The MEN1 gene and associated diseases: an update

Genetic basis of familial isolated hyperparathyroidism: a case series and a narrative review of the literature

Primary hyperparathyroidism is a heterogeneous clinical entity. In the clinical setting, the diagnosis and management of familial isolated hyperparathyroidism (FIHP) and other familial hyperparathyroidism (FHPT) forms continue to rely on clinical, laboratory, and histological findings, with careful examination of the family. In this article, we report a case series of FIHP in a four-generation Greek family, with no identifiable gene mutations. Clinical approach and long-term follow-up are discussed and a narrative review of the genetic basis of this entity has been performed.

Case 200: Gastric enterochromaffinlike cell tumors in a patient with type 1 multiple endocrine neoplasia

History A 55-year-old man presented with chronic epigastric pain lasting for about 1 year and without fever or vomiting. The abdomen was soft and tender at physical examination. Laboratory tests revealed unremarkable liver function, normal hemoglobin level, and normal amylase level. White blood cell count was normal, and there was no inflammatory syndrome. The patient's medical history included pancreatic gastrinoma resected by means of left pancreatectomy 31 years before, hyperparathyroidism treated with subtotal parathyroidectomy 24 years before, and a slowly growing lung mass known for 9 years. Esophagogastroduodenoscopy was performed because of a suspected gastroduodenal ulcer. The results showed numerous small (<10 mm) gastric and duodenal ulcers and multiple 10-15-mm polypoid gastric masses. Contrast material-enhanced dual-phase multidetector row computed tomography (CT) of the chest and abdomen was performed with a 64-section CT scanner (LightSpeed VCT; GE Healthcare, Milwaukee, Wis). Technical parameters for CT were as follows: pitch, 0.98; section thickness and reconstruction interval, 1.25 mm; 120 kVp; and variable milliamperage determined by x-, y-, and z-axis dose modulation. After an unenhanced abdominal scan, iobitridol, a nonionic iodinated contrast agent containing 350 mg of iodine per milliliter (Xenetix 350; Guerbet, Aulnay-sousbois, France), was administered intravenously through a 16-18-gauge catheter. A 120-mL dose of the contrast agent was injected via an antecubital vein at a rate of 4 mL/sec. No oral contrast medium was administered. After preliminary unenhanced abdominal scanning, arterial and portal venous phase acquisitions were obtained 45 and 80 seconds after initiation of contrast medium injection.

MEN1 intragenic deletions may represent the most prevalent somatic event in sporadic primary hyperparathyroidism

OBJECTIVE

Primary hyperparathyroidism (pHPT) is characterised by an inappropriate over production of parathyroid hormone and it is the most frequent pathological condition of the parathyroid glands. A minority of the cases belong to familial forms, but most of them are sporadic. The genetic alterations underlying the sporadic forms of pHPT remain poorly understood. The main goal of our study is to perform the molecular characterisation of a series of sporadic pHPT cases.

DESIGN AND METHODS

We have studied matched blood and tumour from 24 patients with pHPT, who went to a medical appointment in Hospital Pedro Hispano. Informed consent was obtained from all individuals. The MEN1, RET and CDKN1B molecular study was carried out in the germline DNA by PCR/SSCP and direct sequencing. Parathyroid tumours were further analysed by the same methods for MEN1, CDKN1B and CTNNB1 genetic alterations. The multiplex ligation-dependent probe amplification technique enabled the evaluation of MEN1 gene deletions. Protein expression for menin, cyclin D1, parafibromin, p27(Kip1), β-catenin and Ki-67 was conducted by immunohistochemistry.

RESULTS

The study of parathyroid tumours detected two somatic MEN1 mutations (c.249_252delGTCT and c.115_163del49bp) and revealed the presence of MEN1 intragenic deletions in 54% (13/24) of the tumours. In RET and CDKN1B genes only previously described, non-pathogenic variants were found. Cyclin D1 protein was overexpressed in 13% (3/24) of tumours.

CONCLUSIONS

These results suggest that MEN1 alterations, remarkably intragenic deletions, may represent the most prevalent genetic alteration in sporadic parathyroid tumours.

The current strategy for managing pancreatic neuroendocrine tumors in multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is an inherited autosomal dominant disease presenting with pancreatic neuroendocrine tumors (pNETs), parathyroid tumors, or pituitary tumors. Using the PubMed database, we reviewed the literature on information regarding the proper diagnosis and treatment of MEN1-associated pNET. Many cases of MEN1-associated pNET are functioning pNETs. Gastrinomas and insulinomas tend to occur frequently in the duodenum and pancreas, respectively. In addition to diagnostic imaging, the selective arterial secretagogue injection test (SASI test) is useful for localizing functioning pNET. The standard treatment is surgical resection. However, in the case of a functioning pNET, the tumor should first be accurately located using the SASI test before an appropriate surgical method is selected. In cases of a MEN1-associated non-functioning pNET that exceeds 2 cm in diameter, the incidence of distant metastasis is significantly increased, and surgery is recommended. In cases of unresectable pNET, a somatostatin analog has been shown to demonstrate antitumor effects and is considered to be a promising treatment. In addition, molecular-targeted drugs have recently been found to be effective in phase III clinical trials.

Correlation of mutant menin stability with clinical expression of multiple endocrine neoplasia type 1 and its incomplete forms

Germline mutations of the tumor suppressor gene MEN1 are found not only in typical multiple endocrine neoplasia type 1 (MEN1) but also in its incomplete forms such as familial isolated hyperparathyroidism (FIHP) and apparently sporadic parathyroid tumor (ASPT). No definitive genotype-phenotype correlation has been established between these clinical forms and MEN1 gene mutations. We previously demonstrated that mutant menin proteins associated with MEN1 are rapidly degraded by the ubiquitin-proteasome pathway. To examine whether the intracellular stability of mutant menin is correlated with clinical phenotypes, we developed a method of evaluating menin stability and examined 20 mutants associated with typical MEN1 (17 missense, two in-frame deletion, one nonsense) and 21 mutants associated with FIHP or ASPT (19 missense, two in-frame deletion). All tested mutants associated with typical MEN1 showed reduced stability. Some missense and in-frame deletion mutants (G28A, R171W, T197I, E255K, E274A, Y353del and E366D) associated with FIHP or ASPT were almost as stable as or only slightly less stable than wild-type menin, while others were as unstable as those associated with typical MEN1. Some stable mutants exhibited substantial biological activities when tested by JunD-dependent transactivation assay. These findings suggest that certain missense and in-frame mutations are fairly stable and retain intrinsic biological activity, and might be specifically associated with incomplete clinical phenotypes. The menin stability test will provide useful information for the management of patients carrying germline MEN1 mutations especially when they have missense or in-frame variants of ambiguous clinical significance.

MEN1 gene and its mutations: basic and clinical implications

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

Geographical analysis of thyroid cancer in young people from northern England: evidence for a sustained excess in females in Cumbria

A previous study found a thyroid cancer excess in Cumbria following the Chernobyl explosion, but did not analyse sex-specific effects. This study examines sex differences in the incidence of thyroid cancer. Ninety-five primary thyroid carcinomas (69 females, 26 males) diagnosed in those aged 0-24 during 1968-2005 were identified from the Northern Region Young Persons' Malignant Disease Registry. Age-standardised incidence rates (ASRs), rate ratios (RRs) and 95% confidence intervals (CIs) were calculated. For males, the ASR was 0.6 per million person-years during the pre-Chernobyl period (1968-1986), and was 1.8 per million person-years during the post-Chernobyl period (1987-2005). For females, the ASR was 2.4 pre-Chernobyl and was 3.9 post-Chernobyl. The previously noted excess in Cumbria was entirely confined to females (Cumbrian females: RR for post-Chernobyl compared with pre-Chernobyl=10.8; 95% CI: 1.4-85.3). These findings may be consistent with sex-specific differences in susceptibility to an environmental exposure, such as fallout from the Chernobyl nuclear accident.

Menin regulates endocrine diseases by controlling histone modification and gene transcription

Multiple endocrine neoplasia type 1 (MEN1), a human familial tumor syndrome, results from mutations in the Men1 gene. Although much progress has been made in demonstrating the definitive role for menin in suppressing tumorigenesis in endocrine organs, the molecular pathways responsible for menin action in normal tissues and tumors remain poorly defined. Here, we review the recent progress on the molecular functions of menin in controlling cell proliferation, apoptosis, and DNA repair. The majority of these functions are largely executed by menin-mediated influencing of histone modifications and chromatin structure. These findings lead to a new model of understanding menin's tumor-suppressing function, providing insights into understanding of how menin regulates cell proliferation and the development of endocrine tumors. The new knowledge could also be translated into new strategies to improve therapeutic interventions against MEN1 and other endocrine diseases including diabetes.

Clinical and molecular genetics of acromegaly: MEN1, Carney complex, McCune-Albright syndrome, familial acromegaly and genetic defects in sporadic tumors

Pituitary tumors are among the most common neoplasms in man; they account for approximately 15% of all primary intracranial lesions (Jagannathan et al., Neurosurg Focus, 19:E4, 2005). Although almost never malignant and rarely clinically expressed, pituitary tumors may cause significant morbidity in affected patients. First, given the critical location of the gland, large tumors may lead to mass effects, and, second, proliferation of hormone-secreting pituitary cells leads to endocrine syndromes. Acromegaly results from oversecretion of growth hormone (GH) by the proliferating somatotrophs. Despite the significant efforts made over the last decade, still little is known about the genetic causes of common pituitary tumors and even less is applied from this knowledge therapeutically. In this review, we present an update on the genetic syndromes associated with pituitary adenomas and discuss the related genetic defects. We next review findings on sporadic, non-genetic, pituitary tumors with an emphasis on pathways and animal models of pituitary disease. In conclusion, we attempt to present an overall, integrative approach to the human molecular genetics of both familiar and sporadic pituitary tumors.

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

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

Clinical testing for multiple endocrine neoplasia type 1 in a DNA diagnostic laboratory

PURPOSE

Based on results of diagnostic MEN1 testing, we have attempted to further define the mutational spectrum of the MEN1 gene and the clinical features most frequently associated with MEN1 mutations.

METHODS

Mutation testing was performed on blood samples by PCR amplification and sequencing of exons 2 to 10 of the MEN1 gene and the corresponding intron-exon junctions. Pedigree phenotypic information was obtained by written questionnaire.

RESULTS

Among 288 presumably unrelated pedigrees, 73 independent mutations were found in 89 families. Five mutations were found in 2 pedigrees, and 4 mutations were seen in more than 2 pedigrees. There were 17 nonsense mutations (23.3%), 2 in-frame deletions (2.7%), 18 frameshift-deletion mutations (24.7%), 10 frameshift-insertion or -duplication mutations (13.7%), 13 splice-site mutations (17.8%), and 13 presumptive missense mutations (17.8%). Thirty-nine of 56 pedigrees with parathyroid and pancreatic islet neoplasia tested positive, compared with 4/24 and 8/32 pedigrees affected with hyperparathyroidism or hyperparathyroidism and pituitary tumors. MEN1 mutations were found in 6/20 sporadic patients, all of whom had both parathyroid and pancreatic neoplasms. Of 14 mutation-negative sporadic patients, 10 exhibited hyperparathyroidism and pituitary tumors without islet cell neoplasia. Somatic mosaicism was detected in 1 sporadic patient.

CONCLUSION

Patients from pedigrees with hyperparathyroidism and pancreatic islet tumors are most likely to test positive for MEN1 mutations. Mutations are less often detected in patients from pedigrees with hyperparathyroidism alone or in combination with pituitary tumors without pancreatic islet neoplasia. Sporadic cases are less likely to test positive than familial cases, in part due to somatic mosaicism.

Menin missense mutants associated with multiple endocrine neoplasia type 1 are rapidly degraded via the ubiquitin-proteasome pathway

MEN1 is a tumor suppressor gene that is responsible for multiple endocrine neoplasia type 1 (MEN1) and that encodes a 610-amino-acid protein, called menin. While the majority of germ line mutations identified in MEN1 patients are frameshift and nonsense mutations resulting in truncation of the menin protein, various missense mutations have been identified whose effects on menin activity are unclear. For this study, we analyzed a series of menin proteins with single amino acid alterations and found that all of the MEN1-causing missense mutations tested led to greatly diminished levels of the affected proteins in comparison with wild-type and benign polymorphic menin protein levels. We demonstrate here that the reduced levels of the mutant proteins are due to rapid degradation via the ubiquitin-proteasome pathway. Furthermore, the mutants, but not wild-type menin, interact both with the molecular chaperone Hsp70 and with the Hsp70-associated ubiquitin ligase CHIP, and the overexpression of CHIP promotes the ubiquitination of the menin mutants in vivo. These findings reveal that MEN1-causing missense mutations lead to a loss of function of menin due to enhanced proteolytic degradation, which may be a common mechanism for inactivating tumor suppressor gene products in familial cancer.

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.

Multiple endocrine neoplasia type 1 (MEN1) germline mutations in familial isolated primary hyperparathyroidism

BACKGROUND

Familial isolated hyperparathyroidism (FIHP) is an autosomal dominant disorder characterized by uniglandular or multiglandular parathyroid tumours that occur in the absence of other endocrine tumours. The disorder may represent either an early stage of multiple endocrine neoplasia type 1 (MEN1), or an allelic variant of MEN1, or a distinct entity involving another locus. We have explored these possibilities in seven families in whom primary hyperparathyroidism occurred as the sole endocrinopathy.

METHODS

Seven FIHP families were ascertained and venous blood samples obtained from 35 members (17 affected and 18 unaffected) for DNA sequence analysis of the MEN1 gene. The mean (+/- SD) follow-up period in the 17 affected members was 15.06 (+/- 8.83) years.

RESULTS

Four heterozygous germline mutations of the MEN1 gene were identified. These consisted of two 4-bp intragenic deletions that would result in prematurely truncated proteins, and two missense (Asp153Val and Ala411Pro) mutations. Furthermore, analysis of parathyroid tumour DNA from one individual revealed a loss of the wild-type allele and retention of the mutant allele, consistent with Knudson's 'two-hit' model of hereditary cancer and a tumour suppressor role for MEN1 in FIHP.

CONCLUSIONS

Our results provide further support for FIHP being a distinct allelic variant of MEN1, and an analysis of the 16 mutations reported to date indicate that FIHP is associated with a higher frequency of missense MEN1 mutations.

Potential applications of molecular biology in neuroendocrine tumors

The impact of molecular biology procedures on neuroendocrine (NE) tumor biology is gradually evolving from purely academic and research studies to clinical applications. This review deals with applications of molecular techniques in neuroendocrine tumors, with special reference to their potential for diagnostic, prognostic, or therapeutic impact. Since the cloning of the genes involved in inherited endocrine tumor syndromes, molecular analysis of the responsible genetic alterations has become a routine diagnostic tool to select affected patients and their relatives, and also an interesting approach to investigate the pathogenesis of neuroendocrine tumors. Assessment of the clonal composition of endocrine tumors could be useful to differentiate hyperplastic versus either adenomatous or carcinomatous conditions, as well as to better understand the clonal relationship between different neoplastic populations in mixed tumors. In addition, molecular approaches allow high sensitivity both in defining the neuroendocrine phenotype in poorly differentiated tumors and in searching for micrometastasis during the follow up of patients with endocrine tumors. Finally, the detection of peptide hormone receptors (e.g., oxytocin and somatostatin receptors) and the development of potent synthetic analogs of such peptides, are opening promising applications in the diagnosis and therapy of endocrine tumors.

Menin, the multiple endocrine neoplasia type 1 gene product, exhibits GTP-hydrolyzing activity in the presence of the tumor metastasis suppressor nm23

MEN1, the gene responsible for multiple endocrine neoplasia type 1, is a tumor suppressor gene that encodes a protein called menin, of unknown function with no homology to any known protein. Here we demonstrate that menin interacts with a putative tumor metastasis suppressor nm23H1/nucleoside diphosphate (NDP) kinase A in mammalian cells. Given the roles of nm23 as a multi-functional protein, we searched for the possible function of menin. Menin has no effect on the known activities of nm23; that is, nucleoside diphosphate kinase, protein kinase, or GTPase-activating protein for Ras-related GTPase Rad. However, we found that menin hydrolyzes GTP to GDP efficiently in the presence of nm23, whereas nm23 or menin alone shows little or no detectable GTPase activity. Furthermore, menin contains sequence motifs similar to those found in all known GTPases or GTP-binding proteins and shows low affinity but specific binding to GTP/GDP. These results suggest that menin is an atypical GTPase stimulated by nm23.