Echocardiographic and electrocardiographic findings of cardiomyopathy in Duchenne and Becker-Kiener muscular dystrophies

Plasticity occurs in a specific phenotype of neurons in the nucleus tractus solitarius of dystrophin gene-mutated rats

Duchenne muscular dystrophy (DMD) is a severe progressive neuromuscular disorder that causes cardiac and respiratory failure. Patients with DMD have tachycardia and autonomic nervous dysfunction at a young age, which can potentially worsen cardiorespiratory function. Therefore, we hypothesised that plasticity occurs in neurons of the cardiorespiratory brainstem nucleus (nucleus tractus solitarius [NTS]) due to DMD, thus affecting neuronal regulation because afferent information from cardiorespiratory organs changes with disease progression. Patch-clamp experiments were performed on second-order NTS neurons from Dmd-mutated (Dm) rats that showed no functional dystrophin protein expression, as confirmed by immunohistochemistry. NTS neurons are classified into two electrophysiological phenotypes: one showing a delayed onset of spiking from hyperpolarised membrane potentials, namely, delayed-onset spiking (DS)-type neurons, and the other showing a rapid onset, namely, rapid-onset spiking-type neurons. Neuroplasticity mainly occurs in DS-type neurons in Dm rats and is characterised by blunted neuronal excitability accompanied by reduced outward currents and a facilitatory effect on synaptic transmission, that is, an increased frequency of spontaneous and miniature excitatory postsynaptic currents (EPSCs) without changes in the amplitude and an increased amplitude of tractus solitarius-evoked EPSCs without changes in the paired-pulse ratio. Although we cannot rule out the possibility that the neuroplastic changes observed in Dm rats were caused by dystrophin deficiency in the neurons themselves, the plasticity could be caused by cardiorespiratory deterioration and/or adaptation in DMD patients.

Safety and Efficacy of DT-DEC01 Therapy in Duchenne Muscular Dystrophy Patients: A 12 - Month Follow-Up Study After Systemic Intraosseous Administration

Duchenne Muscular Dystrophy (DMD) is a progressive and fatal muscle-wasting disease with no known cure. We previously reported the preliminary safety and efficacy up to six months after the administration of DT-DEC01, a novel Dystrophin Expressing Chimeric (DEC) cell therapy created by fusion of myoblasts of DMD patient and the normal donor. In this 12-month follow-up study, we report on the safety and functional outcomes of three DMD patients after the systemic intraosseous administration of DT-DEC01. The safety of DT-DEC01 was confirmed by the absence of Adverse Events (AE) and Severe Adverse Events (SAE) up to 21 months after intraosseous DT-DEC01 administration. The lack of presence of anti-HLA antibodies and Donors Specific Antibodies (DSA) further confirmed DT-DEC01 therapy safety. Functional assessments in ambulatory patients revealed improvements in 6-Minute Walk Test (6MWT) and timed functions of North Star Ambulatory Assessment (NSAA). Additionally, improvements in PUL2.0 test and grip strength correlated with increased Motor Unit Potentials (MUP) duration recorded by Electromyography (EMG) in both ambulatory and non-ambulatory patients. DT-DEC01 systemic effect was confirmed by improved cardiac and pulmonary parameters and daily activity recordings. This follow-up study confirmed the safety and preliminary efficacy of DT-DEC01 therapy in DMD-affected patients up to 12 months after intraosseous administration. DT-DEC01 introduces a novel concept of personalized myoblast-based cellular therapy that is irrespective of the mutation type, does not require immunosuppression or the use of viral vectors, and carries no risk of off target mutations. This establishes DT-DEC01 as a promising and universally effective treatment option for all DMD patients.

Neuro-Cardio-Autonomic Modulations in Children with Duchenne Muscular Dystrophy

BACKGROUND AND OBJECTIVE

Duchenne muscular dystrophy (DMD) is a degenerative X-linked muscle disease. Death frequently results from complications in cardiopulmonary systems. Preclinical/early diagnosis of cardiac autonomic abnormalities may aid initiate cardioprotective therapy and enhance prognosis.

METHODS

A cross sectional, prospective study of 38 DMD boys compared with 37 age-matched healthy controls was conducted. Lead II electrocardiography and beat-to-beat blood pressure were recorded to assess heart rate variability (HRV), blood pressure variability (BPV), and baroreceptor sensitivity (BRS) in a standardized environment. Data were analysed and correlated with disease severity and genotype.

RESULTS

In the DMD group, the median age at assessment was 8 years [IQR 7-9 years], the median age at disease onset was 3 years [IQR, 2-6 years], and the mean duration of illness was 4 years [IQR, 2.5-5]. DNA sequencing showed deletions in 34/38 (89.5 %) and duplications in 4/38 (10.5%) patients. The median heart rate in DMD children was significantly higher [101.19 (Range, 94.71-108.49)] /min compared to controls [81 (Range, 76.2-92.76)] /min (p < 0.05). All the assessed HRV and BPV parameters were significantly impaired in DMD cases except for the coefficient of variance of systolic blood pressure. Further, BRS parameters were also significantly reduced in DMD, excluding alpha-LF. A positive correlation was found between alpha HF with age at onset and duration of illness.

CONCLUSION

This study demonstrates a distinct early impairment of neuro-cardio-autonomic regulation in DMD. Simple yet effective non-invasive techniques such as HRV, BPV, and BRS may help identify cardiac dysfunction in a pre-clinical state, paving the way for early cardio-protective therapies and limiting disease progression in DMD patients.

Cardiovascular Disease in Duchenne Muscular Dystrophy

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Cardiomyopathy is the leading cause of death in patients with DMD.

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DMD has no cure, and there is no current consensus for treatment of DMD cardiomyopathy.

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This review discusses therapeutic strategies to potentially reduce or prevent cardiac dysfunction in DMD patients.

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Additional studies are needed to firmly establish optimal treatment modalities for DMD cardiomyopathy.

Duchenne muscular dystrophy (DMD) is a devastating disease affecting approximately 1 in every 3,500 male births worldwide. Multiple mutations in the dystrophin gene have been implicated as underlying causes of DMD. However, there remains no cure for patients with DMD, and cardiomyopathy has become the most common cause of death in the affected population. Extensive research is under way investigating molecular mechanisms that highlight potential therapeutic targets for the development of pharmacotherapy for DMD cardiomyopathy. In this paper, the authors perform a literature review reporting on recent ongoing efforts to identify novel therapeutic strategies to reduce, prevent, or reverse progression of cardiac dysfunction in DMD.

Autonomic modulation at rest and in response to postural change in adolescents with Duchenne muscular dystrophy: a cross-sectional study

BACKGROUND

Analysis of autonomic modulation after postural change may inform the prognosis and guide treatment in different populations. However, this has been insufficiently explored among adolescents with Duchenne muscular dystrophy (DMD).

OBJECTIVE

To investigate autonomic modulation at rest and in response to an active sitting test (AST) among adolescents with DMD.

METHODS

Fifty-nine adolescents were included in the study and divided into two groups: 1) DMD group: adolescents diagnosed with DMD; 2) control group (CG): healthy adolescents. Participants' weight and height were assessed. Lower limb function, motor limitations and functional abilities of the participants in the DMD group were classified using the Vignos scale, Egen classification and motor function measurement, respectively. The following variables were assessed before, during and after AST: systolic blood pressure (SBP), diastolic blood pressure (DBP), respiratory rate (f), oxygen saturation and heart rate (HR). To analyze the autonomic modulation, the HR was recorded beat-by-beat. Heart rate variability (HRV) indices were calculated in the time and frequency domains.

RESULTS

Differences in relation to groups were observed for all HRV indices, except LF/HF, oxygen saturation, HR and f (p < 0.05). Differences in relation to time and the interaction effect between group and time were observed for RMSSD, SD1, SD2, SD1/SD2, LFms2 and LFnu, HFun, SBP and DBP (p < 0.05). Differences in relation to time were also observed for the indice SDNN, FC and f (p < 0.05).

CONCLUSIONS

Performing the AST promoted reduced autonomic modulation and increased SBP, DBP and HR in adolescents with DMD.

[Spinal deformity in Duchenne muscular dystrophy]

Boys with Duchenne muscular dystrophy develop scoliosis in 95% of cases. Conservative management to avoid progression of the deformity is not successful. However, treatment with corticosteroids may avoid the onset of scoliosis in some patients. Early surgical treatment and spine fusion is usually recommended before severe cardiopulmonary symptoms have developed. With modern surgical techniques, the sitting ability and quality of life can be preserved with a moderate complication rate. An interdisciplinary approach is mandatory to achieve these goals.

Exercise Cardiac Magnetic Resonance Imaging in Boys With Duchenne Muscular Dystrophy Without Cardiac Disease

BACKGROUND

Duchenne muscular dystrophy is caused by mutations in the DMD gene, resulting in cardiomyopathy in all affected children by 18 years. Although cardiomyopathy is now the leading cause of mortality in these children, there is ongoing debate regarding timely diagnosis, secondary prevention, and treatment of this condition. The purpose of this study was to use exercise cardiac magnetic resonance imaging in asymptomatic young boys with Duchenne muscular dystrophy to describe their heart function and compare this with healthy controls.

METHODS

We studied 11 boys with Duchenne muscular dystrophy aged 8.6 to 13.9 years and 11 healthy age- and sex-matched controls.

RESULTS

Compared with the controls, boys with Duchenne muscular dystrophy had lower ejection fraction at rest (57% versus 63%; P = 0.004). During submaximal exercise, they reached similar peak tachycardia but increased their heart rate and cardiac output only half as much as controls (P = 0.003 and P = 0.014, respectively). End-systolic volume remained higher in boys with Duchenne muscular dystrophy both at rest and during exercise. When transthoracic echocardiography was compared with cardiac magnetic resonance imaging, 45% of the echocardiograms had suboptimal or poor views in the Duchenne muscular dystrophy group.

CONCLUSIONS

Boys with Duchenne muscular dystrophy had abnormalities in left ventricular systolic function that were exaggerated by exercise stress. Exercise cardiac magnetic resonance imaging is feasible in a select population of children with Duchenne muscular dystrophy, and it has the potential to unmask early signs of cardiomyopathy.

Elimination of fukutin reveals cellular and molecular pathomechanisms in muscular dystrophy-associated heart failure

Heart failure is the major cause of death for muscular dystrophy patients, however, the molecular pathomechanism remains unknown. Here, we show the detailed molecular pathogenesis of muscular dystrophy-associated cardiomyopathy in mice lacking the fukutin gene (Fktn), the causative gene for Fukuyama muscular dystrophy. Although cardiac Fktn elimination markedly reduced α-dystroglycan glycosylation and dystrophin-glycoprotein complex proteins in sarcolemma at all developmental stages, cardiac dysfunction was observed only in later adulthood, suggesting that membrane fragility is not the sole etiology of cardiac dysfunction. During young adulthood, Fktn-deficient mice were vulnerable to pathological hypertrophic stress with downregulation of Akt and the MEF2-histone deacetylase axis. Acute Fktn elimination caused severe cardiac dysfunction and accelerated mortality with myocyte contractile dysfunction and disordered Golgi-microtubule networks, which were ameliorated with colchicine treatment. These data reveal fukutin is crucial for maintaining myocyte physiology to prevent heart failure, and thus, the results may lead to strategies for therapeutic intervention.

Mutations in Ftkn cause Fukuyama muscular dystrophy, and heart failure is the main cause of death in thes patients. Here the authors show that acute elimination of Fktn in adult mice causes early mortality, and this is associated with myocyte dysfunction, with disorganised Golg-microtubule networks, and that the pathology can be ameliorated with colchicine treatment.

Cmah-dystrophin deficient mdx mice display an accelerated cardiac phenotype that is improved following peptide-PMO exon skipping treatment

Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin protein, leading to progressive muscle weakness and premature death due to respiratory and/or cardiac complications. Cardiac involvement is characterized by progressive dilated cardiomyopathy, decreased fractional shortening and metabolic dysfunction involving reduced metabolism of fatty acids-the major cardiac metabolic substrate. Several mouse models have been developed to study molecular and pathological consequences of dystrophin deficiency, but do not recapitulate all aspects of human disease pathology and exhibit a mild cardiac phenotype. Here we demonstrate that Cmah (cytidine monophosphate-sialic acid hydroxylase)-deficient mdx mice (Cmah-/-;mdx) have an accelerated cardiac phenotype compared to the established mdx model. Cmah-/-;mdx mice display earlier functional deterioration, specifically a reduction in right ventricle (RV) ejection fraction and stroke volume (SV) at 12 weeks of age and decreased left ventricle diastolic volume with subsequent reduced SV compared to mdx mice by 24 weeks. They further show earlier elevation of cardiac damage markers for fibrosis (Ctgf), oxidative damage (Nox4) and haemodynamic load (Nppa). Cardiac metabolic substrate requirement was assessed using hyperpolarized magnetic resonance spectroscopy indicating increased in vivo glycolytic flux in Cmah-/-;mdx mice. Early upregulation of mitochondrial genes (Ucp3 and Cpt1) and downregulation of key glycolytic genes (Pdk1, Pdk4, Ppara), also denote disturbed cardiac metabolism and shift towards glucose utilization in Cmah-/-;mdx mice. Moreover, we show long-term treatment with peptide-conjugated exon skipping antisense oligonucleotides (20-week regimen), resulted in 20% cardiac dystrophin protein restoration and significantly improved RV cardiac function. Therefore, Cmah-/-;mdx mice represent an appropriate model for evaluating cardiac benefit of novel DMD therapeutics.

Effect and safety of treatment with ACE-inhibitor Enalapril and β-blocker metoprolol on the onset of left ventricular dysfunction in Duchenne muscular dystrophy - a randomized, double-blind, placebo-controlled trial

BACKGROUND

X-linked Duchenne muscular dystrophy (DMD), the most frequent human hereditary skeletal muscle myopathy, inevitably leads to progressive dilated cardiomyopathy. We assessed the effect and safety of a combined treatment with the ACE-inhibitor enalapril and the β-blocker metoprolol in a German cohort of infantile and juvenile DMD patients with preserved left ventricular function.

METHODS TRIAL DESIGN

Sixteen weeks single-arm open run-in therapy with enalapril and metoprolol followed by a two-arm 1:1 randomized double-blind placebo-controlled treatment in a multicenter setting.

INCLUSION CRITERIA

DMD boys aged 10-14 years with left ventricular fractional shortening [LV-FS] ≥ 30% in echocardiography. Primary endpoint: time from randomization to first occurrence of LV-FS < 28%. Secondary: changes of a) LV-FS from baseline, b) blood pressure, c), heart rate and autonomic function in ECG and Holter-ECG, e) cardiac biomarkers and neurohumeral serum parameters, f) quality of life, and g) adverse events.

RESULTS

From 3/2010 to 12/2013, 38 patients from 10 sites were centrally randomized after run-in, with 21 patients continuing enalapril and metoprolol medication and 17 patients receiving placebo. Until end of study 12/2015, LV-FS < 28% was reached in 6/21 versus 7/17 patients. Cox regression adjusted for LV-FS after run-in showed a statistically non-significant benefit for medication over placebo (hazard ratio: 0.38; 95% confidence interval: 0.12 to 1.22; p = 0.10). Analysis of secondary outcome measures revealed a time-dependent deterioration of LV-FS with no statistically significant differences between the two study arms. Blood pressure, maximal heart rate and mean-NN values were significantly lower at the end of open run-in treatment compared to baseline. Outcome analysis 19 months after randomization displayed significantly lower maximum heart rate and higher noradrenalin and renin values in the intervention group. No difference between treatments was seen for quality of life. As a single, yet important adverse event, the reversible deterioration of walking abilities of one DMD patient during the run-in period was observed.

CONCLUSIONS

Our analysis of enalapril and metoprolol treatment in DMD patients with preserved left ventricular function is suggestive to delay the progression of the intrinsic cardiomyopathy to left ventricular failure, but did not reach statistical significance, probably due to insufficient sample size.

CLINICAL TRIAL REGISTRATION

DRKS-number 00000115, EudraCT-number 2009-009871-36.

Acute AT1R blockade prevents isoproterenol-induced injury in mdx hearts

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked disease characterized by skeletal muscle degeneration and a significant cardiomyopathy secondary to cardiomyocyte damage and myocardial loss. The molecular basis of DMD lies in the absence of the protein dystrophin, which plays critical roles in mechanical membrane integrity and protein localization at the sarcolemma. A popular mouse model of DMD is the mdx mouse, which lacks dystrophin and displays mild cardiac and skeletal pathology that can be exacerbated to advance the disease state. In clinical and pre-clinical studies of DMD, angiotensin signaling pathways have emerged as therapeutic targets due to their adverse influence on muscle remodeling and oxidative stress. Here we aim to establish a physiologically relevant cardiac injury model in the mdx mouse, and determine whether acute blockade of the angiotensin II type 1 receptor (AT₁R) may be utilized for prevention of dystrophic injury.

METHODS AND RESULTS

A single IP injection of isoproterenol (Iso, 10 mg/kg) was used to induce cardiac stress and injury in mdx and wild type (C57Bl/10) mice. Mice were euthanized 8 h, 30 h, 1 week, or 1 month following the injection, and hearts were harvested for injury evaluation. At 8 and 30 h post-injury, mdx hearts showed 2.2-fold greater serum cTnI content and 3-fold more extensive injury than wild type hearts. Analysis of hearts 1 week and 1 month after injury revealed significantly higher fibrosis in mdx hearts, with a more robust and longer-lasting immune response compared to wild type hearts. In the 30-hour group, losartan treatment initiated 1 h before Iso injection protected dystrophic hearts from cardiac damage, reducing mdx acute injury area by 2.8-fold, without any significant effect on injury in wild type hearts. However, both wild type and dystrophic hearts showed a 2-fold reduction in the magnitude of the macrophage response to injury 30 h after Iso with losartan.

CONCLUSIONS

This work demonstrates that acute blockade of AT₁R has the potential for robust injury prevention in a model of Iso-induced dystrophic heart injury. In addition to selectively limiting dystrophic cardiac damage, blocking AT₁R may serve to limit the inflammatory nature of the immune response to injury in all hearts. Our findings strongly suggest that earlier adoption of angiotensin receptor blockers in DMD patients could limit myocardial damage and subsequent cardiomyopathy.

Imaging the heart to detect cardiomyopathy in Duchenne muscular dystrophy: A review

Duchenne Muscular Dystrophy is the most common paediatric neuromuscular disorder. Mutations in the DMD gene on the X-chromosome result in progressive skeletal muscle weakness as the main clinical manifestation. However, cardiac muscle is also affected, with cardiomyopathy becoming an increasingly recognised cause of morbidity, and now the leading cause of mortality in this group. The diagnosis of cardiomyopathy has often been made late due to technical limitations in transthoracic echocardiograms and delayed symptomatology in less mobile patients. Increasingly, evidence supports earlier pharmacological intervention in cardiomyopathy to improve outcomes. However, the optimal timing of initiation remains uncertain, and the benefits of prophylactic therapy are unproven. Current treatment guidelines suggest initiation of therapy once cardiac dysfunction is detected. This review focuses on new and evolving techniques for earlier detection of Duchenne muscular dystrophy-associated cardiomyopathy. Transthoracic echocardiography or cardiac magnetic resonance imaging performed under physiological stress (dobutamine or exercise), can unmask early cardiac dysfunction. Cardiac magnetic resonance imaging can define cardiac function with greater accuracy and reliability than an echocardiogram, and is not limited by body habitus. Improved imaging techniques, used in a timely fashion, offer the potential for early detection of cardiomyopathy and improved long-term outcomes.

Heart Rate Variability and Cardiopulmonary Dysfunction in Patients with Duchenne Muscular Dystrophy: A Systematic Review

Duchenne muscular dystrophy (DMD) is a genetic recessive disorder with progressive muscle weakness. Despite the general muscle wasting, degeneration and necrosis of cardiomyocytes have been the main causes of morbidity and death in individuals with DMD. Cardiac failure is generally preceded by disturbances in heart rate variability (HRV), and non-invasive measurement of the autonomic nervous system has been an important tool to predict adverse cardiovascular events. Hence, the application of HRV to study autonomic modulation in DMD individuals, and the establishment of correlations between HRV and heart/lung diseases, age, and mortality will have the potential to improve quality of life and life expectancy of individuals with DMD. In order to evaluate the state of the art in this field, we conducted a systematic search in Medline/PubMed and BVS (virtual library in health) databases. We selected 8 studies using pre-defined criteria and meta-analysis revealed decreased parasympathetic activity and increased sympathetic predominance in individuals with DMD as major observations. Moreover, there is a strong association between diminished HRV and myocardial fibrosis with DMD. These patterns are evident in patients at early-stage DMD and become more prominent as disease severity and age increase. Thus, data minning clearly indicates that HRV assessment can be used as a predictor for sudden death in individuals with DMD. The use of the HRV, which is inexpensive, ubiquitously available in clinics and hospitals, and a non-invasive analysis tool, can save lives and decrease the morbity in DMD by alerting care givers to consider autonomic nervous system intervention.

Cardiac Involvement in Duchenne Muscular Dystrophy and Related Dystrophinopathies

Dystrophinopathies include Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), X-linked dilated cardiomyopathy (XLCM), and facioscapulohumeral muscular dystrophy (FSHD). DMD/BMD are X-linked recessive disorders, related to the synthesis of dystrophin. Most of DMD after the third decade of their age develop cardiomyopathy that remains silent, due to relative physical inactivity. Cardiac disease in female carriers presents with hypertrophy, arrhythmias or dilated cardiomyopathy, clinically overt by increasing age.In ECG, DMD presents increased R/S ratio in the right precordial leads, deep Q waves in the lateral leads, conduction abnormalities, and arrhythmias. Echocardiography, although widely available and inexpensive, is highly depended on the acoustic window and operator's experience. Tissue Doppler can be used to identify early changes of cardiomyopathy and detect progressive cardiac damage. CMR, a noninvasive, nonradiating technique, by evaluation of cardiac volumes, mass, ejection fraction, inflammation, and fibrosis, is ideal for early diagnosis. Subepicardial fibrosis in the inferolateral wall is the typical CMR lesion in DMD/BMD.Early initiation of angiotensin converting enzyme inhibitors (ACEI) treatment, such as perindopril, was associated with lower mortality in DMD with normal LV ejection fraction at study entry. Other studies documented that a beta-blocker (BB), in addition to ACEI, improves LV systolic function in MD. These encouraging results recommend initiation of ACEI and/or BB early after diagnosis of the muscular dystrophy, especially in DMD.

Reduced Myocardial Reserve in Young X-Linked Muscular Dystrophy Mice Diagnosed by Two-Dimensional Strain Analysis Combined with Stress Echocardiography

BACKGROUND

Early, sensitive, and reproducible evaluation of left ventricular function is imperative for the diagnosis of cardiac dysfunction in patients with Duchene muscular dystrophy. The aim of this study was to test the hypothesis that combining two-dimensional strain analysis with catecholamine stress could be a sensitive method for detecting early cardiac dysfunction.

METHODS

Mdx (C57BL/10ScSn-Dmdmdx/J, a mouse model of DMD) and control (C57BL/10ScSn) mice were studied with conventional M-mode and high-frequency ultrasound-based two-dimensional speckle-tracking echocardiography using long- and short-axis images of the left ventricle at baseline and after intraperitoneal isoprenaline (ISO) administration (2 μg/g body weight).

RESULTS

Conventional M-mode analysis showed no differences in left ventricular fractional shortening, wall thickness, or internal diameter at diastole between mdx and control mice before the age of 6 months. ISO increased left ventricular ejection fraction and fractional shortening to the same extent in mdx and control mice at young ages (3, 4, and 5 months). No differences in basal peak systolic strain (PSS) but increased SDs of times to PSS between young mdx and control mice were found. After ISO, PSS and percentile changes of PSS were significantly diminished in mdx mice compared with control mice at young ages. ISO increased the normalized maximum difference of times to PSS in young mdx mice but not in young control mice, suggesting that ISO reduces cardiac contractile synchrony in young mdx mice.

CONCLUSIONS

This study suggests that catecholamine stress coupled with two-dimensional strain analysis is a feasible and sensitive approach for detecting early onset of cardiac dysfunction, which is instrumental for early diagnosis of cardiac dysfunction and early treatment.

Dual Therapy Deflazacort/Doxycyclyne Is Better Than Deflazacort Monotherapy to Alleviate Cardiomyopathy in Dystrophin-Deficient mdx Mice

Cardiomyopathy related to the absence of dystrophin is an important feature in Duchenne muscular dystrophy (DMD) and in the mdx mouse. Doxycycline (DOX) could be a potential therapy for mdx skeletal muscles dystrophy. We investigated whether the corticoid deflazacort (DFZ) plus DOX could improve cardiac mdx dystrophy better than DFZ alone, later (17 months) in dystrophy. Mdx mice (8 months old) received DFZ/DOX or DFZ for 9 months. The combined therapy was greater than DFZ in reducing fibrosis (60% decrease with DFZ/DOX and 40% with DFZ alone) in the right ventricle and transforming growth factor β levels (6.8 ± 3.2 in untreated mdx mice, 2.8 ± 1.4 in combined therapy, and 4.6 ± 1.7 in DFZ; P < .05). Combined therapy more effectively ameliorated cardiac dysfunction (electrocardiogram [ECG]) than DFZ. Improvements were seen in the cardiomyopathy index (0.8 ± 0.1 in combined therapy and 1.0 ± 0.2 in DFZ), heart rate (418 ± 46 bpm in combined therapy and 457 ± 29 bpm in DFZ), QRS interval (11.3 ± 2 in combined therapy and 13.6 ± 1 in DFZ), and Q wave amplitude (-40.7 ± 21 in combined therapy and -90.9 ± 36 in DFZ). Both therapies decreased markers of inflammation (tumor necrosis factor α, nuclear factor κB, and metalloproteinase 9). DFZ/DOX improved mdx cardiomyopathy at this stage of the disease, supporting further clinical investigations.

Duchenne muscular dystrophy: the management of scoliosis

This study summaries the current management of scoliosis in patients with Duchenne Muscular Dystrophy. A literature review of Medline was performed and the collected articles critically appraised. This literature is discussed to give an overview of the current management of scoliosis within Duchenne Muscular Dystrophy. Importantly, improvements in respiratory care, the use of steroids and improving surgical techniques have allowed patients to maintain quality of life and improved life expectancy in this patient group.

Implications for Cardiac Function Following Rescue of the Dystrophic Diaphragm in a Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is caused by absence of the integral structural protein, dystrophin, which renders muscle fibres susceptible to injury and degeneration. This ultimately results in cardiorespiratory dysfunction, which is the predominant cause of death in DMD patients, and highlights the importance of therapeutic targeting of the cardiorespiratory system. While there is some evidence to suggest that restoring dystrophin in the diaphragm improves both respiratory and cardiac function, the role of the diaphragm is not well understood. Here using exon skipping oligonucleotides we predominantly restored dystrophin in the diaphragm and assessed cardiac function by MRI. This approach reduced diaphragmatic pathophysiology and markedly improved diaphragm function but did not improve cardiac function or pathophysiology, with or without exercise. Interestingly, exercise resulted in a reduction of dystrophin protein and exon skipping in the diaphragm. This suggests that treatment regimens may require modification in more active patients. In conclusion, whilst the diaphragm is an important respiratory muscle, it is likely that dystrophin needs to be restored in other tissues, including multiple accessory respiratory muscles, and of course the heart itself for appropriate therapeutic outcomes. This supports the requirement of a body-wide therapy to treat DMD.

Current understanding of molecular pathology and treatment of cardiomyopathy in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic muscle disorder caused by mutations in the Dmd gene resulting in the loss of the protein dystrophin. Patients do not only experience skeletal muscle degeneration, but also develop severe cardiomyopathy by their second decade, one of the main causes of death. The absence of dystrophin in the heart renders cardiomyocytes more sensitive to stretch-induced damage. Moreover, it pathologically alters intracellular calcium (Ca²⁺) concentration, neuronal nitric oxide synthase (nNOS) localization and mitochondrial function and leads to inflammation and necrosis, all contributing to the development of cardiomyopathy. Current therapies only treat symptoms and therefore the need for targeting the genetic defect is immense. Several preclinical therapies are undergoing development, including utrophin up-regulation, stop codon read-through therapy, viral gene therapy, cell-based therapy and exon skipping. Some of these therapies are undergoing clinical trials, but these have predominantly focused on skeletal muscle correction. However, improving skeletal muscle function without addressing cardiac aspects of the disease may aggravate cardiomyopathy and therefore it is essential that preclinical and clinical focus include improving heart function. This review consolidates what is known regarding molecular pathology of the DMD heart, specifically focusing on intracellular Ca²⁺, nNOS and mitochondrial dysregulation. It briefly discusses the current treatment options and then elaborates on the preclinical therapeutic approaches currently under development to restore dystrophin thereby improving pathology, with a focus on the heart.

Feasibility and Reproducibility of Echocardiographic Measures in Children with Muscular Dystrophies

BACKGROUND

Cardiac disease is a major cause of death in patients with muscular dystrophies. The use of feasible and reproducible echocardiographic measures of cardiac function is critical to advance the field of therapeutics for dystrophic cardiomyopathy.

METHODS

Participants aged 8 to 18 years with genetically confirmed Duchenne muscular dystrophy (DMD), Becker muscular dystrophy, or limb-girdle muscular dystrophy were enrolled at five centers, and standardized echocardiographic examinations were performed. Measures of systolic and diastolic function and speckle-tracking echocardiography-derived cardiac strain were reviewed independently by two central readers. Furthermore, echocardiographic measures from participants with DMD were compared with those from retrospective age-matched control subjects from a single site to assess measures of myocardial function.

RESULTS

Forty-eight participants (mean age, 13.3 ± 2.7 years) were enrolled. Shortening fraction had a greater interobserver correlation (intraclass correlation coefficient [ICC] = 0.63) compared with ejection fraction (ICC = 0.49). One reader could measure ejection fraction in only 53% of participants. Myocardial performance index measured by pulse-wave Doppler and Doppler tissue imaging showed similar ICCs (0.55 and 0.54). Speckle-tracking echocardiography showed a high ICC (0.96). Focusing on participants with DMD (n = 33), significantly increased mitral A-wave velocities, lower E/A ratios, and lower Doppler tissue imaging mitral lateral E' velocities were observed compared with age-matched control subjects. Speckle-tracking echocardiography demonstrated subclinical myocardial dysfunction with decreased average circumferential and longitudinal strain in three distinct subgroups: participants with DMD with normal shortening fractions, participants with DMD aged < 13 years, and participants with DMD with myocardial performance index scores < 0.40 compared with control subjects.

CONCLUSIONS

In a muscular dystrophy cohort, assessment of cardiac function is feasible and reproducible using shortening fraction, diastolic measures, and myocardial performance index. Cardiac strain measures identified early myocardial disease in patients with DMD.

Short-term effects of corticosteroid therapy on cardiac and skeletal muscles in muscular dystrophies

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood. It leads to progressive deterioration in cardiac and skeletal muscles. Corticosteroids are considered an effective therapy.

OBJECTIVE

This study aimed to evaluate the role of short-term prednisone therapy in improving left ventricular (LV) systolic function, LV mass (LVM), and motor power in cases of muscular dystrophies.

PATIENTS AND METHODS

Twenty-five cases of muscular dystrophy including 17 cases of DMD, 3 cases of Becker muscular dystrophies, and 5 cases of female patients with DMD-like phenotype were included in the study. The diagnosis of 12 patients was confirmed by muscle biopsy with immunohistochemistry; the patients were subjected to motor assessment, measurement of creatine kinase level, and echocardiographic examination before and after prednisone therapy. Transthoracic echocardiographic assessment of the LV systolic function (fractional shortening) was done. Myocardial performance index and LVM were calculated. Intermittent dosage of prednisone was administered 5 mg/kg per day on 2 consecutive days weekly for 3 months.

RESULTS

Fractional shortening improved on prednisone therapy (P = 0.009) and LVM increased (P = 0.012); improvement in walking was detected in 77% of the patients, climbing stairs improved in 88.9%, Gower sign improved in 70%, and rising from chair improved in 60%. Prednisone had no effect on the patients with marked motor impairment (on wheelchair). The creatine kinase level was significantly lower after steroid therapy (P = 0.04).

CONCLUSIONS

Three months of intermittent prednisone therapy could improve cardiac and skeletal muscle function in congenital muscular dystrophy.

Myocardial fibrosis burden predicts left ventricular ejection fraction and is associated with age and steroid treatment duration in duchenne muscular dystrophy

Background

Patients with Duchenne muscular dystrophy exhibit progressive cardiac and skeletal muscle dysfunction. Based on prior data, cardiac dysfunction in Duchenne muscular dystrophy patients may be influenced by myocardial fibrosis and steroid therapy. We examined the longitudinal relationship of myocardial fibrosis and ventricular dysfunction using cardiac magnetic resonance in a large Duchenne muscular dystrophy cohort.

Methods and Results

We reviewed 465 serial cardiac magnetic resonance studies (98 Duchenne muscular dystrophy patients with ≥4 cardiac magnetic resonance studies) for left ventricular ejection fraction (LVEF) and presence of late gadolinium enhancement (LGE), a marker for myocardial fibrosis. LVEF was modeled by examining LGE status, myocardial fibrosis burden (as assessed by the number of LGE‐positive left ventricular segments), patient age, and steroid treatment duration. An age‐only model demonstrated that LVEF declined 0.58±0.10% per year. In patients with both LGE‐negative and LGE‐positive studies (n=51), LVEF did not decline significantly over time if LGE was absent but declined 2.2±0.31% per year when LGE was present. Univariate modeling showed significant associations between LVEF and steroid treatment duration, presence of LGE, and number of LGE‐positive left ventricular segments; multivariate modeling showed that LVEF declined by 0.93±0.09% for each LGE‐positive left ventricular segment, whereas age and steroid treatment duration were not significant. The number of LGE‐positive left ventricular segments increased with age, and longer steroid treatment duration was associated with lower age‐related increases.

Conclusion

Progressive myocardial fibrosis, as detected by LGE, was strongly correlated with the LVEF decline in Duchenne muscular dystrophy patients. Longer steroid treatment duration was associated with a lower age‐related increase in myocardial fibrosis burden.

Prevention of exercised induced cardiomyopathy following Pip-PMO treatment in dystrophic mdx mice

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disorder caused by mutations in the Dmd gene. In addition to skeletal muscle wasting, DMD patients develop cardiomyopathy, which significantly contributes to mortality. Antisense oligonucleotides (AOs) are a promising DMD therapy, restoring functional dystrophin protein by exon skipping. However, a major limitation with current AOs is the absence of dystrophin correction in heart. Pip peptide-AOs demonstrate high activity in cardiac muscle. To determine their therapeutic value, dystrophic mdx mice were subject to forced exercise to model the DMD cardiac phenotype. Repeated peptide-AO treatments resulted in high levels of cardiac dystrophin protein, which prevented the exercised induced progression of cardiomyopathy, normalising heart size as well as stabilising other cardiac parameters. Treated mice also exhibited significantly reduced cardiac fibrosis and improved sarcolemmal integrity. This work demonstrates that high levels of cardiac dystrophin restored by Pip peptide-AOs prevents further deterioration of cardiomyopathy and pathology following exercise in dystrophic DMD mice.

Application of 3-d echocardiography and gated micro-computed tomography to assess cardiomyopathy in a mouse model of duchenne muscular dystrophy

The purpose of this study was to measure changes in cardiac function as cardiomyopathy progresses in a mouse model of Duchenne muscular dystrophy using 3-D ECG-gated echocardiography. This study is the first to correlate cardiac volumes acquired using 3-D echocardiography with those acquired using retrospectively gated micro-computed tomography (CT). Both were further compared with standard M-mode echocardiography and histologic analyses. We found that although each modality measures a decrease in cardiac function as disease progresses in mdx/utrn(-/-) mice (n = 5) compared with healthy C57BL/6 mice (n = 8), 3-D echocardiography has higher agreement with gold-standard measurements acquired by gated micro-CT, with little standard deviation between measurements. M-Mode echocardiography measurements, in comparison, exhibit considerably greater variability and user bias. Given the radiation dose associated with micro-CT and the geometric assumptions made in M-mode echocardiography to calculate ventricular volume, we suggest that use of 3-D echocardiography has important advantages that may allow for the measurement of early disease changes that occur before overt cardiomyopathy.

Cooperative International Neuromuscular Research Group Duchenne Natural History Study demonstrates insufficient diagnosis and treatment of cardiomyopathy in Duchenne muscular dystrophy

INTRODUCTION

Cardiomyopathy is a common cause of morbidity and death in patients with Duchenne muscular dystrophy (DMD).

METHODS

This investigation was a cross-sectional cross-sectional analysis of clinical data from the multi-institutional Cooperative International Neuromuscular Research Group (CINRG) DMD Natural History Study of 340 DMD patients aged 2-28 years. Cardiomyopathy was defined as shortening fraction (SF) <28% or ejection fraction (EF) <55%.

RESULTS

Two hundred thirty-one participants reported a prior clinical echocardiogram study, and 174 had data for SF or EF. The prevalence of cardiomyopathy was 27% (47 of 174), and it was associated significantly with age and clinical stage. The association of cardiomyopathy with age and clinical stage was not changed by glucocorticoid use as a covariate (P > 0.68). In patients with cardiomyopathy, 57% (27 of 47) reported not taking any cardiac medications. Cardiac medications were used in 12% (15 of 127) of patients without cardiomyopathy.

CONCLUSIONS

We found that echocardiograms were underutilized, and cardiomyopathy was undertreated in this DMD natural history cohort.

Assessment of cardiac autonomic function in patients with Duchenne muscular dystrophy using short term heart rate variability measures

BACKGROUND

Duchenne muscular dystrophy (DMD) is a hereditary neuromuscular disorder frequently associated with progressive cardiac dysfunction, and is one of the common causes of death in these children. Early diagnostic markers of cardiac involvement might help in timely intervention. In this study we compared the short term HRV measures of DMD children with that of healthy subjects.

METHOD

One hundred and twenty-four genetically confirmed boys with DMD and 50 age matched controls were recruited. Error-free, electrocardiogram was recorded in all subjects at rest in the supine position. HRV parameters were computed in time and frequency domains. Time domain measures included standard deviation of NN interval (SDNN), and root of square mean of successive NN interval (RMSSD). Frequency domain consisted of total, low frequency and high frequency power values. Ratio of low frequency and high frequency power values (LF/HF) was determined using customized software.

RESULTS

HRV parameters were significantly altered in DMD children as compared to healthy controls. Following parameters [mean (SD)] were reduced in DMD as compared to controls; RMSSD (in ms) [52.14 (33.2) vs 64.64 (43.2); p = 0.038], High frequency component (nu) [38.77 (14.4) vs 48.02 (17.1); p = 0.001] suggesting a loss of vagal tone. In contrast, measure of sympathovagal balance LF/HF [1.18 (0.87) vs 0.89 (0.79); p = 0.020] was increased in DMD group.

CONCLUSION

In this cross sectional study we have demonstrated alteration in autonomic tone in DMD. Loss of vagal tone and an increase in sympathetic tone were observed in DMD children. Further prospective studies are required to confirm the utility of these measures as predictors of adverse cardiac outcome in DMD.

Genetics in dilated cardiomyopathy

Discoveries made during the last 20 years have revealed a genetic origin in many cases of dilated cardiomyopathy (DCM). Currently, over 40 genes have been associated with the disease. Mutations in DCM-causing genes induce the condition through a variety of different pathological pathways with complex and not completely understood mechanisms. Genes that encode for sarcomeric, cytoskeletal, nuclear membrane, dystrophin-associated glycoprotein complex and desmosomal proteins are the principal genes involved. In this review we discuss the most frequent DCM-causing genes. We propose a classification in which DCM genes are considered as being major or minor genes according to their mutation frequency and the available supporting evidence. The main phenotypic characteristics associated with each gene are discussed.

Presentation, diagnosis, and medical management of heart failure in children: Canadian Cardiovascular Society guidelines

Pediatric heart failure (HF) is an important cause of morbidity and mortality in childhood. This article presents guidelines for the recognition, diagnosis, and early medical management of HF in infancy, childhood, and adolescence. The guidelines are intended to assist practitioners in office-based or emergency room practice, who encounter children with undiagnosed heart disease and symptoms of possible HF, rather than those who have already received surgical palliation. The guidelines have been developed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology, and are accompanied by practical Recommendations for their application in the clinical setting, supplemented by online material. This work does not include Recommendations for advanced management involving ventricular assist devices, or other device therapies.

Cardiomyopathy of Duchenne muscular dystrophy: pathogenesis and prospect of membrane sealants as a new therapeutic approach

Duchenne muscular dystrophy (DMD) is a devastating progressive disease of striated muscle deterioration. This fatal X-linked disorder results from the loss of the protein dystrophin, which in turn causes striated muscle membrane instability. Cardiac dysfunction is a growing problem in patients with DMD, but relatively little is known about the pathophysiology of the dystrophic heart. At present, there is no effective treatment for DMD and the current clinical approaches are primarily supportive in nature. This review will discuss the pathogenesis of DMD in the heart and discuss how these pathogenic processes have led to a new class of agents directed specifically at restoring membrane integrity to dystrophic myocardium. The tri-block poloxamers, specifically poloxamer 188 (P188), are able to stabilize the membranes of dystrophic myocardium in animal models and may offer a new therapeutic approach for cardiac disease in DMD.

A randomized, double-blind trial of lisinopril and losartan for the treatment of cardiomyopathy in duchenne muscular dystrophy

OBJECTIVES

This study sought to compare the effectiveness and safety of an angiotensin converting enzyme inhibitor (ACE-I) (lisinopril) vs. an angiotensin receptor blocker (ARB) (losartan) for the treatment of cardiomyopathy (CM) in boys with Duchenne muscular dystrophy (DMD).

BACKGROUND

Development of CM is universal in boys with DMD. ACE-I and ARB have both been suggested as effective treatment options. ARBs have been associated with skeletal muscle regeneration in a mouse model of DMD. The question of which, if either, is more effective for CM treatment in DMD remains. The purpose of this multicenter double-blind prospective study was to compare efficacy and safety of lisinopril versus losartan in the treatment of newly diagnosed CM in boys with DMD.

METHODS

Echocardiographic technician inter- and intraobserver variability were tested on 2 separate days on 2 different boys with DMD CM. Results were compared with paired t-testing. Twenty-two boys with newly diagnosed DMD CM (echocardiographic ejection fraction (EF) 10% EF drop. Three boys in the aCE-I group had 3 visits, due to study funding termination. Two were withdrawn because of low EF. All their data are included in the analysis for as long as they remained in the study. Mean EF's were similar at baseline (47.5%- ACE-I, 48.4%- ARB). After 1 year each group significantly improved to 54.6% and 55.2% respectively (p=.02). There was no difference between the 2 treatment groups at 1 year.

CONCLUSIONS

Inter-observer and intra-observer reliability studies showed no differences between echocardiographers on serial examinations. EF improved equally in the two groups. There is no therapeutic difference in EF improvement between lisinopril and losartan over the one-year duration for treatment of boys with DMD-related CM.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01982695.

Brain natriuretic peptide is not predictive of dilated cardiomyopathy in Becker and Duchenne muscular dystrophy patients and carriers

Background

Cardiomyopathy is reported in Duchenne and Becker muscle dystrophy patients and female carriers. Brain Natriuretic peptide (BNP) is a hormone produced mainly by ventricular cardiomyocytes and its production is up regulated in reaction to increased wall stretching. N-terminal-proBNP (NT-proBNP) has been shown to be a robust laboratory parameter to diagnose and monitor cardiac failure, and it may be helpful to screen for asymptomatic left ventricular dysfunction. Therefore we tested whether NT-proBNP can distinguish patients with Duchenne or Becker muscular dystrophy patients and carriers of a dystrophin mutation with a dilated cardiomyopathy from those without.

Methods

In a cohort of Duchenne and Becker muscle dystrophy patients (n = 143) and carriers (n = 219) NT-proBNP was measured, and echocardiography was performed to diagnose dilated cardiomyopathy (DCM).

Results

In total sixty-one patients (17%) fulfilled the criteria for DCM, whereas 283 patients (78%) had an elevated NT-pro BNP. The sensitivity of NT-proBNP for DCM in patients or carriers was 85%, the specificity 23%, area under the ROC-curve = 0.56. In the specified subgroups there was also no association.

Conclusion

Measurement of NT-pro BNP in patients suffering from Duchenne or Becker muscular dystrophy and carriers does not distinguish between those with and without dilated cardiomyopathy.

Cardiac management in neuromuscular diseases

This article addresses the pathophysiology, diagnostic approaches, and therapeutic options in the more common forms of muscular dystrophy, especially those seen in pediatric and young adult populations. The major emphasis is on the dystrophinopathies because their treatment options are templates for those used in various other forms of dystrophy. Most patients with cardiomyopathy are treated with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, with other agents added as the disease progresses. Destination therapies and transplantation options are mentioned where appropriate. Some dystrophies can have significant conduction abnormalities requiring pacemaker treatment. Others with ventricular tachydysrhythmias may necessitate internal cardiac defibrillator placement.

Catheter ablation of multiple accessory pathways in duchenne muscular dystrophy

A 23-year-old male with Duchenne muscular dystrophy (DMD) experienced self-limiting palpitations at age 19 years for the first time. Palpitations recurred not earlier than at age 23 years, and were attributed to narrow complex tachycardia, which could be terminated with adenosine. Since electrocardiography showed a delta-wave, Wolff-Parkinson-White (WPW) syndrome was diagnosed, ajmaline prescribed and radio-frequency catheter ablation of three accessory pathways carried out one week later. One day after ablation, however, a relapse of the supraventricular tachycardia occurred and was terminated with ajmaline. Re-entry tachycardia occurred a second time six days after ablation, and as before, it was stopped only with ajmaline. Despite administration of verapamil to prevent tachycardia, it occurred a third time four months after ablation. This case shows that cardiac involvement in DMD may manifest also as WPW-syndrome. In these patients, repeated radio-frequency catheter ablation of accessory pathways may be necessary to completely block the re-entry mechanism.

A case of Becker muscular dystrophy with early manifestation of cardiomyopathy

An 18-year-old boy was admitted with chest discomfort, nausea, and dyspnea at rest. At the age of 3 years, he underwent muscle biopsy and dystrophin gene analysis owing to an enlarged calf muscle and elevated serum kinase level (6,378 U/L) without overt weakness; based on the results, Becker muscular dystrophy (BMD) was diagnosed. The dystrophin gene showed deletion of exons 45 to 49. He remained ambulant and could step upstairs without significant difficulties. A chest roentgenogram showed cardiomegaly (cardiothoracic ratio, 54%), and his electrocardiogram (ECG) showed abnormal ST-T wave, biatrial enlargement, and left ventricular hypertrophy. The 2-dimensional and M-mode ECGs showed a severely dilated left ventricular cavity with diffuse hypokinesis. The systolic indices were reduced, including fractional shortening (9%) and ejection fraction (19%). Despite receiving intensive medical treatment, he died from congestive heart failure 5 months after the initial cardiac symptoms. We report a case of BMD with early-onset dilated cardiomyopathy associated with deletion of exons 45 to 49. Early cardiomyopathy can occur in BMD patients with certain genotypes; therefore, careful follow-up is required even in patients with mild phenotypes of BMD.

Evaluation of the North Star Ambulatory Assessment scale and cardiac abnormalities in ambulant boys with Duchenne muscular dystrophy

AIM

We evaluated ambulatory patients with Duchenne muscular dystrophy from the cardiovascular standpoint and studied the correlation between the results of electrocardiographic (ECG) findings, left ventricular ejection fraction (LVEF), troponin T and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels and patients' North Star Ambulatory Assessment scores.

METHODS

Fifty patients of ages 6-12 (8.9 ± 2.8) were enrolled in this cross-sectional study. Cardiac evaluation included electrocardiography, echocardiography and cardiac enzyme tests.

RESULTS

North Star scores ranged from 6/34 to 34/34. Twenty-eight patients (56%) had ECG changes. The most frequently seen ECG abnormalities were short PR interval (14%, n= 7), right ventricular hypertrophy (16%, n= 8), prolonged QTc interval (10%, n= 5), prominent Q wave (10%, n= 5) and T wave inversion (44%, n= 22). In 10 patients (20%), LVEF was below 55%, troponin T and NT-proBNP levels were significantly elevated (P= 0.003 and P < 0.001, respectively). When North Star scores were compared to patients' age, enzyme levels, ECG and echocardiographic results, we discovered negative correlation with age (P < 0.001) and troponin T levels (P= 0.02) and positive correlation with LVEF (P= 0.02).

CONCLUSION

Patients with North Star scores of ≤16 are more at risk of developing cardiomyopathies. Troponin T is a cardiac index that can be used for evaluating myopathic patients and it seems to be correlated with the proBNP levels and LVEF values.

A defect in dystrophin causes a novel porcine stress syndrome

Background

Losses of slaughter-weight pigs due to transport stress are both welfare and economic concerns to pork producers. Historically, the HAL-1843 mutation in ryanodine receptor 1 was considered responsible for most of the losses; however, DNA testing has effectively eliminated this mutation from commercial herds. We identified two sibling barrows in the USMARC swine herd that died from apparent symptoms of a stress syndrome after transport at 12 weeks of age. The symptoms included open-mouth breathing, skin discoloration, vocalization and loss of mobility.

Results

We repeated the original mating along with sire-daughter matings to produce additional offspring. At 8 weeks of age, heart rate and electrocardiographs (ECG) were monitored during isoflurane anesthesia challenge (3% for 3 min). Four males from the original sire-dam mating and two males from a sire-daughter mating died after one minute of anesthesia. Animals from additional litters were identified as having a stress response, sometimes resulting in death, during regular processing and weighing. Affected animals had elevated plasma creatine phosphokinase (CPK) levels before and immediately after isoflurane challenge and cardiac arrhythmias. A pedigree containing 250 pigs, including 49 affected animals, was genotyped with the Illumina PorcineSNP60 Beadchip and only one chromosomal region, SSCX at 25.1-27.7 Mb over the dystrophin gene (DMD), was significantly associated with the syndrome. An arginine to tryptophan (R1958W) polymorphism in exon 41 of DMD was the most significant marker associated with stress susceptibility. Immunoblots of affected heart and skeletal muscle showed a dramatic reduction of dystrophin protein and histopathology of affected hearts indicated muscle fiber degeneration.

Conclusions

A novel stress syndrome was characterized in pigs and the causative genetic factor most likely resides within DMD that results in less dystrophin protein and cardiac abnormalities that can lead to death under stressful conditions. The identification of predictive markers will allow us to determine the prevalence of this disease in commercial swine populations. This defect also provides a unique biomedical model for human cardiomyopathy associated with muscular dystrophy that may be superior to those available because of the similarities in anatomy and physiology and allow advances in gene therapies for human disease.

Delineating the role of alterations in lipid metabolism to the pathogenesis of inherited skeletal and cardiac muscle disorders: Thematic Review Series: Genetics of Human Lipid Diseases

As the specific composition of lipids is essential for the maintenance of membrane integrity, enzyme function, ion channels, and membrane receptors, an alteration in lipid composition or metabolism may be one of the crucial changes occurring during skeletal and cardiac myopathies. Although the inheritance (autosomal dominant, autosomal recessive, and X-linked traits) and underlying/defining mutations causing these myopathies are known, the contribution of lipid homeostasis in the progression of these diseases needs to be established. The purpose of this review is to present the current knowledge relating to lipid changes in inherited skeletal muscle disorders, such as Duchenne/Becker muscular dystrophy, myotonic muscular dystrophy, limb-girdle myopathic dystrophies, desminopathies, rostrocaudal muscular dystrophy, and Dunnigan-type familial lipodystrophy. The lipid modifications in familial hypertrophic and dilated cardiomyopathies, as well as Barth syndrome and several other cardiac disorders associated with abnormal lipid storage, are discussed. Information on lipid alterations occurring in these myopathies will aid in the design of improved methods of screening and therapy in children and young adults with or without a family history of genetic diseases.

Sarcolemma instability during mechanical activity in Largemyd cardiac myocytes with loss of dystroglycan extracellular matrix receptor function

The abnormal glycosylation and loss of extracellular matrix receptor function of the protein dystroglycan (DG) lead to the development of muscular dystrophy and cardiomyopathy. Dystroglycan is an important receptor for extracellular matrix proteins, such as laminin, in the basement membrane surrounding muscle. Large(myd) mice have a null mutation in a gene encoding the glycosyltransferase LARGE that results in abnormal glycosylation of α-DG and phenotypes similar to those in human α-DG glycosylation-deficient muscular dystrophy. Here, we show that Large(myd) hearts with the loss of DG extracellular matrix receptor function display a cardiomyopathy characterized by myocyte damage in patches of cells positive for membrane impermeant dyes. To examine the cellular mechanisms, we show that isolated adult cardiac myocytes from Large(myd) mice retain normal laminin-dependent cell adhesion, cell surface laminin deposition and basement membrane assembly. However, although isolated adult cardiac myocytes with the loss of α-DG glycosylation adhere normally to laminin substrates both passively and in the presence of mechanical activity, Large(myd) myocytes rapidly take up membrane impermeant dye following cyclical cell stretching. Therefore, while other cell surface laminin receptors are likely responsible for myocardial cell adhesion to the basement membrane, DG has a unique function of stabilizing the cardiac myocyte plasma membrane during repetitive mechanical activity by tightly binding the transmembrane dystrophin-glycoprotein complex to the extracellular matrix. This function of DG to stabilize the myocyte membrane during normal physiologic cell length changes is likely critical for the prevention of the myocardial damage and subsequent remodeling observed in α-DG glycosylation-deficient muscular dystrophies.

Experimental models of duchenne muscular dystrophy: relationship with cardiovascular disease

Almost every boy that has Duchenne Muscular Dystrophy (DMD) will develop cardiac problems. Whereas, it used to be respiratory problems that was the main cause of death in these DMD boys; with the advent of better respiratory care it is now the cardiac involvement that is becoming the most common cause of their death. Once the heart is affected, there is progressive deterioration in the function of the heart over time. The main problem is the death of the cardiomyocytes. The cause of the cardiomyocyte death is due to the loss of dystrophin, this makes the sarcolemma more susceptible to damage, and leads to a cascade of calcium influx, calcium activated proteases and ultimately the death of the cardiomyocyte. The dead cardiomyocytes are replaced by fibrotic tissue, which results in a dilated cardiomyopathy (DCM) developing, which begins in the base of the left ventricle and progresses to involve the entire left ventricle. The treatments used for the DMD cardiomyopathy are based on ones designed for other forms of cardiac weakness and include ACE-inhibitors and β-blockers. New therapies based around the pathophysiology in DMD are now being introduced. This review will look at the pathophysiology of the cardiac problems in DMD and how the various animal models that are available can be used to design new treatment options for DMD boys.

Comparison of magnetic resonance feature tracking for strain calculation with harmonic phase imaging analysis

OBJECTIVES

To compare a steady-state free precession cine sequence-based technique (feature tracking [FT]) to tagged harmonic phase (HARP) analysis for peak average circumferential myocardial strain (epsilon(cc)) analysis in a large and heterogeneous population of boys with Duchenne muscular dystrophy (DMD).

BACKGROUND

Current epsilon(cc) assessment techniques require cardiac magnetic resonance-tagged imaging sequences, and their analysis is complex. The FT method can readily be performed on standard cine (steady-state free precession) sequences.

METHODS

We compared mid-left ventricular whole-slice epsilon(cc) by the 2 techniques in 191 DMD patients grouped according to age and severity of cardiac dysfunction: group B: DMD patients 10 years and younger with normal ejection fraction (EF); group C: DMD patients older than 10 years with normal EF; group D: DMD patients older than 10 years with reduced EF but negative myocardial delayed enhancement (MDE); group E: DMD patients older than 10 years with reduced EF and positive MDE; and group A: 42 control subjects. Retrospective, offline analysis was performed on matched tagged and steady-state free precession slices.

RESULTS

For the entire study population (N = 233), mean FT epsilon(cc) values (-13.3 +/- 3.8%) were highly correlated with HARP epsilon(cc) values (-13.6 +/- 3.4%), with a Pearson correlation coefficient of 0.899. The mean epsilon(cc) of DMD patients determined by HARP (-12.52 +/- 2.69%) and FT (-12.16 +/- 3.12%) was not significantly different (p = NS). Similarly, the mean epsilon(cc) of the control subjects by determined HARP (-18.85 +/- 1.86) and FT (-18.81 +/- 1.83) was not significantly different (p = NS). Excellent correlation between the 2 methods was found among subgroups A through E, except there was no significant difference in strain between groups B and C with FT analysis.

CONCLUSIONS

FT-based assessment of epsilon(cc) correlates highly with epsilon(cc) derived from tagged images in a large DMD patient population with a wide range of cardiac dysfunction and can be performed without additional imaging.