@article {971, title = {Pathogenic deep intronic MTM1 variant activates a pseudo-exon encoding a nonsense codon resulting in severe X-linked myotubular myopathy.}, journal = {Eur J Hum Genet}, volume = {29}, year = {2021}, month = {2021 Jan}, pages = {61-66}, abstract = {

X-linked myotubular myopathy (XLMTM) is a severe congenital myopathy characterised by generalised weakness and respiratory insufficiency. XLMTM is associated with pathogenic variants in MTM1; a gene encoding the lipid phosphatase myotubularin. Whole genome sequencing (WGS) of an exome-negative male proband with severe hypotonia, respiratory insufficiency and centralised nuclei on muscle biopsy identified a deep intronic MTM1 variant NG_008199.1(NM_000252.2):c.1468-577A>G, which strengthened a cryptic 5{\textquoteright} splice site (A>G substitution at the +5 position). Muscle RNA sequencing was non-diagnostic due to low read depth. Reverse transcription PCR (RT-PCR) of muscle RNA confirmed the c.1468-577A>G variant activates inclusion of a pseudo-exon encoding a premature stop codon into all detected MTM1 transcripts. Western blot analysis establishes deficiency of myotubularin protein, consistent with the severe XLMTM phenotype. We expand the genotypic spectrum of XLMTM and highlight benefits of screening non-coding regions of MTM1 in male probands with phenotypically concordant XLMTM who remain undiagnosed following exome sequencing.

}, issn = {1476-5438}, doi = {10.1038/s41431-020-00715-7}, author = {Bryen, Samantha J and Oates, Emily C and Evesson, Frances J and Lu, Jessica K and Waddell, Leigh B and Joshi, Himanshu and Ryan, Monique M and Cummings, Beryl B and McLean, Catriona A and MacArthur, Daniel G and Kornberg, Andrew J and Cooper, Sandra T} } @article {713, title = {Recurrent TTN metatranscript-only c.39974-11T>G splice variant associated with autosomal recessive arthrogryposis multiplex congenita and myopathy.}, journal = {Hum Mutat}, volume = {41}, year = {2020}, month = {2020 02}, pages = {403-411}, abstract = {

We present eight families with arthrogryposis multiplex congenita and myopathy bearing a TTN intron 213 extended splice-site variant (NM_001267550.1:c.39974-11T>G), inherited in trans with a second pathogenic TTN variant. Muscle-derived RNA studies of three individuals confirmed mis-splicing induced by the c.39974-11T>G variant; in-frame exon 214 skipping or use of a cryptic 3{\textquoteright} splice-site effecting a frameshift. Confounding interpretation of pathogenicity is the absence of exons 213-217 within the described skeletal muscle TTN N2A isoform. However, RNA-sequencing from 365 adult human gastrocnemius samples revealed that 56\% specimens predominantly include exons 213-217 in TTN transcripts (inclusion rate >=66\%). Further, RNA-sequencing of five fetal muscle samples confirmed that 4/5 specimens predominantly include exons 213-217 (fifth sample inclusion rate 57\%). Contractures improved significantly with age for four individuals, which may be linked to decreased expression of pathogenic fetal transcripts. Our study extends emerging evidence supporting a vital developmental role for TTN isoforms containing metatranscript-only exons.

}, issn = {1098-1004}, doi = {10.1002/humu.23938}, author = {Bryen, Samantha J and Ewans, Lisa J and Pinner, Jason and MacLennan, Suzanna C and Donkervoort, Sandra and Castro, Diana and Topf, Ana and O{\textquoteright}Grady, Gina and Cummings, Beryl and Chao, Katherine R and Weisburd, Ben and Francioli, Laurent and Faiz, Fathimath and Bournazos, Adam M and Hu, Ying and Grosmann, Carla and Malicki, Denise M and Doyle, Helen and Witting, Nanna and Vissing, John and Claeys, Kristl G and Urankar, Kathryn and Beleza-Meireles, Ana and Baptista, Julia and Ellard, Sian and Savarese, Marco and Johari, Mridul and Vihola, Anna and Udd, Bjarne and Majumdar, Anirban and Straub, Volker and B{\"o}nnemann, Carsten G and MacArthur, Daniel G and Davis, Mark R and Cooper, Sandra T} } @article {688, title = {Pathogenic Abnormal Splicing Due to Intronic Deletions that Induce Biophysical Space Constraint for Spliceosome Assembly.}, journal = {Am J Hum Genet}, volume = {105}, year = {2019}, month = {2019 Sep 05}, pages = {573-587}, abstract = {

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{\textquoteright} splice-site (5{\textquoteright}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{\textquoteright}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{\textquoteright}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{\textquoteright}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.

}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2019.07.013}, author = {Bryen, Samantha J and Joshi, Himanshu and Evesson, Frances J and Girard, Cyrille and Ghaoui, Roula and Waddell, Leigh B and Testa, Alison C and Cummings, Beryl and Arbuckle, Susan and Graf, Nicole and Webster, Richard and MacArthur, Daniel G and Laing, Nigel G and Davis, Mark R and L{\"u}hrmann, Reinhard and Cooper, Sandra T} } @article {649, title = {Recessive DES cardio/myopathy without myofibrillar aggregates: intronic splice variant silences one allele leaving only missense L190P-desmin.}, journal = {Eur J Hum Genet}, volume = {27}, year = {2019}, month = {2019 Aug}, pages = {1267-1273}, abstract = {

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 {\textquoteright}tricky{\textquoteright} variants in neuromuscular conditions.

}, issn = {1476-5438}, doi = {10.1038/s41431-019-0393-6}, author = {Riley, Lisa G and Waddell, Leigh B and Ghaoui, Roula and Evesson, Frances J and Cummings, Beryl B and Bryen, Samantha J and Joshi, Himanshu and Wang, Min-Xia and Brammah, Susan and Kritharides, Leonard and Corbett, Alastair and MacArthur, Daniel G and Cooper, Sandra T} }