BRCA1 and BRCA2 germline mutation spectrum and frequencies in Belgian breast/ovarian cancer families

Abstract

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...

A comprehensive functional characterization of BRCA2 variants associated with Fanconi anemia using mouse ES cell–based assay

“…Both transcripts result in frameshift, generating a premature stop codon in exon 14. 22 Brca2 CKO/KO ES cells expressing the p.R2336H variant (Brca2 CKO/KO ;tg R2336H ) show the presence of these 2 transcripts (⌬exon 13 and ⌬exons 12 and 13, Figure 5A-C) as reported in heterozygous carriers. 22 After Cre expression, we obtained 800-1000 HAT r colonies, which is 75%-80% fewer than the number obtained with WT BRCA2-expressing cells ( Figure 1D).…”

“…22 It results in 2 splice variants: one skipping exon 13 (⌬exon 13) and the other skipping exons 12 and 13 (⌬exons 12 and 13). Both transcripts result in frameshift, generating a premature stop codon in exon 14.…”

“…In addition to IVS7 ϩ 2T Ͼ G, p.R2336H is also known to affect splicing and both are considered to be deleterious. [22][23][24] The other 4 (p.I2490T, p.L2510P, p.W2626C, and p.K2729N) are listed as variants of unknown clinical significance in the Breast Cancer Information database (http://research.nhgri.nih.gov/bic; supplemental Table 1). We have also examined the effect of these variants on the structural integrity of BRCA2, using structural modeling to support the functional data.…”

Rapid and Sensitive Detection of BRCA1/2 Mutations in a Diagnostic Setting: Comparison of Two High-Resolution Melting Platforms

“…Most commonly, a prescreening method such as denaturing high-performance liquid chromatography (dHPLC) 3 or denaturing gradient gel electrophoresis (DGGE) is used, followed by sequencing of aberrant fragments. Screening of BRCA1 and BRCA2 is arduous because of the complex mutational spectrum and the large size of the genes for which the complete coding sequence needs to be analyzed for an increasing number of patients.…”

“…Until recently, our mutation detection strategy consisted of direct sequencing of the large exon 11 of both BRCA1 and BRCA2 and DGGE for all other coding exons (3,4 ). Because we were witnessing an increasing number of patients and aiming at a reduction of costs and workload, we evaluated 2 high-resolution melting instruments for mutation screening of both BRCA1 and BRCA2.…”