Unknown,Transcriptomics,Genomics,Proteomics

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Comparative genomic hybridization of human chronic lymphocytic leukemia CLL patients and subtypes of del13q14

ABSTRACT: Chronic lymphocytic leukemia (CLL) is a biologically heterogeneous illness with a variable clinical course. Loss of chromosomal material on chromosome 13 at cytoband 13q14 is the most frequent genetic abnormality in CLL, but the molecular aberrations underlying del13q14 in CLL remain incompletely characterized. We analyzed 171 CLL cases for LOH and sub-chromosomal copy loss on chromosome 13 in DNA from FACS-sorted CD19+ cells and paired buccal cells using the Affymetrix XbaI 50K SNP-array platform. The resulting high-resolution genomic maps, together with array-based measurements of expression levels of RNA in CLL cases with and without del13q14 and Q-PCR-based expression analysis of selected genes support the following conclusions: i) del13q14 is heterogeneous and composed of multiple subtypes with deletion of Rb or the miR15a/16 loci serving as anatomic landmarks, respectively ii) del13q14 type Ia deletions are relatively uniform in length and extend from breakpoints close to the miR15a/16 cluster to a newly identified telomeric breakpoint cluster at ~50.2-50.5 Mb physical position iii) LATS2 RNA levels are ~2.6-2.8-fold lower in cases with del13q14 type I that do not delete Rb as opposed to all other CLL cases and iv) ~15% of CLL cases display marked reductions in miR15a/16 expression often but not invariably associated with bi-allelic miR15a/16 loss. This data should aid future investigations into biological differences imparted on CLL by different del13q14 subtypes including investigations into LATS2 as one of the genes found deregulated as part of del13q14. Experiment Overall Design: The goal of this analysis is to detect probesets that are differentially expressed between CLL patients with wild type chromosome 13 and 13q-deleted samples. There are a total of 20 arrays.

ORGANISM(S): Homo sapiens

SUBMITTER: Sami Malek

PROVIDER: E-GEOD-9250 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Integrated genomic profiling of chronic lymphocytic leukemia identifies subtypes of deletion 13q14.

Ouillette Peter P Erba Harry H Kujawski Lisa L Kaminski Mark M Shedden Kerby K Malek Sami N SN

Cancer research 20080201 4

Chronic lymphocytic leukemia (CLL) is a biologically heterogeneous illness with a variable clinical course. Loss of chromosomal material on chromosome 13 at cytoband 13q14 is the most frequent genetic abnormality in CLL, but the molecular aberrations underlying del13q14 in CLL remain incompletely characterized. We analyzed 171 CLL cases for loss of heterozygosity and subchromosomal copy loss on chromosome 13 in DNA from fluorescence-activated cell sorting-sorted CD19(+) cells and paired buccal c ...[more]

PMID: 18281475

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Project description:Retinoblastoma (RB, OMIM:180200) is the most common malignant childhood tumor of the eye with an estimated incidence between 1 in 16,000 and 1 in 18,000 live births [1,2]. RB is the first disease for which a genetic etiology of cancer has been described [3] being caused by mutations in the first tumor suppressor gene identified (RB1, Genbank accession # L11910). Mutations in both alleles of the RB1 gene are required for the development of this neoplasm [4], and, depending on the germ-line or somatic origin of the defect, a heritable or sporadic form can be distinguished. RB is unilateral in 60% of cases and only 15% of these are heritable [5]; in contrast, 40% of retinoblastomas are bilateral with risk of transmission to the offspring. Heritable retinoblastoma constitutes a cancer predisposition syndrome [6]. RB1 is located on chromosome 13 at band q14 and can be affected by a heterogeneous spectrum of genetic abnormalities, including chromosome translocation/deletion, genomic rearrangements, ranging from whole gene microdeletion to intragenic exons loss or duplication, and more than 900 different point mutations [7]. Mutational analysis is performed to search for the predisposing RB1 gene mutation in peripheral blood of patients with RB, but the molecular diagnosis requires several technical approaches to cover the entire field of oncogenic RB1 defects, frequently resulting in numerous, expensive and time consuming procedures. In particular, cytogenetic tools, such as classical chromosome investigations and Fluorescent In Situ Hybridization (FISH), in addition to Multiplex Ligation-dependent Probe Amplification (MLPA) technique, may account for detection of about 16% of RB1 abnormalities [8], while the remaining large amount of point mutations need to be investigated using sequencing analysis. Since the 1970s, Sanger sequencing has been recognized as the gold standard for mutation analysis in molecular diagnostics; however, its low-throughput, long turnaround time and overall cost [9] have called for new paradigms. Next Generation Sequencing (NGS) can massively sequence millions of DNA segments, promising low costs, increased workflow speed and enhanced sensitivity in mutation detection [9,10,11] On the other hand, conventional and molecular cytogenetic analysis, have been replaced by modern high-throughput investigations, such as array Comparative Genomic Hybridization (aCGH), that can reveal and measure cryptic genomic imbalances. In addition, aCGH can be focused on specific DNA segments or genes maximizing the resolution via a customized process. Based on these observations, we have recruited a cohort of retinoblastoma patients we previously investigated with conventional cytogenetics and MLPA. Patients diagnosed with RB but negative to the above standard screening have been tested with NGS to assess its ability in identifying RB causative mutations. On the other hand, patients positive to standard screening have been further investigated with RB1-custom array CGH analysis to characterize the genomic rearrangements with a better resolution compared to the conventional techniques. The complementary aCGH data set related to this study has also been deposited at ArrayExpress, under accession number E-MTAB-3492: https://www.ebi.ac.uk/arrayexpress/experiments/E-MTAB-3492/

Project description:Background: Retinoblastoma (RB) is the most common malignant childhood tumor of the eye and results from inactivation of both alleles of the RB1 gene. Nowadays RB genetic diagnosis requires classical chromosome investigations, Multiplex Ligation-dependent Probe Amplification analysis (MLPA) and Sanger sequencing. Nevertheless, these techniques show some limitations. We report our experience on a cohort of RB patients using a combined approach of Next-Generation Sequencing (NGS) and RB1 custom array-Comparative Genomic Hybridization (aCGH). Methods: A total of 65 patients with retinoblastoma were studied: 29 cases of bilateral RB and 36 cases of unilateral RB. All patients were previously tested with conventional cytogenetics and MLPA techniques. Fifty-three samples were then analysed using NGS. Eleven cases were analysed by RB1 custom aCGH. One last case was studied only by classic cytogenetics. Finally, it has been tested, in a lab sensitivity assay, the capability of NGS to detect artificial mosaicism series in previously recognized samples prepared at 3 different mosaicism frequencies: 10%, 5%, 1%. Results: Of the 29 cases of bilateral RB, 28 resulted positive (96.5%) to the genetic investigation: 22 point mutations and 6 genomic rearrangements (four intragenic and two macrodeletion). A novel germline intragenic duplication, from exon18 to exon 23, was identified in a proband with bilateral RB. Of the 36 available cases of unilateral RB, 8 patients resulted positive (22%) to the genetic investigation: 3 patients showed point mutations while 5 carried large deletion. Finally, we successfully validated, in a lab sensitivity assay, the capability of NGS to accurately measure level of artificial mosaicism down to 1%. Conclusions: NGS and RB1-custom aCGH have demonstrated to be an effective combined approach in order to optimize the overall diagnostic procedures of RB. Custom aCGH is able to accurately detect genomic rearrangements allowing the characterization of their extension. NGS is extremely accurate in detecting single nucleotide variants, relatively simple to perform, cost savings and efficient and has confirmed a high sensitivity and accuracy in identifying low levels of artificial mosaicisms.

Dataset Information

Comparative genomic hybridization of human chronic lymphocytic leukemia CLL patients and subtypes of del13q14

Publications

Integrated genomic profiling of chronic lymphocytic leukemia identifies subtypes of deletion 13q14.

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