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Biomedical subjects

H T Lynch

Publications and source records attributed to H T Lynch.

At least 127 records · Page 7Linked to original sources
PubMed1996

Genetic counseling in a Navajo hereditary nonpolyposis colorectal cancer kindred.

BACKGROUND: Cross-cultural genetic counseling was provided to an extended Navajo Indian family in which the MLH1 gene mutation for hereditary nonpolyposis colorectal cancer (HNPCC) had been identified. The family had been observed by the authors since 1983 and over the years had been provided with intensive education regarding the natural history of HNPCC as well as recommendations for cancer surveillance and management that was responsive to this natural history. METHODS: Following identification of the MLH1 mutation, DNA from family members was evaluated by a reference laboratory (OncorMed, Gaithersburg, MD), where sequences were checked in both the forward and reverse directions against the published sequence for MLH1. The 4bp deletion beginning at the first nucleotide of codon 727 was easily visualized in the heterozygous condition in both affected and predispositional individuals. The family was reeducated as a group and then provided further education individually during genetic counseling sessions, at which time they were appraised of potential penalties, such as insurance and employer discrimination, and psychological sequelae that could result from knowledge of the MLH1 mutation. Strict confidentiality of this information was assured. RESULTS: DNA testing was performed on 51 family members. Twenty-three individuals were counseled, seven of whom were positive for MHL1. Reactions ranged from full acceptance of the genetic implications to traditional Navajo reasoning such as the family had been cursed. CONCLUSIONS: DNA-based genetic counseling requires comparison and empathy, coupled with intensive preeducation regarding potential penalties and advantages that might emanate from this knowledge. Special care must be given to patients' culture, beliefs, and traditions.

Adult↗
PubMed1996

Molecular and immunochemical analyses of RB1 and cyclin D1 in human ductal pancreatic carcinomas and cell lines.

Somatic mutations in the retinoblastoma-1 gene (RB1) and loss of RB1 protein function have been implicated in a number of human malignancies, but the role of RB1 gene and protein abnormalities in ductal pancreatic cancer (DPCA) is virtually unknown. We therefore analyzed expression of the RB1 protein immunohistochemically and/or by western blotting in a total of 54 sporadic and eight familial cases of archival and frozen DPCA and in 18 pancreatic carcinoma cell lines by using the antibodies RB-WL-1, 84-B3-1, and PMG3-245. Mutations in the RB1 promotor region and exons 13-21 of the RB1 gene were likewise examined by single-strand conformation polymorphism (SSCP) analyses and DNA sequencing of genomic DNA from 30 microdissected primary pancreatic tumors and the pancreatic carcinoma cell lines. Moreover, amplification and expression of a major regulatory component of RB1 function, cyclin D1, were assessed by southern and immunohistochemical analyses, respectively. The DPCAs were heterogeneous in both the intensity of RB1 nuclear staining and the percentage of immunoreactive cells. The tumors often had areas where RB1 staining was weak or absent adjacent to normal pancreatic tissue; however, only two of 32 archival cases and one of 30 frozen cases of DPCA completely lacked RB1 nuclear staining. Immunohistochemical and western blot analyses of 18 pancreatic carcinoma cell lines demonstrated the absence of RB1 expression in only two cell lines, Capan-1 and QGP-1. Analyses of the RB1 gene and promotor region by SSCP and DNA sequencing largely confirmed the immunochemical findings. Three of 30 primary carcinomas had abnormalities revealed by SSCP analyses. In one case a single base-pair deletion was confirmed in exon 18 and resulted in premature termination and the absence of detectable RB1 protein. A second case had TAC-->TTC missense mutation in exon 13. The third primary carcinoma could not be reliably sequenced because it had a low percentage of epithelial cells. The cyclin D1 gene was not amplified in any of the primary pancreatic tumors or cell lines examined. These immunochemical and molecular analyses of the RB1 tumor suppressor gene and cyclin D1 proto-oncogene in a large series of human pancreatic cancers and cell lines indicate that RB1 and cyclin D1 alterations occur during the development of some human DPCAs. Nevertheless, it is probable that alterations in cell-cycle regulation in DPCAs more frequently involve pathways other than those involving RB1 and cyclin D1.

Base Sequence↗
PubMed1996

Absence of germline mutations in exons 5-9 of the p53 gene in patients with Li-Fraumeni-like (SBLA) and familial adenomatous polyposis heritable cancer syndromes.

Although acquired mutations in the human p53 gene occur in many tumor types, germline mutations are rare. An exception is the occurrence of germline p53 mutations in a fraction of families afflicted with the Li-Fraumeni syndrome (LFS). Previous studies from our laboratory demonstrated increased levels of wild type p53 protein in skin fibroblasts (SF) of patients from heritable cancer syndrome, including familial adenomatous polyposis (FAP), neurofibromatosis type 1 (NF1), and bilateral retinoblastoma (bRB) (Kopelovich and DeLeo, 1984,1986). Here, we further address the association between germline p53 alterations and genetic predisposition to cancer in the SBLA syndrome and in FAP. DNA sequencing and single-stranded conformational polymorphism analysis (SSCP) were utilized to screen for the presence of mutations within exons 5-9 of the p53 gene in SF and in benign tumors. Thus we observed no germline mutations in exons 5-9 of the p53 gene in SF from SBLA or FAP patients, including the Gardner variant. In addition, we observed no acquired mutations in exons 5-9 of the p53 gene in benign tumors from FAP patients. In conclusion, we found no association between germline p53 mutations and SBLA or FAP. How mechanisms that involve nonmutational activation of the p53 protein might affect genetic predisposition to cancer remains to be established.

Adenomatous Polyposis Coli↗
PubMed1996

Ovarian cancer risk in BRCA1 carriers is modified by the HRAS1 variable number of tandem repeat (VNTR) locus.

Women who carry a mutation in the BRCA1 gene (on chromosome 17q21), have an 80% risk of breast cancer and a 40% risk of ovarian cancer by the age of 70 (ref. 1). The variable penetrance of BRCA1 suggests that other genetic and non-genetic factors play a role in tumourigenesis in these individuals. The HRAS1 variable number of tandem repeats (VNTR) polymorphism, located 1 kilobase (kb) downstream of the HRAS1 proto-oncogene (chromosome 11p15.5) is one possible genetic modifier of cancer penetrance. Individuals who have rare alleles of the VNTR have an increased risk of certain types of cancers, including breast cancer (2-4). To investigate whether the presence of rare HRAS1 alleles increases susceptibility to hereditary breast and ovarian cancer, we have typed a panel of 307 female BRCA1 carriers at this locus using a PCR-based technique. The risk for ovarian cancer was 2.11 times greater for BRCA1 carriers harbouring one or two rare HRAS1 alleles, compared to carriers with only common alleles (P = 0.015). The magnitude of the relative risk associated with a rare HRAS1 allele was not altered by adjusting for the other known risk factors for hereditary ovarian cancer (5). Susceptibility to breast cancer did not appear to be affected by the presence of rare HRAS1 alleles. This study is the first to show the effect of a modifying gene on the penetrance of an inherited cancer syndrome.

Adult↗
PubMed1996

Analysis of mismatch repair genes in hereditary non-polyposis colorectal cancer patients.

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant disorder characterized by the early onset of colorectal cancer and linked to germline defects in at least four mismatch repair genes. Although much has been learned about the molecular pathogenesis of this disease, questions related to effective presymptomatic diagnosis are largely unanswered because of its genetic complexity. In this study, we evaluated tumors from 74 HNPCC kindreds for genomic instability characteristic of a mismatch repair deficiency and found such instability in 92% of the kindreds. The entire coding regions of the five known human mismatch repair genes were evaluated in 48 kindreds with instability, and mutations were identified in 70%. This study demonstrates that a combination of techniques can be used to genetically diagnose tumor susceptibility in the majority of HNPCC kindreds and lays the foundation for genetic testing of this relatively common disease.

Base Sequence↗
PubMed1996

Linkage analysis identifies gene carriers among members of families with hereditary nonpolyposis colorectal cancer.

BACKGROUND & AIMS: Uncertainty about genetic risk in hereditary nonpolyposis colorectal cancer (HNPCC) may lead to unnecessary screening. The aims of this study were to show how gene linkage findings can elucidate who is at risk and requires intensive screening and how cancer control can be enhanced by screening high-risk family members. This information can be useful given the public health magnitude of HNPCC. METHODS: An extended family with HNPCC was studied using formal linkage analysis with DNA extraction from blood samples, followed by genotyping with polymerase chain reaction technique for microsatellite markers. Sixty-one blood relatives of a family with HNPCC, 5 of whom had colorectal cancer, and 12 unrelated family members underwent DNA sampling for genetic analysis. RESULTS: Linkage analysis showed that all 5 affected individuals had a haplotype with the same alleles 10/7/9, which was also detected in 13 first-degree healthy gene carriers and absent in the remaining 43 non-gene carriers. In the asymptomatic subjects screened, one incidental colorectal cancer and four adenomas were detected in 3 of 6 gene carriers. An adenoma was found in 1 of 17 noncarriers; the remaining 16 noncarriers have undergone 67 unnecessary colonoscopies. CONCLUSIONS: Linkage analysis can differentiate gene carriers from non carriers. Colorectal cancer screening should be restricted to gene carriers.

Adolescent↗
PubMed1996

A high incidence of BRCA1 mutations in 20 breast-ovarian cancer families.

We have analyzed 20 breast-ovarian cancer families, the majority of which show positive evidence of linkage to chromosome 17q12 for germ-line mutations in the BRCA1 gene. BRCA1 mutations cosegregating with breast and ovarian cancer susceptibility were identified in 16 families, including 1 family with a case of male breast cancer. Nine of these mutations have not been reported previously. The majority of mutations were found to generate a premature stop codon leading to the formation of a truncated BRCA1 protein of 2%-88% of the expected normal length. Two mutations altered the RING finger domain. Sequencing of genomic DNA led to the identification of a mutation in the coding region of BRCA1 in 12 families, and cDNA analysis revealed an abnormal or missing BRCA1 transcript in 4 of the 8 remaining families. A total of eight mutations were associated with a reduced quantity of BRCA1 transcript. We were unable to detect BRCA1 mutations in 4 of the 20 families, but only 1 of these was clearly linked to BRCA1. It is expected that the majority of clear examples of the breast-ovarian syndrome will be associated with germ-line mutations in the coding region of BRCA1.

Alternative Splicing↗
PubMed1996

Familial pancreatic cancer: a review.

The cause of pancreatic cancer remains elusive. The most consistently identified epidemiological risk factor is cigarette smoking. Genetic factors are known to play a significant role in perhaps 5% of the total pancreatic cancer burden. Recent discoveries in molecular biology, particularly germline mutations in inherited conditions which feature pancreatic cancer as an integral part of the tumor spectrum such as in adenomatosis polyposis and hereditary nonpolyposis colorectal cancer, provide powerful incentive to search for other "cancer genes" in this heterogeneous disease. Early detection of this dreadful disease is crucial because its mortality rate approximates its incidence; the ability to identify high-risk patients on the basis of genetic analysis would significantly enhance the potential for early diagnosis. This review addresses the genetic epidemiology of pancreatic cancer and updates our views on screening, surgery, chemotherapy, and genetic counseling, all of which must be used to gain value from genetic predictability of risk status.

Adenomatous Polyposis Coli↗
PubMed1996

Genetic counseling in an extended attenauted familial adenomatous polyposis kindred.

OBJECTIVES: To provide DNA-based genetic counseling to family members in the direct genetic lineage of a family fulfilling phenotypical criteria for the autosomal, dominantly inherited, attenuated familial adenomatous polyp (AFAP) syndrome. This enabled highly targeted cancer risk estimation based on cancer phenotype in concert with the presence or absence of the adenomatous polyposis coli (APC) germline mutation. Management recommendations could then be fully responsive to this syndrome's natural history. METHODS: Detailed family history with pathology verification of colonic polyps and cancer was performed on an extended AFAP kindred. Endoscopic gastrointestinal examinations enabled detailed knowledge of the syndrome's upper and lower gastrointestinal tract phenotype. Molecular genetic evaluation of DNA led to the identification of the APC germline mutation which co-segregated with the phenotype. RESULTS: Forty-two members of this extended AFAP family underwent DNA testing, wherein 27 were found to harbor the APC germline mutation,thereby enabling precision in their genetic counseling. Anecdotal examples of this counseling experience, with particular attention to psychological reactions, as well as concerns about such issues as insurance and employer discrimination, have been described. CONCLUSIONS: When DNA-based testing is offered to AFAP family members, genetic counselors must compassionately consider patients' psychological concerns when providing detailed risk status and available surveillance and management programs.

Adenomatous Polyposis Coli↗
PubMed1996

Two distinct origins of a common BRCA1 mutation in breast-ovarian cancer families: a genetic study of 15 185delAG-mutation kindreds.

We screened 163 women from breast-ovarian cancer-prone families, as well as 178 individuals affected with breast and/or ovarian cancer but unselected for family history, for germ-line mutations in exon 2 of BRCA1, by SSCP analysis and direct sequencing. A total of 25 mutations were detected. Thirteen of 64 Jewish Ashkenazi women and 2 non-Jewish individuals were found to possess the 185delAG mutation. Haplotype data for all 15 individuals, with markers intragenic to BRCA1, suggest that the Jewish Ashkenazi individuals share a common ancestry that is distinct from the lineage shared by the other two women. These data provide the first evidence of two distinct lines of transmission for the 185delAG mutation, only one of which has its origins in the Jewish Ashkenazi population. Our screening also uncovered 10 affected individuals with an 11-bp deletion at nucleotide 188 of BRCA1 (188del11), 4 of whom are Ashkenazi Jews. This is only the third reported mutation detected within the Jewish Ashkenazi population and may represent the second most common alteration in BRCA1 found in Ashkenazi Jews in the United States. The observed overrepresentation of specific mutations within a subgroup of the general population may eventually contribute to the development of inexpensive and routine tests for BRCA1 mutations, as well as to the elucidation of other contributory factors (e.g., diet, environment, and chemical exposures) that may play a key role in cancer initiation and development. The implications of the mutational data, as well as the role that founder effect, demographic history, and penetrance play in the resulting observed phenomena, are discussed.

Adult↗
PubMed1996

Genetic counseling for hereditary cancer.

This paper provides an overview of the current approach to genetic counseling for cancer, using hereditary nonpolyposis colorectal cancer (HNPCC) as a prototype. Heretofore, when evaluating the possibility of an HNPCC diagnosis, physicians had to rely exclusively on a detailed family history of cancer in the context of an extended pedigree. Patients in the direct genetic lineage who had one or more first-degree relatives with an HNPCC syndrome cancer were told that they had a 50% likelihood of inheriting the deleterious gene. However, with the discovery of the HNPCC genes (hMSH2, hMLH1, hPMS1, hPMS2), genetic counseling can now provide a more precise determination of a patient's lifetime cancer destiny. Since these DNA findings are new, guidelines for sharing this information with patients remain preliminary. One must be certain that the patient wants to receive DNA information and that he or she is aware of potential discrimination by insurance companies and employers, as well as the possibility of psychological sequelae.

Colorectal Neoplasms, Hereditary Nonpolyposis↗