Characterization of Two Novel BRCA1 Germ-Line Mutations Involving Splice Donor Sites

Abstract

Deleterious BRCA1 mutations have significant clinical implications for the patients that carry them. Point mutations in critical functional domains and frameshift mutations that lead to early termination of protein translation are associated with a 60-80% risk of breast cancer and a 20-40% risk of ovarian cancer. In contrast, the significance of mutations located in intronic regions of BRCA1, even in the setting of a family history of breast and ovarian cancer, is not always clear. Some of these mutations occur in splice donor/acceptor consensus sites. These mutations can affect heteronuclear RNA (hnRNA) processing, leading to the loss of functional BRCA1 protein and thus may be disease-associated. However, it is important to verify the effect of these mutations, because splicing alterations cannot be predicted from genomic sequence alone. We report here the characterization of two novel BRCA1 mutations identified in families seen in our cancer risk evaluation clinic that alter splice donor sites of BRCA1. We show that both mutations alter transcript splicing and result in truncated BRCA1. IVS17 + 1G --> T leads to inclusion of part of intron 17 after the coding sequence of exon 17, resulting in early termination of BRCA1 protein following codon 1692. 252del5insT abolishes the splice donor site in exon 3, leading to the skipping of exon 5 and BRCA1 protein truncation following codon 45. Thus, both mutations result in loss of BRCA1 function, and carriers of these mutations should be counseled in the same manner as carriers of other truncating BRCA1 mutations.

Evaluation of a 5-Tier Scheme Proposed for Classification of Sequence Variants Using Bioinformatic and Splicing Assay Data: Inter-Reviewer Variability and Promotion of Minimum Reporting Guidelines

“…For an initial pilot to assess feasibility of review, splicing assay data for 21 BRCA1 (NM_007294.3) or BRCA2 (NM_000059.3) sequence variants (22 assays) were drawn from four studies (Table ), published by four different groups across a period of 7 years [Brose et al., ; Claes et al., ; Farrugia et al., ; Walker et al., ]. These data were then comprehensively assessed by basic and clinical researchers from up to nine different ENIGMA study sites from around the world.…”

GT198 Splice Variants Display Dominant-Negative Activities and Are Induced by Inactivating Mutations

“…12 Consistently, germline mutations in BRCA1 exon 11 promote the expression of BRCA1Δ11b. 13 Additional germline mutations in BRCA1 have also been identified, causing aberrant splicing 14,15 or altering alternative splicing. [16][17][18] Since a single pre-mRNA can be processed to generate multiple functional isoforms, it is essential to analyze the interrelationship between wildtype and splice variants when characterizing gene functions in cancer or disease.…”

Assessing the RNA effect of 26 DNA variants in the BRCA1 and BRCA2 genes

“…These variants include missense variants leading to amino acid changes, variants located in intronic regions and silent mutations [8][9][10][11][12]; they are usually referred to as VUS and pose a real problem in genetic counseling. An increasing number of recent studies have demonstrated the effect of several variants on the correct splicing of the BRCA1 and BRCA2 genes [13][14][15][16][17][18][19].…”