107th ENMC international workshop: the management of cardiac involvement in muscular dystrophy and myotonic dystrophy. 7th-9th June 2002, Naarden, the Netherlands

Developing standardized corticosteroid treatment for Duchenne muscular dystrophy

Despite corticosteroids being the only treatment documented to improve strength and function in boys with Duchenne muscular dystrophy (DMD) corticosteroid prescription is inconsistent and in some countries, corticosteroids are not prescribed. We are conducting a clinical trial that (1) compares the 3 most frequently prescribed corticosteroid regimes; (2) standardizes treatment of DMD complications; and (3) standardizes prevention of corticosteroid side effects. Investigators at 38 sites in 5 countries plan to recruit 300 boys aged 4-7 who are randomly assigned to one of three regimens: daily prednisone; daily deflazacort; or intermittent prednisone (10days on/10days off). Boys are followed for a minimum of 3years to assess the relative effectiveness and adverse event profiles of the different regimens. The primary outcome is a 3-dimensional variable consisting of log-transformed time to rise from the floor, forced vital capacity, and subject/parent satisfaction with treatment, each averaged over all post-baseline visits. The study protocol includes evidence- and consensus-based treatment of DMD complications and of corticosteroid side effects. This study seeks to establish a standard corticosteroid regimen for DMD. Since all new interventions for DMD are being developed as add-on therapies to corticosteroids, defining the optimum regimen is of importance for all new treatments.

Disease-modifying effects of orally bioavailable NF-B inhibitors in dystrophin-deficient muscle

Duchenne muscular dystrophy (DMD) is a devastating muscle disease characterized by progressive muscle deterioration and replacement with an aberrant fatty, fibrous matrix. Chronic upregulation of nuclear factor κB (NF-κB) is implicated as a driver of the dystrophic pathogenesis. Herein, 2 members of a novel class of NF-κB inhibitors, edasalonexent (formerly CAT-1004) and CAT-1041, were evaluated in both mdx mouse and golden retriever muscular dystrophy (GRMD) dog models of DMD. These orally bioavailable compounds consist of a polyunsaturated fatty acid conjugated to salicylic acid and potently suppress the pathogenic NF-κB subunit p65/RelA in vitro. In vivo, CAT-1041 effectively improved the phenotype of mdx mice undergoing voluntary wheel running, in terms of activity, muscle mass and function, damage, inflammation, fibrosis, and cardiac pathology. We identified significant increases in dysferlin as a possible contributor to the protective effect of CAT-1041 to sarcolemmal damage. Furthermore, CAT-1041 improved the more severe GRMD phenotype in a canine case study, where muscle mass and diaphragm function were maintained in a treated GRMD dog. These results demonstrate that NF-κB modulation by edasalonexent and CAT-1041 is effective in ameliorating the dystrophic process and these compounds are candidates for new treatments for DMD patients.

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.

Myocardial late gadolinium enhancement is associated with clinical presentation in Duchenne muscular dystrophy carriers

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive disease that occurs in males leading to immobility and death in early adulthood. Female carriers of DMD are generally asymptomatic, yet frequently develop dilated cardiomyopathy. This study aims to detect early cardiac manifestation in DMD using cardiovascular magnetic resonance (CMR) and to evaluate its association with clinical symptoms.

METHODS

Clinical assessment of DMD carriers included six minutes walk tests (6MWT), blood analysis, electrocardiography, echocardiography, and CMR using FLASH sequences to detect late gadolinium enhancement (LGE). T1-mapping using the Modified Look-Locker Inversion recovery (MOLLI) sequence was performed quantify extracellular volume (ECV).

RESULTS

Of 20 carriers (age 39.47 ± 12.96 years) 17 (89.5 %) were clinically asymptomatic. ECV was mildly elevated (29.79 ± 2.92 %) and LGE was detected in nine cases (45 %). LGE positive carriers had lower left ventricular ejection fraction in CMR (64.36 ± 5.78 vs. 56.67 ± 6.89 %, p = 0.014), higher bothCK (629.89 ± 317.48 vs. 256.18 ± 109.10 U/l, p = 0.002) and CK-MB (22.13 ± 5.25 vs. 12.11 ± 2.21 U/l, p = 0.001), as well as shorter walking distances during the 6MWT (432.44 ± 96.72 vs. 514.91 ± 66.80 m, p = 0.037). 90.9 % of subjects without LGE had normal pro-BNP, whereas in 66.7 % of those presenting LGE pro-BNP was elevated (p = 0.027). All individuals without LGE were in the NYHA class I, whereas all those in NYHA classes II and III showed positive for LGE (p = 0.066).

CONCLUSIONS

Myocardial involvement shown as LGE in CMR occurs in a substantial number of DMD carriers; it is associated with clinical and morphometric signs of incipient heart failure. LGE is thus a sensitive parameter for the early diagnosis of cardiomyopathy in DMD carriers.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT01712152 Trial registration: October 19, 2012. First patient enrolled: September 27, 2012 (retrospectively registered).

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.

Tadalafil Treatment Delays the Onset of Cardiomyopathy in Dystrophin-Deficient Hearts

Background

Cardiomyopathy is a leading cause of mortality among Duchenne muscular dystrophy patients and lacks effective therapies. Phosphodiesterase type 5 is implicated in dystrophic pathology, and the phosphodiesterase type 5 inhibitor tadalafil has recently been studied in a clinical trial for Duchenne muscular dystrophy.

Methods and Results

Tadalafil was evaluated for the prevention of cardiomyopathy in the mdx mouse and golden retriever muscular dystrophy dog models of Duchenne muscular dystrophy. Tadalafil blunted the adrenergic response in mdx hearts during a 30‐minute dobutamine challenge, which coincided with cardioprotective signaling, reduced induction of μ‐calpain levels, and decreased sarcomeric protein proteolysis. Dogs with golden retriever muscular dystrophy began daily tadalafil treatment prior to detectable cardiomyopathy and demonstrated preserved cardiac function, as assessed by echocardiography and magnetic resonance imaging at ages 18, 21, and 25 months. Tadalafil treatment improved golden retriever muscular dystrophy histopathological features, decreased levels of the cation channel TRPC6, increased total threonine phosphorylation status of TRPC6, decreased m‐calpain levels and indicators of calpain target proteolysis, and elevated levels of utrophin. In addition, we showed that Duchenne muscular dystrophy patient myocardium exhibited increased TRPC6, m‐calpain, and calpain cleavage products compared with control human myocardium.

Conclusions

Prophylactic use of tadalafil delays the onset of dystrophic cardiomyopathy, which is likely attributed to modulation of TRPC6 levels and permeability and inhibition of protease content and activity. Consequently, phosphodiesterase type 5 inhibition is a candidate therapy for slowing the development of cardiomyopathy in Duchenne muscular dystrophy patients.

[Survey on genetic counseling and health management for symptomatic and asymptomatic female dystrophinopathy carriers in Japan today]

To clarify the current status of genetic counseling and health monitoring for symptomatic and asymptomatic female carriers of dystrophinopathy (Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD)), we sent out questionnaires to 104 member institutions of The Japan's National Liaison Council for Clinical Sections of Medical Genetics, and responses were received from 51 institutions. Between April 2013 and March 2014, 57 carriers at 21 institutions received genetic counseling, and 37 carriers at 15 institutions underwent genetic screening for DMD/BMD mutations. At the 23 institutions that gave genetic counseling, 20 (87%) informed carriers of possible health problems, 14 (61%) informed carriers of cardiomyopathy and heart failure, and 14 (61%) advised carriers about regular medical checkups. Evidence based on accurate and up-to-date epidemiological studies of female carriers is needed and should be widely shared with the families, medical providers, and society.

Corticosteroids for the treatment of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood. Untreated, this incurable disease, which has an X-linked recessive inheritance, is characterised by muscle wasting and loss of walking ability, leading to complete wheelchair dependence by 13 years of age. Prolongation of walking is a major aim of treatment. Evidence from randomised controlled trials (RCTs) indicates that corticosteroids significantly improve muscle strength and function in boys with DMD in the short term (six months), and strength at two years (two-year data on function are very limited). Corticosteroids, now part of care recommendations for DMD, are largely in routine use, although questions remain over their ability to prolong walking, when to start treatment, longer-term balance of benefits versus harms, and choice of corticosteroid or regimen.We have extended the scope of this updated review to include comparisons of different corticosteroids and dosing regimens.

OBJECTIVES

To assess the effects of corticosteroids on prolongation of walking ability, muscle strength, functional ability, and quality of life in DMD; to address the question of whether benefit is maintained over the longer term (more than two years); to assess adverse events; and to compare efficacy and adverse effects of different corticosteroid preparations and regimens.

SEARCH METHODS

On 16 February 2016 we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, EMBASE, CINAHL Plus, and LILACS. We wrote to authors of published studies and other experts. We checked references in identified trials, handsearched journal abstracts, and searched trials registries.

SELECTION CRITERIA

We considered RCTs or quasi-RCTs of corticosteroids (e.g. prednisone, prednisolone, and deflazacort) given for a minimum of three months to patients with a definite DMD diagnosis. We considered comparisons of different corticosteroids, regimens, and corticosteroids versus placebo.

DATA COLLECTION AND ANALYSIS

The review authors followed standard Cochrane methodology.

MAIN RESULTS

We identified 12 studies (667 participants) and two new ongoing studies for inclusion. Six RCTs were newly included at this update and important non-randomised cohort studies have also been published. Some important studies remain unpublished and not all published studies provide complete outcome data.

PRIMARY OUTCOME MEASURE

one two-year deflazacort RCT (n = 28) used prolongation of ambulation as an outcome measure but data were not adequate for drawing conclusions.

SECONDARY OUTCOME MEASURES

meta-analyses showed that corticosteroids (0.75 mg/kg/day prednisone or prednisolone) improved muscle strength and function versus placebo over six months (moderate quality evidence from up to four RCTs). Evidence from single trials showed 0.75 mg/kg/day superior to 0.3 mg/kg/day on most strength and function measures, with little evidence of further benefit at 1.5 mg/kg/day. Improvements were seen in time taken to rise from the floor (Gowers' time), timed walk, four-stair climbing time, ability to lift weights, leg function grade, and forced vital capacity. One new RCT (n = 66), reported better strength, function and quality of life with daily 0.75 mg/kg/day prednisone at 12 months. One RCT (n = 28) showed that deflazacort stabilised muscle strength versus placebo at two years, but timed function test results were too imprecise for conclusions to be drawn.One double-blind RCT (n = 64), largely at low risk of bias, compared daily prednisone (0.75 mg/kg/day) with weekend-only prednisone (5 mg/kg/weekend day), finding no overall difference in muscle strength and function over 12 months (moderate to low quality evidence). Two small RCTs (n = 52) compared daily prednisone 0.75 mg/kg/day with daily deflazacort 0.9 mg/kg/day, but study methods limited our ability to compare muscle strength or function.

ADVERSE EFFECTS

excessive weight gain, behavioural abnormalities, cushingoid appearance, and excessive hair growth were all previously shown to be more common with corticosteroids than placebo; we assessed the quality of evidence (for behavioural changes and weight gain) as moderate. Hair growth and cushingoid features were more frequent at 0.75 mg/kg/day than 0.3 mg/kg/day prednisone. Comparing daily versus weekend-only prednisone, both groups gained weight with no clear difference in body mass index (BMI) or in behavioural changes (low quality evidence for both outcomes, one study); the weekend-only group had a greater linear increase in height. Very low quality evidence suggested less weight gain with deflazacort than with prednisone at 12 months, and no difference in behavioural abnormalities. Data are insufficient to assess the risk of fractures or cataracts for any comparison.Non-randomised studies support RCT evidence in showing improved functional benefit from corticosteroids. These studies suggest sustained benefit for up to 66 months. Adverse effects were common, although generally manageable. According to a large comparative longitudinal study of daily or intermittent (10 days on, 10 days off) corticosteroid for a mean period of four years, a daily regimen prolongs ambulation and improves functional scores over the age of seven, but with a greater frequency of side effects than an intermittent regimen.

AUTHORS' CONCLUSIONS

Moderate quality evidence from RCTs indicates that corticosteroid therapy in DMD improves muscle strength and function in the short term (twelve months), and strength up to two years. On the basis of the evidence available for strength and function outcomes, our confidence in the effect estimate for the efficacy of a 0.75 mg/kg/day dose of prednisone or above is fairly secure. There is no evidence other than from non-randomised trials to establish the effect of corticosteroids on prolongation of walking. In the short term, adverse effects were significantly more common with corticosteroids than placebo, but not clinically severe. A weekend-only prednisone regimen is as effective as daily prednisone in the short term (12 months), according to low to moderate quality evidence from a single trial, with no clear difference in BMI (low quality evidence). Very low quality evidence indicates that deflazacort causes less weight gain than prednisone after a year's treatment. We cannot evaluate long-term benefits and hazards of corticosteroid treatment or intermittent regimens from published RCTs. Non-randomised studies support the conclusions of functional benefits, but also identify clinically significant adverse effects of long-term treatment, and a possible divergence of efficacy in daily and weekend-only regimens in the longer term. These benefits and adverse effects have implications for future research and clinical practice.

ERK1/2 directly acts on CTGF/CCN2 expression to mediate myocardial fibrosis in cardiomyopathy caused by mutations in the lamin A/C gene

Cardiomyopathy caused by lamin A/C gene mutations (LMNA cardiomyopathy) is characterized by increased myocardial fibrosis, which impairs left ventricular relaxation and predisposes to heart failure, and cardiac conduction abnormalities. While we previously discovered abnormally elevated extracellular signal-regulated kinase 1/2 (ERK1/2) activities in heart in LMNA cardiomyopathy, its role on the development of myocardial fibrosis remains unclear. We now showed that transforming growth factor (TGF)-β/Smad signaling participates in the activation of ERK1/2 signaling in LMNA cardiomyopathy. ERK1/2 acts on connective tissue growth factor (CTGF/CCN2) expression to mediate the myocardial fibrosis and left ventricular dysfunction. Studies in vivo demonstrate that inhibiting CTGF/CCN2 using a specific antibody decreases myocardial fibrosis and improves the left ventricular dysfunction. Together, these findings show that cardiac ERK1/2 activity is modulated in part by TGF-β/Smad signaling, leading to altered activation of CTGF/CCN2 to mediate fibrosis and alter cardiac function. This identifies a novel mechanism in the development of LMNA cardiomyopathy.

The Performance of the Upper Limb scores correlate with pulmonary function test measures and Egen Klassifikation scores in Duchenne muscular dystrophy

The Performance of the Upper Limb scale was developed as an outcome measure specifically for ambulant and non-ambulant patients with Duchenne muscular dystrophy and is implemented in clinical trials needing longitudinal data. The aim of this study is to determine whether this novel tool correlates with functional ability using pulmonary function test, cardiac function test and Egen Klassifikation scale scores as clinical measures. In this cross-sectional study, 43 non-ambulatory Duchenne males from ages 10 to 30 years and on long-term glucocorticoid treatment were enrolled. Cardiac and pulmonary function test results were analyzed to assess cardiopulmonary function, and Egen Klassifikation scores were analyzed to assess functional ability. The Performance of the Upper Limb scores correlated with pulmonary function measures and had inverse correlation with Egen Klassifikation scores. There was no correlation with left ventricular ejection fraction and left ventricular dysfunction. Body mass index and decreased joint range of motion affected total Performance of the Upper Limb scores and should be considered in clinical trial designs.

Hypoxia-induced cardiac injury in dystrophic mice

Duchenne muscular dystrophy (DMD) is a disease of progressive destruction of striated muscle, resulting in muscle weakness with progressive respiratory and cardiac failure. Respiratory and cardiac disease are the leading causes of death in DMD patients. Previous studies have suggested an important link between cardiac dysfunction and hypoxia in the dystrophic heart; these studies aim to understand the mechanism underlying this connection. Here we demonstrate that anesthetized dystrophic mice display significant mortality following acute exposure to hypoxia. This increased mortality is associated with a significant metabolic acidosis, despite having significantly higher levels of arterial Po2 Chronic hypoxia does not result in mortality, but rather is characterized by marked cardiac fibrosis. Studies in isolated hearts reveal that the contractile function of dystrophic hearts is highly susceptible to short bouts of ischemia, but these hearts tolerate prolonged acidosis better than wild-type hearts, indicating an increased sensitivity of the dystrophic heart to hypoxia. Dystrophic hearts display decreased cardiac efficiency and oxygen extraction. Isolated dystrophic cardiomyocytes and hearts have normal levels of FCCP-induced oxygen consumption, and mitochondrial morphology and content are normal in the dystrophic heart. These studies demonstrate reductions in cardiac efficiency and oxygen extraction of the dystrophic heart. The underlying cause of this reduced oxygen extraction is not clear; however, the current studies suggest that large disruptions of mitochondrial respiratory function or coronary flow regulation are not responsible. This finding is significant, as hypoxia is a common and largely preventable component of DMD that may contribute to the progression of the cardiac disease in DMD patients.

Ambulatory Monitoring and Arrhythmic Outcomes in Pediatric and Adolescent Patients With Duchenne Muscular Dystrophy

BACKGROUND

Patients with Duchenne Muscular Dystrophy (DMD) develop cardiac fibrosis and dilated cardiomyopathy. We described the frequency of significant Holter findings in DMD, the relationship between cardiac function and arrhythmia burden, and the impact of these findings on clinical management.

METHODS AND RESULTS

A retrospective review was done of patients with DMD who received a Holter from 2010 to 2014. Clinical and arrhythmic outcomes were analyzed. Patients were classified based on left ventricular ejection fraction (LVEF): ≥55%, 35% to 54% and <35%. Significant Holter findings included atrial tachycardia, ventricular tachycardia and atrial fibrillation/flutter. Logistic regression was used to assess predictors of significant Holter findings and change in care. The study included 442 Holters in 235 patients. Mean age was 14±4 years. Patients with cardiac dysfunction were older, and had increased late gadolinium enhancement and left ventricular dilation (P<0.01). There were 3 deaths (1%), all with normal function and none cardiac. Patients with LVEF <35% had more arrhythmias including nonsustained atrial tachycardia (P=0.01), frequent premature ventricular contractions, ventricular couplets/triplets, and nonsustained ventricular tachycardia (P<0.001) compared to the other groups. LVEF <35% (P<0.001) was the only predictor of clinically significant Holter finding. Four patients (40%) had change in medication in the LVEF <35% group compared to 9 (3%) in the ≥55% and 4 (4%) in the 35% to 54% groups (P<0.001).

CONCLUSIONS

Sudden cardiac events are rare in DMD patients with an LVEF >35%. Significant Holter findings are rare in patients with DMD who have an LVEF >35%, and cardiac dysfunction appears to predict significant Holter findings. Holter monitoring is highest yield among DMD patients with cardiac dysfunction.

Diastolic dysfunction precedes hypoxia-induced mortality in dystrophic mice

Duchenne muscular dystrophy (DMD) is a progressive striated muscle disease that is characterized by skeletal muscle weakness with progressive respiratory and cardiac failure. Together respiratory and cardiac disease account for the majority of mortality in the DMD patient population. However, little is known regarding the effects of respiratory dysfunction on the dystrophic heart. The studies described here examine the effects of acute hypoxia on cardiac function. These studies demonstrate, for the first time, that a mouse model of DMD displays significant mortality following acute exposure to hypoxia. This mortality is characterized by a steady decline in systolic function. Retrospective analysis reveals that significant decreases in diastolic dysfunction, especially in the right ventricle, precede the decline in systolic pressure. The initial hemodynamic response to acute hypoxia in the mouse is similar to that observed in larger species, with significant increases in right ventricular afterload and decreases in left ventricular preload being observed. Significant increases in heart rate and contractility suggest hypoxia-induced activation of the sympathetic nervous system. These studies provide evidence that while hypoxia presents significant hemodynamic challenges to the dystrophic right ventricle, global cardiac dysfunction precedes hypoxia-induced mortality in the dystrophic heart. These findings are clinically relevant as the respiratory insufficiency evident in patients with DMD results in significant bouts of hypoxia. The results of these studies indicate that hypoxia may contribute to the acceleration of the heart disease in DMD patients. Importantly, hypoxia can be avoided through the use of ventilatory support.

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.

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.

Risk-benefit considerations when prescribing phosphodiesterase-5 inhibitors in children

INTRODUCTION

Sildenafil (Revatio®) and tadalafil (Adcirca®) are specific inhibitors of the phosphodiesterase-5 enzyme and produce pulmonary vasodilation by inhibiting the breakdown of cyclic guanosine monophosphate (cGMP) in the walls of pulmonary arterioles.

AREAS COVERED

We focus on the efficacy and safety of sildenafil and tadalafil in the treatment of pulmonary hypertension (PH) in children through a PubMed literature search.

EXPERT OPINION

Although used since 1999 in the treatment of PH in children, it is only in the past few years that robust evidence for the use of sildenafil has emerged principally in the pivotal STARTS-1 study. The open-label extension of this study, STARTS-2, has revealed safety concerns substantiated by FDA post marketing surveillance leading to recommendations to use lower doses. More recently, tadalafil has been introduced allowing once daily dosing with apparently similar efficacy to sildenafil in children. Recently there have been suggestions that sildenafil and tadalafil may have a place in treating muscular dystrophy.

Cardiac involvement in Dutch patients with sarcoglycanopathy: a cross-sectional cohort and follow-up study

INTRODUCTION

The aim of this study is to describe the frequency, nature, severity, and progression of cardiac abnormalities in a cohort of Dutch sarcoglycanopathy patients.

METHODS

In this cross-sectional cohort study, patients were interviewed using a standardized questionnaire and assigned a functional score. Electrocardiography (ECG), echocardiography, and 24-h ECG were performed.

RESULTS

Twenty-four patients with sarcoglycanopathy had a median age of 25 years (range, 8-59 years). Beta blockers were used by 13%, and 17% used angiotensin-converting enzyme inhibitors. ECG abnormalities were present in 5 (21%), and 4 (17%) fulfilled the criteria for dilated cardiomyopathy (DCM). There were no significant differences in median age or severity of disease between patients with or without DCM. Eleven patients were examined earlier. Median follow-up time was 10 years. Two of the 11 patients (18%) developed DCM during follow-up.

CONCLUSIONS

Seventeen percent of the patients with sarcoglycanopathy were found to have dilated cardiomyopathy. We recommend biannual cardiac monitoring, including ECG and echocardiography.

Cardiac management of ventilator-assisted individuals with Duchenne muscular dystrophy

As life expectancy of patients with Duchenne muscular dystrophy (DMD) has increased to the 5th decade, in part due to improved ventilatory support, cardiomyopathy is projected to increase as a cause of death. International guidelines recommend an annual assessment of cardiac function and initiation of appropriate pharmacological treatment. We conducted an audit of the cardiac management in patients with DMD requiring ventilatory support and reported a case series of the collated cardiac investigations. Patients with DMD requiring ventilatory support were included in the study. The date of the last electrocardiogram (ECG), echocardiogram (ECHO), cardiology review and pharmacological management were retrieved from the medical records. If an annual cardiac assessment had not been performed this was requested and the latest ECGs and ECHO reports were collated. A total of 30 patients with DMD (29 males, mean (SD) age of 30 (7) years) met the inclusion criteria. Although there was ECG and ECHO documentation in 24 and 21 individuals, respectively, it was only recent in 10 and 6 individuals. In all, 60% of patients had been assessed by a cardiologist, but only 10% within the last year. Over half of the patients failed to attend their new appointments. From the available results, 18 of the 19 patients had an abnormal ECG, 11 of the 16 patients had left ventricular (LV) impairment and 55% of patients had a change in prescription following cardiac investigations. There is a need for a coordinated cardiorespiratory approach towards adult patients with DMD. Over a third of patients had normal LV function suggesting that cardiomyopathy is not inevitable in this group.

Cardiopulmonary Exercise Testing in Children and Adolescents With Dystrophinopathies: A Pilot Study

PURPOSE

To determine exercise response during cardiopulmonary exercise testing in children and adolescents with dystrophinopathies.

METHODS

Exercise response on the cardiopulmonary exercise test (CPET) was compared with a standard care test protocol.

RESULTS

Nine boys (aged 10.8 ± 4.7 years) with Becker muscular dystrophy (n = 6) and Duchenne muscular dystrophy (n = 3) were included. The feasibility of the CPET was similar to a standard care test protocol, and no serious adverse events occurred. In 67% of the subjects with normal or only mildly impaired functional capacity, the CPET could be used to detect moderate to severe cardiopulmonary exercise limitations.

CONCLUSIONS

The CPET seems to be a promising outcome measure for cardiopulmonary exercise limitations in youth with mild functional limitations. Further research with larger samples is warranted to confirm current findings and investigate the additional value of the CPET to longitudinal follow-up of cardiomyopathy and the development of safe exercise programs for youth with dystrophinopathies.

Concise review: mesoangioblast and mesenchymal stem cell therapy for muscular dystrophy: progress, challenges, and future directions

Mesenchymal stem cells (MSCs) and mesoangioblasts (MABs) are multipotent cells that differentiate into specialized cells of mesodermal origin, including skeletal muscle cells. Because of their potential to differentiate into the skeletal muscle lineage, these multipotent cells have been tested for their capacity to participate in regeneration of damaged skeletal muscle in animal models of muscular dystrophy. MSCs and MABs infiltrate dystrophic muscle from the circulation, engraft into host fibers, and bring with them proteins that replace the functions of those missing or truncated. The potential for systemic delivery of these cells increases the feasibility of stem cell therapy for the large numbers of affected skeletal muscles in patients with muscular dystrophy. The present review focused on the results of preclinical studies with MSCs and MABs in animal models of muscular dystrophy. The goals of the present report were to (a) summarize recent results, (b) compare the efficacy of MSCs and MABs derived from different tissues in restoration of protein expression and/or improvement in muscle function, and (c) discuss future directions for translating these discoveries to the clinic. In addition, although systemic delivery of MABs and MSCs is of great importance for reaching dystrophic muscles, the potential concerns related to this method of stem cell transplantation are discussed.

Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy is one of the most severe muscle diseases to affect children. In the last twenty years, treatments have been established that have significantly improved patients' quality of life and life expectancy. The purpose of this article is to outline the main features of the disease and its treatment, and to examine possible future treatment options.

METHOD

The article is based on a literature search in PubMed, current international guidelines and our own clinical experience.

RESULTS

Close monitoring by an interdisciplinary rehabilitation team forms the basis of treatment. Treatment with glucocorticoids can slow disease progression and improve motor function in the short term. The treatment may cause side effects, which must be monitored and which may require intervention. A not insignificant proportion of patients have cognitive and neuropsychiatric problems that must be addressed. Active intervention in response to signs of respiratory or cardiac failure is important. More causal treatment of Duchenne muscular dystrophy is under testing and offers cautious hope for future patients.

INTERPRETATION

With improved treatment and increased life expectancy come new challenges for patients with Duchenne muscular dystrophy and their families, as well as new demands on the support services. This patient group requires close and comprehensive follow-up, also in the transition from child to adult.

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.

Identification of de novo mutations of Duchénnè/Becker muscular dystrophies in southern Spain

BACKGROUND

Duchénnè/Becker muscular dystrophies (DMD/BMD) are X-linked diseases, which are caused by a de novo gene mutation in one-third of affected males. The study objectives were to determine the incidence of DMD/BMD in Andalusia (Spain) and to establish the percentage of affected males in whom a de novo gene mutation was responsible.

METHODS

Multiplex ligation-dependent probe amplification (MLPA) technology was applied to determine the incidence of DMD/BMD in 84 males with suspicion of the disease and 106 female relatives.

RESULTS

Dystrophin gene exon deletion (89.5%) or duplication (10.5%) was detected in 38 of the 84 males by MLPA technology; de novo mutations account for 4 (16.7%) of the 24 mother-son pairs studied.

CONCLUSIONS

MLPA technology is adequate for the molecular diagnosis of DMD/BMD and establishes whether the mother carries the molecular alteration responsible for the disease, a highly relevant issue for genetic counseling.

[Case with Emery-Dreifuss muscular dystrophy diagnosed forty-two years after onset and implanted with a cardiac resynchronization therapy defibrillator]

The patient was a 53-year-old male. He showed steppage gait at the age of 11 and equinus foot at 13. He walked unaided with shoe-insoles to support his heels. Atrial fibrillation and cardiac hypertrophy were found in his 30s, and ventricular tachycardia (VT) was observed at the age of 48. Electrophysiological studies were performed, but VT was not sustained, symptomatic, or showed signs of infra-Hisian block, and a pacemaker was not indicated. At 53, he was introduced to a neurologist because of tetraplegia after the first episode of syncope. A spinal MR showed ossification of posterior longitudinal ligament (OPLL) and central cervical cord injury. Furthermore, he presented not only contracture in his shoulder, elbow, and ankles but also atrophy in his scapulohumeral and gastrocnemius muscles. In accordance with a diagnosis of Emery-Dreifuss muscular dystrophy (EDMD), provocative testing of VT was carried out, and a cardiac resynchronization therapy defibrillator (CRT-D) was implanted. Later, a mutation analysis of the LMNA gene disclosed a known missense mutation of p.Arg377His, and we diagnosed him as EDMD2 (laminopathy). Contractures could be the clue to diagnose EDMD and indicate the need for pacemakers and defibrillators in patients with cardiac conduction disorders.

Myocardial atrophy in children with mitochondrial disease and Duchenne muscular dystrophy

Purpose

Mitochondrial disease (MD) and Duchenne muscular dystrophy (DMD) are often associated with cardiomyopathy, but the myocardial variability has not been isolated to a specific characteristic. We evaluated the left ventricular (LV) mass by echocardiography to identify the general distribution and functional changes of the myocardium in patients with MD or DMD.

Methods

We retrospectively evaluated the echocardiographic data of 90 children with MD and 42 with DMD. Using two-dimensional echocardiography, including time-motion (M) mode and Doppler measurements, we estimated the LV mass, ratio of early to late mitral filling velocities (E/A), ratio of early mitral filling velocity to early diastolic mitral annular velocity (E/Ea), stroke volume, and cardiac output. A "z score" was generated using the lambda-mu-sigma method to standardize the LV mass with respect to body size.

Results

The LV mass-for-height z scores were significantly below normal in children with MD (-1.02±1.52, P<0.001) or DMD (-0.82±1.61, P=0.002), as were the LV mass-for-lean body-mass z scores. The body mass index (BMI)-for-age z scores were far below normal and were directly proportional to the LV mass-for-height z scores in both patients with MD (R=0.377, P<0.001) and those with DMD (R=0.330, P=0.033). The LV mass-for-height z score correlated positively with the stroke volume index (R=0.462, P<0.001) and cardiac index (R=0.358, P<0.001).

Conclusion

LV myocardial atrophy is present in patients with MD and those with DMD and may be closely associated with low BMI. The insufficient LV mass for body size might indicate deterioration of systolic function in these patients.

Clinical and muscle biopsy findings in Norwegian paediatric patients with limb girdle muscular dystrophy 2I

AIM

To describe patients diagnosed with limb girdle muscular dystrophy 2I (LGMD2I) in our paediatric departments between 2004 and 2012.

METHODS

The hospital charts of 17 patients presenting for evaluation at a mean age of 7.8 years (range 1-13 years) were retrospectively reviewed.

RESULTS

With one exception, all patients were homozygous for the common mutation c.826C>A in the FKRP gene. Three patients experienced transient pronounced weakness as toddlers. Fatigue and muscle pain were most prominent, weakness less so, in children presenting at an older age. The degree of severity varied substantially. In certain cases, increased creatine kinase was an incidental finding. All walked independently by 18 months. When last evaluated at a mean age of 14.3 years (range 3.5-18 years), five patients were part-time wheelchair users. One patient was then treated for a cardiomyopathy. Creatine kinase was consistently increased, except presymptomatic in one patient. Muscle biopsies showed focal acute and chronic myopathic changes and pathological expression of α-dystroglycan. No consistent relationship between clinical function and the degree of morphological pathology was found.

CONCLUSION

LGMD2I is a relevant differential diagnosis when creatine kinase is increased in children presenting with fatigue, muscle pain and sometimes weakness.

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.

Current treatment and management of dystrophinopathies

OPINION STATEMENT

• Duchenne muscular dystrophy (DMD), the most common and severe type of dystrophinopathy, is a progressive disease affecting primordially skeletal and cardiac muscle. A coordinated multidisciplinary approach is required to address its multisystemic manifestations and secondary problems.• Treatment with glucocorticosteroids (GCS) is accepted as standard of care in ambulant DMD. Daily and intermittent administrations are both in common use with different efficacy and different side effect profile.• There are no established guidelines for age/stage at initiation and treatment duration of GCS. Common practice is initiation of GCS before the child is starting to decline (between age 3 and 6 years) and continuation of monitored treatment after loss of ambulation, aiming at delaying cardiac and respiratory manifestations and preventing the development of scoliosis.• Prevention, monitoring, and treatment of the side effects of long-term chronic GCS use, such as excessive weight gain, hypertension, osteoporosis, impairment of glucose metabolism, delayed puberty, and cataract, should be integrated in the standards of care.• Noninvasive ventilatory support associated with cough assisting techniques has significantly improved the longevity in DMD.• Pharmacologic treatment for cardiac manifestations includes the standard treatments of dilated cardiomyopathy and arrhythmia such as the use of angiotensin converting enzyme (ACE) inhibitors, beta-blockers and diuretics. The lack of robust controlled data hampers clear recommendations about preventive treatment with ACE inhibitors.• DMD is associated with low bone mineral content, which is aggravated by the use of corticosteroids. The use of biphosphonates can be considered in the treatment of painful vertebral fractures. The use of biphosphonates as a preventive treatment should be investigated in randomized controlled studies.• DMD has evolved from a pediatric disease to an adult condition. This underscores the need to prepare adult neurologists for the optimal surveillance and management of patients with a severe chronic disease that have outgrown the pediatric care and that may develop new disease manifestations with improved longevity.

Muscular dystrophy: new challenges and review of the current clinical trials

PURPOSE OF REVIEW

We provide a review of recent standards of care and therapeutic development in different forms of muscular dystrophies. This topic is relevant as the improved understanding of these disorders has not only led to a better definition of clinical course and to the development of standards of care for individual types of muscular dystrophies, but also culminated in different therapeutic approaches.

RECENT FINDINGS

Recent natural history studies have demonstrated the impact of new standards of care in different forms of muscular dystrophies, and identified areas of clinical management in which further developments are needed. The majority of the experimental studies are focused on Duchenne muscular dystrophy. Some of them target patients with specific mutations, such as antisense oligonucleotides, to induce exon skipping of specific mutations or drugs developed to allow read-through of nonsense mutations, whereas other therapies deal with secondary aspects of muscle degeneration, aiming, for example, at reducing inflammation or apoptosis, and may also be suitable for other forms of muscular dystrophies.

SUMMARY

The advances in the field of muscular dystrophy have resulted in improved clinical course and survival. The encouraging results of early experimental studies could further improve these outcomes in the future.

Mechanical and non-mechanical functions of Dystrophin can prevent cardiac abnormalities in Drosophila

Dystrophin-deficiency causes cardiomyopathies and shortens the life expectancy of Duchenne and Becker muscular dystrophy patients. Restoring Dystrophin expression in the heart by gene transfer is a promising avenue to explore as a therapy. Truncated Dystrophin gene constructs have been engineered and shown to alleviate dystrophic skeletal muscle disease, but their potential in preventing the development of cardiomyopathy is not fully understood. In the present study, we found that either the mechanical or the signaling functions of Dystrophin were able to reduce the dilated heart phenotype of Dystrophin mutants in a Drosophila model. Our data suggest that Dystrophin retains some function in fly cardiomyocytes in the absence of a predicted mechanical link to the cytoskeleton. Interestingly, cardiac-specific manipulation of nitric oxide synthase expression also modulates cardiac function, which can in part be reversed by loss of Dystrophin function, further implying a signaling role of Dystrophin in the heart. These findings suggest that the signaling functions of Dystrophin protein are able to ameliorate the dilated cardiomyopathy, and thus might help to improve heart muscle function in micro-Dystrophin-based gene therapy approaches.

Nestin expression in end-stage disease in dystrophin-deficient heart: implications for regeneration from endogenous cardiac stem cells

Nestin(+) cardiac stem cells differentiate into striated cells following myocardial infarct. Transplantation of exogenous stem cells into myocardium of a murine model for Duchenne muscular dystrophy (DMD) increased proliferation of endogenous nestin(+) stem cells and resulted in the appearance of nestin(+) striated cells. This correlated with, and may be responsible for, prevention of dilated cardiomyopathy. We examined nestin(+) stem cells in the myocardium of dystrophin/utrophin-deficient (mdx/utrn(-/-)) mice, a model for DMD. We found that 92% of nestin(+) interstitial cells expressed Flk-1, a marker present on cardiac progenitor cells that differentiate into the cardiac lineage, and that a subset expressed Sca-1, present on adult cardiac cells that become cardiomyocytes. Nestin(+) interstitial cells maintained expression of Flk-1 but lost Sca-1 expression with age and were present in lower numbers in dystrophin-deficient heart than in wild-type heart. Unexpectedly, large clusters of nestin(+) striated cells ranging in size from 20 to 250 cells and extending up to 500 μm were present in mdx/utrn(-/-) heart near the end stage of disease. These cells were also present in dystrophin-deficient mdx/utrn(+/-) and mdx heart but not wild-type heart. Nestin(+) striated cells expressed cardiac troponin I, desmin, and Connexin 43 and correlated with proinflammatory CD68(+) macrophages. Elongated nestin(+) interstitial cells with striations were observed that did not express Flk-1 or the late cardiac marker cardiac troponin I but strongly expressed the early cardiac marker desmin. Nestin was also detected in endothelial and smooth muscle cells. These data indicate that new cardiomyocytes form in dystrophic heart, and nestin(+) interstitial cells may generate them in addition to other cells of the cardiac lineage.

Role of telomere dysfunction in cardiac failure in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), the most common inherited muscular dystrophy of childhood, leads to death due to cardiorespiratory failure. Paradoxically, mdx mice with the same genetic deficiency of dystrophin exhibit minimal cardiac dysfunction, impeding the development of therapies. We postulated that the difference between mdx and DMD might result from differences in telomere lengths in mice and humans. We show here that, like DMD patients, mice that lack dystrophin and have shortened telomeres (mdx/mTR(KO)) develop severe functional cardiac deficits including ventricular dilation, contractile and conductance dysfunction, and accelerated mortality. These cardiac defects are accompanied by telomere erosion, mitochondrial fragmentation and increased oxidative stress. Treatment with antioxidants significantly retards the onset of cardiac dysfunction and death of mdx/mTR(KO) mice. In corroboration, all four of the DMD patients analysed had 45% shorter telomeres in their cardiomyocytes relative to age- and sex-matched controls. We propose that the demands of contraction in the absence of dystrophin coupled with increased oxidative stress conspire to accelerate telomere erosion culminating in cardiac failure and death. These findings provide strong support for a link between telomere length and dystrophin deficiency in the etiology of dilated cardiomyopathy in DMD and suggest preventive interventions.

Development of multiexon skipping antisense oligonucleotide therapy for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an incurable, X-linked progressive muscle degenerative disorder that results from the absence of dystrophin protein and leads to premature death in affected individuals due to respiratory and/or cardiac failure typically by age of 30. Very recently the exciting prospect of an effective oligonucleotide therapy has emerged which restores dystrophin protein expression to affected tissues in DMD patients with highly promising data from a series of clinical trials. This therapeutic approach is highly mutation specific and thus is personalised. Therefore DMD has emerged as a model genetic disorder for understanding and overcoming of the challenges of developing personalised genetic medicines. One of the greatest weaknesses of the current oligonucleotide approach is that it is a mutation-specific therapy. To address this limitation, we have recently demonstrated that exons 45–55 skipping therapy has the potential to treat clusters of mutations that cause DMD, which could significantly reduce the number of compounds that would need to be developed in order to successfully treat all DMD patients. Here we discuss and review the latest preclinical work in this area as well as a variety of accompanying issues, including efficacy and potential toxicity of antisense oligonucleotides, prior to human clinical trials.

Corticosteroids in Duchenne muscular dystrophy: major variations in practice

INTRODUCTION

In 2004, a Cochrane Review and AAN practice parameter concluded that prednisone 0.75 mg/kg/day is of short-term efficacy in Duchenne muscular dystrophy (DMD). Subsequent efforts to standardize care for DMD indicated wide variation in corticosteroid use.

METHODS

We surveyed physicians who follow patients with DMD, including: (1) clinics in the TREAT-NMD (Translational Research in Europe-Assessment and Treatment of Neuromuscular Diseases) network (predominantly Europe) and (2) U.S. MDA clinic directors. We also documented the co-administered corticosteroids in a trial of a putative treatment (ataluren) for DMD.

RESULTS

Of 105 Treat-NMD clinicians, corticosteroids were not used in 10 clinics, and 29 different regimens were used--the most frequent 0.75 mg/kg/day prednisone (61 centers); 10 days on/10 days off (36 centers); 0.9 mg/kg/day deflazacort (32 centers); and 5 mg/kg/day on weekends (10 centers). Similar diversity was identified in MDA clinics and in the ataluren trial.

CONCLUSIONS

Variability in corticosteroid use suggests uncertainty about risks/benefits of corticosteroid regimens for DMD.

Genetic and clinical characteristics of skeletal and cardiac muscle in patients with lamin A/C gene mutations

Alterations of the lamin A/C (LMNA) gene are associated with different clinical entities, including disorders that affect skeletal and cardiac muscle, peripheral nerves, metabolism, bones, and disorders that cause premature aging. In this article we review the clinical and genetic characteristics of cardiac and skeletal muscle diseases related to alterations in the LMNA gene. There is no single explanation of how LMNA gene alterations may cause these disorders; however, important goals have been achieved in understanding the pathogenic effects of LMNA gene mutations on cardiac and skeletal muscle.

Clinical trials using antisense oligonucleotides in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by mutations in the DMD gene, affecting 1 in 3500 newborn males. Complete loss of muscle dystrophin protein causes progressive muscle weakness and heart and respiratory failure, leading to premature death. Antisense oligonucleotides (AONs) that bind to complementary sequences of the dystrophin pre-mRNA to induce skipping of the targeted exon by modulating pre-mRNA splicing are promising therapeutic agents for DMD. Such AONs can restore the open reading frame of the DMD gene and produce internally deleted, yet partially functional dystrophin protein isoforms in skeletal muscle. Within the last few years, clinical trials using AONs have made considerable progress demonstrating the restoration of functional dystrophin protein and acceptable safety profiles following both local and systemic delivery in DMD patients. However, improvement of AON delivery and efficacy, along with the development of multiple AONs to treat as many DMD patients as possible needs to be addressed for this approach to fulfill its potential. Here, we review the recent progress made in clinical trials using AONs to treat DMD and discuss the current challenges to the development of AON-based therapy for DMD.

Ibuprofen plus isosorbide dinitrate treatment in the mdx mice ameliorates dystrophic heart structure

BACKGROUND

Co-administration of ibuprofen (IBU) and isosorbide dinitrate (ISDN) provides synergistic beneficial effects on dystrophic skeletal muscle. Whether this treatment has also cardioprotective effects in this disease was still unknown.

AIMS

To evaluate the effects of co-administration of IBU and ISDN (a) on left ventricular (LV) structure and function, and (b) on cardiac inflammatory response and fibrosis in mdx mice.

METHODS

Three groups of mice were studied: mdx mice treated with IBU (50 mg kg⁻¹)+ISDN (30 mg kg⁻¹) administered daily in the diet, mdx mice that received standard diet without drugs and wild type aged-matched mice. Animals were analysed after 10-11 months of treatment. Structural and functional parameters were evaluated by echocardiography while histological analyses were performed to evaluate inflammatory response, collagen deposition, cardiomyocyte number and area.

RESULTS

Treatment for 10-11 months with IBU+ISDN preserved LV wall thickness and LV mass. Drug treatment also preserved the total number of cardiomyocytes in the LV and attenuated the increase in cardiomyocyte size, when compared to untreated mdx mice. Moreover, a trend towards a decreased number of inflammatory cells, a reduced LV myocardial interstitial fibrosis and an enhanced global LV function response to stress was observed in treated mdx mice.

CONCLUSIONS

Treatment for 10-11 months with IBU+ISDN is effective in preventing the alterations in LV morphology of mdx mice while not reaching statistical significance on LV function and cardiac inflammation.

Muscular dystrophies

Muscular dystrophies are a heterogeneous group of inherited disorders that share similar clinical features and dystrophic changes on muscle biopsy. An improved understanding of their molecular bases has led to more accurate definitions of the clinical features associated with known subtypes. Knowledge of disease-specific complications, implementation of anticipatory care, and medical advances have changed the standard of care, with an overall improvement in the clinical course, survival, and quality of life of affected people. A better understanding of the mechanisms underlying the molecular pathogenesis of several disorders and the availability of preclinical models are leading to several new experimental approaches, some of which are already in clinical trials. In this Seminar, we provide a comprehensive review that integrates clinical manifestations, molecular pathogenesis, diagnostic strategy, and therapeutic developments.

Beta-blockers, left and right ventricular function, and in-vivo calcium influx in muscular dystrophy cardiomyopathy

Beta-blockers are used to treat acquired heart failure in adults, though their role in early muscular dystrophy cardiomyopathy is unclear. We treated 2 different dystrophic mouse models which have an associated cardiomyopathy (mdx: model for Duchenne Muscular Dystrophy, and Sgcd-/-: model for limb girdle muscular dystrophy type 2F) and wild type controls (C57 Bl10) with the beta blocker metoprolol or placebo for 8 weeks at an early stage in the development of the cardiomyopathy. Left and right ventricular function was assessed with cardiac magnetic resonance imaging (MRI) and in-vivo myocardial calcium influx with manganese enhanced MRI. In the mdx mice at baseline there was reduced stroke volume, cardiac index, and end-diastolic volume with preserved left ventricular ejection fraction. These abnormalities were no longer evident after treatment with beta-blockers. Right ventricular ejection fraction was reduced and right ventricular end-systolic volume increased in the mdx mice. With metoprolol there was an increase in right ventricular end-diastolic and end-systolic volumes. Left and right ventricular function was normal in the Sgcd-/- mice. Metroprolol had no significant effects on left and right ventricular function in these mice, though heart/body weight ratios increased after treatment. In-vivo myocardial calcium influx with MEMRI was significantly elevated in both models, though metoprolol had no significant effects on either. In conclusion, metoprolol treatment at an early stage in the development of cardiomyopathy has deleterious effects on right ventricular function in mdx mice and in both models no effect on increased in-vivo calcium influx. This suggests that clinical trials need to carefully monitor not just left ventricular function but also right ventricular function and other aspects of myocardial metabolism.

Heterogeneous abnormalities of in-vivo left ventricular calcium influx and function in mouse models of muscular dystrophy cardiomyopathy

BACKGROUND

Manganese-enhanced cardiovascular magnetic resonance (MECMR) can non-invasively assess myocardial calcium influx, and calcium levels are known to be elevated in muscular dystrophy cardiomyopathy based on cellular studies.

METHODS

Left ventricular functional studies and MECMR were performed in mdx mice (model of Duchenne muscular dystrophy, 24 and 40 weeks) and Sgcd -/- mice (limb girdle muscular dystrophy 2 F, 16 and 32 weeks), compared to wild type controls (C57Bl/10, WT).

RESULTS

Both models had left ventricular hypertrophy at the later age compared to WT, though the mdx mice had reduced stroke volumes and the Sgcd -/- mice increased heart rate and cardiac index. Especially at the younger ages, MECMR was significantly elevated in both models (both P < 0.05 versus WT). The L-type calcium channel inhibitor diltiazem (5 mg/kg i.p.) significantly reduced MECMR in the mdx mice (P < 0.01), though only with a higher dose (10 mg/kg i.p.) in the Sgcd -/- mice (P < 0.05). As the Sgcd -/- mice had increased heart rates, to determine the role of heart rate in MECMR we studied the hyperpolarization-activated cyclic nucleotide-gated channel inhibitor ZD 7288 which selectively reduces heart rate. This reduced heart rate and MECMR in all mouse groups. However, when looking at the time course of reduction of MECMR in the Sgcd -/- mice at up to 5 minutes of the manganese infusion when heart rates were matched to the WT mice, MECMR was still significantly elevated in the Sgcd -/- mice (P < 0.01) indicating that heart rate alone could not account for all the increased MECMR.

CONCLUSIONS

Despite both mouse models exhibiting increased in-vivo calcium influx at an early stage in the development of the cardiomyopathy before left ventricular hypertrophy, there are distinct phenotypical differences between the 2 models in terms of heart rates, hemodynamics and responses to calcium channel inhibitors.

An urgent need for a change in policy revealed by a study on prenatal testing for Duchenne muscular dystrophy

Prenatal diagnosis for Duchenne muscular dystrophy (DMD) was introduced in the Netherlands in 1984. We have investigated the impact of 26 years (1984-2009) of prenatal testing. Of the 635 prenatal diagnoses, 51% were males; nearly half (46%) of these were affected or had an increased risk of DMD. As a result 145 male fetuses were aborted and 174 unaffected boys were born. The vast majority (78%) of females, now 16 years or older, who were identified prenatally have not been tested for carrier status. Their average risk of being a carrier is 28%. We compared the incidences of DMD in the periods 1961-1974 and 1993-2002. The incidence of DMD did not decline but the percentage of first affected boys increased from 62 to 88%. We conclude that a high proportion of families with de novo mutations in the DMD gene cannot make use of prenatal diagnosis, partly because the older affected boys are not diagnosed before the age of five. Current policy, widely accepted in the genetic community, dictates that female fetuses are not tested for carrier status. These females remain untested as adults and risk having affected offspring as well as progressive cardiac disease. We see an urgent need for a change in policy to improve the chances of prevention of DMD. The first step would be to introduce neonatal screening of males. The next is to test females for carrier status if requested, prenatally if fetal DNA is available or postnatally even before adulthood.