PHIP - a novel candidate breast cancer susceptibility locus on 6q14.1.

Most non-BRCA1/2 breast cancer families have no identified genetic cause. We used linkage and haplotype analyses in familial and sporadic breast cancer cases to identify a susceptibility locus on chromosome 6q. Two independent genome-wide linkage analysis studies suggested a 3 Mb locus on chromosome 6q and two unrelated Swedish families with a LOD >2 together seemed to share a haplotype in 6q14.1. We hypothesized that this region harbored a rare high-risk founder allele contributing to breast cancer in these two families. Sequencing of DNA and RNA from the two families did not detect any pathogenic mutations. Finally, 29 SNPs in the region were analyzed in 44,214 cases and 43,532 controls from BCAC, and the original haplotypes in the two families were suggested as low-risk alleles for European and Swedish women specifically. There was also some support for one additional independent moderate-risk allele in Swedish familial samples. The results were consistent with our previous findings in familial breast cancer and supported a breast cancer susceptibility locus at 6q14.1 around the PHIP gene.

Whole-genome Linkage Analysis and Sequence Analysis of Candidate Loci in Familial Breast Cancer.

BACKGROUND: Known breast cancer-predisposing genes account for fewer than 25% of all familial breast cancer cases and further studies are required to find the remaining high- and moderate-risk genes. We set-out to couple linkage analysis using microsatellite marker data and sequence analysis of linked regions in 13 non-BRCA1/2 families in order to find novel susceptibility loci and high-penetrant genes. MATERIALS AND METHODS: Genotyping with 540 fluorescently-labeled microsatellite markers located on the 23 chromosomes at 7.25 cM resolution was used for primary linkage analysis and an additional 40 markers were used for fine-mapping of loci with a logarithm of odds (LOD) or heterogeneity LOD (HLOD) score greater than one. Whole-exome sequencing data of 28 members from all 13 families were used for the bioinformatics sequence analysis on the linked regions of these families. RESULTS: Linkage analysis identified three loci on chromosome 18q as a putative region of interest (overall LOD=1, HLOD=1.2). Sequencing analysis of the three linked regions on 18q and mutation prediction algorithms did reveal three probable damaging variants. CONCLUSION: Overall, our study identified three weakly linked loci on 18q and three probable damaging variants of interest in the 13 families with breast cancer.

A rare microduplication in a familial case of annular pancreas and duodenal stenosis.

BACKGROUND/PURPOSE: We describe a 3-day-old male infant that was operated on for annular pancreas causing duodenal stenosis. The family history revealed that the mother also underwent surgery as a neonate owing to duodenal stenosis with an annular pancreas. The aim of our study was to perform molecular investigations in this rare and familial congenital malformation. METHODS: We performed high-resolution (180 K) array comparative genomic hybridization using the infant's DNA and multiplex ligation-dependent probe amplification (MLPA) using the parents' and the affected mother's siblings' and parents' DNA. RESULTS: Array comparative genomic hybridization revealed previously unreported duplications on chromosome 6q24.2 and 17q22-q23.1, respectively, in the infant's DNA, and the latter duplication was also found in the healthy father using MLPA, whereas the affected mother carried the 6q24 duplication (0.7 Mb) containing parts of the utrophin gene. We further performed MLPA analysis of the 6q24 region and found that the clinically unaffected grandfather was a carrier of the microduplication, and so were 2 asymptomatic siblings of the affected mother. CONCLUSIONS: The 6q24.2 mircoduplication of the utrophin gene is a potential risk factor for the development of annular pancreas, but further studies will clarify the exact role and if this is a true risk factor or a rare normal variant.

Identification of novel carcinogen-mediated mammary tumor susceptibility loci in the rat using the chromosome substitution technique.

We here report the genetic basis for susceptibility and resistance to carcinogen-mediated [7,12-dimethylbenz[a]anthracene (DMBA)] mammary tumorigenesis using the full panel of SS/BN consomic rat strains, in which substitutions of individual chromosomes from the resistant BN strain onto the genomic background of the susceptible SS strain were made. Analysis of 252 consomic females identified rat mammary Quantitative Trait Loci (QTLs) affecting tumor incidence on chromosomes 3 and 5, latency on chromosomes 3, 9, 14, and 19, and multiplicity on chromosomes 13, 16, and 19. In addition, we unexpectedly identified a novel QTL on chromosome 6 controlling a lethal toxic phenotype in response to DMBA. Upon further investigation with chromosomes 6 and 13 congenic lines, in which an additional 114 rats were investigated, we mapped (1) a novel mammary tumor QTL to a region of 27.1 Mbp in the distal part of RNO6, a region that is entirely separated from the toxicity phenotype, and (2) a novel and powerful mammary tumor susceptibility locus of 4.5 Mbp that mapped to the proximal q-arm of RNO13. Comparison of genetic strain differences using existing rat genome databases enabled us to further construct priority lists containing single breast cancer candidate genes within the defined QTLs, serving as potential functional variants for future testing.

Microalterations of inherently unstable genomic regions in rat mammary carcinomas as revealed by long oligonucleotide array-based comparative genomic hybridization.

The presence of copy number variants in normal genomes poses a challenge to identify small genuine somatic copy number changes in high-resolution cancer genome profiling studies due to the use of unpaired reference DNA. Another problem is the well-known rearrangements of immunoglobulin and T-cell receptor genes in lymphocytes (a commonly used reference), which may misdirect the researcher to a locus with no relevance in tumorigenesis. We here show real gains of the IgG heavy chain V gene region in carcinogen-induced rat mammary tumor samples after normalization to paired mammary gland, a tissue without lymphocyte infiltration. We further show that the segmental duplication region encompassing the IgG heavy chain V genes is a copy number variant between the susceptible (SS) and the resistant (BN) to mammary tumor development inbred rat strains. Our data suggest that the already inherently unstable genomic region is a convenient target for additional structural rearrangements (gains) at the somatic level when exposed to a carcinogen (7,12-dimethylbenz[a]anthracene), which subsequently seem to benefit tumor development in the mammary gland of the susceptible strain. Thus, the selection of an appropriate reference DNA enabled us to identify immunoglobulin genes as novel cancer targets playing a role in mammary tumor development. We conclude that control DNA in array-based comparative genomic hybridization experiments should be selected with care, and DNA from pooled spleen (contains immature lymphocytes and is used as reference in animal studies) or blood may not be the ideal control in the study of primary tumors.

Genetic mapping of mammary tumor traits to rat chromosome 10 using a novel panel of consomic rats.

Identification of novel breast cancer susceptibility and resistance genes in genetically diverse human populations is challenging, and so inbred rats have been used to identify novel mammary cancer susceptibility quantitative trait loci (QTLs) with conventional mapping approaches. An alternative approach for QTL mapping is to use chromosome substitution (consomic) rat strains, which has the advantage of rapid generation of congenic from consomic animals. Using a novel rat strain pair, SS and BN, we identified rat mammary cancer QTLs in one of two consomic rat strains tested. Female rats of inbred parental (SS and BN) and two consomic (SS-10 BN and SS-12 BN) strains were treated with 7,12-dimethylbenz[a]anthracene orally. The phenotypes of tumor incidence, latency, and multiplicity were evaluated. SS rats were highly susceptible to mammary adenocarcinoma development, whereas BN rats were completely resistant. Statistical comparison of the phenotypes between the susceptible parental and the two consomic strains identified QTLs residing within chromosome 10 controlling mammary tumor latency and multiplicity. The study shows that SS-BN consomic rat strains can be used to map mammary tumor QTLs. This novel approach should accelerate positional cloning of mammary cancer susceptibility and resistant genes in the rat and the identification of homologous genes in humans.

Rearrangement and allelic imbalance on chromosome 5 leads to homozygous deletions in the CDKN2A/2B tumor suppressor gene region in rat endometrial cancer.

The inbred BDII rat is a valuable experimental model for the genetic analysis of hormone-dependent endometrial adenocarcinoma (EAC). One common aberration detected previously by comparative genomic hybridization in rat EAC is loss affecting mostly the middle part of rat chromosome 5 (RNO5). First, we applied an RNO5-specific painting probe and four region-specific gene probes onto tumor cell metaphases from 21 EACs, and found that rearrangements involving RNO5 were common. The copy numbers of loci situated on RNO5 were found to be reduced, particularly for the CDKN2A/2B locus. Second, polymerase chain reaction analysis was performed with 22 genes and markers and homozygous deletions of the CDKN2A exon 1beta and CDKN2B genes were detected in 13 EACs (62%) and of CDKN2A exon 1alpha in 12 EACs (57%) Third, the occurrence of allelic imbalance in RNO5 was analyzed using 39 microsatellite markers covering the entire chromosome and frequent loss of heterozygosity was detected. Even more intriguing was the repeated finding of allele switching in a narrow region of 7 Mb across the CDKN2A/2B locus. We conclude that genetic events affecting the middle part of RNO5 (including bands 5q31 approximately q33 and the CDKN2A locus) contribute to the development of EAC in rat, with the CDKN2A locus having a primary role.

Recurrent gene amplifications in human type I endometrial adenocarcinoma detected by fluorescence in situ hybridization.

Determining what genes are actively involved in tumor development is important, because they may provide targets for directed therapy. Human tumors are greatly heterogeneous with respect to etiology and genetic background, which complicates the identification of common genetic aberrations. In contrast, genetic and environmental variation can be in part controlled in experimental animals, which facilitates identification of the important changes. In inbred BDII rats, which are genetically predisposed to endometrial adenocarcinomas (EAC), certain chromosome regions exhibit recurrent amplification in the tumors. Previous CGH analysis had shown that a subset of human EAC tumors exhibited increased copy numbers in the homologous chromosomal regions, located in human 2p21 approximately p25 and 7q21 approximately q31. Using fluorescence in situ hybridization analysis on imprints from 13 human EAC tumors, we determined the average copy numbers of each of 15 probes derived from cancer-related genes situated in these chromosome regions. Among the genes analyzed, those most often targeted by amplification were SDC1 and CYP1B1 in 2p21 approximately p25 and CDK6 and MET in 7q21 approximately q31, but all of the 15 genes tested were found to be amplified in at least two tumors.

Nonrandom pattern of chromosome aberrations in 17beta-estradiol-induced rat mammary tumors: indications of distinct pathways for tumor development.

Estrogens play an important role in breast cancer etiology and the ACI rat provides a novel animal model for defining the mechanisms through which estrogens contribute to mammary cancer development. In crossing experiments between the susceptible ACI strain and two resistant strains, COP (Copenhagen) and BN (Brown Norway), several quantitative trait loci (QTL) that affect development of 17beta-estradiol (E2)-induced mammary tumors have been defined. Using comparative genomic hybridization (CGH), we have analyzed cytogenetic aberrations in E2-induced mammary cancers and have found clear patterns of nonrandom chromosomal involvement. Approximately two thirds of the tumors exhibited copy number changes. Losses of rat chromosome 5 (RNO5) and RNO20 were particularly common, and it was found that these two aberrations often occurred together. A third recurrent aberration involving proximal gain and distal loss in RNO6 probably defined a distinct subgroup of tumors, since it never occurred in combination with RNO5 loss. Interestingly, QTL with powerful effects on mammary cancer development have been mapped to RNO5 and RNO6. These findings suggest that there were at least two genetic pathways to tumor formation in this rat model of E2-induced mammary cancer. By performing CGH on mammary tumors from ACI rats, F1 rats from crosses between the ACI and COP or BN strains and ACI.BN-Emca8 congenic rats, which carry the BN allele of the Emca8 QTL on RNO5 on the ACI genetic background, we were able to determine that the constitution of the germ line influences the pattern of chromosomal aberrations.

Oncogene amplification in the proximal part of chromosome 6 in rat endometrial adenocarcinoma as revealed by combined BAC/PAC FISH, chromosome painting, zoo-FISH, and allelotyping.

The inbred BDII rat is a valuable experimental model for the genetic analysis of endometrial adenocarcinoma (EAC). One common aberration detected by comparative genomic hybridization in rat EAC was gain/amplification affecting the proximal part of rat chromosome 6 (RNO6). We applied rat and mouse chromosome painting probes onto tumor cell metaphase preparations in order to detect and characterize gross RNO6 aberrations. In addition, the RNO6q11-q16 segment was analyzed by fluorescence in situ hybridization with probes representing 12 cancer-related genes in the region. The analysis revealed that seven tumors contained large RNO6-derived homogeneously staining regions (HSRs) in addition to several normal or near-normal RNO6 chromosomes. Five tumors (two of which also had HSRs) exhibited a selective increase of the RNO6q11-q16 segment, sometimes in conjunction with moderate amplification of one or a few genes. Most commonly, the amplification affected the region centered around band 6q16 and included the Mycn, Ddx1, and Rrm2 genes. A second region, centering around Slc8a1 and Xdh, also was affected by gene amplification but to a lesser extent. The aberrations in the proximal part of RNO6 were further analyzed using allelotyping of microsatellite markers in all tumors from animals that were heterozygous in the proximal RNO6 region. We could detect allelic imbalance (AI) in 12 of 20 informative tumors, 6 of which were in addition to those already analyzed by molecular cytogenetic methods as described. Our findings suggest that increase/amplification of genes in this chromosome region contribute to the development of this hormone-dependent tumor.

Cytogenetic aberrations in spontaneous endometrial adenocarcinomas in the BDII rat model as revealed by chromosome banding and comparative genome hybridization.

Female rats of the inbred strain BDII are genetically predisposed to endometrial estrogen-dependent adenocarcinomas (EAC). More than 90% of them spontaneously develop this tumor type before the age of 24 months. In order to dissect out the genetic components behind these tumors we have made crosses between BDII females and rats from 2 other strains that are nonsusceptible to EAC. It was found that EAC tumors developed in a subset of intercross and backcross animals from both interstrain crosses. The chromosomal changes in the developing tumors were studied using cytogenetic and molecular cytogenetic methods. From these studies, we conclude that certain chromosome regions were recurrently engaged in chromosomal changes such as increases in copy number (e.g., trisomy, amplification) or decreases (e.g., deletion). Based on the analysis of 56 tumors, 8 regions were found to be particularly often involved: RNO4prx, gain=34 (61%) (amplification 12 cases); RNO5mid, loss=15 (27%); RNO6prx, gain=25 (45%) (amplification 8 cases); RNO10 loss, prx-mid/gain dst=25 (45%) (amplification 1 case); RNO12q, gain=23 (41%); RNO15p loss/RNO15q gain=29 (52%) (amplification 1 case) [RNO, rat chromosome; prx, proximal; mid, middle; dst, distal; p, short arm; q, long arm]. We begun to analyze these regions in detail using various molecular methods and within them there are certain possible target genes, such as MET (RNO4q21), CDKN2A/2B (RNO5q32), MYCN (RNO6q15 approximately q16), and TP53 (RNO10q24 approximately q25), but it is clear that several other genes, still unidentified, must also be involved.

Recurrent allelic imbalance at the rat Pten locus in DMBA-induced fibrosarcomas.

The tumor-suppressor gene PTEN (phosphatase and tensin homolog) is frequently inactivated in different types of human tumors. Less is known about the involvement of the homologous gene Pten in animal model systems of cancer. By sequencing one of the introns of rat Pten, we found an informative intragenic PCR marker suitable for genetic studies. Through use of this marker, the position of Pten in the genetic linkage map was localized to the distal part of rat chromosome 1 (RNO1) by analysis of F2 progeny from an intercross between inbred strains BN and LE. Subsequently, 22 markers from this region (including the intragenic Pten marker) were used to study the occurrence of allelic imbalance in distal RNO1 in fibrosarcomas that had been induced by DMBA in F1(BNxLE) rats. The analysis revealed that allelic imbalance was common in the vicinity of Pten, and there was loss or reduction of one of the Pten alleles in more than 60% of the fibrosarcomas. DNA sequencing was preformed to investigate whether the Pten allele remaining in the tumors was inactivated by mutation. However, no mutations were detected in the genomic sequence of Pten exons 5 to 9 in any of the fibrosarcomas, and normal mRNA transcripts were expressed in all tumors. Thus, based on the targeted selection for loss of Pten observed in some of these tumors and the absence of inactivation of the remaining allele, we suggest that haploinsufficiency of Pten may be an important factor in rat DMBA-induced fibrosarcomas.