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Montalban G, Bonache S, Moles-Fernández A, Gisbert-Beamud A, Tenés A, Bach V, Carrasco E, López-Fernández A, Stjepanovic N, Balmaña J, Diez O, Gutiérrez-Enríquez S. Screening of BRCA1/2 deep intronic regions by targeted gene sequencing identifies the first germline BRCA1 variant causing pseudoexon activation in a patient with breast/ovarian cancer. J Med Genet 2019; 56:63-74. [PMID: 30472649 DOI: 10.1136/jmedgenet-2018-105606] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Revised: 10/16/2018] [Accepted: 10/28/2018] [Indexed: 12/24/2022]
Abstract
BACKGROUND Genetic analysis of BRCA1 and BRCA2 for the diagnosis of hereditary breast and ovarian cancer (HBOC) is commonly restricted to coding regions and exon-intron boundaries. Although germline pathogenic variants in these regions explain about ~20% of HBOC cases, there is still an important fraction that remains undiagnosed. We have screened BRCA1/2 deep intronic regions to identify potential spliceogenic variants that could explain part of the missing HBOC susceptibility. METHODS We analysed BRCA1/2 deep intronic regions by targeted gene sequencing in 192 high-risk HBOC families testing negative for BRCA1/2 during conventional analysis. Rare variants (MAF <0.005) predicted to create/activate splice sites were selected for further characterisation in patient RNA. The splicing outcome was analysed by RT-PCR and Sanger sequencing, and allelic imbalance was also determined when heterozygous exonic loci were present. RESULTS A novel transcript was detected in BRCA1 c.4185+4105C>T variant carrier. This variant promotes the inclusion of a pseudoexon in mature mRNA, generating an aberrant transcript predicted to encode for a non-functional protein. Quantitative and allele-specific assays determined haploinsufficiency in the variant carrier, supporting a pathogenic effect for this variant. Genotyping of 1030 HBOC cases and 327 controls did not identify additional carriers in Spanish population. CONCLUSION Screening of BRCA1/2 intronic regions has identified the first BRCA1 deep intronic variant associated with HBOC by pseudoexon activation. Although the frequency of deleterious variants in these regions appears to be low, our study highlights the importance of studying non-coding regions and performing comprehensive RNA assays to complement genetic diagnosis.
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Affiliation(s)
- Gemma Montalban
- Oncogenetics Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
| | - Sandra Bonache
- Oncogenetics Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
| | | | | | - Anna Tenés
- Area of Clinical and Molecular Genetics, University Hospital of Vall d'Hebron, Barcelona, Spain
| | - Vanessa Bach
- Oncogenetics Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
| | - Estela Carrasco
- High Risk and Cancer Prevention Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
| | - Adrià López-Fernández
- High Risk and Cancer Prevention Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
| | - Neda Stjepanovic
- High Risk and Cancer Prevention Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
- Medical Oncology Department, University Hospital of Vall d'Hebron, Barcelona, Spain
| | - Judith Balmaña
- High Risk and Cancer Prevention Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
- Medical Oncology Department, University Hospital of Vall d'Hebron, Barcelona, Spain
| | - Orland Diez
- Oncogenetics Group, Vall d'Hebron Institut d'Oncologia, Barcelona, Spain
- Area of Clinical and Molecular Genetics, University Hospital of Vall d'Hebron, Barcelona, Spain
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Non-Coding Variants in BRCA1 and BRCA2 Genes: Potential Impact on Breast and Ovarian Cancer Predisposition. Cancers (Basel) 2018; 10:cancers10110453. [PMID: 30453575 PMCID: PMC6266896 DOI: 10.3390/cancers10110453] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Revised: 11/04/2018] [Accepted: 11/12/2018] [Indexed: 12/21/2022] Open
Abstract
BRCA1 and BRCA2 are major breast cancer susceptibility genes whose pathogenic variants are associated with a significant increase in the risk of breast and ovarian cancers. Current genetic screening is generally limited to BRCA1/2 exons and intron/exon boundaries. Most identified pathogenic variants cause the partial or complete loss of function of the protein. However, it is becoming increasingly clear that variants in these regions only account for a small proportion of cancer risk. The role of variants in non-coding regions beyond splice donor and acceptor sites, including those that have no qualitative effect on the protein, has not been thoroughly investigated. The key transcriptional regulatory elements of BRCA1 and BRCA2 are housed in gene promoters, untranslated regions, introns, and long-range elements. Within these sequences, germline and somatic variants have been described, but the clinical significance of the majority is currently unknown and it remains a significant clinical challenge. This review summarizes the available data on the impact of variants on non-coding regions of BRCA1/2 genes and their role on breast and ovarian cancer predisposition.
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Diaz-Zabala HJ, Ortiz AP, Garland L, Jones K, Perez CM, Mora E, Arroyo N, Oleksyk TK, Echenique M, Matta JL, Dean M, Dutil J. A Recurrent BRCA2 Mutation Explains the Majority of Hereditary Breast and Ovarian Cancer Syndrome Cases in Puerto Rico. Cancers (Basel) 2018; 10:E419. [PMID: 30400234 PMCID: PMC6266560 DOI: 10.3390/cancers10110419] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 10/22/2018] [Accepted: 10/26/2018] [Indexed: 01/04/2023] Open
Abstract
Breast cancer is the most common cause of cancer diagnosis in women and is responsible for considerable mortality among the women of Puerto Rico. However, there are few studies in Puerto Rico on the genetic factors influencing risk. To determine the contribution of pathogenic mutations in BRCA1 and BRCA2, we sequenced these genes in 302 cases from two separate medical centers, who were not selected for age of onset or family history. We identified nine cases that are carriers of pathogenic germline mutation. This represents 2.9% of unselected cases and 5.6% of women meeting National Comprehensive Cancer Network (NCCN) criteria for BRCA testing. All of the identified pathogenic mutations were in the BRCA2 gene and the most common mutation is the p.Glu1308Ter (E1308X) mutation in BRCA2 found in eight out of nine cases, representing 89% of the pathogenic carriers. The E1308X mutation has been identified in breast and ovarian cancer families in Spain, and analysis of flanking DNA polymorphisms shows that all E1308X carriers occur on the same haplotype. This is consistent with BRCA2 E1308X being a founder mutation for the Puerto Rican population. These results will contribute to better inform genetic screening and counseling of breast and ovarian cancer cases in Puerto Rico and Puerto Rican populations in mainland United States.
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Affiliation(s)
- Hector J Diaz-Zabala
- Cancer Biology Division, Ponce Research Institute, Ponce Health Sciences University, Ponce, Ponce, PR 00716-2348, USA.
| | - Ana P Ortiz
- Cancer Control and Population Sciences Program, Comprehensive Cancer Center, University of Puerto Rico, San Juan, PR 00936-5067, USA.
| | - Lisa Garland
- Cancer Genomics Research Laboratory, Leidos Biomedical Research, Inc., Frederick, MD 21702, USA.
| | - Kristine Jones
- Cancer Genomics Research Laboratory, Leidos Biomedical Research, Inc., Frederick, MD 21702, USA.
| | - Cynthia M Perez
- Department of Biostatistics and Epidemiology, Graduate School of Public Health, University of Puerto Rico, San Juan, PR 00936-5067, USA.
| | - Edna Mora
- Department of Surgery, School of Medicine, University of Puerto Rico and University of Puerto Rico Comprehensive Cancer Center, San Juan, PR 00936-5067, USA.
| | - Nelly Arroyo
- Cancer Biology Division, Ponce Research Institute, Ponce Health Sciences University, Ponce, Ponce, PR 00716-2348, USA.
| | - Taras K Oleksyk
- Biology Department, Oakland University, Rochester, MI 48309-4454, USA.
- Department of Biology, University of Puerto Rico in Mayaguez, Mayaguez, PR 00681, USA.
| | - Miguel Echenique
- Cancer Center, Auxilio Mutuo Hospital, San Juan, PR 00936-5067, USA.
| | - Jaime L Matta
- Cancer Biology Division, Ponce Research Institute, Ponce Health Sciences University, Ponce, Ponce, PR 00716-2348, USA.
| | - Michael Dean
- Laboratory of Translational Genomics, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Gaithersburg, MD 20877, USA.
| | - Julie Dutil
- Cancer Biology Division, Ponce Research Institute, Ponce Health Sciences University, Ponce, Ponce, PR 00716-2348, USA.
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