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C Eng

Publications and source records attributed to C Eng.

At least 73 records · Page 4Linked to original sources
PubMed1999

Specific polymorphisms in the RET proto-oncogene are over-represented in patients with Hirschsprung disease and may represent loci modifying phenotypic expression.

Hirschsprung disease (HSCR) is a common genetic disorder presenting with functional intestinal obstruction secondary to enteric aganglionosis. HSCR can be familial or sporadic. Although five putative susceptibility genes have been identified, only germline mutations in the RET proto-oncogene account for a significant minority (up to 50%) of familial HSCR; 3% of sporadic HSCR in a population based series carry RET mutations. From 1998 to February 1999, we prospectively ascertained 64 cases of sporadic HSCR from the western Andalusia region. To determine if polymorphic sequence variants within RET could act as low penetrance predisposing alleles, we examined allelic frequencies at seven polymorphic loci in this population based series. Whether allele frequencies differed from those in the control population were determined by either chi-squared analysis or Fisher's exact test. For two sequence variants, A45A (c 135G-->A) (exon 2) and L769L (c 2307T-->G) (exon 13), the rarer polymorphic allele was over-represented among HSCR cases versus controls (p<0.0006). In contrast, two other polymorphisms, G691S (c 2071C-->A) (exon 11) and S904S (c 2712C-->G) (exon 15), were under-represented in the HSCR patients compared to controls (p=0.02). Polymorphisms in the RET proto-oncogene appear to predispose to HSCR in a complex, low penetrance fashion and may also modify phenotypic expression.

Case-Control Studies↗
PubMed1999

RET proto-oncogene in the development of human cancer.

The RET proto-oncogene, located on chromosome subband 10q11.2, encodes a receptor tyrosine kinase expressed in tissues and tumors derived from neural crest. Germline (present in every cell of the body) mutations in RET cause multiple endocrine neoplasia type 2 (MEN 2), an inherited cancer syndrome characterized by medullary thyroid carcinoma (MTC), pheochromocytoma (PC), and hyperparathyroidism (HPT). This knowledge has allowed molecular diagnosis and presymptomatic DNA-based testing to become possible. RET testing is considered the standard of care in MEN 2 families because clinical decisions are made based on the results of such gene testing. There appears to be a correlation between specific RET mutation type and organ-specific tumor development. Such knowledge might be useful in tailoring targeted surveillance in the near future. Somatic (in the tumor only) RET mutations have been found in a proportion of sporadic MTCs and PCs. Whether the presence of somatic RET mutation is associated with a poor prognosis is currently being investigated as another tool for molecular medicine.

Carcinoma, Papillary↗
PubMed1999

Mutation analysis reveals novel sequence variants in NTRK1 in sporadic human medullary thyroid carcinoma.

Tyrosine kinase NTRK1 is expressed in neural and nonneuronal tissues. Like RET, NTRK1 is often activated by rearrangements that involve one of at least five other genes in papillary thyroid carcinoma (PTC). Because of similarities in involvement of the two tyrosine kinases RET (rearranged during transfection) and NTRK1 in the pathogenesis of PTC, the obvious parallels between RET and NTRK1 and between PTC and medullary thyroid carcinoma (MTC), NTRK1 seemed to be an excellent candidate gene to play a role in the genesis of MTC. Single-strand conformational polymorphism analysis of 16 exons of NTRK1, from 31 sporadic MTC, revealed variants in five exons (exons 4 and 14-17). Sequence analysis demonstrated one sequence variant each in exons 4, 14, 16, and 17, and four different variants in exon 15. Differential restriction enzyme digestion specific for each variant confirmed the sequencing results. All variants were also present in the corresponding germline DNA. Interestingly, the sequence variants at codon 604 (c1810C>T) and codon 613 (c1838G>T) ofexon 15 always occurred together and might represent linkage disequilibrium. The frequencies of the sequence variants in germline DNA from patients with sporadic MTC did not differ significantly from those in a race-matched control group. Although we did not find any somatic mutations of NTRK1 in sporadic MTC, the single-strand conformational polymorphism conditions reported here, together with the knowledge of the frequency of various sequence variants, may help in future mutation analyses of DNA from other neural and nonneural tissues.

Carcinoma, Medullary↗
PubMed1999

Differences in allelic distribution of two polymorphisms in the VHL-associated gene CUL2 in pheochromocytoma patients without somatic CUL2 mutations.

Although the two major familial forms of pheochromocytomas, multiple endocrine neoplasia type 2 and von-Hippel-Lindau disease (VHL), have been associated with mutations of the RET and VHL genes, respectively, the molecular pathogenesis of sporadic pheochromocytomas is largely unknown. Recently, a putative tumor suppressor gene has been identified, CUL2, whose product has been shown to interact with the VHL tumor suppressor. To examine whether CUL2 plays a role in pheochromocytoma pathogenesis, we analyzed a series of 26 distinct tumor samples for mutations in the whole coding region of this gene. There were no somatic pathogenic mutations in CUL2, except for 1 sporadic tumor that had a hemizygous gene deletion. We also found 3 novel polymorphisms in the gene. One of these variants, IVS5-6C/T, as well as another previously described one, c.2057G/A, were overrepresented among the pheochromocytoma patients compared to that in a control population (P < 0.005 and P < 0.01, respectively). Although our findings suggest that CUL2 does not play a major role in the pathogenesis of pheochromocytomas, it is still unknown whether epigenetic mechanisms are involved in its inactivation in VHL-associated tumors. Furthermore, the potential role for the overrepresented alleles in the pheochromocytoma group requires further investigation.

Adolescent↗
PubMed1999

Investigation of germline GFR alpha-1 mutations in Hirschsprung disease.

Inactivating mutations of the RET proto-oncogene and of one of its soluble ligand molecules, glial cell line derived neurotrophic factor (GDNF), have been found in a subset of patients with Hirschsprung disease (HSCR). However, the majority of HSCR mutations remain unidentified. As normal RET function requires a multicomponent ligand complex for activation, other members of the RET ligand complex are primary candidates for these mutations. We investigated the presence of mutations in another member of the RET signalling complex, GDNF family receptor alpha-1 (GFR alpha-1), in a panel of 269 independent cases of HSCR. We identified 10 polymorphisms at the GFR alpha-1 locus. Surprisingly, however, we did not identify any sequence variants in our HSCR population that were not also present in a normal control population. Our data suggest that mutations of the GFR alpha-1 gene are not a common aetiological event in HSCR.

Alternative Splicing↗
PubMed1999

Genomic organization and chromosomal localization of the human CUL2 gene and the role of von Hippel-Lindau tumor suppressor-binding protein (CUL2 and VBP1) mutation and loss in renal-cell carcinoma development.

Germline mutations in the von Hippel-Lindau (VHL) disease tumor suppressor gene (TSG) convey a high risk of clear-cell renal-cell carcinoma (CC-RCC) and most sporadic CC-RCCs demonstrate somatic inactivation of the VHL TSG. However, the existence of further CC-RCC gatekeeper genes is implied by CC-RCC kindreds not linked to the VHL gene and the absence of somatic VHL inactivation in approximately 30% of sporadic CC-RCC. Genes that encode proteins which interact with the VHL gene product (VHL) provide candidate gatekeeper RCC genes. VHL forms a multimeric complex with two subunits (B and C) of the SIII (elongin) transcriptional elongation complex and CUL2, a member of the cullin family. Most pathogenic VHL mutations inhibit formation of the VHL/elonginB+C/CUL2 complex. A further VHL-binding protein of unknown function, VBP1, fails to bind to truncated forms of VHL. We have investigated the possible roles of CUL2 and VBP1 in renal tumorigenesis by analyzing sporadic RCC of known VHL mutation or hypermethylation status, including CC-RCC without VHL inactivation (n = 40); CC-RCC with VHL inactivation (n = 35); and non-CC-RCC (n = 14). No VBP1 mutations were identified in 89 sporadic RCCs, suggesting that VBP1 is not an RCC gatekeeper gene. To investigate CUL2, we mapped the CUL2 gene to chromosome band 10p11.1-p11.2, a region reported to show loss of heterozygosity (LOH) in several human cancers (including non-CC-RCC); determined the genomic organization; and performed mutation analysis of the 21 exons identified. Using novel intragenic polymorphisms, we detected LOH in 6/25 informative RCCs; however, no pathogenic CUL2 mutations were identified in the 89 RCCs analyzed. These findings suggest that unless CUL2 is inactivated by epigenetic events, it is not a major RCC TSG. However, CUL2 remains a candidate TSG for other tumor types demonstrating 10p LOH. Genes Chromosomes Cancer 26:20-28, 1999.

Carcinoma, Renal Cell↗
PubMed1999

The role of PTEN, a phosphatase gene, in inherited and sporadic nonmedullary thyroid tumors.

PTEN/MMACI/TEP1, a tumor suppressor gene located on 10q23.3, encodes an almost ubiquitously expressed dual-specificity phosphatase. Germline mutations in PTEN have been found in the majority of cases of sporadic and familial Cowden syndrome (CS), an autosomal dominant inherited cancer syndrome characterised by multiple hamartomas and benign and malignant disease of the thyroid and breast. Interestingly, germline mutations in PTEN have also been found in about 50% of a related but distinct disorder, Bannayan-Ruvalcaba-Riley syndrome (BRR), which is characterised by neonatal-onset macrocephaly, mental retardation, Hashimoto's thyroiditis, lipomatosis, haemangiomas, hamartomatous polyps, and pigmented macules of the glans penis. Somatic PTEN mutation has been described to a greater or lesser extent in various benign and malignant tumor types. Somatic deletions have been described in follicular adenomas of the thyroid and papillary thyroid carcinomas.

Genes, Tumor Suppressor↗
PubMed1998

Germline PTEN mutation in a family with Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome.

Clinical overlap between Cowden disease and Bannayan-Riley-Ruvalcaba syndrome has rarely been described and identical germline mutations in the PTEN gene have been demonstrated in a few families with Cowden disease and some cases of Bannayan-Riley-Ruvalcaba syndrome. We report on a mother with Cowden disease and a son with Bannayan-Riley-Ruvalcaba syndrome. Mutation analysis of the PTEN gene demonstrated a heterozygous nonsense mutation R130X in both individuals. This might suggest that Cowden disease and Bannayan-Riley-Ruvalcaba syndrome are one causal entity.

Adolescent↗
PubMed1998

Molecular analysis of two putative tumour suppressor genes, PTEN and DMBT, which have been implicated in glioblastoma multiforme disease progression.

The transition from low grade astrocytoma to glioblastoma multiforme is almost always accompanied by the loss of genetic markers from chromosome 10. Recently two genes, PTEN/MMAC1/TEP1 and DMBT, have been isolated from chromosome 10q. We have analysed these two genes for mutations in 21 primary glioblastomas. An exon by exon screen of the PTEN gene using SSCP failed to identify any mutations in this tumour series. In contrast, 38% of tumours showed intragenic homozygous deletions in the DMBT gene. The fact that the majority of gliomas do not carry mutations in either of these genes suggests that there may still be other genes on chromosome 10 which are important in the development of glioblastoma multiforme.

Agglutinins↗
PubMed1998

Germline mutations in PTEN are an infrequent cause of genetic predisposition to breast cancer.

Heterozygous germline mutations in PTEN are responsible for most cases of Cowden Syndrome, a rare familial trait characterized by hamartomas and by predisposition to cancer of the breast and thyroid. The variable and often subtle clinical findings that characterize Cowden Syndrome are frequently unrecognized, raising the possibility that germline PTEN mutations may confer susceptibility to breast cancer in women who have not been diagnosed with this syndrome. To determine whether such mutations contribute to genetic predisposition to breast cancer within the general population, we analysed a cohort of women with early-onset breast cancer (< age 40), a subset of the population at increased risk for genetic susceptibility. Lymphoblast cell lines were analysed using either direct nucleotide sequencing (28 cases), denaturing gradient gel electrophoresis (DGGE) (34 cases) or a yeast-based truncation assay (110 cases). No definitive, truncating mutations were observed in 172 patients. Missense changes were noted in the germline of 2/60 patients analysed by direct nucleotide sequencing or DGGE, including a non-conservative amino acid substitution within the phosphatase domain, but neither showed loss of the wild-type allele in the corresponding breast tumor specimen. We conclude that germline mutations in PTEN are an uncommon cause of genetic predisposition to breast cancer within the general population.

Adult↗
PubMed1998

PTEN/MMAC1/TEP1 involvement in primary prostate cancers.

The PTEN/MMAC1/TEP1 gene, located at 10q23.3, is a tumor suppressor gene responsible for the familial cancer syndromes Cowden disease and Bannayan-Zonana syndrome, and is commonly somatically mutated in several types of cancers. Mutations of the PTEN gene have been found in prostate cancer cell lines and LOH at 10q22-24 in prostate tumors have also been described with a high frequency. To determine the role of this gene in prostate tumorigenesis, we therefore analysed 22 primary tumors for loss of heterozygosity (LOH) within the 10q22-23 region such that tumors hemizygous at those loci may be examined for somatic PTEN mutations. Losses of heterozygosity of at least one locus was found in 12 (55%) of the 22 tumors DNAs. Among these, six tumors exhibited allele loss in the interval between D10S1765 and D10S541 wherein lies the PTEN gene. We searched the entire coding region of PTEN for somatic mutations in these six tumors. One somatic mutation (17%), a 1 bp deletion, was detected in exon 7 of the gene, in one tumor, indicating that somatic mutations of the PTEN gene may occur in primary prostate tumors.

Chromosomes, Human, Pair 10↗
PubMed1998

Rapid design of denaturing gradient-based two-dimensional electrophoretic gene mutational scanning tests.

With the current rapid pace at which human disease genes are identified there is a need for practical, cost-efficient genetic screening tests. Two-dimensional electrophoretic separation of PCR-amplified gene fragments on the basis of size and base pair sequence, in non-denaturing and denaturing gradient polyacrylamide gels respectively, provides a rapid parallel approach to gene mutational scanning. Accuracy of the denaturing gradient gel electrophoresis (DGGE) component of this system strongly depends on the design of the PCR primers and the melting characteristics of the fragments they encompass. We have developed a fully automated generally applicable procedure to generate optimal two-dimensional test designs at a minimum amount of time and effort. Designs were generated for the RB1 , TP53 , MLH1 and BRCA1 genes that can be readily implemented in research and clinical laboratories as low cost genetic screening tests.

Adaptor Proteins, Signal Transducing↗
PubMed1998

A highly conserved processed PTEN pseudogene is located on chromosome band 9p21.

PTEN/MMAC1/TEP1, encoding a dual-specificity phosphatase, is a tumor suppressor gene which has recently been cloned and mapped to chromosome 10q23.3. We have shown that germline mutations of PTEN are present in individuals with two hamartoma syndromes: Cowden Syndrome, associated with a predisposition to breast and thyroid cancers, and Bannayan-Zonana syndrome. Somatic mutations of PTEN have been reported in a variety of human cancer cell lines, suggesting a potential role for this gene in the pathogenesis of human malignancies. We report the identification of a highly conserved PTEN processed pseudogene, psiPTEN, which shares over 98% homology with the coding region of functional PTEN, and its localisation to chromosome 9p21. The high sequence homology of psiPTEN with the PTEN transcript may potentially lead to misinterpretation when performing mutation analyses based on cDNA templates. Caution should be exerted when using such screening approaches.

Amino Acid Sequence↗
PubMed1998

PTEN mutations in gliomas and glioneuronal tumors.

Cytogenetic and loss of heterozygosity studies have suggested the presence of at least one tumor suppressor gene on chromosome 10 involved in the formation of high grade gliomas. Recently, the PTEN gene, also termed MMAC1 or TEP1, on chromosomal band 10q23 has been identified. Initial studies revealed mutations of PTEN in limited series of glioma cell lines and glioblastomas. In order to systematically evaluate the involvement of PTEN in gliomas, we have analysed the entire PTEN coding sequence by SSCP and direct sequencing in a series of 331 gliomas and glioneuronal tumors. PTEN mutations were detected in 20/142 glioblastomas, 1/7 giant cell glioblastomas, 1/2 gliosarcomas, 1/30 pilocytic astrocytomas and 2/22 oligodendrogliomas. No PTEN mutations were detected in 52 astrocytomas, 37 oligoastrocytomas, three subependymal giant cell astrocytomas, four pleomorphic xanthoastrocytomas, 15 ependymomas, 16 gangliogliomas and one dysembryoplastic neuroepithelial tumor. In addition, all tumors were examined for the presence of homozygous deletions of the PTEN gene; these were detected in 7 glioblastomas that did not have PTEN mutations. Therefore, PTEN mutations occur in approximately 20% of glioblastomas but are rare in lower grade gliomas. These findings confirm that PTEN is one of the chromosome 10 tumor suppressor genes involved in the development of glioblastomas.

Female↗
PubMed1998

Analysis of PTEN and the 10q23 region in primary prostate carcinomas.

Deletions involving chromosome 10q23 occur frequently in prostatic carcinomas. Recently, a novel tumour suppressor gene, PTEN, mapping to this interval, has been identified. Mutation or deletion of PTEN has been observed in a proportion of prostate cancer cell lines; however, primary prostate carcinomas have not been studied. We have investigated the involvement of PTEN in primary prostatic adenocarcinomas using a panel of 51 matched normal and prostate tumour DNAs. We first determined the proportion of tumours with allele loss at loci in 10q23 which span the region containing the PTEN gene. Our results show that LOH involving 10q23 is common in primary prostate carcinomas. Twenty-five of 51 (49%) tumours showed loss of heterozygosity (LOH) over the region spanning the PTEN locus. We next directly analysed the PTEN gene for mutations of the coding region using single strand conformation polymorphism (SSCP) and sequence analyses. Of those tumours with LOH, only a single tumour was found to carry a missense mutation in PTEN. No mutations in PTEN were identified in tumours without LOH. Our results suggest either that mutation of PTEN is a late event in prostate tumorigenesis, or that another tumour suppressor gene important in prostate cancer may lie close to PTEN in 10q23.

Adenocarcinoma↗
PubMed1998

Genomic structure and chromosomal localization of the human GDNFR-alpha gene.

GDNFR-alpha is a glycosyl-phosphotidylinositol-linked receptor for glial cell line-derived neurotrophic factor (GDNF). GDNF binds to GDNFR-alpha and this complex, in turn, is believed to interact with the RET receptor tyrosine kinase to effect downstream signalling. GDNFR-alpha belongs to a novel gene family without strong homology to known genes. Thus, little information has been available to help predict genomic structure or location of this gene. In this study, the genomic organization of human GDNFR-alpha was delineated through a combination of PAC clone characterization, long distance PCR and sequence analyses. Exon-intron boundaries were defined by comparing the size and sequence of the genomic PCR products to those predicted by the cDNA sequence. The human GDNFR-alpha gene comprises 9 exons. GDNFR-alpha PAC clones were used for FISH analysis to map this gene to 10q26.

Base Sequence↗
PubMed1998

Allelic imbalance, including deletion of PTEN/MMACI, at the Cowden disease locus on 10q22-23, in hamartomas from patients with Cowden syndrome and germline PTEN mutation.

Cowden disease (CD) is a rare, autosomal dominant inherited cancer syndrome characterized by multiple benign and malignant lesions in a wide spectrum of tissues. While individuals with CD have an increased risk of breast and thyroid neoplasms, the primary features of CD are hamartomas. The gene for CD has been mapped by linkage analysis to a 6 cM region on the long arm of chromosome 10 at 10q22-23. Loss of heterozygosity (LOH) studies of sporadic follicular thyroid adenomas and carcinomas, both component tumors of CD, have suggested that the putative susceptibility gene for CD is a tumor suppressor gene. Somatic missense and nonsense mutations have recently been identified in breast, prostate, and brain tumor cell lines in a gene encoding a dual specificity phosphatase, PTEN/MMACI, mapped at 10q23.3. Furthermore, germline PTEN/MMACI mutations are associated with CD. In the present study, 20 hamartomas from 11 individuals belonging to ten unrelated families with CD have been examined for LOH of markers flanking and within PTEN/MMACI. Eight of these ten families have germline PTEN/MMACI mutations. LOH involving microsatellite markers within the CD interval, and including PTEN/MMACI, was identified in two fibroadenomas of the breast, a thyroid adenoma, and a pulmonary hamartoma belonging to 3 to 11 (27%) of these patients. The wild-type allele was lost in these hamartomas. Semi-quantitative PCR performed on RNA from hamartomas from three different tissues from a CD patient suggested substantial reduction of PTEN/MMACI RNA levels in all of these tissues. The LOH identified in samples from individuals with CD and the suggestion of allelic loss and reduced transcription in hamartomas from a CD patient provide evidence that PTEN/MMACI functions as a tumor suppressor in CD.

Chromosomes, Human, Pair 10↗