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.     

Germline mutations of the MEN1 gene in Korean families with multiple endocrine neoplasia type 1 (MEN1) or MEN1-related disorders

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome characterized by the combined occurrence of tumours of the parathyroid glands, pancreatic islet cells and anterior pituitary gland. Mutation analysis of the MEN1 gene has enabled the genetic diagnosis of patients with MEN1. Two MEN1-related disorders - familial isolated hyperparathyroidism (FIHP) and familial pituitary adenoma - are considered to be variants of MEN1, or at least to be incompletely expressed variants. Germline mutations of the MEN1 gene have been reported in some with FIHP, but familial pituitary adenoma usually lacks the MEN1 mutation and has been described as a genetically distinct disorder. In this work, we investigated five Korean families with MEN1, one family with FIHP and one family with familial pituitary adenoma. Polymerase chain reaction (PCR)-based single-strand conformation polymorphism (PCR-SSCP) analysis, denaturing high-performance liquid chromatography (DHPLC) and sequencing were used to detect the MEN1 mutations. Screening of the genetic variations of the MEN1 gene revealed four germline mutations in five typical MEN1 families. All four germline mutations led to truncated proteins or a change in the amino acids of the functional domains. In this study, we identified three novel MEN1 germline mutations (969C >A, 973G >C and 1213C >T) and one previously reported mutation (200-201insAGCCC). The frequency of the MEN1 germline mutation in Korean MEN1 families (four of five; 80%) was similar to those reported previously. In accordance with previous studies, no MEN1 germline mutation was detected in two families with FIHP or familial pituitary adenoma.     

Familial disorders of parathyroid glands

The molecular mechanisms underlying familial parathyroid diseases continue to be elucidated. The mechanisms of familial parathyroid diseases are better understood than many sporadic parathyroid diseases. Familial parathyroid disease is associated with multiple endocrine neoplasia type 1 which is associated with MEN1 mutation, multiple endocrine neoplasia type 2A caused by RET mutation, and multiple endocrine neoplasia type 4 is caused with CDKN1B mutation. Sporadic parathyroid tumours are identified with mutations of MEN1 but generally not of RET. CDKN1B mutations are also identified in sporadic forms of primary hyperparathyroidism, although very rarely. Calcium sensing receptor gene mutations are involved in familial hyperparathyroidism and hypoparathyroidism, but are generally not identified in sporadic parathyroid tumours. However, the HPRT2 (CDC73) gene, which is mutated in hyperparathyroidism jaw-tumour syndrome and a subset of cases of familial isolated hyperparathyroidism, is frequently mutated in sporadic parathyroid carcinomas. Germline activating GCM2 mutations were recently found associated with a subset of familial isolated hyperparathyroidism. Parafibromin, a protein encoded by HPRT2, has been used in the diagnostic setting. The understanding and pathogenesis of parathyroid disease continues to evolve.     

Identification of five novel germline mutations of the MEN1 gene in Japanese multiple endocrine neoplasia type 1 (MEN1) families.

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by tumours of the parathyroid glands, the anterior pituitary, and endocrine pancreas. The MEN1 gene has recently been cloned and germline mutations have been identified in MEN1 patients in the United States, Canada, and Europe. We examined MEN1 gene mutations in MEN1 and MEN1 related cases in eight unrelated Japanese families. These families include five familial MEN1 (FMEN1), two sporadic MEN1 (SMEN1), and one familial hyperparathyroidism (FHP). Direct sequence analysis of the protein coding regions was carried out in all the probands. We identified six different heterozygous mutations in the coding region, of which five were novel, including one missense mutation (E45G) in both FMEN1 and SMEN1, three deletions (569del, 711del, and 1350del3) in FMEN1 and FHP, and two nonsense mutations (R29X and Y312X) in FMEN1 and SMEN1. Only one of these mutations (Y312X) has previously been reported. One proband with FMEN1 had no mutation in the entire exon sequence including the 5' and 3' untranslated regions. A restriction digestion analysis of 19 relatives from the five families showed a close correlation between the existence of the MEN1 gene mutation and disease onset. Four different polymorphisms, including two novel ones, were identified. These findings imply that a diversity of MEN1 gene mutations exists in Japanese MEN1 and MEN1 related disease, suggesting that analysis of the entire coding region of the MEN1 gene is required for genetic counselling in Japan.     

A report of a national mutation testing service for the MEN1 gene: clinical presentations and implications for mutation testing

Introduction: Mutation testing for the MEN1 gene is a useful method to diagnose and predict individuals who either have or will develop multiple endocrine neoplasia type 1 (MEN 1). Clinical selection criteria to identify patients who should be tested are needed, as mutation analysis is costly and time consuming. This study is a report of an Australian national mutation testing service for the MEN1 gene from referred patients with classical MEN 1 and various MEN 1-like conditions. Results: All 55 MEN1 mutation positive patients had a family history of hyperparathyroidism, had hyperparathyroidism with one other MEN1 related tumour, or had hyperparathyroidism with multiglandular hyperplasia at a young age. We found 42 separate mutations and six recurring mutations from unrelated families, and evidence for a founder effect in five families with the same mutation. Discussion: Our results indicate that mutations in genes other than MEN1 may cause familial isolated hyperparathyroidism and familial isolated pituitary tumours. Conclusions: We therefore suggest that routine germline MEN1 mutation testing of all cases of "classical" MEN1, familial hyperparathyroidism, and sporadic hyperparathyroidism with one other MEN1 related condition is justified by national testing services. We do not recommend routine sequencing of the promoter region between nucleotides 1234 and 1758 (Genbank accession no. {"type":"entrez-nucleotide","attrs":{"text":"U93237","term_id":"1945388","term_text":"U93237"}}U93237) as we could not detect any sequence variations within this region in any familial or sporadic cases of MEN1 related conditions lacking a MEN1 mutation. We also suggest that testing be considered for patients <30 years old with sporadic hyperparathyroidism and multigland hyperplasia.     

Complete genomic landscape of a recurring sporadic parathyroid carcinoma

Parathyroid carcinoma is a rare endocrine malignancy with an estimated incidence of less than 1 per million population. Excessive secretion of parathyroid hormone, extremely high serum calcium level, and the deleterious effects of hypercalcaemia are the clinical manifestations of the disease. Up to 60% of patients develop multiple disease recurrences and although long‐term survival is possible with palliative surgery, permanent remission is rarely achieved. Molecular drivers of sporadic parathyroid carcinoma have remained largely unknown. Previous studies, mostly based on familial cases of the disease, suggested potential roles for the tumour suppressor MEN1 and proto‐oncogene RET in benign parathyroid tumourigenesis, while the tumour suppressor HRPT2 and proto‐oncogene CCND1 may also act as drivers in parathyroid cancer. Here, we report the complete genomic analysis of a sporadic and recurring parathyroid carcinoma. Mutational landscapes of the primary and recurrent tumour specimens were analysed using high‐throughput sequencing technologies. Such molecular profiling allowed for identification of somatic mutations never previously identified in this malignancy. These included single nucleotide point mutations in well‐characterized cancer genes such as mTOR, MLL2, CDKN2C, and PIK3CA. Comparison of acquired mutations in patient‐matched primary and recurrent tumours revealed loss of PIK3CA activating mutation during the evolution of the tumour from the primary to the recurrence. Structural variations leading to gene fusions and regions of copy loss and gain were identified at a single‐base resolution. Loss of the short arm of chromosome 1, along with somatic missense and truncating mutations in CDKN2C and THRAP3, respectively, provides new evidence for the potential role of these genes as tumour suppressors in parathyroid cancer. The key somatic mutations identified in this study can serve as novel diagnostic markers as well as therapeutic targets. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Heritable forms of primary hyperparathyroidism: a current perspective

Primary hyperparathyroidism (PHPT) is one of the most common of all endocrine disorders encountered by the practising histopathologist. The vast majority of lesions are sporadic in nature, approximately 85% of which are parathyroid adenomas, while hyperplasia and carcinoma account for 10–15% and fewer than 1%, of cases, respectively. Heritable forms of PHPT are much less common and present challenges both to clinicians and pathologists, particularly when they are the presenting feature of an endocrine syndrome. In such instances, pathologists play a key role in alerting physicians to the possibility of an underlying heritable endocrine syndrome and the potential for extra‐endocrine manifestations. Therefore, a working knowledge of these disorders is essential for providing guidance to treating physicians. The aim of this update is to review the clinicopathological features, genetic bases and current management for patients with PHPT associated with multiple endocrine neoplasia (MEN) types 1, 2A and 4 and hyperparathyroidism‐jaw tumour (HPT‐JT) syndrome in the context of the 2017 World Health Organization (WHO) Classification of Tumours of the Endocrine Organs. Additionally, familial isolated hyperparathyroidism, familial hypocalciuric hypercalcaemia and neonatal severe hyperparathyroidism are discussed.     

Analysis of the MEN1 gene in sporadic pituitary adenomas

The MEN1 gene on chromosome 11q13 is mutated in patients afflicted with multiple endocrine neoplasia syndrome type 1 (MEN1). These patients develop endocrine tumours of the pancreas, the parathyroid, and the anterior pituitary. In order to determine the role of MEN1 in sporadic pituitary adenomas, 61 pituitary adenomas were analysed from patients without evidence of a familial tumour syndrome. Single strand conformation polymorphism (SSCP) analysis was performed for the entire coding sequence of MEN1. Fragments with aberrant migration patterns were sequenced bidirectionally. Only a single somatic mutation was detected in this series. In addition, several previously reported and three novel polymorphisms were observed. Loss of heterozygosity analysis with 12 polymorphic markers, however, identified 13 pituitary adenomas with allelic deletions on chromosome 11. Allelic losses occurred significantly more often in pituitary adenomas with hormone secretion than in non-functioning adenomas. These data suggest that MEN1 mutations are rare events in sporadic pituitary adenomas. However, the discrepancy of only 1/61 adenomas with MEN1 mutation but 13/61 (22 per cent) with allelic loss on chromosome 11 may suggest the presence of a yet unknown tumour suppressor gene, relevant to the pathogenesis of sporadic pituitary adenomas. Copyright © 1999 John Wiley & Sons, Ltd.     

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.     

Parathyroid carcinoma in familial hyperparathyroidism.

Two families with hereditary hyperparathyroidism are described. One member of each family developed a parathyroid carcinoma. In one case this recurred locally and metastasised. This patient showed hyperplasia of one of the three other parathyroid glands. It is possible that the different parathyroid lesions found in familial hyperparathyroidism may be the result of a progression from hyperplasia to formation of benign or malignant tumours. The remainiing hyperplastic glands may be suppressed by hypercalcaemia. There was no evidence of multiple endocrine neoplasia in either family. Three members of a first family had ichthyosis and both affected members of the second had tumours of the jaw, one of which was an ossifying fibroma, suggesting a possible association of these conditions with familial hyperparathyroidism.     

Familial hyperparathyroidism syndromes

Primary hyperparathyroidism is a common endocrine disorder and the most prevalent cause of hypercalcemia worldwide. While most cases are sporadic, 5–10% of cases are inherited as part of a familial syndrome: multiple endocrine neoplasia (MEN-1, MEN-2A, MEN-4), hyperparathyroidism jaw-tumor syndrome (HPT-JT), familial hypocalciuric hypercalcemia (FHH), neonatal severe hyperparathyroidism (NSHPT), autosomal dominant moderate hyperparathyroidism (ADMH), or familial isolated hyperparathyroidism (FIHPT). Recent developments in molecular pathology identified specific germline mutations (MEN1, RET, CDKIs, CDC73/HRPT2, CaSR, GNA11, AP2S1) implicated in their pathogenesis. In contrast to sporadic primary hyperparathyroidism which is usually caused by a solitary parathyroid adenoma, hereditary hyperparathyroidism tend to present with multiglandular parathyroid disease, with variable penetrance according to the genetic syndrome. As a result, the clinical severity of each familial condition varies tremendously, resulting in distinct prognosis and treatment strategies. With the advent of molecular testing, genetic subtyping has become an integral part of treatment decision making, requiring correlation with clinical and pathologic findings. This review provides an update on the current knowledge of hereditary hyperparathyroidism and its associated genetic syndromes.     

Germline mutations of the MEN1 gene in familial multiple endocrine neoplasia type 1 and related states

Familial multiple endocrine neoplasia type 1 (FMEN1) is an autosomal dominant trait characterized by tumors of the parathyroids, gastro- intestinal endocrine tissue, anterior pituitary and other tissues. We recently cloned the MEN1 gene and confirmed its identity by finding mutations in FMEN1. We have now extended our mutation analysis to 34 more unrelated FMEN1 probands and to two related states, sporadic MEN1 and familial hyperparathyroidism. There was a high prevalence of heterozygous germline MEN1 mutations in sporadic MEN1 (8/11 cases) and in FMEN1 (47/50 probands). One case of sporadic MEN1 was proven to be a new MEN1 mutation. Eight different mutations were observed more than once in FMEN1. Forty different mutations (32 FMEN1 and eight sporadic MEN1) were distributed across the MEN1 gene. Most predicted loss of function of the encoded menin protein, supporting the prediction that MEN1 is a tumor suppressor gene. No MEN1 germline mutation was found in five probands with familial hyperparathyroidism, suggesting that familial hyperparathyroidism often is caused by mutation in another gene or gene(s).      

Genetic testing in familial isolated hyperparathyroidism: unexpected results and their implications

Familial hyperparathyroidism is not uncommon in clinical endocrine practice. It encompasses a spectrum of disorders including multiple endocrine neoplasia types 1 (MEN1) and 2A, hyperparathyroidism-jaw tumour syndrome (HPT-JT), familial hypocalciuric hypercalcaemia (FHH), and familial isolated hyperparathyroidism (FIHP). Distinguishing among the five syndromes is often difficult but has profound implications for the management of patient and family. The availability of specific genetic testing for four of the syndromes has improved diagnostic accuracy and simplified family monitoring in many cases but its current cost and limited accessibility require rationalisation of its use. No gene has yet been associated exclusively with FIHP. FIHP phenotypes have been associated with mutant MEN1 and calcium-sensing receptor (CASR) genotypes and, very recently, with mutation in the newly identified HRPT2 gene. The relative proportions of these are not yet clear. We report results of MEN1, CASR, and HRPT2 genotyping of 22 unrelated subjects with FIHP phenotypes. We found 5 (23%) with MEN1 mutations, four (18%) with CASR mutations, and none with an HRPT2 mutation. All those with mutations had multiglandular hyperparathyroidism. Of the subjects with CASR mutations, none were of the typical FHH phenotype. These findings strongly favour a recommendation for MEN1 and CASR genotyping of patients with multiglandular FIHP, irrespective of urinary calcium excretion. However, it appears that HRPT2 genotyping should be reserved for cases in which other features of the HPT-JT phenotype have occurred in the kindred. Also apparent is the need for further investigation to identify additional genes associated with FIHP.     

Clinical spectrum of MEN2A in a large family caused by the infrequent RET mutation Cys609Phe

Mutations in RET proto‐oncogene cause multiple endocrine neoplasia 2A (MEN2A). Mutations in codons 609 and 611 are not frequent. We identified two MEN2A families with the Cys609Phe RET mutation, which turned out to be the same family. This mutation has been described a couple of times with no clinical details. We have characterized the clinical phenotype of this large kindred. A 54‐year‐old woman, with a medullary thyroid carcinoma (MTC), and a 33‐year‐old woman, who was operated on for an adrenal pheochromocytoma, were the index cases. 35 relatives were studied. Sixteen turned out to be carriers and 12 of them have been operated on. This family showed eight patients with C‐cell hyperplasia, six patients affected by MTC and two showing pheochromocytoma. A papillary thyroid carcinoma was also found, together with the MTC, in one of the carriers. The phenotype in this large kindred is clearly of MEN2A. In carriers presenting the Cys609Phe mutation, the timing of the presentation of the syndrome is highly unpredictable. Therefore, a strict follow up of MTC must be carried out because of risk, and pheochromocytoma should not be ignored. These results reinforce the scarce data observed on this particular mutation.     

Recent advances in the molecular pathology of hyperparathyroidism

Hyperparathyroidism represents a wide spectrum of parathyroid disorders from hyperplasia to adenoma and carcinoma. These disorders can be present as primary or secondary, and as sporadic or hereditary forms. Although the incidence of hyperparathyroidism has increased dramatically, the interpretation of the parathyroid pathology is still of considerable controversy and confusion. Over the past few years, multiple genetic abnormalities have been characterized in sporadic parathyroid tumors. A majority of secondary parathyroid hyperplasia have been shown to be of monoclonal origins by clonal analysis. The ret oncogene responsible for the pathogenesis of multiple endocrine neoplasia type 2 and multiple endocrine neoplasia (MEN) 1 gene for type 1 have been cloned in succession. Mutation of the calcium-sensing receptor gene has been identified to be thegenetic trigger of neonatal severe hyperparathyroidism and familial hypocalciuric hypercalcemia. HRPT 2 gene designated for the syndrome of hereditary hyperparathyroidism and jaw tumors has recently been localized on the 1q21-23, and linkage analysis has established the presence of familial hyperparathyroidism as a distinct entity. These advances provide new insights for understanding the molecular pathology of various types of hyperparathyroidisms and allow us a precise differentiation among them. Based on the results of our study and those reported in literature, this article reviews the recent advances in the molecular basis of various hyperparathyroidisms.     

Common ancestral mutations in the MEN1 gene is likely responsible for the prolactinoma variant of MEN1 (MEN1Burin) in four kindreds from Newfoundland

Familial multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder with affected individuals developing parathyroid, gastrointestinal (GI) endocrine, and anterior pituitary tumors. Four large kindreds from the Burin peninsula/Fortune Bay area of Newfoundland with prominent features of prolactinomas, carcinoids, and parathyroid tumors (referred to as MEN1_Burin) have been described, and they show linkage to 11q13, the same locus as that of MEN1. Haplotype analysis with 16 polymorphic markers now reveals that representative affected individuals from all four families share a common haplotype over a 2.5 Mb region. A nonsense mutation in the MEN1 gene has been found to be responsible for the disease in the affected members in all four of the MEN1_Burin families, providing convincing evidence of a common founder. Hum Mutat 11:264–269, 1998. Published 1998 Wiley-Liss, Inc.     

Multiple Endocrine Neoplasia Type 1 Presenting as Hypoglycemia due to Insulinoma

Multiple endocrine neoplasia (MEN) mutation is an autosomal dominant disorder characterized by the occurrence of parathyroid, pancreatic islet, and anterior pituitary tumors. The incidence of insulinoma in MEN is relatively uncommon, and there have been a few cases of MEN manifested with insulinoma as the first symptom in children. We experienced a 9-year-old girl having a familial MEN1 mutation. She complained of dizziness, occasional palpitation, weakness, hunger, sweating, and generalized tonic-clonic seizure that lasted for 5 minutes early in the morning. At first, she was only diagnosed with insulinoma by abdominal magnetic resonance images of a 1.3 x 1.5 cm mass in the pancreas and high insulin levels in blood of the hepatic vein, but after her father was diagnosed with MEN1. We found she had familial MEN1 mutation, and she recovered hyperinsulinemic hypoglycemia after enucleation of the mass. Therefore, the early genetic identification of MEN1 mutation is considerable for children with at least one manifestation.     

Mutation analysis of the MEN1 gene in Belgian patients with multiple endocrine neoplasia type 1 and related diseases

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by tumors in parathyroids, enteropancreatic endocrine tissues, anterior pituitary, and other tissues. The gene for MEN1 has recently been cloned and shown to code for a 610‐amino acid protein of enigmatic function which probably acts as a tumor suppressor. Several mutations causing the MEN1 phenotype have been recently identified. In order to determine the spectrum of MEN1 gene mutations in a sample of 25 Belgian patients, we have systematically screened the 10 exons and adjacent sequences of the MEN1 gene by means of an automatic sequencing protocol. Twelve different mutations were identified including nonsense, frameshift, splicing, and missense mutations. Two of these mutations (D172Y and 357del4) occurred more than once. A missense mutation was also found in a kindred with familial hyperparathyroidism. We observed no significant correlation between the nature or position of mutation and the clinical status. We have also detected 6 intragenic polymorphisms and DNA sequence variants and have analyzed their frequencies in our population. Hum Mutat 13:54–60, 1999. © 1999 Wiley‐Liss, Inc.     

Parathyroid gastrin and parathormone-producing tumour in the Zollinger-Ellison syndrome of MEN 1 origin

Summary A case of Zollinger-EUison syndrome of multiple endocrine neoplasia type 1 (MEN 1) origin with hyperparathyroidism and with a rise in serum gastrin due to an unusual parathyroid gastrinoma has been investigated. The patient had multiple endocrine tumours (pituitary and parathyroid), but no evidence of pancreatic or duodenal gastrin-producing neoplasm. Radio-immunoassay, immunohistochemistry and electron microscopy showed gastrin in one parathyroid adenoma. These findings, together with a decrease of gastrinaemia after parathyroidectomy suggest that true gastrin was produced by parathyroid tumour cells and that they themselves may be the origin of the hypergastrinaemia. Our ultrastructural investigation extends these observations and the results are discussed.