For DMD patients, supportive therapies such as rehabilitation or ventilator support are clinically employed but no effective way to improve the clinical course is available. Since the discovery of the dystrophin gene, gene therapy is now considered an attractive way to cure the disease. The main aim of DMD gene therapy is to establish a way to inject constructed dystrophin genes consisting of partial- or full-length cDNA joined to an appropriate promoter. Although much progress has been made in this field of study, we still seem to be a long way from achieving a clinically significant result. As an alternative for gene transfection, molecular therapies have been studied including antisense oligonucleotide treatment[21-23] or translational readthrough treatment using gentamicin.
An alternative strategy for DMD treatment is to retard the progression of the clinical symptoms, i.e., to convert DMD into the BMD phenotype. Theoretically, this therapy can be done by changing a frame-shift mutation causing DMD into an in-frame mutation characteristic of BMD by modifying the dystrophin mRNA. Artificial induction of exon skipping with antisense oligonucleo tides is a way to make the out-of-frame dystrophin mRNA in-frame. Artificial induction of exon 19 skipping using an antisense oligonucleotides against the splicing enhancer sequence has been reported, and this treatment was shown to produce dystrophin expression in exon-20-deleted DMD myocytes. Disruption of the splicing enhancer sequence to induce exon skipping was further evidenced by the fact that in the nonsense mutation of exon 27 the dystrophin gene resulted in exon 27 skipping, producing an in-frame dystrophin mRNA. In addition, another natural example causing conversion of DMD to BMD was identified in a nonsense mutation in exons 25 and 29.[26,27] Furthermore, BMD has been shown to have a nonsense mutation in in-frame exons.[28,29]
Antisense oligonucleotides against a purine-rich sequence have been used to induce skipping of exons 44, 45,
In these studies, induction of exon skipping led to the expression of dystrophin in their respective dystrophin-deficient myocytes by correcting the translational reading frame. Recently, double exon skipping of exon 43 and 44 or exon 45 and 51 has been induced. This extends the application of the antisense oligonucleotide treatment to more varieties of deletion mutations of the dystrophin gene.
Phosphorothioate DNA has been the standard choice for the clinical application of antisense technology.[33-37] However, phosphorothioate DNA is associated with a variety of potentially toxic non-antisense effects. In order to develop less toxic antisense oligonucleotides, nucleic acids have been modified in various ways.[39,40] Recently, morpholino modified oligonucleotides were shown to be delivered to muscle cells efficiently. Furthermore, the chimera of 2'-O-methyl RNA and 2'-O, 4'-C-ethylene-bridged nucleic acid (ENA) was shown to induce exon 19 skipping of the dystrophin gene 40 times stronger than the conventional phosphorothioate oligonu-
Aminoglycoside antibiotics have been suggested as possible therapeutic interventions for treating patients who carry a nonsense mutation because of the ability of these antibiotics to lead translational readthrough of stop codons. To evaluate whether aminoglycosides can be used to suppress the nonsense mutation in a human DMD case, four DMD/BMD cases with various stop codon sequences were tested once daily with intravenous gen-tamicin at 7.5 mg/kg/day for 2 weeks. However, the full-length dystrophin protein was not detected in posttreat-ment muscle biopsies. The possible reason for the failure of gentamicin treatment in human cases is the difference in efficiency of aminoglycoside-induced read-through among the different types of nonsense mutations.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.