Mutational analysis of the BRCA2 gene in breast carcinoma patients of Kashmiri descent

Abstract

Breast cancer demonstrates geographical and ethnic variation in its incidence reflecting the effect of local environmental conditions and lifestyle. The genesis of the disease has further been complexed by the involvement of a number of genes with small effects and above all by population heterogeneity. Accordingly, variations in genes, including breast cancer 1, early onset (BRCA1)/breast cancer 2, early onset (BRCA2), that have been markedly associated with the breast cancer phenotype exhibit a scattered mutational pattern in different populations. The present study was aimed to analyze the sequence variations in BRCA2 gene in a case control manner in ethnically pure Kashmiri population using PCR. Sequencing of BRCA2 exons revealed the presence of five sequence variations, four of which present in exon 11 alone were somatic and one was germline located in the U-terminal region (UTR) of exon 2. Out of these, the two somatic mutations comprised of substitutions, one representing a missense mutation leading to an amino-acid substitution at codon 991 and the other was a silent mutation at codon 1131, whereas the other two mutations located in exon 11 represented a loss of polymorphism. Codons for amino acid position 846 and 868 were demonstrated to be heterozygous polymorphic variants in 66% of the normal breast tissue samples, whereas the heterozygous polymorphic variant codons at the two loci were replaced by a homozygous genotype in associated tumor tissue in 88% of cases. These two mutations were always linked. Germline variation observed in exon 2 was located in the UTR region at contig position 13870572 (rs1799943). Other screened exons of BRCA2 did not demonstrate any sequence variation. These variations may contribute to breast cancer susceptibility along with variations in other low penetrating genes in sporadic types of breast cancer in this cohort of the population.