INFLUENCE OF SELECTED POLYMORPHISMS ON THE EXPRESSION OF BREAST CANCER IN AFRIKANER BRCA2 CARRIERS

• Main Author: Schneider, Sue-Rica
• Other Authors: Dr B Visser
• Format: Others
• Language: en-uk
• Published: University of the Free State 2012
• Subjects: Human Genetics
• Online Access: http://etd.uovs.ac.za//theses/available/etd-08232012-144859/restricted/

The aim of the study was to elucidate the variation in phenotypic expression observed within BRCA2 c.8162delG mutation positive families. The study attempted to identify possible genetic factors that contribute to the residual risk conferred by the BRCA2 founder mutation. As BC is a polygenetic disorder, polymorphisms within various low penetrance genes may contribute to the expression of the disease. The selection of the SNPs were based on the results of the CIMBA consortium and have been proven to be associated with an increased BC risk in the general population (Easton et al., 2007) and in BRCA2 mutation carriers specifically (Antoniou et al., 2008). Two SNPs (rs2234693 [PvuII] and rs9340799 [XbaI]) present within ESR1 as well as SNPs present in TNRC9 (rs3803662), LSP1 (rs3817198), MAP3K1 (rs889312) and FGFR2 (rs2981582) identified by GWAS have been implicated in BC risk. These six polymorphisms have been selected to evaluate the risk within the Afrikaner BRCA2 8162delG (c.7934del, p.Arg2645AsnfsX3) mutation carriers specifically. Genotyping of rs2234693 (PvuII) and rs9340799 (XbaI) was done by PCR-RFLP analysis whereas Taqman® assays were used for genotyping rs3803662 (TNRC9), rs3817198 (LSP1), rs889312 (MAP3K1) and rs2981582 (FGFR2). Automated allelic discrimination using the BioRad CFX Manager v1.1.308.1111 software were compared to manual discrimination methods to ensure robust genotyping. Cohenâs kappa analysis suggested a combination of automated (Method 1) and manual (Method 3) genotyping was best suited for accurate allelic discrimination except for LSP1. Due to an putative SNP detected within LSP1, the validity of the LSP1 results should be treated cautiously as no information on the frequency of the second putative SNP in white European individuals is available. Of the six polymorphisms analyzed, only rs2234693 (PvuII), indicated a possible association with BC (P-value = 0.0896), which should be explored within a larger study group. For FGFR2, the HWE results indicated that the deviation observed in the BRCA2 mutation carrier group could possibly be associated with BC. Haplotypes compiled for rs2234693 (PvuII) and rs9340799 (XbaI) as well as the remaining four SNPs were uninformative as it revealed no differences between the BC patients and the Cases. These results may have been due to the high allelic heterogeneity observed within the Afrikaner population, as well as the small test group used.. Although the results of this study did not deliver significant results, it did provide insight into allelic distributions of the SNPs in the Afrikaner BRCA2 8162delG (c.7934del, p.Arg2645AsnfsX3) mutation carriers specifically. Larger scale genotyping could lead to more significant findings to help elucidate the polygenetic nature of BC with the Afrikaner.