statin blockade may be reduced if applied as a supportive therapy. How- ever, above demonstrated data do not permit to differentiate whether observed effects resulted from myostatin blockade or from exon skipping. Experiments to compare the effect of each strategy are on course. doi:10.1016/j.nmd.2008.06.206 G.P.8.08 Codon optimisation of microdystrophin results in improvements in expres- sion and physiological outcome in the mdx mouse following AAV8 gene transfer H. Foster 1 ; D.J. Wells 2 ; C. Trollet 3 ; T. Athanasopoulos 3 ; I. Graham 3 ; K. Foster 3 ; J.G. Dickson 3 1 Royal Holloway University of London, Egham, United Kingdom; 2 Impe- rial College London, London, United Kingdom; 3 Royal Holloway Univer- sity of London, School of Biomedical Sciences, Egham, United Kingdom Duchenne’s muscular dystrophy (DMD) is a severe muscle wasting disorder affecting 1/3500 male births. DMD is caused by a lack of dys- trophin protein in skeletal muscle. Lack of dystrophin compromises the integrity of the muscle cell membrane and results in muscle fibres that are highly prone to contraction induced injury. Consequently there are progressive rounds of degeneration and regeneration of the muscle. Such changes culminate in respiratory or cardiac failure in the third decade of life. Very efficient gene transfer of dystrophin is crucial if restoration of muscle function is to be achieved. AAV mediated strategies for gene transfer of dystrophin to muscle have been limited by the small cloning capacity of AAV vectors. As a result smaller versions of the gene or microdystrophins have been designed based on mutations observed in the milder allelic disorder Becker Muscular Dystrophy (BMD). The aim of the current study was to assess the impact of codon optimisation on microdystrophin (DAB,R3-R18/DCT) expression and function in the mdx mouse and to compare the function of two different configurations of codon optimised microdystrophin genes (DAB, R3-R18/DCT & DR4- R23/DCT), under the control of muscle restrictive promoter. Codon optimisation results in a significant improvement in the expression level of microdystrophin following intramuscular (IM) plasmid electrotransfer (25 lg) and systemic administration of AAV8 (3 Â 1011vg). Specific force and force drop following eccentric contractions were analysed in the mdx mouse following IM injection of AAV8 (7.5 Â 109vg) vectors into neonatal mice. Physiological parameters were assessed at 2 months post injection. Non codon optimised DAB, R3-R18/DCT did not improve any of the physiological parameters tested, codon optimised DAB, R3-R18/DCT resulted in significant improvement of specific force but did not improve resistance to eccentric contractions. However, fol- lowing injection of codon optimised DR4-R23/DCT, specific force mea- surements and resistance to eccentric contractions were not significantly different to age matched wild type mice. doi:10.1016/j.nmd.2008.06.207 G.P.8.09 Evaluating the potential of AAV8 mediated intravenous transfer of myost- atin propeptide to ameliorate the muscle pathology in mdx mouse K. Foster 1 ; I. Graham 1 ; H. Foster 1 ; C. Trollet 1 ; P. Yaworsky 2 ; F. Walsh 2 ; P. Sharp 3 ; D. Wells 3 ; G. Dickson 1 1 Royal Holloway University of London, School of Biological Sciences, Egham, United Kingdom; 2 Wyeth Research, Clinical Discovery, College- ville, United States; 3 Imperial College London, London, United Kingdom Duchenne’s muscular dystrophy (DMD) is a severe muscle wasting disorder affecting 1/3500 male births. Lack of dystrophin within the muscle leads to muscle fibres which are highly prone to exercise induced injury, which consequently results in progressive rounds of degeneration and regeneration of the muscle, leading to respiratory or cardiac failure in the third decade of life. Myostatin is a member of the TGF-b super family and is a negative regulator of muscle mass, by affecting muscle cell proliferation and differentiation. Myostatin is produced almost exclusively in skeletal muscle tissue; like other TGF-b family members is first synthesised as a precursor protein (376 amino acids) that is pro- cessed at the cleavage site (R263SRR266) by calcium-dependent furin proteases to yield the N-terminal propeptide and the C-terminal mature peptide. This myostatin complex is secreted and circulates as a serum protein. The propeptide domain is activated by BMP-1/tolloid family of metalloproteases to release the mature peptide. In the canonical sig- nalling pathway ‘free’ mature peptide first binds the cell surface activin receptor type IIb (ActRIIb), recruiting and phosphorylating of activin receptor type I (either activin-like kinase 4 (ALK4) or ALK5)); subse- quently SMAD2 and SMAD3 are phosphorylated, bind the co-SMAD4 facilitating translocation to the nucleus, whereupon they act as a tran- scriptional modulator. Use of myostatin propetide has been shown to improve pathology in mdx mice. Here we evaluate whether a gene ther- apeutic approach of myostatin inhibition leads to improvement in the pathophysiology of the dystrophic phenotype in the mdx mouse. Recombinant myostatin propeptide was expressed in 6–8 week old mdx male and female mice following tail vein injections of AAV8. Gross body weights were monitored at weekly intervals up to 10 weeks post injection. At 10 weeks post injection the following muscles were recovered from treated and untreated groups; tibialis anterior, gastroc- nemius, extensor digitorum longus, soleus, diaphragm and heart. Serum samples were also collected. Histological, morphometric, biochemical analyses and physiological data will be presented. doi:10.1016/j.nmd.2008.06.208 G.P.8.10 Immunosuppressive regimen fails to improve dystrophic phenotype and impairs muscle function in the dog model of Duchenne muscular dystrophy I. Barthe ´le ´my ; A. Uriarte; J.L. Thibaud; S. Blot ENVA, Laboratoire de Neurobiologie, Maisons-Alfort, France Many therapies for DMD tested in dogs affected by Golden Retrie- ver muscular dystrophy require immune response modulation. Cyclo- sporin and corticosteroids are known to improve dystrophic phenotype at anti-inflammatory dosages. However, the effects of this association at immunosuppressive levels must be characterized in GRMD dogs. In this aim, 5 GRMD dogs underwent CsA (20 mg/kg/ d) and Prednisone (2 mg/kg/d) treatment starting at 2 up to 9 months of age. The consequences of the treatment on the dystrophic phenotype were assessed by clinical scoring and muscle biopsies. Effects on muscu- lar function were examined using force measurements at 4, 6 and 9 months. Many side effects were observed, including growth retardation, overweight, extended papilloma, ectopic calcifications notably in the lungs, and luxations impairing locomotion. No evident influence of treatment on the clinical dystrophic phenotype was observed. Indeed, the clinical scoring evolution appeared heterogeneous, and superimpos- able to the range of scores of untreated GRMD dogs. Moreover, the treatment did not prevent hiatal hernias, a frequent consequence of dia- phragmatic damages. The histological phenotype was not clearly improved, and intracellular calcifications were predominant. Force mea- surements showed that tetanic contraction force of the anterior com- partment of the leg was decreased in comparison to untreated GRMD dogs. Moreover, the force decreased over time whereas it remained sta- ble in untreated GRMD dogs, and increased in healthy dogs. This could be due to reversion of the type I predominance in treated dogs muscles, since the absence of dystrophin is known to impair type II more than type I fibers function. A muscle growth inhibition, due to calcineurin pathway blockade and corticosteroids could also be responsible for this 784 Abstracts / Neuromuscular Disorders 18 (2008) 724–833