Therapeutic Strategies for Duchenne and Becker Dystrophies

Incidence of Duchenne muscular dystrophy in the modern era; an Australian study

Duchenne muscular dystrophy (DMD), an X-linked recessive condition is maternally inherited in two-thirds of affected boys. It is important to establish carrier status of female relatives to restore reproductive confidence for non-carriers and facilitate reproductive options and cardiac surveillance for carriers. This study investigates disease incidence within an Australian model of cascade screening and evolving genetic diagnostic technologies. A retrospective population-based cohort study of all genetically and/or histopathologically confirmed males with DMD, born in New South Wales and the Australian Capital Territory was undertaken from 2002-2012. Cases were identified using state-wide molecular laboratory and clinical databases. The annual disease incidence and "theoretically" preventable cases were extrapolated over the study period. Proband genotype/phenotype, pedigree analysis, carrier-risk and extent of cascade screening were also determined. The cumulative incidence of disease was 19.7 per 100,000 male live births and 1 in 5076 live born males were diagnosed with DMD. Differences in disease incidence were not statistically different when compared between 2002-2007 and 2008-2012 (incidence rate ratio = 1.13, 95% CI 0.76-1.69, p = 0.52). The incidence rate ratio of theoretically preventable cases did not significantly change between 2002-2007 and 2008-2012 (incidence rate ratio = 2.07, 95% CI 0.58-9.21, p = 0.23). Current diagnostic and cascade screening models have limitations in their impact on disease incidence, due to a spectrum of logistical, patient and condition related factors. Innovative approaches to reduce DMD incidence may be better achieved by preconception or early pregnancy carrier screening, prenatal exome sequencing and newborn screening.

Muscular dystrophy: Experimental animal models and therapeutic approaches (Review)

The muscular dystrophies are a heterogeneous group of genetically inherited diseases characterized by muscle weakness and progressive wasting, which can cause premature death in severe forms. Although >30 years have passed since the identification of the first protein involved in a type of muscular dystrophy, there is no effective treatment for these disabling disorders. In the last decade, several novel therapeutic approaches have been developed and investigated as promising therapeutic approaches aimed to ameliorate the dystrophic phenotype either by restoring dystrophin expression or by compensating for dystrophin deficiency. Concurrently, with the development of therapeutic approaches, in addition to naturally occurring animal models, a wide range of genetically engineered animal models has been generated. The use of animals as models of muscular dystrophies has greatly improved the understanding of the pathogenicity of these diseases and has proven useful in gene therapy studies. In this review, we summarize these latest innovative therapeutic approaches to muscular dystrophies and the usefulness of the various most common experimental animal models.

Interventions to prevent and treat corticosteroid-induced osteoporosis and prevent osteoporotic fractures in Duchenne muscular dystrophy

BACKGROUND

Corticosteroid treatment is considered the 'gold standard' for Duchenne muscular dystrophy (DMD); however, it is also known to induce osteoporosis and thus increase the risk of vertebral fragility fractures. Good practice in the care of those with DMD requires prevention of these adverse effects. Treatments to increase bone mineral density include bisphosphonates and vitamin D and calcium supplements, and in adolescents with pubertal delay, testosterone. Bone health management is an important part of lifelong care for patients with DMD.

OBJECTIVES

To assess the effects of interventions to prevent or treat osteoporosis in children and adults with DMD taking long-term corticosteroids; to assess the effects of these interventions on the frequency of vertebral fragility fractures and long-bone fractures, and on quality of life; and to assess adverse events.

SEARCH METHODS

On 12 September 2016, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL Plus to identify potentially eligible trials. We also searched the Web of Science ISI Proceedings (2001 to September 2016) and three clinical trials registries to identify unpublished studies and ongoing trials. We contacted correspondence authors of the included studies in the review to obtain information on unpublished studies or work in progress.

SELECTION CRITERIA

We considered for inclusion in the review randomised controlled trials (RCTs) and quasi-RCTs involving any bone health intervention for corticosteroid-induced osteoporosis and fragility fractures in children, adolescents, and adults with a confirmed diagnosis of DMD. The interventions might have included oral and intravenous bisphosphonates, vitamin D supplements, calcium supplements, dietary calcium, testosterone, and weight-bearing activity.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed reports and selected potential studies for inclusion, following standard Cochrane methodology. We contacted study authors to obtain further information for clarification on published work, unpublished studies, and work in progress.

MAIN RESULTS

We identified 18 potential studies, of which two, currently reported only as abstracts, met the inclusion criteria for this review. Too little information was available for us to present full results or adequately assess risk of bias. The participants were children aged five to 15 years with DMD, ambulant and non-ambulant. The interventions were risedronate versus no treatment in one trial (13 participants) and whole-body vibration versus a placebo device in the second (21 participants). Both studies reported improved bone mineral density with the active treatments, with no improvement in the control groups, but the abstracts did not compare treatment and control conditions. All children tolerated whole-body vibration treatment. No study provided information on adverse events. Two studies are ongoing: one investigating whole-body vibration, the other investigating zoledronic acid.

AUTHORS' CONCLUSIONS

We know of no high-quality evidence from RCTs to guide use of treatments to prevent or treat corticosteroid-induced osteoporosis and reduce the risk of fragility fractures in children and adults with DMD; only limited results from two trials reported in abstracts were available. We await formal trial reports. Findings from two ongoing relevant studies and two trials, for which only abstracts are available, will be important in future updates of this review.

Arginine butyrate: a therapeutic candidate for Duchenne muscular dystrophy

As a strategy to treat Duchenne muscular dystrophy, we used arginine butyrate, which combines two pharmacological activities: nitric oxide pathway activation, and histone deacetylase inhibition. Continuous intraperitoneal administration to dystrophin-deficient mdx mice resulted in a near 2-fold increase in utrophin (protein homologous to dystrophin) in skeletal muscle, heart, and brain, accompanied by an improvement of the dystrophic phenotype in both adult and newborn mice (45 and 70% decrease in creatine kinase level, respectively; 14% increase in tidal volume, 30% decrease in necrotic area in limb and 23% increase in isometric force). Intermittent administration, as performed in clinical trials, was then used to reduce the frequency of injections and to improve safety. This also enhanced utrophin level around 2-fold (EC50=284 mg/ml) and alleviated the dystrophic phenotype (inverted grid and grip test performance near to wild-type values, creatine kinase level decreased by 50%). Skin biopsies were used to monitor treatment efficacy, instead of invasive muscle biopsies, and this could be done a few days after the start of treatment. A 2-fold increase in utrophin expression was also shown in cultured human myotubes. In vivo and in vitro experiments demonstrated that the drug combination acts synergistically. Together, these data constitute a proof of principle of the beneficial effects of arginine butyrate on muscular dystrophy.

Nicotinic acetylcholine receptor activation reduces skeletal muscle inflammation of mdx mice

Mdx mice develop an inflammatory myopathy characterized at different ages by myonecrosis with scattered inflammatory infiltrates followed by muscular regeneration and later persistent fibrosis. This work aimed to verify the putative anti-inflammatory role of nicotinic acetylcholine receptor (nAChR) in the mdx muscular lesion. Mitigation of myonecrosis and decreased TNFα production were accompanied by increased numbers of F4/80 macrophages expressing nAChRα7. In vivo treatment with nicotine attenuated muscular inflammation characterized by reduced metalloprotease MMP-9 activity, TNFα and NFkB content and increased muscular regeneration. Our data indicate that nAChR activation influences local inflammatory responses in the muscular lesion of mdx mice.

Alterações fisiológicas e metabólicas em indivíduo com distrofia muscular de Duchenne durante tratamento fisioterapêutico: um estudo de caso

INTRODUÇÃO: A Distrofia Muscular de Duchenne (DMD) caracteriza-se por uma perda progressiva da força muscular. O tratamento fisioterapêutico tem fundamental importância na manutenção da qualidade de vida desses pacientes. Contudo, existe grande dificuldade em graduar o grau de cansaço e o limite de exigência da musculatura durante o tratamento. Adicionalmente, não existe na literatura descrição sobre alterações fisiológicas e metabólicas durante uma atividade de esforço nessa população específica. OBJETIVOS: O presente trabalho teve como objetivos avaliar as alterações fisiológicas e metabólicas em indivíduo com DMD durante um programa de fisioterapia, relacionando-as com a percepção subjetiva de esforço (PSE). METODOLOGIA: Este estudo foi realizado na Clínica de Prevenção e Reabilitação Física da Universidade do Estado de Santa Catarina (UDESC). O sujeito do estudo foi um paciente com DMD (sexo masculino, 17 anos). Foram coletados dados de concentrações plasmáticas de lactato e glicose, frequência cardíaca e frequência respiratória, pressão arterial e percepção de esforço segundo a escala de PSE CR10 de Borg. Os dados foram coletados aos 0, 15, 30 e 45 minutos de atendimento fisioterapêutico. A sessão de fisioterapia foi dividida em 3 etapas com atividade de intensidade e exigência muscular crescentes. Foram realizados 6 atendimentos. RESULTADOS: Os resultados demonstraram PSE crescente durante a sessão de fisioterapia. Foi verificada uma relação linear entre as variáveis metabólicas e a PSE. Já as variáveis fisiológicas não demonstraram relação proporcional com a PSE. CONCLUSÃO: Sugere-se que a PSE é uma forma simples de monitoramento do cansaço de pacientes com DMD, durante o tratamento fisioterapêutico.

MALDI reveals membrane lipid profile reversion in MDX mice

Duchenne muscular dystrophy (DMD), the most common and severe X-linked myopathy, is characterized by the lack of dystrophin, a sub-sarcolemmal protein necessary for normal muscle functions. In a previous study of the lipid content of skeletal muscles of dystrophic (mdx) mice, the animal model for DMD, by in situ Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry (MALDI-MS), an inversion of the phosphatidylcholine PC34:2/PC34:1 ion peaks intensity ratio was observed between destructured (abnormal fiber morphology) and structured (normal fiber morphology). A possible treatment for this dramatic disease is to introduce an exogenous nitric oxide (NO) donor into the organism, leading to an increase of utrophin and a regression of the dystrophic phenotype. In the present work, after confirmation by tandem mass spectrometry of the structure of these two phospholipids, their intensity ratio inversion was used to evidence a restoration of membrane lipid composition very similar to those of wild-type mice after the treatment of mdx mice with molsidomine, a NO donor. This was associated with the observation by immunohistology of an increase of the regeneration process in the mice.

Oral health considerations in muscular dystrophies

Muscular dystrophies (MD) are a heterogeneous group of inherited neuromuscular disorders characterized by muscle necrosis and progressive muscle weakness. It is important for oral healthcare providers to be familiar with MD as special considerations are necessary to provide appropriate and safe dental care for these medically complex patients. This article briefly reviews the more common types of MD, namely, Duchenne MD, Becker MD, Emery-Dreifuss MD, facioscapulo-humeral MD, limb-girdle MD, oculopharyngeal MD, and myotonic dystrophy. Aspects of their epidemiology, pathophysiology, clinical presentation, diagnosis, and medical management as well as oral health considerations are discussed.

Magnetic resonance imaging of the erector spinae muscles in Duchenne muscular dystrophy: implication for scoliotic deformities

Background

In Duchenne muscular dystrophy (DMD), the muscular degeneration often leads to the development of scoliosis. Our objective was to investigate how anatomical changes in back muscles can lead to scoliosis. Muscular volume and the level of fat infiltration in those muscles were thus evaluated, in non-scoliotic, pre-scoliotic and scoliotic patients. The overlying skin thickness over the apex level of scoliotic deformations was also measured to facilitate the interpretation of electromyographic signals when recorded on the skin surface.

Methods

In 8 DMD patients and two healthy controls with no known muscular deficiencies, magnetic resonance imaging (MRI) was used to measure continuously at 3 mm intervals the distribution of the erector spinae (ES) muscle in the T8-L4 region as well as fat infiltration in the muscle and overlying skin thickness: four patients were non-scoliotic (NS), two were pre-scoliotic (PS, Cobb angle < 15°) and two were scoliotic (S, Cobb angle ≥ 15°). For each subject, 63 images 3 mm thick of the ES muscle were obtained in the T8-L4 region on both sides of the spine. The pixel dimension was 0.39 × 0.39 mm. With a commercial software, on each 12 bits image, the ES contour on the left and on the right sides of the spine were manually determined as well as those of its constituents i.e., the iliocostalis (IL), the longissimus (LO) and the spinalis (SP) muscles. Following this segmentation, the surfaces within the contours were determined, the muscles volume were obtained, the amount of fat infiltration inside each muscle was evaluated and the overlying skin thickness measured.

Findings

The volume of the ES muscle of our S and PS patients was found smaller on the convex side relative to the concave one by 5.3 ± 0.7% and 2.8 ± 0.2% respectively. For the 4 NS patients, the volume difference of this muscle between right and left sides was 2.1 ± 1.5% and for the 2 controls, it was 1.4 ± 1.2%. Fat infiltration for the S and the PS patients was larger on the convex side than on the concave one (4.4 ± 1.6% and 4.5 ± 0.7% respectively) and the difference was more important near the apex. Infiltration was more important in the lateral IL muscle than in the medial SP and it was always larger near L2 than at any other spinal level. Fat infiltration was much more important in the ES for the DMD patients (49.9% ± 1.6%) than for the two controls (2.6 ± 0.8%). As for the overlying skin thickness measured near the deformity of the patients, it was larger on the concave than on the convex side: 14.8 ± 6.1 vs 13.5 ± 5.7 mm for the S and 10.3 ± 6.3 vs 9.8 ± 5.6 mm for the PS.

Interpretation

In DMD patients, our results indicate that a larger replacement of muscles fibers by fat infiltration on one side of the spine is a factor that can lead to the development of scoliosis. Efforts to slow such an infiltration on the most affected side of the spine could thus be beneficial to those patients by delaying the apparition of the scoliotic deformation. In addition to anatomical considerations, results obtained from the same patients but in experiments dealing with electromyography recordings, point to differences in the muscular contraction mechanisms and/or of the neural input to back muscles. This is similar to the adolescent idiopathic scoliosis (AIS) where a role of the nervous system in the development of the deformation has also been suggested.

Utrophin up-regulation by an artificial transcription factor in transgenic mice

Duchenne Muscular Dystrophy (DMD) is a severe muscle degenerative disease, due to absence of dystrophin. There is currently no effective treatment for DMD. Our aim is to up-regulate the expression level of the dystrophin related gene utrophin in DMD, complementing in this way the lack of dystrophin functions. To this end we designed and engineered several synthetic zinc finger based transcription factors. In particular, we have previously shown that the artificial three zinc finger protein named Jazz, fused with the appropriate effector domain, is able to drive the transcription of a test gene from the utrophin promoter “A”. Here we report on the characterization of Vp16-Jazz-transgenic mice that specifically over-express the utrophin gene at the muscular level. A Chromatin Immunoprecipitation assay (ChIP) demonstrated the effective access/binding of the Jazz protein to active chromatin in mouse muscle and Vp16-Jazz was shown to be able to up-regulate endogenous utrophin gene expression by immunohistochemistry, western blot analyses and real-time PCR. To our knowledge, this is the first example of a transgenic mouse expressing an artificial gene coding for a zinc finger based transcription factor. The achievement of Vp16-Jazz transgenic mice validates the strategy of transcriptional targeting of endogenous genes and could represent an exclusive animal model for use in drug discovery and therapeutics.

A highly functional mini-dystrophin/GFP fusion gene for cell and gene therapy studies of Duchenne muscular dystrophy

A promising approach for treating Duchenne muscular dystrophy (DMD) is by autologous cell transplantation of myogenic stem cells transduced with a therapeutic expression cassette. Development of this method has been hampered by a low frequency of cellular engraftment, the difficulty of tracing transplanted cells, the rapid loss of autologous cells carrying marker genes that are unable to halt muscle necrosis and the difficulty of stable transfer of a large dystrophin gene into myogenic stem cells. We engineered a 5.7 kb miniDys-GFP fusion gene by replacing the dystrophin C-terminal domain (DeltaCT) with an eGFP coding sequence and removing much of the dystrophin central rod domain (DeltaH2-R19). In a transgenic mdx(4Cv) mouse expressing the miniDys-GFP fusion protein under the control of a skeletal muscle-specific promoter, the green fusion protein localized on the sarcolemma, where it assembled the dystrophin-glycoprotein complex and completely prevented the development of dystrophy in transgenic mdx(4Cv) muscles. When myogenic and other stem cells from these mice were transplanted into mdx(4Cv) recipients, donor cells can be readily identified in skeletal muscle by direct green fluorescence or by using antibodies against GFP or dystrophin. In mdx(4Cv) mice reconstituted with bone marrow cells from the transgenic mice, we monitored engraftment in various muscle groups and found the number of miniDys-GFP(+) fibers increased with time. We suggest that these transgenic mdx(4Cv) mice are highly useful for developing autologous cell therapies for DMD.

Pharmacological rescue of the dystrophin-glycoprotein complex in Duchenne and Becker skeletal muscle explants by proteasome inhibitor treatment

In this report, we have developed a novel method to identify compounds that rescue the dystrophin-glycoprotein complex (DGC) in patients with Duchenne or Becker muscular dystrophy. Briefly, freshly isolated skeletal muscle biopsies (termed skeletal muscle explants) from patients with Duchenne or Becker muscular dystrophy were maintained under defined cell culture conditions for a 24-h period in the absence or presence of a specific candidate compound. Using this approach, we have demonstrated that treatment with a well-characterized proteasome inhibitor, MG-132, is sufficient to rescue the expression of dystrophin, beta-dystroglycan, and alpha-sarcoglycan in skeletal muscle explants from patients with Duchenne or Becker muscular dystrophy. These data are consistent with our previous findings regarding systemic treatment with MG-132 in a dystrophin-deficient mdx mouse model (Bonuccelli G, Sotgia F, Schubert W, Park D, Frank PG, Woodman SE, Insabato L, Cammer M, Minetti C, and Lisanti MP. Am J Pathol 163: 1663-1675, 2003). Our present results may have important new implications for the possible pharmacological treatment of Duchenne or Becker muscular dystrophy in humans.