Frequency of LOH and MSI in the Breast Cancer Susceptibility Genes BRCA1 (Chromosome 17q) and the Ataxia Telangiectasia Gene ATM (Chromosome llq) in African American Women
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The role of the ATM gene ( Ataxia Telangiectasia, mutated) is currently under investigation. So far, it has been discovered that the A TM gene is located at the 11 q23 loci on chromosome 11. It is suspected that this gene accounts for up to 8% of all breast cancers. Additionally, ATM heterozygotes have a predisposition to breast cancer that is estimated to be three to fourfold the predisposition of the general population. The BRCA1 is a gene that is located at the 17q21 loci on chromosome 17. Mutations in the BRCA1 gene are genetically linked to inherited breast cancer. Loss of heterozygosity (LOH) in the BRCA1 loci in both familial and sporadic tumors has led to the hypothesis that BRCA1 is a tumor suppressor gene. L0H in this region is observed in 31-70% of sporadic breast and ovarian cancers. Using archival specimens of 15 African American women with stage Ill and IV sporadic breast cancer, we obtained DNA from normal and tumor tissues. The mean age of the women at diagnosis was 57. The tumor stage, type and grade of the cohort was distributed in this manner: eleven were at stage 3, three were at stage 4, and one was unidentified; fourteen were classified as invasive ductal carcinomas and only one was invasive lobular; and ten had a tumor grade of three, three had grade two, one had grade one, and one was undefined. These samples were used to investigate the frequency of loss of heterozygosity and/or microsatellite instability in the A TM and BRCA1 genes. The markers used to investigate the A TM gene were: the intragenic marker D11S2179 and the flanking markers D11S1818 and D11S1819. The markers used for the BRCA1 investigation were the intragenic markers D17S1323 and D17S855. The frequency of patients with LOH and/or MSI (microsatellite instability) was found to be 64 % (7/11) in BRCA1 markers D17S855 and D17S1323. Similarly, the total frequency of LOH and/or MSI for the ATM markers D11S2179, D11S1819, and DllS1818 was discovered to be 61 % (8/13). One of the ATM markers exhibited a frequency of 23 % (3/13) for samples that only had LOH or MSI. Meanwhile, the other markers which exhibited either MSI or LOH had a frequency of 15% (2/13). These preliminary results support the role of BRCA1 as a tumor suppressor gene in sporadic breast cancer and suggests a putative tumor suppressor role for the ATM gene.
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