Annemieke Aartsma-Rus

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..Although none of the proposed strategies has yet proven to be of therapeutic value in patients, it is reasonable to expect that clinical efficacy will soon be demonstrated for some of the more advanced approaches...

..This allows retrospective analysis of effective and ineffective AONs to obtain guidelines to optimize future AON design...

..Finally, an overview of clinical trials is given and outstanding questions and hurdles are discussed...

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..This suggests that exons may be better AON targets than introns per se, because of their higher GC content, which generally will result in improved AON binding...

..This review will explain the rationale and current state of affairs of these approaches and will then discuss how these gene-derived therapies might also be applicable to other diseases...

..On the basis of only four parameters, we could correctly classify 79% of all AONs as effective or ineffective, suggesting these parameters can be used to more optimally design splice-modulating AONs...

..We also show that DYSF exon skipping seems to be as straightforward as DMD exon skipping, as AONs to induce efficient skipping of four DYSF exons were readily identified...

..This knowledge allows us to optimize therapeutic exon skipping, but also opens up a range of other applications for the exon skipping approach...

..These mutations are in principle ideal targets for this approach since the specific skipping of duplicated exons would generate original, full-length transcripts...

..In this study we provide an update of the mutational variability in the DMD gene, particularly focusing on genotype-phenotype correlations and mutations that appear to be exceptions to the reading-frame rule...

..In this study, we aim to knockdown myostatin by means of exon skipping, a technique which has been successfully applied to reframe the genetic defect of dystrophin gene in DMD patients...

..We aimed at inducing larger multiexon-skipping stretches, such as exons 17-51, exons 42-55, and exons 45-59. However, this appeared complicated and may be dependent on cotranscriptional splicing and the size of the flanking introns...

..The levels of intended multiexon skips are typically low and highly variable, and may be dependent on the order of intron removal. We hypothesized that the splicing order might favor the induction of multiexon 45-55 skipping...

..In fact, we here demonstrate its feasibility in myotubes from a patient with an exon 48-50 deletion. The application of multiexon skipping may provide a more uniform methodology for a larger group of patients with DMD...

..These data highlight the high sequence specificity of this therapy and present the hDMD mouse as a unique model to optimize human-specific exon skipping in vivo...

..Accordingly, these antisense oligoribonucleotides would allow correction of over 50% of deletions and 22% of duplications reported in the Leiden DMD-mutation Database...

..We explored the safety, adverse-event profile, and local dystrophin-restoring effect of a single, intramuscular dose of an antisense oligonucleotide, PRO051, in patients with this disease...

..The use of the same technique allows comparison between different groups working on exon skipping in the mdx mouse model...

..Our results suggest that effective exon-internal AONs primarily act by blocking SR binding sites (which often correspond to open structures) and that ESEfinder may be used to refine AON design for DMD and other genes...

..In vivo studies are mainly performed using 2'-O-methyl phosphorothioate (2OMePS) or morpholino (PMO) AONs. These compounds were never directly compared...

..This makes mdx/utrn +/- mice valuable for testing the benefit of potential therapies on muscle function parameters...

..Together, our results identify a molecular mechanism that explains the cell-type specific aspects of signaling by myostatin and other TGF-β family members...

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..We conclude that this test regime may be suitable for short-term functional evaluation of therapeutic approaches in the mdx mouse...

..c. administration, we selected this patient-convenient delivery method for future clinical study protocols...

..We propose that different chemistries should be further developed in parallel in order to hasten the transfer of the exon skipping therapy to the clinic...

..Further research is needed to determine the functionality of different in-frame dystrophins and a number of hurdles has to be overcome before this approach can be applied clinically...

..These results document important progress towards a clinically applicable, small-molecule based therapy...

..Antisense-mediated reading frame restoration is the most promising therapy for Duchenne muscular dystrophy. Data from a first clinical trial are encouraging and additional trials are ongoing or are expected to be initiated soon...

..We demonstrated that T cells can be highly efficiently transduced with AONs and are amenable to antisense-mediated exon skipping. Furthermore, we showed that exon skipping (partly) corrects the IL-12Rbeta1 deficiency in patients' cells...

..Our results also indicate that long-term subcutaneous treatment in dystrophic mouse models with these AONs is safe and beneficial.Molecular Therapy-Nucleic Acids (2012) 1, e44; doi:10.1038/mtna.2012.38; published online 4 September 2012...

..Based on these findings, we conclude that while even dystrophin levels below 15% can improve pathology and performance, levels of >20% are needed to fully protect muscle fibers from exercise-induced damage...

..Effective approaches include restoring open reading frames, influencing alternative splicing, and inducing exon inclusion to generate beneficial proteins and remove deleterious ones...

..Therefore magnetic resonance imaging is an adequate technique to determine heart function in dystrophinopathy mouse models and can be used to assess the effect of potential therapies...

..For each application, examples are discussed and the current state of the art is described...

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..Molecular Therapy - Nucleic Acids (2013) 2, e66; doi:10.1038/mtna.2012.58; published online 22 January 2013...

..Overall these results show that the use of prednisone forms no barrier to participation in clinical trials with AONs...

..We conclude that next generation sequencing can significantly empower phage display screenings by accelerating the finding of specific binders and restraining the number of false positive hits...

..In conclusion, our results suggest that repression of BMP signaling may constitute an attractive adjunctive therapy for DMD patients...

..Years of research have come to fruition during the past 18 months with publications on clinical trials for several gene therapy approaches for Duchenne muscular dystrophy. This review covers the present status of these approaches...

..EXPERT OPINION: A lot of progress has been made in the development of antisense-mediated approaches during recent years and they may become clinically applicable in the near future...

..A final application, which is as yet under-explored but has major promise, is the functional in vivo study of protein isoforms by modulating their relative levels by AON-based skipping of alternative exons...

..This nuclear receptor coregulator exists in two splice variants (SRC-1a and SRC-1e) which display differential distribution and opposing activities in the brain, and whose mRNAs differ in a single SRC-1e specific exon...