Muscle pathology in dysferlin deficiency

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.

Miyoshi myopathy associated with spine rigidity and multiple contractures: a case report

BACKGROUND

Dysferlinopathy is a phenotypically heterogeneous group of hereditary diseases caused by mutations in the DYSF gene. Early contractures are considered rare, and rigid spine syndrome in dysferlinopathy has been previously reported only once.

CASE PRESENTATION

We describe a 23-year-old patient with Miyoshi myopathy with a rigid spine and multiple contractures, a rare phenotypic variant. The disease first manifested when the patient was 13 years old, with fatigue of the gastrocnemius muscles and the development of pronounced contractures of the Achilles tendons, flexors of the fingers, and extensors of the toes, followed by the involvement of large joints and the spine. Magnetic resonance imaging revealed signs of connective tissue and fatty replacement of the posterior muscles of the thighs and lower legs. Edema was noted in the anterior and medial muscle groups of the thighs, lower legs, and the multifidus muscle of the back. Whole genome sequencing revealed previously described mutations in the DYSF gene in exon 39 (c.4282 C > T) and intron 51 (c.5785-824 C > T). An immunohistochemical analysis and Western blot showed the complete absence of dysferlin protein expression in the muscle fibers.

CONCLUSIONS

This case expands the range of clinical and phenotypic correlations of dysferlinopathy and complements the diagnostic search for spine rigidity.

Clinical features, imaging findings and molecular data of limb-girdle muscular dystrophies in a cohort of Chinese patients

BACKGROUND

Limb-girdle muscular dystrophies (LGMDs) are a group of heterogeneous inherited diseases predominantly characterized by limb-girdle muscle weakness and dystrophic changes on histological analysis. The frequency of LGMD subtypes varies among regions in China and ethnic populations worldwide. Here, we analyzed the prevalence of LGMD subtypes, their corresponding clinical manifestations, and molecular data in a cohort of LGMD patients in Southeast China.

METHODS

A total of 81 consecutive patients with clinically suspected LGMDs from 62 unrelated families across Southeast China were recruited for targeted next-generation sequencing and whole-exome sequencing from July 2017 to February 2020.

RESULTS

Among 50 patients (41 families) with LGMDs, the most common subtypes were LGMD-R2/LGMD2B (36.6%) and LGMD-R1/LGMD2A (29.3%). Dystroglycanopathies (including LGMD-R9/LGMD2I, LGMD-R11/LGMD2K, LGMD-R14/LGMD2N and LGMD-R20/LGMD2U) were the most common childhood-onset subtypes and were found in 12.2% of the families. A total of 14.6% of the families had the LGMD-R7/LGMD2G subtype, and the mutation c.26_33dupAGGTGTCG in TCAP was the most frequent (83.3%). The only patient with the rare subtype LGMD-R18/LGMD2S had TRAPPC11 mutations; had a later onset than those previously reported, and presented with proximal‒distal muscle weakness, walking aid dependency, fatty liver disease and diabetes at 33 years of age. A total of 22.0% of the patients had cardiac abnormalities, and one patient with LMNA-related muscular dystrophy/LGMD1B experienced sudden cardiac death at 37 years of age. A total of 15.4% of the patients had restrictive respiratory insufficiency. Muscle imaging in patients with LGMD-R1/LGMD2A and LGMD-R2/LGMD2B showed subtle differences, including more severe fatty infiltration of the posterior thigh muscles in those with LGMD-R1/LGMD2A and edema in the lower leg muscles in those with LGMD-R2/LGMD2B.

CONCLUSION

We determined the prevalence of different LGMD subtypes in Southeast China, described the detailed clinical manifestations and distinct muscle MRI patterns of these LGMD subtypes and reported the frequent mutations and the cardiorespiratory involvement frequency in our cohort, all of which might facilitate the differential diagnosis of LGMDs, allowing more timely treatment and guiding future clinical trials.

Dysferlinopathy in Tunisia: clinical spectrum, genetic background and prognostic profile

Dysferlinopathy is a rare group of hereditary muscular dystrophy with an autosomal recessive mode of inheritance caused by a mutation in the DYSF gene. It encodes for the dysferlin protein, which has a crucial role in multiple cellular processes, including muscle fiber membrane repair. This deficit has heterogeneous clinical presentations. In this study, we collected 20 Tunisian patients with a sex ratio of 1 and a median age of 50.5 years old (Interquartile range (IQR) = [36,5-54,75]). They were followed for periods ranging from 5 to 48 years. The median age at onset was 17 years old (IQR = [16,8-28,4]). Five major phenotypes were identified: Limb-girdle muscular dystrophy (LGMDR2) (35%), a proximodistal phenotype (35%), Miyoshi myopathy (10%),  Distal myopathy with anterior tibial onset (DMAT) (10%), and asymptomatic HyperCKemia (10%). At the last evaluation, more than half of patients (55%) were on wheelchair. Loss of ambulation occurred generally during the fourth decade. After 20 years of disease progression, two patients with a proximodistal phenotype (10%) developed dilated cardiomyopathy and mitral valve regurgitation. Restrictive respiratory syndrome was observed in three patients (DMAT: 1 patient, proximodistal phenotype: 1 patient, LGMDR2: 1 patient). Genetic study disclosed five mutations. We observed clinical heterogeneity between families and even within the same family. Disease progression was mainly slow to intermediate regardless of the phenotype.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

A Dysferlin Exon 32 Nonsense Mutant Mouse Model Shows Pathological Signs of Dysferlinopathy

Dysferlinopathies are a group of autosomal recessive muscular dystrophies caused by pathogenic variants in the DYSF gene. While several animal models of dysferlinopathy have been developed, most of them involve major disruptions of the Dysf gene locus that are not optimal for studying human dysferlinopathy, which is often caused by single nucleotide substitutions. In this study, the authors describe a new murine model of dysferlinopathy that carries a nonsense mutation in Dysf exon 32, which has been identified in several patients with dysferlinopathy. This mouse model, called Dysf ^{p.Y1159X/p.Y1159X}, displays several molecular, histological, and functional defects observed in dysferlinopathy patients and other published mouse models. This mutant mouse model is expected to be useful for testing various therapeutic approaches such as termination codon readthrough, pharmacological approaches, and exon skipping. Therefore, the data presented in this study strongly support the use of this animal model for the development of preclinical strategies for the treatment of dysferlinopathies.

Assessment of Extracellular Volume Fraction in Becker Muscular Dystrophy by Using MR Fingerprinting

Background Quantitative MRI is increasingly proposed in clinical trials related to dystrophinopathies, including Becker muscular dystrophy (BMD). Purpose To establish the sensitivity of extracellular volume fraction (ECV) quantification using an MR fingerprinting sequence with water and fat separation as a quantitative imaging biomarker of skeletal muscle tissue alterations in BMD compared with fat fraction (FF) and water relaxation time quantification. Materials and Methods In this prospective study, study participants with BMD and healthy volunteers were included from April 2018 until October 2022 (ClinicalTrials.gov identifier NCT02020954). The MRI examination comprised FF mapping with the three-point Dixon method, water T2 mapping, and water T1 mapping before and after an intravenous injection of a gadolinium-based contrast agent by using MR fingerprinting, from which ECV was calculated. Functional status was measured with use of the Walton and Gardner-Medwin scale. This clinical evaluation tool stratifies disease severity from grade 0 (preclinical; elevated creatine phosphokinase; all activities normal) to grade 9 (unable to eat, drink, or sit without assistance). Mann-Whitney U tests, Kruskal-Wallis tests, and Spearman rank correlation tests were performed. Results Twenty-eight participants with BMD (median age, 42 years [IQR, 34-52 years]; 28 male) and 19 healthy volunteers (median age, 39 years [IQR, 33-55 years]; 19 male) were evaluated. ECV was higher in participants with dystrophy than in controls (median, 0.21 [IQR, 0.16-0.28] vs 0.07 [IQR, 0.07-0.08]; P < .001). In muscles of participants with BMD with normal FF, ECV was also higher than in muscles of healthy controls (median, 0.11 [IQR, 0.10-0.15] vs 0.07 [IQR, 0.07-0.08]; P = .02). ECV was correlated with FF (ρ = 0.56, P = .003), Walton and Gardner-Medwin scale score (ρ = 0.52, P = .006), and serum cardiac troponin T level (ρ = 0.60, P < .001). Conclusion Quantitative MR relaxometry with water and fat separation indicates a significant increase of skeletal muscle extracellular volume fraction in study participants with Becker muscular dystrophy. Clinical trial registration no. NCT02020954 Published under a CC BY 4.0 license. Supplemental material is available for this article.

Miyoshi Muscular Dystrophy Type 1 with Mutated DYSF Gene Misdiagnosed as Becker Muscular Dystrophy: A Case Report and Literature Review

Dysferlinopathy covers a spectrum of muscle disorder categorized by two major phenotypes, namely Miyoshi muscular dystrophy type 1 (MMD1, OMIM #254130) and limb-girdle muscular dystrophy autosomal recessive 2 (LGMDR2, OMIM #253601), and two minor symptoms, including asymptomatic hyperCKemia and distal myopathy with anterior tibial onset (DMAT, OMIM #606768). We report the first Korean MMD1 misdiagnosed as Becker muscular dystrophy (BMD), which was caused by a combination of compound heterozygous c.663 + 1G > C and p.Trp992Arg of the DYSF gene. A 70-year-old male previously diagnosed with BMD was admitted for genetic counseling. Since he was clinically suspected to have dysferlinopathy but not BMD, targeted panel sequencing was performed to discover the potential hereditary cause of the suspected muscular dystrophy in the proband. Consequently, two pathogenic single nucleotide variants of the DYSF gene, c.663 + 1G > C (rs398123800) and p.Trp992Arg (rs750028300), associated with dysferlinopathy were identified. These variants were previously reported with variant allele frequencies of 0.000455 (c.663 + 1G > C) and 0.000455 (c.2974T > C; p.Trp992Arg) in the Korean population. This report emphasizes the need for common variant screening in the diagnostic algorithms of certain muscle disorders or gene panels with potential pathogenic effects and high rates of recurrent variants.

Mechanisms of Myofibre Death in Muscular Dystrophies: The Emergence of the Regulated Forms of Necrosis in Myology

Myofibre necrosis is a central pathogenic process in muscular dystrophies (MD). As post-lesional regeneration cannot fully compensate for chronic myofibre loss, interstitial tissue accumulates and impairs muscle function. Muscle regeneration has been extensively studied over the last decades, however, the pathway(s) controlling muscle necrosis remains largely unknown. The recent discovery of several regulated cell death (RCD) pathways with necrotic morphology challenged the dogma of necrosis as an uncontrolled process, opening interesting perspectives for many degenerative disorders. In this review, we focus on how cell death affects myofibres in MDs, integrating the latest research in the cell death field, with specific emphasis on Duchenne muscular dystrophy, the best-known and most common hereditary MD. The role of regulated forms of necrosis in myology is still in its infancy but there is increasing evidence that necroptosis, a genetically programmed form of necrosis, is involved in muscle degenerating disorders. The existence of apoptosis in myofibre demise will be questioned, while other forms of non-apoptotic RCDs may also have a role in myonecrosis, illustrating the complexity and possibly the heterogeneity of the cell death pathways in muscle degenerating conditions.

Water T2 could predict functional decline in patients with dysferlinopathy

BACKGROUND

Water T2 (T2_H2O ) mapping is increasingly being used in muscular dystrophies to assess active muscle damage. It has been suggested as a surrogate outcome measure for clinical trials. Here, we investigated the prognostic utility of T2_H2O to identify changes in muscle function over time in limb girdle muscular dystrophies.

METHODS

Patients with genetically confirmed dysferlinopathy were assessed as part of the Jain Foundation Clinical Outcomes Study in dysferlinopathy. The cohort included 18 patients from two sites, both equipped with 3-tesla magnetic resonance imaging (MRI) systems from the same vendor. T2_H2O value was defined as higher or lower than the median in each muscle bilaterally. The degree of deterioration on four functional tests over 3 years was assessed in a linear model against covariates of high or low T2_H2O at baseline, age, disease duration, and baseline function.

RESULTS

A higher T2_H2O at baseline significantly correlated with a greater decline on functional tests in 21 out of 35 muscles and was never associated with slower decline. Higher baseline T2_H2O in adductor magnus, vastus intermedius, vastus lateralis, and vastus medialis were the most sensitive, being associated bilaterally with greater decline in multiple timed tests. Patients with a higher than median baseline T2_H2O (>40.6 ms) in the right vastus medialis deteriorated 11 points more on the North Star Ambulatory Assessment for Dysferlinopathy and lost an additional 86 m on the 6-min walk than those with a lower T2_H2O (<40.6 ms). Optimum sensitivity and specificity thresholds for predicting decline were 39.0 ms in adductor magnus and vastus intermedius, 40.0 ms in vastus medialis, and 40.5 ms in vastus lateralis from different sites equipped with different MRI systems.

CONCLUSIONS

In dysferlinopathy, T2_H2O did not correlate with current functional ability. However, T2_H2O at baseline was higher in patients who worsened more rapidly on functional tests. This suggests that inter-patient differences in functional decline over time may be, in part, explained by different severities of the active muscle damage, assessed by T2_H2O measure at baseline. Significant challenges remain in standardizing T2_H2O values across sites to allow determining globally applicable thresholds. The results from the present work are encouraging and suggest that T2_H2O could be used to improve prognostication, patient selection, and disease modelling for clinical trials.

Is it really myositis? Mimics and pitfalls

Idiopathic inflammatory myopathies are a heterogeneous set of systemic inflammatory disorders primarily affecting muscle. Signs and symptoms vary greatly between and within subtypes, requiring supportive laboratory and pathologic evidence to confirm the diagnosis. Several studies are typical assessments for patients with suspected inflammatory myopathy, including muscle enzymes, autoimmune markers, imaging, and muscle biopsy. Misdiagnoses of myositis are not only related to the overlap of clinical phenotype with non-inflammatory myopathies, but also due to the limitations of diagnostic tests employed. Since many of the investigative tests are non-specific, they share features with other disorders, including muscular dystrophies, endocrine, toxic, and metabolic myopathies, and other neuromuscular or rheumatologic conditions. Recognizing the limitations of tests and understanding the shared features between inflammatory and non-inflammatory myopathies can help prevent misdiagnosing myositis with one of its several mimics.

Dysferlinopathy misdiagnosed with juvenile polymyositis in the pre-symptomatic stage of hyperCKemia: a case report and literature review

Background

Dysferlinopathy encompasses a group of rare muscular dystrophies caused by recessive mutations in the DYSF gene. The phenotype ranges from asymptomatic elevated serum creatine kinase (hyperCKemia) to selective and progressive involvement of the proximal and/or distal muscles of the limbs. Bohan and Peter criteria are the most widely used for the diagnosis of polymyositis, but they have limitations and can misclassify muscular dystrophies with inflammation as polymyositis. Most dysferlinopathy patients have muscle biopsies with inflammation and thus are vulnerable to misdiagnosis with polymyositis and inappropriate treatment with steroids and immunosuppressors.

Case presentation

We describe a 14 years-old male patient who was referred for assessment of asymptomatic hyperCKemia (26,372 IU/L). An X-linked dystrophinopathy initially was ruled out by direct genetic testing. Juvenile polymyositis was considered based on muscle biopsy, creatine kinase levels, and electromyography changes. Corticosteroid treatment triggered proximal lower limb muscular weakness, and no full muscular strength recovery was observed after corticosteroid withdrawal. Based on these observations, a limb-girdle muscular dystrophy (LGMD) was suspected, and LGMDR2 was confirmed by whole exome sequencing.

Conclusion

We report a dysferlinopathy patient who was misdiagnosed with juvenile polymyositis and explore in a literature review how common such misdiagnoses are. With diagnosis based only on routine clinicopathological examinations, distinguishing an inflammatory myopathy from dysferlinopathy is quite difficult. We suggest that before establishing a diagnosis of “definite” or “probable” juvenile polymyositis, according to Bohan and Peter or current ACR/EULAR criteria, a muscular dystrophy must first be ruled out.

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.

Speech and swallowing characteristics in patients with facioscapulohumeral muscular dystrophy

BACKGROUND

Although facial muscle weakness is common in patients with Facioscapulohumeral Muscular Dystrophy (FSHD), the literature is scarce on the speech and swallowing aspects.

OBJECTIVE

To investigate speech and swallowing patterns in FSHD and assess the correlation with clinical data.

METHODS

A cross-sectional study was conducted. Patients with clinical confirmation of FSHD and aged above 18 years were included and paired with healthy control individuals by age and gender. Individuals who had neurological conditions that could interfere with test results were excluded. The following assessments were applied: speech tests (acoustic and auditory-perceptual analysis); swallowing tests with the Northwestern Dysphagia Patient Check Sheet (NDPCS), the Eat Assessment Tool (EAT-10), the Speech Therapy Protocol for Dysphagia Risk (PARD), and the Functional Oral Intake Scale (FOIS); disease staging using the modified Gardner-Medwin-Walton scale (GMWS); and quality of life with the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). The correlation between test results and clinical data was verified by non-parametric statistics.

RESULTS

Thirteen individuals with FSHD and 10 healthy controls were evaluated. The groups presented significant differences in the motor bases of phonation and breathing. Regarding swallowing, two (15%) individuals presented mild dysphagia and seven (53.8%) showed reduced facial muscles strength. These results were not correlated with duration of the disease, age at symptoms onset, and quality of life. Dysphagia was related to worsening disease severity.

CONCLUSIONS

FSHD patients presented mild dysarthria and dysphagia. Frequent monitoring of these symptoms could be an important way to provide early rehabilitation and better quality of life.

The inflammatory pathology of dysferlinopathy is distinct from calpainopathy, Becker muscular dystrophy, and inflammatory myopathies

The descriptions of muscle pathology in dysferlinopathy patients have classically included an inflammatory infiltrate that can mimic inflammatory myopathies. Based on over 20 years of institutional experience in evaluating dystrophic and inflammatory myopathy muscle biopsies at the University of Iowa, we hypothesized the inflammatory histopathology of dysferlinopathy is more similar to limb-girdle pattern muscular dystrophies such as calpainopathy and Becker muscular dystrophy, and distinct from true inflammatory myopathies. Muscle biopsies from 32 dysferlinopathy, 30 calpainopathy, 30 Becker muscular dystrophy, and 30 inflammatory myopathies (15 each of dermatomyositis and inclusion body myositis) were analyzed through digital quantitation of CD3, CD4, CD8, CD20, and PU.1 immunostaining. The expression of MHC class I and deposition of complement C5b-9 was also evaluated. Dysferlinopathy, calpainopathy, and Becker muscular dystrophy muscle biopsies had similar numbers of inflammatory cell infiltrates and significantly fewer CD3+ T-lymphocytes than dermatomyositis (p = 0.05) and inclusion body myositis (p < 0.0001) biopsies. There was no statistically significant difference in the number of PU.1+ macrophages identified in any diagnostic group. MHC class I expression was significantly lower in the limb-girdle pattern muscular dystrophies compared to the inflammatory myopathies (p < 0.0001). In contrast, complement C5b-9 deposition was similar among dysferlinopathy, dermatomyositis, and inclusion body myositis biopsies but significantly greater than calpainopathy and Becker muscular dystrophy biopsies (p = 0.05). Compared to calpainopathy, Becker muscular dystrophy, and inflammatory myopathies, the unique profile of minimal inflammatory cell infiltrates, absent to focal MHC class I, and diffuse myofiber complement C5b-9 deposition is the pathologic signature of dysferlinopathy muscle biopsies.

Cognitive profile of patients with facioscapulohumeral muscular dystrophy

Although it is predominantly a muscular disease, impairments in the central nervous system in patients with facioscapulohumeral muscular dystrophy (FSHD) have been described in the literature.

Immune-mediated necrotizing myopathy (IMNM): A myopathological challenge

This review is focused on the myopathological spectrum of immune mediated necrotizing myopathies (IMNMs) and its differentiation with other, potentially mimicking, inflammatory and non-inflammatory myopathies. IMNMs are a subgroup of idiopathic inflammatory myopathies (IIMs) characterized by severe clinical presentation with rapidly progressive muscular weakness and creatine kinase elevation, often requiring early aggressive immunotherapy, associated to the presence of muscle specific autoantibodies (MSA) against signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Muscle biopsy usually shows unspecific features consisting in prominent necrosis and regeneration of muscle fibres with mild or absent inflammatory infiltrates, inconstant and faint expression of major histocompatibility complex (MHC) class I and variable deposition of C5b-9 on sarcolemma. Several conditions could present similar histopathological findings leading to possible misdiagnosis of IMNM with other IIMs or non-inflammatory myopathies (nIMs) and viceversa. This review analyses the muscle biopsy data in IMNMs through a systematic revision of the literature from the last five decades. Several histopathological variables have been considered in both SRP- and HMGCR-IMNM, and compared to other IIMs - as dermatomyositis (DM) and anti-synthethase syndrome (ASS) - or other nIMs -as toxic myopathies (TM), critical illness myopathy (CIM) and muscular dystrophy (MD) - to elucidate similarities and differences among these potentially mimicking conditions. The major histopathological findings of IMNMs were: very frequent necrosis and regeneration of muscle fibres (93%), mild inflammatory component mainly constituted by scattered isolated (65%) CD68-prevalent (68%) cells, without CD8 invading/surrounding non-necrotic fibres, variable expression of MHC-I in non-necrotic fibres (56%) and constant expression of sarcoplasmic p62, confirming those that are widely considered the major histological characteristics of IMNMs. Conversely, only 42% of biopsies showed a sarcolemmal deposition of C5b-9 component. Few differences between SRP and HMGCR IMNMs consisted in more severe necrosis and regeneration in SRP than in HMGCR (p = 0.01); more frequent inflammatory infiltrates (p = 0.007) with perivascular localization (p = 0.01) and clustered expression of MHC-I (p = 0.007) in HMGCR; very low expression of sarcolemmal C5b-9 in SRP (18%) compared to HMGCR (56%) (p = 0.0001). Milder necrosis and regeneration, detection of perifascicular pathology, presence of lymphocytic inflammatory infiltrates and myofibre expression of MxA help to distinguish DM or ASS from IMNM. nIMs can present signs of inflammation at muscle biopsy. Low fibre size variability with overexpression of both MHC-I and II, associated with C5b-9 deposition, could could be observed in CIM, while increased connective tissue should lead to consider MD, or TM in absence of C5b-9 deposition. Nevertheless, these features are not constantly detected and muscle biopsy could not be diriment. For this reason, muscle biopsy should always be critically considered in light of the clinical context before concluding for a definite diagnosis of IMNM, only based on histopathological findings. More rigorous collection and analysis of muscle biopsy is warranted to obtain a higher quality and more homogeneous histopathological data in inflammatory myopathies.

Reactive Changes in Elements of Stromal-Vascular Differons of Dysferlin-Deficient Skeletal Muscles after Procaine Injection

The study assessed reactivity of stromal-vascular skeletal muscle differons to acute chemical injury. Dysferlin-deficient Bla/J mice and the wild-type С57BL/6 mice were intramuscularly injected with 100 μl of 0.5% procaine solution. The middle segment of gastrocnemius muscle was taken on postsurgery days 2, 4, 10, and 14 for routine histological examination. To evaluate proliferation and vascularization, the paraffin sections were stained immunohistochemically with antibodies to α-smooth muscle actin and Ki-67. The connective tissue was stained according to Mallory. The study revealed diminished proliferative activity of stromal-vascular differons and decreased vascular density in muscles of Bla/J mice. Thus, mutations in the DYSF gene coding dysferlin down-regulate the reparation processes in all differons of skeletal muscle.

Dexamethasone accelerates muscle regeneration by modulating kinesin-1-mediated focal adhesion signals

During differentiation, skeletal muscle develops mature multinucleated muscle fibers, which could contract to exert force on a substrate. Muscle dysfunction occurs progressively in patients with muscular dystrophy, leading to a loss of the ability to walk and eventually to death. The synthetic glucocorticoid dexamethasone (Dex) has been used therapeutically to treat muscular dystrophy by an inhibition of inflammation, followed by slowing muscle degeneration and stabilizing muscle strength. Here, in mice with muscle injury, we found that Dex significantly promotes muscle regeneration via promoting kinesin-1 motor activity. Nevertheless, how Dex promotes myogenesis through kinesin-1 motors remains unclear. We found that Dex directly increases kinesin-1 motor activity, which is required for the expression of a myogenic marker (muscle myosin heavy chain 1/2), and also for the process of myoblast fusion and the formation of polarized myotubes. Upon differentiation, kinesin-1 mediates the recruitment of integrin β1 onto microtubules allowing delivery of the protein into focal adhesions. Integrin β1-mediated focal adhesion signaling then guides myoblast fusion towards a polarized morphology. By imposing geometric constrains via micropatterns, we have proved that cell adhesion is able to rescue the defects caused by kinesin-1 inhibition during the process of myogenesis. These discoveries reveal a mechanism by which Dex is able to promote myogenesis, and lead us towards approaches that are more efficient in improving skeletal muscle regeneration.

Null variants in DYSF result in earlier symptom onset

We investigated the clinical, laboratory, and genetic spectra in Korean patients with dysferlinopathy to clarify its genotype-phenotype correlation. We retrospectively reviewed 101 patients from 96 unrelated families with pathogenic variants of DYSF. The most common initial phenotype was Miyoshi myopathy in 50 patients. Median ages at examination and symptom onset were 23 [interquartile range (IQR): 18-30] and 36 years [IQR: 27-48], respectively. We observed 38 variants, including nine novel variants. Four variants (c.2494C > T, c.1284 + 2 T > C, c.663 + 1G > C, and c.2997G > T) in DYSF accounted for 62% of total allele frequencies of pathogenic variants. To analyze the genotype-phenotype correlation, we compared the clinical phenotype between patients with null/null (N/N; n = 55) and null/missense variants (N/M; n = 35). The N/N group had an earlier symptom onset age (median: 20 years [IQR: 17-25]) than the N/M group (median: 29 years [IQR: 23-35], p < .001). Total manual muscle testing scores in lower extremities were lower in the N/N group (median: 80 [IQR: 56-92]) than in the N/M group (median: 89 [IQR: 78-98], p = .013). Our study is the first to report that null variants in DYSF result in an earlier symptom onset than missense variants.

LGMD. Identification, description and classification

The term ‘limb girdle muscular dystrophy’ (LGMD) was first used in the seminal paper by Walton and Nattrass in 1954, were they identified LGMD as a separate clinical entity In LGMD description it is pointed out that the category of LGMD most likely comprises a heterogeneous group of disorders. After that the clinical entity was discussed but the LMGD nosography reached a permanent classification during two ENMC workshops held in 1995 and 2017, in the last one an operating definition of LGMD was agreed. This last classification included dystrophies with proximal or distal-proximal presentation with evidence at biopsy of fibre degeneration and splitting, high CK, MRI imaging consistent with degenerative changes, fibro-fatty infiltration present in individuals that reached independent walking ability. To be considered in this group at least two unrelated families should be identified.

A review is done of the first genetic characterisation of a number of LGMDs during the late twentieth century and a historical summary is given regarding how these conditions were clinically described and identified, the progresses done from identification of genetic loci, to protein and gene discoveries are reported. The LGMD described on which such historical progresses were done are the recessive calpainopathy (LGMD 2A/R1), dysferlinopathy (LGMD 2B/R2), sarcoglycanopathy (LGMD 2C-2F/R3-R6) types and the dominant type due to TPNO3 variants named transportinopathy (LGMD 1F/D2). Because of new diagnostic techniques such as exome and genome sequencing, it is likely that many other subtypes of LGMD might be identified in the future, however the lesson from the past discoveries can be useful for scientists and clinicians.

Incidental Severe Fatty Degeneration of the Erector Spinae in a Patient with L5-S1 Disc Extrusion Diagnosed with Limb-Girdle Muscular Dystrophy R2 Dysferin-Related

Limb-girdle muscular dystrophy type R2 dysferin-related (LGMD R2 dysferin-related), a phenotype of dysferlinopathy, usually begins with pelvic girdle weakness. A 35-year-old male presented with right leg pain for 2 weeks without a previous history of limb weakness. Magnetic resonance imaging of the lumbar spine showed disc extrusion at L5-S1 and incidental severe fatty degeneration of the lumbar erector spinae. Physical examination demonstrated no definite limb weakness. Serum creatine kinase levels were elevated. Genetic testing using a targeted gene-sequencing panel identified compound heterozygous variants NM_003494.3(DYSF) c.[1284+2T>C]; [5303G>A]. Computed tomography revealed fatty degeneration of lower-limb muscles, which was mild in the adductor muscles and severe in the gluteus minimus. Immunohistochemistry staining of the vastus lateralis showed under-expression of dysferlin. This patient was diagnosed with LGMD R2 dysferin-related. Thus, unusual fatty degeneration of the lumbar paraspinalis can be a manifestation of dysferlinopathy.

Myopathies with finger flexor weakness: Not only inclusion-body myositis

Muscle disorders are characterized by differential involvement of various muscle groups. Among these, weakness predominantly affecting finger flexors is an uncommon pattern, most frequently found in sporadic inclusion-body myositis. This finding is particularly significant when the full range of histopathological findings of inclusion-body myositis is not found on muscle biopsy. Prominent finger flexor weakness, however, is also observed in other myopathies. It occurs commonly in myotonic dystrophy types 1 and 2. In addition, individual reports and small case series have documented finger flexor weakness in sarcoid and amyloid myopathy, and in inherited myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. Therefore, the finding of finger flexor weakness requires consideration of clinical, myopathological, genetic, electrodiagnostic, and sometimes muscle imaging findings to establish a diagnosis.

Early pathological signs in young dysf-/- mice are improved by halofuginone

Dysferlinopathies are a non-lethal group of late-onset muscular dystrophies. Here, we evaluated the fusion ability of primary myoblasts from young dysf^-/- mice and the muscle histopathology prior to, and during early stages of disease onset. The ability of primary myoblasts of 5-week-old dysf^-/- mice to form large myotubes was delayed compared to their wild-type counterparts, as evaluated by scanning electron microscopy. However, their fusion activity, as reflected by the presence of actin filaments connecting several cells, was enhanced by the antifibrotic drug halofuginone. Early dystrophic signs were already apparent in 4-week-old dysf^-/- mice; their collagen level was double that in wild-type mice and continued to rise until 5 months of age. Continuous treatment with halofuginone from 4 weeks to 5 months of age reduced muscle fibrosis in a phosphorylated-Smad3 inhibition-related manner. Halofuginone also enhanced myofiber hypertrophy, reduced the percentage of centrally nucleated myofibers, and increased muscle performance. Together, the data suggest an inhibitory effect of halofuginone on the muscle histopathology at very early stages of dysferlinopathy, and enhancement of muscle performance. These results offer new opportunities for early pharmaceutical treatment in dysferlinopathies with favorable outcomes at later stages of life.

Dysferlin-deficiency has greater impact on function of slow muscles, compared with fast, in aged BLAJ mice

Dysferlinopathies are a form of muscular dystrophy caused by gene mutations resulting in deficiency of the protein dysferlin. Symptoms manifest later in life in a muscle specific manner, although the pathomechanism is not well understood. This study compared the impact of dysferlin-deficiency on in vivo and ex vivo muscle function, and myofibre type composition in slow (soleus) and fast type (extensor digitorum longus; EDL) muscles using male dysferlin-deficient (dysf^-/-) BLAJ mice aged 10 months, compared with wild type (WT) C57Bl/6J mice. There was a striking increase in muscle mass of BLAJ soleus (+25%) (p<0.001), with no strain differences in EDL mass, compared with WT. In vivo measures of forelimb grip strength and wheel running capacity showed no strain differences. Ex vivo measures showed the BLAJ soleus had faster twitch contraction (-21%) and relaxation (-20%) times, and delayed post fatigue recovery (ps<0.05); whereas the BLAJ EDL had a slower relaxation time (+11%) and higher maximum rate of force production (+25%) (ps<0.05). Similar proportions of MHC isoforms were evident in the soleus muscles of both strains (ps>0.05); however, for the BLAJ EDL, there was an increased proportion of type IIx MHC isoform (+5.5%) and decreased type IIb isoform (-5.5%) (ps<0.01). This identification of novel differences in the impact of dysferlin-deficiency on slow and fast twitch muscles emphasises the importance of evaluating myofibre type specific effects to provide crucial insight into the mechanisms responsible for loss of function in dysferlinopathies; this is critical for the development of targeted future clinical therapies.

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.

An update on diagnostic options and considerations in limb-girdle dystrophies

INTRODUCTION

Limb-girdle muscular dystrophies (LGMDs) encompass a clinically heterogeneous group of rare, genetic progressive muscle disorders presenting with weakness and atrophy of predominant pelvic and shoulder muscles. The spectrum of disease severity ranges from severe childhood-onset muscular dystrophy to adult-onset dystrophy. Areas covered: The review presents an update of the clinical phenotypes and diagnostic options for LGMD including both dominant and recessive LGMD and consider their differential clinical and histopathological features. An overview of most common phenotypes and of possible complications is given. The management of the main clinical respiratory, cardiac, and central nervous system complications are covered. The instrumental, muscle imaging, and laboratory exams to assess and reach diagnosis are described. The use of recent genetic techniques such as next generation sequencing (NGS), whole-exome sequencing compared to other techniques (e.g. DNA sequencing, protein analysis) is covered. Currently available drugs or gene therapy and rehabilitation management are focused on. Expert commentary: Many LGMD cases, which for a long time previously remained without a molecular diagnosis, can now be investigated by NGS. Gene mutation analysis is always required to obtain a certain molecular diagnosis, fundamental to select homogeneous group of patients for future pharmaceutical and gene trials.

Systemic Delivery of Dysferlin Overlap Vectors Provides Long-Term Gene Expression and Functional Improvement for Dysferlinopathy

Dysferlinopathies comprise a family of disorders caused by mutations in the dysferlin (DYSF) gene, leading to a progressive dystrophy characterized by chronic muscle fiber loss, fat replacement, and fibrosis. To correct the underlying histopathology and function, expression of full-length DYSF is required. Dual adeno-associated virus vectors have been developed, defined by a region of homology, to serve as a substrate for reconstitution of the full 6.5 kb dysferlin cDNA. Previous work studied the efficacy of this treatment through intramuscular and regional delivery routes. To maximize clinical efficacy, dysferlin-deficient mice were treated systemically to target all muscles through the vasculature for efficacy and safety studies. Mice were evaluated at multiple time points between 4 and 13 months post treatment for dysferlin expression and functional improvement using magnetic resonance imaging and magnetic resonance spectroscopy and membrane repair. A systemic dose of 6 × 1012 vector genomes resulted in widespread gene expression in the muscles. Treated muscles showed a significant decrease in central nucleation, collagen deposition, and improvement of membrane repair to wild-type levels. Treated gluteus muscles were significantly improved compared to placebo-treated muscles and were equivalent to wild type in volume, intra- and extramyocellular lipid accumulation, and fat percentage using magnetic resonance imaging and magnetic resonance spectroscopy. Dual-vector treatment allows for production of full-length functional dysferlin with no toxicity. This confirms previous safety data and validates translation of systemic gene delivery for dysferlinopathy patients.

Muscle Cells Fix Breaches by Orchestrating a Membrane Repair Ballet

Skeletal muscle undergoes many micro-membrane lesions at physiological state. Based on their sizes and magnitude these lesions are repaired via different complexes on a specific spatio-temporal manner. One of the major repair complex is a dysferlin-dependent mechanism. Accordingly, mutations in the DYSF gene encoding dysferlin results in the development of several muscle pathologies called dysferlinopathies, where abnormalities of the membrane repair process have been characterized in patients and animal models. Recent efforts have been deployed to decipher the function of dysferlin, they shed light on its direct implication in sarcolemma resealing after injuries. These discoveries served as a strong ground to design therapeutic approaches for dysferlin-deficient patients. This review detailed the different partners and function of dysferlin and positions the sarcolemma repair in normal and pathological conditions.

A novel mutation in the DYSF gene in a patient with a presumed inflammatory myopathy

Dysferlinopathy, a progressive muscular dystrophy, results from mutations in the Dysferlin gene (DYSF, MIM*603009). Traditional diagnosis relies on the reduction or absence of dysferlin. However, altered dysferlin has been observed in other myopathies, leading to a precise diagnosis through molecular genetics. In this study, we report a patient who was previously misdiagnosed as inflammatory myopathy based on routine clinicopathological examinations alone. However, muscle biopsy specimens were analyzed further by immunohistochemistry of muscular dystrophy-related proteins, and gene-targeted next generation sequencing (NGS) was used to correctly identify muscular dystrophy. DNA was sequenced with NGS and the detected mutation was verified by Sanger sequencing. Our targeted NGS found a novel missense mutation (c.5392G > A) in the DYSF gene, allowing correct diagnosis of LGMD2B in our patient. We discovered of a novel missense mutation in the DYSF gene and have broadened the DYSF mutation spectrum, which may be correlated in patients with presumed dysferlinopathy, especially when lymphocytic infiltration is observed.

Which nonautoimmune myopathies are most frequently misdiagnosed as myositis?

PURPOSE OF REVIEW

To discuss the spectrum of nonautoimmune myopathies that may be misdiagnosed as autoimmune myopathy.

RECENT FINDINGS

Inherited myopathies, such as dysferlinopathy, calpainopathy, and facioscapulohumeral dystrophy may be misdiagnosed as autoimmune myopathy, especially when they have inflammatory muscle biopsies. Inclusion body myositis is frequently misdiagnosed as polymyositis when rimmed vacuoles are absent on muscle biopsy, and a careful neuromuscular evaluation is not performed. Hypothyroid myopathy can be misdiagnosed as immune-mediated necrotizing myopathy if thyroid function tests, including a T4 level, are not obtained. Self-limited statin myopathy can be distinguished from statin-associated autoimmune myopathy because patients with the former do not have autoantibodies recognizing 3-hydroxy-3-methylglutaryl-coenzyme A reductase.

SUMMARY

Autoimmune myopathies can usually be distinguished from nonautoimmune myopathies based on a combination of the patient history, neuromuscular exam, laboratory findings, and/or muscle biopsy features.

Characterization of isolated amyloid myopathy

BACKGROUND AND PURPOSE

Amyloid myopathy frequently occurs in the setting of systemic amyloidosis and less commonly in isolation (isolated amyloid myopathy). Anoctaminopathy-5 and dysferlinopathy were recently recognized as causes of isolated amyloid myopathy. The present study aimed to characterize the isolated amyloid myopathy and to compare it with amyloid myopathy associated with systemic amyloidosis.

METHODS

We searched the Muscle Laboratory database to identify patients with pathologically confirmed amyloid myopathy seen in neurology clinics between January 1998 and September 2016. Patients with monoclonal gammopathy, peripheral neuropathy, organomegaly or symptoms or pathologic evidence of amyloid deposition outside skeletal muscle were classified as having systemic amyloidosis-associated myopathy.

RESULTS

Fifty-two patients were identified, including 14 with isolated amyloid myopathy (eight anoctaminopathy-5, two dysferlinopathy and four genetically unknown) and 38 with systemic amyloidosis (32 immunoglobulin light-chain amyloidosis, four familial amyloid polyneuropathy and two senile systemic amyloidosis). Compared with patients with systemic amyloidosis, patients with isolated amyloid myopathy had a younger age of onset (median, 41.5 vs. 65 years), no dysphagia (0% vs. 26%) or weight loss (0% vs. 26%), but more frequent calf atrophy (57% vs. 0%), small collections of inflammatory cells on muscle biopsy (43% vs. 0%) and asymptomatic hyperCKemia at onset (21% vs. 0%). All patients with isolated amyloid myopathy had creatine kinase (CK) values >2.5 times the upper limit of normal.

CONCLUSIONS

Isolated amyloid myopathy accounts for 27% of patients with amyloid myopathy, mostly due to anoctaminopathy-5. There are various clinical and laboratory parameters that can help to differentiate isolated amyloid myopathy from systemic amyloidosis.

Diagnosis and Management of Immune-Mediated Myopathies

Immune-mediated myopathies (IMMs) are a heterogeneous group of acquired muscle disorders characterized by muscle weakness, elevated creatine kinase levels, and myopathic electromyographic findings. Most IMMs feature the presence of inflammatory infiltrates in muscle. However, the inflammatory exudate may be absent. Indeed, necrotizing autoimmune myopathy (NAM), also called immune-mediated necrotizing myopathy, is characterized by a necrotizing pathologic process with no or minimal inflammation in muscle. The recent discovery of antibodies associated with specific subtypes of autoimmune myopathies has played a major role in characterizing these diseases. Although diagnostic criteria and classification of IMMs currently are under revision, on the basis of the clinical and muscle histopathologic findings, IMMs can be differentiated as NAM, inclusion body myositis (IBM), dermatomyositis, polymyositis, and nonspecific myositis. Because of recent developments in the field of NAM and IBM and the controversies around polymyositis, this review will focus on NAM, IBM, and dermatomyositis.

Dysferlin Gene Mutation Spectrum in a Large Cohort of Chinese Patients with Dysferlinopathy

BACKGROUND

Dysferlinopathy is caused by mutations in the dysferlin (DYSF) gene. Here, we described the genetic features of a large cohort of Chinese patients with this disease.

METHODS

Eighty-nine index patients were included in the study. DYSF gene analysis was performed by Sanger sequencing in 41 patients and targeted next generation sequencing (NGS) in 48 patients. Multiplex ligation-dependent probe amplification (MLPA) was performed to detect exon duplication/deletion in patients with only one pathogenic mutation.

RESULTS

Among the 89 index patients, 79 patients were demonstrated to carry two disease-causing (73 cases) or possibly disease-causing mutations (6 cases), including 26 patients with homozygous mutations. We identified 105 different mutations, including 59 novel ones. Notably, in 13 patients in whom only one pathogenic mutation was initially found by Sanger sequencing or NGS, 3 were further identified to carry exon deletions by MLPA. The mutations identified in this study appeared to cluster in the N-terminal region. Mutation types included missense mutations (30.06%), nonsense mutations (17.18%), frameshift mutations (30.67%), in-frame deletions (2.45%), intronic mutations (17.79%), and exonic rearrangement (1.84%). No genotype-phenotype correlation was identified.

CONCLUSIONS

DYSF mutations in Chinese patients clustered in the N-terminal region of the gene. Exonic rearrangements were found in 23% of patients with only one pathogenic mutation identified by Sanger sequencing or NGS. The novel mutations found in this study greatly expanded the mutational spectrum of dysferlinopathy.

Distal myopathy with ADSSL1 mutations in Korean patients

To understand the characteristics of ADSSL1 myopathy, we investigated the clinical manifestation in Korean patients with ADSSL1 mutations. We developed a targeted panel of 16 distal-myopathy genes and recruited a total of 12 patients with genetically undetermined distal myopathy. We found four (33%) with ADSSL1 mutations and one (8%) with GNE mutations. ADSSL1 mutations consisted of c.910G>A, c.1048delA and c.1220T>C mutations. Patients with ADSSL1 mutations demonstrated distal muscle weakness in adolescence, followed by quadriceps muscle weakness in the early 30s. All patients had mild facial weakness and two patients complained of easy fatigue while eating and chewing. Vastus lateralis muscle biopsies revealed non-specific chronic myopathic features with a few nemaline rods. Whole body muscle MR imaging showed more fatty replacement in the distal limb and tongue muscles than in the proximal limb and axial muscles. This study showed that ADSSL1 myopathy was not rare among distal myopathy patients of Korean origin, and expanded the clinical and genetic spectrum. Therefore, we suggest that the screening test of ADSSL1 gene should be considered for the diagnosis of distal myopathy.

Heterogeneous characteristics of MRI changes of thigh muscles in patients with dysferlinopathy

INTRODUCTION

The aim of this study was to evaluate the pattern of thigh muscle MRI changes in a large cohort of patients with dysferlinopathy.

METHODS

MRI of the thigh was performed in 60 patients. We correlated the scale of muscle involvement on MRI with the modified Gardner-Medwin and Walton (GM-W) scale and disease duration. We also analyzed the relationship between muscle changes and genetic mutations.

RESULTS

Fatty infiltration and edema were observed in 95.50% and 86.67% of patients, respectively. The hamstring muscles had the highest frequency and mean score of fatty infiltration, although a posterior-dominant pattern was found in only 56%. Edema most commonly and severely affected the quadriceps and adductor magnus muscles. Fatty infiltration score correlated positively with disease duration and GM-W scale.

CONCLUSIONS

The pattern of fatty infiltration was heterogeneous in dysferlinopathy patients. Muscle edema was common. Fatty infiltration can be used to assess disease progression. Muscle Nerve 54: 1072-1079, 2016.

Genetic Myopathies Initially Diagnosed and Treated as Inflammatory Myopathy

Objectives: Differentiating genetic myopathies from inflammatory myopathies can be challenging because of multiple overlapping clinical features. Examples are presented to highlight important clinical features that assist in the differentiation between the two. Methods: Clinical features including age at onset, history, pattern of weakness, serum creatine kinase activity, electromyography findings, and muscle biopsies are reported in six patients initially thought to have an inflammatory myopathy in whom the final diagnosis was a genetic myopathy. Results: All six patients met Bohan and Peter criteria for at least probable idiopathic polymyositis and were subsequently found to have a genetic myopathy (4 DYSF, RYR1, and GNE). The key distinguishing clinical were minimal to no response to immunosuppression and atypical involvement of distal muscles in the majority of cases. Conclusions: Patients diagnosed with inflammatory myopathies should be reevaluated for the possibility of a genetic myopathy if they fail to respond to a course of disease-modifying agents and/or there is atypical distal muscle involvement.

Dysferlinopathy in Switzerland: clinical phenotypes and potential founder effects

Background

Dysferlin is reduced in patients with limb girdle muscular dystrophy type 2B, Miyoshi myopathy, distal anterior compartment myopathy, and in certain Ethnic clusters.

Methods

We evaluated clinical and genetic patient data from three different Swiss Neuromuscular Centers.

Results

Thirteen patients from 6 non-related families were included. Age of onset was 18.8 ± 4.3 years. In all patients, diallelic disease-causing mutations were identified in the DYSF gene. Nine patients from 3 non-related families from Central Switzerland carried the identical homozygous mutation, c.3031 + 2T>C. A possible founder effect was confirmed by haplotype analysis. Three patients from two different families carried the heterozygous mutation, c.1064_1065delAA. Two novel mutations were identified (c.2869C>T (p.Gln957Stop), c.5928G>A (p.Trp1976Stop)).

Conclusions

Our study confirms the phenotypic heterogeneity associated with DYSF mutations. Two mutations (c.3031 + 2T>C, c.1064_1065delAA) appear common in Switzerland. Haplotype analysis performed on one case (c. 3031 + 2T>C) suggested a possible founder effect.

Upregulated IL-1β in dysferlin-deficient muscle attenuates regeneration by blunting the response to pro-inflammatory macrophages

BACKGROUND

Loss-of-function mutations in the dysferlin gene (DYSF) result in a family of muscle disorders known collectively as the dysferlinopathies. Dysferlin-deficient muscle is characterized by inflammatory foci and macrophage infiltration with subsequent decline in muscle function. Whereas macrophages function to remove necrotic tissue in acute injury, their prevalence in chronic myopathy is thought to inhibit resolution of muscle regeneration. Two major classes of macrophages, classical (M1) and alternative (M2a), play distinct roles during the acute injury process. However, their individual roles in chronic myopathy remain unclear and were explored in this study.

METHODS

To test the roles of the two macrophage phenotypes on regeneration in dysferlin-deficient muscle, we developed an in vitro co-culture model of macrophages and muscle cells. We assayed the co-cultures using ELISA and cytokine arrays to identify secreted factors and performed transcriptome analysis of molecular networks induced in the myoblasts.

RESULTS

Dysferlin-deficient muscle contained an excess of M1 macrophage markers, compared with WT, and regenerated poorly in response to toxin injury. Co-culturing macrophages with muscle cells showed that M1 macrophages inhibit muscle regeneration whereas M2a macrophages promote it, especially in dysferlin-deficient muscle cells. Examination of soluble factors released in the co-cultures and transcriptome analysis implicated two soluble factors in mediating the effects: IL-1β and IL-4, which during acute injury are secreted from M1 and M2a macrophages, respectively. To test the roles of these two factors in dysferlin-deficient muscle, myoblasts were treated with IL-4, which improved muscle differentiation, or IL-1β, which inhibited it. Importantly, blockade of IL-1β signaling significantly improved differentiation of dysferlin-deficient cells.

CONCLUSIONS

We propose that the inhibitory effects of M1 macrophages on myogenesis are mediated by IL-1β signals and suppression of the M1-mediated immune response may improve muscle regeneration in dysferlin deficiency. Our studies identify a potential therapeutic approach to promote muscle regeneration in dystrophic muscle.

Targeted next-generation sequencing for the genetic diagnosis of dysferlinopathy

Dysferlinopathy comprises a group of autosomal recessive muscular dystrophies caused by mutations in the DYSF gene. Due to the large size of the gene and its lack of mutational hot spots, analysis of the DYSF gene is time-consuming and laborious using conventional sequencing methods. By next-generation sequencing (NGS), DYSF gene analysis has previously been validated through its incorporation in multi-gene panels or exome analyses. However, individual validation of NGS approaches for DYSF gene has not been performed. Here, we established and validated a hybridization capture-based target-enrichment followed by next-generation sequencing to detect mutations in patients with dysferlinopathy. With this approach, mean depth of coverage was approximately 450 fold and almost all (99.3%) of the targeted region had sequence coverage greater than 20 fold. When this approach was tested on samples from patients with known DYSF mutations, all known mutations were correctly retrieved. Using this method on 32 consecutive patient samples with dysferlinopathy, at least two pathogenic variants were detected in 28 (87.5%) samples and at least one pathogenic variant was identified in all samples. Our results suggested that the NGS-based screening method could facilitate efficient and accurate genetic diagnosis of dysferlinopathy.

Altered cross-bridge properties in skeletal muscle dystrophies

Force and motion generated by skeletal muscle ultimately depends on the cyclical interaction of actin with myosin. This mechanical process is regulated by intracellular Ca²⁺ through the thin filament-associated regulatory proteins i.e.; troponins and tropomyosin. Muscular dystrophies are a group of heterogeneous genetic affections characterized by progressive degeneration and weakness of the skeletal muscle as a consequence of loss of muscle tissue which directly reduces the number of potential myosin cross-bridges involved in force production. Mutations in genes responsible for skeletal muscle dystrophies (MDs) have been shown to modify the function of contractile proteins and cross-bridge interactions. Altered gene expression or RNA splicing or post-translational modifications of contractile proteins such as those related to oxidative stress, may affect cross-bridge function by modifying key proteins of the excitation-contraction coupling. Micro-architectural change in myofilament is another mechanism of altered cross-bridge performance. In this review, we provide an overview about changes in cross-bridge performance in skeletal MDs and discuss their ultimate impacts on striated muscle function.

Quantitation of the calcium and membrane binding properties of the C2 domains of dysferlin

Dysferlin is a large membrane protein involved in calcium-triggered resealing of the sarcolemma after injury. Although it is generally accepted that dysferlin is Ca(2+) sensitive, the Ca(2+) binding properties of dysferlin have not been characterized. In this study, we report an analysis of the Ca(2+) and membrane binding properties of all seven C2 domains of dysferlin as well as a multi-C2 domain construct. Isothermal titration calorimetry measurements indicate that all seven dysferlin C2 domains interact with Ca(2+) with a wide range of binding affinities. The C2A and C2C domains were determined to be the most sensitive, with Kd values in the tens of micromolar, whereas the C2D domain was least sensitive, with a near millimolar Kd value. Mutagenesis of C2A demonstrates the requirement for negatively charged residues in the loop regions for divalent ion binding. Furthermore, dysferlin displayed significantly lower binding affinity for the divalent cations magnesium and strontium. Measurement of a multidomain construct indicates that the solution binding affinity does not change when C2 domains are linked. Finally, sedimentation assays suggest all seven C2 domains bind lipid membranes, and that Ca(2+) enhances but is not required for interaction. This report reveals for the first time, to our knowledge, that all dysferlin domains bind Ca(2+) albeit with varying affinity and stoichiometry.

An analysis of the sensitivity and specificity of MHC-I and MHC-II immunohistochemical staining in muscle biopsies for the diagnosis of inflammatory myopathies

Although there have been several previous reports of immunohistochemical staining for MHC antigens in muscle biopsies, there appears to be a lack of consensus about its routine use in the diagnostic evaluation of biopsies from patients with suspected inflammatory myopathy. Positive MHC-I staining is nonspecific but is widely used as a marker for inflammatory myopathy, whilst the role of MHC-II staining is not clearly defined. We investigated the sensitivity and specificity of MHC-I and MHC-II immunostaining for the diagnosis of inflammatory myopathy in a large group of biopsies from a single reference laboratory. Positive staining for MHC-I was found to have a high sensitivity in biopsies from patients with inflammatory myopathy but a very low specificity, as it was also common in other non-inflammatory myopathies and neurogenic disorders. On the other hand, MHC-II positivity had a much higher specificity in all major subgroups of inflammatory myopathy, especially inclusion body myositis. The findings indicate that the combination of MHC-I and MHC-II staining results in a higher degree of specificity for the diagnosis of inflammatory myopathy and that in biopsies with inflammation, positive MHC-II staining strongly supports the diagnosis of an immune-mediated myopathy. We recommend that immunohistochemical staining for both MHC-I and MHC-II should be included routinely in the diagnostic evaluation of muscle biopsies from patients with suspected inflammatory myopathy. However, as the sensitivity and interpretation of MHC staining may depend on the technique used, further studies are needed to compare procedures in different centres and develop standardised protocols.