Mutation Screening of BRCA2 Gene Exon12 Splicing Site in a Panel of Sudanese Breast Cancer Patients

Abstract

Breast cancer is one of the major health problems in the Sudan, with high incidence in females and ranking as the top cancer among females. Several breast cancer susceptibility genes had been identified; among those are BRCA1 and BRCA2. Breast cancer is the predominant phenotype associated with mutations in BRCA1 and BRCA2 genes. However, the rate of mutations within the coding regions of the breast cancer susceptibility gene BRCA2 does not fairly explain the pathogenecity of the disease, nor accounting for all 12 variant was shown to be detected in normal and disease causing mutations. BRCA2 tumor breast tissues with increased levels of expression measured in the tumor status. Previous studies suggests that the mechanism generating the BRCA2 mRNA variant in normal breast tissues might be dysregulated in tumors and such an increase might be caused by factors at the transcriptional and/or post transcriptional level. The aim of this study was to detect mutations that might affect the splicing of exon12 of the BRCA2 gene and thus 12 variant in particular and its contribution to the modulating the functions of BRCA2 overall biological functions of BRCA2 in DNA Repair and tumor suppression. DNA was extracted from peripheral blood of 51 Sudanese breast cancer patients, exon12 was amplified and subjected to SSCP analysis. Two mutations were confirmed by sequencing in intron12 of the BRCA2 gene. One of the detected mutations was a deletion and the other was an insertion in an area expected to serve as sequence context for splicing. However, no mutations were detected in the canonical splice sites. According to in silico prediction analysis we hypothesized that the deletion might activate a cryptic 5`splice site that might interfere with the selection of the authentic 5` splice site leading to skipping of exon12 of the BRCA2 and/or shift the selection towards the cryptic 5`splice site resulting in partial intron retention. Future functional studies will address this hypothesis and try to make accurate prediction of the splicing patterns that result from this mutation. Furthermore, the structural and functional consequences for the corresponding protein will help to understand the role played by different BRCA2 variants in breast cancer