Medullary Thyroid Carcinoma, Pheochromocytoma, Paraganglioma, and Familial Primary Hyperparathyroidism are the most frequent entity. Hereditary endocrine tumors usually have a suggestive familial history; they occur earlier than sporadic variants, are multifocal, and have increased recurrence rates. They may be present as isolated variant or associated to other neoplasms in a syndromic setting. Genetic diagnosis should be preferably available before surgery because specific and targeted operative management are needed to achieve the best chance of cure. This review was aimed to discuss the surgical approaches for some of the most frequent hereditary endocrine tumors of thyroid, adrenal and parathyroid glands, focusing on medullary thyroid carcinoma, Pheochromocytoma, Paraganglioma and hereditary primary hyperparathyroidism (pHPT). Hereditary Medullary Thyroid Carcinoma is caused by RET mutations, and may be associated to Pheochromocytomas in MEN 2 setting. Total thyroidectomy and at least central neck nodal dissection is required. The availability of genetic screening allows prophylactic or early surgery in asymptomatic patients, with subsequent definitive cure. Hereditary Pheochromocytomas may be present in several syndromes (MEN 2, VHL, NF1, Paraganglioma/Pheochromocytoma syndrome); it may involve both adrenals; in these cases, a cortical sparing adrenalectomy should be performed to avoid permanent hypocorticosurrenalism. Hereditary Primary Hyperparathyroidism may frequently occur associated to MEN 1, MEN 2A, MEN 4, Hyperparathyroidism-Jaw Tumor Syndrome; it may involve all the parathyroid glands, requiring subtotal parathyroidectomy or total parathyroidectomy plus autotransplantation. In some cases, a selective parathyroidectomy might be performed.

Radiological surveillance in multiple endocrine neoplasia type 1: a double-edged sword?

CONTEXT

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary condition characterised by the predisposition to hyperplasia/tumours of endocrine glands. MEN1-related disease, moreover, malignancy related to MEN1, is increasingly responsible for death in up to two-thirds of patients. Although patients undergo radiological and biochemical surveillance, current recommendations for radiological monitoring are based on non-prospective data with little consensus or evidence demonstrating improved outcome from this approach. Here, we sought to determine whether cumulative radiation exposure as part of the recommended radiological screening programme posed a distinct risk in a cohort of patients with MEN1.

PATIENTS AND STUDY DESIGN

A retrospective review of 43 patients with MEN1 attending our institution between 2007 and 2015 was performed. Demographic and clinical information including phenotype was obtained for all patients. We also obtained details regarding all radiological procedures performed as part of MEN1 surveillance or disease localisation. An estimated effective radiation dose (ED) for each individual patient was calculated.

RESULTS

The mean ED for the total patient cohort was 121 mSv, and the estimated mean lifetime risk of cancer secondary to radiation exposure was 0.49%. Patients with malignant neuroendocrine tumours (NETS) had significantly higher ED levels compared to patients without metastatic disease (P < 0.0022).

CONCLUSIONS

In MEN1, radiological surveillance is associated with clinically significant exposure to ionising radiation. In patients with MEN1, multi-modality imaging strategies designed to minimise this exposure should be considered.

EXPRESSION OF MENIN IN THE HUMAN THYROID GLAND

INTRODUCTION

The expression of menin in the thyroid gland has long been debated. Animal models with targeted inactivation of menin in the thyroid gland have shown that its inactivation might play a role in the progression to a more aggressive type of cancer. Human studies are conflicting, some have identified mutations in the MEN1 gene in a sub-type of oncocytic thyroid carcinomas, while others have not identified a higher prevalence of thyroid cancer in MEN1 patients.

OBJECTIVE

To analyze the immunohistochemical expression of menin in different types of thyroid carcinomas.

MATERIALS AND METHODS

48 thyroid tumours (12 papillary thyroid carcinomas (PTC), 6 anaplastic thyroid carcinomas (ATC), 12 poorly differentiated thyroid carcinomas (PDTC), 5 medullary thyroid carcinomas (MTC), 5 oncocytic follicular carcinomas (OC), 3 oncocytic adenomas (OA) and 5 goiters (G)) were tested for nuclear expression of menin using an anti-menin antibody. The expression was considered positive, negative or decreased.

RESULTS

The expression of menin was positive, identical to normal tissue, in 39 cases (81.25%). The expression was decreased (n=8) or absent (n=1) in 9 tumours (18.75% - 2 PTC, 5 PDTC, 2 OC) accounting for 42% (5/12) of the PDTC and 40% (2/5) of the OC.

CONCLUSIONS

Our results show that the expression of menin is generally preserved in human thyroid carcinomas, but it can be decreased or absent in certain types of thyroid cancer. Further molecular studies are needed to evaluate to potential of menin protein in tumorigenesis.

Gastro-entero-pancreatic neuroendocrine tumors in multiple endocrine neoplasia type 1: a therapy update

Gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs) are the second most common tumors in multiple endocrine neoplasia type 1 (MEN1), mainly occurring in pancreatic islets and duodenum, usually as multiple tumors. They can manifest as both nonfunctioning and functioning tumors. Currently, surgical removal of GEP-NETs in MEN1 represents the gold standard curative approach. Conventional medical therapies for sporadic GEP-NETs showed to be effective also in a percentage of MEN1 patients. Innovative medical therapies, that have demonstrated to be effective on sporadic GEP-NETs, still need to be evaluated on MEN1 patients in prospective clinical trials and long-term follow-up. This review resumes current knowledge of MEN1 GEP-NETs, discussing surgical and medical approaches, genetic and molecular bases of tumorigenesis, and presenting novel possible drug therapies.

Complicated Case Presentation: Management of Pancreatic Neuroendocrine Tumors in Multiple Endocrine Neoplasia Type 1

Multiple endocrine neoplasia type 1 (MEN1) is an inherited predisposition to tumors of the parathyroid glands, anterior pituitary, and pancreatic islet cells. In this review, we discuss the clinical case of a 45-year-old woman with MEN1 that was presented at the 2015 North American Neuroendocrine Tumor Society Symposium. In our review of this patient's complicated clinical course and subsequent operative management, we highlight controversies in the diagnosis and management of pancreatic neuroendocrine tumors in MEN1. In particular, this case illustrates the lack of consensus regarding the optimal biochemical and radiologic screening for pancreatic neuroendocrine tumors and absence of guidelines about the appropriate surgical approach for treatment. We review these controversies and discuss possible approaches to management.

Sporadic pituitary adenomas: the role of germline mutations and recommendations for genetic screening

Although most pituitary adenomas occur sporadically, these common tumors can present in a familial setting in approximately 5% of cases. Germline mutations in several genes with autosomal dominant (AIP, MEN1, CDKN1B, PRKAR1A, SDHx) or X-linked dominant (GPR101) inheritance are causative of familial pituitary adenomas. Due to variable disease penetrance and occurrence of de novo mutations, some patients harboring germline mutations have no family history of pituitary adenomas (simplex cases). Areas covered: We summarize the recent findings on the role of germline mutations associated with familial pituitary adenomas in patients with sporadic clinical presentation. Expert commentary: Up to 12% of patients with young onset pituitary adenomas (age at diagnosis/onset ≤30 years) and up to 25% of simplex patients with gigantism carry mutations in the AIP gene, while most cases of X-linked acrogigantism (XLAG) due to GPR101 duplication are simplex female patients with very early disease onset (<5 years). With regard to the syndromes of multiple endocrine neoplasia (MEN), MEN1 mutations can be identified in a significant proportion of patients with childhood onset prolactinomas. Somatotroph and lactotroph adenomas are the most common pituitary adenomas associated with germline predisposing mutations. Genetic screening should be considered in patients with young onset pituitary adenomas.

Primary Hyperparathyroidism: Effects on Bone Health

Primary hyperparathyroidism (PHPT) is the most common cause of chronic hypercalcemia. With the advent of routine calcium screening, the classic presentation of renal and osseous symptoms has been largely replaced with mild, asymptomatic disease. In hypercalcemia caused by PHPT, serum parathyroid hormone levels are either high, or inappropriately normal. A single-gland adenoma is responsible for 80% of PHPT cases. Less frequent causes include 4-gland hyperplasia and parathyroid carcinoma. Diminished bone mineral density and nephrolithiasis are the major current clinical sequelae. Parathyroidectomy is the only definitive treatment for PHPT, and in experienced hands, cure rates approach 98%.

Loss of p27 expression is associated with MEN1 gene mutations in sporadic parathyroid adenomas

MEN1 is the main gene responsible for tumorigenesis of syndromic and sporadic primary hyperparathyroidism (PHPT). Germline mutations of the CDKN1B/p27^Kip gene have been associated with multiple endocrine tumors in rats and humans. To evaluate the involvement of the CDKN1B gene and its relationship with MEN1 in sporadic PHPT, we carried out sequencing and loss of heterozygosity analyses of the CDKN1B gene in 147 sporadic parathyroid adenomas. p27 immunohistochemistry and genetic screening of the MEN1 gene were performed in 50 cases. Three germline CDKN1B variants (c.-80C>T, c.-29_-26delAGAG, c.397C>A) were identified in 3/147 patients. Reduction of CDKN1B gene transcription rate was demonstrated in vitro for the novel c.-80C>T and the c.-29_-26delAGAG variants. Loss of p27 expression was detected in the tumor carrying the c.-29_-26delAGAG variant. Two tumors carrying the CDKN1B variants also harbored a MEN1 mutation. Fifty-four percent of 50 CDKN1B mutation-negative tumors had a reduction of p27 nuclear staining. Somatic MEN1 mutations, identified in 15/50 samples, significantly segregated in tumors negative for nuclear and cytoplasmic p27 staining. The germline nature of the CDKN1B mutations suggests that they might predispose to PHPT. The lack of somatic CDKN1B mutations in our samples points to a rare involvement in parathyroid adenomas, despite the frequent loss of nuclear p27 expression. MEN1 biallelic inactivation seems to be directly related to down-regulation of p27 expression through the inhibition of CDKN1B gene transcription.

The genetic background of acromegaly

Acromegaly is caused by a somatotropinoma in the vast majority of the cases. These are monoclonal tumors that can occur sporadically or rarely in a familial setting. In the last few years, novel familial syndromes have been described and recent studies explored the landscape of somatic mutations in sporadic somatotropinomas. This short review concentrates on the current knowledge of the genetic basis of both familial and sporadic acromegaly.

Genetics of multiple endocrine neoplasia type 1 syndrome: what's new and what's old

Despite its identification in 1997, the functions of the MEN1 gene-the main gene underlying multiple endocrine neoplasia type 1 syndrome-are not yet fully understood. In addition, unlike the RET-MEN2 causative gene-no hot-spot mutational areas or genotype-phenotype correlations have been identified. More than 1,300 MEN1 gene mutations have been reported and are mostly "private" (family specific). Even when mutations are shared at an intra- or inter-familial level, the spectrum of clinical presentation is highly variable, even in identical twins. Despite these inherent limitations for genetic counseling, identifying MEN1 mutations in individual carriers offers them the opportunity to have lifelong clinical surveillance schemes aimed at revealing MEN1-associated tumors and lesions, dictates the timing and scope of surgical procedures, and facilitates specific mutation analysis of relatives to define presymptomatic carriers.

Challenging Differential Diagnosis of Hypergastremia and Hyperglucagonemia with Chronic Renal Failure: Report of a Case with Multiple Endocrine Neoplasia Type 1

A 53-year-old woman developed end-stage renal failure during a 15-year clinical course of primary hyperparathyroidism and was referred to our hospital for evaluation of suspected multiple endocrine neoplasia type 1 (MEN1). Genetic testing revealed a novel deletion mutation at codon 467 in exon 10 of the MEN1 gene. Systemic and selective arterial calcium injection (SACI) testing revealed hyperglucagonemia and hypergastrinemia with positive gastrin responses. A pathological examination revealed glucagonoma and a lymph node gastrinoma. The findings in this case indicate the importance of early diagnosis of MEN1 and demonstrate the utility of systemic and SACI testing in renal failure cases.

Genetics of parathyroid tumours

Primary hyperparathyroidism (PHPT), due to parathyroid tumours, may occur as part of a complex syndrome or as an isolated (nonsyndromic) disorder, and both forms can occur as familial (i.e. hereditary) or nonfamilial (i.e. sporadic) disease. Syndromic PHPT includes multiple endocrine neoplasia (MEN) types 1 to 4 (MEN1 to MEN4) and the hyperparathyroidism-jaw tumour (HPT-JT) syndrome. Syndromic and hereditary PHPT are often associated with multiple parathyroid tumours, in contrast to sporadic PHPT, in which single parathyroid adenomas are more common. In addition, parathyroid carcinomas may occur in ~15% of patients with the HPT-JT syndrome. MEN1 is caused by abnormalities of the MEN1 gene which encodes a tumour suppressor; MEN2 and MEN3 are due to mutations of the rearranged during transfection (RET) proto-oncogene, which encodes a tyrosine kinase receptor; MEN4 is due to mutations of a cyclin-dependent kinase inhibitor (CDNK1B); and HPT-JT is due to mutations of cell division cycle 73 (CDC73), which encodes parafibromin. Nonsyndromic PHPT, which may be hereditary and referred to as familial isolated hyperparathyroidism, may also be due to MEN1, CDC73 or calcium-sensing receptor (CASR) mutations. In addition, ~10% of patients presenting below the age of 45 years with nonsyndromic, sporadic PHPT may have MEN1, CDC73 or CASR mutations, and overall more than 10% of patients with PHPT will have a mutation in one of 11 genes. Genetic testing is available and of value in the clinical setting, as it helps in making the correct diagnosis and planning the management of these complex disorders associated with parathyroid tumours.

MEN1 redefined, a clinical comparison of mutation-positive and mutation-negative patients

BACKGROUND

Multiple Endocrine Neoplasia type 1 (MEN1) is diagnosed when two out of the three primary MEN1-associated endocrine tumors occur in a patient. Up to 10-30 % of those patients have no mutation in the MEN1 gene. It is unclear if the phenotype and course of the disease of mutation-negative patients is comparable with mutation-positive patients and if these patients have true MEN1. The present study aims to describe and compare the clinical course of MEN1 mutation-negative patients with two out of the three main MEN1 manifestations and mutation-positive patients during long-term follow-up.

METHODS

This is a cohort study performed using the Dutch MEN1 database, including > 90 % of the Dutch MEN1 population.

RESULTS

A total of 293 (90.7 %) mutation-positive and 30 (9.3 %) mutation-negative MEN1 patients were included. Median age of developing the first main MEN1 manifestation was higher in mutation-negative patients (46 vs. 33 years) (P = 0.007). Mutation-negative patients did not develop a third main MEN1 manifestation in the course of follow-up compared to 48.3 % of mutation-positive patients (P < 0.001). Median survival in mutation-positive patients was estimated at 73.0 years (95 % CI, 69.5-76.5) compared to 87.0 years (95 % CI not available) in mutation-negative patients (P = 0.001).

CONCLUSIONS

Mutation-positive and mutation-negative MEN1 patients have a different phenotype and clinical course. Mutation-negative patients develop MEN1 manifestations at higher age and have a life expectancy comparable with the general population. The apparent differences in clinical course suggest that MEN1 mutation-negative patients do not have true MEN1, but another MEN1-like syndrome or sporadic co-incidence of two neuro-endocrine tumors.