Duchenne Muscular Dystrophy Cardiomyopathy Research Articles

Abstract 310: Mechanistic Insights into Duchenne Muscular Dystrophy-Associated Cardiomyopathy

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disorder resulting from a mutation in the dystrophin gene. Loss of dystrophin function leads to progressive muscle wasting and cardiomyopathy. In 2018, advanced cardiomyopathy is the primary mode of death, despite the application of standard of care CHF therapies. Our group has recently undertaken a cardiac MRI study demonstrating that adult DMD patients have small hearts with very low LV mass as compared to patients with non-ischemic cardiomyopathy or healthy patients. The central hypothesis is DMD-associated cardiomyopathy develops secondary to dysregulation of various cardiac signaling pathways that modulate cardiac growth, namely cardiomyocyte proliferation. Utilizing the mdx mouse, a model of DMD, decreased heart/body weight ratios were noted from birth (P1: Hrt/BW 5.6 ± 0.16 vs. 4.8 ± 0.18 NTg vs mdx p<0.005 n=32). NTg and m dx hearts have similar cardiomyocyte cell size (WGA staining: 0.08 ± 0.001 vs 0.08 ± 0.002 NTg vs mdx p<0.05 n=3), suggesting there are fewer cells in mdx hearts. FACS analysis indicated mdx hearts have fewer cardiomyocytes than NTg hearts (35% reduction; 51.7e 4 ± 4.9e 4 vs. 33.8e 4 ± 3.5e 4 NTg vs mdx p<0.05 n=6). Transcriptome profiling demonstrated that molecular pathways governing cardiac proliferation were significantly reduced in mdx hearts (Ki67: 4.8 ± 0.3 vs 2.0 ± 0.1 NTg vs mdx p<0.005 n=3), with a corresponding increase in cardiac atrophy gene expression at later time points (Foxo3 1.4 ± 0.2 vs 2.8 ± 0.3 NTg vs mdx p<0.005 n=3). Furthermore, immunohistochemical analyses showed significantly reduced proliferation in mdx hearts (Ki67: 13.7 ± 1.2 vs. 6.0 ± 1.0 NTg vs mdx p<0.005, n=3; pH3: 118 ± 5.3 vs 59 ± 4.5 p<0.005 n=3). Finally, RNA-Seq data revealed a disruption of the YAP signaling pathway, an important mediator of cardiomyocyte proliferation, in mdx P4 hearts. Cell cycle targets of YAP were reduced in P4 mdx hearts (20/27 genes, n=3) suggesting a disruption of the Hippo-Yap pathways in mdx hearts. Collectively, the current study provides a unique insight into the mechanism leading to the development DMD cardiomyopathy and directs investigation into potential therapeutic targets for the amelioration of DMD-associated cardiomyopathy.

Abstract 241: In Vitro Disease Modeling and Discovery of Small Molecules for the Treatment of Duchenne Muscular Dystrophy Utilizing Patient iPSC-derived Cardiomyocytes

Duchenne Muscular Dystrophy (DMD) is a fatal disease of skeletal and cardiac muscle characterized by progressive muscle weakness and atrophy. Current average life expectancy is in the mid-20s and mortality is often linked to end stage cardiomyopathy. DMD is a monogenic disease caused by loss-of-function mutations in the dystrophin gene. While dystrophin is critical for muscle function by connecting the cytoskeleton to the sarcolemma and extracellular matrix, its absence can be largely compensated for by up-regulation of utrophin (UTRN), the fetal orthologue of dystrophin. Because of the importance of UTRN expression in the heart in both DMD patients and preclinical models, we utilized DMD patient iPSC-derived cardiomyocytes as a relevant cellular model to perform in vitro pharmacology as well as functional assessment. Human iPSC-derived cardiomyocytes recapitulate key properties of bona fide cardiomyocytes, such as expression of cardiac genes, spontaneous contractility, and response to chronotropic drugs (eg. isoproterenol and hERG channel blockers). We have created an isogenic pair of healthy control and DMD iPSC lines with exon 51 deletion using CRISPR/Cas9 technology. Functional measurements of cardiomyocyte electrophysiology were performed by multielectrode array (MEA) and fluorometric imaging plate reader (FLIPR) platforms. High-throughput assays were developed to measure UTRN expression in cardiomyocyte culture in 384-well plates. Importantly, we have identified small molecules that increased UTRN expression in both patient and isogenic DMD iPSC-derived cardiomyocytes. Our study represents a valuable strategy for small molecule drug discovery for the treatment of DMD cardiomyopathy based on iPSC technology.

Cardiovascular health supervision for Duchenne Muscular Dystrophy; data from the MD STARnet

BackgroundIn 2005, the American Academy of Pediatrics (AAP) published a policy statement on cardiovascular health supervision for Duchenne Muscular Dystrophy (DMD). Data is lacking on its effect on cardiovascular care. MethodsUsing the infrastructure of the Muscular Dystrophy Surveillance, Tracking and Research Network, we examined a population-based sample of individuals with DMD, focusing on cardiac testing and prescription of cardiac medication. Comparisons were made pre- (2000–2005) and post- (2006–2011) publication Results731 cases were studied; mean age of diagnosis 3.8 years and mean duration of follow-up 9.3 years. There was a significant decrease in time from diagnosis to first electrocardiogram (ECG) and echocardiogram (ECHO) from pre- to post-publication; 1047 (95% CI: 905–1188) days to 411 (95% CI: 324–498) days for ECG (p < 0.01) and 1153 (95% CI: 1022–1284) days to 352 (95% CI: 280–424) days for ECHO (p < 0.01). Only 4.5% and 8.2% of those ≥10 years of age met the recommendation for yearly ECG and ECHO respectively. Prescription of a cardiac medication with an abnormal ECHO increased post-publication 91/125, 72.8% versus pre- 47/77, 61.0% (p = 0.08). After 2005, cases with a normal ECHO were 2.3 (95% CI 1.23–4.31) times more likely to be prescribed a cardiac medication (p < 0.01). ConclusionsSince publication of the AAP statement, DMD patients are having cardiac testing sooner and cardiac medication is prescribed more often. However, the majority are not having testing with recommended frequency. Overcoming barriers to recommended cardiac care may lead to a better understanding of the natural history of cardiomyopathy in DMD and better treatment strategies.

Inhibition of prostaglandin D2 signaling prevents the progression of dilated cardiomyopathy in Duchenne muscular dystrophy

Inhibition of prostaglandin D2 signaling prevents the progression of dilated cardiomyopathy in Duchenne muscular dystrophy

Evaluation of cardiac functions in children with Duchenne Muscular Dystrophy: A prospective case-control study.

BackgroundDuchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. The incidence of cardiomyopathy in DMD increases with age, so its early detection is important because institution of cardioprotective medical therapies may slow adverse remodeling and attenuate heart failure symptoms in these patients.ObjectiveTo assess the cardiac functions in children clinically suspected to have DMD.MethodsOver a one-year period, 28 male children aged from 3 to 18 years old, who met the criteria for diagnosis of DMD compared to 47 healthy controls children, were approached to participate in the study. The included children were subjected to full clinical examination, and blood samples were collected to determine creatinine phosphokinase (CPK), troponin I enzyme, myoglobin and lactate dehydrogenase (LDH) enzyme level. Echocardiography and 12-leads electrocardiogram (ECG) were also done for children in both groups. Data were analyzed using Independent-samples t-test, Mann-Whitney U, Chi square, and Fisher’s exact test.ResultsThe mean age of the cases group was 7.29±3.24 years versus 8.06±2.86 years for controls. In DMD group, 25% had positive family history of DMD while 35.7% of them had positive consanguinity. All cases had elevated CPK level while CPK level in controls was normal (p<0.0001). LDH level was elevated in 19 cases (67.86%) of DMD while all controls children had normal LDH level (p<0.0001). Furthermore, the mean serum myoglobin level of DMD patients was higher relative to that of healthy controls (39.39±7.25 versus 33.68 ±12.38 ng/ml respectively) (p=0.01). Echocardiography of our patients revealed that seven cases (25%) had low ejection fraction (EF) and fraction shortening (FS). In addition, all controls children had normal EF (p<0.0001) and normal FS (p<0.0001). Interestingly, ECG showed that 28.57% of cases had sinus tachycardia vs. 6.88% for controls (p=0.0001). Prolonged QTc interval was present in 39.29% of cases (mean 431.39±43.60) while all controls had normal QTc duration for age (mean of 415.17±25.2) (p<0.0001).ConclusionECG manifestations in children with DMD in the form of sinus tachycardia and prolonged QTc interval are an early alarm for developing cardiomyopathy before overt echocardiographic findings appear.

NG.I.6 - The heart is a muscle too: the cardiomyopathy of Duchenne muscular dystrophy

NG.I.6 - The heart is a muscle too: the cardiomyopathy of Duchenne muscular dystrophy

P.54 - Increased blood pressure and BMI in relation to cardiomyopathy in Duchenne muscular dystrophy

P.54 - Increased blood pressure and BMI in relation to cardiomyopathy in Duchenne muscular dystrophy

P.321 - Ultrasonography evaluation of long-term taurine effects on cardiac and skeletal muscles of mdx mice

Taurine (Tau) is the most abundant free amino acid in heart and skeletal muscle. In these tissues Tau is involved in normal contractile function by regulating the calcium homeostasis and the calcium sensitivity of the contractile proteins. Preclinical studies in mdx mice disclosed promising effects of Tau as a countermeasure for the early alterations of skeletal muscle in Duchenne muscular dystrophy (DMD). DMD is a rare disease caused by the absence of sub-sarcolemmal protein dystrophin, progressively leading to skeletal muscle wasting and heart failure via altered calcium homeostasis abnormal inflammation and profibrotic signaling. We presently focused on the potential effectiveness of Tau supplementation on later cardiac muscle dysfunction in DMD, since this has never been investigated up to now. Tau was orally administered (1g/kg/daily) in male wild type (WT) and mdx mice at an initial age of 6 months. The treatment duration was 6 months. Tau effects were tested on WT and mdx mice by measuring body mass, in vivo force and resistance to treadmill exercise. In parallel, by using an UBM system (Vevo 2100; VisualSonics, Canada), ultrasound evaluation of the left ventricular function and hindlimb volume (V) and percentage of vascularization (%V) were also performed. Our results showed a significant reduction of stroke volume (SV; -30%), ejection fraction (EF; -18.4%) and fractional shortening (FS; -23%) in 12 months old untreated mdx mice with respect to the age-matched untreated WT. Interestingly, Tau treatment significantly and selectively counteracted the alterations of SV, EF and SF in mdx mice as the values were similar to those of untreated WT mice. No significant effects were observed on the V and %V of hindlimb skeletal muscle as well as on the other functional parameters in response to Tau. This study provide the new evidence that long term Tau supplementation could be an effective specific countermeasure for DMD cardiomyopathy (DPP-NL and PRIN-MIUR).

Interleukin 1 Receptor-Like 1 Protein (ST2) is a Potential Biomarker for Cardiomyopathy in Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a rare, fatal X-linked disorder characterized by the lack of dystrophin, a key sarcolemma muscle protein.Cardiac failure is a significant cause of death in DMD subjects. The purpose of our research was to identify potential cardiac serum biomarkers associated with DMD cardiomyopathy. This is an observational, case-controlled study using subjects from the CINRG DMD natural history study with cardiomyopathy (ejection fraction (EF) <55%; shortening fraction (SF) <28%), subjects without cardiomyopathy (EF≥55%; SF≥28%) compared to normal healthy volunteer subjects. The DMD with cardiomyopathy group had significantly lower average EF and SF (EF=45±10/SF=25±2%) than the DMD without cardiomyopathy group (EF=58±5% and SF=32±3%; p<0.01). Among a selected set of potential biomarkers for cardiomyopathy (MMP9, BNP, GAL3, CRP, LEP, TNC, TLR4 and ST2) we validated ST2 as significantly elevated in the serum of DMD cardiomyopathy group (35,798±4884pg/mL) compared to normal controls (9940±2680pg/mL; p<0.01; n=6). Matrix metallopeptidase 9 (MMP9) levels were found significantly increased in both DMD groups compared to controls (p<0.01). No significant differences were seen in BNP, GAL3, CRP, LEP, TNC or TLR4 levels. Increased ST2 levels were found in serum of DMD subjects compared to healthy volunteers and further elevated in DMD subjects with cardiomyopathy. Future studies correlating cardiomyopathy with ST2 levels may allow for improved non-invasive monitoring of cardiac disease in DMD subjects.

Increased constitutive nitric oxide production by whole body periodic acceleration ameliorates alterations in cardiomyocytes associated with utrophin/dystrophin deficiency

Duchenne Muscular Dystrophy (DMD) cardiomyopathy is a progressive lethal disease caused by the lack of the dystrophin protein in the heart. The most widely used animal model of DMD is the dystrophin-deficient mdx mouse; however, these mice exhibit a mild dystrophic phenotype with heart failure only late in life. In contrast, mice deficient for both dystrophin and utrophin (mdx/utrn−/−, or dKO) can be used to model severe DMD cardiomyopathy where pathophysiological indicators of heart failure are detectable by 8–10weeks of age. Nitric oxide (NO) is an important signaling molecule involved in vital functions of regulating rhythm, contractility, and microcirculation of the heart, and constitutive NO production affects the function of proteins involved in excitation-contraction coupling. In this study, we explored the efficacy of enhancing NO production as a therapeutic strategy for treating DMD cardiomyopathy using the dKO mouse model of DMD. Specifically, NO production was induced via whole body periodic acceleration (pGz), a novel non-pharmacologic intervention which enhances NO synthase (NOS) activity through sinusoidal motion of the body in a headward-footward direction, introducing pulsatile shear stress to the vascular endothelium and cardiomyocyte plasma membrane. Male dKO mice were randomized at 8weeks of age to receive daily pGz (480cpm, Gz±3.0m/s2, 1h/d) for 4weeks or no treatment, and a separate age-matched group of WT animals (pGz-treated and untreated) served as non-diseased controls. At the conclusion of the protocol, cardiomyocytes from untreated dKO animals had, respectively, 4.3-fold and 3.5-fold higher diastolic resting concentration of Ca2+ ([Ca2+]d) and Na+ ([Na+]d) compared to WT, while pGz treatment significantly reduced these levels. For dKO cardiomyocytes, pGz treatment also improved the depressed contractile function, decreased oxidative stress, blunted the elevation in calpain activity, and mitigated the abnormal increase in [Ca2+]d upon mechanical stress. These improvements culminated in a significant reduction in circulating cardiac troponin T (cTnT) and an extension of the median lifespan of dKO mice from 16 to 31weeks. Treatment with L-NAME (NOS inhibitor) significantly decreased overall lifespan and abolished the cardioprotective properties elicited by pGz. Our results provide evidence that enhancement of NO synthesis by pGz can ameliorate cellular dysfunction in dKO cardiomyocytes and may represent a novel therapeutic intervention in DMD cardiomyopathy patients.

Increased blood pressure and BMI in relation to cardiomyopathy in Duchenne muscular dystrophy

Objective: Cardiomyopathy in Duchenne muscular dystrophy (DMD) is characterized by progressive left ventricle dysfunction (LVD). LVD is worsened by increased left ventricular afterload. We studied factors influencing this afterload: systolic blood pressure (SPB), obesity, steroid use and cardiac medication (CM) in DMD patients. Subsequently, we studied the relation between these factors and LV deformation in a subset of young patients without clinical cardiomyopathy. Methods: SBP measurements were evaluated retrospectively from 285 visits of 65 patients aged 4–18 years between February 2003 and December 2016. Values were normalized for age and length using Z-scores (Z-SBP). Age was divided in 14 groups, from 4–5 to 17– 18 years. A linear mixed model was used to analyse longitudinal correlations between Z-SBP and body mass index (BMI), steroid use, age, ambulatory status and CM use. In a subset of 36 patients <11 years, LV deformation, defined by global longitudinal strain (GLS), was quantified with speckle tracking imaging in the apical 4-chamber view of transthoracic echocardiograms. Multiple linear regression was used to assess relations between GLS, BMI, SBP, age and years on steroids. Results: Median follow-up time was 5 years (range 1–12). Z-SBP was significantly elevated in all age groups under 14 years (p < 0.016) and 15–16 years (p = 0.014). Prevalence of hypertension (Z-SBP ≥ 1.65) ranged from 22–39%. Z-SBP correlated positively with BMI (p = 0.001), and negatively with CM use over time (p = 0.017). Mean age of the younger cohort was 8.5 (±1.5) years. Here, reduced GLS was associated with increased BMI (p = 0.004, R2 = 30.8%), but not with other variables. Conclusion: SBP was significantly elevated in the majority of DMD age groups below 18 years. Z-SBP correlated positively with BMI over time. BMI was also associated with decreased LV deformation in younger patients. Prospective studies are needed for confirmation, and to assess the relevance of earlier management of these factors in DMD.

Eplerenone for early cardiomyopathy in Duchenne muscular dystrophy: results of a two-year open-label extension trial

BackgroundCardiomyopathy is a leading cause of morbidity and mortality in boys with Duchenne muscular dystrophy (DMD). We recently showed in a 12-month double-blind randomized controlled trial that adding eplerenone to background medical therapy was cardioprotective in this population. The objective of this study was to evaluate the safety and efficacy of longer-term eplerenone therapy in boys with DMD.ResultsEleven subjects (phase 1 baseline median [range] age: 13 [7 – 25] years) from the original 12-month trial at a single participating center were enrolled. Importantly, those who entered the extension study who had been on eplerenone previously were significantly older than those who had originally been on placebo (median age 10.5 vs. 18.0 years, p = 0.045). During an additional 24-month open-label extension study, all boys received eplerenone 25 mg orally once daily to treat preclinical DMD cardiomyopathy, defined as evident myocardial damage by late gadolinium enhancement cardiac magnetic resonance (LGE) with preserved ejection fraction (EF). The threshold for potassium level, the primary safety measure, was not exceeded in any non-hemolyzed blood sample. Over 24 months, left ventricular (LV) systolic strain, a more sensitive marker whose more negative values indicate greater contractility significantly improved (median change -4.4%, IQR -5.8 to -0.9%) in younger subjects whereas older subjects’ strain remained stable without significant worsening or improvement (median change 0.2%, IQR -1.1 to 4.3%). EF and extent of myocardial damage by LGE remained stable in both groups over 2 years.ConclusionsEplerenone offers effective and safe cardioprotection for boys with DMD, particularly when started at a younger age. Eplerenone is a useful clinical therapeutic option, particularly if treatment is initiated earlier in life when cardiac damage is minimal.Trial registrationhttp://ClinicalTrials.gov identifier NCT01521546. Registered 26 January 2012.

Cardiac function of children with Duchenne muscular dystrophy

Background:Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. Clinical guidelines recommend that evaluations for cardiomyopathy, arrhythmia, and heart failure be performed upon diagnosisThe incidence of cardiomyopathy in DMD increases with age Early detection of muscular dystrophy associated cardiomyopathy is important, because institution of cardioprotective medical therapies may slow adverse remodeling and attenuate heart failure symptoms in these patients. Aim: evaluation of cardiac function in children clinically suspected to have Duchenne muscular dystrophy. Methods:28 male children who met criteria for diagnosis of Duchenne muscular dystrophy aged from 3 to 18 years compared to 47 healthy control children were approached to participate in the study and, after consent, were submitted to full clinical examination, blood samples were collected to determinate CPK (creatinine phosphokinase), Troponin I enzyme, Myoglobin and LDH (lactate dehydrogenase) enzyme level,echocardiography and 12-lead electrocardiogram were done. Results: 28 Duchenne muscular dystrophy children and 47 age matched healthy male control children were included in the study. The mean age of study group was 7.29±3.24 years, and the mean age of the control group was 8.06±2. 86 years (p value 0 .28). 25% of cases had Positive family history of DMD. 35.7% of cases had positive consanguinity.all our cases had elevated CPK level (creatine phosphokinase) .The mean CPK level of cases was 2495.79 ± 3457.02 While CPK level in controls was normal, (p value<0.0001). LDH level was elevated in 19 cases 67.86% of cases. The mean serum LDH level in DMD cases was 1232.07 ± 617.72. All control children have normal LDH level with mean 163.02 ± 109.62, (P value : <0.0001).The mean serum myoglobin level of (DMD) patients was higher relative to that of healthy controls (but still within normal limits) 39.39 ± 7.25 versus 33.68 ±12.38 (ng/ml) respectively with statistically significant difference (P value: 0.01).There was no statistically significant difference between mean serum troponin I level of DMD patients and that of controls 0 .03 ± 0.05 versus 0.01 ±0 .02 (U/L) respectively (p value: 0.37). Echocardiography of our patients revealed that one patient (3.57%) had mild dilation of the left ventricular cavity which was statistically not significant, (P value: 0.37).7 cases (25%) of patients had low Ejection fraction (EF) and fraction shortening (FS) with mean (EF) 59.86 ± 10.20. All control children have normal EF with mean 73.30 ± 5.08 (P value : <0.0001). The mean FS was 20.29±5.59. All control children had normal (FS) with mean ±SD 36.17± 2.58 (P value : <0.0001). Electrocardiogram showed 28.57% of cases had sinus tachycardia with average heart rate (HR) 107 ±12.32 136. While 6.88% of controls had sinus tachycardia; (P value: 0.0001). Prolonged QTc interval was present in39.29% of cases with a mean of 431.39 ± 43.60 and that of controls was 415.17±25.2 (p value : <0.0001). QTc duration of controls were normal for age. Other parameters of ECG were normal for age; no type of arrhythmia could be detected apart from sinus tachycardia. Conclusion:ECG manifestations in children with DMD in the form of sinus tachycardia and prolonged QTC interval are an early alarm for developing cardiomyopathy before overt echocardiographic findings appear

Telomere shortening and metabolic compromise underlie dystrophic cardiomyopathy

Duchenne muscular dystrophy (DMD) is an incurable X-linked genetic disease that is caused by a mutation in the dystrophin gene and affects one in every 3,600 boys. We previously showed that long telomeres protect mice from the lethal cardiac disease seen in humans with the same genetic defect, dystrophin deficiency. By generating the mdx4cv/mTRG2 mouse model with "humanized" telomere lengths, the devastating dilated cardiomyopathy phenotype seen in patients with DMD was recapitulated. Here, we analyze the degenerative sequelae that culminate in heart failure and death in this mouse model. We report progressive telomere shortening in developing mouse cardiomyocytes after postnatal week 1, a time when the cells are no longer dividing. This proliferation-independent telomere shortening is accompanied by an induction of a DNA damage response, evident by p53 activation and increased expression of its target gene p21 in isolated cardiomyocytes. The consequent repression of Pgc1α/β leads to impaired mitochondrial biogenesis, which, in conjunction with the high demands of contraction, leads to increased oxidative stress and decreased mitochondrial membrane potential. As a result, cardiomyocyte respiration and ATP output are severely compromised. Importantly, treatment with a mitochondrial-specific antioxidant before the onset of cardiac dysfunction rescues the metabolic defects. These findings provide evidence for a link between short telomere length and metabolic compromise in the etiology of dilated cardiomyopathy in DMD and identify a window of opportunity for preventive interventions.

Pharmacological therapy for the prevention and management of cardiomyopathy in Duchenne muscular dystrophy: A systematic review

Cardiomyopathy is a major source of morbidity and mortality in Duchenne muscular dystrophy (DMD) patients now that respiratory care has improved. There is currently no definitive evidence guiding the management of DMD-associated cardiomyopathy (DMD-CM). The objective of this systematic review was to evaluate the effectiveness of pharmacotherapies for the prevention and/or management of DMD-CM and to determine the optimal timing to commence these interventions. A systematic search was conducted in January 2016 using MEDLINE, EMBASE and CINAHL databases and grey literature sources for studies evaluating the use of angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers, beta-blockers or aldosterone antagonists. Study quality assessment was conducted using the Downs and Black quality assessment checklist. PRISMA reporting guidelines were used. Of the 15 studies included in this review, most were of low methodological quality. Meta-analysis was not possible due to heterogeneity of studies. ACE inhibitors, angiotensin receptor blockers, beta-blockers and/or aldosterone antagonists tended to improve or preserve left ventricular systolic function and delay the progression of DMD-CM. While there is evidence supporting the use of heart failure medication in patients with DMD, data regarding these interventions for delaying the onset of DMD-CM and when to initiate therapy are lacking. PROSPERO registration: CRD42015029555.

Abstract 255: Role of Connexin 43 in Muscular Dystrophy Cardiomyopathy

Duchenne muscular dystrophy (DMD) is caused by an X-linked mutation that leads to the absence of dystrophin, resulting in life-threatening arrhythmogenesis and associated heart failure. The downstream events that lead to cardiomyopathy are largely unexplored. We unveiled a novel role for the gap junction protein connexin43 (Cx43) in maintaining cardiac conduction and ultimately in preventing heart failure from occurring in DMD. In mild mdx and severe mdx:utr mouse models of DMD, and human DMD tissues, Cx43 was found to be aberrantly upregulated and mislocalized to lateral sides of cardiomyocytes, with an abnormal phosphorylation pattern. We found that a triplet of serine residues, which plays a key role in a variety of cardiac pathologies, was hypophosphorylated in mdx relative to wild-type hearts. Electrocardiography on isoproterenol (Iso) challenged mice showed that both DMD mouse models developed arrhythmias and died within 24 hours, while wild-type mice were free of pathology. Administering peptide mimetic inhibitors of lateralized Cx43 channels prior to Iso challenge protected mdx mice from arrhythmogenesis and death. Cx43 copy number reduction in mdx:Cx43(+/-) mice not only ameliorated acute but also chronic, long-term symptoms of cardiomyopathy in mdx mice. Overall, our findings suggest that Cx43 lateralization contributes significantly to DMD cardiomyopathy and that selective inhibition of misplaced, upregulated channels may provide substantial benefit.

D.09 Pharmacological therapy for the prevention and management of cardiomyopathy in Duchenne muscular dystrophy: a systematic review

Background: Improved respiratory care of Duchenne muscular dystrophy (DMD) patients has unmasked cardiomyopathy as a major source of morbidity and mortality. There is currently no consensus regarding the management of DMD-associated cardiomyopathy (DMD-CM). The objective of this systematic review was to evaluate the efficacy of pharmacological therapies for prevention and management of DMD-CM, and determine the optimal timing to commence these interventions. Methods: A systematic search was conducted in October 2015 and updated in January 2016 using MEDLINE, EMBASE and CINAHL databases and 9 grey literature sources for studies evaluating the use of angiotensin-converting enzyme inhibitors (ACEi), angiotensin receptor blockers (ARB), beta-blockers (BB) or aldosterone antagonists (AA) in DMD patients. References of retrieved records were searched. Quality assessment was conducted using the Downs and Black Quality Assessment Checklist. PRISMA reporting guidelines were used. Results: The 11 included studies were of low methodological quality. However, the use of an ACEi, ARB, BB and AA tended to improve or preserve left ventricular systolic function and delay the progression of cardiomyopathy. Conclusions: While there is evidence supporting the use of heart failure medication in patients with DMD-CM, data regarding these interventions for delaying the onset of DMD-CM and when to initiate therapy is lacking.

Duchenne Muscular Dystrophy Mice and Men: Can Understanding a Genetic Cardiomyopathy Inform Treatment of Other Myocardial Diseases?

Duchenne muscular dystrophy mouse models have a predictable and reproducible time course of cardiomyopathy progression with discrete pathogenic steps, which closely parallel what we know occurs in the cardiomyopathy of patients with Duchenne muscular dystrophy. The slow progression of early pathogenic steps common to many cardiomyopathies may make Duchenne muscular dystrophy models useful for identifying novel treatment targets and testing the therapeutic value of new treatment paradigms for an at-risk patient population far beyond those with muscular dystrophies. Dilated cardiomyopathy is a leading cause of death in individuals affected by Duchenne muscular dystrophy (DMD), and nearly all DMD patients develop dilated cardiomyopathy by age 18. DMD and the milder Becker muscular dystrophy result from mutations in the X-linked gene encoding dystrophin, a membrane-associated protein that helps protect striated muscle cell membranes from damage. Clinical signs resulting from lower limb muscle weakness lead to DMD diagnosis typically by 5 years of age and loss of ambulation by 12 years of age. Skeletal myopathy in Becker muscular dystrophy has a later age of onset and slower progression than DMD, and dilated cardiomyopathy is the primary cause of mortality. Earlier ventilatory support for affected respiratory muscles and timely management of pulmonary infections have led to increased survival for DMD patients into their mid-twenties. These advances have made increasingly evident the underlying cardiomyopathy that presents as heart failure and often fatal arrhythmias in the later decades of life. Despite the devastating consequences of DMD cardiomyopathy, its unique features may provide new insights into myocardial disease. First, the consistent lag between evident skeletal myopathy and cardiomyopathy affords early detection and possible treatment of a patient population that is genetically programmed to develop cardiac dysfunction. Second, the myocardial disease exhibits a relatively slow progression, providing the ability to understand each step involved. Third, there are isogenic …

Suspected acute myocardial infarction in a dystrophin-deficient dog

Golden retriever muscular dystrophy (GRMD) is a model for the genetically homologous human disease, Duchenne muscular dystrophy (DMD). Unlike the mildly affected mdx mouse, GRMD recapitulates the severe DMD phenotype. In addition to skeletal muscle involvement, DMD boys develop cardiomyopathy. While the cardiomyopathy of DMD is typically slowly progressive, rare early episodes of acute cardiac decompensation, compatible with myocardial infarction, have been described. We report here a 7-month-old GRMD dog with an apparent analogous episode of myocardial infarction. The dog presented with acute signs of cardiac disease, including tachyarrhythmia, supraventricular premature complexes, and femoral pulse deficits. Serum cardiac biomarkers, cardiac-specific troponin I (cTnI) and N-terminal prohormone of B-type natriuretic peptide (NT-proBNP), were markedly increased. Echocardiography showed areas of hyperechoic myocardial enhancement, typical of GRMD cardiomyopathy. Left ventricular dyskinesis and elevated cTnI were suggestive of acute myocardial damage/infarction. Over a 3-year period, progression to a severe dilated phenotype was observed.

Detection of the mutation may guide treatment of heart and muscle in Duchenne muscular dystrophy.

We read with great interest the article, by Kono et al, about a 32-year-old male with Duchenne muscular dystrophy (DMD), who was admitted for dilated cardiomyopathy manifesting as heart failure, left bundle branch block, Mobitz-II block, bradycardia, and arterial hypotension. He profited from implantation of a cardiac resynchroniza-tion therapy-D system with a defibrillator and beta-blocker treatment. 1 We have the following comments and concerns. Diagnosing DMD only by muscle biopsy is insufficient. The diagnosis needs to be confirmed by genetic studies. 2 Was the patient investigated for deletions, duplications , or point mutations in the DMD gene? Which were the results of the Western blot for dystrophin? Was there complete absence of dystrophin or were there indications for a truncated protein, compatible with the diagnosis of Becker muscular dystrophy (BMD)? Since the patient was quite old for DMD, it has to be convincingly shown that BMD was definitively excluded. Diagnosing DMD on a molecular genetic level is important as genetic therapy in form of exon skipping is available for a certain type of mutations. 3 It has been shown that patients with DMD profit from the administration of ste-roids, usually deflazacort. 4 There are indications that steroids not only improve the performance of the skeletal muscle but also improve cardiac functions. 5 Furthermore, steroids reduce the myocardial fibrosis burden in these patients as has been shown by cardiac magnetic resonance imaging (MRI). 6 Did the presented patient receive steroids in addition to heart failure therapy? Did he profit from steroids with regard to cardiac and muscle function? Which side effects did he develop from steroids? Dilated cardiomyopathy in DMD is characterized by replacement of the myocar-dium with connective tissue. 6 Myocardial fibrosis in DMD can be best documented by application of cardiac MRI and administration of gadolinium to assess the amount of late gadolinium enhancement (LGE). 6 Did the patient undergo cardiac MRI and was gadolinium administered to assess the amount and location of myocardial fibrosis? Assessment of LGE in DMD is important since the amount of LGE strongly correlates with left ventricular systolic dysfunction. 6 Approximately two-thirds of the DMD patients inherit the mutation from their mothers. DMD carriers may manifest clinically or biochemically. Was the mother of the described patient investigated for her carrier status? Did she manifest clinically or were there other indications for being a DMD carrier? Did she undergo electrocardiography