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ABSTRACT: BACKGROUND: Ovarian carcinoma is a common, and often deadly, gynecological cancer. Mutations in BRCA1 and BRCA2 genes are present in at least a fifth of patients. Uncovering other genes that become mutated subsequent to BRCA1/BRCA2 inactivation during cancer development will be helpful for more effective treatments. METHODS: We performed exome sequencing on the blood, primary tumor, omental metastasis and recurrence following therapy with carboplatinum and paclitaxel, from a patient carrying a BRCA1 S1841R mutation. RESULTS: We observed loss of heterozygosity in the BRCA1 mutation in the primary and subsequent tumors, and somatic mutations in the TP53 and NF1 genes were identified, suggesting their role along with BRCA1 driving the tumor development. Notably, we show that exome sequencing is effective in detecting large chromosomal rearrangements such as deletions and amplifications in cancer. We found that a large deletion was present in the three tumors in the regions containing BRCA1, TP53, and NF1 mutations, and an amplification in the regions containing MYC. We did not observe the emergence of any new mutations among tumors from diagnosis to relapse after chemotherapy, suggesting that mutations already present in the primary tumor contributed to metastases and chemotherapy resistance. CONCLUSIONS: Our findings suggest that exome sequencing of matched samples from one patient is a powerful method of detecting somatic mutations and prioritizing their potential role in the development of the disease.
BMC Cancer 03/2013; 13(1):146. · 3.01 Impact Factor
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Robert K Koenekoop,
Hui Wang, Jacek Majewski,
Xia Wang,
Irma Lopez,
Huanan Ren,
Yiyun Chen,
Yumei Li,
Gerald A Fishman,
Mohammed Genead, [......],
Hussain Jafri,
Yasmin Rashid,
Graham R Taylor,
Vafa Keser,
Graeme Mardon,
Huidan Xu,
Chris F Inglehearn,
Qing Fu,
Carmel Toomes,
Rui Chen
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ABSTRACT: Leber congenital amaurosis (LCA) is a blinding retinal disease that presents within the first year after birth. Using exome sequencing, we identified mutations in the nicotinamide adenine dinucleotide (NAD) synthase gene NMNAT1 encoding nicotinamide mononucleotide adenylyltransferase 1 in eight families with LCA, including the family in which LCA was originally linked to the LCA9 locus. Notably, all individuals with NMNAT1 mutations also have macular colobomas, which are severe degenerative entities of the central retina (fovea) devoid of tissue and photoreceptors. Functional assays of the proteins encoded by the mutant alleles identified in our study showed that the mutations reduce the enzymatic activity of NMNAT1 in NAD biosynthesis and affect protein folding. Of note, recent characterization of the slow Wallerian degeneration (Wld(s)) mouse model, in which prolonged axonal survival after injury is observed, identified NMNAT1 as a neuroprotective protein when ectopically expressed. Our findings identify a new disease mechanism underlying LCA and provide the first link between endogenous NMNAT1 dysfunction and a human nervous system disorder.
Nature Genetics 07/2012; 44(9):1035-9. · 35.53 Impact Factor
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Journal of Medical Genetics 09/2011; 48(9):593-6. · 6.36 Impact Factor
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ABSTRACT: Combined Malonic and Methylmalonic Aciduria (CMAMMA) is a rare recessive inborn error of metabolism characterised by elevations of urine malonic acid (MA) and methylmalonic acid (MMA). Nearly all reported cases are caused by malonyl-CoA decarboxylase (MCD) deficiency. Most patients have metabolic acidosis, developmental delay, seizures and cardiomyopathy. CMAMMA was also described in symptomatic patients with normal MCD activity, suggesting heterogeneity in this disorder.
We identified two probands with a non-classical CMAMMA variant through the Quebec newborn urine screening program. While they share the biochemical phenotype of elevated MA and MMA, the MMA excretion was higher than MA, the clinical courses were benign, MYLCD gene sequencing was normal and MCD activity, measured in one proband, was normal. Using exome sequencing in the single consanguineous proband, we identified a homozygous missense allele in the ACSF3 gene, encoding an Acyl-CoA Synthetase (ACS) with unknown substrate and function. The second proband was homozygous for a different ACSF3 missense allele. Both substitutions were in conserved residues and were identified in less than 0.5% of their respective ethnic control populations.
These results suggest that ACSF3 is a candidate gene for non-classical CMAMMA observed in our patients and document the value of exome sequencing of a limited number of patients for the identification of novel disease genes.
Journal of Medical Genetics 09/2011; 48(9):602-5. · 6.36 Impact Factor
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ABSTRACT: An infant was investigated because of megaloblastic anaemia, atypical hemolytic uraemic syndrome, severe combined immune deficiency, elevated blood levels of homocysteine and methylmalonic acid, and a selective decreased synthesis of methylcobalamin in cultured fibroblasts.
Exome sequencing was performed on patient genomic DNA.
Two mutations were identified in the MTHFD1 gene, which encodes a protein that catalyses three reactions involved in cellular folate metabolism. This protein is essential for the generation of formyltetrahydrofolate and methylenetetrahydrofolate and important for nucleotide and homocysteine metabolism. One mutation (c.727+1G>A) affects the splice acceptor site of intron 8. The second mutation, c.517C>T (p.R173C), changes a critical arginine residue in the NADP-binding site of the protein. Mutations affecting this arginine have previously been shown to affect enzyme activity. Both parents carry a single mutation and an unaffected sibling carries neither mutation. The combination of two mutations in the MTHFRD1 gene, predicted to have severe consequences, in the patient and their absence in the unaffected sibling, supports causality.
This patient represents the first case of an inborn error of folate metabolism affecting the trifunctional MTHFD1 protein. This report reinforces the power of exome capture and sequencing for the discovery of novel genes, even when only a single proband is available for study.
Journal of Medical Genetics 09/2011; 48(9):590-2. · 6.36 Impact Factor
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ABSTRACT: Recent advances in next-generation sequencing technologies have brought a paradigm shift in how medical researchers investigate both rare and common human disorders. The ability cost-effectively to generate genome-wide sequencing data with deep coverage in a short time frame is replacing approaches that focus on specific regions for gene discovery and clinical testing. While whole genome sequencing remains prohibitively expensive for most applications, exome sequencing--a technique which focuses on only the protein-coding portion of the genome--places many advantages of the emerging technologies into researchers' hands. Recent successes using this technology have uncovered genetic defects with a limited number of probands regardless of shared genetic heritage, and are changing our approach to Mendelian disorders where soon all causative variants, genes and their relation to phenotype will be uncovered. The expectation is that, in the very near future, this technology will enable us to identify all the variants in an individual's personal genome and, in particular, clinically relevant alleles. Beyond this, whole genome sequencing is also expected to bring a major shift in clinical practice in terms of diagnosis and understanding of diseases, ultimately enabling personalised medicine based on one's genome. This paper provides an overview of the current and future use of next generation sequencing as it relates to whole exome sequencing in human disease by focusing on the technical capabilities, limitations and ethical issues associated with this technology in the field of genetics and human disease.
Journal of Medical Genetics 07/2011; 48(9):580-9. · 6.36 Impact Factor
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Jacek Majewski,
Jeremy A Schwartzentruber,
Aurore Caqueret,
Lysanne Patry,
Janet Marcadier,
Jean-Pierre Fryns,
Kym M Boycott,
Louis-Georges Ste-Marie,
Fergus E McKiernan,
Ivo Marik,
Hilde Van Esch,
Jacques L Michaud,
Mark E Samuels
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ABSTRACT: Hajdu-Cheney syndrome (HCS) is a rare genetic disorder whose hallmark is acro-osteolysis, shortening of terminal phalanges, and generalized osteoporosis. We assembled a cohort of seven families with the condition and performed whole exome resequencing on a selected set of affected patients. One protein-coding gene, NOTCH2, carried heterozygous truncating variants in all patients and their affected family members. Our results replicate recently published studies of HCS and further support this as the causal gene for the disorder. In total, we identified five novel and one previously reported mutation, all clustered near the carboxyl terminus of the gene, suggesting an allele specific genotype-phenotype effect since other mutations in NOTCH2 have been reported to cause a form of Alagille syndrome. Notch-mediated signaling is known to play a role in bone metabolism. Our results support a potential therapeutic role for Notch pathways in treatment of osteoporosis.
Human Mutation 06/2011; 32(10):1114-7. · 5.69 Impact Factor
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ABSTRACT: Common DNA variants alter the expression levels and patterns of many human genes. Loci responsible for this genetic control are known as expression quantitative trait loci (eQTLs). The resulting variation of gene expression across individuals has been postulated to be a determinant of phenotypic variation and susceptibility to complex disease. In the past, the application of expression microarray and genetic variation data to study populations enabled the rapid identification of eQTLs in model organisms and humans. Now, a new technology promises to revolutionize the field. Massively parallel RNA sequencing (RNA-seq) provides unprecedented resolution, allowing us to accurately monitor not only the expression output of each genomic locus but also reconstruct and quantify alternatively spliced transcripts. RNA-seq also provides new insights into the regulatory mechanisms underlying eQTLs. Here, we discuss the major advances introduced by RNA-seq and summarize current progress towards understanding the role of eQTLs in determining human phenotypic diversity.
Trends in Genetics 02/2011; 27(2):72-9. · 10.06 Impact Factor
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ABSTRACT: Expression levels of many human genes are under the genetic control of expression quantitative trait loci (eQTLs). Despite technological advances, the precise molecular mechanisms underlying most eQTLs remain elusive. Here, we use deep mRNA sequencing of two CEU individuals to investigate those mechanisms, with particular focus on the role of splicing control loci (sQTLs). We identify a large number of genes that are differentially spliced between the two samples and associate many of those differences with nearby single nucleotide polymorphisms (SNPs). Subsequently, we investigate the potential effect of splicing SNPs on eQTL control in general. We find a significant enrichment of alternative splicing (AS) events within a set of highly confident eQTL targets discovered in previous studies, suggesting a role of AS in regulating overall gene expression levels. Next, we demonstrate high correlation between the levels of mature (exonic) and unprocessed (intronic) RNA, implying that ∼75% of eQTL target variance can be explained by control at the level of transcription, but that the remaining 25% may be regulated co- or post-transcriptionally. We focus on eQTL targets with discordant mRNA and pre-mRNA expression patterns and use four examples: USMG5, MMAB, MRPL43, and OAS1, to dissect the exact downstream effects of the associated genetic variants.
Genome Research 02/2011; 21(4):545-54. · 13.61 Impact Factor
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ABSTRACT: Background Combined Malonic and Methylmalonic Aciduria (CMAMMA) is a rare recessive inborn error of metabolism characterised by elevations of urine malonic acid (MA) and methylmalonic acid (MMA). Nearly all reported cases are caused by malonyl-CoA decarboxylase (MCD) deficiency. Most patients have metabolic acidosis, developmental delay, seizures and cardiomyopathy. CMAMMA was also described in symptomatic patients with normal MCD activity, suggesting heterogeneity in this disorder. Methods and results We identified two probands with a non-classical CMAMMA variant through the Quebec newborn urine screening program. While they share the biochemical phenotype of elevated MA and MMA, the MMA excretion was higher than MA, the clinical courses were benign, MYLCD gene sequencing was normal and MCD activity, measured in one proband, was normal. Using exome sequencing in the single consanguineous proband, we identified a homozygous missense allele in the ACSF3 gene, encoding an Acyl-CoA Synthetase (ACS) with unknown substrate and function. The second proband was homozygous for a different ACSF3 missense allele. Both substitutions were in conserved residues and were identified in less than 0.5% of their respective ethnic control populations. Conclusion These results suggest that ACSF3 is a candidate gene for non-classical CMAMMA observed in our patients and document the value of exome sequencing of a limited number of patients for the identification of novel disease genes. Several types of patients with elevated malonic acid (MA) have been described in the literature. The most well characterised is that related to malonyl-coenzyme A (CoA) decarboxylase (MCD) enzyme deficiency (OMIM #248360) in which the biochemical abnormalities include elevated MA alone, or combined elevations of MA and methyl-malonic acid (CMAMMA) with MA mainly being higher than methylmalonic acid (MMA). 1e11 It is speculated that MCD deficiency causes an excess of intramitochondrial malonyl-CoA, leading to the inhibition of methylmalonyl-CoA mutase and, subsequently, an increase in MMA. Two patients have been described with similar combined eleva-tions of MA greater than MMA, but with normal MCD enzyme activity in fibroblast cultures 12 13 suggesting that this disorder is heterogeneous. All of these patients have shown a variety of clinical
Journal of Medical Genetics 01/2011; · 6.36 Impact Factor
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Kevin C H Ha,
Emilie Lalonde,
Lili Li,
Luca Cavallone,
Rachael Natrajan,
Maryou B Lambros,
Costas Mitsopoulos,
Jarle Hakas,
Iwanka Kozarewa,
Kerry Fenwick,
Chris J Lord,
Alan Ashworth,
Anne Vincent-Salomon,
Mark Basik,
Jorge S Reis-Filho, Jacek Majewski,
William D Foulkes
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ABSTRACT: Gene fusions arising from chromosomal translocations have been implicated in cancer. However, the role of gene fusions in BRCA1-related breast cancers is not well understood. Mutations in BRCA1 are associated with an increased risk for breast cancer (up to 80% lifetime risk) and ovarian cancer (up to 50%). We sought to identify putative gene fusions in the transcriptomes of these cancers using high-throughput RNA sequencing (RNA-Seq).
We used Illumina sequencing technology to sequence the transcriptomes of five BRCA1-mutated breast cancer cell lines, three BRCA1-mutated primary tumors, two secretory breast cancer primary tumors and one non-tumorigenic breast epithelial cell line. Using a bioinformatics approach, our initial attempt at discovering putative gene fusions relied on analyzing single-end reads and identifying reads that aligned across exons of two different genes. Subsequently, latter samples were sequenced with paired-end reads and at longer cycles (producing longer reads). We then refined our approach by identifying misaligned paired reads, which may flank a putative gene fusion junction.
As a proof of concept, we were able to identify two previously characterized gene fusions in our samples using both single-end and paired-end approaches. In addition, we identified three novel in-frame fusions, but none were recurrent. Two of the candidates, WWC1-ADRBK2 in HCC3153 cell line and ADNP-C20orf132 in a primary tumor, were confirmed by Sanger sequencing and RT-PCR. RNA-Seq expression profiling of these two fusions showed a distinct overexpression of the 3' partner genes, suggesting that its expression may be under the control of the 5' partner gene's regulatory elements.
In this study, we used both single-end and paired-end sequencing strategies to discover gene fusions in breast cancer transcriptomes with BRCA1 mutations. We found that the use of paired-end reads is an effective tool for transcriptome profiling of gene fusions. Our findings suggest that while gene fusions are present in some BRCA1-mutated breast cancers, they are infrequent and not recurrent. However, private fusions may still be valuable as potential patient-specific biomarkers for diagnosis and treatment.
BMC Medical Genomics 01/2011; 4:75. · 3.69 Impact Factor
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Natascia Anastasio,
Tawfeg Ben-Omran,
Ahmad Teebi,
Kevin C H Ha,
Emilie Lalonde,
Rehab Ali,
Mariam Almureikhi,
Vazken M Der Kaloustian,
Junhui Liu,
David S Rosenblatt, Jacek Majewski,
Loydie A Jerome-Majewska
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ABSTRACT: Van Den Ende-Gupta syndrome (VDEGS) is an extremely rare autosomal-recessive disorder characterized by distinctive craniofacial features, which include blepharophimosis, malar and/or maxillary hypoplasia, a narrow and beaked nose, and an everted lower lip. Other features are arachnodactyly, camptodactyly, peculiar skeletal abnormalities, and normal development and intelligence. We present molecular data on four VDEGS patients from three consanguineous Qatari families belonging to the same highly inbred Bedouin tribe. The patients were genotyped with SNP microarrays, and a 2.4 Mb homozygous region was found on chromosome 22q11 in an area overlapping the DiGeorge critical region. This region contained 44 genes, including SCARF2, a gene that is expressed during development in a number of mouse tissues relevant to the symptoms described above. Sanger sequencing identified a missense change, c.773G>A (p.C258Y), in exon 4 in the two closely related patients and a 2 bp deletion in exon 8, c.1328_1329delTG (p.V443DfsX83), in two unrelated individuals. In parallel with the candidate gene approach, complete exome sequencing was used to confirm that SCARF2 was the gene responsible for VDEGS. SCARF2 contains putative epidermal growth factor-like domains in its extracellular domain, along with a number of positively charged residues in its intracellular domain, indicating that it may be involved in intracellular signaling. However, the function of SCARF2 has not been characterized, and this study reports that phenotypic effects can be associated with defects in the scavenger receptor F family of genes.
The American Journal of Human Genetics 09/2010; 87(4):553-9. · 10.60 Impact Factor
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ABSTRACT: Protein coding genes constitute approximately 1% of the human genome but harbor 85% of the mutations with large effects on disease-related traits. Therefore, efficient strategies for selectively sequencing complete coding regions (i.e., "whole exome") have the potential to contribute our understanding of human diseases. We used a method for whole-exome sequencing coupling Agilent whole-exome capture to the Illumina DNA-sequencing platform, and investigated two unrelated fetuses from nonconsanguineous families with Fowler Syndrome (FS), a stereotyped phenotype lethal disease. We report novel germline mutations in feline leukemia virus subgroup C cellular-receptor-family member 2, FLVCR2, which has recently been shown to cause FS. Using this technology, we identified three types of genetic abnormalities: point-mutations, insertions-deletions, and intronic splice-site changes (first pathogenic report using this technology), in the fetuses who both were compound heterozygotes for the disease. Although revealing a high level of allelic heterogeneity and mutational spectrum in FS, this study further illustrates the successful application of whole-exome sequencing to uncover genetic defects in rare Mendelian disorders. Of importance, we show that we can identify genes underlying rare, monogenic and recessive diseases using a limited number of patients (n=2), in the absence of shared genetic heritage and in the presence of allelic heterogeneity.
Human Mutation 08/2010; 31(8):918-23. · 5.69 Impact Factor
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ABSTRACT: Alternative splicing is known to increase the complexity of mammalian transcriptomes since nearly all mammalian genes express multiple pre-mRNA isoforms. However, our knowledge of the extent and function of alternative splicing in early embryonic development is based mainly on a few isolated examples. High throughput technologies now allow us to study genome-wide alternative splicing during mouse development.
A genome-wide analysis of alternative isoform expression in embryonic day 8.5, 9.5 and 11.5 mouse embryos and placenta was carried out using a splicing-sensitive exon microarray. We show that alternative splicing and isoform expression is frequent across developmental stages and tissues, and is comparable in frequency to the variation in whole-transcript expression. The genes that are alternatively spliced across our samples are disproportionately involved in important developmental processes. Finally, we find that a number of RNA binding proteins, including putative splicing factors, are differentially expressed and spliced across our samples suggesting that such proteins may be involved in regulating tissue and temporal variation in isoform expression. Using an example of a well characterized splicing factor, Fox2, we demonstrate that changes in Fox2 expression levels can be used to predict changes in inclusion levels of alternative exons that are flanked by Fox2 binding sites.
We propose that alternative splicing is an important developmental regulatory mechanism. We further propose that gene expression should routinely be monitored at both the whole transcript and the isoform level in developmental studies.
BMC Genomics 01/2010; 11:399. · 4.07 Impact Factor
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ABSTRACT: Breast cancer is the second most frequent type of cancer affecting women. We are increasingly aware that changes in mRNA splicing are associated with various characteristics of cancer. The most deadly aspect of cancer is metastasis, the process by which cancer spreads from the primary tumor to distant organs. However, little is known specifically about the involvement of alternative splicing in the formation of macroscopic metastases. Our study investigates transcript isoform changes that characterize tumors of different abilities to form growing metastases.
To identify alternative splicing events (ASEs) that are associated with the fully metastatic phenotype in breast cancer, we used Affymetrix Exon Microarrays to profile mRNA isoform variations genome-wide in weakly metastatic (168FARN and 4T07) and highly metastatic (4T1) mammary carcinomas. Statistical analysis identified significant expression changes in 7606 out of 155,994 (4%) exons and in 1725 out of 189,460 (1%) intronic regions, which affect 2623 out of 16,654 (16%) genes. These changes correspond to putative alternative isoforms-several of which are novel-that are differentially expressed between tumors of varying metastatic phenotypes. Gene pathway analysis showed that 1224 of genes expressing alternative isoforms were involved in cell growth, cell interactions, cell proliferation, cell migration and cell death and have been previously linked to cancers and genetic disorders. We chose ten predicted splice variants for RT-PCR validation, eight of which were successfully confirmed (MED24, MFI2, SRRT, CD44, CLK1 and HNRNPH1). These include three novel intron retentions in CD44, a gene in which isoform variations have been previously associated with the metastasis of several cancers.
Our findings reveal that various genes are differently spliced and/or expressed in association with the metastatic phenotype of tumor cells. Identification of metastasis-specific isoforms may contribute to the development of improved breast cancer stage identification and targeted therapies.
PLoS ONE 01/2010; 5(8):e11981. · 4.09 Impact Factor
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ABSTRACT: Recently, thanks to the increasing throughput of new technologies, we have begun to explore the full extent of alternative pre-mRNA splicing (AS) in the human transcriptome. This is unveiling a vast layer of complexity in isoform-level expression differences between individuals. We used previously published splicing sensitive microarray data from lymphoblastoid cell lines to conduct an in-depth analysis on splicing efficiency of known and predicted exons. By combining publicly available AS annotation with a novel algorithm designed to search for AS, we show that many real AS events can be detected within the usually unexploited, speculative majority of the array and at significance levels much below standard multiple-testing thresholds, demonstrating that the extent of cis-regulated differential splicing between individuals is potentially far greater than previously reported. Specifically, many genes show subtle but significant genetically controlled differences in splice-site usage. PCR validation shows that 42 out of 58 (72%) candidate gene regions undergo detectable AS, amounting to the largest scale validation of isoform eQTLs to date. Targeted sequencing revealed a likely causative SNP in most validated cases. In all 17 incidences where a SNP affected a splice-site region, in silico splice-site strength modeling correctly predicted the direction of the micro-array and PCR results. In 13 other cases, we identified likely causative SNPs disrupting predicted splicing enhancers. Using Fst and REHH analysis, we uncovered significant evidence that 2 putative causative SNPs have undergone recent positive selection. We verified the effect of five SNPs using in vivo minigene assays. This study shows that splicing differences between individuals, including quantitative differences in isoform ratios, are frequent in human populations and that causative SNPs can be identified using in silico predictions. Several cases affected disease-relevant genes and it is likely some of these differences are involved in phenotypic diversity and susceptibility to complex diseases.
PLoS Genetics 12/2009; 5(12):e1000766. · 8.69 Impact Factor
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Bing Ge,
Dmitry K Pokholok,
Tony Kwan,
Elin Grundberg,
Lisanne Morcos,
Dominique J Verlaan,
Jennie Le,
Vonda Koka,
Kevin C L Lam,
Vincent Gagné, [......],
Robert Hamon,
Alexandru Graziani,
Ken Dewar,
Eef Harmsen, Jacek Majewski,
Harald H H Göring,
Anna K Naumova,
Mathieu Blanchette,
Kevin L Gunderson,
Tomi Pastinen
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ABSTRACT: Cis-acting variants altering gene expression are a source of phenotypic differences. The cis-acting components of expression variation can be identified through the mapping of differences in allelic expression (AE), which is the measure of relative expression between two allelic transcripts. We generated a map of AE associated SNPs using quantitative measurements of AE on Illumina Human1M BeadChips. In 53 lymphoblastoid cell lines derived from donors of European descent, we identified common cis variants affecting 30% (2935/9751) of the measured RefSeq transcripts at 0.001 permutation significance. The pervasive influence of cis-regulatory variants, which explain 50% of population variation in AE, extend to full-length transcripts and their isoforms as well as to unannotated transcripts. These strong effects facilitate fine mapping of cis-regulatory SNPs, as demonstrated by dissection of heritable control of transcripts in the systemic lupus erythematosus-associated C8orf13-BLK region in chromosome 8. The dense collection of associations will facilitate large-scale isolation of cis-regulatory SNPs.
Nature Genetics 11/2009; 41(11):1216-22. · 35.53 Impact Factor
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ABSTRACT: The emergence of isoform-sensitive microarrays has helped fuel in-depth studies of the human transcriptome. The Affymetrix GeneChip Human Exon 1.0 ST Array (Exon Array) has been previously shown to be effective in profiling gene expression at the isoform level. More recently, the Affymetrix GeneChip Human Gene 1.0 ST Array (Gene Array) has been released for measuring gene expression and interestingly contains a large subset of probes from the Exon Array. Here, we explore the potential of using Gene Array probes to assess expression variation at the sub-transcript level. Utilizing datasets of the high quality Microarray Quality Control (MAQC) RNA samples previously assayed on the Exon Array and Gene Array, we compare the expression measurements of the two platforms to determine the performance of the Gene Array in detecting isoform variations.
Overall, we show that the Gene Array is comparable to the Exon Array in making gene expression calls. Moreover, to examine expression of different isoforms, we modify the Gene Array probe set definition file to enable summarization of probe intensity values at the exon level and show that the expression profiles between the two platforms are also highly correlated. Next, expression calls of previously known differentially spliced genes were compared and also show concordant results. Splicing index analysis, representing estimates of exon inclusion levels, shows a lower but good correlation between platforms. As the Gene Array contains a significant subset of probes from the Exon Array, we note that, in comparison, the Gene Array overlaps with fewer but still a high proportion of splicing events annotated in the Known Alt Events UCSC track, with abundant coverage of cassette exons. We discuss the ability of the Gene Array to detect alternative splicing and isoform variation and address its limitations.
The Gene Array is an effective expression profiling tool at gene and exon expression level, the latter made possible by probe set annotation modifications. We demonstrate that the Gene Array is capable of detecting alternative splicing and isoform variation. As expected, in comparison to the Exon Array, it is limited by reduced gene content coverage and is not able to detect as wide a range of alternative splicing events. However, for the events that can be monitored by both platforms, we estimate that the selectivity and sensitivity levels are comparable. We hope our findings will shed light on the potential extension of the Gene Array to detect alternative splicing. It should be particularly suitable for researchers primarily interested in gene expression analysis, but who may be willing to look for splicing and isoform differences within their dataset. However, we do not suggest it to be an equivalent substitute to the more comprehensive Exon Array.
BMC Genomics 11/2009; 10:519. · 4.07 Impact Factor
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Tony Kwan,
Elin Grundberg,
Vonda Koka,
Bing Ge,
Kevin C L Lam,
Christel Dias,
Andreas Kindmark,
Hans Mallmin,
Osten Ljunggren,
Fernando Rivadeneira,
Karol Estrada,
Joyce B van Meurs,
Andre Uitterlinden,
Magnus Karlsson,
Claes Ohlsson,
Dan Mellström,
Olle Nilsson,
Tomi Pastinen, Jacek Majewski
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ABSTRACT: Current genome-wide association studies (GWAS) are moving towards the use of large cohorts of primary cell lines to study a disease of interest and to assign biological relevance to the genetic signals identified. Here, we use a panel of human osteoblasts (HObs) to carry out a transcriptomic survey, similar to recent studies in lymphoblastoid cell lines (LCLs). The distinct nature of HObs and LCLs is reflected by the preferential grouping of cell type-specific genes within biologically and functionally relevant pathways unique to each tissue type. We performed cis-association analysis with SNP genotypes to identify genetic variations of transcript isoforms, and our analysis indicates that differential expression of transcript isoforms in HObs is also partly controlled by cis-regulatory genetic variants. These isoforms are regulated by genetic variants in both a tissue-specific and tissue-independent fashion, and these associations have been confirmed by RT-PCR validation. Our study suggests that multiple transcript isoforms are often present in both tissues and that genetic control may affect the relative expression of one isoform to another, rather than having an all-or-none effect. Examination of the top SNPs from a GWAS of bone mineral density show overlap with probeset associations observed in this study. The top hit corresponding to the FAM118A gene was tested for association studies in two additional clinical studies, revealing a novel transcript isoform variant. Our approach to examining transcriptome variation in multiple tissue types is useful for detecting the proportion of genetic variation common to different cell types and for the identification of cell-specific isoform variants that may be functionally relevant, an important follow-up step for GWAS.
PLoS Genetics 09/2009; 5(8):e1000608. · 8.69 Impact Factor
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ABSTRACT: In this proposal, we set out to a) systematically monitor splicing variant profiles in breast cancer susceptibility genes and b) explore the role of alternative splicing in breast chemotherapy using a global strategy. In doing so, we hope to identify and validate candidate splicing variants involved in tumorigenesis using polony digital exon-profiling and functional assays. We are moving forward on four fronts - 1) the barcode methodology is in development; 2) we are working with state-of-the art capture arrays; 3) we are using the very latest RNA sequencing technology and 4) we are conducting comprehensive analyses of existing splice site variants in known breast cancer susceptibility genes. In part 3, we have generated over 5 million reads that have been aligned to the splice junction libraries, and we are using these reads to quantify and characterize alternative splicing events. Moreover, we will add value to this project by attempting to identify fusion proteins. In part 4, we have determined that the BRCA2 isoform known as BRCA2deltaex12 is not associated with a recognizable phenotype. This work is now in press in Human Mutation.
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