Amelia A. Langston

BRCA1 Mutations in a Population-Based Sample of Young Women with Breast Cancer

BACKGROUND Inherited mutations in the BRCA1 gene are associated with a high risk of breast and ovarian cancer in some families. However, little is known about the contribution of BRCA1 mutations to breast cancer in the general population. We analyzed DNA samples from women enrolled in a population-based study of early-onset breast cancer to assess the spectrum and frequency of germ-line BRCA1 mutations in young women with breast cancer. METHODS We studied 80 women in whom breast cancer was diagnosed before the age of 35, and who were not selected on the basis of family history. Genomic DNA was studied for BRCA1 mutations by analysis involving single-strand conformation polymorphisms and with allele-specific assays. Alterations were defined by DNA sequencing. RESULTS Germ-line BRCA1 mutations were identified in 6 of the 80 women. Four additional rare sequence variants of unknown functional importance were also identified. Two of the mutations and three of the rare sequence variants were found among the 39 women who reported no family history of breast or ovarian cancer. None of the mutations and only one of the rare variants was identified in a reference population of 73 unrelated subjects. CONCLUSIONS Alterations in BRCA1 were identified in approximately 10 percent of this cohort of young women with breast cancer. The risk of harboring a mutation was not limited to women with family histories of breast or ovarian cancer. These results represent a minimal estimate of the frequency of BRCA1 mutations in this population. Comprehensive methods of identifying BRCA1 mutations and understanding their importance will be needed before testing of women in the general population can be undertaken.

Tissue-specific extinguisher loci in the human genome: A screening study based on random marking and transfer of human chromosomes

Expression of many liver-specific genes is extinguished when cultured hepatoma cells are fused with fibroblasts, but liver genes can be reexpressed in hybrid segregants that have lost fibroblast chromosomes. To map extinguisher loci involved in this process, hepatoma microcell hybrids retaining single fibroblast chromosomes have been employed. Two different,trans-dominant loci that affect liver gene expression have been defined in this way. To determine whether other monochromosomal extinction phenotypes could be observed, we inserted a selectable marker into many human chromosomal sites and transferred the marked human chromosomes into rat hepatoma recipient cells by microcell fusion. Nearly 200 microcell hybrid clones were isolated and screened for expression of liver-specific mRNAs. Most liver transcripts continued to be expressed. However, PEPCK mRNA was extinguished in 12 hybrid clones. Some of these hybrids contained humanTSE1, the previously characterized extinguisher locus on chromosome 17, but others contained a novel extinguishing function that mapped to human chromosome 14. The implications of these findings are discussed.

Identification of a RAPD marker linked to progressive rod-cone degeneration in dogs

Abstract. Random amplified polymorphic DNA (RAPD) analysis has been used widely in plant and fungi for identification of markers linked to genetic traits and mapping, but its use is limited to identification of intra- and inter-species difference in domestic mammals. We report here identification of a RAPD-derived marker linked to progressive rod-cone degeneration (prcd), an inherited autosomal recessive retinal disease of dogs. A total of 400 standard 10-mer primers were used for amplification by use of DNA samples from normal (+/+) and affected (prcd/prcd) dogs. A single primer was identified which amplified a 1.5-kb DNA fragment only from normal dogs. PCR with longer primers designed from the sequence-characterized amplified region of the 1.5-kb DNA fragment identified a co-dominant multi-allelic polymorphism in the prcd-informative pedigree. Three recombinants were identified among 34 informative offsprings, yielding a LOD score of 5.568 at θ= 0.091. This marker was mapped to two canine–rodent hybrid cell lines in which two genes (canine homologues of human breast cancer 1 susceptibility gene, and cGMP phosphodiesterase γ-subunit gene), and three anonymous microsatellites have been identified. This is the first reported identification of a RAPD-derived marker with multiple alleles linked to a mammalian disease locus.