Practical approach to the genetic diagnosis of unsolved dystrophinopathies: a stepwise strategy in the genomic era

2020 ◽  
pp. jmedgenet-2020-107113 ◽  
Author(s):  
Zhiying Xie ◽  
Chengyue Sun ◽  
Yilin Liu ◽  
Meng Yu ◽  
Yiming Zheng ◽  
...  
Keyword(s):  
Genetic Testing ◽  
Comprehensive Evaluation ◽  
Genetic Diagnosis ◽  
Regulatory Elements ◽  
Diagnostic Value ◽  
Molecular Defect ◽  
Aberrant Splicing ◽  
Splicing Regulatory Elements ◽  
Long Read ◽  
Complex Structural

ObjectiveTo investigate the diagnostic value of implementing a stepwise genetic testing strategy (SGTS) in genetically unsolved cases with dystrophinopathies.MethodsAfter routine genetic testing in 872 male patients with highly suspected dystrophinopathies, we identified 715 patients with a pathogenic DMD variant. Of the 157 patients who had no pathogenic DMD variants and underwent a muscle biopsy, 142 patients were confirmed to have other myopathies, and 15 suspected dystrophinopathies remained genetically undiagnosed. These 15 patients underwent a more comprehensive evaluation as part of the SGTS pipeline, which included the stepwise analysis of dystrophin mRNA, short-read whole-gene DMD sequencing, long-read whole-gene DMD sequencing and in silico bioinformatic analyses.ResultsSGTS successfully yielded a molecular diagnosis of dystrophinopathy in 11 of the 15 genetically unsolved cases. We identified 8 intronic and 2 complex structural variants (SVs) leading to aberrant splicing in 10 of 11 patients, of which 9 variants were novel. In one case, a molecular defect was detected on mRNA and protein level only. Aberrant splicing mechanisms included 6 pseudoexon inclusions and 4 alterations of splice sites and splicing regulatory elements. We showed for the first time the exonisation of a MER48 element as a novel pathogenic mechanism in dystrophinopathies.ConclusionOur study highlights the high diagnostic utility of implementing a SGTS pipeline in dystrophinopathies with intronic variants and complex SVs.

scholarly journals Targeted long-read sequencing resolves complex structural variants and identifies missing disease-causing variants

2020 ◽  
Author(s):  
Danny E. Miller ◽  
Arvis Sulovari ◽  
Tianyun Wang ◽  
Hailey Loucks ◽  
Kendra Hoekzema ◽  
...  
Keyword(s):  
Copy Number ◽  
Genetic Diagnosis ◽  
Clinical Testing ◽  
Structural Variants ◽  
Single Nucleotide Variants ◽  
Single Nucleotide ◽  
Pathogenic Variants ◽  
Long Read ◽  
Repeat Expansions ◽  
Complex Structural

ABSTRACTBACKGROUNDDespite widespread availability of clinical genetic testing, many individuals with suspected genetic conditions do not have a precise diagnosis. This limits their opportunity to take advantage of state-of-the-art treatments. In such instances, testing sometimes reveals difficult-to-evaluate complex structural differences, candidate variants that do not fully explain the phenotype, single pathogenic variants in recessive disorders, or no variants in specific genes of interest. Thus, there is a need for better tools to identify a precise genetic diagnosis in individuals when conventional testing approaches have been exhausted.METHODSTargeted long-read sequencing (T-LRS) was performed on 33 individuals using Read Until on the Oxford Nanopore platform. This method allowed us to computationally target up to 100 Mbp of sequence per experiment, resulting in an average of 20x coverage of target regions, a 500% increase over background. We analyzed patient DNA for pathogenic substitutions, structural variants, and methylation differences using a single data source.RESULTSThe effectiveness of T-LRS was validated by detecting all genomic aberrations, including single-nucleotide variants, copy number changes, repeat expansions, and methylation differences, previously identified by prior clinical testing. In 6/7 individuals who had complex structural rearrangements, T-LRS enabled more precise resolution of the mutation, which led, in one case, to a change in clinical management. In nine individuals with suspected Mendelian conditions who lacked a precise genetic diagnosis, T-LRS identified pathogenic or likely pathogenic variants in five and variants of uncertain significance in two others.CONCLUSIONST-LRS can accurately predict pathogenic copy number variants and triplet repeat expansions, resolve complex rearrangements, and identify single-nucleotide variants not detected by other technologies, including short-read sequencing. T-LRS represents an efficient and cost-effective strategy to evaluate high-priority candidate genes and regions or to further evaluate complex clinical testing results. The application of T-LRS will likely increase the diagnostic rate of rare disorders.

scholarly journals Systematic characterization of short intronic splicing-regulatory elements

2021 ◽  
Author(s):  
Yuan Gao ◽  
Kuan-Ting Lin ◽  
Yang Yang ◽  
Jialin Bai ◽  
Li Wang ◽  
...  
Keyword(s):  
Splice Site ◽  
Enrichment Analysis ◽  
Regulatory Elements ◽  
Hek293 Cells ◽  
Splice Site Selection ◽  
Aberrant Splicing ◽  
Rna Sequences ◽  
Splicing Regulatory Elements ◽  
Alternatively Spliced

Intronic splicing enhancers and silencers (ISEs and ISSs) are two groups of splicing-regulatory elements (SREs) that play critical roles in determining splice-site selection, particularly for alternatively spliced introns or exons. SREs are often short motifs; their mutation or dysregulation of their cognate proteins frequently causes aberrant splicing and results in disease. To date, however, knowledge about SRE sequences and how they regulate splicing remains limited. Here, using an SMN2 minigene, we generated a complete pentamer-sequence library that comprises all possible combinations of 5 nucleotides in intron 7, at a fixed site downstream of the 5′ splice site. We systematically analyzed the effects of all 1023 mutant pentamers on exon 7 splicing, in comparison to the wild-type minigene, in HEK293 cells. Our data show that the majority of pentamers significantly affect exon 7 splicing: 584 of them are stimulatory and 230 are inhibitory. To identify actual SREs, we utilized a motif set enrichment analysis (MSEA), from which we identified groups of stimulatory and inhibitory SRE motifs. We experimentally validated several strong SREs in SMN1/2 and MAPT minigene settings. Our results provide a valuable resource for understanding how short RNA sequences regulate splicing. Many novel SREs can be explored further to elucidate their mechanism of action.

scholarly journals A Comprehensive Analysis and Splicing Characterization of Naturally Occurring Synonymous Variants in the ATP7B Gene

2021 ◽  
Vol 11 ◽  
Author(s):  
Xiaoying Zhou ◽  
Wei Zhou ◽  
Chunli Wang ◽  
Lan Wang ◽  
Yu Jin ◽  
...  
Keyword(s):  
Rna Splicing ◽  
Genetic Diseases ◽  
Genetic Diagnosis ◽  
Exon Skipping ◽  
Computational Prediction ◽  
Regulatory Elements ◽  
Naturally Occurring ◽  
Splicing Regulatory Elements ◽  
The Impact

Next-generation sequencing is effective for the molecular diagnosis of genetic diseases. However, the identification of the clinical significance of synonymous variants remains a challenge. Our previous study showed that some synonymous variants in ATP7B gene produced splicing disruptions, leading to Wilson disease (WD). To test the hypothesis that synonymous variants of ATP7B cause abnormal splicing by disrupting authentic splice sites or splicing regulatory elements, we used computational tools and minigene assays to characterize 253 naturally occurring ATP7B gene synonymous variants in this study. Human Splicing Finder (HSF) and ESE Finder 3.0 were used to predict the impact of these rare synonymous variants on pre-mRNA splicing. Then, we cloned 14 different wild-type Minigene_ATP7B_ex constructs for in vitro minigene assay, including 16 exons of ATP7B gene. After computational prediction, 85 candidate variants were selected to be introduced into the corresponding Minigene_ATP7B_ex constructs for splicing assays. Using this two-step procedure, we demonstrated that 11 synonymous variants in ExAc database (c.1620C>T, c.3888C>T, c.1554C>T, c.1677C>T, c.1830G>A, c.1875T>A, c.2826C>A, c.4098G>A, c.2994C>T, c.3243G>A, and c.3747G>A) disrupted RNA splicing in vitro, and two (c.1620C>T and c.3243G>A) of these caused a complete exon skipping. The results not only provided a reliable experimental basis for the genetic diagnosis of WD patients but also offered some new insights into the pathogenicity of synonymous variants in genetic diseases.

scholarly journals RAD51D Aberrant Splicing in Breast Cancer: Identification of Splicing Regulatory Elements and Minigene-Based Evaluation of 53 DNA Variants

Cancers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2845
Author(s):  
Elena Bueno-Martínez ◽  
Lara Sanoguera-Miralles ◽  
Alberto Valenzuela-Palomo ◽  
Víctor Lorca ◽  
Alicia Gómez-Sanz ◽  
...  
Keyword(s):  
Splice Site ◽  
Regulatory Elements ◽  
Site Directed Mutagenesis ◽  
Loss Of Function ◽  
Nucleotide Substitutions ◽  
Aberrant Splicing ◽  
Single Nucleotide ◽  
Splicing Pattern ◽  
Powerful Approach ◽  
Splicing Regulatory Elements

RAD51D loss-of-function variants increase lifetime risk of breast and ovarian cancer. Splicing disruption is a frequent pathogenic mechanism associated with variants in susceptibility genes. Herein, we have assessed the splicing and clinical impact of splice-site and exonic splicing enhancer (ESE) variants identified through the study of ~113,000 women of the BRIDGES cohort. A RAD51D minigene with exons 2–9 was constructed in splicing vector pSAD. Eleven BRIDGES splice-site variants (selected by MaxEntScan) were introduced into the minigene by site-directed mutagenesis and tested in MCF-7 cells. The 11 variants disrupted splicing, collectively generating 25 different aberrant transcripts. All variants but one produced negligible levels (<3.4%) of the full-length (FL) transcript. In addition, ESE elements of the alternative exon 3 were mapped by testing four overlapping exonic microdeletions (≥30-bp), revealing an ESE-rich interval (c.202_235del) with critical sequences for exon 3 recognition that might have been affected by germline variants. Next, 26 BRIDGES variants and 16 artificial exon 3 single-nucleotide substitutions were also assayed. Thirty variants impaired splicing with variable amounts (0–65.1%) of the FL transcript, although only c.202G > A demonstrated a complete aberrant splicing pattern without the FL transcript. On the other hand, c.214T > C increased efficiency of exon 3 recognition, so only the FL transcript was detected (100%). In conclusion, 41 RAD51D spliceogenic variants (28 of which were from the BRIDGES cohort) were identified by minigene assays. We show that minigene-based mapping of ESEs is a powerful approach for identifying ESE hotspots and ESE-disrupting variants. Finally, we have classified nine variants as likely pathogenic according to ACMG/AMP-based guidelines, highlighting the complex relationship between splicing alterations and variant interpretation.

scholarly journals The Continuing Need for Electron Microscopy in Examination of Medical Renal Biopsies: Examples in Practice

2021 ◽  
pp. 1-15
Author(s):  
Michifumi Yamashita ◽  
Mercury Y. Lin ◽  
Jean Hou ◽  
Kevin Y.M. Ren ◽  
Mark Haas
Keyword(s):  
Electron Microscopy ◽  
Renal Biopsy ◽  
Renal Allograft ◽  
Comprehensive Evaluation ◽  
Diagnostic Value ◽  
Ultrastructural Studies ◽  
The Past ◽  
Biopsy Diagnosis ◽  
Renal Biopsies ◽  
Clinical Consequences

<b><i>Background:</i></b> For the better part of the past 6 decades, transmission electron microscopy (EM), together with routine light microscopy and immunofluorescence and/or immunohistochemistry (IHC), has been an essential component of the diagnostic workup of medical renal biopsies, particularly native renal biopsies, with increasing frequency in renal allograft biopsies as well. Studies performed prior to the year 2000 have indeed shown that a substantial fraction of renal biopsies cannot be accurately diagnosed without EM. Still, EM remains costly and labor-intensive, and with increasing pressure to reduce healthcare costs, some centers are de-emphasizing diagnostic EM. This trend has been coupled with advances in IHC and other methods in renal biopsy diagnosis over the past 2–3 decades. <b><i>Summary:</i></b> Nonetheless, it has been our experience that the diagnostic value of EM in the comprehensive evaluation of renal biopsies remains similar to what it was 20–30 years ago. In this review, we provide several key examples from our practice where EM was essential in making the correct renal biopsy diagnosis, ranging from relatively common glomerular lesions to rare diseases. <b><i>Key Messages:</i></b> EM remains an important component of the diagnostic evaluation of medical renal biopsies. Failure to perform EM in certain cases will result in an incorrect diagnosis, with possible clinical consequences. We strongly recommend that tissue for EM be taken and stored in an appropriate fixative and ultrastructural studies be performed for all native renal biopsies, as well as appropriate renal allograft biopsies as recommended by the Banff consortium.

scholarly journals Aberrant Bcl-x splicing in cancer: from molecular mechanism to therapeutic modulation

2021 ◽  
Vol 40 (1) ◽  
Author(s):  
Zhihui Dou ◽  
Dapeng Zhao ◽  
Xiaohua Chen ◽  
Caipeng Xu ◽  
Xiaodong Jin ◽  
...  
Keyword(s):  
Cancer Cells ◽  
Human Cancer ◽  
Structural Characteristics ◽  
Therapy Resistance ◽  
Regulatory Elements ◽  
Aberrant Splicing ◽  
Clinical Role ◽  
Splicing Isoforms ◽  
The Impact ◽  
Splicing Patterns

AbstractBcl-x pre-mRNA splicing serves as a typical example to study the impact of alternative splicing in the modulation of cell death. Dysregulation of Bcl-x apoptotic isoforms caused by precarious equilibrium splicing is implicated in genesis and development of multiple human diseases, especially cancers. Exploring the mechanism of Bcl-x splicing and regulation has provided insight into the development of drugs that could contribute to sensitivity of cancer cells to death. On this basis, we review the multiple splicing patterns and structural characteristics of Bcl-x. Additionally, we outline the cis-regulatory elements, trans-acting factors as well as epigenetic modifications involved in the splicing regulation of Bcl-x. Furthermore, this review highlights aberrant splicing of Bcl-x involved in apoptosis evade, autophagy, metastasis, and therapy resistance of various cancer cells. Last, emphasis is given to the clinical role of targeting Bcl-x splicing correction in human cancer based on the splice-switching oligonucleotides, small molecular modulators and BH3 mimetics. Thus, it is highlighting significance of aberrant splicing isoforms of Bcl-x as targets for cancer therapy.

scholarly journals Local Laboratory Testing of Germline BRCA Mutations vs. Myriad: A Single-Institution Experience in Korea

Diagnostics ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 370
Author(s):  
Joohyun Hong ◽  
Jiyun Lee ◽  
Minsuk Kwon ◽  
Ji-Yeon Kim ◽  
Jong-Won Kim ◽  
...  
Keyword(s):  
Genetic Testing ◽  
High Risk ◽  
Salt Lake ◽  
Medical Center ◽  
Brca Mutation ◽  
Genetic Diagnosis ◽  
Metastatic Breast ◽  
Breast Cancer Patients ◽  
Brca 1 ◽  
Local Laboratory

Genetic diagnosis for human epidermal growth factor receptor 2-negative metastatic breast cancer patients with the germline BRCA (gBRCA) mutation has been emphasized since the development of polyadenosine diphosphate-ribose polymerase inhibitors. Myriad Genetics, Inc.’s (Salt Lake City, UT, USA) companion diagnostics service is almost exclusively used for genetic testing. The aim of this study was to compare the results of germline BRCA mutation tests returned by a local laboratory and those performed by Myriad. Between April 2014 and February 2018, 31 patients with gBRCA 1/2 mutation test results from both Samsung Medical Center (Seoul, Korea) and Myriad were enrolled. “Discordant: Opposite classification” was observed for only one among 27 (3.7%). This discrepancy was due to the detection of a deleterious large genomic rearrangement of BRCA 1 by Myriad. Samsung Medical Center performed multiple ligation-dependent probe amplifications (MLPA) to detect large genomic rearrangements only in high-risk patients. This one case was not suspected as high risk and MLPA was not performed. The concordant rate was 74.1% for all 27 patients. “Discordant: Laboratory’s uncertain classification” was found in 22.2% of the sample (six patients). All discrepancies were generated during interpretation of BRCA 2 gene sequencing. Further studies and standardization of genetic testing for BRCA 1/2 genes are required.

Combined Muscle Biopsy and Comprehensive Electrophysiology in General Anesthesia is Valuable in Diagnosis of Neuromuscular Disease in Children

2021 ◽  
Author(s):  
Christina E. Hoei-Hansen ◽  
Marie L. B. Tygesen ◽  
Morten Dunø ◽  
John Vissing ◽  
Martin Ballegaard ◽  
...  
Keyword(s):  
Genetic Testing ◽  
Muscle Biopsy ◽  
Neuromuscular Disease ◽  
Genetic Diagnosis ◽  
Congenital Myasthenic Syndrome ◽  
Diagnostic Quality ◽  
Pathogenic Variants ◽  
Combined Use ◽  
Myasthenic Syndrome ◽  
Size Variability

Abstract Aim The diagnostic workup in patients with delayed motor milestones suspected of having either myopathy or a congenital myasthenic syndrome is complex. Our hypothesis was that performance of a muscle biopsy and neurophysiology including stimulated single-fiber electromyography during an anesthetic procedure, combined with genetic testing has a high diagnostic quality. Materials and Methods Clinical and paraclinical data were retrospectively collected from 24 patients aged from 1 month to 10 years (median: 5.2 years). Results Neurophysiology examination was performed in all patients and was abnormal in 11 of 24. No patients had findings suggestive of a myasthenic syndrome. Muscle biopsy was performed in 21 of 24 and was normal in 16. Diagnostic findings included nemaline rods, inclusion bodies, fiber size variability, and type-II fiber atrophy. Genetic testing with either a gene panel or exome sequencing was performed in 18 of 24 patients, with pathogenic variants detected in ACTA1, NEB, SELENON, GRIN2B, SCN8A, and COMP genes. Conclusion Results supporting a neuromuscular abnormality were found in 15 of 24. In six patients (25%), we confirmed a genetic diagnosis and 12 had a clinical neuromuscular diagnosis. The study suggests that combined use of neurophysiology and muscle biopsy in cases where genetic testing does not provide a diagnosis can be useful in children with delayed motor milestones and clinical evidence of a neuromuscular disease.

scholarly journals Cascade health service use in family members following genetic testing in children: a scoping literature review

2021 ◽  
Author(s):  
Alexandra Cernat ◽  
Robin Z. Hayeems ◽  
Wendy J. Ungar
Keyword(s):  
Genetic Testing ◽  
Health Service ◽  
Literature Review ◽  
English Language ◽  
Service Use ◽  
Genetic Diagnosis ◽  
Health Service Use ◽  
Cascade Testing ◽  
Scoping Literature Review ◽  
Genetic Technologies

AbstractCascade genetic testing is the identification of individuals at risk for a hereditary condition by genetic testing in relatives of people known to possess particular genetic variants. Cascade testing has health system implications, however cascade costs and health effects are not considered in health technology assessments (HTAs) that focus on costs and health consequences in individual patients. Cascade health service use must be better understood to be incorporated in HTA of emerging genetic tests for children. The purpose of this review was to characterise published research related to patterns and costs of cascade health service use by relatives of children with any condition diagnosed through genetic testing. To this end, a scoping literature review was conducted. Citation databases were searched for English-language papers reporting uptake, costs, downstream health service use, or cost-effectiveness of cascade investigations of relatives of children who receive a genetic diagnosis. Included publications were critically appraised, and findings were synthesised. Twenty publications were included. Sixteen had a paediatric proband population; four had a combined paediatric and adult proband population. Uptake of cascade testing varied across diseases, from 37% for cystic fibrosis, 39% to 65% for hypertrophic cardiomyopathy, and 90% for rare monogenic conditions. Two studies evaluated costs. It was concluded that cascade testing in the child-to-parent direction has been reported in a variety of diseases, and that understanding the scope of cascade testing will aid in the design and conduct of HTA of emerging genetic technologies to better inform funding and policy decisions.

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