Degenerative Muscle Disorders Research Articles

RBP4 promotes denervation-induced muscle atrophy through STRA6-dependent pathway.

Fat infiltration of skeletal muscle has been recognized as a common feature of many degenerative muscle disorders. Retinol binding protein 4 (RBP4) is an adipokine that has been demonstrated to be correlated with the presence and severity of sarcopenia in the elderly. However, the exact role and the underlying mechanism of RBP4 in muscle atrophy remains unclear. Denervation-induced muscle atrophy model was constructed in wild-type and RBP4 knockout mice. To modify the expression of RBP4, mice were received intramuscular injection of retinol-free RBP4 (apo-RBP4), retinol-bound RBP4 (holo-RBP4) or oral gavage of RBP4 inhibitor A1120. Holo-RBP4-stimulated C2C12 myotubes were treated with siRNAs or specific inhibitors targeting signalling receptor and transporter of retinol 6 (STRA6)/Janus kinase 2 (JAK2)/Signal transducer and activator of transcription 3 (STAT3) pathway. Fat accumulation, myofibre cross-sectional area, myotube diameter and the expression of muscle atrophy markers and myogenesis markers were analysed. The expression levels of RBP4 in skeletal muscles were significantly up-regulated more than 2-fold from 7days and sustained for 28days after denervation. Immunofluorescence analysis indicated that increased RBP4 was localized in the infiltrated fatty region in denervated skeletal muscles. Knockout of RBP4 alleviated denervation-induced fatty infiltration and muscle atrophy together with decreased expression of atrophy marker Atrogin-1 and MuRF1 as well as increased expression of myogenesis regulators MyoD and MyoG. By contrast, injection of retinol-bound holo-RBP4 aggregated denervation-induced ectopic fat accumulation and muscle atrophy. Consistently, holo-RBP4 stimulation also had a dose-dependent effect on the reduction of C2C12 myotube diameter and myofibre cross-sectional area, as well as on the increase of Atrogin-1and MuRF1 expression and decrease of MyoD and MyoG expression. Mechanistically, holo-RBP4 treatment increased the expression of its membrane receptor STRA6 (>3-fold) and promoted the phosphorylation of downstream JAK2 and STAT3. Inhibition of STRA6/JAK2/STAT3 pathway either by specific siRNAs or inhibitors could decrease the expression of Atrogin-1 and MuRF1 (>50%) and decrease the expression of MyoD and MyoG (>3-fold) in holo-RBP4-treated C2C12 myotube. RBP4 specific pharmacological antagonist A1120 significantly inhibited the activation of STRA6/JAK2/STAT3 pathway, ameliorated ectopic fat infiltration and protected against denervation-induced muscle atrophy (30% increased myofibre cross-sectional area) in mice. In conclusion, our data reveal that RBP4 promotes fat infiltration and muscle atrophy through a STRA6-dependent and JAK2/STAT3 pathway-mediated mechanism in denervated skeletal muscle. Our results suggest that lowering RBP4 levels might serve as a promising therapeutic approach for prevention and treatment of muscle atrophy.

Receptor interacting protein kinase-3 mediates both myopathy and cardiomyopathy in preclinical animal models of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a progressive muscle degenerative disorder, culminating in a complete loss of ambulation, hypertrophic cardiomyopathy and a fatal cardiorespiratory failure. Necroptosis is the form of necrosis that is dependent upon the receptor-interacting protein kinase (RIPK) 3; it is involved in several inflammatory and neurodegenerative conditions. We previously identified RIPK3 as a key player in the acute myonecrosis affecting the hindlimb muscles of the mdx dystrophic mouse model. Whether necroptosis also mediates respiratory and heart disorders in DMD is currently unknown. Evidence of activation of the necroptotic axis was examined in dystrophic tissues from Golden retriever muscular dystrophy (GRMD) dogs and R-DMDdel52 rats. A functional assessment of the involvement of necroptosis in dystrophic animals was performed on mdx mice that were genetically depleted for RIPK3. Dystrophic mice aged from 12 to 18months were analysed by histology and molecular biology to compare the phenotype of muscles from mdxRipk3+/+ and mdxRipk3-/- mice. Heart function was also examined by echocardiography in 40-week-old mice. RIPK3 expression in sartorius and biceps femoris muscles from GRMD dogs positively correlated to myonecrosis levels (r=0.81; P=0.0076). RIPK3 was also found elevated in the diaphragm (P≤0.05). In the slow-progressing heart phenotype of GRMD dogs, the phosphorylated form of RIPK1 at the Serine 161 site was dramatically increased in cardiomyocytes. A similar p-RIPK1 upregulation characterized the cardiomyocytes of the severe DMDdel52 rat model, associated with a marked overexpression of Ripk1 (P=0.007) and Ripk3 (P=0.008), indicating primed activation of the necroptotic pathway in the dystrophic heart. MdxRipk3-/- mice displayed decreased compensatory hypertrophy of the heart (P=0.014), and echocardiography showed a 19% increase in the relative wall thickness (P<0.05) and 29% reduction in the left ventricle mass (P=0.0144). Besides, mdxRipk3-/- mice presented no evidence of a regenerative default or sarcopenia in skeletal muscles, moreover around 50% less affected by fibrosis (P<0.05). Our data highlight molecular and histological evidence that the necroptotic pathway is activated in degenerative tissues from dystrophic animal models, including the diaphragm and the heart. We also provide the genetic proof of concept that selective inhibition of necroptosis in dystrophic condition improves both histological features of muscles and cardiac function, suggesting that prevention of necroptosis is susceptible to providing multiorgan beneficial effects for DMD.

A large pedigree study confirmed the CGG repeat expansion of RILPL1 Is associated with oculopharyngodistal myopathy

BackgroundOculopharyngodistal myopathy (OPDM) is an autosomal dominant adult-onset degenerative muscle disorder characterized by ptosis, ophthalmoplegia and weakness of the facial, pharyngeal and limb muscles. Trinucleotide repeat expansions in non-coding regions of LRP12, G1PC1, NOTCH2NLC and RILPL1 were reported to be the etiologies for OPDM.ResultsIn this study, we performed long-read whole-genome sequencing in a large five-generation family of 156 individuals, including 21 patients diagnosed with typical OPDM. We identified CGG repeat expansions in 5’UTR of RILPL1 gene in all patients we tested while no CGG expansion in unaffected family members. Repeat-primed PCR and fluorescence amplicon length analysis PCR were further confirmed the segregation of CGG expansions in other family members and 1000 normal Chinese controls. Methylation analysis indicated that methylation levels of the RILPL1 gene were unaltered in OPDM patients, which was consistent with previous studies. Our findings provide evidence that RILPL1 is associated OPDM in this large pedigree.ConclusionsOur results identified RILPL1 is the associated the disease in this large pedigree.

VP.58 Golodirsen induced DMD transcripts localization and dystrophin production in MyoD-converted fibroblasts from 4053-101 clinical trial patients

Antisense oligonucleotides (AONs) are short, synthetic nucleic acid sequences that work by modulating exon incorporation at the level of pre-mRNA. In Duchenne muscular dystrophy (DMD), a fatal muscle degenerative disorder caused by mutations in the DMD gene, AONs skip specific exons to correct the reading frame, producing an internally shortened but partly functional dystrophin protein. Golodirsen is an approved AON phosphorodiamidate morpholino oligomer (PMO) that specifically targets DMD exon 53. In the clinical study 4053-101, we demonstrated that intravenous golodirsen administration induces an unequivocal exon skipping and protein restoration in all the treated patients, but with inter-patient variability. We used fibroblasts isolated from the patients in this clinical trial, that were induced to undergo myogenic differentiation in vitro by expression of MyoD, to better understand the reasons behind the observed variability. We evaluated the amount and the molecular weight of dystrophin protein in treated and non-treated patient cells, by an automated capillary-based immunoassay (WES) system. In these in-vitro studies we demonstrated that the amount of protein was comparable to the previous in-vivo study and that the size of the restored protein was compatible with the different genomic deletions carried by patients. Next, we used an in-situ RNA hybridization technique, BaseScope, to investigate the sub-cellular localization of the DMD transcript in treated and non-treated differentiated patient-derived myogenic cells in vitro, which allowed us to assess the ratio of skipped and unskipped products. Our study provides additional information on the dynamics of DMD mRNA in patients and may help to better understand the biological reasons underpinning variability in dystrophin restoration that can be seen in AON clinical trials.

Evaluating Genetic Modifiers of Duchenne Muscular Dystrophy Disease Progression Using Modeling and MRI.

Duchenne muscular dystrophy (DMD) is a progressive muscle degenerative disorder with a well-characterized disease phenotype but considerable interindividual heterogeneity that is not well understood. The aim of this study was to evaluate the effects of dystrophin variations and genetic modifiers of DMD on rate and age of muscle replacement by fat. One hundred seventy-five corticosteroid treated participants from the ImagingDMD natural history study underwent repeated magnetic resonance spectroscopy (MRS) of the vastus lateralis (VL) and soleus (SOL) to determine muscle fat fraction (FF). MRS was performed annually in most instances; however, some individuals had additional visits at 3 or 6 monthss intervals. FF changes over time were modeled using nonlinear mixed effects to estimate disease trajectories based on the age that the VL or SOL reached half-maximum change in FF (mu) and the time required for FF change (sigma). Computed mu and sigma values were evaluated for dystrophin variations that have demonstrated the ability to lead to a mild phenotype as well as compared between different genetic polymorphism groups. Participants with dystrophin gene deletions amenable to exon 8 skipping (n = 4) had minimal increases in SOL FF and had an increase in VL mu value by 4.4 years compared with a reference cohort (p = 0.039). Participants with nonsense variations within exons that may produce milder phenotypes (n = 11) also had minimal increases in SOL and VL FFs. No differences in estimated FF trajectories were seen for individuals amenable to exon 44 skipping (n = 10). Modeling of the SPP1, LTBP4, and thrombospondin-1 (THBS1) genetic modifiers did not result in significant differences in muscle FF trajectories between genotype groups (p > 0.05); however, trends were noted for the polymorphisms associated with long-range regulation of LTBP4 and THBS1 that deserve further follow-up. The results of this study link the historically mild phenotypes seen in individuals amenable to exon 8 skipping and with certain nonsense variations with alterations in trajectories of lower extremity muscle replacement by fat.

Human-induced pluripotent stem cell line (FDHSi001-A) derived from a patient with a CGG repeat expansion in the 5′UTR of GIPC1

Oculopharyngodistal myopathy (OPDM) is a late-onset degenerative muscle disorder characterized by ptosis and weakening of the facial, pharyngeal, and distal limb muscles. Our study reprogrammed human-induced pluripotent stem cells (iPSC) from the peripheral blood mononuclear cells (PBMCs) of a patient with a CGG repeat expansion in the 5′UTR of GIPC1 gene that co-segregated with the disease. The generated iPSCs express the pluripotent cell markers with no mycoplasma contamination. Besides, it showed normal karyotypes and the capacity to differentiate into three germ layers. We also identified that it had the same specific mutation as the patient did.

Reduced Sarcolemmal Membrane Repair Exacerbates Striated Muscle Pathology in a Mouse Model of Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a common X-linked degenerative muscle disorder that involves mutations in the DMD gene that frequently reduce the expression of the dystrophin protein, compromising the structural integrity of the sarcolemmal membrane and leaving it vulnerable to injury during cycles of muscle contraction and relaxation. This results in an increased frequency of sarcolemma disruptions that can compromise the barrier function of the membrane and lead to death of the myocyte. Sarcolemmal membrane repair processes can potentially compensate for increased membrane disruptions in DMD myocytes. Previous studies demonstrated that TRIM72, a muscle-enriched tripartite motif (TRIM) family protein also known as mitsugumin 53 (MG53), is a component of the cell membrane repair machinery in striated muscle. To test the importance of membrane repair in striated muscle in compensating for the membrane fragility in DMD, we crossed TRIM72/MG53 knockout mice into the mdx mouse model of DMD. These double knockout (DKO) mice showed compromised sarcolemmal membrane integrity compared to mdx mice, as measured by immunoglobulin G staining and ex vivo muscle laser microscopy wounding assays. We also found a significant decrease in muscle ex vivo contractile function as compared to mdx mice at both 6 weeks and 1.5 years of age. As the DKO mice aged, they developed more extensive fibrosis in skeletal muscles compared to mdx. Our findings indicate that TRIM72/MG53-mediated membrane repair can partially compensate for the sarcolemmal fragility associated with DMD and that the loss of membrane repair results in increased pathology in the DKO mice.

Human pluripotent stem cell-derived myogenic progenitors undergo maturation to quiescent satellite cells upon engraftment.

Human pluripotent stem cell (hPSC)-derived myogenic progenitor cell (MPC) transplantation is a promising therapeutic approach for a variety of degenerative muscle disorders. Here, using an MPC-specific fluorescent reporter system (PAX7::GFP), we demonstrate that hPSC-derived MPCs can contribute to the regeneration of myofibers in mice following local injury and in mice deficient of dystrophin (mdx). We also demonstrate that a subset of PAX7::GFP MPCs engraft within the basal lamina of regenerated myofibers, adopt a quiescent state, and contribute to regeneration upon reinjury and in mdx mouse models. This subset of PAX7::GFP MPCs undergo a maturation process and remodel their molecular characteristics to resemble those of late-stage fetal MPCs/adult satellite cells following invivo engraftment. These in-vivo-matured PAX7::GFP MPCs retain a cell-autonomous ability to regenerate and can repopulate in the niche of secondary recipient mice, providing a proof of principle for future hPSC-based cell therapy for muscle disorders.

EP394: Investigation and functional characterization of genomic signatures in congenital muscular dystrophy and congenital myopathy patients from India

Congenital muscular dystrophies (CMDs) and congenital myopathies (CMs) are a group of genetically and clinically heterogeneous degenerative primary muscle disorders with onset at birth or during infancy. The aim of this study was to genetically diagnose a cohort of 36 difficult-to-diagnose CMD and CM cases of Indian origin using next-generation sequencing methods. Furthermore, functional characterization of the novel pathogenic stop-gain variant NM_001927.4:c.448C>T in the DES gene identified in one patient of our cohort was done in order to understand their pathological role in disease phenotypes.

Abstract 13301: Microarray Reveals Differentially Expressed Long Non-coding Ribonucleic Acids In Dysferlinopathy

Introduction: Dysferlinopathy is a type of muscular dystrophy, a group of inherited degenerative muscle disorders characterized by progressive muscle weakness. It is caused by the deficiency of dysferlin, a type II transmembrane protein highly expressed in the skeletal muscle and the heart. Dysferlin interacts with several proteins and plays a crucial role in calcium dependent membrane repair in skeletal muscles. Long non-coding RNAs (lncRNAs) are non-coding RNA transcripts greater than 200 nucleotides that participate in regulating gene expression through multiple mechanisms. Hypothesis: We hypothesized the disease process in dysferlinopathy is linked to an aberrant expression of lncRNAs. Methods: LncRNA and mRNA expression profiling between the normal and dysferlin deficient murine myoblasts (C2C12 cells) were performed using a microarray (n=3). Several differentially expressed lncRNAs were validated using qRT-PCR. Tissue expression analysis was performed for selected lncRNAs across ten mice tissues. Further bioinformatics analysis was used to explore the potential function, lncRNA-mRNA correlation and potential targets of the differentially expressed lncRNAs. Results: We found 3470 lncRNAs and 2335 mRNAs that are differentially expressed by more than two fold. A set of 13 lncRNAs were selected based on their fold change, and were validated using qRT-PCR. Six out of the 13 lncRNAs tested were predominantly expressed in either myoblasts or skeletal muscle tissue. Pathway analysis of the differentially expressed genes indicated the involvement of several signaling pathways including PI3K-Akt, FoxO, Wnt, cAMP and Hippo. The differentially expressed genes were also enriched for the GO terms, developmental process and muscle system process. Conclusion: The results thus far imply that dysferlinopathy is associated with an aberrant expression of multiple lncRNAs many of which may have a specific function in the disease process. Identification of lncRNAs that are predominantly expressed in the skeletal muscle lineage suggests a muscle specific role for these lncRNAs. We are currently working on overexpressing selected lncRNAs in the normal and dysferlin deficient cells to understand their role in regulating key cellular functions.

Dystrophin and mini-dystrophin quantification by mass spectrometry in skeletal muscle for gene therapy development in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, degenerative muscle disorder caused by mutations in the DMD gene, leading to severe reduction or absence of the protein dystrophin. Gene therapy strategies that aim to increase expression of a functional dystrophin protein (mini-dystrophin) are under investigation. The ability to accurately quantify dystrophin/mini-dystrophin is essential in assessing the level of gene transduction. We demonstrated the validation and application of a novel peptide immunoaffinity liquid chromatography–tandem mass spectrometry (IA-LC-MS/MS) assay. Data showed that dystrophin expression in Becker muscular dystrophy and DMD tissues, normalized against the mean of non-dystrophic control tissues (n = 20), was 4–84.5% (mean 32%, n = 20) and 0.4–24.1% (mean 5%, n = 20), respectively. In a DMD rat model, biceps femoris tissue from dystrophin-deficient rats treated with AAV9.hCK.Hopti-Dys3978.spA, an adeno-associated virus vector containing a mini-dystrophin transgene, showed a dose-dependent increase in mini-dystrophin expression at 6 months post-dose, exceeding wildtype dystrophin levels at high doses. Validation data showed that inter- and intra-assay precision were ≤20% (≤25% at the lower limit of quantification [LLOQ]) and inter- and intra-run relative error was within ±20% (±25% at LLOQ). IA-LC-MS/MS accurately quantifies dystrophin/mini-dystrophin in human and preclinical species with sufficient sensitivity for immediate application in preclinical/clinical trials.

Characterizing Expiratory Respiratory Muscle Degeneration in Duchenne Muscular Dystrophy Using MRI

Expiratory muscle weakness and impaired airway clearance are early signs of respiratory dysfunction in Duchenne muscular dystrophy (DMD), a degenerative muscle disorder in which muscle cells are damaged and replaced by fibrofatty tissue. Little is known about expiratory muscle pathology and its relationship to cough and airway clearance capacity; however, the level of muscle replacement by fat can be estimated using MRI and expressed as a fat fraction (FF). How does abdominal expiratory muscle fatty infiltration change over time in DMD and relate to clinical expiratory function? Individuals with DMD underwent longitudinal MRI of the abdomen to determine FF in the internal oblique, external oblique, and rectus abdominis expiratory muscles. FF data were used to estimate a model of expiratory muscle degeneration by using nonlinear mixed effects and a cumulative distribution function. FVC, maximal inspiratory and expiratory pressures, and peak cough flow were collected as clinical correlates to MRI. Forty individuals with DMD (aged 6-18 years at baseline) participated in up to five visits over 36months. Modeling estimated the internal oblique progresses most quickly and reached 50%replacement by fat at a mean patient age of 13.0 years (external oblique, 14.0 years; rectus abdominis, 16.2 years). Corticosteroid-untreated individuals (n= 4) reached 50%muscle replacement by fat 3 to 4 years prior to treated individuals. Individuals with mild clinical dystrophic phenotypes (n= 3) reached 50%muscle replacement by fat 4 to 5 years later than corticosteroid-treated individuals. Internal and external oblique FFs near 50%were associated with maximal expiratory pressures< 60cm H2O and peak cough flows< 270 L/min. These data improve understanding of the early phase of respiratory compromise in DMD, which typically presents as airway clearance dysfunction prior to the onset of hypoventilation, and links expiratory muscle fatty infiltration to pulmonary function measures.

Hypoxia and Hypoxia-Inducible Factor Signaling in Muscular Dystrophies: Cause and Consequences.

Muscular dystrophies (MDs) are a group of inherited degenerative muscle disorders characterized by a progressive skeletal muscle wasting. Respiratory impairments and subsequent hypoxemia are encountered in a significant subgroup of patients in almost all MD forms. In response to hypoxic stress, compensatory mechanisms are activated especially through Hypoxia-Inducible Factor 1 α (HIF-1α). In healthy muscle, hypoxia and HIF-1α activation are known to affect oxidative stress balance and metabolism. Recent evidence has also highlighted HIF-1α as a regulator of myogenesis and satellite cell function. However, the impact of HIF-1α pathway modifications in MDs remains to be investigated. Multifactorial pathological mechanisms could lead to HIF-1α activation in patient skeletal muscles. In addition to the genetic defect per se, respiratory failure or blood vessel alterations could modify hypoxia response pathways. Here, we will discuss the current knowledge about the hypoxia response pathway alterations in MDs and address whether such changes could influence MD pathophysiology.

Coenzyme Q10: Clinical Applications beyond Cardiovascular Diseases.

Coenzyme Q10 (CoQ10) is an essential cofactor in oxidative phosphorylation (OXPHOS), present in mitochondria and cell membranes in reduced and oxidized forms. Acting as an energy transfer molecule, it occurs in particularly high levels in the liver, heart, and kidneys. CoQ10 is also an anti-inflammatory and antioxidant agent able to prevent the damage induced by free radicals and the activation of inflammatory signaling pathways. In this context, several studies have shown the possible inverse correlation between the blood levels of CoQ10 and some disease conditions. Interestingly, beyond cardiovascular diseases, CoQ10 is involved also in neuronal and muscular degenerative diseases, in migraine and in cancer; therefore, the supplementation with CoQ10 could represent a viable option to prevent these and in some cases might be used as an adjuvant to conventional treatments. This review is aimed to summarize the clinical applications regarding the use of CoQ10 in migraine, neurodegenerative diseases (including Parkinson and Alzheimer diseases), cancer, or degenerative muscle disorders (such as multiple sclerosis and chronic fatigue syndrome), analyzing its effect on patients’ health and quality of life.

Improved Bone Quality and Bone Healing of Dystrophic Mice by Parabiosis.

Duchenne muscular dystrophy (DMD) is a degenerative muscle disorder characterized by a lack of dystrophin expression in the sarcolemma of muscle fibers. DMD patients acquire bone abnormalities including osteopenia, fragility fractures, and scoliosis indicating a deficiency in skeletal homeostasis. The dKO (dystrophin/Utrophin double knockout) is a more severe mouse model of DMD than the mdx mouse (dystrophin deficient), and display numerous clinically-relevant manifestations, including a spectrum of degenerative changes outside skeletal muscle including bone, articular cartilage, and intervertebral discs. To examine the influence of systemic factors on the bone abnormalities and healing in DMD, parabiotic pairing between dKO mice and mdx mice was established. Notably, heterochronic parabiosis with young mdx mice significantly increased bone mass and improved bone micro-structure in old dKO-hetero mice, which showed progressive bone deterioration. Furthermore, heterochronic parabiosis with WT C56/10J mice significantly improved tibia bone defect healing in dKO-homo mice. These results suggest that systemic blood-borne factor(s) and/or progenitors from WT and young mdx mice can influence the bone deficiencies in dKO mice. Understanding these circulating factors or progenitor cells that are responsible to alleviate the bone abnormalities in dKO mice after heterochronic parabiosis might be useful for the management of poor bone health in DMD.

5′ UTR CGG repeat expansion inGIPC1is associated with oculopharyngodistal myopathy

Oculopharyngodistal myopathy is a late-onset degenerative muscle disorder characterized by ptosis and weakness of the facial, pharyngeal, and distal limb muscles. A recent report suggested a non-coding trinucleotide repeat expansion in LRP12 to be associated with the disease. Here we report a genetic study in a Chinese cohort of 41 patients with the clinical diagnosis of oculopharyngodistal myopathy (21 cases from seven families and 20 sporadic cases). In a large family with 12 affected individuals, combined haplotype and linkage analysis revealed a maximum two-point logarithm of the odds (LOD) score of 3.3 in chromosomal region chr19p13.11-p13.2 and narrowed the candidate region to an interval of 4.5 Mb. Using a comprehensive strategy combining whole-exome sequencing, long-read sequencing, repeat-primed polymerase chain reaction and GC-rich polymerase chain reaction, we identified an abnormal CGG repeat expansion in the 5' UTR of the GIPC1 gene that co-segregated with disease. Overall, the repeat expansion in GIPC1 was identified in 51.9% independent pedigrees (4/7 families and 10/20 sporadic cases), while the repeat expansion in LRP12 was only identified in one sporadic case (3.7%) in our cohort. The number of CGG repeats was <30 in controls but >60 in affected individuals. There was a slight correlation between repeat size and the age at onset. Both repeat expansion and retraction were observed during transmission but somatic instability was not evident. These results further support that non-coding CGG repeat expansion plays an essential role in the pathogenesis of oculopharyngodistal myopathy.

Whole-exome analyses of congenital muscular dystrophy and congenital myopathy patients from India reveal a wide spectrum of known and novel mutations.

Congenital muscular dystrophies (CMDs) and congenital myopathies (CMs) are a group of genetically and clinically heterogeneous degenerative primary muscle disorders with onset at birth or during infancy. Due to vast heterogeneity, clinical examination and protein-based analyses often fail to identify the genetic causes of these diseases. The aim of this study was to genetically diagnose a cohort of 36 difficult-to-diagnose CMD and CM cases of Indian origin using next-generation sequencing methods. Whole-exome sequencing (WES) was performed to identify pathogenic mutations in previously reported CMD and CM-related genes using variant calling and stringent variant filtration process. Subsequently, in silico homology modelling and molecular dynamics simulations (MDS) studies were undertaken for a number of novel and missense variants. A total of 33 and 21 rare and deleterious mutations were identified in 28 genes previously reported in CMD and CM based on OMIM, ClinVar and Orphanet, respectively. We could accurately diagnose 54% patients (n=12/22) in the CMD group and 35% patients (n=5/14) in the CM group. Furthermore, MDS studies for mutations located in LMNA, LAMA2 and RYR1 suggest that the wild-type proteins are more stable than their mutant counterparts, implying a potential mechanism of pathogenesis. The WES findings led us to identify reported as well as novel variants for the first time in Indian patients with CMD and CM. This allowed us to achieve an accurate genetic diagnosis, which was difficult using conventional diagnostic tools. Transferring these WES findings to clinical practice will help guide clinical care of the affected patients and inform genetic counselling.

LATE BREAKING NEWS E-POSTER PRESENTATION: LBP 7 Characterization of Novel Exon-51 Skipping Oligonucleotides that Safely Rescues Dystrophin Expression in a Severe Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is a severe childhood degenerative muscle disorder, caused by the absence of functional dystrophin. Antisense oligonucleotide (AON)-mediated exon skipping aims to restore the disrupted dystrophin reading frame, leading to synthesis of internally deleted, partially functional dystrophin. B152869 and B152575 are exon-51 targeting 2′-O-methyl phosphorothioate AONs, designed to improve pharmacodynamics and safety via length optimization, chemical modifications and targeting capabilities. In transgenic dystrophic del52hDMD/mdx mice, lacking both human and mouse dystrophin, intravenous (IV) administration of B152869 or B152575 (13 weekly doses; 18 mg/kg) induced increases in dystrophin, reaching up to ∼50% and ∼6% of normal controls in quadriceps and heart, respectively, as determined by capillary Western immunoassay. Dystrophin increases were accompanied by correction of disease pathogenic markers, including neuronal nitric oxide synthase, and improvement in motor function. AON treatments did not result in adverse renal effects, known to be a clinically translatable endpoint in mice. Absence of renal findings were confirmed in CD-1 mice (13 weekly IV doses at 9-18 mg/kg). Cynomolgus monkeys treated IV with B152869 and B152575 for 8-13 weeks at dose levels of 1-3 mg/kg, demonstrated a lack of kidney or major organ toxicity. Unlike previous generations of AONs these candidates exhibited minimal activation of the alternative complement pathway that was transient and at sub-clinical levels; coagulation effects were also mild and transient (< 5 sec prolongation of APTT). B152869 and B152575, with highly potent pharmacodynamic activity and an improved safety profile, are promising next generation exon-51 skipping therapeutics, warranting further evaluation.

Magnetic Resonance Imaging Studies in Duchenne Muscular Dystrophy: Linking Findings to the Physical Therapy Clinic

Duchenne muscular dystrophy (DMD) is a muscle degenerative disorder that manifests in early childhood and results in progressive muscle weakness. Physical therapists have long been an important component of the multidisciplinary team caring for people with DMD, providing expertise in areas of disease assessment, contracture management, assistive device prescription, and exercise prescription. Over the last decade, magnetic resonance imaging of muscles in people with DMD has led to an improved understanding of the muscle pathology underlying the clinical manifestations of DMD. Findings from magnetic resonance imaging (MRI) studies in DMD, paired with the clinical expertise of physical therapists, can help guide research that leads to improved physical therapist care for this unique patient population. The 2 main goals of this perspective article are to (1) summarize muscle pathology and disease progression findings from qualitative and quantitative muscle MRI studies in DMD and (2) link MRI findings of muscle pathology to the clinical manifestations observed by physical therapists with discussion of any potential implications of MRI findings on physical therapy management.

Hereditary inclusion body myopathy: a clinical and genetic review

Introduction. Inclusion body myositis represents the most common acquired myopathy in clinical practice in patients over 50 years old. Despite classical approach to this myopathy as an inflammatory disorder, a muscle degenerative disorder is now considered the main mechanism linked to these vacuolar myopathies. Hereditary presentations, although quite rare, represent an expanding and underrecognized group in clinical practice. Objective. perform a structured review of the current literature regarding hereditary inclusion body myopathies. Method. review of U.S. NLM PubMed and MEDLINE database of original articles, case reports, case series and review articles including the terms “inclusion body myositis” OR “inclusion body myopathy” AND “genetics” OR “hereditary”. Results. We present in this article a wide review regarding the main clinical, imaging, pathophysiological, genetic and therapeutic aspects related to hereditary myopathies linked to seven different clinical and genetic presentations (GNE, MATR3, VCP, SQSTM1, MYH2, HNRNPA2B1 and HNRNPA1). Conclusion. Hereditary inclusion body myopathy is associated with at least 7 distinct clinic and genetic monogenic forms.