MEN1 Gene Mutation Research Articles

9123 Screening of lung carcinoids for somatic mutations of MEN1 gene

9123 Screening of lung carcinoids for somatic mutations of MEN1 gene

Multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal-dominant inherited tumor syndrome characterized by hyperplasia and/or tumors in the parathyroid glands, the pancreatic islets, the anterior pituitary and adrenal glands, as well as neuroendocrine tumors in the thymus, lungs and stomach, and tumors in nonendocrine tissues. In 1997, the responsible MEN1 gene was identified as a tumor-suppressor gene and its product was named menin. In this review, guidelines for early diagnosis, including MEN1 gene mutation analysis, and treatment, including periodic clinical monitoring, have been formulated, enabling improvement of life expectancy and quality of life. Identification of menin-interacting proteins has provided new insights into the function of menin, notably involving regulation of gene transcription related to proliferation and apoptosis, genome stability and DNA repair, and endocrine/metabolic homeostasis. In the near future, target-directed intervention may prevent or delay the onset of MEN 1-related tumors.

Multiple Endocrine Neoplasia Type I Variants and Phenocopies: More than a Nosological Issue?

Multiple endocrine neoplasia type I (MEN1) is a rare hereditary tumor syndrome, transmitted as an autosomal dominant trait, caused by mutations in the MEN1 gene encoding menin, a 610-amino-acid tumor suppressor protein, widely expressed in both endocrine and nonendocrine tissues (1). In fact, MEN1 patients display a large spectrum of benign and malignant endocrine lesions, including hyperparathyroidism as well as pituitary and enteropancreatic tumors, and also nonendocrine tumors (e.g. lipomas, skin tumors, and meningiomas). Germline heterozygous loss-of-function mutations are generally found in MEN1 patients, and additional somatic loss of heterozygosity in the MEN1 locus leads to the lack of both MEN1 alleles in tumors, with acquisition of a homozygous recessive state at the tissue level (2, 3). MEN1 syndrome frequently exhibits a familial pattern, whereas only the minority of affected individuals present as a simplex, or sporadic, case defined as a single occurrence of MEN1 syndrome in a family. Generally, MEN1 germline mutations are identified with an average prevalence of 70% in the familial forms, whereas the sporadic cases, associated with de novo mutation of the MEN1 gene, represent about 10% of cases. According to this, a crucial issue is still represented by some clinical phenotypes presenting as a MEN1-related status in which MEN1 gene analysis failed to detect germline mutations: MEN1 variants and MEN1 phenocopies. MEN1 variants can be defined as differing clinical expressions from one gene such as familial isolated hyperparathyroidism (FIHP) in which germline mutations in MEN1 gene have been reported with a different prevalence in families with FIHP (4–6). Instead, a MEN1 phenocopy consists of a trait that strongly resembles a MEN1 phenotype in a patient or a family without identified MEN1 mutation and not related to the gene itself (7). A practical example could be a case of FIHP in which MEN1 mutation analysis results negative, being caused by mutation in another familial hyperparathyroidism-related gene, such as either the calcium-sensing receptor gene (8), whose inactivating mutations account for familial hypocalciuria hypercalcemia syndrome, or the HRPT2 gene responsible for the hyperparathyroidism-jaw tumor syndrome (9). Recently described is an interesting small family meeting the criteria of MEN1 but exhibiting atypical MEN1 tumors such as somatotropinoma and renal angiomyolipoma associated to the more typical parathyroid tumors (10). No MEN1 germline mutation was detected in affected members, whereas they had a CDKN1B mutation linked to their MEN1 trait (10). Interestingly, a spontaneous strain of rat shows a similar spectrum of tumors caused by homozygous mutation of Cdkn1b (10). Thus, this phenotype may represent a rare and important phenocopy of classic MEN1, but more families will need to be studied to understand the complete phenotype. Concerning the possible causes of nondetection of MEN1 mutation, several points have to be addressed, as also made by Agarwal et al. (11) in this issue of The Journal. First, the germline mutation could rely on regulatory/noncoding regions of the gene, such as the promoter region. Currently, such mutations of the MEN1 gene have not been reported. Second, the germline mutation could consist of a large deletion of MEN1 gene, but it seems to rarely occur, being found in approximately 4% of cases (12, 13). Consequently, the attention of researchers has to be directed to look for other causes that could explain both the MEN1-related clinical phenotype and the nondetection of MEN1 mutation, such as the involvement of other genes. In the last decade, menin has been reported to interact with a multitude of proteins including jun D proto-oncogene, Mothers against decapentaplegic homolog family members, Pem, nuclear factorB, Fanconi anemia complementation group D2, Replication Protein A2, Nonmuscle Myosin IIA, glial fibrillary acidic protein, vimentin, and heat-shock protein 70, although to date none of the interacting partners have been directly proven important in MEN1 pathophysiology (14). Moreover, it has been hypothesized that menin mediates its tumor suppressor action by regulating histone methylation in promoters of HOX genes and/or CDKN2C,CDKN1B, andpossiblyother cyclin-dependent kinase

Somatic Mutational Analysis of MEN1 and Phenotypic Correlation in Sporadic Parathyroid Tumors

Purpose: MEN1 gene mutation causes multiple endocrine neoplasia type 1. It also suggests that somatic MEN1 gene mutation plays a role in sporadic endocrine tumor. In this study, we examined whether somatic mutations of MEN1 gene are responsible for sporadic parathyroid tumors and correlate with clinical manifestations of parathyroid tumors. Methods: Somatic mutation of MEN1 gene in the formalin-fixed, paraffin-embedded parathyroid tumor tissue from 8 adenomas, 2 carcinomas and 1 hyperplasia were analyzed by direct sequencing. Clinicopathological parameters were reviewed from medical records and compared with the mutational data. Results: Eight of eleven (73%) sporadic parathyroid tumors had somatic MEN1 mutations of 14 different types. In the 14 types, 13 were a point mutation which is composed of 8 missense mutations, 2 nonsense mutations and 3 silent mutations. One of 14 types is a frameshift deletion of 27 base pairs in exon 2. Somatic mutation was frequent in the exon 2 and exon 10. Four types of polymorphism were found. There was no correlation between the presence of mutations and clinicopathological phenotype of parathyroid tumors. Conclusion: This result suggests that somatic mutation of MEN1 gene plays a definite role in sporadic parathyroid tumor formation.

An association between invasive breast cancer and familial idiopathic hyperparathyroidism: a case series and review of the literature

The possibility of an association between primary hyperparathyroidism and breast cancer has been postulated. We report here a sibship with three premenopausal breast cancers and hyperparathyroidism, and no detectable BRCA or MEN1 gene mutations. We explore genetic and molecular rationales for an association between these metabolic and neoplastic processes.

Characteristics of familial isolated pituitary adenomas

The familial occurrence of pituitary adenomas has been recognized for many years and currently accounts for approximately 5% of all cases. Molecular, genetic and clinical features of familial pituitary adenomas have been well characterized in multiple endocrine neoplasia type 1 (MEN-1) and Carney’s complex (CNC), which account for the majority of familial pituitary tumor cases. These conditions are caused by MEN1 and PRKAR1A gene mutations, respectively, and the clinical and pathological features of pituitary pathology in these diseases differ from those of sporadic pituitary tumors. Familial acromegaly has been recognized for many years and, more recently, the clinical features of this clinical phenotype, referred to as isolated familial somatotropinoma, have been clarified. Over the past decade, the concept of non-MEN-1/CNC familial pituitary tumors has been expanded significantly to include all phenotypes, a condition known as familial isolated pituitary adenomas (FIPA). In FIPA, tumors can present homogeneously (same phenotype) or heterogeneously (different tumor phenotypes) within the same family. Compared with sporadic pituitary adenomas, patients with FIPA have a younger age at diagnosis and have larger tumors. The clinical features of FIPA differ from those of MEN-1 in terms of a higher frequency of somatotropinomas and a lower frequency of prolactinomas. The recent discovery of the involvement of mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene in association with pituitary tumors has provided new information regarding potential mechanisms of tumorigenesis in FIPA patients. While very infrequent in sporadic pituitary tumors, approximately 15% of FIPA patients have AIP mutations, rising to half of patients with familial acromegaly. In this review, we detail the clinical features of FIPA and discuss tumor pathology and genetic findings in this increasingly recognized clinical condition.

Mutational Analysis of p27 (CDKN1 B) and p18 (CDKN2C) in Sporadic Pancreatic Endocrine Tumors Argues against Tumor-Suppressor Function

Pancreatic endocrine tumors (PETs) arise sporadically or are associated with multiple endocrine neoplasia type 1 (MENi) syndrome or von Hippel-Lindau syndrome. About 90% of patients with familial MENi display detectable MEN1 gene (menin) mutations. The cyclin-dependent kinase inhibitor p27 (CDKN1 B) is a downstream target of menin and has been recently shown to be responsible for the multiple endocrine neoplasia-like syndrome in rats, where affected animals develop multiple tumors and hyperplasia in endocrine tissues, including the pancreatic islets of Langerhans. A germline nonsense truncation mutation of p27 has been recently described in a suspected MENi family without MENi mutation, raising the possibility that p27 mutation could be responsible for MENi phenotype. Somatic MENi mutations occur at low frequency in sporadic PETs; here, we subjected p27 to mutational analysis in 27 sporadic PETs. As an additional menin target, analysis of the p18(CDKN2C) gene was included. In the p27 gene, one common polymorphism (V1 09G) and one novel polymorphism (g/a) in the noncoding part of exon 2 were identified. Three known polymorphisms were found in the p18 gene. These data suggest that p27 and p18 are unlikely to present classic tumor-suppressor genes in sporadic PETs.

Hypokalemia as a sign for Cushing's disease

A 61-year-old male patient with hypokalemia, acroedema and hyperglycaemia was referred to our endocrinology ward for recompensation and further diagnostic. The endocrine laboratory data showed an elevated ACTH-level, a nullified circadian rhythm of cortisol as well as no cortisol suppression after low-dose and high-dose dexamethasone suppression test. CRH stimulation revealed no significant increase in ACTH- and cortisol-levels. Abdominal ultrasound as well as endoscopic ultrasound showed a significant tumour mass in the head of the pancreas. Moreover, distinct lymphnode metastases surrounding the pancreatic head were described. Gene testing for typical MEN-1 gene mutations was negative. Therapeutically abdominal surgery with pylorus preserving pancreatic head resection was performed. The pathohistological examination of the tumour established the diagnosis of an ACTH-producing neuroendocrine carcinoma accompanied by multiple lymphnode metastases. Testing 12 weeks after surgery showed a normal circadian rhythm and suppression of cortisol after low dose dexamethasone. This case report demonstrates that hypokalemia could be a rare sign for Cushing's disease.

LOH on chromosome 11q, but not SDHD and men1 mutations was frequently detectable in chinese patients with pheochromocytoma and paraganglioma

Recently, the succinate dehydrogenase subunit D (SDHD) gene has been reported as one of the major susceptibility genes for pheochromocytoma (PCC) and paraganglioma (PGL). In addition, loss of heterozygosity (LOH) on chromosome 11, mainly in 11q23 and 11q13, is observed frequently in PGL. Based on the fact that mutation frequency of the SDHD gene is less than that of allelic loss at chromosome11q, where the SDHD gene is located, this region may contain other candidate tumor-suppressor genes involved in pathogenesis of PCC/PGL. The tumor-suppressor gene Men1 located in 11q13 is responsible for multiple endocrine neoplasia type 1 (Men1). However, the involvement of the Men1 gene in tumorigenesis of sporadic PCC/PGL is yet to be determined. To understand the roles of the two tumor-suppressor genes and LOH on chromosome 11q in Chinese patients with sporadic PCC or PGL, we performed mutation detection of the SDHD and Men1 genes in tumors from 35 Chinese patients with PCC/PGL; we also did LOH analysis at chromosome 11q for 25 patients out of the 35. No mutation was found in all of 35 patients. However, LOH was detected at one or more loci in 11 of the 25 (44%) tumor samples. The highest frequency of LOH occurred at D11S2006 (41%). Our results suggested that mutation in SDHD or Men1 gene was not found in Chinese patients with sporadic PCC/PGL. However the loss of chromosome 11q might be critical in development of PCC or PGL.

Loss of parafibromin expression in a subset of parathyroid adenomas

Inactivation of the hyperparathyroidism-jaw tumour syndrome (HPT- JT) gene, HRPT2, was recently established as a genetic mechanism in the development of parathyroid tumours. Its encoded protein parafibromin has tumour-suppressor properties that play an important role in tumour development in the parathyroids, jaws and kidneys. Inactivating HRPT2 mutations are common in HPT- JT and parathyroid carcinomas, and have been described in a few cases of parathyroid adenomas with cystic features. In this study, 46 cases of cystic parathyroid adenomas previously investigated for HRPT2 mutations were characterized with regard to MEN1 gene mutations, cyclin D1 expression and parafibromin expression. In normal tissues and cell lines, parafibromin was ubiquitously expressed. Furthermore, parafibromin was detected as a dominating nuclear and a weaker cytoplasmic signal in transfected cell lines. In the three parathyroid tumours with inactivating HRPT2 mutations parafibromin expression was not detectable, and in one of two cases with aberrantly sized parafibromin the protein was delocalized. Both high and low cyclin D1 levels were found among HRPT2-mutated and -unmutated tumours, suggesting that these events are not mutually exclusive in parathyroid tumour development. The presented data suggest that in the majority of benign parathyroid tumours the expression of parafibromin remains unaltered, while the loss of parafibromin expression is strongly indicative of gene inactivation through mutation of the HRPT2 gene.

A Case of Familial Multiple Endocrine Neoplasia with MEN1 Gene Mutation

Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal dominant disorder that's characterized by the combined occurrence of primary hyperparathyroidism, endocrine pancreatic tumors and anterior pituitary adenomas, but such manifestations as carcinoid tumors, adrenal adenoma and lipoma are also seen. We report here on a case of a 52-years old man with MEN type 1. He had a parathyroid adenoma, empty sella and a non-functioning pancreatic and adrenal mass. On the genetic analysis, he was proven to have a mutation in the MEN1 gene (exon 2, 200-201, INS AGCCC). On the family study for the mutation, one of his siblings and his son proved to have the same mutation. (J Kor Endocrinol Soc 21:560~566, 2006)

Novel candidate tumour suppressor gene loci on chromosomes 11q23–24 and 22q13 involved in human insulinoma tumourigenesis

Insulinomas represent the predominant syndromic subtype of endocrine pancreatic tumours. Previous molecular studies have shown that gain of chromosome 9q rather than MEN1 gene mutation is an important early event in tumour development and that chromosomal instability is associated with metastatic disease. In order to identify new gene loci and to define further the critical genetic events in insulinoma tumourigenesis, 27 insulinomas were investigated by array-based comparative genomic hybridization (array CGH) on 3.7 k genomic BAC arrays (resolution < or =1 Mb). Fluorescence in situ hybridization was used to validate alterations in a subset of tumours. Array CGH most frequently detected loss of chromosomes 11q and 22q and gains of chromosome 9q. The chromosomal regions of interest (CRI) included 11q24.1 (56%), 22q13.1 (67%), 22q13.31 (56%), and 9q32 (63%). Evaluation of the simultaneous occurrence of these aberrations in the individual tumours revealed that gain of 9q32 and loss of 22q13.1 are early genetic events in insulinomas, occurring independently of the other alterations. In tumours with increased genomic complexity, these alterations were often detected simultaneously, occurring in the same tumour cells. Losses of 11q24.1 and 22q13.31 were also associated with these more advanced tumour cases. The CRIs identified most likely harbour crucial candidate genes important in insulinoma tumourigenesis.

Coincidence of Multiple Endocrine Neoplasia Types 1 and 2: Mutations in theRETProtooncogene andMEN1Tumor Suppressor Gene in a Family Presenting with Recurrent Primary Hyperparathyroidism

Primary hyperparathyroidism (HPT) presents as a part of inherited syndromes such as multiple endocrine neoplasia (MEN) types 1 and 2. In patients with MEN1, parathyroid hyperplasia or multiple adenomas occur in approximately 90-95%. MEN2A-related HPT is characterized by a mild hypercalcemia, which is mostly asymptomatic. Here we present a family with coexistence of MEN1 gene mutation and RET mutation. Six family members carrying MEN1 gene mutation IVS5 + 1G>A only, one family member with RET mutation Y791F, and three family members with both MEN1 gene and RET mutation were studied. The key to diagnosis was recurrent HPT in a young male carrying RET mutation Y791F, a mutation not likely to give rise to recurrent HPT. MEN1 gene mutation and RET codon 791 mutation in the same patient did not affect the typical phenotype of MEN1 or MEN2, and also the course of diseases seems to be unchanged. The reason may be that both mutations, although contributing to tumor pathogenesis, do not interact and induce a worsening of the cancer syndromes.

Novel somatic MEN1 gene alterations in sporadic primary hyperparathyroidism and correlation with clinical characteristics

Primary hyperparathyroidism (pHPT) is a common endocrine disease that in more than 95% of cases is sporadic and only in some cases is caused by inherited disorders, isolated or as part of multiple endocrine neoplasia (MEN1 and 2). Somatic mutations of MEN1 gene have also been described in sporadic parathyroid tumors. In our study, we examined the presence of alterations in MEN1 gene in a series of 39 patients who had undergone surgery for sporadic pHPT (35 with parathyroid adenoma or hyperplasia, 4 with a carcinoma). A genotype-phenotype correlation was also analysed. After DNA extraction from paraffin-embedded tissues, we amplified by PCR and sequenced the exons 2-10 of the MEN1 gene. Somatic MEN1 mutations were detected in 6 of the 35 patients with a benign parathyroid lesion examined (17.1%), whereas no alterations were found in the carcinomas. Four novel MEN1 gene mutations were identified as follows: one frameshift mutation (222insT, exon 2), one frameshift deletion (912delTA, exon 5), one in-frame deletion (835del18, exon 4) and one missense mutation (P291A, exon 6). In addition, one missense mutation (L89R, exon 2) and one nonsense mutation (Q536X, exon 10) were previously reported. Moreover, two polymorphisms were also found: one allele carried a R171Q polymorphism (1/39 tumors), while a D418D polymorphism (GAC/GAT) was found in 15 and 8 tumors in hetero (CT) and homozygosity (TT), respectively. In no case (mutations and/or polymorphisms) did we find a genotype-phenotype correlation. In conclusion, our data demonstrate the presence of somatic alterations of the MEN1 tumor suppressor gene in about one fifth of benign sporadic parathyroid tumors. The absence of a genotype-phenotype correlation, however, suggests the involvement of other genetic/epigenetic factors for the full expression of the disease.

MEN1 gene mutations are a rare event in patients with sporadic neuroendocrine tumors

Background: Neuroendocrine tumors of the gastroenteropancreatic (GEP) tract are encountered either as a sporadic type or as part of multiple endocrine neoplasia type 1 (MEN-1) syndrome. Inactivating MEN1 gene mutations have been found to be responsible for this syndrome and have also been described in sporadic cases. The aim of the present study was to evaluate the presence of mutations in the MEN1 gene in a series of 10 well-differentiated neuroendocrine tumors: five of the foregut and five of the midgut tract. Methods: Retrospective screening for MEN1 gene mutations was carried out in 10 archived, paraffin-embedded neuroendocrine tumors. Polymerase chain reaction amplification and automated sequence analysis of the DNA extracted from the tumors were performed. Results: One mutation (359 del 4) in exon 2 of the MEN1 gene was identified in a neuroendocrine tumor of the foregut (VIPoma of the pancreas). No mutation was identified in midgut neuroendocrine tumors. Conclusions: Our data confirm that retrospective genetic analysis can be used to identify mutations in the MEN1 gene and indicate that somatic MEN1 gene mutations are a rare event in sporadic neuroendocrine GEP tumors. The frequency of these mutations was 10% in our series, which may differ from that in other studies, due to the small number of cases analyzed.

MEN1 gene alterations do not correlate with the phenotype of sporadic primary hyperparathyroidism.

Loss of heterozygosity (LOH) in the MEN1 region on chromosome 11q13 and MEN1 gene mutations have been found in a subset of sporadic parathyroid tumors. The question of whether these genetic abnormalities in the parathyroid tumors might influence the clinical and biochemical characteristics of primary hyperparathyroidism (PHPT) remains to be elucidated. The aim of the present study was to correlate the presence of MEN1 gene alterations in PHPT tumors with the clinical phenotype. Using microsatellite analysis for LOH at 11q13 and DNA sequencing of the coding exons, the MEN1 gene was studied in 38 parathyroid tumors of patients with sporadic PHPT. Fourteen tumors showed LOH at 11q13, and mutations of MEN1 gene were detected in 7 cases. The clinical and biochemical characteristics of patients were unrelated to the presence or absence of LOH and/or MEN1 gene mutations. In conclusion, MEN1 gene alterations are rather common in sporadic PHPT and their presence does not correlate with the clinical manifestations of the disease.

A patient with multiple endocrine neoplasia type 1 with a novel MEN1 gene mutation (237delC)

A patient with multiple endocrine neoplasia type 1 with a novel MEN1 gene mutation (237delC)

Genotype-Phenotype Analysis in Multiple Endocrine Neoplasia Type 1

Multiple endocrine neoplasia type 1 (MEN 1) syndrome is an autosomal dominant disorder caused by germline mutations in the MEN1 gene and characterized by multiple endocrine tumors, most notably in the parathyroid glands, pituitary, and pancreas. The syndrome demonstrates variable expressivity and considerable genetic heterogeneity. Patient data were examined for possible associations between genotype and phenotype. We reviewed recorded medical data from 1975 to 2001 on patients with MEN 1 and compared specific types and locations of MEN1 gene mutations with manifestations of the syndrome. We identified 109 affected patients from 24 MEN 1 kindreds. The phenotypic expression of MEN 1 in affected individuals included hyperparathyroidism in 74%, pancreatic endocrine tumors in 51%, and pituitary tumors in 35%. Twelve of 14 insulinomas occurred in patients with pituitary tumors. Mutation analysis was completed in 14 of 24 kindreds (80 of the 109 patients). Mutations were most common in exons 2 (31%), 9 (15%), and 10 (23%). All 21 patients with frameshift mutations (and known pancreatic endocrine tumor status) had such tumors. Pituitary tumors were associated with frameshift mutations in exon 2. The type and location of MEN1 mutations may be associated with the phenotypic expression of specific tumors. Such information may assist in the genetic counseling and surveillance of at-risk patients. A specific genotype-phenotype correlation is unlikely because of the heterogeneity of the mutations in the MEN1 gene.

Genetic analysis of the MEN1 gene and HPRT2 locus in two Italian kindreds with familial isolated hyperparathyroidism.

Familial hyperparathyroidism may occur as part of hereditary syndromes, including multiple endocrine neoplasia types 1 and 2 (MEN1 and MEN2A), hyperparathyroidism-jaw tumour (HPT-JT) syndrome and familial isolated hyperparathyroidism (FIHP). It is unclear whether the latter is a distinct genetic entity or a variant of MEN1 or HPT-JT, where, because of reduced penetrance, only primary hyperparathyroidism (PHPT) is present. In the present study, we describe two unrelated Italian kindreds with FIHP, in which the clinical, histopathological and genetic analyses of the MEN1 gene and HPRT2 locus at 1q21-32 suggest that both might be a variant of MEN1 and HPT-JT syndromes. We studied 16 members, aged 14-50 years, of two unrelated kindreds with FIHP. Genomic DNA was isolated from peripheral blood leucocytes in all family members, and from parathyroid tissue in those who underwent parathyroidectomy. Ionized calcium and PTH were measured in all family members. The nine coding exons and 16 splice junctions of the MEN1 gene from constitutional DNA were amplified by the polymerase chain reaction (PCR) and sequenced. Parathyroid glands were obtained from five subjects. Allelic deletions (loss of heterozygosity, LOH) of chromosomes 11q13 and 1q21-q32 were assessed using PYGM and D11S449, and D1S215, D1S222, D1S428, D1S412, D1S413 and D1S477, respectively. Forward primers were conjugated with 5' fluorescent dye. PCR products were analysed using an ABI PRISM 310 sequencer. Five members of family 1 and three of family 2 had PHPT. A heterozygous deletion of 1 bp of the MEN1 gene in exon 10 (1785delA) was found in affected members of family 1. No MEN1 gene mutation was found in any member of family 2. LOH at 11q13 was observed in family 1 tumours, but not in those from family 2. Studies at 1q21-32 showed LOH in two family 2 tumours, whereas a retained heterozygosity was found in the remaining member. No LOH at 1q21-32 was found in family 1 tumours. The pathology of family 1 showed chief cell hyperplasia with a diffuse-nodular pattern of growth. Cut surface showed no cystic structures. Typical parathyroid adenoma was diagnosed in one member of family 2 and atypical adenoma in the remaining two. These tumours showed cystic structures. In conclusion, we describe two unrelated kindreds with FIHP which, on the basis of histopathological and genetic studies, could be labelled as variants of the MEN1 and HPT-JT syndromes, respectively. Therefore, an extensive analysis of the genes involved in these diseases should be performed in families with familial isolated hyperparathyroidism to identify the subset linked to the MEN1 gene or to the HPRT2 locus.

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

To determine the spectrum of MEN1 mutations in Portuguese kindreds, and identify mutation-carriers. Six unrelated MEN1 families were studied for MEN1 gene mutations by single-strand conformational polymorphism (SSCP) and DNA sequence analysis of the coding region and exon-intron boundaries of the MEN1 gene. These methods identified 4 different heterozygous mutations in four families: two mutations are novel (mt 1539 delG and mt 655 ims 11 bp) and two have been previously observed (mt 735 del 46p and mt 1656 del C) all resulting in a premature stop codon. In the remaining two families, in whom no mutations or abnormal MEN1 transcripts were detected, segregation studies of the 5' intragenic marker D11S4946 and codon 418 polymorphism in exon 9 revealed two large germline deletions of the MEN1 gene. Southern blot and tumour loss of heterozygosity analysis confirmed and refined the limits of these deletions, which spanned the MEN1 gene at least from: exon 7 to the 3' untranslated region, in one family, and the 5' polymorphic site D11S4946 to exon 9 (obliterating the initiation codon), in the other family. Twenty-six mutant-gene carriers were identified, 6 of which were asymptomatic. These results emphasize the importance of the detection of MEN1 germline deletions in patients who do not have mutations of the coding region. Important clues indicating the presence of such deletions may be obtained by segregation studies using the intragenic polymorphisms D11S4946 and at codon 418. The detection of these mutations will help in the genetic counselling of clinical management of the MEN1 families in Portugal.