Recessive DES cardio/myopathy without myofibrillar aggregates: intronic splice variant silences one allele leaving only missense L190P-desmin

We establish autosomal recessive DES variants p.(Leu190Pro) and a deep intronic splice variant causing inclusion of a frameshift-inducing artificial exon/intronic fragment, as the likely cause of myopathy with cardiac involvement in female siblings. Both sisters presented in their twenties with slowly progressive limb girdle weakness, severe systolic dysfunction, and progressive, severe respiratory weakness. Desmin is an intermediate filament protein typically associated with autosomal dominant myofibrillar myopathy with cardiac involvement. However a few rare cases of autosomal recessive desminopathy are reported. In this family, a paternal missense p.(Leu190Pro) variant was viewed unlikely to be causative of autosomal dominant desminopathy, as the father and brothers carrying this variant were clinically unaffected. Clinical fit with a DES-related myopathy encouraged closer scrutiny of all DES variants, identifying a maternal deep intronic variant within intron-7, predicted to create a cryptic splice site, which segregated with disease. RNA sequencing and studies of muscle cDNA confirmed the deep intronic variant caused aberrant splicing of an artificial exon/intronic fragment into maternal DES mRNA transcripts, encoding a premature termination codon, and potently activating nonsense-mediate decay (92% paternal DES transcripts, 8% maternal). Western blot showed 60-75% reduction in desmin levels, likely comprised only of missense p.(Leu190Pro) desmin. Biopsy showed fibre size variation with increased central nuclei. Electron microscopy showed extensive myofibrillar disarray, duplication of the basal lamina, but no inclusions or aggregates. This study expands the phenotypic spectrum of recessive DES cardio/myopathy, and emphasizes the continuing importance of muscle biopsy for functional genomics pursuit of 'tricky' variants in neuromuscular conditions.Lisa G. Riley, Leigh B. Waddell, Roula Ghaoui, Frances J. Evesson, Beryl B. Cummings, Samantha J. Bryen, Himanshu Joshi, Min-Xia Wang, Susan Brammah, Leonard Kritharides, Alastair Corbett, Daniel G. MacArthur, Sandra T. Coope

Pathogenic abnormal splicing due to intronic deletions that induce biophysical space constraint for spliceosome assembly

A precise genetic diagnosis is the single most important step for families with genetic disorders to enable personalized and preventative medicine. In addition to genetic variants in coding regions (exons) that can change a protein sequence, abnormal pre-mRNA splicing can be devastating for the encoded protein, inducing a frameshift or in-frame deletion/insertion of multiple residues. Non-coding variants that disrupt splicing are extremely challenging to identify. Stemming from an initial clinical discovery in two index Australian families, we define 25 families with genetic disorders caused by a class of pathogenic non-coding splice variant due to intronic deletions. These pathogenic intronic deletions spare all consensus splice motifs, though they critically shorten the minimal distance between the 5' splice-site (5'SS) and branchpoint. The mechanistic basis for abnormal splicing is due to biophysical constraint precluding U1/U2 spliceosome assembly, which stalls in A-complexes (that bridge the 5'SS and branchpoint). Substitution of deleted nucleotides with non-specific sequences restores spliceosome assembly and normal splicing, arguing against loss of an intronic element as the primary causal basis. Incremental lengthening of 5'SS-branchpoint length in our index EMD case subject defines 45-47 nt as the critical elongation enabling (inefficient) spliceosome assembly for EMD intron 5. The 5'SS-branchpoint space constraint mechanism, not currently factored by genomic informatics pipelines, is relevant to diagnosis and precision medicine across the breadth of Mendelian disorders and cancer genomics.Samantha J.Bryen, Himanshu Joshi, Frances J.Evesson, Cyrille Girard, Roula Ghaoui, Leigh B.Waddell ... et al

Standardized practices for RNA diagnostics using clinically accessible specimens reclassifies 75% of putative splicing variants

Purpose: Genetic variants causing aberrant premessenger RNA splicing are increasingly being recognized as causal variants in genetic disorders. In this study, we devise standardized practices for polymerase chain reaction (PCR)-based RNA diagnostics using clinically accessible specimens (blood, fibroblasts, urothelia, biopsy). Methods: A total of 74 families with diverse monogenic conditions (31% prenatal-congenital onset, 47% early childhood, and 22% teenage-adult onset) were triaged into PCR-based RNA testing, with comparative RNA sequencing for 19 cases. Results: Informative RNA assay data were obtained for 96% of cases, enabling variant reclassification for 75% variants that can be used for genetic counseling (71%), to inform clinical care (32%) and prenatal counseling (41%). Variant-associated mis-splicing was highly reproducible for 28 cases with samples from ≥2 affected individuals or heterozygotes and 10 cases with ≥2 biospecimens. PCR amplicons encompassing another segregated heterozygous variant was vital for clinical interpretation of 22 of 79 variants to phase RNA splicing events and discern complete from partial mis-splicing. Conclusion: RNA diagnostics enabled provision of a genetic diagnosis for 64% of recruited cases. PCR-based RNA diagnostics has capacity to analyze 81.3% of clinically significant genes, with long amplicons providing an advantage over RNA sequencing to phase RNA splicing events. The Australasian Consortium for RNA Diagnostics (SpliceACORD) provide clinically-endorsed, standardized protocols and recommendations for interpreting RNA assay data.Field, Ron Fleischer, Chiara Folland, Lucy Fox, Mary- Louise Freckmann, Clara Gaff, Melanie Galea, Roula Ghaoui, Himanshu Goel, Ilias Gornanitis, Thuong Ha, Bernadette Hanna, James Harraway, Rippei Hayashi, Ian Hayes, Alex Henderson, Luke Hesson, Erin Heyer, Michael Hildebrand, Michael Hipwell, Gladys Ho, Ari E. Horton, Cass Hoskins, Matthew F. Hunter, Matilda Jackson, Paul James, Kristi J. Jones, Justin Jong-Leong Wong, Sarah Josephi-Taylor, Himanshu Joshi, Karin Kassahn, Peter Kaub, Lucy Kevin, Edwin Kirk, Emma Krzesinski, Smitha Kumble, Sarah Kummerfeld, Nigel Laing, Chiyan Lau, Eric Lee, Sarah Leighton, Ben Lundie, Sebastian Lunke, Amali Mallawaarachchi, Chelsea Mayoh, Julie McGaughran, Ali- son McLean, Mary McPhillips, Cliff Meldrum, Edwina Middleton, Di Milnes, Kym Mina, David Mowat, Amy Nisselle, Emily Oates, Alicia Oshlack, Elizabeth E. Palmer, Gayathri Parasivam, Michael Parsons, Chirag Patel, Jason R. Pinner, Michael Quinn, John Rasko, Gina Ravenscroft, Anja Ravine, Krista Recsei, Matthew Regan, Jacqueline Rehn, Lisa G. Riley, Stephen Robertson, Anne Ronan, Tony Roscioli, Georgina Ryland, Simon Sadedin, Sarah A. San- daradura, Andreas Schreiber, Hamish Scott, Rodney Scott, Christopher Semsarian, Cas Simons, Emma Singer, Janine M. Smith, Renee Smyth, Amanda Spurdle, Zornitza Stark, Patricia Sullivan, Samantha Sundercombe, Tiong Y. Tan, Michel C. Tchan, Bryony A. Thompson, David Thorburn, John Toubia, Ronald Trent, Emma Tudini, Irina Voneague, Leigh Waddell, Logan Walker, Mathew Wallis, Nick War- nock, Robert Weatheritt, Deborah White, Susan M. White, Mark G. Williams, Meredith J. Wilson, Ingrid Winship, Lisa Worgan, Dale C. Wright, Kathy Wu, Alison Yeung, Andrew Ziolowski. Additional Information The online version of this article, https, doi.org, ., j. gim., ., ., contains supplementary material, which is available to authorized users. Authors Adam M. Bournazos, Lisa G. Riley, Shobhana Bommireddipalli, Lesley Ades, Lauren S. Akesson, Mohammad Al-Shinnag, Stephen I. Alexander, Alison D. Archibald, Shanti Balasubramaniam, Yemima Berman, Victoria Beshay, Kirsten Boggs, Jasmina Bojadzieva, Natasha J. Brown, Samantha J. Bryen, Michael F. Buckley, Belinda Chong, Mark R. Davis, Ruebena Dawes, Martin Delatycki, Liz Donaldson, Lilian Downie, Caitlin Edwards, Matthew Edwards, Amanda Engel, Lisa J. Ewans, Fathimath Faiz, Andrew Fennell, Michael Field, Mary-Louise Freckmann, Lyndon Gallacher, Russell Gear, Himanshu Goel, Shuxiang Goh, Linda Goodwin, Bernadette Hanna, James Harraway, Megan Higgins, Gladys Ho, Bruce K. Hopper, Ari E. Horton, Matthew F. Hunter, Aamira J. Huq, Sarah Josephi-Taylor, Himanshu Joshi, Edwin Kirk, Emma Krzesinski, Kishore R. Kumar, Frances Lemckert, Richard J. Leventer, Suzanna E. Lindsey-Temple, Sebastian Lunke, Alan Ma, Steven Macaskill, Amali Mallawaarachchi, Melanie Marty, Justine E. Marum, Hugh J. McCarthy, Manoj P. Menezes, Alison McLean, Di Milnes, Shekeeb Mohammad, David Mowat, Aram Niaz, Elizabeth E. Palmer, Chirag Patel, Shilpan G. Patel, Dean Phelan, Jason R. Pinner, Sulekha Rajagopalan, Matthew Regan, Jonathan Rodgers, Miriam Rodrigues, Richard H. Roxburgh, Rani Sachdev, Tony Roscioli, Ruvishani Samarasekera, Sarah A. Sandaradura, Elena Savva, Tim Schindler, Margit Shah, Ingrid B. Sinnerbrink, Janine M. Smith, Richard J. Smith, Amanda Springer, Zornitza Stark, Samuel P. Strom, Carolyn M. Sue, Kenneth Tan, Tiong Y. Tan, Esther Tantsis, Michel C. Tchan, Bryony A. Thompson, Alison H. Trainer, Karin van Spaendonck-Zwarts, Rebecca Walsh, Linda Warwick, Stephanie White, Susan M. White, Mark G. Williams, Meredith J. Wilson, Wui Kwan Wong, Dale C. Wright, Patrick Yap, Alison Yeung, Helen Young, Kristi J. Jones, Bruce Bennetts, Sandra T. Cooper, on behalf of the Australasian Consortium for RNA Diagnostic