Sequential targeted exome sequencing of 1001 patients affected by unexplained limb-girdle weakness.

PURPOSE: Several hundred genetic muscle diseases have been described, all of which are rare. Their clinical and genetic heterogeneity means that a genetic diagnosis is challenging. We established an international consortium, MYO-SEQ, to aid the work-ups of muscle disease patients and to better understand disease etiology. METHODS: Exome sequencing was applied to 1001 undiagnosed patients recruited from more than 40 neuromuscular disease referral centers; standardized phenotypic information was collected for each patient. Exomes were examined for variants in 429 genes associated with muscle conditions. RESULTS: We identified suspected pathogenic variants in 52% of patients across 87 genes. We detected 401 novel variants, 116 of which were recurrent. Variants in CAPN3, DYSF, ANO5, DMD, RYR1, TTN, COL6A2, and SGCA collectively accounted for over half of the solved cases; while variants in newer disease genes, such as BVES and POGLUT1, were also found. The remaining well-characterized unsolved patients (48%) need further investigation. CONCLUSION: Using our unique infrastructure, we developed a pathway to expedite muscle disease diagnoses. Our data suggest that exome sequencing should be used for pathogenic variant detection in patients with suspected genetic muscle diseases, focusing first on the most common disease genes described here, and subsequently in rarer and newly characterized disease genes.

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.

Long-term blocking of calcium channels in mdx mice results in differential effects on heart and skeletal muscle.

The disease mechanisms underlying dystrophin-deficient muscular dystrophy are complex, involving not only muscle membrane fragility, but also dysregulated calcium homeostasis. Specifically, it has been proposed that calcium channels directly initiate a cascade of pathological events by allowing calcium ions to enter the cell. The objective of this study was to investigate the effect of chronically blocking calcium channels with the aminoglycoside antibiotic streptomycin from onset of disease in the mdx mouse model of Duchenne muscular dystrophy (DMD). Treatment in utero onwards delayed onset of dystrophic symptoms in the limb muscle of young mdx mice, but did not prevent degeneration and regeneration events occurring later in the disease course. Long-term treatment had a positive effect on limb muscle pathology, reduced fibrosis, increased sarcolemmal stability, and promoted muscle regeneration in older mice. However, streptomycin treatment did not show positive effects in diaphragm or heart muscle, and heart pathology was worsened. Thus, blocking calcium channels even before disease onset does not prevent dystrophy, making this an unlikely treatment for DMD. These findings highlight the importance of analyzing several time points throughout the life of the treated mice, as well as analyzing many tissues, to get a complete picture of treatment efficacy.

Contrasting effects of steroids and angiotensin-converting-enzyme inhibitors in a mouse model of dystrophin-deficient cardiomyopathy.

AIMS: Duchenne muscular dystrophy (DMD) is associated with progressive cardiomyopathy. Oral corticosteroids are the gold standard for the treatment of skeletal muscle weakness; however, the effects of steroids on cardiac function have not been prospectively studied. In addition, the early role of ACE-inhibitors (ACE-I) is controversial. We aimed to determine the effects of steroids and ACE-I on development of left ventricular dysfunction in the mdx mouse, a model for dystrophin-deficient cardiomyopathy. METHODS AND RESULTS: Orally administered captopril or prednisolone was given for 8 weeks to 16-week-old, male mdx mice. In vivo pressure-volume loops, fibrosis, in vivo myocyte sarcolemmal injury, and cytokine expression were assessed in treated and untreated mdx mice and age-matched controls. Untreated mdx mice showed compensated cardiomyopathy with reduced myocardial contractility, patchy myocardial fibrosis but preserved stroke volume. Captopril treatment resulted in indirect myocardial effects of reduced afterload and direct effects of increased contractility. Prednisolone caused acute sarcolemmal injury, increased expression of myocardial TNF alpha and fibrosis, resulting in left ventricular dilatation and diastolic dysfunction. CONCLUSION: In a mouse model of dystrophin-deficient cardiomyopathy, ACE-I produced haemodynamic benefit, whereas steroids accelerated progression of cardiomyopathy. Although mouse models may not entirely replicate the human condition, comprehensive monitoring of cardiac function with these therapies is essential.

Peptide-conjugated phosphodiamidate oligomer-mediated exon skipping has benefits for cardiac function in mdx and Cmah-/-mdx mouse models of Duchenne muscular dystrophy.

Cardiac failure is a major cause of mortality in patients with Duchenne muscular dystrophy (DMD). Antisense-mediated exon skipping has the ability to correct out-of-frame mutations in DMD to produce truncated but functional dystrophin. Traditional antisense approaches have however been limited by their poor uptake into cardiac muscle. The addition of cell-penetrating peptides to antisense molecules has increased their potency and improved their uptake into all muscles, including the heart. We have investigated the efficacy of the Peptide-conjugated phosphodiamidate morpholino oligomer (P-PMO) Pip6a-PMO, for restoration of cardiac dystrophin and functional rescue in DMD mice- the mdx mouse and the less well characterised Cmah-/-mdx mouse (which carry a human-like mutation in the mouse Cmah gene as well as a mutation in DMD). In our first study male mdx mice were administered Pip6a-PMO, i.v, fortnightly from 12 to 30 weeks of age alongside mock-injected age-matched mdx and C57BL10 controls. Mice received 4 doses of 18 mg/kg followed by 8 doses of 12.5 mg/kg. The cardiac function of the mice was analysed 2 weeks after their final injection by MRI followed by conductance catheter and their muscles were harvested for dystrophin quantification. In the second study, male Cmah-/-mdx mice, received 12.5 mg/kg Pip6a-PMO, i.v fortnightly from 8 to 26 weeks and assessed by MRI at 3 time points (12, 18 and 28 weeks) alongside mock-injected age-matched mdx, C57BL10 and Cmah-/-mdx controls. The mice also underwent MEMRI and conductance catheter at 28 weeks. This allowed us to characterise the cardiac phenotype of Cmah-/-mdx mice as well as assess the effects of P-PMO on cardiac function. Pip6a-PMO treatment resulted in significant restoration of dystrophin in mdx and Cmah-/-mdx mice (37.5% and 51.6%, respectively), which was sufficient to significantly improve cardiac function, ameliorating both right and left ventricular dysfunction. Cmah-/-mdx mice showed an abnormal response to dobutamine stress test and this was completely ameliorated by PIP6a-PMO treatment. These encouraging data suggest that total restoration of dystrophin may not be required to significantly improve cardiac outcome in DMD patients and that it may be realistic to expect functional improvements with modest levels of dystrophin restoration which may be very achievable in future clinical trials.

Standard Operating Procedures (SOPs) for Evaluating the Heart in Preclinical Studies of Duchenne Muscular Dystrophy.

A recent working group meeting focused on contemporary cardiac issues in Duchenne muscular dystrophy (DMD) was hosted by the National Heart, Lung, and Blood Institute in collaboration with the Parent Project Muscular Dystrophy. An outcome of this meeting was to provide freely available detailed protocols for preclinical animal studies. The goal of these protocols is to improve the quality and reproducibility of cardiac preclinical studies aimed at developing new therapeutics for the prevention and treatment of DMD cardiomyopathy.

Absence of Cardiac Benefit with Early Combination ACE Inhibitor and Beta Blocker Treatment in mdx Mice.

Most patients with Duchenne muscular dystrophy (DMD) will develop cardiomyopathy; however, the evidence for prophylactic treatment of children with cardiac medications is limited. We have used the mdx mouse model of DMD to assess if early combination treatment with beta blocker (BB) and ACE inhibitor (AI) is superior to single treatment with either one of these drugs. Mice were assessed with cardiac MRI (ventricular structure and function, in vivo calcium influx (manganese-enhanced MRI)), pressure-volume loops, and histopathology. Combination treatment did not show benefits over treatment with AI or BB alone. Indeed, some beneficial aspects of BB and AI were lost when used in combination. None of the treatments impacted RV function. Combination treatment had no significant effect on sarcolemmal damage or histopathology. The study suggests that combined BB and AI may not confer an advantage at an early stage in DMD cardiomyopathy. However, limitations of the mdx model should be considered.

Assessment of ventricular function in mouse models of muscular dystrophy: a comparison of MRI with conductance catheter.

Outcomes of clinical trials depend on the quality of preceding preclinical research, yet functional assays and outcome measures for mouse models of disease are often poorly standardized or inappropriate. Muscular dystrophies are associated with cardiomyopathy so preclinical research requires reliable measures of cardiac function in animal models of the disease. MRI and conductance catheter were compared as preclinical tools to detect cardiomyopathy in two mouse models of muscular dystrophy. Sgcd-/-, mdx and C57Bl10 mice (n = 7/group) were assessed by catheter following MRI at an early stage of cardiomyopathy. Volumetric measurements were higher from MRI compared to catheter. In particular, by catheter, the measurement of end-systolic volume (and its related measures) was disproportionately lower in dystrophic mice compared to controls. This was related to greater calculated parallel conductance in dystrophic mice. Catheter highlighted differences in pressure generation between the two models while MRI detected differences in left ventricular hypertrophy and right ventricular function. Although MRI and conductance catheter provide unique but complimentary information regarding the nature of cardiomyopathy in dystrophic mice, we present the possibility that pathology itself may affect the accuracy of the catheter technique and that particular caution must be taken when interpreting catheter volume data in dystrophic mice.

Development and Application of an Ultrasensitive Hybridization-Based ELISA Method for the Determination of Peptide-Conjugated Phosphorodiamidate Morpholino Oligonucleotides.

Antisense oligonucleotide (AON)-induced exon skipping is one of the most promising strategies for treating Duchenne muscular dystrophy (DMD) and other rare monogenic conditions. Phosphorodiamidate morpholino oligonucleotides (PMOs) and 2'-O-methyl phosphorothioate (2'OMe) are two of the most advanced AONs in development. The next generation of peptide-conjugated PMO (P-PMO) is also showing great promise, but to advance these therapies it is essential to determine the pharmacokinetic and biodistribution (PK/BD) profile using a suitable method to detect AON levels in blood and tissue samples. An enzyme-linked immunosorbent assay (ELISA)-based method, which shows greater sensitivity than the liquid chromatography-mass spectrometry method, is the method of choice for 2'OMe detection in preclinical and clinical studies. However, no such assay has been developed for PMO/P-PMO detection, and we have, therefore, developed an ultrasensitive hybridization-based ELISA for this purpose. The assay has a linear detection range of 5-250 pM (R(2)>0.99) in mouse serum and tissue lysates. The sensitivity was sufficient for determining the 24-h PK/BD profile of PMO and P-PMO injected at standard doses (12.5 mg/kg) in mdx mice, the dystrophin-deficient mouse model for DMD. The assay demonstrated an accuracy approaching 100% with precision values under 12%. This provides a powerful cost-effective assay for the purpose of accelerating the development of these emerging therapeutic agents.

Identification of novel, therapy-responsive protein biomarkers in a mouse model of Duchenne muscular dystrophy by aptamer-based serum proteomics.

There is currently an urgent need for biomarkers that can be used to monitor the efficacy of experimental therapies for Duchenne Muscular Dystrophy (DMD) in clinical trials. Identification of novel protein biomarkers has been limited due to the massive complexity of the serum proteome and the presence of a small number of very highly abundant proteins. Here we have utilised an aptamer-based proteomics approach to profile 1,129 proteins in the serum of wild-type and mdx (dystrophin deficient) mice. The serum levels of 96 proteins were found to be significantly altered (P < 0.001, q < 0.01) in mdx mice. Additionally, systemic treatment with a peptide-antisense oligonucleotide conjugate designed to induce Dmd exon skipping and recover dystrophin protein expression caused many of the differentially abundant serum proteins to be restored towards wild-type levels. Results for five leading candidate protein biomarkers (Pgam1, Tnni3, Camk2b, Cycs and Adamts5) were validated by ELISA in the mouse samples. Furthermore, ADAMTS5 was found to be significantly elevated in human DMD patient serum. This study has identified multiple novel, therapy-responsive protein biomarkers in the serum of the mdx mouse with potential utility in DMD patients.

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.

δ-Sarcoglycan-deficient muscular dystrophy: from discovery to therapeutic approaches.

Mutations in the δ-sarcoglycan gene cause limb-girdle muscular dystrophy 2F (LGMD2F), an autosomal recessive disease that causes progressive weakness and wasting of the proximal limb muscles and often has cardiac involvement. Here we review the clinical implications of LGMD2F and discuss the current understanding of the putative mechanisms underlying its pathogenesis. Preclinical research has benefited enormously from various animal models of δ-sarcoglycan deficiency, which have helped researchers to explore therapeutic approaches for both muscular dystrophy and cardiomyopathy.

Intolerance to ß-blockade in a mouse model of δ-sarcoglycan-deficient muscular dystrophy cardiomyopathy.

AIMS: Patients with mutations predisposing to cardiomyopathy often have routine assessments of left ventricular function. It is unclear whether asymptomatic mild cardiomyopathy should be treated with standard heart failure therapies. METHODS AND RESULTS: We tested the effect of metoprolol on cardiac haemodynamics and pathology in two animal models for muscular dystrophy and cardiomyopathy. Treatment started at an early stage in the development of the cardiomyopathy. Metoprolol was given orally (2.5 mg/kg/day) over 8 weeks to mdx mice (model for Duchenne muscular dystrophy) and δ-sarcoglycan-deficient (Sgcd(null)) mice (model for Limb girdle muscular dystrophy type 2F). In vivo pressure-volume loops, fibrosis, in vivo myocyte sarcolemmal injury, and ß-adrenergic receptor mRNA were assessed. In ß-blocked mdx mice, there was a beneficial reduction in afterload and restored contractility resulting in an increased stroke volume. In contrast, in Sgcd(null) mice, there was marked deterioration in haemodynamics (prolonged relaxation, Tau, and reduced stroke volume). Furthermore, challenging the ß-blocked Sgcd(null) mice with the ß-adrenergic agonist dobutamine led to markedly increased mortality. Patterns of sarcolemmal injury or ß-adrenergic receptor mRNA could not account for this, though the acute rise in markers of active relaxation suggested abnormally high levels of intracellular calcium. CONCLUSION: ß-Blockers may not necessarily be beneficial in all cardiomyopathies, even when given at an early stage of development. Clinical trials of ß-blockers in muscular dystrophy-associated cardiomyopathy may need to stratify patients by genotype.

Attenuation of adverse cardiac effects in prednisolone-treated delta-sarcoglycan-deficient mice by mineralocorticoid-receptor-antagonism.

We have tested the hypothesis that the adverse effects of glucocorticoids in the delta-sarcoglycan-deficient (Sgcd-null) mouse are due to additional mineralocorticoid effects. We investigated the effects of spironolactone, an unselective mineralocorticoid-receptor antagonist, on in vivo cardiac haemodynamics, cardiomyocyte damage and fibrosis in prednisolone treated Sgcd-null mice. Oral spironolactone given to 8-week-old Sgcd-null non-steroid treated mice had beneficial effects on systolic function by improving myocardial contractility when assessed by pressure-volume loops. Given in combination with prednisolone, spironolactone prevented steroid-induced deterioration of cardiac haemodynamics and acute sarcolemmal damage but not cardiac fibrosis. This study demonstrates the beneficial effects of oral spironolactone on cardiac haemodynamics in Sgcd-null mice and its ability to prevent some of the adverse effects of glucocorticoids.