| Description |
Approximately 10% of American women develop breast cancer during their lifetimes. Of the cases of breast cancer, about 10% are attributed to a genetic trait; the remaining appear to be sporadic. Two genes involved in the genetic cases of breast cancer have been discovered in the last decade, BRCAl and BRCA2. Patients who carry a mutation in BRCAl or BRCA2 have an 85% risk during their lifetime of developing breast cancer. Patients with a mutation in BRCAl have a 44% chance of developing ovarian cancer and mutations in BRCA2 are associated with an increased risk of male breast cancer. Since the discovery of the two breast/ovarian cancer predisposition genes, several thousand patients have been screened for variants in these genes by several methods. Over 700 genetic variants have been reported in BRCAl and over 600 in BRCAl. These variants are categorized as mutations, polymorphisms, or uncertain variants. Mutations have been characterized by their obvious deleterious effects on the protein or by linkage with disease. Polymorphisms have been characterized by their high frequency in the control population and lack of effect on the protein. Uncertain variants can not be placed in either of these two categories. The research described here details work that attempts to characterize those uncertain variants that occur in or near the splice consensus or branch sites and may affect mRNA splicing. The assay described was developed to provide useful clinical information for patients who had received a test result indicating they carried an uncertain variant. These patients make important decisions regarding their healthcare, surgery, or families, and this extra information would potentially benefit several thousand patients. The assay involves examining mRNA transcripts of patients who carry uncertain variants and determining if these transcripts are correctly spliced. Also, associations are made that connect the aberrant RNA transcripts to the chromosome carrying the variant. This association is made by tracking the chromosomal contribution to all RNA species through the use of a coding region polymorphism. Wherever possible, genetic haplotype analysis is performed to associate the variant to the defective transcript. If this analysis is not possible, this association is established biochemically using allele-specific amplification and sequencing. Twenty variants to date have been characterized using this technique. The variants analyzed so far have provided a definitive clinical testing result for over 4000 patients. Although the vast majority of these were attributed to one variant that was determined to be a polymorphism, these patients would have been given an uncertain test result without the results of this new assay and would not know if they were predisposed to breast/ovarian cancer. This assay is a critical part of a comprehensive clinical testing program. |
