A tandem duplication of BRCA1 exons 1-19 through DHX8 exon 2 in four families with hereditary breast and ovarian cancer syndrome.

PURPOSE: The purpose of this study is to characterize a novel structural variant, a large duplication involving exons 1-19 of the BRCA1 gene in four independent families, and to provide diagnostically valuable information including the position of the breakpoints as well as clues to its clinical significance. METHODS: The duplication of exons 1-19 of the BRCA1 gene was initially detected by routine laboratory testing including MLPA analysis and next generation sequencing. For detailed characterization we performed array-comparative genome hybridization analysis, fluorescent in situ hybridization, next generation mapping, and long-distance PCR for break-point sequencing. RESULTS: Our data revealed a tandem duplication on chromosome 17 that encompassed 357 kb and included exons 1-19 of the BRCA1 gene and the genes NBR2, NBR1, TMEM106A, LOC100130581, ARL4D, MIR2117 up to parts of the DHX8 gene. This structural variant appeared as a tandem duplication with breakpoints in intron 19 of the BRCA1 gene and in intron 3 of the DHX8 gene (HGVS:chr17(hg19):g.41210776_41568516dup). Segregation analysis indicated that this structural rearrangement is phased in trans with a known pathogenic exon deletion of the BRCA1 gene in one family. CONCLUSIONS: The copy number variation initially recognized as duplication of exon 1-19 of the BRCA1 gene by MLPA analysis is a structural variation with breakpoints in the BRCA1 and DHX8 genes. Although currently to be classified as a variant of unknown significance, our family data indicates that this duplication may be a benign variation or at least of markedly reduced penetrance since it occurs in trans with another known fully pathogenic variant in the BRCA1 gene.

Breast cancer patients suggestive of Li-Fraumeni syndrome: mutational spectrum, candidate genes, and unexplained heredity.

BACKGROUND: Breast cancer is the most prevalent tumor entity in Li-Fraumeni syndrome. Up to 80% of individuals with a Li-Fraumeni-like phenotype do not harbor detectable causative germline TP53 variants. Yet, no systematic panel analyses for a wide range of cancer predisposition genes have been conducted on cohorts of women with breast cancer fulfilling Li-Fraumeni(-like) clinical diagnostic criteria. METHODS: To specifically help explain the diagnostic gap of TP53 wild-type Li-Fraumeni(-like) breast cancer cases, we performed array-based CGH (comparative genomic hybridization) and panel-based sequencing of 94 cancer predisposition genes on 83 breast cancer patients suggestive of Li-Fraumeni syndrome who had previously had negative test results for causative BRCA1, BRCA2, and TP53 germline variants. RESULTS: We identified 13 pathogenic or likely pathogenic germline variants in ten patients and in nine genes, including four copy number aberrations and nine single-nucleotide variants or small indels. Three patients presented as double-mutation carriers involving two different genes each. In five patients (5 of 83; 6% of cohort), we detected causative pathogenic variants in established hereditary breast cancer susceptibility genes (i.e., PALB2, CHEK2, ATM). Five further patients (5 of 83; 6% of cohort) were found to harbor pathogenic variants in genes lacking a firm association with breast cancer susceptibility to date (i.e., Fanconi pathway genes, RECQ family genes, CDKN2A/p14ARF, and RUNX1). CONCLUSIONS: Our study details the mutational spectrum in breast cancer patients suggestive of Li-Fraumeni syndrome and indicates the need for intensified research on monoallelic variants in Fanconi pathway and RECQ family genes. Notably, this study further reveals a large portion of still unexplained Li-Fraumeni(-like) cases, warranting comprehensive investigation of recently described candidate genes as well as noncoding regions of the TP53 gene in patients with Li-Fraumeni(-like) syndrome lacking TP53 variants in coding regions.