Loss of heterozygosity on chromosome 11 in sporadic gastrinomas

A novel likely pathogenetic variant p.(Cys235Arg) of the MEN1 gene in multiple endocrine neoplasia type 1 with multifocal glucagonomas

PURPOSE

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary endocrine syndrome caused by pathogenic variants in MEN1 tumor suppressor gene. Diagnosis is commonly based on clinical criteria and confirmed by genetic testing. The objective of the present study was to report on a MEN1 case characterized by multiple pancreatic glucagonomas, with particular concern on the possible predisposing genetic defects.

METHODS

While conducting an extensive review of the most recent scientific evidence on the unusual glucagonoma familial forms, we analyzed the MEN1 gene in a 35-year-old female with MEN1, as well as her son and daughter, using Sanger and next-generation sequencing (NGS) approaches. We additionally explored the functional and structural consequences of the identified variant using in silico analyses.

RESULTS

NGS did not show any known pathogenic variant in the tested regions. However, a new non-conservative variant in exon 4 of MEN1 gene was found in heterozygosity in the patient and in her daughter, resulting in an amino acid substitution from hydrophobic cysteine to hydrophilic arginine at c.703T > C, p.(Cys235Arg). This variant is absent from populations databases and was never reported in full papers: its characteristics, together with the high specificity of the patient's clinical phenotype, pointed toward a possible causative role.

CONCLUSION

Our findings confirm the need for careful genetic analysis of patients with MEN1 and establish a likely pathogenic role for the new p.(Cys235Arg) variant, at least in the rare subset of MEN1 associated with glucagonomas.

Identification of a parasitic symbiosis between respiratory metabolisms in the biogeochemical chlorine cycle

A key step in the chlorine cycle is the reduction of perchlorate (ClO₄^-) and chlorate (ClO₃^-) to chloride by microbial respiratory pathways. Perchlorate-reducing bacteria and chlorate-reducing bacteria differ in that the latter cannot use perchlorate, the most oxidized chlorine compound. However, a recent study identified a bacterium with the chlorate reduction pathway dominating a community provided only perchlorate. Here we confirm a metabolic interaction between perchlorate- and chlorate-reducing bacteria and define its mechanism. Perchlorate-reducing bacteria supported the growth of chlorate-reducing bacteria to up to 90% of total cells in communities and co-cultures. Chlorate-reducing bacteria required the gene for chlorate reductase to grow in co-culture with perchlorate-reducing bacteria, demonstrating that chlorate is responsible for the interaction, not the subsequent intermediates chlorite and oxygen. Modeling of the interaction suggested that cells specialized for chlorate reduction have a competitive advantage for consuming chlorate produced from perchlorate, especially at high concentrations of perchlorate, because perchlorate and chlorate compete for a single enzyme in perchlorate-reducing cells. We conclude that perchlorate-reducing bacteria inadvertently support large populations of chlorate-reducing bacteria in a parasitic relationship through the release of the intermediate chlorate. An implication of these findings is that undetected chlorate-reducing bacteria have likely negatively impacted efforts to bioremediate perchlorate pollution for decades.

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.

New splicing mutation of MEN1 gene affecting the translocation of menin to the nucleus

Multiple endocrine neoplasia type 1 (MEN1) is a syndrome inherited in an autosomal dominant trait caused by the inactivation of the tumor suppressor gene MEN1.

OBJECTIVE

To communicate a family with a new heterozygous germ line mutation in the intronic region of MEN1 gene and to study its influence in the menin expression.

PATIENTS AND METHODS

We studied 5 members of a family with symptomatic hyperparathyroidism (HPT). One of them had also a neuroendocrine pancreatic tumor, and 2 had non-functional multinodular cortical adrenal hyperplasia compatible with the diagnosis of MEN1. After the mutation was identified, HSP92II restriction enzyme was used to determine both zygosity and segregation of the mutation. RT-PCR from leukocyte's isolated mRNA and western blot from pancreatic tumor tissue were performed. In vitro studies were done in Chinese hamster ovary (CHO) cells transfected with reporter minigenes carrying the coding regions spanning exon (EX)-intron 9 and EX10 with the mutant and the wild type sequences.

RESULTS

We identified a heterozygous G-to-T substitution in the intron-EX junction (IVS9-1 G>T) of MEN1 gene in the index case and the family members. The mRNA from patient's leukocytes was larger (934 bp) in comparison to the normal transcript (717 bp). Immunoblot analysis demonstrated that wild type (67 kDa) and two additional mutant proteins (approximately 55 and approximately 90 kDa) were expressed in the pancreatic tissue. The in vitro study showed a 45% nuclear localization of the mutated menin signal and a 95% in the wild type protein.

CONCLUSIONS

We identified a new intronic heterozygous germ line mutation (IVS9-1G>T) of MEN1 gene in a family affected by MEN1 syndrome. This mutation alters the splice acceptor site of intron 9 that promotes an incorrect splicing, generating aberrant proteins without the nuclear localization signals necessary for the normal menin translocation to the nucleus.

Molecular insights into gastrointestinal neuroendocrine tumours: importance and recent advances

A subset of gastrointestinal neuroendocrine tumours (carcinoids and pancreatic endocrine tumours) show aggressive growth. Early identification of this subset is essential for management; however, clinical, laboratory and histologic features frequently fail to achieve this. Currently, there is an increased understanding of the molecular pathogenesis/changes in neuroendocrine tumours and this may identify important prognostic factors and possibly, new treatments. Recent findings and progress in this area are briefly reviewed in this article.

Frequent deletion of chromosome 3 in malignant sporadic pancreatic endocrine tumors

Pancreatic endocrine tumors (PETs) arise from neuroendocrine cells in and around the pancreas. As loss of heterozygosity (LOH) of chromosome 3 has been reported in sporadic PETs, we examined 16 sporadic PETs for LOH of 10 polymorphic DNA markers spanning both arms of chromosome 3. LOH was demonstrated in 4 of 8 (50%) sporadic PETs with hepatic metastasis, but in none of 8 sporadic PETs without hepatic involvement. The smallest common-deleted region (SCDR) mapped to 3q27-qter. Analysis of this data with the status of markers on chromosomes 1, 11, and MEN1 mutations in these 16 sporadic PETs revealed that chromosome 3q loss may be a late event in sporadic PET tumorigenesis. These data, combined with reports from other investigators, indicate that chromosome 3q27-qter may contain a tumor suppressor gene that's important in the tumorigenesis of sporadic PETs.

Characterization of the MEN1 ortholog in zebrafish

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant syndrome predisposing to multiple tumors. The responsible gene, MEN1, has been identified and inactivating mutations reported. It encodes a protein named menin, which lacks homology to any known proteins. Comparative genomics is used to ascertain important functional domains via the identification of evolutionary conserved regions. Here we report the sequencing and characterization of the MEN1 gene in zebrafish (Danio rerio) at the cDNA level. Zebrafish menin is a 617 amino acid protein and, when compared with human and rodent proteins, shows 75% and 76% similarity, respectively. The most conserved region is amino acid residues 41-322 which shows a human/zebrafish similarity of 83%. Amino acids affected by inactivating missense mutations in MEN1 patients in this region are completely conserved between human and zebrafish. Such high correlation between conservation throughout evolution and mutation position strongly emphasizes the importance of this region.

[Multiple endocrine neoplasia Type I. Diagnosis and therapy in a case with classical family history]

BACKGROUND

A classical family history, representative of the multiple endocrine neoplasia type I (MEN I) syndrome, is reported to illustrate the clinical manifestations, diagnostic procedures and therapeutic modalities of the various endocrine disorders of this syndrome.

DIAGNOSIS

Today genetic analysis clearly identifies gene carriers. In these patients screening of all involved endocrine organs (parathyroid, pituitary, pancreas) at regular time intervals is necessary because also at higher ages additional endocrine manifestations may develop. Due to consequent screening the age at time of diagnosis was reduced by 10 to 20 years. As a consequence the rate of malignancy of pancreatic endocrine tumors which is the limiting factor with regard to long-term prognosis was reduced to about one third. At present it is not known whether this procedure can also increase the survival rate of MEN I patients as could be demonstrated in the MEN II syndrome.

Molecular abnormalities associated with endocrine tumors of the uterine cervix

Objective. We studied the molecular abnormalities involved in the pathogenesis of endocrine tumors of the uterine cervix. Methods. We obtained DNA from precisely microdissected archival tissue from 15 endocrine tumors of the uterine cervix, consisting of 5 carcinoids (1 typical, 4 atypical), 2 large cell neuroendocrine carcinomas, and 8 small cell carcinomas. We investigated the presence of high-risk (types 16 and 18) and intermediate-risk (types 31 and 33) human papilloma virus (HPV) sequences, TP53 and K-ras gene mutations, and loss of heterozygosity (LOH) at 9 genes/chromosomal regions, including 3p14.2/FHIT, 3p14-p21, 3p21, 3p22-p24, 5q21-q22/APC-MCC region, 9p21/CDKN2, 11q23/MEN1, 13q/RB, and 17p/TP53. Results. HPV sequences were detected in 8 (53%) tumors, HPV 16 in 2 cases, and HPV 18 in 2 cases. LOH at 9p21 (43%) and localized 3p deletions (47%) were the most frequent allelic losses found. Allelic losses at 5q21-q22/APC-MCC region, 11q23/MEN1, and 13q/RB were infrequent. TP53 gene mutations were detected in 7 (47%) tumors (1 atypical carcinoid and 6 carcinomas). HPV sequences were demonstrated in 4 of the 7 cases with TP53 gene mutations. No K-ras mutations were detected. Conclusion. The molecular changes present in endocrine tumors of the uterine cervix have distinct features. They incorporate those present in the neuroendocrine tumors of the lung (high frequency of TP53 gene abnormalities and 9p21 deletions) with those detected in squamous cell carcinomas of the cervix (high-risk HPV sequences and localized 3p deletions).

Human Insulinomas: Clinical, Cellular, and Molecular Aspects

Insulinoma is the most frequently encountered functioning endocrine pancreatic tumor in humans. In this overview we summarize morphological and clinical features of insulinomas, report about the proinsulin-insulin conversion in normal and neoplastic B-cells, discuss the new classification, the criteria of malignancy, and the clonal composition of endocrine pancreatic tumors, and outline recent findings on the molecular pathology of these tumors.

Identification of MEN1 Mutations in Sporadic Enteropancreatic Neuroendocrine Tumors by Analysis of Paraffin-embedded Tissue

Gastrinomas and other gastrointestinal neuroendocrine tumors may occur sporadically or as part of the inherited syndrome multiple endocrine neoplasia type 1 (MEN1). Mutations in the recently identified MEN1 gene have been described in sporadic gastrinomas and insulinomas. This study describes techniques used to identify mutations in the MEN1 gene in DNA extracted from paraffin-preserved tissue. Two novel mutations are identified in the MEN1 gene from nine archived paraffin-embedded neuroendocrine tumors, demonstrating that retrospective genetic analysis can be used to identify mutations in the MEN1 gene from preserved tissue. Conditions are provided by which paraffin-embedded tissue can be used as a source of genetic material for sequence information of sufficient quality for mutational studies of the MEN1 gene. It should also be possible to apply this retrospective genetic analysis of paraffin-embedded tissue to other disease models.

Loss of heterozygosity in squamous cell carcinomas of the head and neck defines a tumor suppressor gene region on 11q13

Tumor suppressor genes APC, RB1, and DCC, as well as genes localized to 3p and 11q, have been implicated in the development of a number of human tumors. To determine whether allelic deletions occur at these loci in squamous cell carcinomas (SSCs) of the head and neck, 25 primary, 1 metastatic, and 3 recurrent tumors, along with the corresponding constitutional tissues, were analyzed by using a battery of polymorphic DNA markers. For two primary tumors, we also analyzed subsequent metastatic tumors of the lung. Polymerase chain reaction-based restriction fragment length polymorphism studies demonstrated loss of heterozygosity for the APC gene in 2 of 12 (17%), the RB1 gene in 5 of 22 (23%), and the DCC gene in 5 of 13 (38%) informative cases. Alleles on chromosomes 3p, 11q13, and 18q21.1 were lost in 7 of 20 (35%), 9 of 23 (39%), and 4 of 17 (24%) informative cases, respectively. A breakpoint was identified within the chromosomal region 3p13-21.2 in a SCC of the tongue. Breakpoints within 11q13 were identified in 2 additional tumors. Thus, allelic deletions of DCC, 3p, and 11q13 appear to be common in head and neck cancers, suggesting that these genes play a critical and complex role in the development of these tumors. Furthermore, the present study provides definitive evidence for a tumor suppressor gene at chromosome band 11q13 and localizes this gene to the INT2-D11S533 interval for future cloning and sequencing.

Pathology of MEN-1: morphology, clinicopathologic correlations and tumour development

Multiple endocrine neoplasia type 1 (MEN-1) is an inherited syndrome which is characterized by the occurrence of neoplastic lesions in the parathyroids, the pancreas, duodenum, anterior pituitary and, less commonly, also in the stomach, thymus and lung. Its genetic defect has recently been identified and appears to involve a new type of tumour suppressor gene called mu on chromosome 11q13. In this overview, we will summarize the morphological features of the MEN-1 phenotype, discuss its clinicopathologic profile and prognosis and outline the recent findings on the molecular pathology of this syndrome.

Deletion mapping of endocrine tumors localizes a second tumor suppressor gene on chromosome band 11q13

Multiple endocrine neoplasia type 1 syndrome (MEN1, MIM 131100), an autosomal dominant disease, is characterized by parathyroid hyperplasia, pancreatic endocrine tumors, and pituitary adenomas. These tumors also occur sporadically. Both the familial (MEN1) and the sporadic tumors reveal loss of heterozygosity (LOH) for chromosome band 11q13 sequences. Based on prior linkage and LOH analyses, the MEN1 gene was localized between PYGM and D11S460. Recently, the MEN1 gene (menin) has been cloned from sequences 30-kb distal to PYGM. We performed deletion mapping on 25 endocrine tumors (5 MEN1 and 20 sporadic) by using 21 polymorphic markers on chromosome band 11q13. Of these, two (137C7A, 137C7B) were derived from PYGM-containing BAC (bacterial artificial chromosome-137C7) sequences, one from INT2-containing cosmid sequences and the marker D11S4748, a (CA)20 repeat marker that was developed by us. The LOH analysis shows that the markers close to the MEN1 (menin) gene were not deleted in three of the tumors. These tumors, however, showed LOH for distal markers. Thus, the data suggest the existence of a second tumor suppressor gene on chromosome band 11q13.

Tracking the MEN1 gene

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary autosomal dominant disease characterized by parathyroid hyperplasia, pancreatic endocrine tumors, and pituitary adenomas. Sporadic forms of these tumors are more common than their inherited counterparts and share common genetic abnormalities. We have been studying the molecular genetics of sporadic pancreatic endocrine tumors to identify the tumor suppressor gene responsible for MEN1 by positional cloning. This review introduces the reader to the fundamentals of these molecular genetic techniques and outlines the general strategy used to isolate this gene.

A transcript map encompassing the multiple endocrine neoplasia type-1 (MEN1) locus on chromosome 11q13

A transcription map of a 1200-kb region encompassing the MEN1 locus was constructed by direct cDNA selection and mapping ESTs. A total of 29 genes were mapped. Ten transcripts were identified by cDNA selection of a focused 300-kb genomic region telomeric to the MEN1 consensus region. Since many of the sequences cloned by cDNA selection also identified ESTs from the region, 19 additional RH-mapped ESTs were mapped to the entire contig region by PCR amplification of genomic clones. Nine known genes, 2 putative human homologues to mouse genes, and 18 novel transcripts map to the region. Transcripts that map to the MEN1 interval PYGM-D11S449 include SGC35223, IB1256, AA147620, ZFM1, FAU, and CAPN1. The latter 3 known genes have already been excluded as candidate MEN1 genes. The 2 putative human homologues of mouse genes Ltbp2 and Spa-1 may be candidate tumor suppressor genes, but they map telomeric to D11S449. Although both of these genes map outside the MEN1 consensus region they may play a role in sporadic endocrine tumors independent of the MEN1 gene or in other tumors, such as breast cancer, that have loss of heterozygosity within this region.

Pancreatic endocrine tumors with loss of heterozygosity at the multiple endocrine neoplasia type I locus

BACKGROUND

Loss of heterozygosity (LOH) at chromosome 11q13 has been demonstrated in multiple endocrine neoplasia type I (MEN I) and sporadic parathyroid tumors, pituitary adenomas, and a few types of pancreatic endocrine tumors. Gastrinomas are the most common pancreatic endocrine tumor in MEN I. We hypothesized that all pancreatic endocrine tumors have LOH at 11q13, resulting in inactivation of the previously described tumor suppressor gene in this region.

METHODS

We analyzed a sporadic gastrinoma, a MEN I-associated gastrinoma, and a nonfunctional pancreatic endocrine tumor from a patient with Von Hippel-Lindau (VHL) disease for LOH at seven loci at 11q13: D11S149, PYGM, D11S427, D11S546, SEA, D11S97, and D11S146.

RESULTS AND CONCLUSIONS

We found LOH at 11q13 in all three tumors. The MEN I-associated gastrinoma we analyzed is the first tumor of this type to have LOH. This is also the first report of LOH at 11q13 in a pancreatic endocrine tumor from a patient with VHL. These findings suggest that the etiology of pancreatic endocrine tumor formation involves a common genetic pathway for sporadic, MEN I, and VHL tumors.

Gastrointestinal endocrine tumours. Gastrinoma

Since the description of the Zollinger-Ellison syndrome in two patients in 1955, there have been significant advances in the understanding of its pathogenesis, natural history, relationship to multiple endocrine neoplasia type 1, diagnosis, methods of tumour localization and management. The main focus in treatment is now shifting from management of the gastric acid hypersecretory state which can now be controlled medically in almost every patient, to the management of the gastrinoma. Recent studies are beginning to provide insights into the natural history of gastrinomas, factors that are associated with invasiveness in some gastrinomas, defining the role of surgery in managing patients with different disease extents, or with MEN 1 and being able to provide insights into molecular abnormalities that may be important in their pathogenesis. In this article each of these advances is briefly reviewed with emphasis primarily on recent advances.

Genetic mapping of the multiple endocrine neoplasia type 1 locus at 11q13

Oncogenesis of tumours related to multiple endocrine neoplasia type 1 (MEN1) is associated with somatic deletions involving the MEN1 locus at chromosomal region 11q13, suggesting inactivation of a tumour-suppressor gene in this region. Here we describe the localization of the MEN1 gene to a 900-kb region, based on linkage analysis in affected families and deletion mapping of MEN1-associated tumours. In addition, a set of microsatellite markers mapped to the 11q11-13 region were used for linkage analysis in a large Tasmanian MEN1 pedigree, demonstrating the usefulness of these markers for presymptomatic testing in affected families.

Human chromosome 11 inhibits tumorigenicity of a murine squamous cell carcinoma cell line

Loss of heterozygosity (LOH) of mouse chromosome 7 has been consistently demonstrated in chemically induced murine squamous cell carcinomas (SCCs). The region of this chromosome presenting LOH in the mouse tumors is syntenic to human chromosome segments 11p15 and 11q. To determine whether the introduction of human chromosome (Hchr) 11 can suppress the growth of murine SCC, we injected four clones of a chemically induced murine SCC cell line bearing an Hchr 11 into athymic BALB/c nude mice. All microcell hybrid clones with Hchr 11 (CH72/Hchr 11) had latency periods twice as long as those of the parental CH72 cells and control hybrids containing a Hchr 12. Tumor-derived cells from CH72/Hchr 11 hybrids had lost centromeric and telomeric sequences from Hchr 11. All repressed cell lines grew significantly more slowly in vitro than did the controls. These results suggest that Hchr 11 contains a tumor-suppressor gene capable of inhibiting tumorigenicity in chemically induced SCC, confirming common pathways in the development of human neoplasias and the murine model.

Chromosome analysis of nine endocrine neoplasms of the pancreas

Endocrine neoplasms of the pancreas differ from the more common adenocarcinomas of the pancreas not only in histologic appearance, but also in clinical presentation and biologic behavior. Chromosomes were analyzed from nine fresh pancreatic endocrine neoplasms. Clonal chromosomal abnormalities were found in five; all were malignant neoplasms. One showed only a loss of the Y chromosome and another had a small triploid population of cells in addition to a normal mainline, with a karyotype of 61-66,XX, -X, -1, -2, -3, -4, +5, -6, +7, -11, -14, +17, +18, +20, +mar1,x2, +mar2,inc. Three neoplasms had near-haploid clones. One neoplasm had a composite karyotype of 31-36<n>,X, +1, +3, +5, +7, +9, +10, +17, +18, +mar. Two were from the same patient, who had the autosomal dominant syndrome MEN-1. The same clone, described as 29<n>,X, +add(1)(p12), +5, +7, +8, +18, +19, was found in both the primary pancreatic neoplasm and in the metastatic tumor. To our knowledge, this is the first report of a haploid clone in both a primary and metastatic solid tumor, and suggests that the near-haploid state is at least compatible with metastasis. These data, combined with the limited reports of cytogenetic data from endocrine pancreatic neoplasms, suggest that at least half of such neoplasms will have an abnormal karyotype.

Gastrinomas demonstrate amplification of the HER-2/neu proto-oncogene

OBJECTIVE

This study determined whether genomic amplification of HER-2/neu or mutations of the p53 and ras genes were present in gastrinomas.

SUMMARY BACKGROUND DATA

Amplification of HER-2/neu, a proto-oncogene related to the epidermal growth factor receptor, and mutation of the ras proto-oncogene and p53 tumor suppressor gene appear to play a role in the pathogenesis of some human cancers. Little is known about possible molecular alterations in gastrinomas, tumors that may be particularly virulent because of gastrin overproduction, resulting in the severe ulcer diathesis, the Zollinger-Ellison syndrome.

METHODS

The differential polymerase chain reaction (PCR) procedure was used to detect amplification of the HER-2/neu gene in DNA samples from the novel human gastrinoma cell line (PT) and from paraffin-embedded samples of gastrinomas. Sequencing techniques were used to determine whether mutations of the p53 or ras (Ha-ras, N-ras, Ki-ras) genes were present.

RESULTS

Amplification (> twofold) occurred in all gastrinoma tumor samples. Compared with normal pancreas or ileum, a 4- to 12-fold amplification of HER-2/neu was found in 3 gastrinomas, 3 to 3.3-fold in four samples and 2.1- to 2.4-fold in the remaining five tumors. A heterozygous point mutation in the p53 gene (codon 273) was found in a single sample; none of the gastrinomas contained a mutation of the ras genes.

CONCLUSIONS

Amplification of the HER-2/neu gene, but not alterations of either p53 or ras, may be involved in the pathogenesis of gastrinomas. The unique PT cell line will be a useful model to further elucidate the molecular mechanisms that contribute to gastrinoma formation and growth.

Putative tumor-suppressor gene on chromosome 11 is important in sporadic endocrine tumor formation

Endocrine tumors arising sporadically or as a manifestation of the multiple endocrine neoplasia type I syndrome (MEN I) have been shown to have mutations on chromosome 11. These mutations can be detected at the molecular level by loss of heterozygosity (LOH) for DNA markers from chromosome 11. This study represents one of the largest collections of sporadic endocrine tumors in which LOH was systematically assessed on chromosome 11 for the loci flanking the proposed MEN I region. DNA was isolated from 39 endocrine tumors and probed with 7 DNA probes spanning the region of chromosome 11q13 from the loci PYGM to INT-2. Eleven tumors demonstrated LOH at any two loci in this region. The remaining 28 tumors showed no LOH or were noninformative at these loci. Thus, nearly 30% of these tumors showed LOH in the region (from PYGM to INT-2) that is thought to contain the MEN I gene(s). Previous studies of sporadic endocrine tumors have suggested that these tumors may arise via the same mechanism as tumors of the MEN I syndrome. Namely, these sporadic tumors are thought to result from mutations leading to genetic loss on the long arm of chromosome 11, thereby inactivating a possible tumor-suppressor gene (or genes). These findings strongly support the hypothesis that sporadic pancreatic endocrine tumors share a similar etiology of tumorigenesis with tumors of the MEN I syndrome, which principally involves deletion of a tumor-suppressor element (or elements).

Cytogenetic studies in sporadic and multiple endocrine neoplasia type 1-associated pituitary adenomas

Four sporadic and two multiple endocrine neoplasia type 1-associated pituitary adenomas were studied. A t(1;21)(q32;22) was discovered in one of the two hereditary tumors.