Duchenne Muscular Dystrophy: the Heart of the Matter

Pharmacology and macrophage modulation of HPGDS inhibitor PK007 demonstrate reduced disease severity in DMD-affected muscles of the mdx mouse model

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is an X-linked disease characterised by chronic inflammation, progressive muscle damage, and muscle loss. Typically, initial symptoms affect lower limb muscles, including the gastrocnemius (GA), tibialis anterior (TA), and extensor digitorum longus (EDL). During the acute phase of DMD, particularly in boys aged 2-8 years, muscle damage resulting in necrosis (myonecrosis) involves a complex immune-inflammatory response. Prostaglandin D2 (PGD2) is recognised for enhancing pro-inflammatory chemokine and interleukin signalling and recruiting infiltrating immune cells such as pro-inflammatory macrophages, exacerbating myonecrosis.

METHODS

To reduce levels of PGD2, a novel hematopoietic prostaglandin D2 synthase (HPGDS) inhibitor, PK007, was characterised (i) for potency and pharmacokinetic profiles and then tested in the mdx mouse model of DMD during the acute early onset of disease progression. Juvenile mdx and wild type (WT) C57Bl/10Scsn mice were orally treated with PK007 and control vehicle solution for 10 days, from postnatal day 18 to 28. This builds upon a previous study with PK007 with (ii) additional analyses of disease progression assessed for muscle grip strength, metabolic and locomotor activity, myonecrosis in a wide range of muscles (3 from hindlimb, diaphragm, heart, and tongue), macrophage infiltration and pro-inflammatory cytokines (TNF-α, IL-1β and iNOS).

RESULTS

PK007 exhibited high potency (17.23 ± 12 nM), a long half-life (3.0 ± 0.3 h), and good oral bioavailability (81%). Treatment with PK007 decreased serum PGD2 levels (33.36%) in mdx mice compared to control (vehicle-treated) mdx mice. In mdx mice (compared with controls), PK007 enhanced grip strength (69.05% increase) and improved locomotor activity (69.05% increase). Histological analysis revealed a significant reduction in the total myonecrotic area in PK007-treated GA (49.75%), TA (73.87%), EDL (60.31%), diaphragm (48.02%), and tongue (37.93%) muscles of mdx mice (compared with controls). Additionally, PK007 decreased macrophage cell area by 55.56% in GA and 47.83% in EDL muscles. Further expression of pro-inflammatory cytokines and enzymes such as TNF-α, IL-1β and iNOS were significantly reduced in PK007 treated mice. These results demonstrate that PK007 significantly reduces the inflammatory response, protects muscles from necrosis and increases strength in juvenile mdx mice.

CONCLUSION

This study lays a strong foundation for progressing the use of HPDGS inhibitors such as PK007, which specifically inhibit PGD2 and reduce inflammation, as a viable therapeutic approach for DMD. This approach protects dystrophic muscles from necrosis and reduces the severity of this debilitating disease, improving outcomes and quality of life.

Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy

Becker muscular dystrophy (BMD) is an X-linked disorder due to in-frame mutations in the DMD gene, leading to a less abundant and truncated dystrophin. BMD is less common and severe than Duchenne muscular dystrophy (DMD) as well as less investigated. To accelerate the search for innovative treatments, we developed a rat model of BMD by deleting the exons 45-47 of the Dmd gene. Here, we report a functional and histopathological evaluation of these rats during their first year of life, compared to DMD and control littermates. BMD rats exhibit moderate damage to locomotor and diaphragmatic muscles but suffer from a progressive cardiomyopathy. Single nuclei RNA-seq analysis of cardiac samples revealed shared transcriptomic abnormalities in BMD and DMD rats and highlighted an altered end-addressing of TMEM65 and Connexin-43 at the intercalated disc, along with electrocardiographic abnormalities. Our study documents the natural history of a translational preclinical model of BMD and reports a cellular mechanism for the cardiac dysfunction in BMD and DMD offering opportunities to further investigate the organization role of dystrophin in intercellular communication.

Segregation of the COL6A2 Variant (c.1817-3C>G) in a Consanguineous Saudi Family with Bethlem Myopathy

Introduction: Bethlem myopathy is a rare genetic disease caused by a variant mapped to 21q22, which harbors the collagen type VI alpha 2 chain (COL6A2) and collagen type VI alpha 1 chain (COL6A1) genes, and 2q37, which harbors the collagen type VI alpha 3 chain (COL6A3) gene. Disease onset can occur at any age, and the symptoms are related to those of muscular dystrophy. Since Bethlem myopathy is a rare disease, no previous studies have been conducted in Arab countries, including Saudi Arabia. Its variable presentation of nonspecific muscular contractions and severity represents a diagnostic dilemma. Case presentation: Here, we report a Saudi pediatric patient, who is 9 years old (proband), brought to the pediatric clinic of King Saud's Hospital by his mother. The boy presented with difficulty standing, walking, and running with his classmates and unaffected siblings. He has a younger sibling, aged 6 years old, who reported having a limping gait and difficulty bending his right knee. Laboratory results for the proband were unremarkable except for a slight increase in creatine kinase (CK). Whole-exome sequencing (WES) was performed for five family members, including the proband and his symptomatic brother, their mother and two asymptomatic siblings. A very rare 3' splice site acceptor intronic variant, NM_001849.4: c.1817-3C>G, located three nucleotides before exon 25, was identified in COL6A2. Bioinformatics tools (SpliceAI, dbscSNV, FATHMM-MKL, and MaxEntScan) predicted this variant as pathogenic. The proband and his 6-year-old sibling presented a homozygous genotype for the variant, whereas the mother and one asymptomatic sibling were heterozygous, and the other sibling carried homozygous wild-type alleles. Conclusions: This is the first study to report a case of Bethlem myopathy confirmed by WES in Saudi Arabia and all Arab nations. The identified variant is rare, and its segregation pattern suggests autosomal recessive inheritance. The segregation pattern and bioinformatics tool results may qualify this variant to be annotated as pathogenic, addressing the reported uncertainty of its classification. Our findings contribute to linking and filling the knowledge gap of diagnosing and managing patients with collagen VI-related myopathies, providing greater clinical and genetic understanding to the existing knowledge.

Duchenne muscular dystrophy in Saudi Arabia: a review of the current literature

In the past three decades, significant improvements have occurred in the study of Duchenne muscular dystrophy (DMD). DMD is a rare, severe neuromuscular disease that causes death due to cardiovascular and respiratory complications among affected boys. Since the 1980s, ongoing preclinical and clinical studies have been conducted to explore the disease in depth and discover potential therapeutic strategies. In Saudi Arabia, it is unclear whether health services and research efforts are keeping pace with global achievements. Therefore, this review aims to explore the diagnostic and management strategies and research efforts in Saudi Arabia over the past three decades. I searched the PubMed/Medline, Scopus, and Web of Science databases and included all published articles on the epidemiology, genetics, diagnosis, and management of DMD/BMD in this review. The findings suggest a lack of local standardized diagnostic strategies, a poor understanding of epidemiology and common pathogenic variants, and a critical need for preclinical and clinical research. At the time of writing, no such comprehensive review has been published. Challenges, limitations, and future perspectives are also discussed in this article.

Cardiomyopathy in Duchenne Muscular Dystrophy and the Potential for Mitochondrial Therapeutics to Improve Treatment Response

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by mutations to the dystrophin gene, resulting in deficiency of dystrophin protein, loss of myofiber integrity in skeletal and cardiac muscle, and eventual cell death and replacement with fibrotic tissue. Pathologic cardiac manifestations occur in nearly every DMD patient, with the development of cardiomyopathy-the leading cause of death-inevitable by adulthood. As early cardiac abnormalities are difficult to detect, timely diagnosis and appropriate treatment modalities remain a challenge. There is no cure for DMD; treatment is aimed at delaying disease progression and alleviating symptoms. A comprehensive understanding of the pathophysiological mechanisms is crucial to the development of targeted treatments. While established hypotheses of underlying mechanisms include sarcolemmal weakening, upregulation of pro-inflammatory cytokines, and perturbed ion homeostasis, mitochondrial dysfunction is thought to be a potential key contributor. Several experimental compounds targeting the skeletal muscle pathology of DMD are in development, but the effects of such agents on cardiac function remain unclear. The synergistic integration of small molecule- and gene-target-based drugs with metabolic-, immune-, or ion balance-enhancing compounds into a combinatorial therapy offers potential for treating dystrophin deficiency-induced cardiomyopathy, making it crucial to understand the underlying mechanisms driving the disorder.

Ablation of the dystrophin Dp71f alternative C-terminal variant increases sarcoma tumour cell aggressiveness

Alterations in Dp71 expression, the most ubiquitous dystrophin isoform, have been associated with patient survival across tumours. Intriguingly, in certain malignancies, Dp71 acts as a tumour suppressor, while manifesting oncogenic properties in others. This diversity could be explained by the expression of two Dp71 splice variants encoding proteins with distinct C-termini, each with specific properties. Expression of these variants has impeded the exploration of their unique roles. Using CRISPR/Cas9, we ablated the Dp71f variant with the alternative C-terminus in a sarcoma cell line not expressing the canonical C-terminal variant, and conducted molecular (RNAseq) and functional characterisation of the knockout cells. Dp71f ablation induced major transcriptomic alterations, particularly affecting the expression of genes involved in calcium signalling and ECM-receptor interaction pathways. The genome-scale metabolic analysis identified significant downregulation of glucose transport via membrane vesicle reaction (GLCter) and downregulated glycolysis/gluconeogenesis pathway. Functionally, these molecular changes corresponded with, increased calcium responses, cell adhesion, proliferation, survival under serum starvation and chemotherapeutic resistance. Knockout cells showed reduced GLUT1 protein expression, survival without attachment and their migration and invasion in vitro and in vivo were unaltered, despite increased matrix metalloproteinases release. Our findings emphasise the importance of alternative splicing of dystrophin transcripts and underscore the role of the Dp71f variant, which appears to govern distinct cellular processes frequently dysregulated in tumour cells. The loss of this regulatory mechanism promotes sarcoma cell survival and treatment resistance. Thus, Dp71f is a target for future investigations exploring the intricate functions of specific DMD transcripts in physiology and across malignancies.

Cardioprotective Effects of Hydrogen Sulfide and Its Potential Therapeutic Implications in the Amelioration of Duchenne Muscular Dystrophy Cardiomyopathy

Hydrogen sulfide (H2S) belongs to the family of gasotransmitters and can modulate a myriad of biological signaling pathways. Among others, its cardioprotective effects, through antioxidant, anti-inflammatory, anti-fibrotic, and proangiogenic activities, are well-documented in experimental studies. Cardiorespiratory failure, predominantly cardiomyopathy, is a life-threatening complication that is the number one cause of death in patients with Duchenne muscular dystrophy (DMD). Although recent data suggest the role of H2S in ameliorating muscle wasting in murine and Caenorhabditis elegans models of DMD, possible cardioprotective effects have not yet been addressed. In this review, we summarize the current understanding of the role of H2S in animal models of cardiac dysfunctions and cardiac cells. We highlight that DMD may be amenable to H2S supplementation, and we suggest H2S as a possible factor regulating DMD-associated cardiomyopathy.

Qualitative and Quantitative Electrocardiogram Parameters in a Large Cohort of Children with Duchenne Muscle Dystrophy in Comparison with Age-Matched Healthy Subjects: A Study from South India

Background

Electrocardiography (ECG) remains an excellent screening tool for cardiac assessment in Duchenne muscular dystrophy (DMD), but an accurate interpretation requires comparison with age-matched healthy controls.

Objective

We examined various ECG parameters in children with DMD, in comparison with age-matched controls.

Methods

Standard 12-lead ECG tracings of serial patients were screened for quality and selected. Controls were healthy, age-matched school-going children. Both quantitative and qualitative ECG parameters were analyzed.

Results

After screening, ECGs from 252 patients with DMD (8.32 ± 3.12 years, 2-21 years) and ECGs from 151 age-matched healthy controls (9.72 ± 2.23, 4-19 years) were included. A significantly higher heart rate, shorter R-R interval, and taller R wave in V1 were seen across all age group of DMD in comparison to controls, with the difference increasing with age. While QT prolongation was seen in all age groups of DMD, QTc prolongation was seen only at 10 years or more. Incomplete right bundle branch block (RBBB) and pathological Q waves in inferolateral leads were exclusive in DMD, with the latter declining with age. Evidence for left ventricular (LV) pathology, such as tall R in V5/V6, increase in SV1 + RV6 height, and QRS complex duration, were seen only in the age group of 10 years or more.

Conclusion

Stratification based on age and comparison with age-matched healthy subjects showed that several ECG parameters were influenced by age, and it also identified age-dependent evidence for LV pathology and QTc prolongation in DMD.

Regional 4D Cardiac Magnetic Resonance Strain Predicts Cardiomyopathy Progression in Duchenne Muscular Dystrophy

Background

Cardiomyopathy (CMP) is the leading cause of death in Duchenne muscular dystrophy (DMD). Characterization of disease trajectory can be challenging, especially in the early stage of CMP where onset and clinical progression may vary. Traditional metrics from cardiovascular magnetic resonance (CMR) imaging such as LVEF (left ventricular ejection fraction) and LGE (late gadolinium enhancement) are often insufficient for assessing disease trajectory. We hypothesized that strain patterns from a novel 4D (3D+time) CMR regional strain analysis method can be used to predict the rate of DMD CMP progression.

Methods

We compiled 115 short-axis cine CMR image stacks for n=40 pediatric DMD patients (13.6±4.2 years) imaged yearly for 3 consecutive visits and computed regional strain metrics using custom-built feature tracking software. We measured regional strain parameters by determining the relative change in the localized 4D endocardial surface mesh using end diastole as the initial reference frame.

Results

We first separated patients into two cohorts based on their initial CMR: LVEF≥55% (n=28, normal cohort) and LVEF<55% (n=12, abnormal cohort). Using LVEF decrease measured two years following the initial scan, we further subclassified these cohorts into slow (ΔLVEF%≤5) or fast (ΔLVEF%>5) progression groups for both the normal cohort (n=12, slow; n=15, fast) and the abnormal cohort (n=8, slow; n=4, fast). There was no statistical difference between the slow and fast progression groups in standard biomarkers such as LVEF, age, or LGE status. However, basal circumferential strain (Ecc) late diastolic strain rate and basal surface area strain (Ea) late diastolic strain rate magnitude were significantly decreased in fast progressors in both normal and abnormal cohorts (p<0.01, p=0.04 and p<0.01, p=0.02, respectively). Peak Ea and Ecc magnitudes were also decreased in fast progressors, though these only reached statistical significance in the normal cohort (p<0.01, p=0.24 and p<0.01, p=0.18, respectively).

Conclusion

Regional strain metrics from 4D CMR can be used to differentiate between slow or fast CMP progression in a longitudinal DMD cohort. These results demonstrate that 4D CMR strain is useful for early identification of CMP progression in patients with DMD.

Clinical Perspective

Cardiomyopathy is the number one cause of death in Duchenne muscular dystrophy, but the onset and progression of the disease are variable and heterogeneous. In this study, we used a novel 4D cardiovascular magnetic resonance regional strain analysis method to evaluate 40 pediatric Duchenne patients over three consecutive annual visits. From our analysis, we found that peak systolic strain and late diastolic strain rate were early indicators of cardiomyopathy progression. This method offers promise for early detection and monitoring, potentially improving patient outcomes through timely intervention and management.

Dystrophic cardiomyopathy: role of the cardiac myofilaments

Dystrophic cardiomyopathy arises from mutations in the dystrophin gene. Dystrophin forms part of the dystrophin glycoprotein complex and is postulated to act as a membrane stabilizer, protecting the sarcolemma from contraction-induced damage. Duchenne muscular dystrophy (DMD) is the most severe dystrophinopathy, caused by a total absence of dystrophin. Patients with DMD present with progressive skeletal muscle weakness and, because of treatment advances, a cardiac component of the disease (i.e., dystrophic cardiomyopathy) has been unmasked later in disease progression. The role that myofilaments play in dystrophic cardiomyopathy is largely unknown and, as such, this study aimed to address cardiac myofilament function in a mouse model of muscular dystrophy. To assess the effects of DMD on myofilament function, isolated permeabilized cardiomyocytes of wild-type (WT) littermates and Dmd^mdx-4cv mice were attached between a force transducer and motor and subjected to contractile assays. Maximal tension and rates of force development (indexed by the rate constant, k _tr) were similar between WT and Dmd^mdx-4cv cardiac myocyte preparations. Interestingly, Dmd^mdx-4cv cardiac myocytes exhibited greater sarcomere length dependence of peak power output compared to WT myocyte preparations. These results suggest dystrophin mitigates length dependence of activation and, in the absence of dystrophin, augmented sarcomere length dependence of myocyte contractility may accelerate ventricular myocyte contraction-induced damage and contribute to dystrophic cardiomyopathy. Next, we assessed if mavacamten, a small molecule modulator of thick filament activation, would mitigate contractile properties observed in Dmd^mdx-4cv permeabilized cardiac myocyte preparations. Mavacamten decreased maximal tension and k _tr in both WT and Dmd^mdx-4cv cardiac myocytes, while also normalizing the length dependence of peak power between WT and Dmd^mdx-4cv cardiac myocyte preparations. These results highlight potential benefits of mavacamten (i.e., reduced contractility while maintaining exquisite sarcomere length dependence of power output) as a treatment for dystrophic cardiomyopathy associated with DMD.

Bioinformatic Analysis of the Subproteomic Profile of Cardiomyopathic Tissue

Following large-scale protein separation by two-dimensional gel electrophoresis or liquid chromatography, mass spectrometry-based proteomics can be used for the swift identification and characterization of cardiac proteins and their various proteoforms. Comparative cardiac proteomics has been widely applied for the systematic analysis of heart disease and the establishment of novel diagnostic protein biomarkers. The X-linked neuromuscular disorder Duchenne muscular dystrophy is a multisystemic disease that is characterized by late-onset cardiomyopathy. This chapter outlines the bioinformatic analysis of the subproteomic profile of cardiac tissue from wild-type versus the dystrophic mdx-4cv mouse model of dystrophinopathy.

The multifaceted view of heart problem in Duchenne muscular dystrophy

Dystrophin is a large protein serving as local scaffolding repetitively bridging cytoskeleton and the outside of striated muscle cell. As such dystrophin is a critical brick primarily in dystrophin-associated protein complex (DAGC) and in a larger submembranous unit, costamere. Accordingly, the lack of functional dystrophin laying at the root of Duchenne muscular dystrophy (DMD) drives sarcolemma instability. From this point on, the cascade inevitably leading to the death of myocyte begins. In cardiomyocytes, intracellular calcium overload and related mitochondrial-mediated cell death mainly contribute to myocardial dysfunction and dilation while other protein dysregulation and/or mislocalization may affect electrical conduction system and favor arrhythmogenesis. Although clinically DMD manifests as progressive muscle weakness and skeletal muscle symptoms define characteristic of DMD, it is the heart problem the biggest challenge that most often develop in the form of dilated cardiomyopathy (DCM). Current standards of treatment and recent progress in respiratory care, introduced in most settings in the 1990s, have improved quality of life and median life expectancy to 4th decade of patient's age. At the same time, cardiac causes of death related to DMD increases. Despite preventive and palliative cardiac treatments available, the prognoses remain poor. Direct therapeutic targeting of dystrophin deficiency is critical, however, hindered by the large size of the dystrophin cDNA and/or stochastic, often extensive genetic changes in DMD gene. The correlation between cardiac involvement and mutations affecting specific dystrophin isoforms, may provide a mutation-specific cardiac management and novel therapeutic approaches for patients with CM. Nonetheless, the successful cardiac treatment poses a big challenge and may require combined therapy to combat dystrophin deficiency and its after-effects (critical in DMD pathogenesis). This review locates the multifaceted heart problem in the course of DMD, balancing the insights into basic science, translational efforts and clinical manifestation of dystrophic heart disease.

New diagnostic and therapeutic modalities in neuromuscular disorders in children

Pediatric neuromuscular disorders are a diverse group of conditions that affect how muscle and nerve function. They involve the motor neurons, nerves, neuromuscular junction and muscles. Pathology of any of these regions leads to the inability to perform voluntary movements. Over time, the natural progression of most of these disorders is followed by significant disability, and at the most extreme, almost complete paralysis and death secondary to complications. Diagnostic measures for pediatric neuromuscular disorders, like that of most medical conditions, relies heavily on clinical presentation, history and a detailed physical examination. Primary additional diagnostic measures have included serum creatine kinase (CK) levels, electromyography (EMG), nerve conduction studies (NCS) and muscle or nerve biopsies, which has historically been the gold standard. In the last several decades less invasive testing has become more common such as muscle magnetic resonance imaging (MRI) and genetic testing.  The advances of molecular genetics, such as next generation sequencing (NGS) which includes whole-exome sequencing (WES) and whole-genome sequencing (WGS), enable clinicians to pinpoint more accurately exact gene mutations. The advent of genetic testing enhances personalized medicine. The field of pediatric neuromuscular disorders is also undergoing a remarkable evolution in therapeutic modalities including novel targeted therapies such as exon skipping/inclusion and gene replacement therapies. This is a review of the initial approach to suspected neuromuscular disorders in children as well as up to date diagnostic and therapeutic modalities for the most common pediatric neuromuscular disorders. As the world enters the new decade, there are encouraging therapeutic results. However, there remain key challenges to these modalities including limitations in its applicability, optimization for delivery of gene replacement therapies and in its effectiveness.

The role of imaging in characterizing the cardiac natural history of Duchenne muscular dystrophy

Duchene muscular dystrophy (DMD) is a rare but devastating disease resulting in progressive loss of ambulation, respiratory failure, DMD-associated cardiomyopathy (DMD-CM), and premature death. The use of corticosteroids and supportive respiratory care has improved outcomes, such that DMD-CM is now the leading cause of death. Historically, most programs have focused on skeletal myopathy with less attention to the cardiac phenotype. This omission is rather astonishing since patients with DMD possess an absolute genetic risk of developing cardiomyopathy. Unfortunately, heart failure signs and symptoms are vague due to skeletal muscle myopathy leading to limited ambulation. Traditional assessment of cardiac symptoms by the New York Heart Association American College of Cardiology/American Heart Association Staging (ACC/AHA) classification is of limited utility, even in advanced stages. Echocardiographic assessment can detect cardiac dysfunction late in the disease course, but this has proven to be a poor surrogate marker of early cardiovascular disease and an inadequate predictor of DMD-CM. Indeed, one explanation for the paucity of cardiac therapeutic trials for DMD-CM has been the lack of a suitable end-point. Improved outcomes require a better proactive treatment strategy; however, the barrier to treatment is the lack of a sensitive and specific tool to assess the efficacy of treatment. The use of cardiac imaging has evolved from echocardiography to cardiac magnetic resonance imaging to assess cardiac performance. The purpose of this article is to review the role of cardiac imaging in characterizing the cardiac natural history of DMD-CM, highlighting the prognostic implications and an outlook on how this field might evolve in the future.

Therapeutic Approaches for Duchenne Muscular Dystrophy: Old and New

Duchenne muscular dystrophy (DMD) is marked by pathogenic variants in the DMD gene, leading to reduced or absent dystrophin translation, muscle fiber destruction, loss of ambulation, cardiomyopathy, respiratory failure, and eventually death. Disease progression is slowed with use of prednisone or other corticosteroid agents. Gene replacement therapy, which is one of the focus points of this review, has emerged as the most promising potential treatment for DMD, though alternative RNA-based strategies have been employed for patients with specific pathogenic variants. While challenges remain, many of these novel therapeutic approaches hold promise for treating this devastating disease.

Impaired myocardial strain in early stage of Duchenne muscular dystrophy: its relation with age and motor performance

Duchenne muscular dystrophy (DMD) is complicated by an early and progressive left ventricular (LV) dysfunction. Despite the reduction of ejection fraction (EF) usually manifests in the second decade, subtle alterations in LV mechanics can be detected earlier. Longitudinal and circumferential LV deformation, evaluated by speckle tracking echocardiography (STE), are considered sensitive markers of early dysfunction. We retrospectively examined clinical and echocardiographic data of 32 DMD children with preserved LV function. According to the median age, patients were then divided into younger and older than 9 years, and compared to 24 age-matched healthy subjects. Six-minute-walk test (6MWT), North Star Ambulatory Assessment (NSAA), and a comprehensive cardiac evaluation were performed. Although EF was within the normal range, DMD patients had significantly lower values than healthy controls, and the same occurred for the remaining conventional systolic and diastolic indices. Global longitudinal strain (GLS) was reduced in all patients (older and younger, both p < 0.001). Global circumferential strain (GCS) was reduced only in older patients (< 0.001). Both GLS and GCS worsened with age in DMD patients (GLS p = 0.005; GCS p = 0.024). GLS was significantly worse in the apical segments and in the postero-lateral wall. GCS in the antero-septal, anterior and antero-lateral segments was significantly reduced in older patients, with a prevalent involvement of the sole septal wall in the younger boys. 6MWT appeared to be correlated inversely to GLS and directly to EF. A longitudinal evaluation should be scheduled in DMD boys to assess the global cardiac performance over time and to evaluate the impact of therapies.

Progressive Proteome Changes in the Myocardium of a Pig Model for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene, is characterized by progressive muscle weakness. Even though DMD manifests first in skeletal muscle, heart failure is a major cause of death in late-stage DMD. To get insights into DMD-associated cardiomyopathy, we performed a proteome analysis of myocardium from a genetically engineered porcine DMD model resembling clinical and pathological hallmarks of human DMD. To capture DMD progression, samples from 2-day- and 3-month-old animals were analyzed. Dystrophin was absent in all DMD samples, and components of the dystrophin-associated protein complex were decreased, suggesting destabilization of the cardiomyocyte plasma membrane and impaired cellular signaling. Furthermore, abundance alterations of proteins known to be associated with human cardiomyopathy were observed. Compared with data from skeletal muscle, we found clear evidence that DMD progression in myocardium is not only slower than in skeletal muscle but also involves different biological and biochemical pathways.