Unknown,Transcriptomics,Genomics,Proteomics

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Advantages of a Next Generation Sequencing targeted approach for the molecular diagnosis of Retinoblastoma.

ABSTRACT: 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.

ORGANISM(S): Homo sapiens

SUBMITTER: Cecilia Surace

PROVIDER: E-MTAB-3492 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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:Chemotherapy resistance is one of the reasons for the loss of the eye in retinoblastoma (RB) pa-tients. RB chemotherapy resistance has been investigated in different cell culture models like WERI RB1. Furthermore, chemotherapy resistant RB subclones like the etoposide resistant WERI ETOR cell line have been established to improve understanding of chemotherapy resistance in RB. Ob-jective of this study was to characterize the cell line models of an etoposide sensitive WERI RB1 and its etoposide resistant subclone WERI ETOR by proteomics analysis. Subsequently, quantitative proteomic data served for correlation analysis with known drug perturbation profiles. . WERI RB1 and WERI ETOR were cultured and prepared for quantitative mass spectrometry. Comparative proteomic profiling was performed with electrospray ionization tandem mass spectrometry in data-independent acquisition mode (SWATH). The raw SWATH files were processed using neural networks in library free mode along with machine learning algorithms. Pathway enrichment was performed using the REACTOME pathway resource and correlated to the Molecular Signature Database (MSigDB) hallmark gene set collections for functional annotation. Also, a drug connec-tivity analysis using the L1000 database was used to correlate the mechanism-of-action (MOA) for different anticancer reagents to WERI RB1 / WERI ETOR signatures. A total 4,756 proteins were identified across all samples which revealed a distinct clustering between groups. Of these pro-teins, 64 proteins were significantly altered (q < 0.05 & log2FC |>2|, 22% higher in WERI ETOR). Pathway analysis showed an enriched metabolic pathway for retinoid metabolism and transport pathway in WERI ETOR and for sphingolipid de novo biosynthesis in WERI RB1. In addition, this study showed similar protein signatures of topoisomerase inhibitors and WERI ETOR as well as of ATPase inhibitors, acetylcholine receptor antagonists and VEGFR inhibitors and WERI RB1. In this study, WERI RB1 and WERI ETOR were characterized as a cell line model for chemotherapy re-sistance in RB by using data-independent mass spectrometry. The global proteome revealed the activation of sphingolipid de novo biosynthesis in WERI RB1 and potential treatment options for etoposide resistant RB.

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Advantages of a Next Generation Sequencing targeted approach for the molecular diagnosis of Retinoblastoma.

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