Identification of the breast cancer susceptibility gene BRCA2

Cancer risks in two large breast cancer families linked to BRCA2 on chromosome 13q12-13

The penetrance of the BRCA2 gene on chromosome 13q12-13 has been estimated in two large, systematically ascertained, linked families, by use of a maximum-likelihood method to incorporate both cancer-incidence data and 13q marker typings in the families. The cumulative risk of breast cancer in female gene carriers was estimated to be 59.8% by age 50 years (95% confidence interval [95% CI] 25.9%-78.5%) and 79.5% by age 70 years (95% CI 28.9%-97.5%). The cumulative risk of breast cancer in male carriers was estimated to be 6.3% (95% CI 1.4%-25.6%) by age 70 years. There was no evidence of any risk difference between the two families. These results indicate that the lifetime breast cancer risk in BRCA2 carriers, for at least a subset of mutations, is comparable to that for BRCA1. A significant excess of ovarian cancer in gene carriers was observed (relative risk 17.69, based on three cases), but the absolute risk of ovarian cancer was less than that reported for BRCA1. Significant excesses of laryngeal cancer (relative risk 7.67, based on two possible carriers) and prostate cancer (relative risk 2.89, based on five possible carriers) were also observed. One case of ocular melanoma, as well as a second eye cancer of unspecified histology, occurred in obligate gene carriers.

Genomic deletions in the BRCA1, BRCA2 and TP53 regions associate with low expression of the estrogen receptor in sporadic breast carcinoma

Sporadic breast carcinoma is associated with multiple genetic alterations. The clinical relevance of these alterations, however, needs further clarification. In the present study we analyzed 266 spontaneously arising breast carcinomas for allelic losses in the BRCA1 and TP53 regions on chromosome 17, the BRCA2 region on chromosome 13, the ATM (mutated in ataxia-telangiectasia) region on chromosome 11 and on the chromosomal arms 7q and 16q. In addition the following clinical and pathological parameters were evaluated: age at diagnosis, tumor size, presence or absence of regional and distant metastases, hormone-receptor status, histopathological classification and tumor grading. The analysis of genetic and clinical observations revealed significant associations: absence of expression of the estrogen receptor was linked to a high rate of allelic losses of markers in the BRCA1, TP53 and BRCA2 regions. Expression of the progesterone receptor coincided with allelic loss on the long arm of chromosome 16. High-grade malignant lesions and ductal differentiation were frequently associated with allelic losses in the proximal portion of chromosome 17q. The accumulation of multiple allelic deletions was linked to high-grade malignant tumors, to tumor size, and to loss of expression of the estrogen receptor. Our data point to a relationship between clinically relevant prognostic factors and specific genomic deletions in the BRCA1, BRCA2 and TP53 region.

A descriptive study of BRCA1 testing and reactions to disclosure of test results

BACKGROUND

The identification of the BRCA1 gene is a powerful tool for predicting a patient's lifetime risk for carcinoma of the breast and ovary when she has hereditary breast/ovarian carcinoma (HBOC) syndrome. The process of BRCA1 testing and genetic counseling and participants' reactions to test results, are described.

METHODS

Education about the natural history of HBOC syndrome and the pros and cons of genetic testing was provided to 14 HBOC families comprised of 2549 bloodline relatives. Of these, 388 underwent DNA testing. After informed consent was given by participants, formal linkage analysis and gene mutation studies were performed on the families. Qualitative data on intentions and emotional reactions were collected by physicians/counselors during the genetic counseling sessions.

RESULTS

Of those tested, 181 received their results after further genetic counseling. Seventy-eight of them were positive and 100 were negative for BRCA1 gene mutation. Three had ambiguous findings. The most common reasons given for seeking DNA testing were concern about risk to children and concern about surveillance and prevention. Prophylactic mastectomy was considered by 35% of women who tested positive, whereas prophylactic oophorectomy was considered an important option by 76%. Twenty-five percent of both BRCA1 positive and negative individuals were concerned about discrimination by insurance companies. Eighty percent of those who tested negative reported emotional relief, whereas over one-third of those who tested positive reported sadness, anger, or guilt.

CONCLUSIONS

DNA testing of patients with HBOC syndrome must be performed in the context of genetic counseling. The authors' results demonstrate the many complex clinical and nonclinical issues that are important in this process.

Genetic testing for susceptibility to breast cancer: findings from women's focus groups

Before designing an intervention to assist women in making informed decisions about BRCA1 testing, we conducted focus groups with women who had breast cancer and unaffected women whose relatives had it to better understand women's knowledge, concerns about testing, and potential influences and support needs in making a decision about genetic testing for susceptibility to breast cancer. Findings show a general lack of knowledge about genetic testing for breast cancer and what it means to have a positive test result, a strong concern for family members, particularly daughters, to use information from testing to help them make better decisions about their health and lifestyle choices, a strong sense of altruism, particularly among affected women, about being tested to help other women, not just family, and various support needs surrounding the testing experience, including an active role for physicians in the decision process. The major advantages to testing seem to be for information that could help reduce uncertainty and assist with making future decisions about medical treatment and plans for surveillance and some lifestyle changes. The major disadvantages to testing were concerns about confidentiality and loss of insurance, the lack of proven options for women after testing, and stress from knowing one had the BRCA1 mutation. These focus group discussions show women's concerns and ambivalence about genetic testing. We need to provide women with balanced information about the positive and negative aspects of such testing, determine how best to involve physicians in women's decisions about testing, consider the effects of testing on family relationships, and provide more public education about what genetic testing is and what it means.

Immunohistochemically detected p53 and HER-2/neu expression and nuclear DNA content in familial epithelial ovarian carcinomas

BACKGROUND

Some epithelial ovarian carcinomas tend to occur more frequently in certain families. This clustering may be due to a genetic predisposition, but the role of inherited susceptibility in all families with multiple cases of ovarian carcinoma is currently unresolved. Studies characterizing familial ovarian carcinomas are few.

METHODS

From a population-based study of 559 patients with epithelial ovarian carcinoma, 27 families with 2 or more ovarian carcinoma cases occurring in first-degree relatives were identified. Histopathology, ploidy, and immunohistochemically detected p53 and HER-2/neu expression in these tumors were examined.

RESULTS

The mean age of the patients with familial ovarian carcinoma was 56.7 years. Approximately 67% of the tumors were either serous or undifferentiated adenocarcinomas. The percentage of aneuploid tumors was 46%, that of p53 positive tumors was 51%, and that of HER-2/neu positive tumors was 69%. When the families were divided into families with cases of breast carcinoma in addition to ovarian carcinoma cases and/or ovarian carcinoma in 2 consecutive generations (12 families) and families with ovarian carcinoma occurring in sisters only without cases of breast carcinoma (15 families), no differences were noted in the frequency of any of the studied variables.

CONCLUSIONS

Familial ovarian carcinomas do not appear to differ from sporadic ovarian carcinomas with regard to patient age at presentation, histopathology, ploidy, and immunohistochemically detected p53 expression. Immunohistochemically detected HER-2/neu expression was found to occur more frequently in familial ovarian carcinomas than has been reported in sporadic ovarian carcinomas.

Family history and the risk of breast cancer: a systematic review and meta-analysis

An increased risk of breast cancer in women with a family history of breast cancer has been demonstrated by many studies using a variety of study designs. However, the extent of this risk varies according to the nature of the family history (type of relative affected, age at which relative developed breast cancer and number of relatives affected) and may also vary according to age of the individual. The aim of our study was to identify all the published studies which have quantified the risk of breast cancer associated with a family history of the disease, and to summarise the evidence from these studies, with particular emphasis on age-specific risks according to subject and relative age. Seventy-four published studies were identified. The pooled estimate of relative risk (RR) associated with various family histories was as follows: any relative, RR = 1.9 (95% CI, 1.7-2.0); a first-degree relative, RR = 2.1 (CI = 2.0, 2.2); mother, RR = 2.0 (CI = 1.8, 2.1); sister, RR = 2.3 (CI = 2.1, 2.4); daughter, RR = 1.8 (CI = 1.6, 2.0); mother and sister, RR = 3.6 (CI = 2.5, 5.0); and a second-degree relative, RR = 1.5 (CI = 1.4, 1.6). Risks were increased in subjects under age 50 and when the relative had been diagnosed before age 50.

The risk of cancer associated with specific mutations of BRCA1 and BRCA2 among Ashkenazi Jews

BACKGROUND

Carriers of germ-line mutations in BRCA1 and BRCA2 from families at high risk for cancer have been estimated to have an 85 percent risk of breast cancer. Since the combined frequency of BRCA1 and BRCA2 mutations exceeds 2 percent among Ashkenazi Jews, we were able to estimate the risk of cancer in a large group of Jewish men and women from the Washington, D.C., area.

METHODS

We collected blood samples from 5318 Jewish subjects who had filled out epidemiologic questionnaires. Carriers of the 185delAG and 5382insC mutations in BRCA1 and the 6174delT mutation in BRCA2 were identified with assays based on the polymerase chain reaction. We estimated the risks of breast and other cancers by comparing the cancer histories of relatives of carriers of the mutations and noncarriers.

RESULTS

One hundred twenty carriers of a BRCA1 or BRCA2 mutation were identified. By the age of 70, the estimated risk of breast cancer among carriers was 56 percent (95 percent confidence interval, 40 to 73 percent); of ovarian cancer, 16 percent (95 percent confidence interval, 6 to 28 percent); and of prostate cancer, 16 percent (95 percent confidence interval, 4 to 30 percent). There were no significant differences in the risk of breast cancer between carriers of BRCA1 mutations and carriers of BRCA2 mutations, and the incidence of colon cancer among the relatives of carriers was not elevated.

CONCLUSIONS

Over 2 percent of Ashkenazi Jews carry mutations in BRCA1 or BRCA2 that confer increased risks of breast, ovarian, and prostate cancer. The risks of breast cancer may be overestimated, but they fall well below previous estimates based on subjects from high-risk families.

BRCA1 mutations in women attending clinics that evaluate the risk of breast cancer

BACKGROUND

To define the incidence of BRCA1 mutations among patients seen in clinics that evaluate the risk of breast cancer, we analyzed DNA samples from women seen in this setting and constructed probability tables to provide estimates of the likelihood of finding a BRCA1 mutation in individual families.

METHODS

Clinical information, family histories, and blood for DNA analysis were obtained from 263 women with breast cancer. Conformation-sensitive gel electrophoresis and DNA sequencing were used to identify BRCA1 mutations.

RESULTS

BRCA1 mutations were identified in 16 percent of women with a family history of breast cancer. Only 7 percent of women from families with a history of breast cancer but not ovarian cancer had BRCA1 mutations. The rates were higher among women from families with a history of both breast and ovarian cancer. Among family members, an average age of less than 55 years at the diagnosis of breast cancer, the presence of ovarian cancer, the presence of breast and ovarian cancer in the same woman, and Ashkenazi Jewish ancestry were all associated with an increased risk of detecting a BRCA1 mutation. No association was found between the presence of bilateral breast cancer or the number of breast cancers in a family and the detection of a BRCA1 mutation, or between the position of the mutation in the BRCA1 gene and the presence of ovarian cancer in a family.

CONCLUSIONS

Among women with breast cancer and a family history of the disease, the percentage with BRCA1 coding-region mutations is less than the 45 percent predicted by genetic-linkage analysis. These results suggest that even in a referral clinic specializing in screening women from high-risk families, the majority of tests for BRCA1 mutations will be negative and therefore uninformative.

Brca2 is required for embryonic cellular proliferation in the mouse

Mutations of the tumor suppressor gene BRCA2 are associated with predisposition to breast and other cancers. Homozygous mutant mice in which exons 10 and 11 of the Brca2 gene were deleted by gene targeting (Brca2(10-11)) die before day 9.5 of embryogenesis. Mutant phenotypes range from severely developmentally retarded embryos that do not gastrulate to embryos with reduced size that make mesoderm and survive until 8.5 days of development. Although apoptosis is normal, cellular proliferation is impaired in Brca2(10-11) mutants, both in vivo and in vitro. In addition, the expression of the cyclin-dependent kinase inhibitor p21 is increased. Thus, Brca2(10-11) mutants are similar in phenotype to Brca1(5-6) mutants but less severely affected. Expression of either of these two genes was unaffected in mutant embryos of the other. This study shows that Brca2, like Brca1, is required for cellular proliferation during embryogenesis. The similarity in phenotype between Brca1 and Brca2 mutants suggests that these genes may have cooperative roles or convergent functions during embryogenesis.

Differential contributions of BRCA1 and BRCA2 to early-onset breast cancer

BACKGROUND

Germ-line mutations in the BRCA1 and BRCA2 genes predispose women to breast cancer. BRCA1 mutations are found in approximately 12 percent of women with breast cancer of early onset, and the specific mutation causing a deletion of adenine and guanine (185delAG), which is present in 1 percent of the Ashkenazi Jewish population, contributes to 21 percent of breast cancers among young Jewish women. The contribution of BRCA2 mutations to breast cancer of early onset is unknown.

METHODS

Lymphocyte specimens from 73 women with breast cancer diagnosed by the age of 32 were studied for heterozygous mutations of BRCA2 by a complementary-DNA-based protein-truncation assay, followed by automated nucleotide sequencing. In addition, specimens from 39 Jewish women with breast cancer diagnosed by the age of 40 were tested for specific mutations by an allele-specific polymerase chain reaction.

RESULTS

Definite BRCA2 mutations were found in 2 of the 73 women with early-onset breast cancer (2.7 percent; 95 percent confidence interval, 0.4 to 9.6 percent), suggesting that BRCA2 is associated with fewer cases than BRCA1 (P=0.03). The specific BRCA2 mutation causing a deletion of thymine (6174delT), which is found in 1.3 percent of the Ashkenazi Jewish population, was observed in 1 of the 39 young Jewish women with breast cancer (2.6 percent; 95 percent confidence interval, 0.09 to 13.5 percent), indicating that it has a small role as a risk factor for early-onset breast cancer. Among young women with breast cancer, there are BRCA2 mutations that cause truncation of the extreme C terminus of the protein and that may be functionally silent, along with definite truncating mutations.

CONCLUSIONS

Germ-line mutations in BRCA2 contribute to fewer cases of breast cancer among young women than do mutations in BRCA1. Carriers of BRCA2 mutations may have a smaller increase in the risk of early-onset breast cancer.

Targeted mutations of breast cancer susceptibility gene homologs in mice: lethal phenotypes of Brca1, Brca2, Brca1/Brca2, Brca1/p53, and Brca2/p53 nullizygous embryos

Mutations of the human BRCA1 and BRCA2 genes encoding tumor suppressors have been implicated in inherited predisposition to breast and other cancers. Disruption of the homologous mouse genes Brca1 and Brca2 by targeting showed that they both have indispensable roles during embryogenesis, because nullizygous embryos become developmentally retarded and disorganized, and die early in development. In Brca1 mutants, the onset of abnormalities is earlier by one day and their phenotypic features and time of death are highly variable, whereas the phenotype of Brca2 null embryos is more uniform, and they all survive for at least 8.5 embryonic days. Observations with Brca1/Brca2 double nullizygotes raise the possibility that the two developmental pathways could be linked. Interestingly, the impact of the Brca1 or Brca2 null mutation is less severe in a p53 null background.

Changes in BRCA2 expression during progression of the cell cycle

It has been shown that genetic alterations in BRCA1 and BRCA2 can predispose an individual to develop breast cancer. We investigated the expression of both BRCA2 and BRCA1 during the progression of the cell cycle by northern blot analysis. In MCF-10F (normal breast epithelial cell line) and MCF-7 (breast cancer cell line) cells the expression of BRCA2 RNA was low in G0 and early G1 phases then up-regulated at the G1/S phase junction. Expression of BRCA2 was maintained at relatively high levels when cells progressed through S and G2/M phases. For MCF-7 cells, the level of BRCA2 transcript decreased as cells were released from nocodazole-mediated metaphase arrest. This is consistent with the observation of low but detectable BRCA2 RNA level in G1 phase of the cell cycle. For both cell lines, the patterns of RNA expression of BRCA1 and BRCA2 were similar during the proliferation phase of cell cycle. However, the transcripts from both genes were undetectable in quiescent cells. These results suggest important functions for both BRCA2 and BRCA1 in regulation of cell growth.

Genetic factors in the pathogenesis of breast cancer: their role and relative importance

Aggregation of breast cancer in families is an established risk factor associated with increased incidence of the disease, which is a leading cause of morbidity and mortality among women in this country. Three genes have now been identified that confer increased susceptibility in families with a clear hereditary (i.e., Mendelian) pattern of expression: BRCA1, BRCA2 and p53. However, a significant number of women have an identified family history of breast cancer without clear Mendelian patterns of disease. Such patterns are consistent with the effect of more common genes with lower associated risk. Some evidence is available to implicate three additional genes that fit this category: AT, ESR and HRAS1. An area of active interest is genetically mediated variation in the metabolism of estrogens, a process controlled by several genes, each with more modest effects. The interaction of genes and environmental factors in breast cancer pathogenesis is of considerable public health importance.

Predisposition testing for breast and ovarian cancer susceptibility

OBJECTIVES

To provide an overview of breast cancer predisposition syndromes and the breast and Ovarian cancer susceptibility genes identified to date. To describe the clinical implications of genetic testing for breast and ovarian cancer susceptibility.

DATA SOURCES

Published research and educational manuscripts, books, conference proceedings, and personal experiences.

CONCLUSION

Nurses must become knowledgeable of predisposition genetic testing for inherited breast cancer risk including: understanding of the gene being analyzed and associated cancer risks, indications for testing, the limitations of the test, the management options for mutation carriers, risks and benefits of testing, and the long-term psychosocial sequelae.

IMPLICATIONS FOR NURSING PRACTICE

Predisposition testing for alterations in breast cancer susceptibility genes is rapidly moving into the general oncology and primary care community where nurses will play a major role in the provision of genetic services. The role of nursing in cancer genetics includes practice and education, nursing research, and policy initiatives.

Embryonic lethality and radiation hypersensitivity mediated by Rad51 in mice lacking Brca2

Inherited mutations in the human BRCA2 gene cause about half of the cases of early-onset breast cancer. The embryonic expression pattern of the mouse Brca2 gene is now defined and an interaction identified of the Brca2 protein with the DNA-repair protein Rad51. Developmental arrest in Brca2-deficient embryos, their radiation sensitivity, and the association of Brca2 with Rad51 indicate that Brca2 may be an essential cofactor in the Rad51-dependent DNA repair of double-strand breaks, thereby explaining the tumour-suppressor function of Brca2.

BRCA2 germline mutations in Japanese breast cancer families

Germline mutations of BRCA2 were examined in 20 Japanese breast cancer families without BRCA1 mutations, including one demonstrating cancer development in a male. Three different mutations, resulting in truncation of the BRCA2 protein, were detected in 3 different families. They were 9474insA (exon 24, termination at codon 3110), C8729A (exon 20, S2834 ter) and 982del4 (exon 9, termination at codon 275). The 982del4 mutation was detected in the family with a case of male breast cancer. Age at onset was young, with a range of 28-43 years, in the 2 female breast cancer families with truncation mutations. One probable missense mutation, A10462G (13412V), was further detected in 2 families, although cosegregation of this allele with the breast cancer phenotype was not complete. The rate of BRCA2 mutations in Japanese families was suggested to be almost the same as in Western countries, and larger than it is the case for BRCA1.

Developmental expression of Brca2 colocalizes with Brca1 and is associated with proliferation and differentiation in multiple tissues

Germline mutations in the putative tumor suppressor gene, BRCA1, predispose women to dramatically elevated risks of breast cancer, while germline mutations in the structurally unrelated gene, BRCA2, predispose both men and women to breast cancer. Recent studies have suggested an important developmental role for the murine homologue of BRCA1 in the regulation of proliferation and differentiation. At the present time, however, little is known about the developmental role of BRCA2 or the regulation of its expression in vivo. We have determined the spatial and temporal pattern of expression of the murine homologue of BRCA2 during fetal development, in adult tissues, and in the mammary gland during postnatal development. Our results indicate that Brca2 mRNA expression is highest in proliferating cellular compartments, particularly those undergoing differentiation. In the breast, Brca2 expression is developmentally regulated and is induced during puberty and pregnancy and as a result of parity. Surprisingly, in multiple fetal and adult tissues the spatial and temporal pattern of Brca2 mRNA expression is virtually indistinguishable from that of Brca1, despite the fact that these genes display no homology. These observations suggest that Brca2 is involved in the processes of proliferation and differentiation in the mammary gland and other tissues, and that Brca1 and Brca2 mRNA expression may be regulated by similar pathways and stimuli in multiple cell types. Interestingly, however, our analysis reveals that Brca1 and Brca2 expression are differentially regulated during the development of specific endocrine target tissues, such as the testis during spermatogenesis and the breast during pregnancy. In addition, the ratio of mRNA expression in the mammary glands of adult females relative to adult males is significantly greater for Brca1 than for Brca2. These observations imply that Brca1 and Brca2 mRNA expression are differentially regulated by sex hormones. In order to test this hypothesis, we have analyzed the expression of these two breast cancer susceptibility genes in ovariectomized mice treated with 17beta-estradiol and progesterone. Our results demonstrate that the up-regulation of mRNA expression in the breast by ovarian hormones is significantly greater for Brca1 than for Brca2. These observations suggest that the gender-specific differences in phenotype associated with germline mutations in BRCA2 versus BRCA1 may be related to the differential regulation of these genes by sex hormones.

Mutations of the BRCA1 and BRCA2 genes and the possibilities for predictive testing

Two cancer susceptibility genes, BRCA1 on chromosome 17q12-21 and BRCA2 on chromosome 13q12-13, are thought to be responsible for approximately 80% of families containing multiple cases of early-onset female breast cancer. Germline mutations of BRCA1 are also associated with ovarian cancer and mutations of BRCA2 are associated with an increased risk of male breast cancer, ovarian cancer, prostate cancer and pancreatic cancer. The recent isolation of both genes should make possible the identification of the genetic defect that predisposes affected individuals to breast and ovarian cancer and might lead to the use of genetic information for predictive testing.

A review of hereditary breast cancer: from screening to risk factor modification

The identification of genetic mutations thought to be directly responsible for the development of breast cancer represents a major advance in our understanding of this disease. Mutations in BRCA1 and BRCA2 are thought to be responsible for the majority of inherited breast cancer. Although these mutations account for approximately 5% of breast cancer cases, the identification of these genes will have a profound impact on the way patients and their physicians view breast cancer risk. Genetic testing for BRCA1 and BRCA2 mutations is already available. Interpreting results of genetic tests for these mutations is problematic and the clinical management of women carrying these gene mutations is far from straightforward. The purpose of this paper is to review recent developments in the genetic aspects of breast cancer, including genetic testing, to critically review risk factor modification, and to discuss screening and potential prophylactic measures.

Identification of an alternative form of human lactoferrin mRNA that is expressed differentially in normal tissues and tumor-derived cell lines

Lactoferrin (LF), traditionally known as an iron-binding protein present in high concentrations in milk and various secretions, has emerged as a multifunctional protein involved in many aspects of the host defense against infection. Recently, LF has been shown to inhibit the growth of solid tumors and reduce experimental metastasis in mice, suggesting that LF also may play a role in the defense against tumorigenesis. Here we provide the sequence of the cDNA and promoter region, the chromosome assignment, and tissue expression pattern of a novel form of LF mRNA (delta LF). The sequence of delta LF mRNA is nearly identical to that of LF mRNA; however, at the 5' end, we find a novel sequence that replaces the N-terminal signal peptide sequence of LF mRNA. We map the delta LF mRNA to human chromosome 3 and find that both delta LF and LF sequences colocalize to the same cloned 90- to 150-kb genomic DNA fragment. We further show that the delta LF mRNA is the product of alternative splicing of the LF gene and likely is specified by use of an alternative promoter. Although we find delta LF mRNA at various levels in 20 of 20 adult and fetal human tissues, we do not find delta LF mRNA in any of 14 diverse tumor-derived cell lines.

Murine Brca2: sequence, map position, and expression pattern

Mutations in the human BRCA2 gene are responsible for about 45% of hereditary early onset breast cancer. Recently, the human BRCA2 gene was cloned, and several germline mutations were identified. Here we describe the cloning of the mouse homologue of BRCA2. The mouse cDNA sequence predicts a 3328-amino-acid Brca2 protein, 90 amino acids shorter than the human protein. The overall identity between the mouse and the human proteins is 59%, while the similarity is 72%. At the nucleotide level the homology is 74%. By comparing the amino acid sequences of the two homologues we have identified five highly conserved novel domains that may be functionally significant. Brca2 has been mapped to the distal end of mouse chromosome 5, a region of the mouse genome that contains other genes that also map to human chromosome 13q12-q13, confirming the conservation of this linkage group between the two species. Expression of Brca2 was detected in midgestation embryos and adult testis, thymus, and ovary.

Interphase cytogenetics in chronic lymphocytic leukemia

The incidence of trisomy 12 and 13q12-q14 abnormalities in patients with chronic lymphocytic leukemia (CLL) was determined by conventional cytogenetics and interphase fluorescence in situ hybridization (FISH). In the analysis of 580 consecutive patients, trisomy 12 was detected by conventional cytogenetics in 39 cases (9%) and 117 cases (20%) by FISH. Trisomy 12 was shown to be associated with advanced clinical stage, atypical morphology, and higher proliferative activity. Combined immunophenotyping and FISH showed that trisomy 12 was present only in a proportion of the clonal B-cells. These data suggest that trisomy 12 is a secondary event associated with features of disease progression. Sequential FISH showed clonal progression of the trisomic clone over time. Three hundred patients also were investigated for 13q deletions using FISH analysis of the RB1 locus (13q14). Monoallelic RB1 deletion was seen in 104 (34%) of cases. One case had a homozygous deletion in 90% of the cells. Dual-color FISH detected the presence of trisomy 12 and RB1 in 17 (5%) cases. DNA probes for 13q12.3 (BRCA2) and 13q14 (RB1 and DBM locus) were used in 35 cases. Twenty-eight (80%) cases showed deletion of a 1Mb 13q12.3 encompassing the BRCA2 locus, whereas 22/35 (63%) were deleted at 13q14. Our data suggest that abnormalities of 13q are more frequent than trisomy 12 in CLL and provide evidence for the presence of a new candidate gene at 13q12.3 that may be involved in the pathogenesis of CLL.

High throughput parallel analysis of hundreds of patient samples for more than 100 mutations in multiple disease genes

As more mutations are identified in genes of known sequence, there is a crucial need in the areas of medical genetics and genome analysis for rapid, accurate and cost-effective methods of mutation detection. We have developed a multiplex allele-specific diagnostic assay (MASDA) for analysis of large numbers of samples (> 500) simultaneously for a large number of known mutations (> 100) in a single assay. MASDA utilizes oligonucleotide hybridization to interrogate DNA sequences. Multiplex DNA samples are immobilized on a solid support and a single hybridization is performed with a pool of allele-specific oligonucleotide (ASO) probes. Any probes complementary to specific mutations present in a given sample are in effect affinity purified from the pool by the target DNA. Sequence-specific band patterns (fingerprints), generated by chemical or enzymatic sequencing of the bound ASO(s), easily identify the specific mutation(s). Using this design, in a single diagnostic assay, we tested samples for 66 cystic fibrosis (CF) mutations, 14 beta-thalassemia mutations, two sickle cell anemia (SCA) mutations, three Tay-Sachs mutations, eight Gaucher mutations, four mutations in Canavan disease, four mutations in Fanconi anemia, and five mutations in BRCA1. Each mutation was correctly identified. Finally, in a blinded study of 106 of these mutations in > 500 patients, all mutations were properly identified. There were no false positives or false negatives. The MASDA assay is capable of detecting point mutations as well as small insertion or deletion mutations. This technology is amenable to automation and is suitable for immediate utilization for high-throughput genetic diagnostics in clinical and research laboratories.

Patterns of allelic loss on chromosome 17 in sporadic breast carcinomas detected by fluorescent-labeled microsatellite analysis

Loss of heterozygosity (LOH) on chromosome 17 is a frequent genetic alteration in breast cancer. To assess whether the location of potential tumor suppressor genes is compatible with the LOH pattern in individual tumors, we analyzed allele loss on chromosome 17 in 121 invasive ductal breast carcinomas and 16 benign breast tumors with 14 polymorphic microsatellite markers (4 on 17p and 10 on 17q). Fluorescent polymerase chain reaction (PCR) for typing microsatellites coupled with DNA fragment analysis in an automated DNA sequencer was applied. Frequencies of LOH varied from 29.4% (D17S1322) to 57.4% (TP53-Alu). No LOH could be detected in benign breast tumors. In 54 tumors the deletion patterns were consistent with the complete loss of 17p (n = 28), 17q (n = 9) or the whole chromosome 17 (n = 17). Five smallest regions of overlap (SROs) were identified in tumors with interstial deletion patterns. On 17p, two foci were detected affecting the TP53 locus and the hypermethylated in cancer I (HICI) region (17p13.3). On 17q, SRO1 was localized between markers THRAI and D17S855, centromeric to the breast/ovarian cancer gene BRCAI; SRO2 was flanked by markers AFM234 and NMEI, and SRO3 was centered between markers MPO and GH. Associations between LOH and histopathological characteristics were determined. Significant correlations were found between higher grade and loss of the TP53 gene (marker TP53, P = 0.019), loss of the BRCAI region (P < 0.009), LOH of marker AFM155 (P = 0.003) and marker NMEI (P = 0.026). For positive estrogen receptor status, only LOH of the THRAI marker correlated significantly, whereas highly significant correlations were determined between positive progesterone receptor and markers centromeric to the BRCAI region D17S250 (P = 0.00002), THRAI (P = 0.0006), and the intragenic BRCAI markers [D17S1322 (P = 0.021), D17S855 (P = 0.029)]. Results presented in this study identify five independent regions of chromosome 17 which are likely to contain potential tumor suppressor genes involved in the carcinogenesis of sporadic breast cancer.

Tumour-suppressor genes in prostatic oncogenesis: a positional approach

Genetic alterations, such as mutation, methylation and aneuploidy, are thought to underlie the multistep genesis and progression of many human cancers. However, the genetic events occurring in prostatic oncogenesis are still relatively poorly understood. This is especially so in early-stage tumours, in which mutations of known oncogenes or tumour-suppressor genes appear to be quite infrequent. Allelic losses of chromosome arms 7q, 8p, 10, 16q and 18q suggest the involvement of novel suppressor loci on these chromosomes; allelic losses of chromosome arm 8p are especially frequent and may be detected even in early-stage tumours. We have used a positional approach to seek novel genetic targets in prostate cancer, including allelic-loss mapping of chromosome 8p and physical mapping of chromosome band 8p22 around the MSR gene. A homozygous somatic deletion in one prostatic nodal metastasis was mapped in this region and spanned 730-970 kb. This region was then examined in detail for expressed sequences. One novel gene, called N33, was found to be silenced by a methylation mechanism in most colon cancer cell lines and some primary colorectal tumours. Characterization of additional chromosome 8p22 candidates is in progress.

Deletion of three distinct regions on chromosome 13q in human non-small-cell lung cancer

We examined loss of heterozygosity (LOH) at the retinoblastoma susceptibility gene (RB1) locus on chromosome 13q14 in 20 non-small-cell lung cancers (NSCLCs) using polymorphic markers. The expression of RB protein was examined by immunohistochemical analysis of paraffin-embedded specimens of the same tumors. The results revealed that 10 of 16 informative cases showed an LOH at the RB1 locus, whereas only 2 of the 10 tumors lost expression of the RB protein. These 2 tumors had mutations in the remaining RB1 allele. Thus, inactivation of the RB1 gene appears to be involved in a small subset of NSCLCs only. To elucidate the presence of tumor-suppressor genes other than RB1 on 13q, heterozygosity at 15 different loci was investigated. Of 20 tumors analyzed, 15 showed an LOH at least at one locus, and the regions 13q12.1-qter, 13q12.2-14.2 and 13q14.1-q14.3, including the RB1 locus, were deleted in significant numbers of the tumors. Our results suggest that, in addition to the RB1 gene, abnormalities of other tumor-suppressor genes on chromosome 13q are involved in the development of human NSCLCs.

Probability of carrying a mutation of breast-ovarian cancer gene BRCA1 based on family history

BACKGROUND

Heritable mutations of the breast cancer gene BRCA1 are rare, occurring in fewer than 1% of women in the general population, and therefore account for a small proportion of cases of breast and ovarian cancers. Nevertheless, the presence of such mutations is highly predictive of the development of these cancers.

PURPOSE

We developed and applied a mathematic model for calculating the probability that a woman with a family history of breast and/or ovarian cancer carries a mutation of BRCA1.

METHODS AND RESULTS

As a basis for the model, we use Mendelian genetics and apply Bayes' theorem to information on the family history of these diseases. Of importance are the exact relationships of all family members, including both affected and unaffected members, and ages at diagnosis of the affected members and current ages of the unaffected members. We used available estimates of BRCA1 mutation frequencies in the general population and age-specific incidence rates of breast and ovarian cancers in carriers and noncarriers of mutations to estimate the probability that a particular member of the family carries a mutation. This probability is based on cancer statuses of all first- and second-degree relatives. We first describe the model by considering single individuals: a woman diagnosed with breast and/or ovarian cancer and also a woman free of cancer. We next considered two artificial and two actual family histories and addressed the sensitivity of our calculations to various assumptions. Particular relationships of family members with and without cancer can have a substantial impact on the probability of carrying a susceptibility gene. Ages at diagnosis of affected family members and their types of cancer are also important. A woman with two primary cancers can have a probability of carrying a mutation in excess of 80%, even with no other information about family history. The number and relationships of unaffected members, along with their current ages or ages at death, are critical determinants of one's carrier probability. An affected woman with several cancers in her family can have a probability of carrying a mutation that ranges from close to 100% to less than 5%.

CONCLUSION

Our model gives informative and specific probabilities that a particular woman carries a mutation.

IMPLICATIONS

This model focuses on mutations in BRCA1 and assumes that all other breast cancer is sporadic. With the cloning of BRCA2, we now know that this assumption is incorrect. We have adjusted the model to include BRCA2, but the use of this version must await publication of penetrance data for BRCA2, including those for male breast cancer that are apparently associated with BRCA2 but not with BRCA1. The current model is, nevertheless, appropriate and useful. Of principal importance is its potential and that of improved versions for aiding women and their health care providers in assessing the need for genetic testing.

Cloning, chromosomal mapping and expression pattern of the mouse Brca2 gene

A proportion of human breast cancers result from an inherited predisposition to the disease. Mutations in the BRCA2 gene confer a high risk of breast cancer and are responsible for almost half of these cases. The recent cloning of the human BRCA2 gene has revealed that it encodes a large protein having little significant homology to known proteins. Here we describe the mouse Brca2 gene. The gene maps to mouse chromosome 5, consistent with its location on human chromosome 13q12. We have sequenced cDNA for the entire 3329 amino acid Brca2 protein and this has revealed that, like Brca1, Brca2 is relatively poorly conserved between humans and mice. Brca2 is transcribed in a diverse range of mouse tissues, and the pattern of expression is strikingly similar to that of Brca1. Taken together, our data highlight some intriguing similarities between two genes involved in inherited breast cancer susceptibility.

Retrofitting vectors for Escherichia coli-based artificial chromosomes (PACs and BACs) with markers for transfection studies

P1-based artificial chromosomes (PACs) and bacterial artificial chromosomes (BACs) have significantly expanded the size of fragments from eukaryotic genomes that can be stably cloned in Escherichia coli as plasmid molecules. Functional characterization of a gene within a given PAC or BAC clone often requires transferring the DNA into eukaryotic cells for transient or long-term expression. To facilitate transfection studies, we have developed protocols using the Notl restriction sites of any PAC or BAC clone to introduce a transfection reporter gene, lacZ, together with a selectable marker, neo. This enables transfected cells to be detected by X-Gal staining to verify DNA uptake, and clones of stably transformed cells may be selected for in the presence of the antibiotic G418. The same retrofitting protocols may be applied with other markers of interest to extend the functionality of PAC and BAC libraries, and specialized aspects of such manipulation of E. coli-based artificial chromosomes are outlined.

Identification of protein coding regions in the human genome by quadratic discriminant analysis

A new method for predicting internal coding exons in genomic DNA sequences has been developed. This method is based on a prediction algorithm that uses the quadratic discriminant function for multivariate statistical pattern recognition. Substantial improvements have been made (with only 9 discriminant variables) when compared with existing methods: HEXON [Solovyev, V. V., Salamov, A. A. & Lawrence, C. B. (1994) Nucleic Acids Res. 22, 5156-5163] (based on linear discriminant analysis) and GRAIL2 [Uberbacher, E. C. & Mural, R. J. (1991) Proc. Natl. Acad. Sci. USA 88, 11261-11265] (based on neural networks). A computer program called MZEF is freely available to the genome community and allows users to adjust prior probability and to output alternative overlapping exons.

Clinical applications of tumor suppressor genes and oncogenes in cancer

In the search for new ways to better diagnose and monitor cancer, scientists have turned to oncogenes and tumor suppressor genes. These genes are involved in cell differentiation, communication and proliferation and their alteration is frequently associated with cancer. Such alterations include mutations, translocations, amplifications and deletions. In this review, I give examples of using the detection of such alterations for patient diagnosis and monitoring. The practical examples are restricted to a few cancer types, but the identification of new tumor suppressor genes, like BRCA-1 and BRCA-2, is creating new possibilities for determining cancer risk of individual family members. There is no doubt that the cloning of new genes which predispose to sporadic cancer will lead to the introduction of widespread testing to assess risk and to the application of preventive measures.

Controlled trial of pretest education approaches to enhance informed decision-making for BRCA1 gene testing

BACKGROUND

In response to the isolation of the BRCA1 gene, a breast-ovarian cancer-susceptibility gene, biotechnology companies are already marketing genetic tests to health care providers and to the public. Initial studies indicate interest in BRCA1 testing in the general public and in populations at high risk. However, the optimal strategies for educating and counseling individuals have yet to be determined.

PURPOSE

Our goal was to evaluate the impact of alternate strategies for pretest education and counseling on decision-making regarding BRCA1 testing among women at low to moderate risk who have a family history of breast and/or ovarian cancer.

METHODS

A randomized trial design was used to evaluate the effects of education only (educational approach) and education plus counseling (counseling approach), as compared with a waiting-list (control) condition (n = 400 for all groups combined). The educational approach reviewed information about personal risk factors, inheritance of cancer susceptibility, the benefits, limitations, and risks of BRCA1 testing, and cancer screening and prevention options. The counseling approach included this information, as well as a personalized discussion of experiences with cancer in the family and the potential psychological and social impact of testing. Data on knowledge of inherited cancer and BRCA1 test characteristics, perceived risk, perceived benefits, limitations and risks of BRCA1 testing, and testing intentions were collected by use of structured telephone interviews at baseline and at 1-month follow-up. Provision of a blood sample for future testing served as a proxy measure of intention to be tested (in the education and counseling arms of the study). The effects of intervention group on study outcomes were evaluated by use of hierarchical linear regression modeling and logistic regression modeling (for the blood sample outcome). All P values are for two-sided tests.

RESULTS

The educational and counseling approaches both led to significant increases in knowledge, relative to the control condition (P < .001 for both). The counseling approach, but not the educational approach, was superior to the control condition in producing significant increases in perceived limitations and risks of BRCA1 testing (P < .01) and decreases in perceived benefits (P < .05). However, neither approach produced changes in intentions to have BRCA1 testing. Prior to and following both education only and education plus counseling, approximately one half of the participants stated that they intended to be tested; after the session, 52% provided a blood sample.

CONCLUSIONS

Standard educational approaches may be equally effective as expanded counseling approaches in enhancing knowledge. Since knowledge is a key aspect of medical decision-making, standard education may be adequate in situations where genetic testing must be streamlined. On the other hand, it has been argued that optimal decision-making requires not only knowledge, but also a reasoned evaluation of the positive and negative consequences of alternate decisions. Although the counseling approach is more likely to achieve this goal, it may not diminish interest in testing, even among women at low to moderate risk. Future research should focus on the merits of these alternate approaches for subgroups of individuals with different backgrounds who are being counseled in the variety of settings where BRCA1 testing is likely to be offered.

The TSG101 tumor susceptibility gene is located in chromosome 11 band p15 and is mutated in human breast cancer

Recent work has identified a mouse gene (tsg101) whose inactivation in fibroblasts results in cellular transformation and the ability to produce metastatic tumors in nude mice. Here, we report that the human homolog, TSG101, which we isolated and mapped to chromosome 11, bands 15.1-15.2, a region proposed to contain tumor suppressor gene(s), is mutated at high frequency in human breast cancer. In 7 of 15 uncultured primary human breast carcinomas, intragenic deletions were shown in TSG101 genomic DNA and transcripts by gel and sequence analysis, and mutations affecting two TSG101 alleles were identified in four of these cancers. No TSG101 defects were found in matched normal breast tissue from the breast cancer patients. These findings strongly implicate TSG101 mutations in human breast cancer.

Germline BRCA2 mutations in men with breast cancer

Breast cancer in men is rare and is clearly due in some cases to an inherited predisposition. A total of 28 male breast cancer patients were tested for BRCA2 mutations; two frameshifts and one putative missense mutation were identified. One of the frameshifts was detected in the same position as a mutation estimated to be responsible for 40% of all male breast cancer cases in Iceland.

Absence of methylation of CpG dinucleotides within the promoter of the breast cancer susceptibility gene BRCA2 in normal tissues and in breast and ovarian cancers

Germline mutations of the BRCA2 gene on chromosome 13q12-q13 predispose to the development of early-onset breast cancer and ovarian cancer. Loss of heterozygosity detected using chromosome 13q markers in the vicinity of BRCA2 is observed in most cancers arising in carriers of germline BRCA2 mutations and also in 30-50% of sporadic breast and ovarian cancers. However, somatic mutations of BRCA2 are extremely rare in sporadic cancers. We have examined the hypothesis that expression of the BRCA2 gene may be suppressed in sporadic breast cancers by a mechanism that is associated with increased methylation of cytosine residues in the promoter region. Using a HpaII/MspI digestion-polymerase chain reaction based assay, the presence of 5-methylcytosine in three CpG dinucleotides within the BRCA2 promoter was assessed in 18 breast or ovarian cancer cell lines, in an SV40 large T antigen immortalized cell line derived from normal breast epithelial cells, in 64 primary sporadic breast cancers and peripheral blood leucocytes from these cases and in a number of other normal human tissues. Methylation was not detected in any of the tissues examined, suggesting that this mechanism of transcriptional repression is unlikely to explain the absence of somatic mutations in sporadic cancers.

Genetics of breast cancer

Familial breast cancer is characterized by young age at diagnosis, an increased risk of bilateral breast cancer, an increasing risk in conjunction with increasing numbers of affected family members, and a strong association with ovarian cancer. At least eight candidate breast cancer susceptibility genes have been identified. Mutations in BRCA1, BRCA2, p53, and the Cowden disease gene are relatively uncommon, are highly penetrant, and produce striking familial clusters of breast cancer. BRCA1 and BRCA2 are the most important of these, accounting for an estimated 80% of hereditary breast cancer and 5 to 6% of all breast cancers. Specific BRCA1 and BRCA2 mutations are of particular importance in population subgroups, such as those identified among Jewish women of central European (Ashkenazi) origin. Mutations in the ataxia-telangiectasia gene and the rare HRAS1 variable number of tandem repeats polymorphisms are much more common but also much less penetrant. They do not produce dramatic familial aggregations of breast cancer but may prove to be responsible for a substantial proportion of all breast cancers if their epidemiologic association with breast cancer is confirmed. Predictive genetic testing for breast cancer risk is under way. Oncologists and primary-care physicians must become familiar with these genetic disorders and the issues surrounding predictive testing in order to make appropriate management decisions about women thought to have a high genetic risk of breast cancer.