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DMD pathogenic variants for Duchenne and Becker muscular dystrophy are detectable with high sensitivity by standard clinical exome analyses of genomic DNA. However, up to 7% of DMD mutations are deep intronic and analysis of muscle-derived RNA is an important diagnostic step for patients who have negative genomic testing but abnormal dystrophin expression in muscle. In this study, muscle biopsies were evaluated from 19 patients with clinical features of a dystrophinopathy, but negative clinical DMD mutation analysis. Reverse transcription-polymerase chain reactionor high-throughput RNA sequencingmethods identified 19 mutations with one of three pathogenic pseudoexon types: deep intronic point mutations, deletions or insertions, and translocations. In association with point mutations creating intronic splice acceptor sites, we observed the first examples of DMD pseudo 3'-terminal exon mutations causing high efficiency transcription termination within introns. This connection between splicing and premature transcription termination is reminiscent of U1 snRNP-mediating telescripting in sustaining RNA polymerase II elongation across large genes, such as DMD. We propose a novel classification of three distinct types of mutations identifiable by muscle RNA analysis, each of which differ in potential treatment approaches. Recognition and appropriate characterization may lead to therapies directed toward full-length dystrophin expression for some patients.

The recently discovered neurological disorder NEDAMSS is caused by heterozygous truncations in the transcriptional regulator IRF2BPL. Here, we reprogram patient skin fibroblasts to astrocytes and neurons to study mechanisms of this newly described disease. While full-length IRF2BPL primarily localizes to the nucleus, truncated patient variants sequester the wild-type protein to the cytoplasm and cause aggregation. Moreover, patient astrocytes fail to support neuronal survival in coculture and exhibit aberrant mitochondria and respiratory dysfunction. Treatment with the small molecule copper ATSM (CuATSM) rescues neuronal survival and restores mitochondrial function. Importantly, the in vitro findings are recapitulated in vivo, where co-expression of full-length and truncated IRF2BPL in Drosophila results in cytoplasmic accumulation of full-length IRF2BPL. Moreover, flies harboring heterozygous truncations of the IRF2BPL ortholog (Pits) display progressive motor defects that are ameliorated by CuATSM treatment. Our findings provide insights into mechanisms involved in NEDAMSS and reveal a promising treatment for this severe disorder.

Therapeutic exon skipping as a treatment for Duchenne muscular dystrophy (DMD) has largely concentrated on the delivery of antisense oligomers to treat out-of-frame exon deletions. Here we report o...

Duchenne muscular dystrophy (DMD) is an X-linked progressive disease characterized by loss of dystrophin protein that typically results from truncating mutations in the DMD gene. Current exon-skipping therapies have sought to treat deletion mutations that abolish an open reading frame (ORF) by skipping an adjacent exon, in order to restore an ORF that allows translation of an internally deleted yet partially functional protein, as is seen with many patients with the milder Becker muscular dystrophy (BMD) phenotype. In contrast to that approach, skipping of one copy of a duplicated exon would be expected to result in a full-length transcript and production of a wild-type protein. We have developed an adeno-associated virus (AAV)-based U7snRNA exon-skipping approach directed toward exon 2, duplications of which represent 10% of all DMD duplication mutations. Deletion of exon 2 results in utilization of an exon 5 internal ribosome entry site (IRES) that allows translation beginning in exon 6 of a highly protective dystrophin protein, providing a wide therapeutic window for treatment. Both intramuscular and systemic administration of this vector in the Dup2 mouse model results in robust dystrophin expression and correction of muscle physiologic defects, allowing dose escalation to establish a putative minimal efficacious dose for a human clinical trial.

Facioscapulohumeral muscular dystrophy (FSHD) arises from epigenetic changes that de-repress the DUX4 gene in muscle. The full-length DUX4 protein causes cell death and muscle toxicity, and therefore we hypothesize that FSHD therapies should center on inhibiting full-length DUX4 expression. In this study, we developed a strategy to accomplish DUX4 inhibition using U7-small nuclear RNA (snRNA) antisense expression cassettes (called U7-asDUX4). These non-coding RNAs were designed to inhibit production or maturation of the full-length DUX4 pre-mRNA by masking the DUX4 start codon, splice sites, or polyadenylation signal. In so doing, U7-asDUX4 snRNAs operate similarly to antisense oligonucleotides. However, in contrast to oligonucleotides, which are limited by poor uptake in muscle and a requirement for lifelong repeated dosing, U7-asDUX4 snRNAs can be packaged within myotropic gene therapy vectors and may require only a single administration when delivered to post-mitotic cells in vivo. We tested several U7-asDUX4s that reduced DUX4 expression in vitro and improved DUX4-associated outcomes. Inhibition of DUX4 expression via U7-snRNAs could be a new prospective gene therapy approach for FSHD or be used in combination with other strategies, like RNAi therapy, to maximize DUX4 silencing in individuals with FSHD.

Renewable energy carriers are expected to play a key role in the defossilization of the energy and chemical sector. For renewable methanol synthesis, membrane reactors (MR) have been tested on a laboratory-scale with promising results. However, membrane performance requirements that allow an economic benefit for their large-scale deployment are missing. Therefore, a 1D Python MR model is coupled with an AspenPlus process simulation to conduct a techno-economic assessment with focus on membrane performance. Two synthesis loop configurations are investigated: one where feed and sweep recycle are operated at the same pressure and one where the sweep recycle operates at atmospheric pressure. The results show that both configurations can offer technical benefits, if sufficiently high product separation can be achieved, but that for a compressed sweep recycle no economic benefits are possible. As a consequence, membranes used for methanol synthesis must endure operation at high pressure differences. Furthermore, the results highlight the critical role of the H2 permeance, which should remain below 1 × 10−9 mol m−2 s−1 Pa−1. From an economic standpoint high water permeation has a more beneficial effect than high methanol permeation.

Exon skipping therapies for Duchenne muscular dystrophy that restore an open reading frame can be induced by the use of non-coding U7 small nuclear RNA (U7snRNA) modified by an antisense exon-targeting sequence delivered by an adeno-associated virus (AAV) vector. We have developed an AAV vector (AAV9.U7-ACCA) containing four U7snRNAs targeting the splice donor and acceptor sites of dystrophin exon 2, resulting in highly efficient exclusion of DMD exon 2. We assessed the specificity of splice variation induced by AAV9.U7-ACCA delivery in the Dmd exon 2 duplication (Dup2) mouse model via an unbiased RNA-seq approach. Treatment-related effects on pre-mRNA splicing were quantified using local splicing variation (LSV) analysis. Filtering the transcriptome for differences in treatment-related splicing resulted in only 16 candidate off-target LSVs. Only a single candidate off-target LSV was found in both tissues and occurred at a known variable cassette exon. In contrast, four LSVs represented significant on-target correction of Dmd exon 2 splicing and transcriptome analysis showed correction of known dystrophin-deficient gene dysregulation. We conclude that the absence of off-target splicing induced by treatment with the U7-ACCA vector supports the continued clinical development of this approach.

The uridine-rich 7 (U7) small nuclear RNA (snRNA) is a component of a small nuclear ribonucleoprotein (snRNP) complex. U7 snRNA naturally contains an antisense sequence that identifies histone premessenger RNAs (pre-mRNAs) and is involved in their 3' end processing. By altering this antisense sequence, researchers have turned U7 snRNA into a versatile tool for targeting pre-mRNAs and modifying splicing. Encapsulating a modified U7 snRNA into a viral vector such as adeno-associated virus (also referred as vectorized exon skipping/inclusion, or VES/VEI) enables the delivery of this highly efficacious splicing modulator into a range of cell lines, primary cells, and tissues. In addition, and in contrast to antisense oligonucleotides, viral delivery of U7 snRNA enables long-term expression of antisense sequences in the nucleus as part of a stable snRNP complex. As a result, VES/VEI has emerged as a promising therapeutic platform for treating a large variety of human diseases caused by errors in pre-mRNA splicing or its regulation. Here we provide an overview of U7 snRNA's natural function and its applications in gene therapy.

Exon skipping therapies for Duchenne muscular dystrophy that restore an open reading frame can be induced by the use of noncoding U7 small nuclear RNA (U7snRNA) modified by an antisense exon-targeting sequence delivered by an adeno-associated virus (AAV) vector. We have developed an AAV vector (AAV9.U7-ACCA) containing four U7snRNAs targeting the splice donor and acceptor sites of dystrophin exon 2, resulting in highly efficient exclusion of

Therapeutic exon skipping as a treatment for Duchenne muscular dystrophy (DMD) has largely concentrated on the delivery of antisense oligomers to treat out-of-frame exon deletions. Here we report on the preclinical development of an adeno-associated virus (AAV)-encapsidated viral vector containing four copies of the noncoding U7 small nuclear RNA (U7snRNA), each targeted to either the splice donor or the splice acceptor sites of

Duchenne muscular dystrophy (DMD) is an X-linked progressive disease characterized by loss of dystrophin protein that typically results from truncating mutations in the DMD gene. Current exon-skipping therapies have sought to treat deletion mutations that abolish an open reading frame (ORF) by skipping an adjacent exon, in order to restore an ORF that allows translation of an internally deleted yet partially functional protein, as is seen with many patients with the milder Becker muscular dystrophy (BMD) phenotype. In contrast to that approach, skipping of one copy of a duplicated exon would be expected to result in a full-length transcript and production of a wild-type protein. We have developed an adeno-associated virus (AAV)-based U7snRNA exon-skipping approach directed toward exon 2, duplications of which represent 10% of all DMD duplication mutations. Deletion of exon 2 results in utilization of an exon 5 internal ribosome entry site (IRES) that allows translation beginning in exon 6 of a highly protective dystrophin protein, providing a wide therapeutic window for treatment. Both intramuscular and systemic administration of this vector in the Dup2 mouse model results in robust dystrophin expression and correction of muscle physiologic defects, allowing dose escalation to establish a putative minimal efficacious dose for a human clinical trial., Graphical abstract, Flanigan and colleagues report the results of an intravenous dose-escalation study using an AAV9-encapsidated U7snRNA vector to skip DMD exon 2 and restore dystrophin expression in the Dup2 mouse model of Duchenne muscular dystrophy. The results informed dose considerations for an ongoing clinical trial.

Facioscapulohumeral muscular dystrophy (FSHD) arises from epigenetic changes that de-repress the DUX4 gene in muscle. The full-length DUX4 protein causes cell death and muscle toxicity, and therefore we hypothesize that FSHD therapies should center on inhibiting full-length DUX4 expression. In this study, we developed a strategy to accomplish DUX4 inhibition using U7-small nuclear RNA (snRNA) antisense expression cassettes (called U7-asDUX4). These non-coding RNAs were designed to inhibit production or maturation of the full-length DUX4 pre-mRNA by masking the DUX4 start codon, splice sites, or polyadenylation signal. In so doing, U7-asDUX4 snRNAs operate similarly to antisense oligonucleotides. However, in contrast to oligonucleotides, which are limited by poor uptake in muscle and a requirement for lifelong repeated dosing, U7-asDUX4 snRNAs can be packaged within myotropic gene therapy vectors and may require only a single administration when delivered to post-mitotic cells in vivo. We tested several U7-asDUX4s that reduced DUX4 expression in vitro and improved DUX4-associated outcomes. Inhibition of DUX4 expression via U7-snRNAs could be a new prospective gene therapy approach for FSHD or be used in combination with other strategies, like RNAi therapy, to maximize DUX4 silencing in individuals with FSHD., Graphical Abstract, Treatments for facioscapulohumeral muscular dystrophy (FSHD) are designed to suppress the toxic DUX4 gene that underlies the disorder. This study describes a novel approach to inhibit DUX4 production at the mRNA level by using designed U7-antisense RNA expression cassettes to sterically hinder maturation and translation of DUX4 mRNA.

Background Canine models of Duchenne muscular dystrophy (DMD) are valuable to evaluate therapies because they faithfully reproduce the human disease. Several cases of dystrophinopathies have been described in canines, but the GRMD (Golden Retriever Muscular Dystrophy) model remains the one used in most preclinical studies. Methods We report a new spontaneous dystrophinopathy in a Labrador retriever strain, named LRMD (Labrador Retriever Muscular Dystrophy), for which a colony was established. Fourteen LRMD dogs were followed-up and compared to the GRMD standard. Results The clinical features of the GRMD disease were found in LRMD dogs, and the functional tests provided data roughly overlapping those measured in GRMD dogs, with similar inter-individual heterogeneity. Molecular techniques including RNA-sequencing allowed to map and identify the LRMD causal mutation, consisting in a 2.2-Mb inversion disrupting the DMD gene within its intron 20, and involving TMEM47 gene. In skeletal muscles, the Dp71 isoform was ectopically expressed as a probable consequence of the mutation. We found no evidence of polymorphism in the two LTBP4 and Jagged1 modifier genes that would explain the observed inter-individual variability. Conclusions This study provides a full comparative description of a new spontaneous canine dystrophinopathy, that we demonstrate is phenotypically equivalent to the GRMD model. We report a novel large DNA mutation within the DMD gene and provide evidence that LRMD is a relevant model to pinpoint additional DMD modifier genes.

Background Canine models of Duchenne muscular dystrophy (DMD) are a valuable tool to evaluate potential therapies because they faithfully reproduce the human disease. Several cases of dystrophinopathies have been described in canines, but the Golden Retriever muscular dystrophy (GRMD) model remains the most used in preclinical studies. Here, we report a new spontaneous dystrophinopathy in a Labrador Retriever strain, named Labrador Retriever muscular dystrophy (LRMD). Methods A colony of LRMD dogs was established from spontaneous cases. Fourteen LRMD dogs were followed-up and compared to the GRMD standard using several functional tests. The disease causing mutation was studied by several molecular techniques and identified using RNA-sequencing. Results The main clinical features of the GRMD disease were found in LRMD dogs; the functional tests provided data roughly overlapping with those measured in GRMD dogs, with similar inter-individual heterogeneity. The LRMD causal mutation was shown to be a 2.2-Mb inversion disrupting the DMD gene within intron 20 and involving the TMEM47 gene. In skeletal muscle, the Dp71 isoform was ectopically expressed, probably as a consequence of the mutation. We found no evidence of polymorphism in either of the two described modifier genes LTBP4 and Jagged1. No differences were found in Pitpna mRNA expression levels that would explain the inter-individual variability. Conclusions This study provides a full comparative description of a new spontaneous canine model of dystrophinopathy, found to be phenotypically equivalent to the GRMD model. We report a novel large DNA mutation within the DMD gene and provide evidence that LRMD is a relevant model to pinpoint additional DMD modifier genes.

Dystrophinopathies are diseases caused by mutations in the Duchenne Muscular Dystrophy gene (DMD) encoding the dystrophin protein. Depending on the type of mutation, patients develop either the severe DMD or the milder Becker Muscular Dystrophy. Although substantial effort was made, the pathophysiology and variation in disease severity are still poorly understood. During the last two decades, relentless efforts were made to develop therapeutic strategies. Among these, gene therapy and cell replacement therapy appear very promising. These approaches are based on the replacement and/or repair of the mutated DMD gene or transcript at the molecular level, or at the cellular level via replacement of the damaged muscle cells. While highly successful in animal models, these therapies showed only modest efficacy in human clinical trials. More importantly, variable effects were observed in patients carrying the same mutation, suggesting that several factors (e.g., genetic modifiers, environmental factors) can affect treatment outcomes. In this review, we will describe recent advancements and new approaches of gene and cell therapies for dystrophinopathies that pave the way for a medicine "à la carte".

Background:Exon skipping strategies in Duchenne muscular dystrophy (DMD) have largely been directed toward altering splicing of exons flanking out-of-frame deletions, with the goal of restoring an open mRNA reading frame that leads to production of an internally deleted but partially functional dystrophin protein. Objective:We sought to apply exon skipping to duplication mutations, assuming that the inherently limited efficiency of antisense oligonucleotide-induced exon skipping would more frequently skip a single copy of a duplicated exon, rather than both and result in significant amounts of wild-type DMD mRNA. Methods:We tested this hypothesis in fibroblast cell lines derived from patients with a variety of single or multiple exon duplications that have been modified to allow transdifferentiation into a myogenic lineage. Results:Using a variety of 2’O-methyl antisense oligonucleotides, significant skipping was induced for each duplication leading to a wild-type transcript as a major mRNA product. Conclusions:This study provides another proof of concept for the feasibility of therapeutic skipping in patients carrying exon duplications in order to express wild-type, full-length mRNA, although careful evaluation of the skipping efficiency should be performed as some exons are easier to skip than others. Such a personalized strategy is expected to be highly beneficial for this subset of DMD patients, compared to inducing expression of an internally-deleted dystrophin.

A founder allele in the DMD gene results in a syndrome ranging from minimally symptomatic Becker muscular dystrophy to asymptomatic hyperCKemia via expression of a highly functional N-terminal deleted version of the dystrophin protein (the ΔCH1 isoform). Translation of this protein results from utilization of a recently discovered internal ribosome entry site (IRES) within exon 5. The IRES is not active in the presence of a duplication of exon 2—the most common single-exon duplication—but is active in its absence. We have developed an AAV-encapsidated U7snRNA vector that targets and induces skipping of exon 2, resulting in either expression of a wild-type dystrophin or of the ΔCH1 isoform, either of which is therapeutic.

Exon duplication mutations account for up to 11% of all cases of Duchenne muscular dystrophy (DMD), and a duplication of exon 2 is the most common duplication in patients. For use as a platform for testing of duplication-specific therapies, we developed a mouse model that carries a Dmd exon 2 duplication. By using homologous recombination we duplicated exon 2 within intron 2 at a location consistent with a human duplication hotspot. mRNA analysis confirms the inclusion of a duplicated exon 2 in mouse muscle. Dystrophin expression is essentially absent by immunofluorescent and immunoblot analysis, although some muscle specimens show very low-level trace dystrophin expression. Phenotypically, the mouse shows similarities to mdx, the standard laboratory model of DMD. In skeletal muscle, areas of necrosis and phagocytosis are seen at 3 weeks, with central nucleation prominent by four weeks, recapitulating the "crisis" period in mdx. Marked diaphragm fibrosis is noted by 6 months, and remains unchanged at 12 months. Our results show that the Dup2 mouse is both pathologically (in degree and distribution) and physiologically similar to mdx. As it recapitulates the most common single exon duplication found in DMD patients, this new model will be a useful tool to assess the potential of duplicated exon skipping.

Mutations in the DMD gene result in Duchenne or Becker muscular dystrophy due to absent or altered expression of the dystrophin protein. The more severe Duchenne muscular dystrophy typically presents around ages 2 to 5 with gait disturbance, and historically has led to the loss of ambulation by age 12. It is important for the practicing pediatrician, however, to be aware of other presenting signs, such as delayed motor or cognitive milestones, or elevated serum transaminases. Becker muscular dystrophy is milder, often presenting after age 5, with ambulation frequently preserved past 20 years and sometimes into late decades.

Objective Exon-skipping therapies aim to convert Duchenne muscular dystrophy (DMD) into less severe Becker muscular dystrophy (BMD) by altering pre-mRNA splicing to restore an open reading frame, allowing translation of an internally deleted and partially functional dystrophin protein. The most common single exon deletion—exon 45 (Δ45)—may theoretically be treated by skipping of either flanking exon (44 or 46). We sought to predict the impact of these by assessing the clinical severity in dystrophinopathy patients. Methods Phenotypic data including clinical diagnosis, age at wheelchair use, age at loss of ambulation, and presence of cardiomyopathy were analyzed from 41 dystrophinopathy patients containing equivalent in-frame deletions. Results As expected, deletions of either exons 45 to 47 (Δ45–47) or exons 45 to 48 (Δ45–48) result in BMD in 97% (36 of 37) of subjects. Unexpectedly, deletion of exons 45 to 46 (Δ45–46) is associated with the more severe DMD phenotype in 4 of 4 subjects despite an in-frame transcript. Notably, no patients with a deletion of exons 44 to 45 (Δ44–45) were found within the United Dystrophinopathy Project database, and this mutation has only been reported twice before, which suggests an ascertainment bias attributable to a very mild phenotype. Interpretation The observation that Δ45–46 patients have typical DMD suggests that the conformation of the resultant protein may result in protein instability or altered binding of critical partners. We conclude that in DMD patients with Δ45, skipping of exon 44 and multiexon skipping of exons 46 and 47 (or exons 46–48) are better potential therapies than skipping of exon 46 alone. Ann Neurol 2015 Ann Neurol 2015;77:668–674

Duchenne muscular dystrophy (DMD) is associated with the loss of dystrophin, which plays an important role in myofiber integrity via interactions with β-dystroglycan and other members of the transmembrane dystrophin-associated protein complex. The ZZ domain, a cysteine-rich zinc-finger domain near the dystrophin C-terminus, is implicated in forming a stable interaction between dystrophin and β-dystroglycan, but the mechanism of pathogenesis of ZZ missense mutations has remained unclear because not all such mutations have been shown to alter β-dystroglycan binding in previous experimental systems. We engineered three ZZ mutations (p.Cys3313Phe, p.Asp3335His, and p.Cys3340Tyr) into a short construct similar to the Dp71 dystrophin isoform for in vitro and in vivo studies and delineated their effect on protein expression, folding properties, and binding partners. Our results demonstrate two distinct pathogenic mechanisms for ZZ missense mutations. The cysteine mutations result in diminished or absent subsarcolemmal expression because of protein instability, likely due to misfolding. In contrast, the aspartic acid mutation disrupts binding with β-dystroglycan despite an almost normal expression at the membrane, confirming a role for the ZZ domain in β-dystroglycan binding but surprisingly demonstrating that such binding is not required for subsarcolemmal localization of dystrophin, even in the absence of actin binding domains.

The protein dysferlin is abundantly expressed in skeletal and cardiac muscles, where its main function is membrane repair. Mutations in the dysferlin gene are involved in two autosomal recessive muscular dystrophies: Miyoshi myopathy and limb-girdle muscular dystrophy type 2B. Development of effective therapies remains a great challenge. Strategies to repair the dysferlin gene by skipping mutated exons, using antisense oligonucleotides (AONs), may be suitable only for a subset of mutations, while cell and gene therapy can be extended to all mutations. AON-treated blood-derived CD133+ stem cells isolated from patients with Miyoshi myopathy led to partial dysferlin reconstitution in vitro but failed to express dysferlin after intramuscular transplantation into scid/blAJ dysferlin null mice. We thus extended these experiments producing the full-length dysferlin mediated by a lentiviral vector in blood-derived CD133+ stem cells isolated from the same patients. Transplantation of engineered blood-derived CD133+ stem cells into scid/blAJ mice resulted in sufficient dysferlin expression to correct functional deficits in skeletal muscle membrane repair. Our data suggest for the first time that lentivirus-mediated delivery of full-length dysferlin in stem cells isolated from Miyoshi myopathy patients could represent an alternative therapeutic approach for treatment of dysferlinopathies.

We report for the first time the characterization of disease-causing exonic rearrangements in the large-sized gene encoding dysferlin. A newly developed kit for multiplex ligation-dependent probe amplification analysis of the dysferlin gene was used for a total of 12 samples from patients with suspected diagnosis of primary dysferlinopathy. This analysis and subsequent genomic quantitative real-time PCR evidenced exonic rearrangements in five patients, including four different exonic deletions and one duplication. Altogether, our findings confirm the existence of exonic rearrangements as disease-causing mutations in primary dysferlinopathies.

International audience; Dysferlinopathies are a family of disabling muscular dystrophies with LGMD2B and Miyoshi myopathy as the main phenotypes. They are associated with molecular defects in DYSF, which encodes dysferlin, a key player in sarcolemmal homeostasis. Previous investigations have suggested that exon skipping may be a promising therapy for a subset of patients with dysferlinopathies. Such an approach aims to rescue functional proteins when targeting modular proteins and specific tissues. We sought to evaluate the dysferlin functional recovery following exon 32 skipping in the cells of affected patients. Exon skipping efficacy was characterized at several levels by use of in vitro myotube formation assays and quantitative membrane repair and recovery tests. Data obtained from these assessments confirmed that dysferlin function is rescued by quasi-dysferlin expression in treated patient cells, supporting the case for a therapeutic antisense-based trial in a subset of dysferlin-deficient patients.

Background Duchenne muscular dystrophy (DMD) is a devastating X-linked recessive genetic myopathy. DMD physiopathology is still not fully understood and a prenatal onset is suspected but difficult to address. Methods The bone morphogenetic protein 4 (BMP4) is a critical signaling molecule involved in mesoderm commitment. Human induced pluripotent stem cells (hiPSCs) from DMD and healthy individuals and human embryonic stem cells (hESCs) treated with BMP4 allowed us to model the early steps of myogenesis in normal and DMD contexts. Results Unexpectedly, 72h following BMP4 treatment, a new long DMD transcript was detected in all tested hiPSCs and hESCs, at levels similar to that found in adult skeletal muscle. This novel transcript named “Dp412e” has a specific untranslated first exon which is conserved only in a sub-group of anthropoids including human. The corresponding novel dystrophin protein of 412-kiloDalton (kDa), characterized by an N-terminal-truncated actin-binding domain, was detected in normal BMP4-treated hiPSCs/hESCs and in embryoid bodies. Finally, using a phosphorodiamidate morpholino oligomer (PMO) targeting the DMD exon 53, we demonstrated the feasibility of exon skipping validation with this BMP4-inducible hiPSCs model. Conclusions In this study, the use of hiPSCs to analyze early phases of human development in normal and DMD contexts has led to the discovery of an embryonic 412 kDa dystrophin isoform. Deciphering the regulation process(es) and the function(s) associated to this new isoform can contribute to a better understanding of the DMD physiopathology and potential developmental defects. Moreover, the simple and robust BMP4-inducible model highlighted here, providing large amount of a long DMD transcript and the corresponding protein in only 3 days, is already well-adapted to high-throughput and high-content screening approaches. Therefore, availability of this powerful cell platform can accelerate the development, validation and improvement of DMD genetic therapies. Electronic supplementary material The online version of this article (doi:10.1186/s13395-015-0062-6) contains supplementary material, which is available to authorized users.

We recently identified an internal ribosome entry site (IRES) within exon 5 of the DMD gene. Mutations that truncate the reading frame 5’ of this exon can result in use of the IRES for alternate translational initiation beginning within exon 6 that results in expression of an N-truncated isoform. Despite lacking the calponin homology domain 1 (CH1) of the actin binding domain 1 (ABD1), this isoform is highly functional, as demonstrated by the minimal symptoms in patients who express it. Consistent with genotype-phenotype correlations in DMD patients, the IRES is not active in the presence of exon 2 duplication but is active when exon 2 is deleted. We developed an AAV9.U7snRNA vector to that truncates DMD reading frame by skipping of exon 2, and have shown that in a Duchenne muscular dystrophy (DMD) mouse model carrying a duplication of exon 2 (the Dup2 mouse), postnatal intramuscular (IM) or intravascular (IV) treatment results in functional and pathologic improvement in skeletal muscle. Relevant to efforts to identify and treat DMD patients at an earlier age, we sought here to determine whether earlier gene transfer might slow down or even prevent the development of pathology. Dup2 mice were injected via facial vein at postnatal day 1 (P1) with 1E12 total vector genomes of the AAV9.U7snRNA vector and sacrificed at either 1, 3, 6, or 12 months post-injection for evaluation of exon 2 skipping by RT-PCR, quantification of dystrophin expression, and characterization of histopathology. To model the applicability of this approach beyond exon 2 duplication patients, the same vector was used to treat 6 human patient fibroblast-derived transdifferentiated myoblasts (FibroMyoD cells) harboring various mutations within exons 1 to 4. In the Dup2 mouse, efficient skipping and abundant dystrophin expression were present up to one year following the single AAV injection. Dystrophic pathology was absent at all-time points; at one year, less than 1% of fibers showed central nucleation, in comparison to ~70% in untreated Dup2 mice. Two tests on the ex vivo diaphragm preparations: isometric force (providing assessment of strength), and eccentric contractions (evaluating sarcolemma stability) were performed at 3 and 6 months following P1 injection. Both tests demonstrated little to no difference between treated animals and wild type mice. In all FibroMyoD cultures, abundant exon 2 skipping and dystrophin expression were detected in myotubes at 14 days of culture after treatment. These results suggest that this exon-skipping vector offers a therapeutic approach not only to patients with exon 2 duplications but with all mutations within the first four DMD exons (~6% of patients), an area of the gene largely ignored by the current therapeutic approaches. This work strongly supports the idea that early treatment of these patients will have longstanding and significant benefit resulting in a better outcome.

Most mutations that truncate the reading frame of the DMD gene cause loss of dystrophin expression and lead to Duchenne muscular dystrophy. However, amelioration of disease severity has been shown to result from alternative translation initiation beginning in DMD exon 6 that leads to expression of a highly functional N-truncated dystrophin. Here we demonstrate that this isoform results from usage of an internal ribosome entry site (IRES) within exon 5 that is glucocorticoid inducible. We confirmed IRES activity by both peptide sequencing and ribosome profiling in muscle from individuals with minimal symptoms despite the presence of truncating mutations. We generated a truncated reading frame upstream of the IRES by exon skipping, which led to synthesis of a functional N-truncated isoform in both human subject-derived cell lines and in a new DMD mouse model, where expression of the truncated isoform protected muscle from contraction-induced injury and corrected muscle force to the same level as that observed in control mice. These results support a potential therapeutic approach for patients with mutations within the 5' exons of DMD.

Most mutations that truncate the reading frame of the DMD gene result in loss of dystrophin expression and lead the severe Duchenne muscular dystrophy. However, frame-truncating mutations within the first five exons of DMD result in mild dystrophinopathy with expression of a N-truncated dystrophin. We have recently shown that this is due to activation of an internal ribosome entry site (IRES) within exon 5 resulting in translation from an exon 6 AUG codon.We demonstrated that this IRES is active in patients expressing the N-truncated dystrophin, raising the possibility of the therapeutic use of this isoform. To explore this we developed a novel out-of-frame exon-skipping approach that uses AAV-mediated U7snRNA to efficiently skip exon 2. By injecting this AAV vector into a DMD mouse model carrying a duplication of exon 2 (Dup2), this generates a truncated reading frame, leading to activation of the IRES and synthesis of the N-truncated isoform.We now demonstrate that despite lacking the first half of the canonical actin binding domain 1, this N-truncated protein is highly functional. Intramuscular injection of the AAV1.U7snRNA vector into Dup2 mice results in high levels of expression of the N-truncated isoform by 4 to 6 weeks post-injection, along with complete correction of the physiologic and pathologic features as measured by Evans blue dye uptake, hindlimb grip strength, tibialis anterior specific force, and force correction after eccentric contraction. Preliminary results supports that systemic delivery of AAV9.U7snRNA vector into Dup2 mice induce expression of this functional isoform into all muscle including heart and diaphragm, thereby improving muscle histopathology.Following treatment, a genome-wide normalized RPF-Seq data analysis (Ribosome Protected Fragment) was performed to check if the treatment restored the Haslett gene lists (gene altered in DMD) to a ‘non-dystrophic’ pattern. Our data clearly indicates that the treatment restored the global expression pattern to a more normal pattern. This level of correction to that of control mice supports the idea that this novel therapeutic approach should be beneficial for the 6% of patients with mutations within the first five exons of DMD.

Currently, exon skipping therapies for Duchenne muscular dystrophy (DMD) have been developed for patients with out-of-frame deletions where treatment will lead translation of an internally truncated but partially functional dystrophin protein. In contrast, we are focusing on treating duplications mutations, accounting for around 6% of all mutations, resulting in wild-type transcript and a full-length protein. Modeling the most common single exon duplication we have developed the first duplication mouse containing a duplicated exon 2. We have performed a proof-of-principle study using antisense oligomer (AO)-induced exon 2 skipping using this Dup2 mouse. Intramuscular (TA) injections of exon 2-directed different antisense peptide-morpholino conjugates (PPMO) were performed at either 10 or 20 ug total PPMO (N=6 muscles each) doses. Mice were injected at 8 weeks and sacrificed 1 month later for muscle analysis of DMD mRNA and dystrophin protein expression. Additionally, systemic (tail vein) injections are being conducted of at a dose of 30 ug/kg, at 1 week, 2 week and 1 month timepoints. For the IM studies, a gradient of exon 2 exclusion was seen by RT-PCR at both doses with corresponding high levels of properly localized dystrophin protein by IF and western blot.Analyses of RT-PCR and protein expression are underway for the systemic delivery PPMOs. These data suggest that skipping of a duplicated exon 2 may be a feasible therapeutic approach, particularly because skipping of exon 2 may be associated with an apparently unlimited therapeutic window. Over-skipping - to the exclusion of exon 2 entirely - results in activation of an internal ribosome entry site (IRES) located in exon 5 of dystrophin that allows for cap-independent translation from an alternative initiation site within exon 6. This alternate dystrophin isoform is highly functional despite being N-truncated, consistent with the observation that patients expressing it have minimally symptomatic (or even asymptomatic) Becker muscular dystrophy (BMD), and suggesting a potential route to therapy for any of the approximately 5% of patients with mutations in the 5’ end of the gene.

International audience; no abstract

International audience; Mutations in the dysferlin gene (DYSF) lead to a complete or partial absence of the dysferlin protein in skeletal muscles and are at the origin of dysferlinopathies, a heterogeneous group of rare autosomal recessive inherited neuromuscular disorders. As a step towards a better understanding of the DYSF mutational spectrum, and towards possible inclusion of patients in future therapeutic clinical trials, we set up the Universal Mutation Database for Dysferlin (UMD-DYSF), a Locus-Specific Database developed with the UMD (R) software. The main objective of UMD-DYSF is to provide an updated compilation of mutational data and relevant interactive tools for the analysis of DYSF sequence variants, for diagnostic and research purposes. In particular, specific algorithms can facilitate the interpretation of newly identified intronic, missense- or isosemantic-exonic sequence variants, a problem encountered recurrently during genetic diagnosis in dysferlinopathies. UMD-DYSF v1.0 is freely accessible at www.umd.be/DYSF/. It contains a total of 742 mutational entries corresponding to 266 different disease-causing mutations identified in 558 patients worldwide diagnosed with dysferlinopathy. This article presents for the first time a comprehensive analysis of the dysferlin mutational spectrum based on all compiled DYSF disease-causing mutations reported in the literature to date, and using the main bioinformatics tools offered in UMD-DYSF.

Duchenne Muscular Dystrophy (DMD) is a lethal X-linked disorder caused by truncating mutations in the DMD gene which result in an absence of the dystrophin protein. However, deletion mutations that preserve an open reading frame, lead to an internally truncated functional dystrophin which is associated with the milder Becker Muscular Dystrophy (BMD). This observation as led to exon-skipping therapies in DMD patients to restore the reading frame and generate a BMD phenotype. Our group has recently shown that mutations in the 5 ′ exons of the DMD gene that disrupt the open reading frame (ORF) induce expression of a functional N-truncated dystrophin via IRES-driven translation initiation within exon 6. We have previously shown that the exon 5 IRES can be activated by disruption of the ORF by AAV9. U7snRNA-mediated skipping of exon 2 by intramuscular (IM) or intravascular (IV) injection. We have now extended those studies to address the minimal efficacious dose (MED), a prerequisite for clinical development. To assess dose ranging with IM delivery, TA (tibialis anterior) injections were performed at 5 different doses, ranging from 1.1×10 10 to 1.1×10 12 total vector genomes (vg) in half-log steps ( N =6 TAs per dose). A gradient of exon 2 exclusion was seen by RT-PCR at all doses, but high levels of properly localized dystrophin expression were seen at 3.5×10 11 vg and above. Experiments to determine the correction of TA physiology at this dose are underway. Similarly, dose ranging experiments using IV tail vein injections with 5 doses ( N =3 per dose) ranging from 1×10 12 to 1×10 14 vg/kg are underway, and results of both protein expression and physiology studies will be presented. Our results show that U7snRNA-mediated exon skipping in Dup2 is both titratable and highly efficient. The establishment of a IV MED for this vector will allow planning of IND-enabling GLP toxicology studies.

International audience; Dysferlinopathies are autosomal recessive, progressive muscle dystrophies caused by mutations in DYSF, leading to a loss or a severe reduction of dysferlin, a key protein in sarcolemmal repair. Currently, no etiological treatment is available for patients affected with dysferlinopathy. As for other muscular dystrophies, gene therapy approaches based on recombinant adeno-associated virus (rAAV) vectors are promising options. However, because dysferlin messenger RNA is far above the natural packaging size of rAAV, full-length dysferlin gene transfer would be problematic. In a patient presenting with a late-onset moderate dysferlinopathy, we identified a large homozygous deletion, leading to the production of a natural ``minidysferlin'' protein. Using rAAV-mediated gene transfer into muscle, we demonstrated targeting of the minidysferlin to the muscle membrane and efficient repair of sarcolemmal lesions in a mouse model of dysferlinopathy. Thus, as previously demonstrated in the case of dystrophin, a deletion mutant of the dysferlin gene is also functional, suggesting that dysferlin's structure is modular. This minidysferlin protein could be used as part of a therapeutic strategy for patients affected with dysferlinopathies.

International audience; Dysferlinopathies are autosomal recessive muscular dystrophies caused by DYSF mutations, Which lead to a reduced amount or a complete lack of dysferlin. One step in dysferlinopathies diagnosis consists in Western blot analysis of proteins extracted from Muscle biopsy, or blood monocytes. We have taken advantage of dysferlin expression in monocytes to develop a whole blood flow cytometry (WBFC), using antibodies directed against dysferlin. Six patients were submitted to WBFC analysis and immunofluorescence analysis oil monocytes. Results obtained are correlated to Western blot from monocytes and muscle biopsies. The possible usefulness of this flow cytometry analysis in routine diagnosis is presented. (C) 2009 Elsevier B.V. All rights reserved.

We read with interest but also some surprise, the recent ‘Therapeutic exon skipping for Dysferlinopathies?' article by Aartsma-Rus et al,1 published in the Eur J Hum Genet (advance online publication, 10 February 2010; doi:10.1038/ejhg.2010.4). This report contains some inaccuracies and mistakes, and we do not agree with some of its main contents. Therefore, for the sake of the scientific and patients communities, we consider it essential to point out and discuss some of the results and subsequent conclusions appearing in the ‘results and discussion' section, as well as in figures and tables. Antisense-mediated exon skipping constitutes a relevant therapy for several genetic diseases associated with premature termination codons (PTCs) or frameshift mutations lying in dispensable in frame exons. However, knowledge of the specific targeted gene, mRNA and resulting protein, is, among others, an essential pre-requisite toward designing pertinent exon-skipping strategies. In the report by Aartsma-Rus et al,1 it appears that several of these pre-requisites have been overlooked. Here we intend to discuss and contradict some important assertions and results that appear in both the text and the figures of the article by Aartsma-Rus et al,1 and place our comments in the perspective of a recently published report from our group on the same matter.2

International audience; Mutations in DYSF encoding dysferlin cause primary dysferlinopathies, autosomal recessive diseases that mainly present clinically as Limb Girdle Muscular Dystrophy type 213 and Miyoshi myopathy. More than 350 different sequence variants have been reported in DYSE. Like dystrophin, the size of the dysferlin mRNA is above the limited packaging size of AAV vectors. Alternative strategies to AAV gene transfer in muscle cells must then be addressed for patients. A gene therapy approach for Duchenne muscular dystrophy was recently developed, based on exon-skipping strategy. Numerous sequences are recognized by splicing protein complexes and, when specifically blocked by antisense oligoucleotides (AON), the corresponding exon is skipped. We hypothesized that this approach could be useful for patients affected with dysferlinopathics. To confirm this assumption, exon 32 was selected as a prioritary target for exon skipping strategy. This option was initially driven by the report from Sinnreich and colleagues of a patient with a very mild and late-onset phenotype associated to a natural skipping of exon 32. Three different antisense oligonucleotides were tested in myoblasts generated from control and patient MyoD transduced fibroblasts, either as oligonucleotides or after incorporation into lentiviral vectors. These approaches led to a high efficiency of exon 32 skipping. Therefore, these results seem promising, and could be applied to several other exons in the DYSF gene. Patients carrying mutations in exons whose the in-frame suppression has been proven to have no major consequences on the protein function, might benefit of exon-skipping based gene correction.