About 4% of all BRCA1 and BRCA2 alterations reported to the Breast Information Core database are splice site variants. Only a limited number of them have been studied at the RNA level. By BRCA1 and BRCA2 mutation analysis of breast/ovarian cancer families, we identified two novel and eight previously reported potential splice site mutations, never characterized at the cDNA level before. RT-PCR was performed to determine whether these variants disrupted correct splicing. To ensure efficient detection of transcripts containing premature termination codons, a nonsense-mediated mRNA decay inhibitor was added to the lymphoblastoid cell lines of the patients before RNA extraction. We found that BRCA1 IVS3+3A>C, 4304G>A (in the last codon of exon 12), and IVS19+2delT and BRCA2 IVS6+1G>A, IVS23-2A>G, and IVS24+1G>A lead to aberrant transcripts in lymphocytes. Therefore, they were considered to be true pathogenic mutations, predisposing carriers to cancers of the hereditary breast/ovarian cancer syndrome. BRCA2 IVS24-16T>C is a frequent polymorphism in linkage disequilibrium, with a polymorphic stop codon in exon 27, K3326X. BRCA1 IVS2-14C>T and BRCA2 IVS9-5insT and IVS25+9A>C represent rare variants, not disrupting normal splicing in blood lymphocytes. However, some of the alterations may act differently, qualitatively and/or quantitatively, in breast or ovarian tissues. The data provided in this paper allowed more accurate risk estimation of patients and relatives carrying the mutations described herein and have facilitated genetic counseling. Furthermore, our study is important for a better understanding of splicing mechanisms and revealed new patterns of alternative splicing in BRCA1 and BRCA2.

BackgroundThe incidence of breast cancer has doubled over the past 20 years in the Czech Republic. Hereditary factors may be a cause of young onset, bilateral breast or ovarian cancer, and familial accumulation of the disease. BRCA1 and BRCA2 mutations account for an important fraction of hereditary breast and ovarian cancer cases. One thousand and ten unrelated high-risk probands with breast and/or ovarian cancer were analysed for the presence of a BRCA1 or BRCA2 gene mutation at the Masaryk Memorial Cancer Institute (Czech Republic) during 1999–2006.MethodsThe complete coding sequences and splice sites of both genes were screened, and the presence of large intragenic rearrangements in BRCA1 was verified. Putative splice-site variants were analysed at the cDNA level for their potential to alter mRNA splicing.ResultsIn 294 unrelated families (29.1% of the 1,010 probands) pathogenic mutations were identified, with 44 different BRCA1 mutations and 41 different BRCA2 mutations being detected in 204 and 90 unrelated families, respectively. In total, three BRCA1 founder mutations (c.5266dupC; c.3700_3704del5; p.Cys61Gly) and two BRCA2 founder mutations (c.7913_7917del5; c.8537_8538del2) represent 52% of all detected mutations in Czech high-risk probands. Nine putative splice-site variants were evaluated at the cDNA level. Three splice-site variants in BRCA1 (c.302-3C>G; c.4185G>A and c.4675+1G>A) and six splice-site variants in BRCA2 (c.475G>A; c.476-2>G; c.7007G>A; c.8755-1G>A; c.9117+2T>A and c.9118-2A>G) were demonstrated to result in aberrant transcripts and are considered as deleterious mutations.ConclusionThis study represents an evaluation of deleterious genetic variants in the BRCA1 and 2 genes in the Czech population. The classification of several splice-site variants as true pathogenic mutations may prove useful for genetic counselling of families with high risk of breast and ovarian cancer.

BACKGROUND: High-resolution melting is an emerging technique for detection of nucleic acid sequence variations. Developments in instrumentation and saturating intercalating dyes have made accurate high-resolution melting analysis possible and created opportunities to use this technology in diagnostic settings. We evaluated 2 high-resolution melting instruments for screening BRCA1 and BRCA2 mutations.

We report two novel mutations in the splice sites of BRCA1 exon 5: IVS5+3A4G, a Belgian founder mutation, and IVS376T4G, identi®ed in one family with a strong family history of breast cancer. Real-time RT ± PCR showed that IVS376T4G leads to a ®vefold increase of the BRCA1-Dex5 (isoform with an in frame skip of exon 5) ratio to the total BRCA1 expression level. IVS5+3A4G results in a 10-fold increase of the BRCA1-D22ntex5 ratio (isoform with an out of frame skip of the last 22 nucleotides of exon 5) and a twofold increase of the BRCA1-Dex5 ratio. These altered ratios are most likely to result from increased expression of the alternative transcripts, although we cannot completely rule out a small decrease of the total BRCA1 expression level due to highly variable BRCA1 levels in cultured cell lines. In order to explore the functional signi®cance of the isoforms, we evaluated their prevalence in normal tissues and cancer cell lines. The BRCA1-D22ntex5 ratio was signi®cantly higher in an ovarian cancer cell line compared to normal ovarian tissue. Our ®ndings suggest that revealing the defects caused by some splice mutations requires accurate quantitative methods. We hypothesize that disruption of alternative transcript ratios of BRCA1 may be a dominant mechanism a ecting predisposition to hereditary breast and/or ovarian cancer. Oncogene (2002) 21, 4171 ± 4175. doi:10.1038/sj.onc. 1205520Keywords: BRCA1; splice mutation; real time RT ± PCR; breast cancer By extensive linkage studies on families with a strong predisposition for breast and/or ovarian cancer and by positional cloning BRCA1 was mapped to 17q21 and BRCA2 to 13q12.3 (Easton et al., 1993;Miki et al., 1994;Wooster et al., 1995). A large number of di erent mutations in BRCA1 and BRCA2 implicated in the familial occurrence of breast and/or ovarian cancer, have been described in many pedigrees. In the BIC (Breast Information Core) database (http:// www. nhgri.nih.gov/Intramural_research / Lab_transfer/ Bic/Member/) splicing mutations only account for 7% of the germline mutations reported in BRCA1 and for 5% in BRCA2. In this study we report two novel splice site mutations outside the highly conserved 3' AG-acceptor (IVS376T4G) and 5' GT-donor (IVS5+3A4G) of exon 5 of the BRCA1 gene and showed how both mutations exert their pathological e ect.Both mutations were identi®ed by DGGE (denaturing gradient gel electrophoresis) on gDNA. IVS5+3A4G was identi®ed in nine apparently unrelated families and is a Belgian founder mutation (Claes et al., 1999, Claes et al., manuscript in preparation). IVS376T4G was detected in a proband diagnosed with breast cancer at age 43, who developed a second cancer in the same breast at age 46 years. Her sister developed a brain tumor at age 40 and is also carrying the mutation. Both inherited the mutation from their father. Several other family members in the paternal branch of the family have been diagnosed with breast cancer. Unfortunately, these patients were not available for further study.In all patients the complete coding regi...

Worldwide variation in the distribution of BRCA1 and BRCA2 mutations is well recognised, and for the Belgian population no comprehensive studies about BRCA1/2 mutation spectra or frequencies have been published. We screened the complete coding region of both genes in 451 individuals from 349 Belgian families referred to a family cancer clinic and identified 49 families with a BRCA1 and 26 families with a BRCA2 mutation. Six major recurrent mutations (BRCA1 IVS5 þ 3A4G, 2478 -2479insG, E1221X and BRCA2 IVS6 þ 1G4A, 6503-6504delTT, 9132delC) accounted for nearly 60% of all mutations identified. Besides 75 true pathogenic mutations, we identified several variants of unknown clinical significance. In combination with a family history, an early average age of female breast cancer diagnosis (Po0.001), and the presence of a relative with ovarian cancer (Po0.0001) or multiple primary breast cancers (P ¼ 0.002), increased the chance for finding a mutation. Male breast cancer was indicative of a BRCA2 mutation segregating in the family (P ¼ 0.002). Mutations in the 5 0 -end of BRCA1 and BRCA2 were associated with a significantly increased risk for ovarian cancer relative to the central portion of the gene. Our study suggests a role for additional breast cancer susceptibility genes in the Belgian population, since mutation detection ratios were low in high-risk breast cancer-only families as compared to breast -ovarian cancer families. Given the large proportion of recurring mutations, molecular testing can now be organised in a more cost-effective way. Our data allow optimisation of genetic counselling and disease prevention in Belgian breast/ovarian cancer families. Since the mapping and the cloning of two genes that confer susceptibility to both breast and ovarian cancer, BRCA1 and BRCA2 (Miki et al, 1994;Wooster et al, 1995;Tavtigian et al, 1996), it became possible to offer genetic testing to families with a predisposition for breast and/or ovarian cancer. Consequently, individuals at risk can now be identified as candidates for surveillance programmes. A large number of distinct mutations in the BRCA1 and BRCA2 genes have been reported worldwide, but population-specific variation in the distribution of BRCA1/2 mutations is well recognised. In some populations or ethnic groups, founder mutations form a sufficient proportion of the total to justify the adoption of specific molecular screening strategies.To date, no comprehensive studies in the Belgian population have been published. Only data from small series are available (Claes et al, 1999a, b) or from studies in which the analysis was restricted to a few BRCA1/2 exons or to BRCA1 only Sibille-Hoang et al, 1998;Goelen et al, 1999). We performed mutation screening of the complete coding region of BRCA1 and BRCA2 in 349 unrelated Belgian families referred to our family cancer clinic and report here the nature and distribution of the mutations identified. We found phenotypic differences between families in whom a disease-causing mutation was identified vs BRCA1/2 muta...