Haplotype and quantitative transcript analyses of Portuguese breast/ovarian cancer families with the BRCA1 R71G founder mutation of Galician origin.
We investigated the functional effect of the missense variant c.211A>G (R71G) localized at position -2 of exon 5 donor splice site in the BRCA1 gene and evaluated whether Portuguese and Galician families with this mutation share a common ancestry. Three unrelated Portuguese breast/ovarian cancer families carrying this variant were studied through qualitative and quantitative transcript analyses. We also evaluated the presence of loss of heterozigosity and the histopathologic characteristics of the carcinomas in those families. Informative families (two from Portugal and one from Galicia) were genotyped for polymorphic microsatellite markers flanking BRCA1 to reconstruct haplotypes. Qualitative RNA analysis revealed the presence of two alternative transcripts both in carriers of the BRCA1 R71G variant and in controls. Semi-quantitative fragment analysis and real-time RT-PCR showed a significant increase of the transcript with an out of frame deletion of the last 22nt of exon 5 (BRCA1-Delta22ntex5) and a decrease of the full-length transcript (BRCA1-ex5FL) in patients carrying the R71G mutation as compared to controls, whereas no significant differences were found for the transcript with in frame skipping of exon 5 (BRCA1-Deltaex5). One haplotype was found to segregate in the two informative Portuguese families and in the Galician family. We demonstrate that disruption of alternative transcript ratios is the mechanism causing hereditary breast/ovarian cancer associated with the BRCA1 R71G mutation. Furthermore, our findings indicate a common ancestry of the Portuguese and Galician families sharing this mutation.
Santos
Catarina
C
Department of Genetics, Portuguese Oncology Institute, 4200-072 Porto, Portugal.
Peixoto
Ana
A
Rocha
Patrícia
P
Vega
Ana
A
Soares
Maria José
MJ
Cerveira
Nuno
N
Bizarro
Susana
S
Pinheiro
Manuela
M
Pereira
Deolinda
D
Rodrigues
Helena
H
Castro
Fernando
F
Henrique
Rui
R
Teixeira
Manuel R
MR
D017398:Alternative Splicing; D019943:Amino Acid Substitution; D001120:Arginine / Q000235:genetics; D019313:BRCA1 Protein / Q000235:genetics*; D001943:Breast Neoplasms / Q000235:genetics*; D004252:DNA Mutational Analysis; D005838:Genotype; D005998:Glycine / Q000235:genetics; D006239:Haplotypes; D006801:Humans; D020641:Polymorphism, Single Nucleotide; D011174:Portugal; D020133:Reverse Transcriptase Polymerase Chain Reaction
D019313:BRCA1 Protein; D001120:Arginine; D005998:Glycine