Allelic imbalance of the mutant and wild-type RET allele in MEN 2A-associated medullary thyroid carcinoma

Germline mutations of the RET proto-oncogene are responsible for the familial tumor syndrome called multiple endocrine neoplasia type 2 (MEN 2) that includes medullary thyroid carcinoma (MTC). Although inherited mutations of RET lead to tumor formation in patients with MEN 2, it is not understood why only selected cells develop into tumors. We have recently shown that duplication of the mutated RET allele or loss of the wild-type allele might represent mechanisms of tumorigenesis in patients with MEN 2A-related pheochromocytoma. We now analysed 19 DNA samples of MTC (15 of which were non-microdissected, four of which were microdissected) from patients with MEN 2A. Using polymorphic marker and phosphorimage densitometry analyses, we found allelic imbalance of the mutated and wild-type RET allele in six of 19 DNA MTC samples. Of note, two of the four microdissected tumor DNA samples showed allelic imbalance of RET, whereas only four of the 15 non-microdissected MTC samples did. These results underscore the significance of microdissection in the analysis of tumor DNA. In our study, some of the non-microdissected tumor DNA samples may have failed to display allelic imbalance of RET, because of contamination of tumor DNA with nonneoplastic DNA or noninformative microsatellite marker analysis. Taken together, our results suggest allelic imbalance between mutated and wild-type RET as a possible mechanism for tumor formation in some patients with MEN 2A-related MTC.

Estimating historical respirable crystalline silica exposures for Chinese pottery workers and iron/copper, tin, and tungsten miners

Collaborative studies of Chinese workers, using over four decades of dust monitoring data, are being conducted by the National Institute for Occupational Safety and Health (NIOSH) and Tongji Medical University in China. The goal of these projects is to establish exposure-response relationships for the development of diseases such as silicosis or lung cancer in cohorts of pottery and mine workers. It is necessary to convert Chinese dust measurements to respirable silica measurements in order to make results from the Chinese data comparable to other results in the literature. This article describes the development of conversion factors and estimates of historical respirable crystalline silica exposure for Chinese workers. Ambient total dust concentrations (n>17000) and crystalline silica concentrations (n=347) in bulk dust were first gathered from historical industrial hygiene records. Analysis of the silica content in historical bulk samples revealed no trend from 1950 up to the present. During 1988-1989, side-by-side airborne dust samples (n=143 pairs) were collected using nylon cyclones and traditional Chinese samplers in 20 metal mines and nine pottery factories in China. These data were used to establish conversion factors between respirable crystalline silica concentrations and Chinese total dust concentrations. Based on the analysis of the available evidence, conversion factors derived from the 1988-1989 sampling campaign are assumed to apply to other time periods in this paper. The conversion factors were estimated to be 0.0143 for iron/copper, 0.0355 for pottery factories, 0.0429 for tin mines, and 0.0861 for tungsten mines. Conversion factors for individual facilities within each industry were also calculated. Analysis of variance revealed that mean conversion factors are significantly different among facilities within the iron/copper industry and within the pottery industry. The relative merits of using facility-specific conversion factors, industry-wide conversion factors, or a weighted average of the two are discussed. The exposure matrix of the historical Chinese total dust concentrations was multiplied by these conversion factors to obtain an exposure matrix of historical respirable crystalline silica concentrations.

Intramedullary Ewing sarcoma of the spinal cord: consequences of molecular diagnostics. Case report

Molecular biological techniques have begun to transform modern medicine. These techniques have shown promise in the pathological diagnosis of difficult or uncommon tumors. Accurate molecular diagnosis of the small round-cell tumors, for example, is especially important because divergent therapies may be required to eradicate such disparate lesions as neuroblastoma, lymphoma, rhabdomyosarcoma, central primitive neuroectodermal tumors/medulloblastoma, or Ewing sarcoma (ES). The authors present an unusual case of a primary, extraosseous ES arising from the intramedullary spinal cord, in which molecular studies were required for specific diagnosis and therapeutic guidance.

Reassignment of the EPB4.1 gene to 1p36 and assessment of its involvement in neuroblastomas

OBJECTIVES

EPB4.1 has been previously mapped to human chromosome 1p33-p34.2. In contradiction to this chromosomal location, we have mapped EPB4.1-1p36 by using fluorescence in situ hybridization and radiation hybrid mapping. In neuroblastomas, deletions of the telomeric end of chromosome 1 (1p36) are the most common genetic aberration.

METHODS

We investigated whether genetic aberrations of EPB4.1 can be detected in some neuroblastomas by analyzing 72 tumours for EPB4.1 mutation, expression, and alternative splicing pattern. Furthermore, EPB4.1 protein from a neuroblastoma cell line was studied for its subcellular localization.

RESULTS

Sequence changes could be detected in 14 out of 72 neuroblastomas, including missense, silent, and intronic changes. Duplex RT-PCR analysis revealed a subset of 11 tumours expressing significantly low levels of EPB4.1. Significant EPB4.1 sequence changes that were detected included an exon 4 G/A missense mutation (amino acid: V/I) that was shown to be associated with absence of wild-type EPB4.1 expression (3 tumours), an exon 8 G/A missense mutation (V/M) (1 tumour), and an intronic sequence change that was shown to be associated with the presence of an aberrant transcript (1 tumour). Splicing pattern analysis revealed that all EPB4.1 transcripts from tumours exclude exon 3, a splicing pattern for generating the 135 kDa isoform. EPB4.1 cDNA cloned from a neuroblastoma cell line produced a 135-kDa protein with a cytoplasm/membrane localization.

CONCLUSIONS

Out of 72 neuroblastomas we have identified 11 tumours with impaired EPB4.1 expression and 5 tumours with significant sequence changes. We also found that the 135 kDa isoform is the main EPB4.1 product in neuroblastoma. EPB4.1 cDNA from a neuroblastoma cell line produced a 135-kDa protein and displayed a cytoplasm/membrane localization in transfected cells.

[Effect of Ce3+ on reactive oxygen species in cells]

The effect of Ce3+ on the content of (reactive oxygen species ROS) in hepatocytes and V79 cells was studied with microfluorometry. The results showed that Ce3+ could enhance the concentration of ROS in hepatocytes in high dose and reduce the concentration of ROS in low dose. These results suggested that Ce3+ might decrease the damage of lipid peroxidation and DNA in low dose and might increase the damage of lipid peroxidaion and DNA in high dose.

Conserved genetic findings in metastatic bladder cancer: a possible utility of allelic loss of chromosomes 9p21 and 17p13 in diagnosis

CONTEXT

Molecular analysis of microsatellite alterations of biologically distinct tumor cell subpopulations from the same patient may aid in the determination of tumor origin and further our understanding of the genetic basis of cancer progression.

DESIGN

The authors examined the pattern of allelic loss with polymorphic microsatellite markers on chromosome 9p21 (D9S161, D9S171, IFNA), regions of putative tumor suppressor gene p16, and on chromosome 17p13 (TP53), the p53 locus, in matched primary and metastatic bladder cancers from 9 patients. All patients underwent cystectomy for bladder cancer and had regional lymph node metastases at the time of surgery. Genomic DNA was prepared from primary cancers and matched synchronous lymph node metastases using a microdissection method.

RESULTS

The overall frequency of allelic loss was 78% in primary cancer and 89% in paired metastatic cancer. The frequency of allelic loss in the primary cancer was 86% with D9S161, 67% with D9S171, 71% with IFNA, and 80% with TP53. The frequency of allelic loss in matched metastatic cancer was 100% with D9S161, 62% with D9S171, 71% with IFNA, and 80% with TP53. An identical pattern of allelic imbalance (allelic loss or retention) at multiple DNA loci was observed in matched primary and metastatic carcinoma in 8 (88%) cases. One case showed allelic loss in the metastasis, but not in the primary cancer.

CONCLUSIONS

The pattern of allelic loss at chromosome 9p21 (p16) and 17p13 (p53) was generally maintained during cancer progression to metastasis, and identical allelic loss in primary cancer was conserved in paired metastatic carcinoma. These data suggest that these genetic changes may be useful in establishing a diagnosis and determining tumor origins in difficult cases.

Potassium channel blocker TEA prevents CA1 hippocampal injury following transient forebrain ischemia in adult rats

It has been recently reported that potassium channel increases activities in CA1 pyramidal neurons of rat hippocampus following transient forebrain ischemia. To understand the role of the enhanced potassium current in the pathogenesis of neuronal damage after ischemia, we examined the effects of tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on the neuronal injury of CA1 region induced by 15 min forebrain ischemia using a four-vessel occlusion model. Adult rats received intracerebroventricular administration of either TEA or 4-AP after ischemia or TEA before ischemia and once each day for 7 days. In the postischemic TEA treated-rats, the neuronal injury in hippocampal CA1 region was significantly less than that of the controls. In contrast, neither preischemic infusion of TEA nor postischemic treatment of 4-AP had any neuroprotective effects. The present study demonstrates that postischemic application of TEA protects hippocampal CA1 pyramidal neurons against ischemic insult, suggesting that potassium channels may play important roles in the pathogenesis of CA1 neuronal death after transient forebrain ischemia.

VAM-1: a new member of the MAGUK family binds to human Veli-1 through a conserved domain

The MAGUKs (membrane-associated guanylate kinase homologues) constitute a family of peripheral membrane proteins that function in tumor suppression and receptor clustering by forming multiprotein complexes containing distinct sets of transmembrane, cytoskeletal, and cytoplasmic signaling proteins. Here, we report the characterization of the human vam-1 gene that encodes a novel member of the p55 subfamily of MAGUKs. The complete cDNA sequence of VAM-1, tissue distribution of its mRNA, genomic structure, chromosomal localization, and Veli-1 binding properties are presented. The vam-1 gene is composed of 12 exons and spans approx. 115 kb. By fluorescence in situ hybridization the vam-1 gene was localized to 7p15-21, a chromosome region frequently disrupted in some human cancers. VAM-1 mRNA was abundant in human testis, brain, and kidney with lower levels detectable in other tissues. The primary structure of VAM-1, predicted from cDNA sequencing, consists of 540 amino acids including a single PDZ domain near the N-terminus, a central SH3 domain, and a C-terminal GUK (guanylate kinase-like) domain. Sequence alignment, heterologous transfection, GST pull-down experiments, and blot overlay assays revealed a conserved domain in VAM-1 that binds to Veli-1, the human homologue of the LIN-7 adaptor protein in Caenorhabditis. LIN-7 is known to play an essential role in the basolateral localization of the LET-23 tyrosine kinase receptor, by linking the receptor to LIN-2 and LIN-10 proteins. Our results therefore suggest that VAM-1 may function by promoting the assembly of a Veli-1 containing protein complex in neuronal as well as epithelial cells.

Genetic aspects of pheochromocytoma

We here review the literature on genetics related to pheochromocytoma. About 10 percent of these neuroendocrine tumors are hereditary and are most often associated with multiple endocrine neoplasia type 2 (MEN 2), von Hippel-Lindau disease, and neurofibromatosis type 1 (NF 1). Hereditary tumor syndromes such as the aforementioned ones, are ideal to study the molecular pathogenesis of tumorigenesis as opposed to sporadic tumors in which genetic alterations often merely represent epigenetic tumor progression phenomena. Recent advances in molecular genetics, especially of RET, VHL, NF1, and SDHD, helped better understand the pathogenesis of pheochromocytoma. In this paper, we not only summarize key points of genetic discoveries related to pheochromocytoma, but also report in table format all known RET germline mutations related to pheochromocytoma.

[Nontargeted mutagenesis of plasmid pSP189 induced by nickel acetate and its relation with DNA damage in Vero cells]

OBJECTIVE

To detect the nontargeted mutagenesis and DNA damage in Vero cells induced by nickel acetate and to analyze their association, to provide clues to carcinogenic mechanism of nickel.

METHOD

Vero cells were treated with nickel acetate for 2.5 hours and cultivated in routine condition for 24 hours, and transfected with wild plasmid pSP189. Plasmid replicated in mammalian cells was collected and was transferred into E. coli MBM7070. The mutant was selected with special culture media. DNA damage in Vero cells was detected with modified single cell gel electrophoresis.

RESULTS

Nontargeted mutagenesis occurred in the cells pretreated with 250 mumol and 1,000 mumol nickel acetate, with mutagenesis frequencies of 9.46 x 10(-4) and 15.01 x 10(-4), 4.41 and 6.98 folds more as compared with the control group, respectively. Frequencies of DNA damage, DNA chain breaks, DNA-protein cross-links and DNA-DNA cross-links in all pretreated cells were significantly higher than those in the control group, but without dose-effect relationship. There was dose leap for mutagenesis frequencies and DNA-DNA cross-links.

CONCLUSION

Nickel acetate could induce nontargeted mutagenesis in the system of shuttle plasmid vectors, which could be related to DNA-DNA cross-links.

Exposure to silica and silicosis among tin miners in China: exposure-response analyses and risk assessment

OBJECTIVES

To investigate the risk of silicosis among tin miners and to investigate the relation between silicosis and cumulative exposure to dust (Chinese total dust and respirable crystalline silica dust).

METHODS

A cohort study of 3010 miners exposed to silica dust and employed for at least 1 year during 1960-5 in any of four Chinese tin mines was conducted. Historical total dust data from China were used to create a job exposure matrix for facility, job title, and calendar year. The total dust exposure data from China were converted to estimates of exposure to respirable crystalline silica for comparison with findings from other epidemiological studies of silicosis. Each worker's work history was abstracted from the complete employment records in mine files. Diagnoses of silicosis were based on 1986 Chinese pneumoconiosis Roentgen diagnostic criteria, which classified silicosis as stages I-III-similar to an International Labour Organisation (ILO) classification of 1/1 or greater.

RESULTS

There were 1015 (33.7%) miners identified with silicosis, who had a mean age of 48.3 years, with a mean of 21.3 years after first exposure (equivalent to 11.0 net years in a dusty job). Among those who had silicosis, 684 miners (67.4%) developed silicosis after exposure ended (a mean of 3.7 years after). The risk of silicosis was strongly related to cumulative exposure to silica dust and was well fitted by the Weibull distribution, with the risk of silicosis less than 0.1% when the Chinese measure of cumulative exposure to total dust (CTD) was under 10 mg/m(3)-years (or 0.36 mg/m(3)-years of respirable crystalline silica), increasing to 68.7% when CTD exposure was 150 mg/m(3)-years (or 5.4 mg/m(3)-years of respirable crystalline silica). Latency period was not correlated to the risk of silicosis or cumulative dose of exposure. This study predicts about a 36% cumulative risk of silicosis for a 45 year lifetime exposure to these tin mine dusts at the CTD exposure standard of 2 mg/m(3), and a 55% risk at 45 years exposure to the current United States Occupational Safety and Health Administration and Mine Safety and Health Administration standards of 0.1 mg/m(3) 100% respirable crystalline silica dust.

CONCLUSIONS

A clear exposure-response relation was detected for silicosis in Chinese tin miners. The study results were similar to most, but not all, findings from other large scale exposure-response studies.

Pituitary macroadenoma in a 5-year-old: an early expression of multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN 1) is associated with parathyroid, enteropancreatic, pituitary, and other tumors. The MEN1 gene, a tumor suppressor, is located on chromosome 11. Affected individuals inherit a mutated MEN1 allele, and tumorigenesis in specific tissues follows inactivation of the remaining MEN1 allele. MEN 1-associated endocrine tumors usually become clinically evident in late adolescence or young adulthood, as high levels of PTH, gastrin, or PRL. Because each of these tumors can usually be controlled with medications and/or surgery, MEN 1 has been regarded mainly as a treatable endocrinopathy of adults. Unlike in MEN 2, early testing of children in MEN 1 families is not recommended. We report a 2.3-cm pituitary macroadenoma in a 5-yr-old boy with familial MEN 1. He presented with growth acceleration, acromegaloid features, and hyperprolactinemia. We tested systematically to see whether his pituitary tumor had causes similar to or different from a typical MEN 1 tumor. Germ line DNA of the propositus and his affected relatives revealed a heterozygous point mutation in the MEN1 gene, which leads to a His139Asp (H139D) amino acid substitution. The patient had no other detectable germ-line mutations on either MEN1 allele. DNA sequencing and fluorescent in situ hybridization with a MEN1 genomic DNA sequence probe each demonstrated one copy of the MEN1 gene to be deleted in the pituitary tumor and not in normal DNA, proving MEN1 "second hit" as a tumor cause. Gsalpha mutation, common in nonhereditary GH-producing tumors, was not detected in this tumor. We conclude that this pituitary macroadenoma showed molecular genetic features of a typical MEN 1-associated tumor. This patient represents the earliest presentation of any morbid endocrine tumor in MEN 1. A better understanding of early onset MEN 1 disease is needed to formulate recommendations for early MEN 1 genetic testing.

[Effect of yinchen dandao decoction on plasma fibronectin, biliary thromboxane A2 and prostaglandin I2 in human and animal suffering from acute cholangitis]

OBJECTIVE

To study the therapeutic mechanism of Yinchen Dandao decoction (YCDDD) in treating acute cholangitis.

METHODS

Twenty-four patients with acute cholangitis and 36 cholangiolithiasis patients were randomly classified into the treated group and the control group, and all of these patients had undergone surgical operation. The treated group were given orally YCDDD 3 days after operation for 1 week, and plasma fibronectin (FN), biliary thromboxane A2(TXA2) and prostaglandin I2(PGI2) were measured and compared before and after oral administration of the drug. The models of cholangitis were established in rabbits, which were also randomly grouped into the treated group and the control group, and the same parameters (FN, TXA2, PGI2) were observed as in rabbits.

RESULTS

The level of FN was significantly lower in cholangitis patients than that in the cholangiolithiasis patients before operation (P < 0.01), and compared to the control group, it obviously raised after YCDDD treatment (P < 0.01), the same happened in the cholangiolithiasis patients. The value of TXA2 and PGI2 in the bile was obviously higher (P < 0.01, P < 0.05) in cholangitis patients than those in chlangiolithiasis, and obviously reduced after YCDDD administration (P < 0.01). The level of FN in the treated group and the level of biliary TXA2 and PGI2 in rabbits with cholangitis were significantly higher than those in the control group (P < 0.01).

CONCLUSION

YCDDD caused the increase of FN and decrease of biliary TXA2 and PGI2, which might be one of the mechanisms of the drug carried out in cholangitis patients.

Duplication of the mutant RET allele in trisomy 10 or loss of the wild-type allele in multiple endocrine neoplasia type 2-associated pheochromocytomas

Inherited mutations of the RET proto-oncogene are tumorigenic in patients with multiple endocrine neoplasia type 2 (MEN 2). However, it is not understood why only few of the affected cells in the target organs develop into tumors. Genetic analysis of nine pheochromocytomas from five unrelated patients with MEN 2 showed either duplication of the mutant RET allele in trisomy 10 or loss of the wild-type RET allele. Our results suggest a "second hit" causing a dominant effect of the mutant RET allele, through either duplication of the mutant allele or loss of the wild-type allele, as a possible mechanism for pheochromocytoma tumorigenesis in patients with MEN 2.

Ovarian lesions in Carney complex: clinical genetics and possible predisposition to malignancy

Carney complex (CNC) is a familial multiple neoplasia and lentiginosis syndrome (OMIM 160980, http://www.ncbi.nlm.nih.gov/omim) with features overlapping those of other multiple endocrine neoplasias and hamartomatoses, Peutz-Jeghers syndrome (PJS) in particular. Although a number of patients with CNC and ovarian tumors have been described in individual patient reports, it is unclear whether ovarian lesions constitute a component of the syndrome or are coincidental events. We investigated 18 women with CNC [age at first evaluation, 31.3+/-12.1 yr (mean +/- SD)] prospectively for the development of ovarian tumors over a period of 35.7+/-30.6 months by physical examination and pelvic ultrasonography. They were compared with 11 women (age at first evaluation, 32.9+/-17 yr) who were enrolled under the same protocol (follow up, 32.3+/-25.1 months) and served as a control group. In addition, a registry of 178 women from among a total of 309 patients with CNC was searched retrospectively for any having ovarian tumors. Seven available histological specimens were rereviewed. None of the CNC patients had ovarian tumors analogous to those of PJS. Two patients with CNC in the prospective group developed ovarian tumors and were operated upon. One had bilateral oophorectomy for asynchronous serous cystadenomas. The second patient had a unilateral serous cystadenoma. Resected tumor tissue from both patients was tested for genetic abnormalities of the chromosomal regions to which CNC genetic loci have been mapped. Both showed genomic amplification of chromosomal region 2p16. An additional 10 patients had at least 1 sonogram positive for ovarian cysts. Only 1 of the patients in the control group was found to have a persistent, simple ovarian cyst by ultrasonography. The registry of 178 CNC patients included 4 who had undergone surgery for ovarian tumors. The diagnoses included endometrioid adenocarcinoma (1 patient) and metastatic mucinous adenocarcinoma (the primary site was probably ovarian; 1 patient). In addition, 7 of 12 patients (58%) with CNC, who died of other causes, had ovarian lesions at autopsy. In conclusion, although the same stromal tumor, large-cell calcifying Sertoli cell tumor, affects the testes in CNC and PJS, we did not find such tumors in a small population of CNC patients that was studied prospectively or a larger group of CNC patients that was studied retrospectively. The results of our study also suggested that women with CNC commonly develop ovarian cysts and may be at risk for ovarian carcinoma. The chromosome 2p16 CNC locus was involved in ovarian pathology with apparent copy number gain, suggesting that at least molecularly there is some involvement of the CNC gene(s) in these lesions. Although ovarian tumors do not seem to be a major manifestation of CNC, sonography of the ovaries may be part of the initial evaluation for this genetic syndrome in women with CNC; follow-up of any identified lesion is recommended because of the possible risk for malignancy.

Somatic von Hippel-Lindau gene mutations detected in sporadic endolymphatic sac tumors

Endolymphatic sac tumors (ELSTs) occur sporadically or in association with an autosomal dominantly inherited tumor syndrome, von Hippel-Lindau (VHL) disease. In VHL disease, a germline mutation of the VHL tumor suppressor gene is inherited, and loss of function of the wild-type allele occurs through genetic deletion with subsequent development of neoplastic growth. Genetic alterations associated with sporadic ELSTs are less well understood. In this study, we used tissue microdissection to selectively analyze neoplastic cells from four sporadic ELSTs. In two cases, we detected somatic mutations involving VHL gene exons 1 and 2, respectively. Additionally, one of these cases revealed deletion of the VHL gene locus. Two cases did not reveal VHL gene mutation; one of these two cases showed VHL gene deletion. These results suggest that mutations and allelic deletions of the VHL tumor suppressor gene play a role in the tumorigenesis of sporadic ELSTs.

Genetic and histologic studies of somatomammotropic pituitary tumors in patients with the "complex of spotty skin pigmentation, myxomas, endocrine overactivity and schwannomas" (Carney complex)

Carney complex (CNC) is a familial multiple neoplasia and lentiginosis syndrome with features overlapping those of McCune-Albright syndrome (MAS) and other multiple endocrine neoplasia (MEN) syndromes, MEN type 1 (MEN 1), in particular. GH-producing pituitary tumors have been described in individual reports and in at least two large CNC patient series. It has been suggested that the evolution of acromegaly in CNC resembles that of the other endocrine manifestations of CNC in its chronic, often indolent, progressive nature. However, histologic and molecular evidence has not been presented in support of this hypothesis. In this investigation, the pituitary glands of eight patients with CNC and acromegaly [age, 22.9+/-11.6 yr (mean +/- SD)] were studied histologically. Tumor DNA was used for comparative genomic hybridization (CGH) (four tumors). All tumors stained for both GH and prolactin PRL (eight of eight), and some for other hormones, including alpha-subunit. Evidence for somatomammotroph hyperplasia was present in five of the eight patients in proximity to adenoma tissue; in the remaining three only adenoma tissue was available for study. CGH showed multiple changes involving losses of chromosomal regions 6q, 7q, 11p, and 11q, and gains of 1pter-p32, 2q35-qter, 9q33-qter, 12q24-qter, 16, 17, 19p, 20p, 20q, 22p and 22q in the most aggressive tumor, an invasive macroadenoma; no chromosomal changes were seen in the microadenomas diagnosed prospectively (3 tumors). We conclude that, in at least some patients with CNC, the pituitary gland is characterized by somatotroph hyperplasia, which precedes GH-producing tumor formation, in a pathway similar to that suggested for MAS-related pituitary tumors. Three GH-producing microadenomas showed no genetic changes by CGH, whereas a macroadenoma in a patient, whose advanced acromegaly was not cured by surgery, showed extensive CGH changes. We speculate that these changes represent secondary and tertiary genetic "hits" involved in pituitary oncogenesis. The data (1) underline the need for early investigation for acromegaly in patients with CNC; (2) provide a molecular hypothesis for its clinical progression; and (3) suggest a model for MAS- and, perhaps, MEN 1-related GH-producing tumor formation.

Missense mutation of the MET gene detected in human glioma

Multiple mechanisms, such as gene mutations, amplifications, and rearrangements, as well as perturbed mitogen and receptor function, are likely to contribute to glioma formation. The MET (also known as c-met proto-oncogene located at 7q31-34 has been shown to be amplified in human gliomas, and activating mutations within the tyrosine kinase domain of MET have been causally related to tumorigenesis in hereditary papillary renal cell carcinoma. To elucidate the role of MET gene in glioma formation, sporadic gliomas from 11 patients were examined for MET gene mutations and allelic duplications or deletions by polymerase chain reaction-single strand conformational polymorphism analysis and fluorescence in situ hybridization. Three of 11 sporadic gliomas showed a deletion of one copy of the MET gene, and a specific METgene missense mutation in the remaining gene copy was detected in one of those tumors. The corresponding sequence in non-tumor DNA was normal in all cases. Three of 11 sporadic gliomas showed duplication of one copy of the MET gene, but none of them contained mutations. One tumor showed METamplification without mutation. Three showed neither allelic change nor mutation. These data suggest that somatic MET gene mutation may play a role in the development of a subgroup of sporadic gliomas. However, MET mutations appear to be absent in the majority of sporadic gliomas.

Analysis of recurrent germline mutations in the MEN1 gene encountered in apparently unrelated families

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder that manifests as varying combinations of tumors of endocrine and other tissues (parathyroids, pancreatic islets, duodenal endocrine cells, the anterior pituitary and others). The MEN1 gene is on chromosome 11q13; it was recently identified by positional cloning. We previously reported 32 different germline mutations in 47 of the 50 familial MEN1 probands studied at the NIH. Eight different germline MEN1 mutations were encountered repeatedly in two or more apparently unrelated families. We analyzed the haplotypes of families with recurrent MEN1 mutations with seven polymorphic markers in the 11q13 region surrounding the MEN1 gene (from D11S1883 to D11S4908). Disease haplotypes were inferred from germline DNA and also from tumors with 11ql3 loss of heterozygosity. Two different disease haplotype cores were shared by apparently unrelated families for two mutations in exon 2 (five families with 416delC and six families with 512delC). These two repeat mutations were associated with the two founder effects that we reported in a prior haplotype analysis. The disease haplotypes for each of the other six repeat mutations (seen twice each) were discordant, suggesting independent origins of these recurrent mutations. Most of the MEN1 germline mutations including all of those recurring independently occur in regions of CpG/CpNpG, short DNA repeats or single nucleotide repeat motifs. In conclusion, recurring germline mutations account for about half of the mutations in North American MEN1 families. They result from either founder effects or independent occurrence of one mutation more than one time.

Sporadic trichoepithelioma demonstrates deletions at 9q22.3

BACKGROUND

Trichoepithelioma (TE) is a benign cutaneous tumor that originates from hair follicles and occurs either in multiple or solitary lesions. Multiple TE is transmitted as an autosomal dominant trait, and a region at 9p21 is thought to be involved in the tumorigenesis. Solitary TE occurs more commonly than multiple TE and is not inherited. Histologically, TE tumors contain horn cysts and abortive hair papillae. A basal cell carcinoma appearance in some or all regions of a TE tumor can happen. In sporadic basal cell carcinoma, frequent deletions at 9q22.3 (Drosophila patched gene) have occurred. The objective of this study is to test whether loss of heterozygosity (LOH) on either 9p21 or on chromosome 9q22.3 could be detected in archival sporadic TE.

OBSERVATIONS

We studied 29 randomly selected cases of sporadic TE by microdissection and polymerase chain reaction using paraffin-embedded, formalin-fixed tissue specimens on glass slides. Analysis was performed with the polymorphic markers IFNA and D9S171 (9p21) as well as D9S15, D9S303, D9S287, and D9S252 (9q22.3).

RESULTS

The LOH at 9q22.3 was identified in 14 (48%) of 29 cases with at least 1 marker, while LOH could not be demonstrated using the markers IFNA and D9S171 (9p21).

CONCLUSIONS

The results show that the Drosophila patched gene LOH can be frequently identified in paraffin-embedded sporadic TE after routine processing and indicates a common gatekeeper mechanism for both TE and basal cell carcinoma.

Limitations on the quantitative determination of telomerase activity by the electrophoretic and ELISA based TRAP assays

Telomerase is a promising new tumor marker and can be detected using the TRAP (Telomeric Repeat Amplification Protocol) method. To address factors affecting its quantitative determination, we evaluated two commercial TRAP assays, an electrophoretic and an ELISA assay formats, using cultured cells and human tumor samples. We found that both TRAP assays had a limited linearity from 250 to 5000 tumor cells, with a similar intra-assay variation. The quantification of TRAP products was affected by high cell number in sample, the presence of non-tumor cells, and interfering substances in patient specimens. Because both assays have different limitations, determination of telomerase by a combined use of the two may provide more accurate information on the telomerase activity in a specimen. Extracts of specimens should also be tested at several concentrations to insure that the result is not being falsely decreased by an inhibitor. The quantitative results for telomerase activity by the TRAP assays, however, should be interpreted cautiously.