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High occurrence of BRCA1 intragenic rearrangements in hereditary breast and ovarian cancer syndrome in the Czech Republic.

Vasickova P, Machackova E, Lukesova M, Damborsky J, Horky O, Pavlu H, Kuklova J, Kosinova V, Navratilova M, Foretova L - BMC Med. Genet. (2007)

Bottom Line: Positive MLPA results were confirmed and located by long-range PCR.Destabilization and global unfolding of the mutated BRCT domains explain the molecular and genetic defects associated with the exon 20 in-frame deletion and the exon 21 and 22 in-frame deletion, respectively.Screening for large genomic rearrangements in the BRCA1 gene in the Czech high-risk patients is highly supported by this study.

View Article: PubMed Central - HTML - PubMed

Affiliation: Masaryk Memorial Cancer Institute, Brno, Czech Republic. vasickova@mou.cz

ABSTRACT

Background: Alterations in the highly penetrant cancer susceptibility gene BRCA1 are responsible for the majority of hereditary breast and/or ovarian cancers. However, the number of detected germline mutations has been lower than expected based upon genetic linkage data. Undetected deleterious mutations in the BRCA1 gene in some high-risk families could be due to the presence of intragenic rearrangements as deletions, duplications or insertions spanning whole exons. Standard PCR-based screening methods are mainly focused on detecting point mutations and small insertions/deletions, but large rearrangements might escape detection.The purpose of this study was to determine the type and frequency of large genomic rearrangements in the BRCA1 gene in hereditary breast and ovarian cancer cases in the Czech Republic.

Methods: Multiplex ligation-dependent probe amplification (MLPA) was used to examine BRCA1 rearrangements in 172 unrelated patients with hereditary breast and/or ovarian cancer syndrome without finding deleterious mutation after complete screening of whole coding regions of BRCA1/2 genes. Positive MLPA results were confirmed and located by long-range PCR. The breakpoints of detected rearrangements were characterized by sequencing.

Results: Six different large deletions in the BRCA1 gene were identified in 10 out of 172 unrelated high-risk patients: exons 1A/1B and 2 deletion; partial deletion of exon 11 and exon 12; exons 18 and 19 deletion; exon 20 deletion; exons 21 and 22 deletion; and deletion of exons 5 to 14. The breakpoint junctions were localized and further characterized. Destabilization and global unfolding of the mutated BRCT domains explain the molecular and genetic defects associated with the exon 20 in-frame deletion and the exon 21 and 22 in-frame deletion, respectively.

Conclusion: Using MLPA, mutations were detected in 6% of high-risk patients previously designated as BRCA1/2 mutation-negative. The breakpoints of five out of six large deletions detected in Czech patients are novel. Screening for large genomic rearrangements in the BRCA1 gene in the Czech high-risk patients is highly supported by this study.

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Pedigrees of ovarian cancer family with detected deletion of BRCA1 exons 11–12 (g.34845_41405del6561). Circles – females, squares – males, partially filled symbols – affected individuals, arrow – proband. Type of cancer and age of onset are indicated below each affected individual (ov – ovarian). Mutation status: + carrier, - no carrier (wt).
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Figure 3: Pedigrees of ovarian cancer family with detected deletion of BRCA1 exons 11–12 (g.34845_41405del6561). Circles – females, squares – males, partially filled symbols – affected individuals, arrow – proband. Type of cancer and age of onset are indicated below each affected individual (ov – ovarian). Mutation status: + carrier, - no carrier (wt).

Mentions: The deletion of the second part of the exon 11 and exon 12 was found by MLPA in a family with ovarian cancer phenotype only. Altogether, five women in two generations were affected with ovarian cancer at ages ranging from 34 to 56 years (Figure 3). Long-range PCR confirmed a deletion of 6.5 kb of genomic DNA spanning nearly one-half of the BRCA1 gene coding sequence. The exact breakpoints were characterized by sequencing as g.34845_41405del6561 (Figure 2C, Table 3). An aberrant splicing of mRNA that might further extend a defect on the BRCA1 protein is suspected in this case. This deletion lies within a central-risk region where mutations were associated with a significantly higher ovarian/breast cancer ratio [41].


High occurrence of BRCA1 intragenic rearrangements in hereditary breast and ovarian cancer syndrome in the Czech Republic.

Vasickova P, Machackova E, Lukesova M, Damborsky J, Horky O, Pavlu H, Kuklova J, Kosinova V, Navratilova M, Foretova L - BMC Med. Genet. (2007)

Pedigrees of ovarian cancer family with detected deletion of BRCA1 exons 11–12 (g.34845_41405del6561). Circles – females, squares – males, partially filled symbols – affected individuals, arrow – proband. Type of cancer and age of onset are indicated below each affected individual (ov – ovarian). Mutation status: + carrier, - no carrier (wt).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1904436&req=5

Figure 3: Pedigrees of ovarian cancer family with detected deletion of BRCA1 exons 11–12 (g.34845_41405del6561). Circles – females, squares – males, partially filled symbols – affected individuals, arrow – proband. Type of cancer and age of onset are indicated below each affected individual (ov – ovarian). Mutation status: + carrier, - no carrier (wt).
Mentions: The deletion of the second part of the exon 11 and exon 12 was found by MLPA in a family with ovarian cancer phenotype only. Altogether, five women in two generations were affected with ovarian cancer at ages ranging from 34 to 56 years (Figure 3). Long-range PCR confirmed a deletion of 6.5 kb of genomic DNA spanning nearly one-half of the BRCA1 gene coding sequence. The exact breakpoints were characterized by sequencing as g.34845_41405del6561 (Figure 2C, Table 3). An aberrant splicing of mRNA that might further extend a defect on the BRCA1 protein is suspected in this case. This deletion lies within a central-risk region where mutations were associated with a significantly higher ovarian/breast cancer ratio [41].

Bottom Line: Positive MLPA results were confirmed and located by long-range PCR.Destabilization and global unfolding of the mutated BRCT domains explain the molecular and genetic defects associated with the exon 20 in-frame deletion and the exon 21 and 22 in-frame deletion, respectively.Screening for large genomic rearrangements in the BRCA1 gene in the Czech high-risk patients is highly supported by this study.

View Article: PubMed Central - HTML - PubMed

Affiliation: Masaryk Memorial Cancer Institute, Brno, Czech Republic. vasickova@mou.cz

ABSTRACT

Background: Alterations in the highly penetrant cancer susceptibility gene BRCA1 are responsible for the majority of hereditary breast and/or ovarian cancers. However, the number of detected germline mutations has been lower than expected based upon genetic linkage data. Undetected deleterious mutations in the BRCA1 gene in some high-risk families could be due to the presence of intragenic rearrangements as deletions, duplications or insertions spanning whole exons. Standard PCR-based screening methods are mainly focused on detecting point mutations and small insertions/deletions, but large rearrangements might escape detection.The purpose of this study was to determine the type and frequency of large genomic rearrangements in the BRCA1 gene in hereditary breast and ovarian cancer cases in the Czech Republic.

Methods: Multiplex ligation-dependent probe amplification (MLPA) was used to examine BRCA1 rearrangements in 172 unrelated patients with hereditary breast and/or ovarian cancer syndrome without finding deleterious mutation after complete screening of whole coding regions of BRCA1/2 genes. Positive MLPA results were confirmed and located by long-range PCR. The breakpoints of detected rearrangements were characterized by sequencing.

Results: Six different large deletions in the BRCA1 gene were identified in 10 out of 172 unrelated high-risk patients: exons 1A/1B and 2 deletion; partial deletion of exon 11 and exon 12; exons 18 and 19 deletion; exon 20 deletion; exons 21 and 22 deletion; and deletion of exons 5 to 14. The breakpoint junctions were localized and further characterized. Destabilization and global unfolding of the mutated BRCT domains explain the molecular and genetic defects associated with the exon 20 in-frame deletion and the exon 21 and 22 in-frame deletion, respectively.

Conclusion: Using MLPA, mutations were detected in 6% of high-risk patients previously designated as BRCA1/2 mutation-negative. The breakpoints of five out of six large deletions detected in Czech patients are novel. Screening for large genomic rearrangements in the BRCA1 gene in the Czech high-risk patients is highly supported by this study.

Show MeSH
Related in: MedlinePlus