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Linkage analysis and allelic imbalance in human breast cancer kindreds using microsatellite markers from the short arm of chromosome 3

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Abstract

Eight Icelandic breast cancer kindreds were subjected to linkage analyses with respect to 28 microsatellite loci dispersed along the short arm of chromosome 3. Breast tumors derived from these kindreds were concurrently scored for allelic imbalance with ten of the markers. Linkage to most markers could be excluded on the basis of negative LOD scores and haplotype analyses, although some moderately positive LOD scores resulted. A high frequency of imbalance in the familial tumors was seen with two of the markers in comparison with results obtained from sporadic material. The highest frequency (68%) of imbalance was detected with the marker D3S1217, which is located on 3p14.2-p14.1. Imbalance at the D3S1211 locus, which is more telomeric (3p24.2-p22), was not significantly elevated in the familial tumors. We suggest that the genetic defect responsible for breast cancer susceptibility in these families either promotes instability in the 3p14.2-p14.1 region or enhances the selective advantage of such changes.
... This could be part of the story, but not the only explanation. When comparing our LOH data from chromosomes that carry the most common fragile sites in the genome, FRA3B, FRA16D and FRA6E, only chromosomes 3p and 6q show elevated LOH in BRCA2 associated tumours compared to sporadic breast tumours, but not chromosome 16q (Bergthorsson 1995Bergthorsson , 1998 Ingvarsson 1998 Ingvarsson , 1999). Similarly, there is higher LOH at chromosome 8p in BRCA2 associated tumours compared to sporadic tumours, but this chromosome region is considered to be stable (Sigbjornsdottir 2000). ...
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Gene and chromosome changes in breast cancer have been analysed using molecular and cytological methods. No single gene alterations are frequent in breast cancer, but several alterations have been detected, in line with multigenetic disease, although malignant progression in relation to gene changes is poorly documented. The most common tumour suppressor gene mutations, detected in about ¼ of breast tumours are in the TP53 gene, that encodes a transcription factor. Mutations and other alterations in the CDH1 gene, encoding the E-cadherin adhesion protein, in the CHK2 gene, encoding a cell cycle checkpoint kinase, in the BRCA1 and BRCA2 genes, encoding DNA repair proteins and FHIT, encoding a diadenosine hydrolase, will be reviewed. The molecular mechanism behind the frequently detected instability of the genome of breast cancer cells is poorly understood, but some studies have associated it with mutations in the TP53, BRCA1 or BRCA2 genes.
Thesis
Human cancers are caused by mutations affecting the products of oncogenes, tumour suppressor genes and DNA repair genes. Identification of tumour suppressor genes that give rise to sporadic cancers has often been achieved by isolating rare familial cancer genes via a reverse genetic approach. Loss of heterozygosity (LOH) studies have suggested that somatic mutations of a tumour suppressor gene or genes on 3p are critical in the pathogenesis of non familial renal cell carcinoma (RCC). Different studies have implicated differing critical loci. To further investigate the role that 3p genes may have in the tumourigenesis of sporadic RCC, 55 paired normal-tumour DNA's were analysed for allele loss, and at regions of known or putative tumour suppressor genes on chromosomes 5, 11, 17 and 22. 64% (35/55) of informative tumours displayed LOH of at least one or more loci on 3p, compared with 13% at the p53 locus and 6% at 17q21. LOH at 5q21 and 22q was uncommon. The LOH study identified three critical regions of loss on chromosome 3, at 3p25-26, 3p21 and at 3p12-14. The von Hippel Lindau (VHL) tumour suppressor gene was isolated in 1993. It maps to chromosome 3p25-26, coincident with a region of LOH. VHL disease manifests as a variety of benign and malignant neoplasms, and is the most common cause of familial RCC. The role that mutations of the VHL gene may have in the pathogenesis of sporadic RCC was investigated. 99 primary RCC were analysed for SSCP and heteroduplex formations. Somatic mutations were identified in 46% (30/65) sporadic RCC's with 3p LOH and in 3% (1/34) with no 3p LOH. Histology was available for 59 tumours: 42% (18/43) of RCC with a clear cell phenotype had VHL mutations, whereas none of 16 with a non clear cell phenotype (8 chromophilic, 3 chromophobic, and 5 oncocytomas) had VHL mutations (χ2=7.77, p<0.025). These results confirm that mutations in the VHL gene are events that initiate the development of RCC. 3p allele loss is a frequent event in gonadal tumours. 60 gonadal (36 ovarian and 24 testicular) tumours were analysed for VHL gene mutations and 3p allele loss. 3p LOH was detected in 38% (10/26) of informative ovarian and 56% (7/13) testicular tumours, but no VHL mutations were found. This suggests that chromosome 3p tumour suppressor gene(s) other than VHL are involved in gonadal tumourigenesis.
Chapter
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