Systemic Antisense Therapeutics for Dystrophin and Myostatin Exon Splice Modulation Improve Muscle Pathology of Adult mdx Mice

Targeted Antisense Oligonucleotide-Mediated Skipping of Murine Postn Exon 17 Partially Addresses Fibrosis in D2.mdx Mice

Periostin, a multifunctional 90 kDa protein, plays a pivotal role in the pathogenesis of fibrosis across various tissues, including skeletal muscle. It operates within the transforming growth factor beta 1 (Tgf-β1) signalling pathway and is upregulated in fibrotic tissue. Alternative splicing of Periostin's C-terminal region leads to six protein-coding isoforms. This study aimed to elucidate the contribution of the isoforms containing the amino acids encoded by exon 17 (e17+ Periostin) to skeletal muscle fibrosis and investigate the therapeutic potential of manipulating exon 17 splicing. We identified distinct structural differences between e17+ Periostin isoforms, affecting their interaction with key fibrotic proteins, including Tgf-β1 and integrin alpha V. In vitro mouse fibroblast experimentation confirmed the TGF-β1-induced upregulation of e17+ Periostin mRNA, mitigated by an antisense approach that induces the skipping of exon 17 of the Postn gene. Subsequent in vivo studies in the D2.mdx mouse model of Duchenne muscular dystrophy (DMD) demonstrated that our antisense treatment effectively reduced e17+ Periostin mRNA expression, which coincided with reduced full-length Periostin protein expression and collagen accumulation. The grip strength of the treated mice was rescued to the wild-type level. These results suggest a pivotal role of e17+ Periostin isoforms in the fibrotic pathology of skeletal muscle and highlight the potential of targeted exon skipping strategies as a promising therapeutic approach for mitigating fibrosis-associated complications.

Vamorolone improves Becker muscular dystrophy and increases dystrophin protein in bmx model mice

There is no approved therapy for Becker muscular dystrophy (BMD), a genetic muscle disease caused by in-frame dystrophin deletions. We previously developed the dissociative corticosteroid vamorolone for treatment of the allelic, dystrophin-null disease Duchenne muscular dystrophy. We hypothesize vamorolone can treat BMD by safely reducing inflammatory signaling in muscle and through a novel mechanism of increasing dystrophin protein via suppression of dystrophin-targeting miRNAs. Here, we test this in the bmx mouse model of BMD. Daily oral treatment with vamorolone or prednisolone improves bmx grip strength and hang time phenotypes. Both drugs reduce myofiber size and decrease the percentage of centrally nucleated fibers. Vamorolone shows improved safety versus prednisolone by avoiding or reducing key side effects to behavior and growth. Intriguingly, vamorolone increases dystrophin protein in both heart and skeletal muscle. These data indicate that vamorolone, nearing approval for Duchenne, shows efficacy in bmx mice and therefore warrants clinical investigation in BMD.

Zoledronic acid improves bone quality and muscle function in a high bone turnover state

SUMMARY

Zoledronic acid (ZA) prevents muscle weakness in mice with bone metastases; however, its role in muscle weakness in non-tumor-associated metabolic bone diseases and as an effective treatment modality for the prevention of muscle weakness associated with bone disorders, is unknown. We demonstrate the role of ZA-treatment on bone and muscle using a mouse model of accelerated bone remodeling, which represents the clinical manifestation of non-tumor associated metabolic bone disease. ZA increased bone mass and strength and rescued osteocyte lacunocanalicular organization. Short-term ZA treatment increased muscle mass, whereas prolonged, preventive treatment improved muscle mass and function. In these mice, muscle fiber-type shifted from oxidative to glycolytic and ZA restored normal muscle fiber distribution. By blocking TGFβ release from bone, ZA improved muscle function, promoted myoblast differentiation and stabilized Ryanodine Receptor-1 calcium channel. These data demonstrate the beneficial effects of ZA in maintaining bone health and preserving muscle mass and function in a model of metabolic bone disease.

Context and significance

TGFβ is a bone regulatory molecule which is stored in bone matrix, released during bone remodeling, and must be maintained at an optimal level for the good health of the bone. Excess TGFβ causes several bone disorders and skeletal muscle weakness. Reducing excess TGFβ release from bone using zoledronic acid in mice not only improved bone volume and strength but also increased muscle mass, and muscle function. Progressive muscle weakness coexists with bone disorders, decreasing quality of life and increasing morbidity and mortality. Currently, there is a critical need for treatments improving muscle mass and function in patients with debilitating weakness. Zoledronic acid's benefit extends beyond bone and could also be useful in treating muscle weakness associated with bone disorders.

Systemic Delivery of a Monoclonal Antibody to Immunologically Block Myostatin in the A17 Mouse Model of OPMD

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset rare muscle disease affecting approximately 1 in 80,000 individuals worldwide. However, it can affect as much as 1:600 individuals in some populations due to a strong founder effect. The muscle pathology is characterized by progressive eyelid drooping (ptosis), swallowing difficulties (dysphagia), and limb weakness at later stages of disease progression. The genetic defect is associated with significant fibrotic deposition and atrophy in affected muscles. No treatments are available to cure the disease. Only surgical techniques to correct ptosis and swallowing are currently possible, though they carry a risk of recurrence. Myostatin is a negative regulator of muscle growth, and several strategies to downregulate its expression have been developed with the aim of improving muscle mass and strength in muscular pathologies. We recently showed that weekly systemic treatment of the A17 murine model of OPMD with a monoclonal antibody for myostatin improves body and muscle mass, increases muscle strength, and reduces muscle fibrosis. Here, we describe the methodology for repeated intraperitoneal delivery of myostatin antibody in the murine model. Furthermore, we detail the most relevant analyses to assess histopathological and functional improvements of this treatment in this mouse model.

In vivo restoration of dystrophin expression in mdx mice using intra-muscular and intra-arterial injections of hydrogel microsphere carriers of exon skipping antisense oligonucleotides

Duchenne muscular dystrophy (DMD) is a genetic disease caused by a mutation in the X-linked Dytrophin gene preventing the expression of the functional protein. Exon skipping therapy using antisense oligonucleotides (AONs) is a promising therapeutic strategy for DMD. While benefits of AON therapy have been demonstrated, some challenges remain before this strategy can be applied more comprehensively to DMD patients. These include instability of AONs due to low nuclease resistance and poor tissue uptake. Delivery systems have been examined to improve the availability and stability of oligonucleotide drugs, including polymeric carriers. Previously, we showed the potential of a hydrogel-based polymeric carrier in the form of injectable PEG-fibrinogen (PF) microspheres for delivery of chemically modified 2'-O-methyl phosphorothioate (2OMePs) AONs. The PF microspheres proved to be cytocompatible and provided sustained release of the AONs for several weeks, causing increased cellular uptake in mdx dystrophic mouse cells. Here, we further investigated this delivery strategy by examining in vivo efficacy of this approach. The 2OMePS/PEI polyplexes loaded in PF microspheres were delivered by intramuscular (IM) or intra-femoral (IF) injections. We examined the carrier biodegradation profiles, AON uptake efficiency, dystrophin restoration, and muscle histopathology. Both administration routes enhanced dystrophin restoration and improved the histopathology of the mdx mice muscles. The IF administration of the microspheres improved the efficacy of the 2OMePS AONs over the IM administration. This was demonstrated by a higher exon skipping percentage and a smaller percentage of centered nucleus fibers (CNF) found in H&E-stained muscles. The restoration of dystrophin expression found for both IM and IF treatments revealed a reduced dystrophic phenotype of the treated muscles. The study concludes that injectable PF microspheres can be used as a carrier system to improve the overall therapeutic outcomes of exon skipping-based therapy for treating DMD.

Use of Small Animal Models for Duchenne and Parameters to Assess Efficiency upon Antisense Treatment

Duchenne muscular dystrophy (DMD) is a rare genetic disease affecting 1 in 5000 newborn boys. It is caused by mutations in the DMD gene with a consequent lack of dystrophin protein that leads to deterioration of myofibers and their replacement with fibro-adipogenic tissue. Using antisense oligonucleotides (AONs) to modify out-of-frame mutations in the DMD gene, named exon skipping, is currently considered among the most promising treatments for DMD patients. The development of this strategy is rapidly moving forward, and AONs designed to skip exons 51 and 53 have received accelerated approval in the USA. In preclinical setting, the mdx mouse model, carrying a point mutation in exon 23 of the murine Dmd gene that prevents production of dystrophin protein, has emerged as a valuable tool, and it is widely used to study in vivo therapeutic approaches for DMD. Here we describe the methodology for intravenous delivery of AONs targeting dystrophin through tail vein of mdx mice. Furthermore, the most relevant functional analyses to be performed in living mice, and the most informative histopathological and molecular assays to evaluate the effect of this treatment are detailed.

ActRIIB:ALK4-Fc alleviates muscle dysfunction and comorbidities in murine models of neuromuscular disorders

Patients with neuromuscular disorders suffer from a lack of treatment options for skeletal muscle weakness and disease comorbidities. Here, we introduce as a potential therapeutic agent a heterodimeric ligand-trapping fusion protein, ActRIIB:ALK4-Fc, which comprises extracellular domains of activin-like kinase 4 (ALK4) and activin receptor type IIB (ActRIIB), a naturally occurring pair of type I and II receptors belonging to the TGF-β superfamily. By surface plasmon resonance (SPR), ActRIIB:ALK4-Fc exhibited a ligand binding profile distinctly different from that of its homodimeric variant ActRIIB-Fc, sequestering ActRIIB ligands known to inhibit muscle growth but not trapping the vascular regulatory ligand bone morphogenetic protein 9 (BMP9). ActRIIB:ALK4-Fc and ActRIIB-Fc administered to mice exerted differential effects - concordant with SPR results - on vessel outgrowth in a retinal explant assay. ActRIIB:ALK4-Fc induced a systemic increase in muscle mass and function in wild-type mice and in murine models of Duchenne muscular dystrophy (DMD), amyotrophic lateral sclerosis (ALS), and disuse atrophy. Importantly, ActRIIB:ALK4-Fc improved neuromuscular junction abnormalities in murine models of DMD and presymptomatic ALS and alleviated acute muscle fibrosis in a DMD model. Furthermore, in combination therapy ActRIIB:ALK4-Fc increased the efficacy of antisense oligonucleotide M12-PMO on dystrophin expression and skeletal muscle endurance in an aged DMD model. ActRIIB:ALK4-Fc shows promise as a therapeutic agent, alone or in combination with dystrophin rescue therapy, to alleviate muscle weakness and comorbidities of neuromuscular disorders.

[Update on Duchenne muscular dystrophy]

Duchenne muscular dystrophy, DMD*(ICD-9-C: 359.1; ICD-10-ES: G71.01, ORPHA: 98896) is a dystrophic type, autosomal recessive myopathy linked to the X chromosome, low incidence 1/3300, with full penetrance and multi-organ involvement (neuro-muscular, respiratory, digestive and metabolic). It has great clinical variability. Symptoms begin in pediatric age (mobility limitation and early respiratory complications). Respiratory complications reduce the life expectancy of those affected. There is no treatment that modifies its evolution, although corticosteroids and new gene therapies are increasing the half-life of this disease. The role of the Primary Care Physician (PCP) is decisive in the monitoring and control of the complications of DMD, either coordinating the different specialties involved in it.

Systemic antisense therapeutics inhibiting DUX4 expression ameliorates FSHD-like pathology in an FSHD mouse model

Aberrant expression of the double homeobox 4 (DUX4) gene in skeletal muscle causes muscle deterioration and weakness in Facioscapulohumeral muscular dystrophy (FSHD). Since the presence of a permissive pLAM1 polyadenylation signal is essential for stabilization of DUX4 mRNA and translation of DUX4 protein, disrupting the function of this structure can prevent expression of DUX4. We and others have shown promising results using antisense approaches to reduce DUX4 expression in vitro and in vivo following local intramuscular administration. Here we demonstrate that further development of the antisense chemistries enhances in vitro antisense efficacy. The optimal chemistry was conjugated to a cell-penetrating moiety and was systemically administered into the tamoxifen-inducible Cre-driver FLExDUX4 double-transgenic mouse model of FSHD. After four weekly treatments, mRNA quantities of DUX4 and target genes were reduced by 50% that led to 12% amelioration in muscle atrophy, 52% improvement in in situ muscle strength, 17% reduction in muscle fibrosis and prevention of shift in the myofiber type profile. Systemic DUX4 inhibition also significantly improved the locomotor activity and reduced the fatigue level by 22%. Our data demonstrate that the optimized antisense approach has potential of being further developed as a therapeutic strategy for FSHD.

Knockdown of Muscle-Specific Ribosomal Protein L3-Like Enhances Muscle Function in Healthy and Dystrophic Mice

Ribosomal protein L3-like (RPL3L) is a poorly characterized ribosomal protein that is exclusively expressed in skeletal and cardiac muscle. RPL3L is also downregulated in Duchenne muscular dystrophy (DMD), suggesting that it may play an important role in muscle biology. In this study, we investigated the role of RPL3L in skeletal muscle of healthy C57 and dystrophic mdx mice. We show that RPL3L is developmentally regulated and that intramuscular adeno-associated virus (AAV)-mediated RPL3L knockdown in the tibialis anterior of C57 and mdx mice results in increased specific force with improved resistance to eccentric contraction induced muscle damage in dystrophic muscles. The mechanism by which RPL3L knockdown improves muscle function remains unclear. Histological observations showed a significant increase in muscle length and decrease in muscle cross-sectional area after RPL3L inhibition suggesting that this ribosomal protein may play a role in myofiber morphology. The endogenous downregulation of RPL3L in DMD may be a protective mechanism that attempts to improve skeletal muscle function and counteract the dystrophic phenotype.

Antimyostatin Treatment in Health and Disease: The Story of Great Expectations and Limited Success

In the past 20 years, myostatin, a negative regulator of muscle mass, has attracted attention as a potential therapeutic target in muscular dystrophies and other conditions. Preclinical studies have shown potential for increasing muscular mass and ameliorating the pathological features of dystrophic muscle by the inhibition of myostatin in various ways. However, hardly any clinical trials have proven to translate the promising results from the animal models into patient populations. We present the background for myostatin regulation, clinical and preclinical results and discuss why translation from animal models to patients is difficult. Based on this, we put the clinical relevance of future antimyostatin treatment into perspective.

Myogenesis modelled by human pluripotent stem cells: a multi-omic study of Duchenne myopathy early onset

BACKGROUND

Duchenne muscular dystrophy (DMD) causes severe disability of children and death of young men, with an incidence of approximately 1/5000 male births. Symptoms appear in early childhood, with a diagnosis made mostly around 4 years old, a time where the amount of muscle damage is already significant, preventing early therapeutic interventions that could be more efficient at halting disease progression. In the meantime, the precise moment at which disease phenotypes arise-even asymptomatically-is still unknown. Thus, there is a critical need to better define DMD onset as well as its first manifestations, which could help identify early disease biomarkers and novel therapeutic targets.

METHODS

We have used both human tissue-derived myoblasts and human induced pluripotent stem cells (hiPSCs) from DMD patients to model skeletal myogenesis and compared their differentiation dynamics with that of healthy control cells by a comprehensive multi-omic analysis at seven time points. Results were strengthened with the analysis of isogenic CRISPR-edited human embryonic stem cells and through comparisons against published transcriptomic and proteomic datasets from human DMD muscles. The study was completed with DMD knockdown/rescue experiments in hiPSC-derived skeletal muscle progenitor cells and adenosine triphosphate measurement in hiPSC-derived myotubes.

RESULTS

Transcriptome and miRnome comparisons combined with protein analyses demonstrated that hiPSC differentiation (i) leads to embryonic/foetal myotubes that mimic described DMD phenotypes at the differentiation endpoint and (ii) homogeneously and robustly recapitulates key developmental steps-mesoderm, somite, and skeletal muscle. Starting at the somite stage, DMD dysregulations concerned almost 10% of the transcriptome. These include mitochondrial genes whose dysregulations escalate during differentiation. We also describe fibrosis as an intrinsic feature of DMD skeletal muscle cells that begins early during myogenesis. All the omics data are available online for exploration through a graphical interface at https://muscle-dmd.omics.ovh/.

CONCLUSIONS

Our data argue for an early developmental manifestation of DMD whose onset is triggered before the entry into the skeletal muscle compartment, data leading to a necessary reconsideration of dystrophin roles during muscle development. This hiPSC model of skeletal muscle differentiation offers the possibility to explore these functions as well as find earlier DMD biomarkers and therapeutic targets.

Sarcopenia - Molecular mechanisms and open questions

Sarcopenia represents a muscle-wasting syndrome characterized by progressive and generalized degenerative loss of skeletal muscle mass, quality, and strength occurring during normal aging. Sarcopenia patients are mainly suffering from the loss in muscle strength and are faced with mobility disorders reducing their quality of life and are, therefore, at higher risk for morbidity (falls, bone fracture, metabolic diseases) and mortality. Several molecular mechanisms have been described as causes for sarcopenia that refer to very different levels of muscle physiology. These mechanisms cover e. g. function of hormones (e. g. IGF-1 and Insulin), muscle fiber composition and neuromuscular drive, myo-satellite cell potential to differentiate and proliferate, inflammatory pathways as well as intracellular mechanisms in the processes of proteostasis and mitochondrial function. In this review, we describe sarcopenia as a muscle-wasting syndrome distinct from other atrophic diseases and summarize the current view on molecular causes of sarcopenia development as well as open questions provoking further research efforts for establishing efficient lifestyle and therapeutic interventions.

Functional muscle recovery following dystrophin and myostatin exon splice modulation in aged mdx mice

Duchenne muscular dystrophy (DMD) is a rare genetic disease affecting 1 in 3500-5000 newborn boys. It is due to mutations in the DMD gene with a consequent lack of dystrophin protein that leads to deterioration of myofibres and their replacement with fibro-adipogenic tissue. Out-of-frame mutations in the DMD gene can be modified by using antisense oligonucleotides (AONs) to promote skipping of specific exons such that the reading frame is restored and the resulting protein produced, though truncated, is functional. We have shown that AONs can also be used to knock down myostatin, a negative regulator of muscle growth and differentiation, through disruption of the transcript reading frame, and thereby enhance muscle strength. In young mdx mice, combined dystrophin and myostatin exon skipping therapy greatly improved DMD pathology, compared to the single dystrophin skipping approach. Here we show that in aged (>15-month-old) mdx mice, when the pathology is significantly more severe and more similar to the one observed in DMD patients, the effect of the combined therapy is slightly attenuated but still beneficial in improving the disease phenotype. These results confirm the beneficial outcome of the combination approach and support its translation into DMD clinical trials.

Inhibition of Myostatin Reduces Collagen Deposition in a Mouse Model of Oculopharyngeal Muscular Dystrophy (OPMD) With Established Disease

Background

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset muscle disease presented by ptosis, dysphagia, and limb weakness. Affected muscles display increased fibrosis and atrophy, with characteristic inclusion bodies in the nucleus. Myostatin is a negative regulator of muscle mass, and inhibition of myostatin has been demonstrated to improve symptoms in models of muscular dystrophy.

Methods

We systemically administered a monoclonal antibody to block myostatin in the A17 mouse model of OPMD at 42 weeks of age. The mice were administered a weekly dose of 10 mg/kg RK35 intraperitonially for 10 weeks, following which serum and histological analyses were performed on muscle samples.

Results

The administration of the antibody resulted in a significant decrease in serum myostatin and collagen deposition in muscles. However, minimal effects on body mass, muscle mass and myofiber diameter, or the density of intranuclear inclusions (INIs) (a hallmark of disease progression of OPMD) were observed.

Conclusion

This study demonstrates that inhibition of myostatin does not revert muscle atrophy in a mouse model with established OPMD disease, but is effective at reducing observed histological markers of fibrosis in the treated muscles.

Systemic Intravenous Administration of Antisense Therapeutics for Combinatorial Dystrophin and Myostatin Exon Splice Modulation

Using antisense oligonucleotides (AOs) to reframe mutated dystrophin, a recently developed therapeutic approach for Duchenne muscular dystrophy (DMD) named exon skipping, is considered among the most promising treatments for DMD patients. The development of this strategy is rapidly moving forward and the AO designed to skip exon 51 has received accelerated approval in the USA. However the strong complexity of the DMD pathology suggests that at least in older patients, where the muscle structure is almost completely compromised and the muscle is wasted and significantly infiltrated with fat and connective tissue, combined therapeutic approaches should be developed to approach the disease more effectively. Here we describe the methodology for the systemic intravenous delivery of AOs targeting dystrophin and myostatin in mdx mice, a DMD mouse model, in order to express dystrophin while downregulating myostatin, aiming for an increase in the muscle size and muscle strength. Furthermore the most relevant functional analyses to be performed in living mice and the most informative histopathological and molecular assays to evaluate the effect of this treatment are detailed.

Nucleic acids delivering nucleic acids

Nucleic acid therapeutics, including siRNAs, miRNAs/antimiRs, gRNAs and ASO, represent innovative and highly promising molecules for the safe treatment of a wide range of pathologies. The efficiency of systemic treatments is impeded by 1) the need to overcome physical and functional barriers in the organism, and 2) to accumulate in the intracellular active site at therapeutic concentrations. Although oligonucleotides either as modified naked molecules or complexed with delivery carriers have revealed to be effectively delivered to the affected target cells, this is restricted to topic treatments or to a few highly vascularized tissues. Therefore, the development of effective strategies for therapeutic nucleic acid selective delivery to target tissues is of primary importance in order to reduce the occurrence of undesired effects on non-target healthy tissues and to permit their translation to clinic. Due to their high affinity for specific ligands, high tissue penetration and chemical flexibility, short single-stranded nucleic acid aptamers are emerging as very attractive carriers for various therapeutic oligonucleotides. Yet, different aptamer-based bioconjugates, able to provide accumulation into target tissues, as well as efficient processing of therapeutic oligonucleotides, have been developed. In this respect, nucleic acid aptamer-mediated delivery strategies represent a powerful approach able to increase the therapeutic efficacy also highly reducing the overall toxicity. In this review, we will summarize recent progress in the field and discuss achieved objectives and optimization of aptamers as delivery carriers of short oligonucleotides.

Targeting TGFβ Signaling to Address Fibrosis Using Antisense Oligonucleotides

Fibrosis results from the excessive accumulation of extracellular matrix in chronically injured tissue. The fibrotic process is governed by crosstalk between many signaling pathways. The search for an effective treatment is further complicated by the fact that there is a degree of tissue-specificity in the pathways involved, although the process is not completely understood for all tissues. A plethora of drugs have shown promise in pre-clinical models, which is not always borne out translationally in clinical trial. With the recent approvals of two antisense oligonucleotides for the treatment of the genetic diseases Duchenne muscular dystrophy and spinal muscular atrophy, we explore here the potential of antisense oligonucleotides to knockdown the expression of pro-fibrotic proteins. We give an overview of the generalized fibrotic process, concentrating on key players and highlight where antisense oligonucleotides have been used effectively in cellular and animal models of different fibrotic conditions. Consideration is given to the advantages antisense oligonucleotides would have as an anti-fibrotic therapy alongside factors that would need to be addressed to improve efficacy. A prospective outlook for the development of antisense oligonucleotides to target fibrosis is outlined.

Cell-Penetrating Peptides to Enhance Delivery of Oligonucleotide-Based Therapeutics

The promise of nucleic acid based oligonucleotides as effective genetic therapies has been held back by their low bioavailability and poor cellular uptake to target tissues upon systemic administration. One such strategy to improve upon delivery is the use of short cell-penetrating peptides (CPPs) that can be either directly attached to their cargo through covalent linkages or through the formation of noncovalent nanoparticle complexes that can facilitate cellular uptake. In this review, we will highlight recent proof-of-principle studies that have utilized both of these strategies to improve nucleic acid delivery and discuss the prospects for translation of this approach for clinical application.

Combined Therapies for Duchenne Muscular Dystrophy to Optimize Treatment Efficacy

Duchene Muscular Dystrophy (DMD) is the most frequent muscular dystrophy and one of the most severe due to the absence of the dystrophin protein. Typical pathological features include muscle weakness, muscle wasting, degeneration, and inflammation. At advanced stages DMD muscles present exacerbated extracellular matrix and fat accumulation. Recent progress in therapeutic approaches has allowed new strategies to be investigated, including pharmacological, gene-based and cell-based therapies. Gene and cell-based therapies are still limited by poor targeting and low efficiency in fibrotic dystrophic muscle, therefore it is increasingly evident that future treatments will have to include “combined therapies” to reach maximal efficiency. The scope of this mini-review is to provide an overview of the current literature on such combined therapies for DMD. By “combined therapies” we mean those that include both a therapy to correct the genetic defect and an additional one to address one of the secondary pathological features of the disease. In this mini-review, we will not provide a comprehensive view of the literature on therapies for DMD, since many such reviews already exist, but we will focus on the characteristics, efficiency, and potential of such combined therapeutic strategies that have been described so far for DMD.

Multiple Species Comparison of Cardiac Troponin T and Dystrophin: Unravelling the DNA behind Dilated Cardiomyopathy

Animals have frequently been used as models for human disorders and mutations. Following advances in genetic testing and treatment options, and the decreasing cost of these technologies in the clinic, mutations in both companion and commercial animals are now being investigated. A recent review highlighted the genes associated with both human and non-human dilated cardiomyopathy. Cardiac troponin T and dystrophin were observed to be associated with both human and turkey (troponin T) and canine (dystrophin) dilated cardiomyopathies. This review gives an overview of the work carried out in cardiac troponin T and dystrophin to date in both human and animal dilated cardiomyopathy.