Can unknown predisposition in familial breast cancer be family-specific?

Genetic predisposition plays a key role in the development of familial breast cancer. In spite of strong familial clustering of the disease and extensive efforts made during the past decade; however, progress has been slow in identifying genetic predisposition for the majority of familial breast cancer families. The question arises therefore as to whether current approaches are adequate in identifying the unknown genetic predisposition. We analyzed eight members of a BRCA1-, BRCA2-, p53-, and PTEN-negative breast cancer family, of which five had breast cancer, one is an obligate gene carrier, and two were unaffected. We sequenced the entire coding region of the genome for each member using exome sequencing to identify nonsynonymous variants. We identified 55 nonsynonymous germline variants affecting 49 genes in multiple members of the family, of which 22 are predicted to have damaging effects. We validated 20 of the 22 selected variants in the family by Sanger sequencing. Two variants in KAT6B, an acetal transferase gene, were identified in six family members of which five were affected with breast cancer and one is the unaffected obligate carrier. We further examined the presence of the identified variants in a cohort of 40 additional breast cancer cases from 22 familial breast cancer families, but none of the 22 variants was detected in these cases. Sequencing the entire coding exons in KAT6B detects no variants in these cases. Our results show that genetic predisposition for familial breast cancer can be rich in an affected family, but the predisposition can be family-specific. As such, it will be difficult to detect them by applying population-based approach. Our study supports the concept that focusing on each affected family will be required to determine the genetic predisposition for many familial breast cancer families whose genetic dispositions remain unknown.

Familial sarcoma: challenging pedigrees.

BACKGROUND: Partially due to the rare occurrence of soft tissue and osteogenic sarcomas in the general population, scant attention has been given to their hereditary etiology. Their overall poor prognosis might be ameliorated through an understanding of their environmental and hereditary causal factors, and/or their interactions, thereby contributing to earlier diagnosis and even the development of molecularly based targeted therapy. METHODS: The authors selected 10 sarcoma-prone families from their extensive hereditary cancer-prone family resource and focused on their challenging diagnostic, surveillance, and management features. The family study protocol included the compilation of a detailed family history of malignant disease of all anatomic sites and the collection of all available primary medical and pathology documents for verification. Genetic counseling was provided before DNA collection and at disclosure of results. RESULTS: These families displayed marked phenotypic and genotypic heterogeneity. In one of these families, 16 relatives had sarcomas, with 2 of the 16 each having 2 metachronous sarcomas; to our knowledge, this represents the greatest number of sarcomas reported in any family described to date. Two familial atypical multiple-mole melanoma syndrome kindreds with the CDKN2A mutation showed the association of sarcoma with malignant melanoma, whereas one family had several pancreatic carcinomas. Other families with sarcoma had hereditary nonpolyposis colorectal carcinoma with MSH2 mutation, hereditary breast carcinoma with BRCA1 mutation, and p53 mutation in a Li-Fraumeni syndrome. CONCLUSIONS: Sarcoma-prone families reported in the current study were selected carefully to depict clinicopathology and compliance features, the understanding of which could elucidate the etiologic role of genetic factors in concert with the phenotypic and genotypic heterogeneity encountered in such families. The lack of a population-based data set for these families posed a limitation.

Hereditary nonpolyposis colorectal carcinoma (HNPCC) and HNPCC-like families: Problems in diagnosis, surveillance, and management.

BACKGROUND: To the authors' knowledge, hereditary nonpolyposis colorectal carcinoma (HNPCC) is the most commonly occurring hereditary disorder that predisposes to colorectal carcinoma (CRC), accounting for approximately 2-7% of all CRC cases diagnosed in the U.S each year. Its diagnosis is wholly dependent on a meticulously obtained family history of cancer of all anatomic sites, with particular attention to the pattern of cancer distribution within the family. METHODS: The objective of the current study was to illustrate various vexing problems that can deter the diagnosis of HNPCC and, ultimately, its management. This was an observational cohort study. Sixteen HNPCC and HNPCC-like families were selected from a large resource of highly extended HNPCC families. High-risk patients were selected from these HNPCC families. An ascertainment bias was imposed by the lack of a population-based data set. Personal interviews and questionnaires were used for data collection. RESULTS: There was an array of difficulties highlighted by limitations in compliance, lack of a clinical or molecular basis for an HNPCC diagnosis, ambiguous DNA findings, problems in genetic counseling, failure to meet Amsterdam or Bethesda criteria, small families, lack of medical and pathologic documentation, poor cooperation of family members and/or their physicians, cultural barriers, economic stress, frequent patient fear and anxiety, perception of insurance discrimination, and limited patient and/or physician knowledge regarding hereditary cancer. CONCLUSIONS: The diagnosis and management of HNPCC is predicated on physician knowledge of its phenotypic and genotypic heterogeneity, in concert with the multifaceted problems that impact on patient compliance.

A 10-Mb paracentric inversion of chromosome arm 2p inactivates MSH2 and is responsible for hereditary nonpolyposis colorectal cancer in a North-American kindred.

Genomic deletions of the MSH2 gene are a frequent cause of hereditary nonpolyposis colorectal cancer (HNPCC), a common hereditary predisposition to the development of tumors in several organs including the gastrointestinal and urinary tracts and endometrium. The mutation spectrum at the MSH2 gene is extremely heterogeneous because it includes nonsense and missense point mutations, small insertions and deletions leading to frameshifts, and larger genomic deletions, the latter representing approximately 25% of the total mutation burden. Here, we report the identification and molecular characterization of the first paracentric inversion of the MSH2 locus known to cause HNPCC. Southern blot analysis and inverse PCR showed that the centromeric and telomeric breakpoints of the paracentric inversion map within intron 7 and to a contig 10 Mb 3' of MSH2, respectively. Pathogenicity of the paracentric inversion was demonstrated by conversion analysis. The patient's lymphocytes were employed to generate somatic cell hybrids to analyze the expression of the inverted MSH2 allele in an Msh2-deficient rodent cellular background. The inversion was shown to abolish MSH2 expression by both northern and western analysis. This study confirms that Southern blot analysis still represents a useful and informative tool to screen for and identify complex genomic rearrangements in HNPCC. Moreover, monoallelic expression analysis represents an attractive approach to demonstrate pathogenicity of unusual mutations in autosomal dominant hereditary conditions.