MAPPING AND CLONING THE 17Q-LINKED BREAST CANCER LOCUS

乳腺癌易感等位基因的定位

The localization of a susceptibility allele for breast cancer to chromosome 17q is the first successful mapping of a common cancer. The goal of this proposal is to clone and genetically characterize this 17q breast cancer susceptibility locus. Just as localizing common diseases to a specific chromosome has proven to be difficult and error-prone, the subsequent fine structure mapping and gene isolation will be more difficult than for rare mendelian traits. The unique characteristics of the Utah population for genetic analysis will be an essential asset for this project. Our project will be one of many tied together in a scientific consortium jointly providing the resources necessary for the analysis of the 17q susceptibility locus. A key to the success of this project is the ability to identify large informative kindreds for mapping studies. Highly informative kindreds with a high likelihood of segregating a breast cancer susceptibility will be studied. Linkage analysis will determine whether a kindred's susceptibility is linked to 17q. A map of highly informative markers will be developed around the susceptibility locus. We have identified recombinants which flank the breast cancer susceptibility locus and characterized a hybrid panel created by K. Fournier with breakpoints surrounding the gene. A cosmid library will be constructed from a Fournier hybrid which contains 10 to 15 megabases of human DNA including the region containing the gene. Clones which map genetically and physically within the candidate gene region are used as nucleation points to develop a contig of the region. The final product will be a YAC contig, a pulsed field map of rare cutters, and a cosmid contig of the region with genetic boundaries defining the candidate region where the susceptibility locus must lie. We have eliminated seven potential candidate genes (EDBH17, ERB B2, HOX2, NM23, WNT3, RARA, and Prohibitin) from the region; therefore, it is virtually certain that the susceptibility locus is a novel gene. Clones derived from cDNA libraries will be selected by subtractive hybridization, hybridization of cDNAs to an affinity column, and direct hybridization of cosmid clones to cDNA clones. All cDNAs will be screened for DNA sequence differences between cases and controls once intron-exon boundaries are defined. We will characterize the phenotypic effect of the 17q-linked susceptibility locus in terms of its site and age-specific penetrance. We will examine questions of laterality of disease and try to identify any histopathologic features characteristic of 17q-linked breast cancer. Data on reproductive history will be gathered and interaction with the susceptibility locus will be assessed. If, during the course of this study the 17q gene is identified, we will screen for mutations in each family and stratify the analyses described on a mutation-specific basis.