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1.  Dystrophin quantification and clinical correlations in Becker muscular dystrophy: implications for clinical trials 
Brain  2011;134(12):3544-3556.
Duchenne muscular dystrophy is caused by mutations in the DMD gene that disrupt the open reading frame and prevent the full translation of its protein product, dystrophin. Restoration of the open reading frame and dystrophin production can be achieved by exon skipping using antisense oligonucleotides targeted to splicing elements. This approach aims to transform the Duchenne muscular dystrophy phenotype to that of the milder disorder, Becker muscular dystrophy, typically caused by in-frame dystrophin deletions that allow the production of an internally deleted but partially functional dystrophin. There is ongoing debate regarding the functional properties of the different internally deleted dystrophins produced by exon skipping for different mutations; more insight would be valuable to improve and better predict the outcome of exon skipping clinical trials. To this end, we have characterized the clinical phenotype of 17 patients with Becker muscular dystrophy harbouring in-frame deletions relevant to on-going or planned exon skipping clinical trials for Duchenne muscular dystrophy and correlated it to the levels of dystrophin, and dystrophin-associated protein expression. The cohort of 17 patients, selected exclusively on the basis of their genotype, included 4 asymptomatic, 12 mild and 1 severe patient. All patients had dystrophin levels of >40% of control and significantly higher dystrophin (P = 0.013), β-dystroglycan (P = 0.025) and neuronal nitric oxide synthase (P = 0.034) expression was observed in asymptomatic individuals versus symptomatic patients with Becker muscular dystrophy. Furthermore, grouping the patients by deletion, patients with Becker muscular dystrophy with deletions with an end-point of exon 51 (the skipping of which could rescue the largest group of Duchenne muscular dystrophy deletions) showed significantly higher dystrophin levels (P = 0.034) than those with deletions ending with exon 53. This is the first quantitative study on both dystrophin and dystrophin-associated protein expression in patients with Becker muscular dystrophy with deletions relevant for on-going exon skipping trials in Duchenne muscular dystrophy. Taken together, our results indicate that all varieties of internally deleted dystrophin assessed in this study have the functional capability to provide a substantial clinical benefit to patients with Duchenne muscular dystrophy.
doi:10.1093/brain/awr291
PMCID: PMC3235564  PMID: 22102647
Becker muscular dystrophy; Duchenne muscular dystrophy; nNOS; dystrophin-associated glycoprotein complex; therapy
2.  The Polyproline Site in Hinge 2 Influences the Functional Capacity of Truncated Dystrophins 
PLoS Genetics  2010;6(5):e1000958.
Mutations in dystrophin can lead to Duchenne muscular dystrophy or the more mild form of the disease, Becker muscular dystrophy. The hinge 3 region in the rod domain of dystrophin is particularly prone to deletion mutations. In-frame deletions of hinge 3 are predicted to lead to BMD, however the severity of disease can vary considerably. Here we performed extensive structure-function analyses of truncated dystrophins with modified hinges and spectrin-like repeats in mdx mice. We found that the polyproline site in hinge 2 profoundly influences the functional capacity of a microdystrophinΔR4-R23/ΔCT with a large deletion in the hinge 3 region. Inclusion of polyproline in microdystrophinΔR4-R23/ΔCT led to small myofibers (12% smaller than wild-type), Achilles myotendinous disruption, ringed fibers, and aberrant neuromuscular junctions in the mdx gastrocnemius muscles. Replacing hinge 2 of microdystrophinΔR4-R23/ΔCT with hinge 3 significantly improved the functional capacity to prevent muscle degeneration, increase muscle fiber area, and maintain the junctions. We conclude that the rigid α-helical structure of the polyproline site significantly impairs the functional capacity of truncated dystrophins to maintain appropriate connections between the cytoskeleton and extracellular matrix.
Author Summary
Dystrophin functions like a large molecular spring between the muscle cytoskeleton and the extracellular matrix in order to protect the membrane from contraction-induced injury. Mutations in dystrophin can lead to a severe muscle wasting disease called Duchenne muscular dystrophy (DMD) in young boys. DMD patients are typically wheelchair bound by 9–13 years of age and die at approximately 30 years. There are also mutations within the dystrophin gene that lead to internal truncations of non-essential regions, such as the internal rod domain that leads to a mild form of the disease called Becker Muscular Dystrophy. However, these internal truncations frequently occur at a “hot spot” within the rod domain where the resulting disease severity is difficult to predict. Here we found that consecutive proline residues, that function much like a molecular ruler, can dramatically influence the function of these internally truncated dystrophins within skeletal muscles. Using this information, we designed a dystrophin mini-gene that can accommodate the limited packaging size of recombinant adeno-associated virus. This virus can deliver the dystrophin mini-gene to most muscles throughout a dystrophic mouse to prevent muscle degeneration and partially restore muscle function.
doi:10.1371/journal.pgen.1000958
PMCID: PMC2873924  PMID: 20502633
3.  Functional Substitution by TAT-Utrophin in Dystrophin-Deficient Mice 
PLoS Medicine  2009;6(5):e1000083.
James Ervasti and colleagues show that injection of a truncated form of utrophin transduced all tissues examined, integrated with members of the dystrophin complex, and reduced serum levels of creatine kinase in a mouse model of muscular dystrophy.
Background
The loss of dystrophin compromises muscle cell membrane stability and causes Duchenne muscular dystrophy and/or various forms of cardiomyopathy. Increased expression of the dystrophin homolog utrophin by gene delivery or pharmacologic up-regulation has been demonstrated to restore membrane integrity and improve the phenotype in the dystrophin-deficient mdx mouse. However, the lack of a viable therapy in humans predicates the need to explore alternative methods to combat dystrophin deficiency. We investigated whether systemic administration of recombinant full-length utrophin (Utr) or ΔR4-21 “micro” utrophin (μUtr) protein modified with the cell-penetrating TAT protein transduction domain could attenuate the phenotype of mdx mice.
Methods and Findings
Recombinant TAT-Utr and TAT-μUtr proteins were expressed using the baculovirus system and purified using FLAG-affinity chromatography. Age-matched mdx mice received six twice-weekly intraperitoneal injections of either recombinant protein or PBS. Three days after the final injection, mice were analyzed for several phenotypic parameters of dystrophin deficiency. Injected TAT-μUtr transduced all tissues examined, integrated with members of the dystrophin complex, reduced serum levels of creatine kinase (11,290±920 U versus 5,950±1,120 U; PBS versus TAT), the prevalence of muscle degeneration/regeneration (54%±5% versus 37%±4% of centrally nucleated fibers; PBS versus TAT), the susceptibility to eccentric contraction-induced force drop (72%±5% versus 40%±8% drop; PBS versus TAT), and increased specific force production (9.7±1.1 N/cm2 versus 12.8±0.9 N/cm2; PBS versus TAT).
Conclusions
These results are, to our knowledge, the first to establish the efficacy and feasibility of TAT-utrophin-based constructs as a novel direct protein-replacement therapy for the treatment of skeletal and cardiac muscle diseases caused by loss of dystrophin.
Editors' Summary
Background
Muscular dystrophies are genetic (inherited) diseases in which the body's muscles gradually weaken and degenerate. The commonest and most severe muscular dystrophy—Duchenne muscular dystrophy—affects 1 in 3,500 boys (girls can be carriers of the disease but rarely have any symptoms). At birth, these boys seem normal but the symptoms of their disease begin to appear in early childhood. Affected children may initially have difficulty walking or find it to hard to sit or stand independently. As they age, their muscle strength progressively declines and most affected boys are confined to a wheelchair by the time they are 12 years old. The muscles involved in breathing also weaken and the heart muscle becomes enlarged. Few boys with Duchenne muscular dystrophy live beyond their early 20 s, usually dying from breathing or heart problems. At present there is no cure for Duchenne muscular dystrophy. However, physical therapy and treatment with steroids can prolong the ability of patients to walk, and assisted ventilation can help with their breathing.
Why Was This Study Done?
In all muscular dystrophies, one of the proteins needed to build and maintain healthy muscles is missing or nonfunctional because of a genetic change (mutation). In Duchenne muscular dystrophy the mutation is in dystrophin, a protein that is involved in the formation of the dystrophin–glycoprotein complex. This complex normally sits in the membranes that surround muscle fibers and protects these membranes from damage during muscle contraction. Consequently, in Duchenne muscular dystrophy, the muscle fiber membranes become damaged and eventually the muscle fibers die. Thus, if functional dystrophin could be introduced into the muscles of patients with Duchenne muscular dystrophy, it might be possible to reduce their symptoms and prolong their lives. Indeed, the effects of dystrophin deficiency in the dystrophin-deficient mdx mouse can be reduced by the introduction of an artificial gene that expresses dystrophin or the closely related protein utrophin. Unfortunately, this gene therapy approach has not yet been effectively demonstrated in humans. In this study, therefore, the researchers investigate whether utrophin protein can be introduced directly into dystrophin-deficient mouse muscles by exposing the muscle cells to utrophin fused to the protein transduction domain of the HIV-1 TAT protein. Most proteins will not cross cell membranes, but proteins fused to this cell-penetrating domain readily enter many cell types, including muscle cells.
What Did the Researchers Do and Find?
The researchers injected full-length utrophin fused to the TAT protein transduction domain (TAT-Utr) and a short, “micro” version of utrophin fused to the same domain (TAT-μUtr) into the abdomens of mdx mice and looked to see where the proteins ended up. After two injections, both proteins were present in a wide range of tissues and organs, including several types of muscle. However, the levels of TAT-Utr were much lower than those of TAT-μUtr. Next, the researchers injected another group of mdx mice with TAT-μUtr six times over three weeks. Again, TAT-μUtr was present in all the tissues that the researchers examined. Furthermore, μUtr–glycoprotein complexes formed in the TAT-μUtr injected mdx mice and the membrane integrity and overall health of the dystrophin-deficient muscles of the mdx mice improved compared to mdx mice treated with saline. Finally, the researchers report, TAT-μUtr injections greatly improved the contractile performance of the muscles of the mdx mice.
What Do These Findings Mean?
These findings provide the first demonstration that injection of TAT-utrophin protein fusions may provide a way to treat muscular dystrophies caused by the loss of dystrophin. However, although this direct protein-replacement therapy looks hopeful, approaches that work in animals do not necessarily work in people. In particular, for this approach to work in patients with muscular dystrophy, it would be necessary to give frequent, high-dose injections of the TAT-μUtr fusion protein, a process that could eventually trigger a deleterious immune response. Nevertheless, the researchers suggest that by combining this novel approach with other approaches that also increase utrophin expression, it might be possible to prevent or delay the development of the symptoms of Duchenne muscular dystrophy.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000085.
The US National Institute of Neurological Disorders and Stroke provides information on muscular dystrophy and ongoing research into possible treatments (in English and Spanish)
The US National Human Genome Research Institute also provides basic information on Duchenne muscular dystrophy and links to additional resources
The UK National Health Service Choices Web site has pages for patients and caregivers on muscular dystrophy
The Nemours Foundation provides information about muscular dystrophy for parents, children, and teenagers
For links to further resources on muscular dystrophy, see also MedlinePlus
doi:10.1371/journal.pmed.1000083
PMCID: PMC2680620  PMID: 19478831
4.  Local restoration of dystrophin expression with the morpholino oligomer AVI-4658 in Duchenne muscular dystrophy: a single-blind, placebo-controlled, dose-escalation, proof-of-concept study 
Lancet Neurology  2009;8(10):918-928.
Summary
Background
Mutations that disrupt the open reading frame and prevent full translation of DMD, the gene that encodes dystrophin, underlie the fatal X-linked disease Duchenne muscular dystrophy. Oligonucleotides targeted to splicing elements (splice switching oligonucleotides) in DMD pre-mRNA can lead to exon skipping, restoration of the open reading frame, and the production of functional dystrophin in vitro and in vivo, which could benefit patients with this disorder.
Methods
We did a single-blind, placebo-controlled, dose-escalation study in patients with DMD recruited nationally, to assess the safety and biochemical efficacy of an intramuscular morpholino splice-switching oligonucleotide (AVI-4658) that skips exon 51 in dystrophin mRNA. Seven patients with Duchenne muscular dystrophy with deletions in the open reading frame of DMD that are responsive to exon 51 skipping were selected on the basis of the preservation of their extensor digitorum brevis (EDB) muscle seen on MRI and the response of cultured fibroblasts from a skin biopsy to AVI-4658. AVI-4658 was injected into the EDB muscle; the contralateral muscle received saline. Muscles were biopsied between 3 and 4 weeks after injection. The primary endpoint was the safety of AVI-4658 and the secondary endpoint was its biochemical efficacy. This trial is registered, number NCT00159250.
Findings
Two patients received 0·09 mg AVI-4658 in 900 μL (0·9%) saline and five patients received 0·9 mg AVI-4658 in 900 μL saline. No adverse events related to AVI-4658 administration were reported. Intramuscular injection of the higher-dose of AVI-4658 resulted in increased dystrophin expression in all treated EDB muscles, although the results of the immunostaining of EDB-treated muscle for dystrophin were not uniform. In the areas of the immunostained sections that were adjacent to the needle track through which AVI-4658 was given, 44–79% of myofibres had increased expression of dystrophin. In randomly chosen sections of treated EDB muscles, the mean intensity of dystrophin staining ranged from 22% to 32% of the mean intensity of dystrophin in healthy control muscles (mean 26·4%), and the mean intensity was 17% (range 11–21%) greater than the intensity in the contralateral saline-treated muscle (one-sample paired t test p=0·002). In the dystrophin-positive fibres, the intensity of dystrophin staining was up to 42% of that in healthy muscle. We showed expression of dystrophin at the expected molecular weight in the AVI-4658-treated muscle by immunoblot.
Interpretation
Intramuscular AVI-4658 was safe and induced the expression of dystrophin locally within treated muscles. This proof-of-concept study has led to an ongoing systemic clinical trial of AVI-4658 in patients with DMD.
Funding
UK Department of Health.
doi:10.1016/S1474-4422(09)70211-X
PMCID: PMC2755039  PMID: 19713152
5.  A Duchenne Muscular Dystrophy Gene Hot Spot Mutation in Dystrophin-Deficient Cavalier King Charles Spaniels Is Amenable to Exon 51 Skipping 
PLoS ONE  2010;5(1):e8647.
Background
Duchenne muscular dystrophy (DMD), which afflicts 1 in 3500 boys, is one of the most common genetic disorders of children. This fatal degenerative condition is caused by an absence or deficiency of dystrophin in striated muscle. Most affected patients have inherited or spontaneous deletions in the dystrophin gene that disrupt the reading frame resulting in unstable truncated products. For these patients, restoration of the reading frame via antisense oligonucleotide-mediated exon skipping is a promising therapeutic approach. The major DMD deletion “hot spot” is found between exons 45 and 53, and skipping exon 51 in particular is predicted to ameliorate the dystrophic phenotype in the greatest number of patients. Currently the mdx mouse is the most widely used animal model of DMD, although its mild phenotype limits its suitability in clinical trials. The Golden Retriever muscular dystrophy (GRMD) model has a severe phenotype, but due to its large size, is expensive to use. Both these models have mutations in regions of the dystrophin gene distant from the commonly mutated DMD “hot spot”.
Methodology/Principal Findings
Here we describe the severe phenotype, histopathological findings, and molecular analysis of Cavalier King Charles Spaniels with dystrophin-deficient muscular dystrophy (CKCS-MD). The dogs harbour a missense mutation in the 5′ donor splice site of exon 50 that results in deletion of exon 50 in mRNA transcripts and a predicted premature truncation of the translated protein. Antisense oligonucleotide-mediated skipping of exon 51 in cultured myoblasts from an affected dog restored the reading frame and protein expression.
Conclusions/Significance
Given the small size of the breed, the amiable temperament and the nature of the mutation, we propose that CKCS-MD is a valuable new model for clinical trials of antisense oligonucleotide-induced exon skipping and other therapeutic approaches for DMD.
doi:10.1371/journal.pone.0008647
PMCID: PMC2800183  PMID: 20072625
6.  Targeted Exon Skipping to Address “Leaky” Mutations in the Dystrophin Gene 
Protein-truncating mutations in the dystrophin gene lead to the progressive muscle wasting disorder Duchenne muscular dystrophy, whereas in-frame deletions typically manifest as the milder allelic condition, Becker muscular dystrophy. Antisense oligomer-induced exon skipping can modify dystrophin gene expression so that a disease-associated dystrophin pre-mRNA is processed into a Becker muscular dystrophy-like mature transcript. Despite genomic deletions that may encompass hundreds of kilobases of the gene, some dystrophin mutations appear “leaky”, and low levels of high molecular weight, and presumably semi-functional, dystrophin are produced. A likely causative mechanism is endogenous exon skipping, and Duchenne individuals with higher baseline levels of dystrophin may respond more efficiently to the administration of splice-switching antisense oligomers. We optimized excision of exons 8 and 9 in normal human myoblasts, and evaluated several oligomers in cells from eight Duchenne muscular dystrophy patients with deletions in a known “leaky” region of the dystrophin gene. Inter-patient variation in response to antisense oligomer induced skipping in vitro appeared minimal. We describe oligomers targeting exon 8, that unequivocally increase dystrophin above baseline in vitro, and propose that patients with leaky mutations are ideally suited for participation in antisense oligomer mediated splice-switching clinical studies.
doi:10.1038/mtna.2012.40
PMCID: PMC3499695  PMID: 23344648
antisense oligomers; Duchenne muscular dystrophy; exon skipping; personalized genetic therapy; splice-switching
7.  Splicing analysis disclosed a determinant single nucleotide for exon skipping caused by a novel intraexonic four‐nucleotide deletion in the dystrophin gene 
Journal of Medical Genetics  2006;43(12):924-930.
Background
Mutations in exonic splicing enhancer sequences are known to cause splicing errors. Although exonic splicing enhancers have been identified as a stretch of purine‐rich sequences, it has been difficult to precisely pinpoint the determinant nucleotides in these sequences. This article reports that a 4‐bp deletion in exon 38 of the dystrophin gene induced complete exon 38 skipping in vivo. Moreover, the third nucleotide of the deletion was shown to be determinant for the exonic splicing enhancer activity in in vivo splicing analysis of hybrid minigenes encoding mutant exons.
Method
Genomic DNA analysis of a 2‐year‐old boy with a raised level of serum creatine kinase yielded a 4‐bp deletion 11 bp upstream of the 3′ end of exon 38 of the dystrophin gene (c. 5434–5437del TTCA), disrupting a predicted SC35‐binding site.
Result
Interestingly, his dystrophin mRNA was shown to completely lack exon 38 (exon 38− transcript). As the exon 38− transcript coded for a truncated dystrophin protein, this exon skipping was determined to be a modifying factor of his phenotype. In an in vivo splicing assay, a hybrid minigene encoding exon 38 with the 4‐bp deletion was shown to induce complete exon 38 skipping, confirming the deleted region as a splicing enhancer sequence. Site‐directed mutagenesis of the deleted sequence showed that the complete exon 38 skipping was caused by mutation of the third nucleotide position of the deletion (C5436), whereas mutations at the other three nucleotide positions induced partial exon skipping.
Conclusion
Our results underline the potential of understanding the regulation of exonic splicing enhancer sequences and exon skipping therapy for treatment of Duchenne's muscular dystrophy.
doi:10.1136/jmg.2006.042317
PMCID: PMC2563197  PMID: 16738009
8.  Chemical treatment enhances skipping of a mutated exon in the dystrophin gene 
Nature Communications  2011;2:308-.
Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by a loss of the dystrophin protein. Control of dystrophin mRNA splicing to convert severe DMD to a milder phenotype is attracting much attention. Here we report a dystrophinopathy patient who has a point mutation in exon 31 of the dystrophin gene. Although the mutation generates a stop codon, a small amount of internally deleted, but functional, dystrophin protein is produced in the patient cells. An analysis of the mRNA reveals that the mutation promotes exon skipping and restores the open reading frame of dystrophin. Presumably, the mutation disrupts an exonic splicing enhancer and creates an exonic splicing silencer. Therefore, we searched for small chemicals that enhance exon skipping, and found that TG003 promotes the skipping of exon 31 in the endogenous dystrophin gene in a dose-dependent manner and increases the production of the dystrophin protein in the patient's cells.
Duchenne muscular dystrophy is caused by a loss of the dystrophin gene, and control of dystrophin mRNA splicing could aid treatment of the disease. Nishida et al. show that a small molecule promotes skipping of exon 31 and increases production of a functional dystrophin protein in a patient.
doi:10.1038/ncomms1306
PMCID: PMC3113229  PMID: 21556062
9.  Investigation of a female manifesting Becker muscular dystrophy. 
Journal of Medical Genetics  1992;29(8):578-582.
Females manifesting Becker muscular dystrophy (BMD) are even more rarely observed than for the allelic condition Duchenne muscular dystrophy. The male proband has typical BMD with greatly raised CK activity and a myopathic muscle biopsy. His mother experienced walking difficulties from 35 years of age and has a myopathy with marked calf hypertrophy, a raised CK, and a myopathic muscle biopsy. Dystrophin analysis was undertaken on both the proband and his mother. Immunoblotting showed a protein of normal size but of reduced abundance in both. Immunocytochemical analysis in the proband indicated that the majority of the fibres showed weak dystrophin labelling and in his mother both dystrophin positive and dystrophin negative fibres were present. Non-random X inactivation at locus DXS255, was observed in DNA isolated from peripheral lymphocytes of the mother. Neither extended multiplex PCR performed on DNA from the proband nor analysis of lymphocyte derived mRNA showed a structural alteration in the dystrophin gene suggesting that an unusual mutation was responsible for BMD in this family.
Images
PMCID: PMC1016067  PMID: 1518025
10.  Assessment of the structural and functional impact of in-frame mutations of the DMD gene, using the tools included in the eDystrophin online database 
Background
Dystrophin is a large essential protein of skeletal and heart muscle. It is a filamentous scaffolding protein with numerous binding domains. Mutations in the DMD gene, which encodes dystrophin, mostly result in the deletion of one or several exons and cause Duchenne (DMD) and Becker (BMD) muscular dystrophies. The most common DMD mutations are frameshift mutations resulting in an absence of dystrophin from tissues. In-frame DMD mutations are less frequent and result in a protein with partial wild-type dystrophin function. The aim of this study was to highlight structural and functional modifications of dystrophin caused by in-frame mutations.
Methods and results
We developed a dedicated database for dystrophin, the eDystrophin database. It contains 209 different non frame-shifting mutations found in 945 patients from a French cohort and previous studies. Bioinformatics tools provide models of the three-dimensional structure of the protein at deletion sites, making it possible to determine whether the mutated protein retains the typical filamentous structure of dystrophin. An analysis of the structure of mutated dystrophin molecules showed that hybrid repeats were reconstituted at the deletion site in some cases. These hybrid repeats harbored the typical triple coiled-coil structure of native repeats, which may be correlated with better function in muscle cells.
Conclusion
This new database focuses on the dystrophin protein and its modification due to in-frame deletions in BMD patients. The observation of hybrid repeat reconstitution in some cases provides insight into phenotype-genotype correlations in dystrophin diseases and possible strategies for gene therapy. The eDystrophin database is freely available: http://edystrophin.genouest.org/.
doi:10.1186/1750-1172-7-45
PMCID: PMC3748829  PMID: 22776072
Dystrophin; DMD gene mutations; Spectrin-like repeats; Duchenne muscular dystrophy; Becker muscular dystrophy; Phenotype-genotype correlation
11.  Dystromirs as Serum Biomarkers for Monitoring the Disease Severity in Duchenne Muscular Dystrophy 
PLoS ONE  2013;8(11):e80263.
Duchenne muscular Dystrophy (DMD) is an inherited disease caused by mutations in the dystrophin gene that disrupt the open reading frame, while in frame mutations result in Becker muscular dystrophy (BMD). Ullrich congenital muscular dystrophy (UCMD) is due to mutations affecting collagen VI genes. Specific muscle miRNAs (dystromirs) are potential non-invasive biomarkers for monitoring the outcome of therapeutic interventions and disease progression. We quantified miR-1, miR-133a,b, miR-206 and miR-31 in serum from patients with DMD, BMD, UCMD and healthy controls. MiR-1, miR-133a,b and miR-206 were upregulated in DMD, but unchanged in UCMD compared to controls. Milder DMD patients had higher levels of dystromirs than more severely affected patients. Patients with low forced vital capacity (FVC) values, indicating respiratory muscle weakness, had low levels of serum miR-1 and miR-133b. There was no significant difference in the level of the dystromirs in BMD compared to controls.
We also assessed the effect of dystrophin restoration on the expression of the five dystromirs in serum of DMD patients treated systemically for 12 weeks with antisense oligomer eteplirsen that induces skipping of exon 51 in the dystrophin gene. The dystromirs were also analysed in muscle biopsies of DMD patients included in a single dose intramuscular eteplirsen clinical trial. Our analysis detected a trend towards normalization of these miRNA between the pre- and post-treatment samples of the systemic trial, which however failed to reach statistical significance. This could possibly be due to the small number of patients and the short duration of these clinical trials.
Although longer term studies are needed to clarify the relationship between dystrophin restoration following therapeutic intervention and the level of circulating miRNAs, our results indicate that miR-1 and miR-133 can be considered as exploratory biomarkers for monitoring the progression of muscle weakness and indirectly the remaining muscle mass in DMD.
doi:10.1371/journal.pone.0080263
PMCID: PMC3840009  PMID: 24282529
12.  Targeted Exon Skipping to Correct Exon Duplications in the Dystrophin Gene 
Duchenne muscular dystrophy is a severe muscle-wasting disease caused by mutations in the dystrophin gene that ablate functional protein expression. Although exonic deletions are the most common Duchenne muscular dystrophy lesion, duplications account for 10–15% of reported disease-causing mutations, and exon 2 is the most commonly duplicated exon. Here, we describe the in vitro evaluation of phosphorodiamidate morpholino oligomers coupled to a cell-penetrating peptide and 2′-O-methyl phosphorothioate oligonucleotides, using three distinct strategies to reframe the dystrophin transcript in patient cells carrying an exon 2 duplication. Differences in exon-skipping efficiencies in vitro were observed between oligomer analogues of the same sequence, with the phosphorodiamidate morpholino oligomer coupled to a cell-penetrating peptide proving the most effective. Differences in exon 2 excision efficiency between normal and exon 2 duplication cells, were apparent, indicating that exon context influences oligomer-induced splice switching. Skipping of a single copy of exon 2 was induced in the cells carrying an exon 2 duplication, the simplest strategy to restore the reading frame and generate a normal dystrophin transcript. In contrast, multiexon skipping of exons 2–7 to generate a Becker muscular dystrophy-like dystrophin transcript was more challenging and could only be induced efficiently with the phosphorodiamidate morpholino oligomer chemistry.
doi:10.1038/mtna.2014.8
PMCID: PMC3982197  PMID: 24643206
antisense oligomers; Duchenne muscular dystrophy; duplication mutations; dystrophin; exon skipping
13.  Optimizing exon skipping therapies for DMD 
Acta Myologica  2007;26(3):179-184.
Summary
Exon skipping is one of the more promising therapeutic options for Duchenne Muscular Dystrophy (DMD). The idea is to use antisense oligonucleotides to splice out selected exons from the pre-mRNA, at or next to the mutation site, so as to generate a translatable transcript from the mutant dystrophin gene. In principle, the majority of DMD mutations can be rescued by targeting selected exons. Recent developments of antisense oligonucleotides (AOs) such as 2`O-methylated antisense oligonucleotides (2OMeAOs) or phosphorodiamidate morpholino oligomers (morpholinos, PMOs) have made it possible to restore dystrophin expression body-wide in dystrophic mice and dystrophic dogs by single or multi-exon skipping with no obvious side-effect. Since such treatment would, in many cases, require bespoke design of AOs, it is important to demonstrate treatment of a variety of mutations in dystrophic animals. In-frame deletion patterns usually result in a mix of Duchenne and milder Becker Muscular Dystrophy (BMD), but the ratio of Duchenne to Becker varies between patterns, and this provides useful information for selection of the exons that might most profitably be targeted. This review summarizes recent progress in exon skipping therapy and discusses future strategies.
PMCID: PMC2949311  PMID: 18646569
Duchenne/Becker muscular dystrophy; dystrophin; revertant fibers; morpholinos
14.  Exon skipping and dystrophin restoration in patients with Duchenne muscular dystrophy after systemic phosphorodiamidate morpholino oligomer treatment: an open-label, phase 2, dose-escalation study 
Lancet  2011;378(9791):595-605.
Summary
Background
We report clinical safety and biochemical efficacy from a dose-ranging study of intravenously administered AVI-4658 phosphorodiamidate morpholino oligomer (PMO) in patients with Duchenne muscular dystrophy.
Method
We undertook an open-label, phase 2, dose-escalation study (0·5, 1·0, 2·0, 4·0, 10·0, and 20·0 mg/kg bodyweight) in ambulant patients with Duchenne muscular dystrophy aged 5–15 years with amenable deletions in DMD. Participants had a muscle biopsy before starting treatment and after 12 weekly intravenous infusions of AVI-4658. The primary study objective was to assess safety and tolerability of AVI-4658. The secondary objectives were pharmacokinetic properties and the ability of AVI-4658 to induce exon 51 skipping and dystrophin restoration by RT-PCR, immunohistochemistry, and immunoblotting. The study is registered, number NCT00844597.
Findings
19 patients took part in the study. AVI-4658 was well tolerated with no drug-related serious adverse events. AVI-4658 induced exon 51 skipping in all cohorts and new dystrophin protein expression in a significant dose-dependent (p=0·0203), but variable, manner in boys from cohort 3 (dose 2 mg/kg) onwards. Seven patients responded to treatment, in whom mean dystrophin fluorescence intensity increased from 8·9% (95% CI 7·1–10·6) to 16·4% (10·8–22·0) of normal control after treatment (p=0·0287). The three patients with the greatest responses to treatment had 21%, 15%, and 55% dystrophin-positive fibres after treatment and these findings were confirmed with western blot, which showed an increase after treatment of protein levels from 2% to 18%, from 0·9% to 17%, and from 0% to 7·7% of normal muscle, respectively. The dystrophin-associated proteins α-sarcoglycan and neuronal nitric oxide synthase were also restored at the sarcolemma. Analysis of the inflammatory infiltrate indicated a reduction of cytotoxic T cells in the post-treatment muscle biopsies in the two high-dose cohorts.
Interpretation
The safety and biochemical efficacy that we present show the potential of AVI-4658 to become a disease-modifying drug for Duchenne muscular dystrophy.
Funding
UK Medical Research Council; AVI BioPharma.
doi:10.1016/S0140-6736(11)60756-3
PMCID: PMC3156980  PMID: 21784508
15.  A case of Becker muscular dystrophy with early manifestation of cardiomyopathy 
Korean Journal of Pediatrics  2012;55(9):350-353.
An 18-year-old boy was admitted with chest discomfort, nausea, and dyspnea at rest. At the age of 3 years, he underwent muscle biopsy and dystrophin gene analysis owing to an enlarged calf muscle and elevated serum kinase level (6,378 U/L) without overt weakness; based on the results, Becker muscular dystrophy (BMD) was diagnosed. The dystrophin gene showed deletion of exons 45 to 49. He remained ambulant and could step upstairs without significant difficulties. A chest roentgenogram showed cardiomegaly (cardiothoracic ratio, 54%), and his electrocardiogram (ECG) showed abnormal ST-T wave, biatrial enlargement, and left ventricular hypertrophy. The 2-dimensional and M-mode ECGs showed a severely dilated left ventricular cavity with diffuse hypokinesis. The systolic indices were reduced, including fractional shortening (9%) and ejection fraction (19%). Despite receiving intensive medical treatment, he died from congestive heart failure 5 months after the initial cardiac symptoms. We report a case of BMD with early-onset dilated cardiomyopathy associated with deletion of exons 45 to 49. Early cardiomyopathy can occur in BMD patients with certain genotypes; therefore, careful follow-up is required even in patients with mild phenotypes of BMD.
doi:10.3345/kjp.2012.55.9.350
PMCID: PMC3454578  PMID: 23049593
Becker muscular dystrophy; Early onset cardiomyopathy; Genotype
16.  Deletions in the 5' region of dystrophin and resulting phenotypes. 
Journal of Medical Genetics  1994;31(11):843-847.
Deletions in the dystrophin gene give rise to both Duchenne and Becker muscular dystrophies. Good correlation is generally found between the severity of the phenotype and the effect of the deletion on the reading frame: deletions that disrupt the reading frame result in a severe phenotype, while in frame deletions are associated with a milder disease course. Rare exceptions to this rule, mainly owing to frameshift mutations in the 5' region of the gene (in particular deletions involving exons 3 to 7) which are associated with a milder than expected phenotype, have been reported previously. In order to characterise better the relationship between genotype and phenotype as a result of mutations arising in the 5' region of the gene, we have studied a large cohort of patients with small in frame and out of frame deletions in the first 13 exons of the dystrophin gene. Fifty-five patients with a deletion in this area were identified; approximately one third of them had a phenotype different from that theoretically expected. Patients were divided into two groups: (1) patients with a severe clinical phenotype despite the presence of a small, in frame deletion and (2) patients with a mild phenotype and an out of frame deletion. Noticeable examples observed in the first group were Duchenne boys with a deletion of exon 5, of exon 3, and of exons 3-13. In the second group we observed several patients with an intermediate or Becker phenotype and out of frame deletions involving not only the usual exons 3-7 but also 5-7 and 3-6. These data indicate that a high proportion of patients with a deletion in the 5' end of the gene have a phenotype that is not predictable on the basis of the effect of the deletion on the reading frame. The N-terminus of dystrophin has at least one actin binding domain that might be affected by the small, in frame deletions in this area. The effect of the in frame deletions of exon 3, 5, and 3-13 on this domain might account for the severe phenotype observed in these patients. Other mechanisms, such as unexpected effect of the deletion on splicing behaviour, might, however, also be implicated in determining the phenotype outcome.
PMCID: PMC1016656  PMID: 7853367
17.  Induction of revertant fibres in the mdx mouse using antisense oligonucleotides 
Background
Duchenne muscular dystrophy is a fatal genetic disorder caused by dystrophin gene mutations that result in premature termination of translation and the absence of functional protein. Despite the primary dystrophin gene lesion, immunostaining studies have shown that at least 50% of DMD patients, mdx mice and a canine model of DMD have rare dystrophin-positive or 'revertant' fibres. Fine epitope mapping has shown that the majority of transcripts responsible for revertant fibres exclude multiple exons, one of which includes the dystrophin mutation.
Methods
The mdx mouse model of muscular dystrophy has a nonsense mutation in exon 23 of the dystrophin gene. We have shown that antisense oligonucleotides (AOs) can induce the removal of this exon, resulting in an in-frame mRNA transcript encoding a shortened but functional dystrophin protein. To emulate one exonic combination associated with revertant fibres, we target multiple exons for removal by the application of a group of AOs combined as a "cocktail".
Results
Exons 19–25 were consistently excluded from the dystrophin gene transcript using a cocktail of AOs. This corresponds to an alternatively processed gene transcript that has been sporadically detected in untreated dystrophic mouse muscle, and is presumed to give rise to a revertant dystrophin isoform. The transcript and the resultant correctly localised smaller protein were confirmed by RT-PCR, immunohistochemistry and western blot analysis.
Conclusion
This work demonstrates the feasibility of AO cocktails to by-pass dystrophin mutation hotspots through multi-exon skipping. Multi-exon skipping could be important in expediting an exon skipping therapy to treat DMD, so that the same AO formulations may be applied to several different mutations within particular domains of the dystrophin gene.
doi:10.1186/1479-0556-4-3
PMCID: PMC1481566  PMID: 16719929
18.  Functional significance of dystrophin positive fibres in Duchenne muscular dystrophy. 
Archives of Disease in Childhood  1993;68(5):632-636.
The age when boys lose the ability to walk independently is one of the milestones in the progression of Duchenne muscular dystrophy (DMD). We have used this as a measure of disease severity in a group of 30 patients with DMD and six patients with intermediate Duchenne/Becker dystrophy (D/BMD). Dystrophin analysis was performed on tissue sections and western blots of muscle biopsy specimens from these patients and the relationships that were found between clinical severity and abundance of dystrophin labelling are reported. All patients with intermediate D/BMD had dystrophin labelling that was detected on sections and blots. Weak dystrophin labelling was found in sections from 21/30 DMD cases and on blots in 18/30 cases. Two non-exclusive patterns of dystrophin labelling were observed on sections: very clear labelling on a small percentage of fibres (usually < 1%) or very weak labelling on a much higher proportion (about 25%). The mean age at loss of mobility among the DMD patients with no dystrophin labelling on tissue sections was 7.9 years (range 6.3-9.5) while the mean age among those with some labelling was 9.9 years (range 8.0-11.9); this is a significant difference. Quantitative estimates of dystrophin abundance were obtained from densitometric analysis of dystrophin bands on blots. In the whole group of 36 patients, a significant positive relationship was found between the abundance of dystrophin and the age at loss of independent mobility. It is concluded that even the very low concentrations of dystrophin found in DMD patients may have some functional significance.
Images
PMCID: PMC1029331  PMID: 8323331
19.  Dilated cardiomyopathy and the dystrophin gene: an illustrated review. 
British Heart Journal  1994;72(4):344-348.
Cardiomyopathy is often found in patients with Duchenne and Becker muscular dystrophy, which are X linked muscle diseases caused by mutations in the dystrophin gene. Dystrophin defects present in many different ways and cases of mild Becker muscular dystrophy have been described in which cardiomyopathy was severe. Female carriers of Duchenne muscular dystrophy can develop symptomatic skeletal myopathy alone or combined with dilated cardiomyopathy. They can also develop dilated cardiomyopathy alone. X linked dilated cardiomyopathy has been found in association with dystrophin defects. The relation between the molecular defects and the cardiac phenotypes has not yet been established. New mutations in the dystrophin gene are common and such mutations cause one third of the cases with Duchenne and Becker muscular dystrophy. This means that sporadic cases of cardiomyopathy caused by dystrophin defects are likely. This paper reports such a case in a boy of 14 who died of dilated cardiomyopathy. Before the cardiac investigation, which was performed one month before he died, he had not complained of muscular weakness. He had minor signs of limb girdle myopathy and slightly increased concentrations of serum creatine kinase. He was found to have an unusual deletion in the dystrophin gene.
Images
PMCID: PMC1025544  PMID: 7833192
20.  Identification and Quantitation of Potential Protein Biomarkers from Patients with Muscular Dystrophy 
Journal of Biomolecular Techniques : JBT  2010;21(3 Suppl):S61-S62.
RP-127
Duchenne Muscular Dystrophy (DMD) is a muscle disorder resulting from mutations or deletions in the dystrophin gene that results in loss of protein expression. Loss of dystrophin in muscle leads to defects in physiology and progressive muscle wasting that typically result in premature death due to cardiac dysfunction or respiratory failure. One approach to therapy in DMD involves delivery of therapeutics designed to cause skipping of the relevant mutated or deleted exon in the dystrophin gene, ultimately stimulating production of a truncated, but functional, dystrophin protein. To evaluate various therapeutic strategies like exon skipping, we attempted to identify potential biomarkers and to develop a quantitative strategy to measure and identify dystrophin protein isoforms in human skeletal muscles by MS. We used human muscle biopsy specimens to analyze dystrophin isoforms from normal human muscle and DMD muscle. Proteins from normal and DMD muscles were extracted and separated. LC/MS/MS spectra were acquired in a data-dependent mode. Proteins were searched against the human IPI Database. Data processing was done using Bioworks 3.3 for peptide ID based on Xcorr vs Charge state. The identified proteins of Normal (1013) vs DMD (865) muscle were classified by Babelomics. Their cellular component distributions were mitochondria (5.2/ 8.8%), intracellular (24.1/24.8%), membrane (14.8/11%), cytoskeleton (17.1/13.6%), cytoplasm (17.6/14.7%), nucleus (7.1/10.8%). Our results revealed the identification of proteins involved in nucleotide metabolism, Ca2+ handling, cellular stress response, key bioenegetic processes and biomarkers like dystrophin, utrophin, calpain and troponin. ICAT analysis followed by mass spectrometry detected levels of dystrophin. Improvements on the yield and recovery of dystrophy-related and clinically relevant tagged proteins are currently in progress.
PMCID: PMC2918150
21.  Antisense PMO Found in Dystrophic Dog Model Was Effective in Cells from Exon 7-Deleted DMD Patient 
PLoS ONE  2010;5(8):e12239.
Background
Antisense oligonucleotide-induced exon skipping is a promising approach for treatment of Duchenne muscular dystrophy (DMD). We have systemically administered an antisense phosphorodiamidate morpholino oligomer (PMO) targeting dystrophin exons 6 and 8 to a dog with canine X-linked muscular dystrophy in Japan (CXMDJ) lacking exon 7 and achieved recovery of dystrophin in skeletal muscle. To date, however, antisense chemical compounds used in DMD animal models have not been directly applied to a DMD patient having the same type of exon deletion. We recently identified a DMD patient with an exon 7 deletion and tried direct translation of the antisense PMO used in dog models to the DMD patient's cells.
Methodology/Principal Findings
We converted fibroblasts of CXMDJ and the DMD patient to myotubes by FACS-aided MyoD transduction. Antisense PMOs targeting identical regions of dog and human dystrophin exons 6 and 8 were designed. These antisense PMOs were mixed and administered as a cocktail to either dog or human cells in vitro. In the CXMDJ and human DMD cells, we observed a similar efficacy of skipping of exons 6 and 8 and a similar extent of dystrophin protein recovery. The accompanying skipping of exon 9, which did not alter the reading frame, was different between cells of these two species.
Conclusion/Significance
Antisense PMOs, the effectiveness of which has been demonstrated in a dog model, achieved multi-exon skipping of dystrophin gene on the FACS-aided MyoD-transduced fibroblasts from an exon 7-deleted DMD patient, suggesting the feasibility of systemic multi-exon skipping in humans.
doi:10.1371/journal.pone.0012239
PMCID: PMC2923599  PMID: 20805873
22.  Splicing mutations in DMD/BMD detected by RT-PCR/PTT: detection of a 19AA insertion in the cysteine rich domain of dystrophin compatible with BMD. 
Journal of Medical Genetics  1996;33(11):935-939.
We have used an RNA based mutation detection method to screen the total coding region of the dystrophin gene of a Duchenne and a Becker muscular dystrophy patient in whom DNA based mutation detection methods have so far failed to detect mutations. By RT-PCR and the protein truncation test (PTT) we could identify point mutations in both cases. DMD patient DL184.3 has a T-->A mutation in intron 59 at position -9, creating a novel splice acceptor site for exon 60. As a result seven intronic bases are spliced into the mRNA, causing a frameshift and premature translation termination 20 codons downstream. Since this patient had died and only fibroblasts were available, we applied MyoD induced myodifferentiation of stored fibroblasts to enhance muscle specific gene expression. With the results of this mutation analysis, prenatal diagnosis could subsequently be performed in this family. BMD patient BL207.1 carries a G-->C mutation at position +5 of intron 64, disrupting the splice donor consensus sequence and activating a cryptic splice donor site 57bp downstream. The inclusion of these 57 intronic bases in the mRNA leaves the reading frame open and results in the insertion of 19 amino acids into the cysteine rich domain of dystrophin. Interestingly, this insertion in a part of the dystrophin considered to interact with the dystrophin binding complex of the sarcolemma is apparently compatible with mild BMD-like clinical features. Both mutations reported are missed by analysis of multiplex PCR products designed for deletion screening of the coding region. Extrapolation from existing point mutation detection efficiencies by DNA and RNA based methods emphasises that RNA based methods are more sensitive and that most of the remaining undetected mutations may affect splice or branch sites or create cryptic splice sites.
Images
PMCID: PMC1050788  PMID: 8950674
23.  Prednisolone Treatment Does Not Interfere with 2′-O-Methyl Phosphorothioate Antisense-Mediated Exon Skipping in Duchenne Muscular Dystrophy 
Human Gene Therapy  2011;23(3):262-273.
Abstract
In Duchenne muscular dystrophy (DMD), dystrophin deficiency leading to progressive muscular degeneration is caused by frame-shifting mutations in the DMD gene. Antisense oligonucleotides (AONs) aim to restore the reading frame by skipping of a specific exon(s), thereby allowing the production of a shorter, but semifunctional protein, as is found in the mostly more mildly affected patients with Becker muscular dystrophy. AONs are currently being investigated in phase 3 placebo-controlled clinical trials. Most of the participating patients are treated symptomatically with corticosteroids (mainly predniso[lo]ne) to stabilize the muscle fibers, which might affect the uptake and/or efficiency of AONs. Therefore the effect of prednisolone on 2′-O-methyl phosphorothioate AON efficacy in patient-derived cultured muscle cells and the mdx mouse model (after local and systemic AON treatment) was assessed in this study. Both in vitro and in vivo skip efficiency and biomarker expression were comparable between saline- and prednisolone-cotreated cells and mice. After systemic exon 23-specific AON (23AON) treatment for 8 weeks, dystrophin was detectable in all treated mice. Western blot analyses indicated slightly higher dystrophin levels in prednisolone-treated mice, which might be explained by better muscle condition and consequently more target dystrophin pre-mRNA. In addition, fibrotic and regeneration biomarkers were normalized to some extent in prednisolone- and/or 23AON-treated mice. Overall these results show that the use of prednisone forms no barrier to participation in clinical trials with AONs.
Verhaart and colleagues examine the effects of prednisolone, a corticosteroid, on the function of antisense oligonucleotide (AON) therapy for Duchenne muscular dystrophy. They show that prednisolone treatment does not interfere with AON uptake and exon-skipping levels in patient-derived muscle cells in vitro and in mdx mice in vivo. In fact, they suggest that prednisolone might even enhance the dystrophin expression induced by exon 23-specific AONs in mdx mice.
doi:10.1089/hum.2011.127
PMCID: PMC3300076  PMID: 22017442
24.  Categorization of 77 dystrophin exons into 5 groups by a decision tree using indexes of splicing regulatory factors as decision markers 
BMC Genetics  2012;13:23.
Background
Duchenne muscular dystrophy, a fatal muscle-wasting disease, is characterized by dystrophin deficiency caused by mutations in the dystrophin gene. Skipping of a target dystrophin exon during splicing with antisense oligonucleotides is attracting much attention as the most plausible way to express dystrophin in DMD. Antisense oligonucleotides have been designed against splicing regulatory sequences such as splicing enhancer sequences of target exons. Recently, we reported that a chemical kinase inhibitor specifically enhances the skipping of mutated dystrophin exon 31, indicating the existence of exon-specific splicing regulatory systems. However, the basis for such individual regulatory systems is largely unknown. Here, we categorized the dystrophin exons in terms of their splicing regulatory factors.
Results
Using a computer-based machine learning system, we first constructed a decision tree separating 77 authentic from 14 known cryptic exons using 25 indexes of splicing regulatory factors as decision markers. We evaluated the classification accuracy of a novel cryptic exon (exon 11a) identified in this study. However, the tree mislabeled exon 11a as a true exon. Therefore, we re-constructed the decision tree to separate all 15 cryptic exons. The revised decision tree categorized the 77 authentic exons into five groups. Furthermore, all nine disease-associated novel exons were successfully categorized as exons, validating the decision tree. One group, consisting of 30 exons, was characterized by a high density of exonic splicing enhancer sequences. This suggests that AOs targeting splicing enhancer sequences would efficiently induce skipping of exons belonging to this group.
Conclusions
The decision tree categorized the 77 authentic exons into five groups. Our classification may help to establish the strategy for exon skipping therapy for Duchenne muscular dystrophy.
doi:10.1186/1471-2156-13-23
PMCID: PMC3350383  PMID: 22462762
Splicing; Dystrophin; Exon; Splicing enhancer; Decision tree
25.  Sensitivity and Frequencies of Dystrophin Gene Mutations in Thai DMD/BMD Patients As Detected by Multiplex PCR 
Disease markers  2008;25(2):115-121.
Background: Duchenne muscular dystrophy (DMD), a lethal X-linked disease affecting 1 in 3500 male births, and its more benign variant, Becker muscular dystrophy (BMD), are caused by mutations in the dystrophin gene. Because of its large size, analysing the whole gene is impractical. Methods have been developed to detect the commonest mutations i.e. the deletions of the exons. Although these tests are highly specific, their sensitivity is inherently limited by the prevalence of deletions, which differs among different populations.
Methods: We reviewed our database for the detection of Dystrophin gene mutation by means of 31-exon multiplex PCR in Thai males, diagnosed clinically and biochemically with DMD or BMD from July 1994 to November 2006. One index patient was chosen from each family for statistical analysis. The overall sensitivity of the test, the number of fragment deleted, and the deletion frequency of each fragment were calculated, along with their 95% confidence intervals (C.I.).
Results: We found deletions in 99 out of the 202 index patients (49%; Bayesian 95% C.I. = 42%–56%). 51% of these had deletion in only one of the 31 exons tested, while the patient with the most extensive deletions had 14 exons deleted. The mean number of deleted exons were 2.84 (BCa bootstrap 95% C.I. = 2.37–3.48), or 5.02 (3.81–6.85) if all the untested exons adjacent to the confirmed deleted exons were assumed to be deleted. The region spanning exons 44-52 was the most frequently deleted. These were similar to those reported in the Japanese.
Conclusion: The multiplex PCR detected deletions only in about half of the Thai patients. The diseases therefore should not be excluded solely on the negative result if DMD/BMD is strongly suspected.
doi:10.1155/2008/521568
PMCID: PMC3827792  PMID: 18957722
Duchenne muscular dystrophy; dystrophin; gene deletion; multiplex PCR; sensitivity; Thai people

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