Limb-girdle Muscular Dystrophy Type 2B Research Articles

Limb Girdle Muscular Dystrophy Type 2B (LGMD2B): Diagnosis and Therapeutic Possibilities

Dysferlin is a large transmembrane protein involved in critical cellular processes including membrane repair and vesicle fusion. Mutations in the dysferlin gene (DYSF) can result in rare forms of muscular dystrophy; Miyoshi myopathy; limb girdle muscular dystrophy type 2B (LGMD2B); and distal myopathy. These conditions are collectively known as dysferlinopathies and are caused by more than 600 mutations that have been identified across the DYSF gene to date. In this review, we discuss the key molecular and clinical features of LGMD2B, the causative gene DYSF, and the associated dysferlin protein structure. We also provide an update on current approaches to LGMD2B diagnosis and advances in drug development, including splice switching antisense oligonucleotides. We give a brief update on clinical trials involving adeno-associated viral gene therapy and the current progress on CRISPR/Cas9 mediated therapy for LGMD2B, and then conclude by discussing the prospects of antisense oligomer-based intervention to treat selected mutations causing dysferlinopathies.

The Influence of a Genetic Variant in CCDC78 on LMNA-Associated Skeletal Muscle Disease.

Mutations in the LMNA gene-encoding A-type lamins can cause Limb-Girdle muscular dystrophy Type 1B (LGMD1B). This disease presents with weakness and wasting of the proximal skeletal muscles and has a variable age of onset and disease severity. This variability has been attributed to genetic background differences among individuals; however, such variants have not been well characterized. To identify such variants, we investigated a multigeneration family in which affected individuals are diagnosed with LGMD1B. The primary genetic cause of LGMD1B in this family is a dominant mutation that activates a cryptic splice site, leading to a five-nucleotide deletion in the mature mRNA. This results in a frame shift and a premature stop in translation. Skeletal muscle biopsies from the family members showed dystrophic features of variable severity, with the muscle fibers of some family members possessing cores, regions of sarcomeric disruption, and a paucity of mitochondria, not commonly associated with LGMD1B. Using whole genome sequencing (WGS), we identified 21 DNA sequence variants that segregate with the family members possessing more profound dystrophic features and muscle cores. These include a relatively common variant in coiled-coil domain containing protein 78 (CCDC78). This variant was given priority because another mutation in CCDC78 causes autosomal dominant centronuclear myopathy-4, which causes cores in addition to centrally positioned nuclei. Therefore, we analyzed muscle biopsies from family members and discovered that those with both the LMNA mutation and the CCDC78 variant contain muscle cores that accumulated both CCDC78 and RyR1. Muscle cores containing mislocalized CCDC78 and RyR1 were absent in the less profoundly affected family members possessing only the LMNA mutation. Taken together, our findings suggest that a relatively common variant in CCDC78 can impart profound muscle pathology in combination with a LMNA mutation and accounts for variability in skeletal muscle disease phenotypes.

6-month treatment with galectin-1 improves LGMD2B disease pathology in dysferlin-deficient mice

Limb-girdle muscular dystrophy type 2B (LGMD2B) is a devastating autosomal recessive disease for which there are no current FDA-approved treatments. Our previous research shows that short-term recombinant human Galectin-1 (rHsGal-1) treatment is effective in improving muscle repair and decreasing fat deposition in the BLA/J mouse model. Our current objective is to determine the efficacy of a long-term (6-month) weekly treatment with rHsGal-1 in improving disease pathology in BLA/J mice. Mice treated weekly with intraperitoneal injections of 2.7 mg/kg rHsGal-1 show significant improvements in the time it takes to cross a 10 mm wide balance beam in comparison with saline-injected mice. Treated mice also show less decline over time in how often they rear on their hind legs while exploring a new environment, which suggests improved pathology of the psoas and gluteus muscles, which are especially affected in the BLA/J model. Oil Red O staining of the psoas muscles shows decreased lipid deposition in the muscle of rHsGal-1 treated mice. Other histological stains show improved pathology in various affected muscles. We conclude that weekly treatment with rHsGal-1 is a promising therapeutic for individuals with LGMD2B. This research is funded by the Jain Foundation This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Characterization of cardiac involvement in children with LMNA-related muscular dystrophy.

Introduction: LMNA-related muscular dystrophy is a rare entity that produce "laminopathies" such as Emery-Dreifuss muscular dystrophy (EDMD), limb-girdle muscular dystrophy type 1B (LGMD1B), and LMNA-related congenital muscular dystrophy (L-CMD). Heart failure, malignant arrhythmias, and sudden death may occur. No consensus exists on cardiovascular management in pediatric laminopathies. The aim was to perform an exhaustive cardiologic follow-up in pediatric patients diagnosed with LMNA-related muscular dystrophy. Methods: Baseline cardiac work-up consisted of clinical assessment, transthoracic Doppler echocardiography, 12-lead electrocardiogram, electrophysiological study, and implantation of a long-term implantable cardiac loop recorder (ILR). Results: We enrolled twenty-eight pediatric patients diagnosed with EDMD (13 patients), L-CMD (11 patients), LGMD1B (2 patients), and LMNA-related mild weakness (2 patients). Follow-up showed dilated cardiomyopathy (DCM) in six patients and malignant arrhythmias in five (four concomitant with DCM) detected by the ILR that required implantable cardioverter defibrillator (ICD) implantation. Malignant arrhythmias were detected in 20% of our cohort and early-onset EDMD showed worse cardiac prognosis. Discussion: Patients diagnosed with early-onset EDMD are at higher risk of DCM, while potentially life-threatening arrhythmias without DCM appear earlier in L-CMD patients. Early onset neurologic symptoms could be related with worse cardiac prognosis. Specific clinical guidelines for children are needed to prevent sudden death.

A case of dysferlinopathy (Miyoshi distal myopathy limb-girdle muscular dystrophy type 2b phenotype) from a tertiary care hospital

Limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy are caused by similar mutations in the dysferlin gene. The phenotype of these allelic disease variants can vary considerably. We report a young male with severe and rapidly progressing muscle disorder with increased creatine phosphokinase (CPK) and confirmatory muscle biopsy findings. Genetic testing was done. A homozygous nonsense variation in exon 23 of the DYSF gene, which was consistent with the patient’s clinical reports of dysferlinopathy. Clinical phenomenology and preferential muscle involvement lead one to the gold standard genetic testing in heritable myopathies, which was well established in this report.

Limb-Girdle Muscular Dystrophy Type 2B (LGMD2B) caused by Pathogenic Splice and Missense Variants of DYSF Gene among Iranians with Muscular Dystrophy.

The phenotypic range of limb-girdle muscular dystrophies (LGMDs) varies significantly because of genetic heterogeneity ranging from very mild to severe forms. Molecular analysis of the DYSF gene is challenging due to the wide range of mutations and associated complications in interpretations of novel DYSF variants with uncertain significance. Thus, in the current study, we performed the NGS analysis and its results are confirmed with Sanger sequencing to find the plausible disease-causing variants in patients with muscular dystrophy and their relatives via segregation analysis. Nine patients with LGMD type 2B (LGMD2B) characteristics were screened for putative mutations by the whole-exome sequencing (WES) test. Either the patients themselves or their parents and first relatives were investigated in the segregation analysis through Sanger sequencing. The majority of variants were classified as pathogenic through American College of Medical Genetics and Genomics (ACMG) guidelines, segregation results, and in silico predictions. Results revealed eight variants in DYSF gene, including three splicing (c.1149+4A>G, c.2864+1G>A, and c.5785-7G>A), two nonsense (p.Gln112Ter and p.Trp2084Ter), two missense (p.Thr1546Pro and p.Tyr1032Cys), and one frameshift (p.Asp1067Ilefs), among nine Iranian families. One of the eight identified variants was novel, including p.Asp1067Ilefs, which was predicted to be likely pathogenic based on the ACMG guidelines. Notably, prediction tools suggested the damaging effects of studied variants on dysferlin structure. Conclusively, the current report introduced eight variants including a novel frameshift in DYSF gene with noticeable pathogenic effects. This study significantly can broaden the diagnostic spectrum of LGMD2B in combination with previous reports about DYSF mutations and may pave the way for a rapidly high-ranked identification of the accurate type of dysferlinopathy.

Somatic and germinal mosaicism in a Han Chinese family with laminopathies.

"Laminopathies" refers to a wide spectrum of myopathies caused by mutations in the LMNA gene. These myopathies include limb girdle muscular dystrophy type 1B (LGMD1B) and dilated cardiomyopathy 1 A (DCM1A), which are both autosomal dominant neurogenetic diseases. There have been few studies on mosaicism in laminopathies. Herein, a Han Chinese family with laminopathies was enrolled in our study. Genetic analysis revealed that the proband carried a novel splice site mutation, c. 1158-3 C > T, in the LMNA gene due to her mother having de novo somatic and gonadal mosaicism. Reverse-transcription polymerase chain reaction (RT-PCR) analysis revealed reduced levels of LMNA mRNA in the proband, which were probably due to nonsense-mediated mRNA decay (NMD). Western blotting revealed reduced lamin A/C protein levels in the skeletal muscle tissue of the proband. In this family, the clinical phenotypes of the proband's mother were normal, and the c. 1158-3 C > T splicing mutation was identified in the blood sample of the proband's mother. Thus, the mutation could be easily considered to be nonpathogenic. Our study emphasizes the importance of mosaicism in the identification of pathogenic variants and genetic counseling.

Evaluation of cardiomyopathy with two-dimensional speckle tracking echocardiography in limb-girdle muscular dystrophy type 2A and 2B.

Cardiac involvement in limb-girdle muscular dystrophy (LGMD)2A and LGMD2B, the most common subgroups of LGMD, is controversial. Our study aims to determine whether myocardial dysfunction develops in LGMD2A and LGMD2B patients. The study included 16 LGMD2A, 12 LGMD2B patients, and 48 healthy individuals. Comparisons included demographic, clinical, and laboratory parameters of LGMD2A and LGMD2B subgroups and traditional echocardiography and two-dimensional speckle tracking echocardiography (2D-STE) parameters with the normal population. The median age was 33 (22-39 interquartile range [IQR]) in the LGMD2A group, 33 (27-38 IQR) in the LGMD2B group, and 28 (25-35 IQR) in the control group. The left ventricular (LV) ejection fraction of both LGMD2A and LGMD2B groups was similar to the control group (p=0.296 and p=0.918). Apical 4-chamber longitudinal strain (LS), Apical 2-chamber LS, Apical 3-chamber LS, left ventricular global longitudinal strain (LVGLS)-mid-myocardial, LVGLS-endocardium, and LVGLS-epicardium were lower (less negative) in the LGMD2B group compared to the control group (p=0.006, p=0.001, p < 0.001, p < 0.001, p < 0.001, and p < 0.001, respectively). LV 2D-STE parameters of LGMD2A patients were similar to the control group, while they decreased significantly (less negative) in LGMD2B patients, indicating that LV subclinical myocardial dysfunction may develop in LGMD2B patients.

A Patient of Limb-girdle Muscular Dystrophy Type 1B Presenting with Heart Failure and Cardiac Conduction Defects: A Case Report

Background: Limb-girdle muscular dystrophy type 1B (LGMD1B) are characterised by cardiac dysrhythmias, late-onset cardiomyopathy, slowly progressive skeletal myopathy and contractures of the neck, elbows and ankles. The causative mutation is in lamin A/C gene (autosomal dominant LGMD1B). Objective: To assess the clinical outcome of a patient of limb-girdle muscular dystrophy type 1B with heart failure and cardiac conduction defects. The case: We report a case of 47-yr-old male with proximal muscle weakness who presented with repeated exertional dyspnea and repeated presyncope. ECG revealed junctional bradycardia. Echocardiography revealed global wall motion abnormality with EF 48%. EMG showed myopathic pattern. Next genome sequencing showed that the patient has a missense mutation in exon 4 region of LMNA gene (c.G662A/p.Arg221His). Cardiac involvement is very common in this disease which includes AV block, bradycardia, atrial tachycardia, atrial fibrillation and ventricular dysrhythmia causing sudden death. Our patient presented with symptomatic junctional bradycardia which necessitates implantation of permanent pacemaker. Conclusion: Cardiologists should be aware of these unusual genetic diseases with conduction defects, especially in young adults. Bangladesh Med Res Counc Bull 2022; 48(1): 76-80

Thermoneutral Housing and a Western Diet Combination Exacerbates Dysferlin-Deficient Muscular Dystrophy.

Most mouse models of muscular dystrophy (MD) show mild phenotypes, which limits the translatability of experimental therapies to patients. A growing body of evidence suggests that MD is accompanied by metabolic abnormalities that could potentially exacerbate the primary muscle wasting process. Since thermoneutral (TN) housing of mice (~30°C) has been shown to affect many metabolic parameters, particularly when combined with a Western diet (WD), our aim was to determine whether the combination of TN and WD exacerbates muscle wasting in dysferlin-deficient BLAJ mice, a common model of limb-girdle MD type 2b (LGMD2b). The 2-mo-old wild-type (WT) and BLAJ mice were housed at TN or room temperature (RT) and fed a WD or regular chow for 9 mo. Ambulatory function, muscle histology, and protein immunoblots of skeletal muscle were assessed. BLAJ mice at RT and fed a chow diet showed normal ambulation function similar to WT mice, whereas 90% of BLAJ mice under WD and TN combination showed ambulatory dysfunction (p < 0.001), and an up to 4.1-fold increase in quadriceps and gastrocnemius fat infiltration. Western blotting revealed decreased autophagy marker microtubules-associated protein 1 light chain 3-B (LC3BII/LC3BI) ratio and up-regulation of protein kinase B/AKT and ribosomal protein S6 phosphorylation, suggesting inefficient cellular debris and protein clearance in TN BLAJ mice fed a WD. Male and female BLAJ mice under TN and WD combination showed heterogenous fibro-fatty infiltrate composition. TN and WD combination exacerbates rodent LGMD2b without affecting WT mice. This improves rodent modeling of human MD and helps elucidate how metabolic abnormalities may play a causal role in muscle wasting.

Cholesterol absorption blocker ezetimibe prevents muscle wasting in severe dysferlin-deficient and mdx mice.

BackgroundMuscular dystrophy (MD) causes muscle wasting and is often lethal in patients due to a lack of proven therapies. In contrast, mouse models of MD are notoriously mild. We have previously shown severe human‐like muscle pathology in mdx [Duchenne MD (DMD)] and dysferlin‐deficient limb‐girdle MD type 2B (LGMD2B) mice by inactivating the gene encoding for apolipoprotein E (ApoE), a lipid transporter synthesized by the liver, brain and adipocytes to regulate lipid and fat metabolism. Having recently established that human DMD is a novel type of primary genetic dyslipidaemia with elevated cholesterol, we sought to determine whether cholesterol could exacerbate the muscle wasting process observed in severe rodent MD.MethodsSevere mdx and dysferlin knock‐out mice lacking ApoE were treated with ezetimibe (15 mg/kg/day), a clinically approved drug exhibiting few pleiotropic effects. In separate studies, dietary cholesterol was raised (from 0.2% to 2% cholesterol) in combination with experimental micro‐injury and direct cholesterol injection assays. Muscles were assessed histologically for changes in collagen and adipocyte infiltration and both transcriptomic and cellular changes by RNA‐seq and fluorescence‐activated cell sorting analysis.ResultsTreatment of severe DMD and LGMD2B mice with ezetimibe completely prevented clinical signs of ambulatory dysfunction (0% incidence vs. 33% for vehicle treatment; P < 0.05). Histological analyses revealed that ezetimibe‐reduced fibro‐fatty infiltration up to 84% and 63% in severely affected triceps (P ≤ 0.0001) and gastrocnemius (P ≤ 0.003) muscles, resulting in a respective 1.9‐fold and 2.2‐fold retention of healthy myofibre area (P ≤ 0.0001). Additionally, raising dietary cholesterol and thus concentrations of plasma low‐density lipoprotein‐associated cholesterol (by 250%; P < 0.0001) reduced overall survivability (by 100%; P < 0.001) and worsened muscle damage in the LGMD2B triceps by 767% (P < 0.03). Micro‐pin‐induced mechanical injury in LGMD2B mice fed a high cholesterol diet exacerbated muscle damage by 425% (P < 0.03) and increased macrophage recruitment (by 98%; P = 0.03) compared with those injured on a chow diet. Parallel RNA‐seq analyses revealed that injury in cholesterol‐fed mice also modulated the expression of 3671 transcripts (1953 up‐regulated), with fibrogenic, inflammatory and programmed cell death‐associated pathways among the most enriched. Mice lacking dysferlin also displayed heightened muscle necrosis (by 123%; P < 0.0001) following a direct intramuscular injection of cholesterol compared with control mice.ConclusionsCholesterol exacerbates rodent MD. Specific inhibition of cholesterol absorption with ezetimibe may safely attenuate human MD severity and delay death.

Generation and Analysis of Genetically Modified CD14+ Monocytes with Dysferlin Overexpression

IntroductionDysferlinopathies is a group of orphan neuromuscular diseases associated with impairment of mRNA and defect in dysferlin protein expression in skeletal muscle tissue due to mutations in DYSF (Dystrophy-associated fer-1-like) gene. This group of diseases is having autosomal recessive type of inheritance and the frequency of occurrence is 1/1,300-1/200,000 in different populations. There are three main clinical phenotypes associated with dysferlin gene mutations: Limb girdle muscular dystrophy type 2B (LGMD2B), Miyoshi myopathy (MM) and distal myopathy with anterior tibial onset (DMAT) (Yakovlev et. al. Human Gene Therapy 2016). Currently there is no treatment for these diseases. Hence, the development of new methods of treating this group of diseases remains an urgent task, in particular, with the use of gene therapy. According to the literature, CD14+ cells play a key role in the pathogenesis of human dysferlinopathies and are involved in inflammatory reactions and pathological angiogenesis.MethodsIn the present work, by using previously created recombinant adenovirus Ad5-Dysf (Starostina et. al. Medicine 2016) that encodes human cDNA dysferlin gene and enables the expression of the recombinant dysferlin protein, genetic modification of CD14 + monocytes was carried out. Therefore, the following aims were set:1. Isolation of CD14+ cells from a patient with dysferlinopathy and a healthy donor.2. Genetic modification of CD14+ monocytes.3. Conduct western blot analysis of mRNA expression of recombinant dysferlin protein in modified cells after viral transduction. Evaluate the effectiveness of viral transduction by analyzing the expression of EGFP protein (adenovirus Ad5-EGFP) which was taken as a positive control by fluorescence microscopy.ResultsCD14+ cells were isolated from the freshly prepared peripheral blood leukocyte buffy coat layer of the patient with dysferlinopathy and a healthy donor by use of EasySep ™ Human Buffy Coat CD14 Positive Selection Kit. Since the correct assembly and effective DYSF gene delivery of the adenovirus Ad5-Dysf was confirmed in previous work, the viral transduction of human monocytes was carried out successfully. Ad5-EGFP adenovirus was used as a positive control to evaluate the effectiveness of viral transduction. EGFP protein expression analysis was conducted by fluorescence microscopy on an inverted fluorescent microscope of the research class AxioObserver.Z1 (Carl Zeiss) and demonstrated 100% of EGFP protein expression (Fig. 1). After genetic modification of the cells with resulting Ad5-Dysf adenovirus the evaluation of the recombinant dysferlin protein expression in cells was carried out by western blot analysis. Positive reaction was revealed with rabbit polyclonal antibodies to dysferlin (Fig. 2).ConclusionsIn this work we demonstrated that genetically modified CD14+ cells with DYSF overexpression can be successfully geberated and considered as one of the approaches for the therapy of human dysferlinopathies. Future studies are needed to analyze the functionality of the obtained genetic construct in animal models. SVV was supported by RFBR grant 16-34-00657.Fig. 1. CD14+ monocytes genetically modified with Ad5-EGFP. A - phase-contrast microscopy. B - fluorescence microscopy. 48 hours after genetic modification. Magnification 200X.Fig. 2. Western blot analysis of DYSF protein expression in CD14+ monocytes isolated from the peripheral blood of a patient with dysferlinopathy. Electrophoresis in 12% SDS-PAGE gel according to the Laemmli system. Antibodies to dysferlin (Abcam, ab15108) were used in a dilution of 1:250. The expected size of DYSF protein is 231 kDa. Well 1 - transduced CD14+ monocytes with Ad5-Dysf. Well 2 - native CD14+ monocytes. M - molecular weight marker. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

A Rare Case of Dysferlinopathy Causing Cardiomyopathy

Introduction We report a case of a 30-year-old man who presented with advanced heart failure secondary to dilated cardiomyopathy. The patient was diagnosed with limb girdle muscular dystrophy type 2B (LGMD2B), a rare autosomal recessive disease. Cardiomyopathy is only rarely described in dysferlinopathies. Case This patient is a 30-year old African American male with medical history of left foot crush injury in 2016. The following year after injury he developed progressive exercise intolerance and palpitations. An electrocardiogram (ECG) showed sinus tachycardia. Echocardiogram revealed a severely dilated left ventricle, with increased wall thickness, apical trabeculations and ejection fraction (EF) of 20%. Right ventricle had normal size and function, and there was no significant valvular disease. His functional capacity and cardiac performance on imaging tests did not improve despite guideline directed medical therapy. He also had persistently elevated transaminases. Chronic liver disease workup was negative with liver biopsy showing mild sinusoidal dilatation without significant fibrosis. Persistently elevated transaminases in the absence of liver disease and significant systemic congestion prompted testing for muscle enzymes, which were severely elevated (CK-16,196; Aldolase 84.3 U/l). Neurologic examined revealed mild proximal muscle weakness. Further evaluation included electromyography (EMG), which was consistent with chronic myopathy. Genetic testing revealed a pathogenic splice site variant (c.2643+1GA), and two variants of uncertain significance (p.Asn367Lys, p.Arg553His) in the dysferlin gene. Muscle biopsy was performed which showed active myopathic features with myofiber necrosis and regeneration (Figure 1A, 1B). No chronic remodeling was present. Immunohistochemical staining showed loss of dysferlin expression (figure 1C; insert normal control). Expression of other sarcolemmal proteins like dystrophin was preserved (figure 1D). The biopsy findings support a diagnosis of a dysferlinopathy in the context of the described genetic variants and argue for the combination of the described variants to be disease causing. Conclusion LGMD2B is a rare limb girdle muscular dystrophy with very few previously reported cases of cardiac muscle involvement. Our case highlights the importance of a comprehensive diagnostic evaluation of idiopathic cardiomyopathy in young patients. Chronically elevated transaminases in young patients should prompt evaluation for myopathy, and genetic evaluation in the appropriate clinical context.

Treatment with galectin-1 improves myogenic potential and membrane repair in dysferlin-deficient models.

Limb-girdle muscular dystrophy type 2B (LGMD2B) is caused by mutations in the dysferlin gene, resulting in non-functional dysferlin, a key protein found in muscle membrane. Treatment options available for patients are chiefly palliative in nature and focus on maintaining ambulation. Our hypothesis is that galectin-1 (Gal-1), a soluble carbohydrate binding protein, increases membrane repair capacity and myogenic potential of dysferlin-deficient muscle cells and muscle fibers. To test this hypothesis, we used recombinant human galectin-1 (rHsGal-1) to treat dysferlin-deficient models. We show that rHsGal-1 treatments of 48 h-72 h promotes myogenic maturation as indicated through improvements in size, myotube alignment, myoblast migration, and membrane repair capacity in dysferlin-deficient myotubes and myofibers. Furthermore, increased membrane repair capacity of dysferlin-deficient myotubes, independent of increased myogenic maturation is apparent and co-localizes on the membrane of myotubes after a brief 10min treatment with labeled rHsGal-1. We show the carbohydrate recognition domain of Gal-1 is necessary for observed membrane repair. Improvements in membrane repair after only a 10 min rHsGal-1treatment suggest mechanical stabilization of the membrane due to interaction with glycosylated membrane bound, ECM or yet to be identified ligands through the CDR domain of Gal-1. rHsGal-1 shows calcium-independent membrane repair in dysferlin-deficient and wild-type myotubes and myofibers. Together our novel results reveal Gal-1 mediates disease pathologies through both changes in integral myogenic protein expression and mechanical membrane stabilization.

Clinical spectrum and genetic variations of LMNA-related muscular dystrophies in a large cohort of Chinese patients

BackgroundLMNA-related muscular dystrophy is caused by mutations in LMNA gene. We aimed to identify genetic variations and clinical features in a large cohort of Chinese patients with LMNA mutations in...

Functions of Vertebrate Ferlins.

Ferlins are multiple-C2-domain proteins involved in Ca2+-triggered membrane dynamics within the secretory, endocytic and lysosomal pathways. In bony vertebrates there are six ferlin genes encoding, in humans, dysferlin, otoferlin, myoferlin, Fer1L5 and 6 and the long noncoding RNA Fer1L4. Mutations in DYSF (dysferlin) can cause a range of muscle diseases with various clinical manifestations collectively known as dysferlinopathies, including limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy. A mutation in MYOF (myoferlin) was linked to a muscular dystrophy accompanied by cardiomyopathy. Mutations in OTOF (otoferlin) can be the cause of nonsyndromic deafness DFNB9. Dysregulated expression of any human ferlin may be associated with development of cancer. This review provides a detailed description of functions of the vertebrate ferlins with a focus on muscle ferlins and discusses the mechanisms leading to disease development.

Transcriptomic Analysis Reveals Involvement of the Macrophage Migration Inhibitory Factor Gene Network in Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a progressive hereditary muscular disease with X-linked recessive inheritance, that leads patients to premature death. The loss of dystrophin determines membrane instability, causing cell damage and inflammatory response. Macrophage migration inhibitory factor (MIF) is a cytokine that exerts pleiotropic properties and is implicated in the pathogenesis of a variety of diseases. Recently, converging data from independent studies have pointed to a possible role of MIF in dystrophic muscle disorders, including DMD. In the present study, we have investigated the modulation of MIF and MIF-related genes in degenerative muscle disorders, by making use of publicly available whole-genome expression datasets. We show here a significant enrichment of MIF and related genes in muscle samples from DMD patients, as well as from patients suffering from Becker’s disease and limb-girdle muscular dystrophy type 2B. On the other hand, transcriptomic analysis of in vitro differentiated myotubes from healthy controls and DMD patients revealed no significant alteration in the expression levels of MIF-related genes. Finally, by analyzing DMD samples as a time series, we show that the modulation of the genes belonging to the MIF network is an early event in the DMD muscle and does not change with the increasing age of the patients, Overall, our analysis suggests that MIF may play a role in vivo during muscle degeneration, likely promoting inflammation and local microenvironment reaction.

GENE EDITING AND MOLECULAR THERAPY: P.285Effective gene editing of the human DYSF founder mutation c.1624delG in patient-derived cells and generation of analogous "humanized" mouse models for in vivo treatment

Dysferlinopathy, also known as limb-girdle muscular dystrophy type 2B (LGMD2B), is caused by mutations in DYSF. It is one of the most frequent of > 40 untreatable muscular dystrophies leading to progressive muscle degeneration and wheel-chair-dependency. We generated hiPSC from two patients carrying a founder frameshift mutation (c.1624delG) in DYSF exon 44 that results in a complete absence of dysferlin protein and developed various gene editing approaches to repair this mutation using CRISPR/Cas9. First, using mutation-specific sgRNAs in combination with the enhanced specificity Cas9 variant eSpCas9(1.1), we were able to restore the mutant sequence to its wild-type form via homology directed repair without introducing any silent mutations in the repair template. Second, we used Cas9-induced NHEJ, in particular the indel signature bias of specific sgRNAs, to restore the DYSF reading frame in patient-derived cells with a high efficiency. We could readily demonstrate rescue of the re-framed dysferlin protein by western blot after editing. In parallel, we generated two related transgenic mouse lines, one with the murine Dysf exon 44 exchanged for the human wild-type DYSF exon 44 and the other containing the human c.1624delG founder mutation within the human DYSF exon 44. The latter lacks dysferlin protein and recapitulates the progressive muscular dystrophy phenotype seen in LGMD2B patients. Using these models, we are assessing ways to re-create in vivo our DYSF editing approaches directly on the human sequence, utilizing genetic tools that can be applied to patient cells.

Correction of pseudoexon splicing caused by a novel intronic dysferlin mutation.

ObjectiveDysferlin is a large transmembrane protein that functions in critical processes of membrane repair and vesicle fusion. Dysferlin‐deficiency due to mutations in the dysferlin gene leads to muscular dystrophy (Miyoshi myopathy (MM), limb girdle muscular dystrophy type 2B (LGMD2B), distal myopathy with anterior tibial onset (DMAT)), typically with early adult onset. At least 416 pathogenic dysferlin mutations are known, but for approximately 17% of patients, one or both of their pathogenic variants remain undefined following standard exon sequencing methods that interrogate exons and nearby flanking intronic regions but not the majority of intronic regions.MethodsWe sequenced RNA from myogenic cells to identify a novel dysferlin pathogenic variant in two affected siblings that previously had only one disease‐causing variant identified. We designed antisense oligonucleotides (AONs) to bypass the effects of this mutation on RNA splicing.ResultsWe identified a new pathogenic point mutation deep within dysferlin intron 50i. This intronic variant causes aberrant mRNA splicing and inclusion of an additional pseudoexon (PE, we term PE50.1) within the mature dysferlin mRNA. PE50.1 inclusion alters the protein sequence, causing premature translation termination. We identified this mutation in 23 dysferlinopathy patients (seventeen families), revealing it to be one of the more prevalent dysferlin mutations. We used AON‐mediated exon skipping to correct the aberrant PE50.1 splicing events in vitro, which increased normal mRNA production and significantly restored dysferlin protein expression.InterpretationDeep intronic mutations can be a common underlying cause of dysferlinopathy, and importantly, could be treatable with AON‐based exon‐skipping strategies.

Membrane Stabilization by Modified Steroid Offers a Potential Therapy for Muscular Dystrophy Due to Dysferlin Deficit.

Mutations of the DYSF gene leading to reduced dysferlin protein level causes limb girdle muscular dystrophy type 2B (LGMD2B). Dysferlin facilitates sarcolemmal membrane repair in healthy myofibers, thus its deficit compromises myofiber repair and leads to chronic muscle inflammation. An experimental therapeutic approach for LGMD2B is to protect damage or improve repair of myofiber sarcolemma. Here, we compared the effects of prednisolone and vamorolone (a dissociative steroid; VBP15) on dysferlin-deficient myofiber repair. Vamorolone, but not prednisolone, stabilized dysferlin-deficient muscle cell membrane and improved repair of dysferlin-deficient mouse (B6A/J) myofibers injured by focal sarcolemmal damage, eccentric contraction-induced injury or injury due to spontaneous in vivo activity. Vamorolone decreased sarcolemmal lipid mobility, increased muscle strength, and decreased late-stage myofiber loss due to adipogenic infiltration. In contrast, the conventional glucocorticoid prednisolone failed to stabilize dysferlin deficient muscle cell membrane or improve repair of dysferlinopathic patient myoblasts and mouse myofibers. Instead, prednisolone treatment increased muscle weakness and myofiber atrophy in B6A/J mice—findings that correlate with reports of prednisolone worsening symptoms of LGMD2B patients. Our findings showing improved cellular and pre-clinical efficacy of vamorolone compared to prednisolone and better safety profile of vamorolone indicates the suitability of vamorolone for clinical trials in LGMD2B.