Identification of novel BRCA large genomic rearrangements in Singapore Asian breast and ovarian patients with cancer.

Large genomic rearrangements have been reported to account for about 10-15% of BRCA1 gene mutations. Approximately, 90 BRCA rearrangements have been described to date, all of which but one have been reported in Caucasian populations of predominantly Western European descent. Knowledge of BRCA genomic rearrangements in Asian populations is still largely unknown. In this study, we have investigated for the presence of BRCA rearrangements among Asian patients with early onset or familial history of breast or ovarian cancer. Using multiplex ligation-dependent probe amplification (MLPA), we have analyzed 100 Singapore patients who previously tested negative for deleterious BRCA mutations by the conventional polymerase chain reaction-based mutation detection methods. Three novel BRCA rearrangements were detected, two of which were characterized. The patients with the rearrangements, a BRCA1 exon 13 duplication, a BRCA1 exon 13-15 deletion and a BRCA2 exon 4-11 duplication, comprise 3% of those previously tested negative for BRCA mutations. Of the BRCA1 and BRCA2 pathogenic mutations identified in our studies on Asian high-risk breast and ovarian patients with cancer to date, these rearrangements constitute 2/19 and 1/2 of the BRCA1 and BRCA2 pathogenic mutations, respectively. Given the increasing number of rearrangements reported in recent years and their contribution to the BRCA mutation spectrum, the presence of BRCA large exon rearrangements in Asian populations should be investigated where clinical, diagnostic service is recommended.

The founder mutation BRCA1c.2845insA identified in a fallopian tube cancer patient: a case report.

Fallopian tube carcinoma is a very rare tumor, comprising less than 1% of all gynecologic cancers and found primarily in postmenopausal women. With the disease being so uncommon, little is known about its causes and/or risk factors, and treatment approaches have been taken from experiences with ovarian cancer. We describe a case of a 42-year-old woman with fallopian tube cancer in which the founder mutation BRCA1c.2845insA was detected by mutational analysis. This same mutation was subsequently detected in four unaffected members of her family following genetic counseling. We report an association between this founder mutation and fallopian tube cancer as part of the hereditary breast cancer syndrome in an Asian population. A literature review of the association between this rare malignancy and BRCA mutation carriers and its implications to prophylactic surgery is discussed.

Are medullary breast cancers an indication for BRCA1 mutation screening? A mutation analysis of 42 cases of medullary breast cancer.

Recommended guidelines have limited breast cancer gene ( BRCA1 ) mutation testing to individuals with a personal or family history of early onset breast and/or ovarian cancer, and those with multiple affected close relatives. Such large breast cancer families are rare in the general population, limiting the clinical application of the BRCA1 discovery. Previous reports have suggested an association between medullary breast cancer and BRCA1 mutation carriers. To test the feasibility of using these rare histological subtypes as an alternative to epidemiological factors, 42 cases of medullary cancer unselected for family history were screened for BRCA1 point mutations and large exon rearrangements. The large majority (83%) of these patients did not have significant family of breast or ovarian cancer. Two deleterious mutations resulting in a premature stop codon, and one exon 13 duplication were found. All mutations were detected in patients with typical medullary cancer, who had family history of multiple breast and ovarian cancers. Our findings suggest that medullary breast cancers are not an indication for BRCA1 mutation screening in the absence of significant family risk factors.

Pathological features and BRCA1 mutation screening in premenopausal breast cancer patients.

PURPOSE: Risk calculations for carrying BRCA1/BRCA2 mutations are based on family history and the age of onset of cancers. However, women may carry these deleterious mutations without a strong family history. Additional criteria for risk estimation would be of value. It has been recently established that BRCA1-associated breast cancers are associated with poor tumor differentiation (TD3) and estrogen receptor (ER) negativity. The aim of this study is to determine whether morphological features of breast cancers in premenopausal patients (age < 45 years) could determine additional women who may benefit from BRCA1 screening. EXPERIMENTAL DESIGN: In a prospective, systematic study of 76 consecutive breast cancer patients (age < 45 years), genomic DNA was obtained from peripheral blood, and eight mutations in BRCA1 (10.5%) were found. Archival paraffin-embedded breast cancer specimens were then analyzed for tumor differentiation and ER status. RESULTS: In patients < 45 years of age, 25% (6 of 24) of ER-negative and TD3 breast cancers were found to harbor mutations in BRCA1. Only 5.6% (2 of 36) of BRCA1-associated breast cancers did not have this morphological profile, compared with 94.4% (34 of 36) patients without BRCA1 mutations, giving an odds ratio of 5.67 (95% confidence interval, 1.04-32; P = 0.05). Finally, only one patient with BRCA1 mutations had a significant family history. CONCLUSIONS: In patients with early-onset breast cancer, the use of morphological criteria provides an additional strategy to determine those patients who might benefit from genetic testing.

Hereditary breast cancer: a brief overview.

INTRODUCTION: Breast cancer, one of the most common and serious malignancies affecting women, occurs in sporadic and hereditary forms. The recent identification of breast cancer predisposing genes involved in the aetiology of breast cancer has provided us with new insights into this field. METHODS: In order to understand the molecular basis of familial breast cancer, English literature identified through Medline between 1995 and February 2000 were reviewed using the search terms: breast cancer, genetics, hereditary, BRCA1 and BRCA2, amongst others. RESULTS: In this brief overview, some of the advances in the aetiology of breast cancer will be highlighted. This overview is divided into the following categories: cancer genes, inherited genetic predisposition to breast cancer, BRCA1 and BRCA2.

The prevalence of BRCA1 mutations in Chinese patients with early onset breast cancer and affected relatives.

The purpose of this study was to determine the prevalence of BRCA1 mutations in Chinese breast cancer patients in Singapore. BRCA1 analysis was conducted in consecutive patients with breast cancer before the age of 40 years (76 women), or whose relatives had breast or ovarian cancer (16 women). Ten patients had both early onset breast cancer and affected relatives. Genomic DNA from peripheral mononuclear blood cells was studied by using the protein transcription-translation assay (exon 11) and single-strand conformational polymorphism, with subsequent DNA sequencing. All six disease-causing mutations occurred in women under 40 years (8.6%) with three occurring in patients under 35 years (three out of 22 patients, 13.6%). Mis-sense mutations of unknown significance were found in three patients. Two of the ten women with affected relatives under 40 years had BRCA1 mutations. The prevalence of BRCA1 mutations in Chinese patients with early onset breast cancer is similar to that observed in Caucasian women. Most Chinese patients with affected relatives were not carriers of BRCA1 mutations.

Molecular cloning and characterization of the human topoisomerase IIalpha and IIbeta genes: evidence for isoform evolution through gene duplication.

Human DNA topoisomerase II is essential for chromosome segregation and is the target for several clinically important anticancer agents. It is expressed as genetically distinct alpha and beta isoforms encoded by the TOP2alpha and TOP2beta genes that map to chromosomes 17q21-22 and 3p24, respectively. The genes display different patterns of cell cycle- and tissue-specific expression, with the alpha isoform markedly upregulated in proliferating cells. In addition to the fundamental role of TOP2alpha and TOP2beta genes in cell growth and development, altered expression and rearrangement of both genes are implicated in anticancer drug resistance. Here, we report the complete structure of the human topoisomerase IIalpha gene, which consists of 35 exons spanning 27.5 kb. Sequence data for the exon-intron boundaries were determined and examined in the context of topoisomerase IIalpha protein structure comprising three functional domains associated with energy transduction, DNA breakage-reunion activity and nuclear localization. The organization of the 3' half of human TOP2beta, including sequence specifying the C-terminal nuclear localization domain, was also elucidated. Of the 15 introns identified in this 20 kb region of TOP2beta, the first nine and the last intron align in identical positions and display the same phases as introns in TOP2alpha. Though their extreme 3' ends differ, the striking conservation suggests the two genes diverged recently in evolutionary terms consistent with a gene duplication event. Access to TOP2alpha and TOP2beta gene structures should aid studies of mutations and gene rearrangements associated with anticancer drug resistance.

Novel HeLa topoisomerase II is the II beta isoform: complete coding sequence and homology with other type II topoisomerases.

DNA topoisomerase (topo) II mediates DNA strand passage in an ATP-dependent reaction. Human cell lines express at least two genetically distinct forms of the enzyme, topo II alpha (p170) and II beta (p180). Previously, we isolated a novel HeLa cDNA clone (CAA5) that partially encodes a protein homologous to topo II alpha (Austin, C.A. and Fisher, L.M. (1990) FEBS Lett. 266, 115-117). In this paper we show that CAA5 encodes a C-terminal segment of human topo II beta. We report here for the first time cDNA clones spanning the entire coding sequence. Overlapping clones specifying the 3' end of the cDNA have been isolated, mapped and sequenced. The missing 5' coding sequence was obtained by an inverse PCR protocol and from a specifically primed cDNA library. Human topo II beta is a 1621 amino acid protein which is closely homologous to topo II alpha in the N-terminal three quarters of its sequence. In contrast, the C-terminal segments of the alpha and beta sequences show considerable divergence suggesting these regions may mediate different cellular functions of the two isoforms. Southern blot analysis of yeast and Drosophila DNA using human alpha and beta specific probes detected a single topo II homologue in these lower eukaryotes. Comparison of the protein sequence for human topo II beta with other type II topoisomerases revealed several conserved motifs and has allowed identification of the likely ATPase- and DNA breakage-reunion domains.

DNA supercoiling and relaxation by ATP-dependent DNA topoisomerases.

Bacterial DNA gyrase and the eukaryotic type II DNA topoisomerases are ATPases that catalyse the introduction or removal of DNA supercoils and the formation and resolution of DNA knots and catenanes. Gyrase is unique in using ATP to drive the energetically unfavourable negative supercoiling of DNA, an example of mechanochemical coupling: in contrast, eukaryotic topoisomerase II relaxes DNA in an ATP-requiring reaction. In each case, the enzyme-DNA complex acts as a 'gate' mediating the passage of a DNA segment through a transient enzyme-bridged double-strand DNA break. We are using a variety of genetic and enzymic approaches to probe the nature of these complexes and their mechanism of action. Recent studies will be described focusing on the role of DNA wrapping on the A2B2 gyrase complex, subunit activities uncovered by using ATP analogues and the coumarin and quinolone inhibitors, and the identification and functions of discrete subunit domains. Homology between gyrase subunits and the A2 homodimer of eukaryotic topo II suggests functional conservation between these proteins. The role of ATP hydrolysis by these topoisomerases will be discussed in regard to other energy coupling systems.