Death In Duchenne Muscular Dystrophy Research Articles

Functional cardiac consequences of β-adrenergic stress-induced injury in the mdx mouse model of Duchenne muscular dystrophy.

Cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD), however, in the mdx mouse model of DMD, the cardiac phenotype differs from that seen in DMD-associated cardiomyopathy. Although some have used pharmacologic stress to stimulate injury and enhance cardiac pathology in the mdx model, many methods lead to high mortality with variable cardiac outcomes, and do not recapitulate the structural and functional cardiac changes seen in human disease. Here, we describe a simple and effective method to enhance the cardiac phenotype model in mdx mice using advanced 2D and 4D high-frequency ultrasound to monitor cardiac dysfunction progression in vivo. For our study, mdx and wild-type (WT) mice received daily low-dose (2 mg/kg/day) isoproterenol injections for 10 days. Histopathologic assessment showed that isoproterenol treatment increased myocyte injury, elevated serum cardiac troponin I levels, and enhanced fibrosis in mdx mice. Ultrasound revealed reduced ventricular function, decreased wall thickness, increased volumes, and diminished cardiac reserve in mdx mice compared to wild-type. Our findings highlight the utility of challenging mdx mice with low-dose isoproterenol as a valuable model for exploring therapies targeting DMD-associated cardiac pathologies.

Rate of Change in Cardiac Magnetic Resonance Imaging Measures Is Associated With Death in Duchenne Muscular Dystrophy.

Cardiovascular disease is the leading cause of death among patients with Duchenne muscular dystrophy (DMD). Identifying patients at risk of early death could allow for increased monitoring and more intensive therapy. Measures that associate with death could serve as surrogate outcomes in clinical trials. Duchenne muscular dystrophy subjects prospectively enrolled in observational studies were included. Models using generalized least squares were used to assess the difference of cardiac magnetic resonance measurements between deceased and alive subjects. A total of 63 participants underwent multiple cardiac magnetic resonance imaging and were included in the analyses. Twelve subjects (19.1%) died over a median follow-up of 5 years (interquartile range, 3.1-7.0). Rate of decline in left ventricular ejection fraction was faster in deceased than alive subjects (P<0.0001). Rate of increase in indexed left ventricular end-diastolic (P=0.0132) and systolic (P<0.0001) volumes were higher in deceased subjects. Faster worsening in midcircumferential strain was seen in deceased subjects (P=0.049) while no difference in global circumferential strain was seen. The rate of increase in late gadolinium enhancement, base T1, and mid T1 did not differ between groups. Duchenne muscular dystrophy death is associated with the rate of change in left ventricular ejection fraction, midcircumferential strain, and ventricular volumes. Aggressive medical therapy to decrease the rate of progression may improve the mortality rate in this population. A decrease in the rate of progression may serve as a valid surrogate outcome for therapeutic trials.

Abstract 16904: Low-Dose Isoproterenol Administration in the Murine MDX Model Unmasks Progression of Duchenne-Associated Cardiomyopathy

Introduction: The cardiovascular phenotype resulting from Duchenne muscular dystrophy (DMD) includes cardiomyopathy (CMP) leading to congestive heart failure and early mortality. CMP is the leading cause of death in DMD. Our objective was to characterize the progression of CMP in a murine model of DMD. We hypothesized that a genetic mouse model of DMD will exhibit significantly lower function over time as measured by ejection fraction when given an isoproterenol (IPT) challenge. Methods: We examined a mouse model of DMD from the Jackson Laboratory: C57BL/10ScSn- Dmd mdx /J (B10.mdx; n=6 female). The genetic group was paired with the wild type control strain C57BL/10ScSnJ (B10; n=6 female mice). B10.mdx (MDX) and B10 (WT) mice received intraperitoneal IPT administered via daily injections at 3 mg/kg. Cardiac function was assessed by 2D ultrasound using a Vevo3100 imaging system (FUJIFILM, VisualSonics) from the baseline, immediate effects of IPT injection at 1 minute, after 7, 14, and 21 days. Results: At 1 minute following the first IPT injection in WT and MDX, we observed increases in EF and HR for both groups ( Figure 1 ). While the changes in EF were notable yet not reaching significance, the differences within groups between baseline and 1 minute after injection were significant due to HR response ( p &lt;0.05).We observed decreases in EF for both groups between baseline and day 7 following IPT injections ( Figure 1 ). The changes in MDX EF between baseline and day 7 approached significance. The EF in both groups was maintained through day 7, day 14, and day 21. 2 deaths in MDX occurred during the treatment period and 1 death followed day 7. A WT sacrifice was made after day 14 due to severe dermatitis. Conclusion: Murine mdx models exhibit DMD-associated CMP comparable to humans. Associated humanlike phenotype includes decreased EF, FS, ESV, EDS, and SV. A low dose of IPT in MDW mice has the potential to unmask these changes within 7 days, reducing the need for longer term murine studies.

Abstract 14417: Regional 4D Cardiac Magnetic Resonance Strain Associates With Late Gadolinium Enhancement in Duchenne Muscular Dystrophy Associated Cardiomyopathy

Introduction: Cardiomyopathy (CM) is the leading cause of death in Duchenne muscular dystrophy (DMD). Onset and clinical progression are varied. Cardiac magnetic resonance (CMR) late gadolinium enhancement (LGE) can detect fibrofatty replacement prior to decreased left ventricular ejection fraction (LVEF) but requires administration of gadolinium contrast agents. Non-contrast methods to characterize CM onset and progression could decrease scan time and exposure to gadolinium. Using a novel 4D (3D+time) regional strain analysis method, we hypothesized that the regional magnitude of surface area strain (E a ) would be significantly decreased in DMD patients with LGE and that E a would correlate with decreased LVEF . Methods: Short-axis cine CMR images for 43 pediatric DMD patients (13.6 ± 4.2 years) were compiled into 4D sequences for regional strain analysis (Fig. 1A). For all 4D sequences, epi- and endocardial borders were segmented across one cardiac cycle for kinematic analysis using a custom-built MATLAB graphical user interface (MathWorks, Natick, MA). Regional E a was measured by determining the relative change in the localized 4D endocardial surface mesh compared to end-diastole. Unpaired t-test and Spearman’s rho were used to determine statistical significance and correlation. Results: DMD patients had a range of CM severity: 13 with reduced LVEF of &lt;55% (30% of total) and 28 with LGE (65% of total). Peak E a was significantly different between patients with and without LGE in the basal inferior ( p =0.022), basal inferolateral ( p &lt;0.001), basal anterolateral ( p =0.002), mid inferolateral ( p =0.004), mid anterolateral ( p =0.018), and apical anterior ( p &lt;0.032), regions (Fig.1B). Basal E a also correlated significantly with LVEF ( rho =-0.45, p&lt; 0.001; Fig. 1C). Conclusion: Regional E a from 4D CMR in DMD was reduced in patients with LGE compared to those without LGE particularly in the basolateral regions. Peak basal E a correlated with a reduction in LVEF. LVEF.

Cardiomyopathy as cause of death in Duchenne muscular dystrophy: a longitudinal observational study.

Cardiomyopathy has become an important life-limiting factor since survival in Duchenne muscular dystrophy (DMD) has greatly increased with long-term ventilation and cough assistance. The aim of this study was to investigate the association between impaired left ventricular ejection fraction (LVEF) and survival. In a >20-year observational study in patients with DMD (age ≥16 years) with at least three echocardiograms, the association between LVEF and survival and time to cardiac or non-cardiac death was investigated using Kaplan-Meier survival analysis and Cox regression (for LVEF). In 67 DMD patients (430 echocardiograms), the decrease in LVEF over a mean±sd follow-up period of 9.1±5.1 years was -10.0±13.9% absolute, but LVEF progression varied widely. 84% were receiving an angiotensin-converting enzyme inhibitor and 54% a β-blocker at last follow-up with an LVEF of 37.5±12.4% at that time-point. Median (interquartile range) survival was 33 (25-40) years. 28 out of 67 (42%) of the cohort had died and LVEF was a significant negative predictor of survival (hazard ratio 0.95 (95% CI 0.91-0.99); p<0.007). Those who died of cardiac death (53% of known causes of death) had significantly lower LVEF at the time of death (LVEF -11.0% (95% CI -21.1- -0.9%); p=0.035) compared with non-cardiac death and tended to die at a younger age. Cardiomyopathy with systolic heart failure is the leading cause of death and lower LVEF is an independent predictor of mortality at younger ages in patients with DMD. Patients with DMD appear to be undertreated with respect to heart failure drug therapy.

Cardiovascular Measures of All-Cause Mortality in Duchenne Muscular Dystrophy.

Cardiopulmonary failure is the leading cause of death in Duchenne muscular dystrophy (DMD). Research into DMD-specific cardiovascular therapies is ongoing, but there are no Food and Drug Administration-approved cardiac end points. To adequately power a therapeutic trial, appropriate end points must be chosen and the rate of change for these end points reported. The objective of this study was to evaluate rate of change for cardiac magnetic resonance and blood biomarkers and to determine which measures associate with all-cause mortality in DMD. Seventy-eight DMD subjects underwent 211 cardiac magnetic resonance studies analyzed for left ventricular (LV) ejection fraction, indexed LV end diastolic and systolic volumes, circumferential strain, late gadolinium enhancement presence and severity (global severity score, and full width half maximum), native T1 mapping, T2 mapping, and extracellular volume. Blood samples were analyzed for BNP (brain natriuretic peptide), NT-proBNP (N-terminal pro-B-type natriuretic peptide), and troponin I. Cox proportional hazard regression modeling was performed with all-cause mortality as the outcome. Fifteen subjects (19%) died. LV ejection fraction, indexed end systolic volumes, global severity score, and full width half maximum worsened at 1 and 2 years while circumferential strain and indexed LV end diastolic volumes worsened at 2 years. LV ejection fraction, indexed LV end diastolic and systolic volumes, late gadolinium enhancement full width half maximum, and circumferential strain associated with all-cause mortality (P<0.05). NT-proBNP was the only blood biomarker that associated with all-cause mortality (P<0.05). LV ejection fraction, indexed LV volumes, circumferential strain, late gadolinium enhancement full width half maximum, and NT-proBNP are associated with all-cause mortality in DMD and may be the best end points for use in cardiovascular therapeutic trials. We also report change over time of cardiac magnetic resonance and blood biomarkers.

Right ventricular function in hearts of a mouse model of Duchenne muscular dystrophy following increased ventricular load

Duchenne muscular dystrophy (DMD) is an X-linked recessive myopathy caused by mutations in the gene encoding dystrophin. Dystrophin is present in striated muscle cells and stabilizes the sarcolemma to mitigate contraction-induced damage. The main cause of death in DMD is cardiopulmonary failure by age 30. Diaphragmatic weakness in DMD causes restrictive lung disease and excessive afterload on the right ventricle (RV). Thus, RV dysfunction in DMD patients is typically observed early in disease progression. The objective of this study was to investigate ex vivo RV function in a mouse model of muscular dystrophy and test the hypothesis that RV function is impaired following a sustained increase in ventricular preload and afterload. Right-ventricular pressure development (P dev ) and rate of pressure decay (dP/dt Min ) were monitored in isolated perfused hearts of 2-6 month normal (C57BL/6, n=5) and dystrophic (mdx 4CV , n=5) male mice. Measurements were obtained under unloaded conditions and during right-ventricular load challenge (10 mmHg preload; 20 mmHg afterload). Coronary effluent lactate dehydrogenase (LDH) levels were measured following 30 minutes of sustained load challenge to assess cardiac damage. Our results show dystrophic hearts exhibited greater RV P dev than normal hearts under unloaded conditions (24±2 mmHg mdx 4CV vs 15±2 mmHg C57BL/6, P=0.015). In response to load challenge, P dev increased (P&lt;0.05) in both groups, but it was similar between dystrophic and normal hearts (32±1 mmHg mdx 4CV vs 33±3 mmHg C57BL/6). Rate of pressure decay was similar between dystrophic and normal hearts under both conditions. Levels of LDH following load challenge were higher (P&lt;0.05) in dystrophic versus normal hearts. In conclusion, in the absence of ventricular load RV contractile function was enhanced in dystrophic hearts. With RV load both dystrophic and normal hearts exhibited similar contractile function, yet sustained load challenge increased cellular damage in dystrophic versus normal hearts. National Institutes of Health, University of Missouri School of Medicine, University of Missouri System This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comprehensive cardiac magnetic resonance T1, T2, and extracellular volume mapping to define Duchenne cardiomyopathy

BackgroundCardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Cardiac magnetic resonance (CMR) parametric mapping sequences offer insights into disease pathophysiology. We propose a novel approach by leveraging T2 mapping in conjunction with T1 and extracellular volume (ECV) mapping to perform a virtual myocardial biopsy. While previous work has attempted to describe myocardial changes in DMD, our inclusion of T2 mapping enables comprehensive categorization of myocardial tissue characteristics of fibrosis, edema, and fat to better understand the pathological composition of the myocardium with disease progression. MethodsDMD patients (n = 49; median: 12 years-old) underwent CMR, including T1, T2, and ECV. Categories were defined as normal, isolated high T1 (normal ECV, high T1, normal T2), fibrosis (high ECV, normal or high T1, normal T2), edema (normal or high ECV, normal or high T1, high T2), fat (normal ECV, low T1, high T2) or fibrofatty (high ECV, low T1, high T2). ResultsMedian left ventricular ejection fraction (LVEF) was 59% with 27% having LVEF < 55%. Those with normal LVEF and no late gadolinium enhancement (37%) were younger in age (10.5 ± 2.6 vs. 15.0 ± 4.3 years-old, p < 0.001). Native T1 was elevated in at least one slice in 82% of patients. Those with high T2 at any slice (27%) were older (p = 0.005) and had lower LVEF (p = 0.005) compared with subjects with normal T2 (73%). The most common myocardial characterization was fibrosis (43%) followed by isolated high T1 (24%). Of the 13 with high T2, ten were categorized as edema, two as fibrofatty, and one as fat. ConclusionCMR parametric mapping sequences offer insights into Duchenne cardiomyopathy pathophysiology, which should drive development of therapeutic interventions aimed at these targets. Myocardial fibrosis is common in DMD. Patients with elevated T2 were older and had lower LVEF. Though fat infiltration was present, the majority of subjects with elevated T2 met criteria for myocardial edema.

Abstract 14062: Longitudinal Rate of Change for Cardiac Magnetic Resonance Biomarkers Associates With Mortality in Duchenne Muscular Dystrophy

Introduction: Cardiomyopathy (CM) is the leading cause of death in Duchenne muscular dystrophy (DMD). Progression is variable. Multiple DMD-specific CM medications are in development, but there are no established outcome measures for therapeutic trials. Our prior work demonstrated an association between cardiac magnetic resonance (CMR) metrics and mortality, including left ventricular ejection fraction (LVEF), ventricular volumes, and native T1 mapping. The objective of this study was to determine whether longitudinal change in these metrics associates with all-cause mortality. Methods: Seventy-eight DMD subjects underwent 211 comprehensive CMR studies, including LVEF, indexed LV end diastolic and systolic volumes (LVESVi and LVEDVi), and native T1 mapping. To explore how the slope of CMR biomarkers affects mortality, multivariable linear regression was used to model age, mortality, and the interaction term of age and mortality on predictors of interest (LVEF, LVEDVi, LVESVi, native T1). Results: At baseline CMR, the median age was 12.5 years (range 7.4-27.5), and the median LVEF was 57%; 32 subjects (41%) had LVEF &lt; 55%. LGE was present in 54 subjects (71%). Fifteen subjects (19%) died over a median follow up of 5 years (IQR 3.1,7). The slope of LVEF decline differentiated between subjects with and without mortality (p&lt;0.001) ( Figure 1 ). A steeper increase in LVEDVi and LVESVi also associated with mortality (p&lt;0.001), while change in native T1 did not. Conclusions: DMD all-cause mortality is associated with the slope of progression of LVEF and ventricular volumes. Aggressive medical therapy to decrease the rate of progression may improve mortality in this patient population. In addition, a decrease in the rate of progression may serve as a valid surrogate outcome measure for therapeutic trials.

Abstract 13519: 4D Cardiac Magnetic Resonance Strain Associates With Mortality in Duchenne Muscular Dystrophy Associated Cardiomyopathy

Introduction: Cardiomyopathy (CM) is the leading cause of death in Duchenne muscular dystrophy (DMD) but the pace of CM progression is variable. Identification of biomarkers that associate with mortality could allow clinicians to intensify cardiac therapy. Our objective was to determine whether novel 4D (3D+time) cardiac magnetic resonance (CMR) strain analysis predicts mortality. We hypothesized that the magnitude of regional surface strain (E a ) would be significantly decreased in DMD patients that progressed to mortality within 5 years of analysis. Methods: Short axis cine CMR images for DMD survival (n=40) and non-survival (n=9) groups were compiled into 4D sequences. For all 4D sequences, epi- and endocardial borders were segmented across one cardiac cycle for kinematic analysis using a custom-built MATLAB graphical user interface (MathWorks, Natick, MA). Regional E a was measured by determining the relative change in the localized 4D endocardial surface mesh compared to end diastole. Unpaired t-test was used to determine statistical significance. Results: DMD survival patients were younger (13 years [8-24]; median [range]) than non-survival patients (16[12-19]) and a smaller portion had LVEF&lt;55% (11 (28% of total) vs. 6 (67% of total). 63% (n=26) of the survival group had late gadolinium enhancement vs. 100% (n=9) in the non-survival group. Median time to mortality for the non-survival group was 27 months [8-58]. Peak E a was significantly worse in the non-survival group globally and in the basal, mid, and apical regions ( p &lt;0.001 for all; Fig1C). Qualitative E a maps show dramatic differences between groups (Fig1A,B). Conclusion: Regional E a from 4D CMR in DMD was reduced in patients that progressed to mortality within 5 years compared to those that survived. Figure 1: Example colorized surface strain (E a ) from A) survival and B) non-survival patients in both polar map (left) and 3D representations (right). C) Regional E a differences between groups. * p &lt;0.001.

A microtubule-connexin-43 regulatory link suppresses arrhythmias and cardiac fibrosis in Duchenne muscular dystrophy mice.

Dilated cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD), an inherited degenerative disease of the cardiac and skeletal muscle caused by absence of the protein dystrophin. We showed one hallmark of DMD cardiomyopathy is the dysregulation of cardiac gap junction channel protein connexin-43 (Cx43). Proper Cx43 localization and function at the cardiac intercalated disc (ID) is regulated by post-translational phosphorylation of Cx43-carboxy-terminus residues S325/S328/S330 (pS-Cx43). Concurrently, Cx43 traffics along microtubules (MTs) for targeted delivery to the ID. In DMD hearts, absence of dystrophin results in a hyperdensified and disorganized MT cytoskeleton, yet the link with pS-Cx43 remains unaddressed. To gain insight into the relationship between MTs and pS-Cx43, DMD mice (mdx) and pS-Cx43-deficient (mdxS3A) mice were treated with an inhibitor of MT polymerization, colchicine (Colch). Colch treatment protected mdx, not mdxS3A mice, against Cx43 remodeling, improved MT directionality, and enhanced pS-Cx43/tubulin interaction. Likewise, severe arrhythmias were prevented in isoproterenol-stressed mdx, not mdxS3A mice. Furthermore, MT directionality was improved in pS-Cx43-mimicking mdx (mdxS3E). Mdxutr+/- and mdxutr+/-S3A mice, lacking one copy of dystrophin homolog utrophin, displayed enhanced cardiac fibrosis and reduced lifespan compared with mdxutr+/-S3E; and Colch treatment corrected cardiac fibrosis in mdxutr+/- but not mdxutr+/-S3A. Collectively, the data suggest that improved MT directionality reduces Cx43 remodeling and that pS-Cx43 is necessary and sufficient to regulate MT organization, which plays crucial role in correcting cardiac dysfunction in DMD mice. Thus, identification of novel organizational mechanisms acting on pS-Cx43-MT will help develop novel cardioprotective therapies for DMD cardiomyopathy.NEW & NOTEWORTHY We found that colchicine administration to Cx43-phospho-deficient dystrophic mice fails to protect against Cx43 remodeling. Conversely, Cx43-phospho-mimic dystrophic mice display a normalized MT network. We envision a bidirectional regulation whereby correction of the dystrophic MTs leads to correction of Cx43 remodeling, which in turn leads to further correction of the MTs. Our findings suggest a link between phospho-Cx43 and MTs that provides strong foundations for novel therapeutics in DMD cardiomyopathy.

Angiotensin receptor-neprilysin inhibitor in symptomatic patients with Duchenne dilated cardiomyopathy: A primetime.

Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder, characterized by significant long-term cardiac involvement. Dilated cardiomyopathy (DCM) is the main cause of death in DMD, and angiotensin-converting enzyme inhibitors (ACEi) and beta-blockers (BB) are first-line treatments in DCM. It is unknown whether angiotensin receptor-neprilysin inhibitor (ARNi) could provide greater benefits in this setting. Our aim is to assess whether ARNi use may prevent deterioration in ejection fraction (EF) or is associated with EF improvement compared with ACEi in DMD patients with heart failure and to report the tolerability of ARNi in this group of patients. We followed 22 DMD patients, 6 of them with an EF<40% and 16 with an EF>40%. The first group received ARNi on top of BB, while the control group started or continued first-line therapy with ACEi±BB. From December 2016 to December 2021, we recorded EF values at baseline and at follow-up, comparing EF changes. Median follow-up was 7months (interquartile range 4.7-9.1). At baseline, the mean of EF (%) in the ARNi group was 31±2%, while it was 59±9% in the control group. At follow-up, we recorded an EF improvement in the ARNi group (38±6%, P-value<0.05). Among controls, EF at follow-up was substantially unchanged from baseline. Our data suggest that the use of ARNi in DMD patients with DCM and an EF<40% might be associated with an EF improvement and a safe tolerability profile.

Abstract 9370: Myocardial Tissue Characterization of Pediatric Patients With Duchenne Muscular Dystrophy

Introduction: Cardiomyopathy (CM) is the leading cause of death in Duchenne muscular dystrophy (DMD). Cardiac magnetic resonance (CMR) parametric mapping sequences, Native T1, T2, and extracellular volume (ECV), can offer insights into disease pathophysiology. The objective of this abstract was to leverage parametric mapping sequences to define the tissue characteristics of DMD CM progression. We hypothesized DMD subjects could be categorized based on fibrosis, myocardial edema, and fat infiltration. Methods: DMD patients (n=52; median 12.1 years) underwent CMR including T1, T2, and ECV at the base, mid, and apex. Categories were defined as normal, early fibrosis (normal ECV, high T1, normal T2), fibrosis (high ECV, normal or high T1, normal T2), edema (normal or high ECV, normal or high T1, high T2), fat (normal ECV, low T1, high T2) or fibrofatty (high ECV, normal or low T1, high T2). Statistical analysis included Chi-square, Wilcoxon rank sum, Wilcoxon signed rank, and Spearman’s rho. Results: Median left ventricular ejection fraction (LVEF) was 59% and 15 (29%) had LVEF &lt; 55%; 18 subjects (35%) had normal LVEF and no late gadolinium enhancement. These subjects were younger (10.2 years [8.4,11.6] vs 14.7 [11.5,17.8], p&lt;0.001). Native T1 was elevated in at least one slice in 42 (81%). Patients with high T2 at any slice (n=13) were older (p=0.009) and had lower LVEF (p=0.009) compared with normal T2 (n=39). The most common stratifications (Figure 1) were early fibrosis (n=14) and fibrosis (n=21). Of the 13 with high T2, 9 were categorized as edema, 2 as fibrofatty, and 2 as fat. T2 at the base, mid, and apex increased from first to second CMR (all p&lt;0.05) and T2 at mid and apex correlated with age (rho=0.2 and rho=0.38, p&lt;0.05). Conclusion: Myocardial fibrosis is common in DMD. CM progresses with age and higher T2 suggesting fatty/fibrofatty infiltration. CMR parametric mapping sequences offer insights into disease pathophysiology, which should drive therapeutic innovation.

Duchenne muscular dystrophy patients: troponin leak in asymptomatic and implications for drug toxicity studies.

Cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD), but studies suggest heart failure biomarkers correlate poorly with cardiomyopathy severity. DMD clinical trials have used troponin I (cTnI) as a biomarker of toxicity, but it is unclear if asymptomatic DMD patients have elevated cTnI. We longitudinally evaluated cTnI, brain natriuretic peptide (BNP), and N-terminal pro-BNP (NT-proBNP) in a DMD cohort. DMD patients were prospectively enrolled and followed for 3 years. Serum was drawn at the time of cardiac magnetic resonance (CMR). Normal biomarker values were derived from healthy subjects. Biomarkers were correlated with CMR markers. All subjects were asymptomatic at the time of enrollment. Several DMD subjects had transiently elevated cTnI. Those with elevated cTnI were more likely to have late gadolinium enhancement on baseline CMR. NT-proBNP correlated with indexed left ventricular end diastolic and maximum left atrial volumes. Otherwise, standard cardiac biomarkers did not correlate with CMR markers of cardiomyopathy. CTnI, BNP, and NT-proBNP do not correlate with CMR assessment of cardiomyopathy progression. A subset of DMD patients have asymptomatic cTnI leak of uncertain clinical significance, though of critical importance if cTnI is used to assess for cardiac toxicity in future drug trials. Asymptomatic patients with Duchenne muscular dystrophy (DMD) exhibit transient troponin I leak. NT-proBNP correlated with indexed left ventricular end diastolic volume and indexed maximum left atrial volume. Other cardiac biomarkers did not correlate with cardiac magnetic resonance (CMR) markers of cardiomyopathy.

Dystrophin Deficiency Causes Progressive Depletion of Cardiovascular Progenitor Cells in the Heart.

Duchenne muscular dystrophy (DMD) is a devastating condition shortening the lifespan of young men. DMD patients suffer from age-related dilated cardiomyopathy (DCM) that leads to heart failure. Several molecular mechanisms leading to cardiomyocyte death in DMD have been described. However, the pathological progression of DMD-associated DCM remains unclear. In skeletal muscle, a dramatic decrease in stem cells, so-called satellite cells, has been shown in DMD patients. Whether similar dysfunction occurs with cardiac muscle cardiovascular progenitor cells (CVPCs) in DMD remains to be explored. We hypothesized that the number of CVPCs decreases in the dystrophin-deficient heart with age and disease state, contributing to DCM progression. We used the dystrophin-deficient mouse model (mdx) to investigate age-dependent CVPC properties. Using quantitative PCR, flow cytometry, speckle tracking echocardiography, and immunofluorescence, we revealed that young mdx mice exhibit elevated CVPCs. We observed a rapid age-related CVPC depletion, coinciding with the progressive onset of cardiac dysfunction. Moreover, mdx CVPCs displayed increased DNA damage, suggesting impaired cardiac muscle homeostasis. Overall, our results identify the early recruitment of CVPCs in dystrophic hearts and their fast depletion with ageing. This latter depletion may participate in the fibrosis development and the acceleration onset of the cardiomyopathy.

Low human dystrophin levels prevent cardiac electrophysiological and structural remodelling in a Duchenne mouse model

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disorder caused by loss of dystrophin. This lack also affects cardiac structure and function, and cardiovascular complications are a major cause of death in DMD. Newly developed therapies partially restore dystrophin expression. It is unclear whether this will be sufficient to prevent or ameliorate cardiac involvement in DMD. We here establish the cardiac electrophysiological and structural phenotype in young (2–3 months) and aged (6–13 months) dystrophin-deficient mdx mice expressing 100% human dystrophin (hDMD), 0% human dystrophin (hDMDdel52-null) or low levels (~ 5%) of human dystrophin (hDMDdel52-low). Compared to hDMD, young and aged hDMDdel52-null mice displayed conduction slowing and repolarisation abnormalities, while only aged hDMDdel52-null mice displayed increased myocardial fibrosis. Moreover, ventricular cardiomyocytes from young hDMDdel52-null animals displayed decreased sodium current and action potential (AP) upstroke velocity, and prolonged AP duration at 20% and 50% of repolarisation. Hence, cardiac electrical remodelling in hDMDdel52-null mice preceded development of structural alterations. In contrast to hDMDdel52-null, hDMDdel52-low mice showed similar electrophysiological and structural characteristics as hDMD, indicating prevention of the cardiac DMD phenotype by low levels of human dystrophin. Our findings are potentially relevant for the development of therapeutic strategies aimed at restoring dystrophin expression in DMD.

Abstract 16916: Asymptomatic Patients With Duchenne Muscular Dystrophy Have Elevated Troponin

Introduction: Cardiomyopathy is the leading cause of death in Duchenne Muscular Dystrophy (DMD), but traditional heart failure biomarkers have limited utility. Cardiac Troponin I (cTnI) has been used in DMD research studies as a marker of toxicity, but little is known about cTnI levels in asymptomatic patients. The goal of this study was to longitudinally evaluate cTnI, NTproBNP, and BNP in an asymptomatic DMD cohort. We hypothesized the biomarkers would not correlate with cardiac function, but some asymptomatic patients would exhibit a cTnI leak, reflecting ongoing myocardial inflammation related to disease progression. Methods: Asymptomatic DMD patients (N=69) and controls with normal cardiac evaluations (N=18) were enrolled. In DMD subjects, biomarker levels were obtained at time of cardiac magnetic resonance imaging (CMR), which included assessment of atrial and ventricular volumes, function, and late gadolinium enhancement (LGE). Normal ranges for biomarkers were created based on control values. Spearman correlation was used for analysis. Results: There was no consistent correlation between biomarkers and disease progression by CMR (Table 1). Several DMD subjects had transiently elevated cTnI (Fig 1). Those with elevated cTnI trended towards being more likely to have LGE on baseline CMR, though this did not reach statistical significance (p= 0.08). Conclusions: CTnI, BNP, and NTproBNP do not correlate with CMR assessment of cardiomyopathy progression. There is a subset of the DMD cohort with asymptomatic cTnI leak. While this cTnI leak is of uncertain clinical significance, it is important to recognize if cTnI is used to assess for cardiac toxicity in future drug trials.

The ACTN3 577XX Null Genotype Is Associated with Low Left Ventricular Dilation-Free Survival Rate in Patients with Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a fatal progressive muscle-wasting disease caused by mutations in the DMD gene. Dilated cardiomyopathy is the leading cause of death in DMD; therefore, further understanding of this complication is essential to reduce morbidity and mortality. A common null variant (R577X) in the ACTN3 gene, which encodes α-actinin-3, has been studied in association with muscle function in healthy individuals; however it has not yet been examined in relationship to the cardiac phenotype in DMD. In this study, we determined the ACTN3 genotype in 163 patients with DMD and examined the correlation between ACTN3 genotypes and echocardiographic findings in 77 of the 163 patients. The genotypes 577RR(RR), 577RX(RX) and 577XX(XX) were identified in 13 (17%), 44 (57%) and 20 (26%) of 77 patients, respectively. We estimated cardiac involvement-free survival rate analyses using Kaplan-Meier curves. Remarkably, the left ventricular dilation (> 55 mm)-free survival rate was significantly lower in patients with the XX null genotype (P < 0.01). The XX null genotype showed a higher risk for LV dilation (hazard ratio 9.04). This study revealed that the ACTN3 XX null genotype was associated with a lower left ventricular dilation-free survival rate in patients with DMD. These results suggest that the ACTN3 genotype should be determined at the time of diagnosis of DMD to improve patients' cardiac outcomes.

Motor axonopathies in a mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disease caused by deleterious mutations in the DMD gene which encodes the dystrophin protein. Skeletal muscle weakness and eventual muscle degradation due to loss of dystrophin are well-documented pathological hallmarks of DMD. In contrast, the neuropathology of this disease remains understudied despite the emerging evidence of neurological abnormalities induced by dystrophin loss. Using quantitative morphological analysis of nerve sections, we characterize axonopathies in the phrenic and hypoglossal (XII) nerves of mdx mice. We observe dysfunction in these nerves – which innervate the diaphragm and genioglossus respectively – that we propose contributes to respiratory failure, the most common cause of death in DMD. These observations highlight the importance in the further characterization of the neuropathology of DMD. Additionally, these observations underscore the necessity in correcting both the nervous system pathology in addition to skeletal muscle deficits to ameliorate this disease.

Troponin I Levels Correlate with Cardiac MR LGE and Native T1 Values in Duchenne Muscular Dystrophy Cardiomyopathy and Identify Early Disease Progression.

Cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Elevated troponin levels are observed in DMD and may vary with disease progression. We studied troponin levels in DMD related to cardiac fibrosis and native T1 measures. This is a prospective, cross-sectional, observational study of 30 DMD subjects measuring native T1 levels and late gadolinium enhancement (LGE) on cardiac MR imaging (CMR) correlated with temporally associated serum troponin I levels. Non-parametric analyses including Spearman correlations and Kruskal-Wallis test were performed between groups. p values resulting from the pair-wise comparisons were adjusted for multiple comparisons using the Sidak method where appropriate. There were 15 DMD subjects with no LGE (age 12 ± 3 yo; EF% 60 ± 5) and troponin I level of 0.05 ± 0.08ng/ml, of which three had an abnormal troponin level (over 0.04ng/ml); 7 DMD subjects with mild LGE (age 17 ± 5 yo, EF% 52 ± 8) and troponin I level of 0.28 ± 0.36ng/ml, of which five had an abnormal troponin level; and 8 DMD subjects with moderate-to-severe LGE (age 16 ± 6 yo; EF% 54 ± 8) and troponin I level of 0.11 ± 0.14ng/ml, of which four had an abnormal troponin level. Troponin I levels in DMD subjects with mild LGE was significantly increased compared to subjects with no LGE (p = 0.02). There was a statistically significant positive correlation between troponin I levels and MOLLI septal native T1 values (r2 = 0.173, p = 0.02). Overall, MOLLI lateral native T1 levels were increased with moderate-severe LGE compared to mild and none (p < 0.01). Serum biomarker troponin I levels were increased in DMD subjects with mild LGE and correlated with MOLLI septal native T1 values. Troponin I levels may be a useful minimally invasive outcome marker to monitor myocardial disease progression in DMD cardiomyopathy.