Unknown,Transcriptomics,Genomics,Proteomics

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Normalization of Illumina Infinium whole-genome SNP data improves copy number estimates and allelic intensity ratios

ABSTRACT: Illumina Infinium whole genome genotyping (WGG) arrays are increasingly being applied in cancer genomics to study gene copy number alterations and allele-specific aberrations such as loss-of-heterozygosity (LOH). Methods developed for normalization of WGG arrays have mostly focused on diploid, normal samples. However, for cancer samples genomic aberrations may confound normalization and data interpretation. Therefore, we examined the effects of the conventionally used normalization method for Illumina Infinium arrays when applied to cancer samples. We demonstrate an asymmetry in the detection of the two alleles for each SNP, which deleteriously influences both allelic proportions and copy number estimates. The asymmetry is caused by a remaining bias between the two dyes used in the Infinium II assay after using the normalization method in Illumina’s proprietary software (BeadStudio). We propose a quantile normalization strategy for correction of this dye bias. We tested the normalization strategy using 535 individual hybridizations from 10 data sets from the analysis of cancer genomes and normal blood samples generated on Illumina Infinium II 300k version 1 and 2, 370k and 550k BeadChips. We show that the proposed normalization strategy successfully removes asymmetry in estimates of both allelic proportions and copy numbers. Additionally, the normalization strategy reduces the technical variation for copy number estimates while retaining the response to copy number alterations. The proposed normalization strategy represents a valuable low-level analysis tool that improves the quality of data obtained from Illumina Infinium arrays, in particular when used for LOH and copy number variation studies. To investigate the effects of a quantile normalization of Illumina Infinium data, compared to conventional normalization using BeadStudio (www.illumina.com), we renormalized 535 individual hybridizations conducted on Illumina 300K, 370K and 550K BeadChips. Sample types included breast cancer, colon cancer, urothelial carcinoma, leukemia as well as normal blood and HapMap samples. This series includes the 6 breast cancers hybridized on Illumina HumanHap 550K BeadChips.

ORGANISM(S): Homo sapiens

SUBMITTER: Ake Borg

PROVIDER: E-GEOD-11977 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Normalization of Illumina Infinium whole-genome SNP data improves copy number estimates and allelic intensity ratios.

Staaf Johan J Vallon-Christersson Johan J Lindgren David D Juliusson Gunnar G Rosenquist Richard R Höglund Mattias M Borg Ake A Ringnér Markus M

BMC bioinformatics 20081002

<h4>Background</h4>Illumina Infinium whole genome genotyping (WGG) arrays are increasingly being applied in cancer genomics to study gene copy number alterations and allele-specific aberrations such as loss-of-heterozygosity (LOH). Methods developed for normalization of WGG arrays have mostly focused on diploid, normal samples. However, for cancer samples genomic aberrations may confound normalization and data interpretation. Therefore, we examined the effects of the conventionally used normaliz ...[more]

PMID: 18831757

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Project description:We applied whole-genome single nucleotide polymorphism (SNP) arrays to define a comprehensive genetic profile of 23 esophageal adenocarcinoma (EAC) primary tumor biopsies based on loss of heterozygosity (LOH) and DNA copy number changes. Alterations were common, averaging 97 (range 23-208) per tumor. LOH and gains averaged 33 (range 3-83) and 31 (range 11-73) per tumor, respectively. Copy neutral LOH events averaged 27 (range 7-57) per EAC. We noted 126 homozygous deletions (HDs) across the EAC panel (range 0-11 in individual tumors). Frequent HDs within FHIT (17/23), WWOX (8/23) and DMD (6/23) suggest a role for common fragile sites or genomic instability in EAC etiology. HDs were also noted for known tumor suppressor genes (TSGs) including: CDKN2A, CDKN2B, SMAD4 and GALR1, and identified PDE4D and MGC48628 as potentially novel TSGs. All tumors showed LOH for most of chromosome 17p, suggesting that TSGs other than TP53 maybe targeted. Frequent gains were noted around MYC (13/23), BCL9 (12/23), CTAGE1 (14/23) and ZNF217 (12/23). Thus, we have confirmed previous reports indicating frequent changes to FHIT, CDKN2A, TP53 and MYC in EAC and identified additional genes of interest. Meta analysis of previous genome-wide EAC studies together with the data presented here, highlighted consistent regions of gain on 8q, 18q and 20q, and multiple LOH regions on 4q, 5q, 17p and 18q, suggesting that more than one gene may be targeted on each of these chromosome arms. The focal gains and deletions documented here are a step towards identifying the key genes involved in EAC development. Keywords: High Density SNP array Here we use Illumina 317K whole-genome single-nucleotide polymorphism arrays to define a comprehensive allelotype of melanoma based on loss of heterozygosity (LOH) and copy number changes in a panel of 23 esophageal adenocarcinoma (EAC) primary tumor biopsies. Each EAC was paired to normal squamous biopsy from 40328 (GSM266078) to generate the log_R_ratio.

Dataset Information

Normalization of Illumina Infinium whole-genome SNP data improves copy number estimates and allelic intensity ratios

Publications

Normalization of Illumina Infinium whole-genome SNP data improves copy number estimates and allelic intensity ratios.

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