Targeted exome analysis identifies the genetic basis of disease in over 50% of patients with a wide range of ataxia-related phenotypes
Miao SunAmy Knight JohnsonViswateja NelakuditiLucia GuidugliDavid S. FischerKelly ArndtLan MaErin SandfordVikram G. ShakkottaiKym M. BoycottJodi Warman‐ChardonZejuan LiDaniela del GaudioMargit BurmeisterChristopher M. GómezDarrel WaggonerSoma Das
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Exome
Etiology
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More than 7,000 rare Mendelian diseases have been reported, but less than half of all rare monogenic disorders has been discovered. In addition, the majority of mutations that are known to cause Mende- lian disorders are located in protein-coding regions. Therefore, exome sequencing is an efficient strategy to selectively sequence the coding regions of the human genome to identify novel genes associated with rare genetic disorders. The exome represents all of the exons in the human genome, constituting about 1.5% of the human genome. Exome sequencing is carried out by targeted capture and intense parallel sequencing. After the first report of successful exome sequencing for the identification of causal genes and mutations in Freeman Sheldon syndrome, exome sequencing has become a standard approach to identify genes in rare Mendelian disorders. Exome sequencing is also used to search the causal genes and variants in complex diseases. The successful use of exome sequencing in Mendelian disorders and complex diseases will facilitate the development of personalized genomic medicine.
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Abstract The majority of patients undergoing exome or genome sequencing receive a nondiagnostic result. Periodic reanalysis is known to increase diagnostic yield from exome sequencing, yet laboratory reanalysis practices are obscure. We sought to define the landscape of exome and genome reanalysis across clinical laboratories. Genetic testing registries were queried to identify eligible clinical genetic laboratories offering exome and/or genome sequencing in the United States. A survey administered to lab representatives investigated reanalysis offerings, policies, perceived uptake, bioinformatic steps, and billing options. The analysis consisted of descriptive statistics. Survey data were collected from 30 of 32 eligible laboratories (93%), comprising 28 exome products and 13 genome products. Reanalysis was widely available for both exomes ( n = 27/28, 96%) and genomes ( n = 12/13, 92%). Most participating laboratories required ordering providers to initiate reanalysis ( n = 24/28, 86%). Most respondents estimated providers initiated reanalysis in less than 10% of all exomes ( n = 12/22) or genomes ( n = 6/9) sequenced. The approach to reanalysis varied greatly by laboratory. Laboratory approaches to exome and genome reanalysis are highly variable and typically require provider initiation. This could contribute to low reanalysis uptake and increased administrative burden on providers. Further work should emphasize development of clinical exome and genome reanalysis standards.
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Advances in technology are rapidly changing the field of medical genetics in both the research laboratory and the clinic. With the use of next-generation, or massively parallel, DNA sequencing, it is possible to determine the sequence of essentially all genes in an individual's genome — referred to as the exome — within a matter of days.This technology became widely available in 2005, and the first proof-of-principle experiment showing the power of exome sequencing for the discovery of genes associated with disease was published a few years later.1 Since then, exome analysis has been used in the research setting to . . .
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It is estimated that approximately 85% of human disease mutations are located in protein coding regions, therefore selectively sequencing all protein coding regions (exome) would be cost-effective and an alternative strategy to identify diseases' varaints. In 2009, scientists successfully identified one missense mutation in MYH3 among 4 individuals with Freeman Sheldon syndrome (one autosomal dominant disease) through exome sequencing. Since then, exome sequencing has been widely used to identify disease causative or susceptibility genes in Mendelian disorders and complex diseases. The application of exome sequencing in human diseases were summarized in this review.
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Abstract Consisting of only ~2% of the human genome, the exome accounts for ~85% of genetic disorders. Efficient sequencing of the human exome with complete and high coverage depth at low cost is invaluable for furthering research in clinical applications. IDT's xGen Exome Panel has proven to be a high performing option. Here, we present the updated xGen Exome Research Panel v2.0 in direct comparison with two other leading commercial human exome panels, using workflows per manufacturer's specifications. NA12878 genomic DNA libraries were pooled together for 8-plex captures for all three platforms and sequenced on the Illumina NextSeq 500. Equivalent number of reads per sample were analyzed against a universal human exome target space to compare across the different exome panels. IDT's Exome NGS solution provided significantly highest on-target percentage at >90% as well as the greatest depth of coverage at >96% bases covered at >20X and >98% bases covered at >10X. Importantly, IDT's platform also reported the most complete gene-level coverage, demonstrated by minimal exon drop-outs in difficult-to-target genes. While 8-plex is the upper limit supported by other suppliers, IDT's platform supports 12-plex workflow. The higher multiplex in combination with high coverage and on-target performance enables IDT to present the lowest total sequencing cost per sample. Since IDT hybridization capture baits are individually synthesized and qualified with the same high standards as standalone oligonucleotide products, lot-to-lot variability is negligible. This presents researchers with an option they can rely on for long-term use and places the focus on the true variabilities of the sample. In conclusion, this study demonstrates xGen Exome Research Panel v2.0, when combined with IDT's DNA Library Prep Kit, provides researchers with a complete Exome NGS solution that is competitive both in performance and sequencing cost. Citation Format: Manqing Hong, Bosun Min, Nicole Roseman, Ekaterina Star, Timothy Rusch, Krishnalekha Datta, Steve Groenewold, Longhui Ren, Jinglie Zhou, Kevin Lai, Xiaohui Wang, Nick Downey, Kristina Giorda, Alexandra Wang, Yu Wang, Lynette A. Lewis, Patrick J. Lau, Steven Henck. Improved human exome sequencing workflow with the most complete coverage [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1349.
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Human exome resequencing using commercial target capture kits has been and is being used for sequencing large numbers of individuals to search for variants associated with various human diseases. We rigorously evaluated the capabilities of two solution exome capture kits. These analyses help clarify the strengths and limitations of those data as well as systematically identify variables that should be considered in the use of those data. Each exome kit performed well at capturing the targets they were designed to capture, which mainly corresponds to the consensus coding sequences (CCDS) annotations of the human genome. In addition, based on their respective targets, each capture kit coupled with high coverage Illumina sequencing produced highly accurate nucleotide calls. However, other databases, such as the Reference Sequence collection (RefSeq), define the exome more broadly, and so not surprisingly, the exome kits did not capture these additional regions. Commercial exome capture kits provide a very efficient way to sequence select areas of the genome at very high accuracy. Here we provide the data to help guide critical analyses of sequencing data derived from these products.
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Sequencing the coding regions, the exome, of the human genome is one of the major current strategies to identify low frequency and rare variants associated with human disease traits. So far, the most widely used commercial exome capture reagents have mainly targeted the consensus coding sequence (CCDS) database. We report the design of an extended set of targets for capturing the complete human exome, based on annotation from the GENCODE consortium. The extended set covers an additional 5594 genes and 10.3 Mb compared with the current CCDS-based sets. The additional regions include potential disease genes previously inaccessible to exome resequencing studies, such as 43 genes linked to ion channel activity and 70 genes linked to protein kinase activity. In total, the new GENCODE exome set developed here covers 47.9 Mb and performed well in sequence capture experiments. In the sample set used in this study, we identified over 5000 SNP variants more in the GENCODE exome target (24%) than in the CCDS-based exome sequencing.
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Reporting clinically actionable incidental genetic findings in the course of clinical exome testing is recommended by the American College of Medical Genetics and Genomics (ACMG). However, the performance of clinical exome methods for reporting small subsets of genes has not been previously reported.In this study, 57 exome data sets performed as clinical (n = 12) or research (n = 45) tests were retrospectively analyzed. Exome sequencing data was examined for adequacy in the detection of potentially pathogenic variant locations in the 56 genes described in the ACMG incidental findings recommendation. All exons of the 56 genes were examined for adequacy of sequencing coverage. In addition, nucleotide positions annotated in HGMD (Human Gene Mutation Database) were examined.The 56 ACMG genes have 18 336 nucleotide variants annotated in HGMD. None of the 57 exome data sets possessed a HGMD variant. The clinical exome test had inadequate coverage for >50% of HGMD variant locations in 7 genes. Six exons from 6 different genes had consistent failure across all 3 test methods; these exons had high GC content (76%-84%).The use of clinical exome sequencing for the interpretation and reporting of subsets of genes requires recognition of the substantial possibility of inadequate depth and breadth of sequencing coverage at clinically relevant locations. Inadequate depth of coverage may contribute to false-negative clinical exome results.
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