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Duchenne muscular dystrophy (DMD) is characterised by the absence of dystrophin in muscle biopsies, although residual dystrophin can be present, either as dystrophin-positive (revertant) fibres or traces. As restoration of dystrophin expression is the end point of clinical trials, such residual dystrophin is a key factor in recruitment of patients and may also confound the analysis of dystrophin restoration in treated patients, if, as previously observed in the mdx mouse, revertant fibres increase with age. In 62% of the diagnostic biopsies reports of 65 DMD patients studied, traces or revertants were recorded with no correlation between traces or revertants, the patients' performance, or corticosteroids response. In nine of these patients, there was no increase in traces or revertants in biopsies taken a mean of 8.23 years (5.8-10.4 years) after the original diagnostic biopsy. This information should help in the design and execution of clinical trials focused on dystrophin restoration strategies. (C) 2010 Elsevier B.V. All rights reserved.

Stem cell therapy holds promise for treating muscle diseases. Although satellite cells regenerate skeletal muscle, they only have a local effect after intra-muscular transplantation. Alternative cell types, more easily obtainable and systemically-deliverable, were therefore sought. Human synovial stem cells (hSSCs) have been reported to regenerate muscle fibres and reconstitute the satellite cell pool. We therefore determined if these cells are able to regenerate skeletal muscle after intra-muscular injection into cryodamaged muscles of Rag2-/γ chain-/C5-mice. We found that hSSCs possess only limited capacity to undergo myogenic differentiation in vitro or to contribute to muscle regeneration in vivo. However, this is enhanced by over-expression of human MyoD1. Interestingly, hSSCs express extracellular matrix components laminin α2 and collagen VI within grafted muscles. Therefore, despite their limited capacity to regenerate skeletal muscle, hSSCs could play a role in treating muscular dystrophies secondary to defects in extracellular matrix proteins.

FVC by an average of 7.7%. The average time to regain weight was 7.6 months. 43% episodes had weight loss of >5% and 70% took longer than 3 months to regain weight. Conclusion: Unexpected weight loss in this patient group might be more frequent than expected with almost 25% in our group. Our study shows that majority of patients with DMD combined respiratory, cardiovascular and gastroenterological causes were responsible for weight loss and most patients took longer to recover. Unexpected weight loss can be a marker for potential significant respiratory and/ or cardiac deterioration prompting targeted investigations and supportive management.

Exon skipping using antisense oligonucleotides (AONs) is a promising therapy for Duchenne muscular dystrophy (DMD) which aims to genocopy the milder Becker muscular dystrophy (BMD) by restoring the reading frame of an out-of-frame deletion. The less severe phenotype of BMD patients suggests that internally truncated dystrophin retains some functionality. We previously demonstrated that dystrophin and dystrophin-associated protein expression is correlated to clinical severity in BMD patients with in-frame deletions relevant to current exon skipping strategies (exons 51 and 53), and that BMD patients with deletions ending in exon 51 have significantly higher dystrophin levels than those ending in exon 53. We have now studied deletions relevant for skipping exons 44 and 45 which are now being considered for clinical trials. We studied a total of 25 patients; 11 patients had out-of-frame mutations correctable by skipping exons 44 or 45, and 14 patients had in-frame deletions corresponding to the skipping of exon 45. We quantified dystrophin and dystrophin-associated protein expression using immunohistochemistry and total dystrophin mRNA levels using qRT-PCR. DMD patients skippable for exons 44 and 45 had high levels of revertant and trace dystrophin expression (mean: 14% of control) with 6/11 out-of-frame patients presenting with an intermediate phenotype. Corresponding in frame deletions presented with phenotypes ranging from mild to severe BMD, and showed remarkably lower dystrophin levels (∼42% of control) than patients with deletions modelling the skipping of exons 51 or 53 (80% and 56% of control, respectively). Our study provides valuable insights into the stability and/or function of internally truncated dystrophin suggesting that higher levels of the dystrophin produced by skipping exons 44 and 45 are required to achieve the same level of functionality observed with exon 51 and 53 skipping studies.

The UK MDEX Consortium (http://www.mdex.org.uk/) is involved in close collaboration with AVI BioPharma, in clinical trials using antisense oligonucleotides (AOs) to induce exon skipping in boys with DMD. In 2008 we completed a dose-escalation IM study of a morpholino (PMO) AO, AVI-4658, which induces skipping exon 51 in dystrophin mRNA. In February 2009 we initiated a dose escalation study in ambulant DMD boys aged 5–15 years with deletions benefitting from skipping exon 51. This study consists of 12 weekly administrations of AVI-4658 followed by a muscle biopsy to assess dystrophin expression at baseline and 14 weeks. Clinical parameters are followed for 26 weeks, consisting of safety (adverse events, physical examinations, laboratory tests), muscle, pulmonary and cardiac function, and pharmacokinetics at 1, 6 and 12 doses. A Data Safety Monitoring Board guides dose escalation decisions. Cohorts 1–5 completed 12 weeks of dosing (January 2010), while cohort 6 will complete dosing in March 2010 and clinical observations in June. No drug related SAEs or severe drug related AEs have been reported so far. To date, single doses of 900mg and cumulative exposure exceeding 10,000mg have been well tolerated. Exon skipping and dystrophin protein expression in the cohorts analysed so far indicates a dose response in exon skipping and protein expression in the cohorts up to 4.0mg/kg, with data in the 10.0 and 20.0mg/kg cohorts available soon. These results suggest that AVI-4658 has the potential to lead to the development of a drug that could play a role in the treatment of DMD.