Related Myopathy Research Articles

Whole-body muscle magnetic resonance imaging in SEPN1-related myopathy shows a homogeneous and recognizable pattern.

The aim of this study was to delineate the spectrum of muscle involvement in patients with a myopathy due to mutations in SEPN1 (SEPN1-RM). Whole-body magnetic resonance imaging (WBMRI) was used in 9 patients using T1-weighted turbo spin-echo (T1-TSE) sequences and short tau inversion recovery (STIR) in 5 patients. Analysis of signal and volume abnormalities by T1-TSE sequences in 109 muscles showed a homogeneous pattern characterized by a recognizable combination of atrophy and signal abnormalities in selected muscles of the neck, trunk, pelvic girdle, and lower limbs. Severe wasting of sternocleidomastoid muscle and atrophy of semimembranosus were detected. Selective paraspinal, gluteus maximus, and thigh muscle involvement was also observed. The lower leg was less constantly affected. WBMRI scoring of altered signal and atrophy in muscle can be represented by heatmaps and is associated with a homogeneous, recognizable pattern in SEPN1-RM, distinct from other genetic muscle diseases.

Laminin α2 Deficiency-Related Muscular Dystrophy Mimicking Emery-Dreifuss andCollagen VI related Diseases.

Background: Laminin α2 deficient congenital muscular dystrophy, caused by mutations in the LAMA2 gene, is characterized by early muscle weakness associated with abnormal white matter signal on cerebral MRI. Objective: To report on 4 patients with LAMA2 gene mutations whose original clinical features complicated the diagnosis strategy. Methods: Clinical, electrophysiological, muscle imaging and histopathological data were retrospectively collected from all patients. DNA samples were analysed by next-generation sequencing or direct gene sequencing. Laminin α2 was analysed by western-blot and immunohistochemistry. Results: The four patients achieved independent walking. All had proximal muscle weakness with scapular winging and prominent joint contractures without peripheral neuropathy. During follow-up, two patients suffered from refractory epilepsy associated with brain leukoencephalopathy in one, polymicrogyria and lissencephaly without white matter changes in the other. In two patients, the distribution of fatty infiltration resembles that of collagen-VI related myopathies. Dilated cardiomyopathy contstartabstractwith conduction defects, suggestive of Emery-Dreifuss myopathy, emerged in two of them within the 4th decade. Molecular diagnosis remained elusive for many years. Finally, targeted capture-DNA sequencing unveiled the involvement of the LAMA2 gene in two families, and led us to further identify LAMA2 mutations in the remaining family using Sanger sequencing.Conclusions: This report extends the clinical and radiological features of partial Laminin α2 deficiency since patients showed atypical manifestations including dilated cardiomyopathy with conduction defects in 2, epilepsy in 2, one of whom also had sole cortical brain abnormalities. Importantly, clinical findings and muscle imaging initially pointed to collagen-VI related disorders and Emery-Dreifuss muscular dystrophy.

LAMA2-related myopathy: Frequency among congenital and limb-girdle muscular dystrophies.

Muscular dystrophy caused by LAMA2-gene mutations is an autosomal recessive disease typically presenting as a severe, early-onset congenital muscular dystrophy (CMD). However, milder cases with a limb-girdle type muscular dystrophy (LGMD) have been described. In this study, we assessed the frequency and phenotypic spectrum of LAMA2-related muscular dystrophy in CMD (n = 18) and LGMD2 (n = 128) cohorts identified in the last 15 years in eastern Denmark. The medical history, brain-MRI, muscle pathology, muscle laminin-α2 expression, and genetic analyses were assessed. Molecular genetics revealed 2 pathogenic LAMA2 mutations in 5 of 18 CMD and 3 of 128 LGMD patients, corresponding to a LAMA2-mutation frequency of 28% in the CMD and 2.3% in the LGMD cohorts, respectively. This study demonstrates a wide clinical spectrum of LAMA2-related muscular dystrophy and its prevalence in an LGMD2 cohort, which indicates that LAMA2 muscular dystrophy should be included in the LGMD2 nomenclature.

RYR1-related myopathies: a wide spectrum of phenotypes throughout life.

Although several recent studies have implicated RYR1 mutations as a common cause of various myopathies and the malignant hyperthermia susceptibility (MHS) trait, many of these studies have been limited to certain age groups, confined geographical regions or specific conditions. The aim of the present study was to investigate the full spectrum of RYR1-related disorders throughout life and to use this knowledge to increase vigilance concerning malignant hyperthermia. A retrospective cohort study was performed on the clinical, genetic and histopathological features of all paediatric and adult patients in whom an RYR1 mutation was detected in a national referral centre for both malignant hyperthermia and inherited myopathies (2008-2012). The cohort of 77 non-related patients (detection rate 28%) included both congenital myopathies with permanent weakness and 'induced' myopathies such as MHS and non-anaesthesia-related episodes of rhabdomyolysis or hyperCKemia, manifested throughout life and triggered by various stimuli. Sixty-one different mutations were detected, of which 24 were novel. Some mutations are present in both dominant (MHS) and recessive modes (congenital myopathy) of inheritance, even within families. Histopathological features included an equally wide spectrum, ranging from only subtle abnormalities to prominent cores. This broad range of RYR1-related disorders often presents to the general paediatric and adult neurologist. Its recognition is essential for genetic counselling and improving patients' safety during anaesthesia. Future research should focus on in vitro testing by the in vitro contracture test and functional characterization of the large number of RYR1 variants whose precise effects currently remain uncertain.

Deconditioning Or Myopathy? Inactivity Is The Predominant Correlate Of Low Muscle Oxidative Capacity In COPD

Low locomotor muscle oxidative capacity contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). It is debated whether low muscle oxidative capacity is due to disease related myopathy e.g. inflammation, hypoxia, smoking, reduced growth factors, or to deconditioning induced by physical inactivity. PURPOSE: To determine correlates of muscle oxidative capacity in a large group of smokers with and without COPD. METHODS: Current and former smokers with COPD (GOLD 1-4, n=10/11/6/8; 67±10 yr) and with normal spirometry (GOLD 0, n=36; 61±9 yr) from the COPDGene study volunteered. 7-day triaxial accelerometry estimated daily total energy expenditure (TEE), physical activity level (PAL), and number of steps. Near-infrared spectroscopy (NIRS) was used to determine resting gastrocnemius blood flow (BF), O2 consumption (VO2), O2 saturation, and vasoreactivity. Muscle oxidative capacity was measured by NIRS from the VO2 recovery rate constant (k, min-1), using 10 s light contractions followed by intermittent arterial occlusions: a greater k constitutes a greater oxidative capacity. Blood CRP, IL6, testosterone, TNFα, IGF1 and albumin were measured. Smoking history was assessed by questionnaire. RESULTS: There were no significant differences between subjects with and without COPD in resting muscle BF, VO2, or O2 saturation, vasoreactivity, current smoking, pack years of smoking, or any blood biomarker. k was ∼33% greater (p=0.001) in subjects with normal spirometry (2.0±0.8 min-1) compared to those with airflow obstruction (1.5±0.6 min-1). In univariable analysis, k was significantly (p<0.01) positively associated with TEE (r2=0.26), PAL (r2=0.17), FEV1 %pred (r2=0.09), and negatively with age (r2=0.06, p=0.03). In stepwise multivariable analysis, PAL and daily steps accounted for 34% of variance in k (p<0.001). CONCLUSIONS: Low muscle oxidative capacity was associated with physical inactivity, airflow obstruction and age. A greater fraction of the variance in muscle oxidative capacity was explained by physical inactivity than by disease severity. These data are consistent with the notion that deconditioning represents the predominant cause of muscle dysfunction in current and former smokers with and without COPD. Supported by NIH R01 HL089856, R01 HL089897; SNSF-Novartis P3SMP3_151705/1; UCLA CTSI UL1TR000124.

Utility of next generation sequencing in genetic diagnosis of early onset neuromuscular disorders

BackgroundNeuromuscular disorders are a clinically, pathologically, and genetically heterogeneous group. Even for the experienced clinician, an accurate diagnosis is often challenging due to the complexity of these disorders. Here, we...

Linker of nucleoskeleton and cytoskeleton (LINC) complex-mediated actin-dependent nuclear positioning orients centrosomes in migrating myoblasts

Myoblast migration is essential for muscle development and repair; however, the factors that contribute to the polarity of migrating myoblasts are relatively unknown. We find that randomly migrating C2C12 myoblasts orient their centrosomes in the direction of migration. Using wounded monolayers, we further show that centrosome orientation is stimulated by the serum factor lysophosphatidic acid (LPA) and involves the rearward movement of the nucleus while the centrosome is maintained at the cell centroid. The rate of nuclear movement correlated with that of actin retrograde flow and both cytochalasin D and blebbistatin prevented nuclear movement and centrosome orientation. Actin-dependent rearward nuclear movement in fibroblasts is mediated by assembly of nuclear membrane nesprin-2G and SUN2 LINC complexes into transmembrane actin-associated nuclear (TAN) lines anchored by A-type lamins and emerin. In C2C12 myoblasts, depletion of nesprin-2G, SUN2 or lamin A/C prevented nuclear movement and endogenous nesprin-2G and a chimeric GFP-mini-nesprin-2G formed TAN lines during nuclear movement. Depleting nesprin-2G strongly interfered with directed cell migration and reduced the efficiency of myoblast fusion into multinucleated myotubes. Our results show that nuclear movement contributes to centrosome orientation and polarity for efficient migration and fusion of myoblasts. Given that mutations in the genes encoding A-type lamins, nesprin-2 and SUN2 cause Emery-Dreifuss muscular dystrophy and related myopathies, our results have implications for understanding the mechanism of disease pathogenesis.

Muscle pathology patterns in possibly adjuvant related autoimmune/inflammatory syndrome (ASIA)

Growing evidence shows a link for biologically inert molecules, such as vaccine adjuvants and silicone implants, with the occurrence of autoimmunity-related disorders, defined as autoimmune/inflammatory syndrome induced by adjuvant-ASIA (1). Clinical conditions encompass siliconosis, the Gulf war syndrome, the macrophagic myofasciitis syndrome (MMF), post-vaccination phenomena and the spectrum of related syndromes is expanding (2). Involvement of skeletal muscle in ASIA is acknowledged in MMF, defined by long-term persistence of vaccine alum adjuvants within macrophages at sites of previous immunization. A few reports describe vaccine and silicone implants related autoimmune inflammatory myopathies (3). We carried out an immunopathological analysis of skeletal muscle biopsy in a case of MMF and two cases of possible ASIA myositis, chronologically subsequent to breast silicone implant. MMF showed the typical fascial/ perimysial macrophagic invasion, with no endomysial mononuclear infiltrates and fibral neolocalization of MHC-I complex restricted to the adjacency of macrophage deposits. The first myositis case presented with a subacute onset twenty years after an uneventful additive breast silicone implant. Endomysial inflammation, microangiopathy and multifocal fibral localization of MHC-II complex were observed. In the second patient, the onset of proximal weakness, myalgiae and a tenfold increase of creatinkinase levels occurred seven years after an unsuccessful additive mastoplasty, with rupture of prostheses and re-implantation three years later. Muscle biopsy, besides inflammation changes, showed peculiar myofibrillar disruption, with MHC-I reactive sarcoplasmic inclusions expressing several structural muscle proteins. Molecular pathogenesis of ASIA is yet undefined: genetical susceptibility is currently investigated (1,2). Due to the role of vaccines in medicine and the wide use of silicon medical devices, identification of their cause/effect link with autoimmunity is of great interest.

Endocrine Myopathies: Clinical Review

Endocrinopathy is generally associated with hormonally-mediated systemic disorders. Myopathy is a result of this association and sometimes can be the first manifestation of endocrine diseases. This condition generally misdiagnosed as weakness and diagnosis and treatment of endocrine diseases are delayed. Especially cushing’s disease, exogen glucocorticoid use, hypothyroidism, hyperaldesteronism and osteomalacia can mimic inflammatory myopathies clinically. Endocrine myopathies are group of disease which must be part of differential diagnosis who has proximal muscle weakness. Statin and glucocorticoid use come to the knowledge of physician because these are the most common cause of drug related proximal myopathy. While evaluating patient with proximal myopathy, thyroid function tests, vitamin D levels, parathyroid hormone must be measured and primary hyperaldesteronism work up when clinically suspicion occurs. Treatment of endocrine myopathies are based on correction of endocrine disorder

Phenotype of matrin-3-related distal myopathy in 16 German patients.

To characterize the phenotype of patients with distal myopathy with vocal cord and pharyngeal weakness due to the p.S85C mutation in the matrin-3 gene (MATR3, Mendelian Inheritance in Man 164015). Recently, it has been suggested that patients with this mutation may suffer from familial amyotrophic lateral sclerosis. Sixteen patients from 6 families with late onset distal myopathy associated with the p.S85C MATR3 mutation were characterized. Patients had a predominantly distal muscle weakness, most severely affecting ankle and wrist dorsiflexion. Relevant proximal and axial weakness was found in 6 and respiratory impairment in 5 patients. Dysphagia was diagnosed in 6 and mild voice abnormalities were found in 7 patients. However, laryngoscopy revealed normal vocal cord function. Creatine kinase was normal or mildly elevated. Electromyographically, spontaneous activity was found in 10 of 14 patients and complex repetitive discharges in 9 of 14 patients. Magnetic resonance imaging revealed severe fatty degeneration of distal and upper posterior leg and of paraspinal muscles. Histopathology ranged from mild myopathic to severe dystrophic changes including vacuoles. Absence of sarcomeres in the perinuclear region and abnormal invaginations of nuclei were found ultrastructurally. Haplotype analysis showed a common disease-specific haplotype of the 6 families and suggested that these families form a separate cluster. In contrast to the 2 previously reported families, MATR3-related distal myopathy might be associated with relevant axial, proximal, and respiratory muscle weakness but without vocal cord palsy. There were no clinical, electrophysiological, or histopathological signs of lower motor neuron involvement.

Muscular dystrophy-associated SUN1 and SUN2 variants disrupt nuclear-cytoskeletal connections and myonuclear organization.

Proteins of the nuclear envelope (NE) are associated with a range of inherited disorders, most commonly involving muscular dystrophy and cardiomyopathy, as exemplified by Emery-Dreifuss muscular dystrophy (EDMD). EDMD is both genetically and phenotypically variable, and some evidence of modifier genes has been reported. Six genes have so far been linked to EDMD, four encoding proteins associated with the LINC complex that connects the nucleus to the cytoskeleton. However, 50% of patients have no identifiable mutations in these genes. Using a candidate approach, we have identified putative disease-causing variants in the SUN1 and SUN2 genes, also encoding LINC complex components, in patients with EDMD and related myopathies. Our data also suggest that SUN1 and SUN2 can act as disease modifier genes in individuals with co-segregating mutations in other EDMD genes. Five SUN1/SUN2 variants examined impaired rearward nuclear repositioning in fibroblasts, confirming defective LINC complex function in nuclear-cytoskeletal coupling. Furthermore, myotubes from a patient carrying compound heterozygous SUN1 mutations displayed gross defects in myonuclear organization. This was accompanied by loss of recruitment of centrosomal marker, pericentrin, to the NE and impaired microtubule nucleation at the NE, events that are required for correct myonuclear arrangement. These defects were recapitulated in C2C12 myotubes expressing exogenous SUN1 variants, demonstrating a direct link between SUN1 mutation and impairment of nuclear-microtubule coupling and myonuclear positioning. Our findings strongly support an important role for SUN1 and SUN2 in muscle disease pathogenesis and support the hypothesis that defects in the LINC complex contribute to disease pathology through disruption of nuclear-microtubule association, resulting in defective myonuclear positioning.

G.P.270: A large genomic rearrangement affecting TPM3 causing severe nemaline myopathy

Using our self-designed NM-CGH microarray, which we have developed to identify large copy number variations in the currently known nine nemaline myopathy (NM) genes, we identified the first large (>20kb) aberration in the alpha-tropomyosin gene (<i>TPM3</i>). This homozygous mutation deletes the promoter as well as the muscle- specific exons 1 and 2 of <i>TPM3</i>. The promoter and exon 1 of the non-muscle isoform seem to be intact. The deletion also spans the micro-RNA-encoding <i>MIR190B</i> gene and the last two exons of the <i>C1orf189</i> gene upstream of <i>TPM3</i>. Our attempts to sequence the promoter and exon 1 of TPM3 have constantly failed, supporting the array result, showing an approximately 6kb deletion including the musclespecific exons 1 and 2 as well as regions upstream from the gene. Before analyzing the patient sample using our array, we had analyzed other NM genes including nebulin (<i>NEB</i>), in which we identified a heterozygous nonsense mutation in exon 42. No second mutation, however, was identified in <i>NEB</i> and this nonsense mutation likely has a modifying impact on the phenotype of the patient. We also performed whole-exome sequencing, but no other pathogenic mutations were revealed. The patient was born to consanguineous parents. He deceased at the age of approximately 1.5years. His biopsy confirmed the diagnosis of NM. Unfortunately, to date, no further clinical details are available. We have screened 250 samples from 185 NM and related myopathy families using the NM-CGH-array and identified nine large aberrations in <i>NEB</i> in nine families, but we have not detected such mutations in other NM genes except the one discussed here. Therefore large aberrations in known NM genes other than NEB are likely a very rare cause of NM. The NM-CGH microarray method is currently available for mutation analysis in our laboratory.

G.P.150: Clinical heterogeneity in adult forms of FHL1 related myopathies. The “Institut de Myologie” experience

FHL1 gene mutations are responsible for reducing body myopathy (RBM), a rare condition characterized by progressive muscle weakness and the presence of intracytoplasmic aggregates. Age at onset ranges from early onset in infancy, through childhood and in some cases adult age. FHL1 mutations may also lead to allelic disorders including Emery-Dreifuss like muscular dystrophy (EDMD), hypertrophic cardiomyopathy (HCM), X-linked myopathy with postural muscle atrophy and generalized hypertrophy (X-MPMA) and X-linked scapuloperoneal myopathy (X-SM). To report clinical, muscle imaging, histological and genetic features found of adult patients carrying FHL1 mutations, we retrospectively reviewed their medical reports of the 11 patients (6 M, 5 F) belonging to 8 families followed at the “Institute de Myologie”, Pitie-Salpetriere hospital, Paris. The 11 patients were assessed from 13 to 52 years old. Pseudodominant mode of inheritance was suggested in 4 families, X-linked in 3 and sporadic in one. Four had EDMD, 2 X-SM, 1 X-MPMA, 1 HCM while 2 patients had atypical features and 1 was still asymptomatic. When symptomatic, female patients had a striking asymmetric muscle involvement. Five patients had hypertrophic cardiomyopathy requiring heart transplantation in one patient at 18 years old. Two patients required night time ventilation due to diaphragm paralysis. Histologically, only 3 patients among the 8 probands had reducing bodies (RBs) at muscle biopsy, while 3 had non specific pattern, 1 had neuropathic pattern and one muscle biopsy was considered as normal. In contrast to infantile forms of FHL1 related myopathy that usually show RBs at muscle biopsy and lead to early death, adult forms had wider clinical and histological presentations. Moreover, FHL1 gene screening should be considered in those undiagnosed patients suffering from myopathies with diaphragm paralysis and/or HCM where X-linked inheritance is not excluded even in the absence of RBs at muscle pathology.

Col6a1 null mice as a model to study skin phenotypes in patients with collagen VI related myopathies: expression of classical and novel collagen VI variants during wound healing.

Patients suffering from collagen VI related myopathies caused by mutations in COL6A1, COL6A2 and COL6A3 often also display skin abnormalities, like formation of keloids or “cigarette paper” scars, dry skin, striae rubrae and keratosis pilaris (follicular keratosis). Here we evaluated if Col6a1 null mice, an established animal model for the muscle changes in collagen VI related myopathies, are also suitable for the study of mechanisms leading to the skin pathology. We performed a comprehensive study of the expression of all six collagen VI chains in unwounded and challenged skin of wild type and Col6a1 null mice. Expression of collagen VI chains is regulated in both skin wounds and bleomycin-induced fibrosis and the collagen VI α3 chain is proteolytically processed in both wild type and Col6a1 null mice. Interestingly, we detected a decreased tensile strength of the skin and an altered collagen fibril and basement membrane architecture in Col6a1 null mice, the latter being features that are also found in collagen VI myopathy patients. Although Col6a1 null mice do not display an overt wound healing defect, these mice are a relevant animal model to study the skin pathology in collagen VI related disease.

Pulmonary pathologic manifestations of anti-glycyl-tRNA synthetase (anti-EJ)-related inflammatory myopathy

AimsAntisynthetase syndromes are a subset of the idiopathic inflammatory myopathies characterised by the presence of autoantibodies to aminoacyl transfer-RNA synthetases (ARS) and monotypic clinical features including Raynaud phenomenon, fever, non-erosive...

Utility of optical facial feature and arm movement tracking systems to enable text communication in critically ill patients who cannot otherwise communicate

PurposePatients recovering from critical illness especially those with critical illness related neuropathy, myopathy, or burns to face, arms and hands are often unable to communicate by writing, speech (due to tracheostomy) or lip reading. This may frustrate both patient and staff.Two low cost movement tracking systems based around a laptop webcam and a laser/optical gaming system sensor were utilised as control inputs for on-screen text creation software and both were evaluated as communication tools in volunteers. MethodsTwo methods were used to control an on-screen cursor to create short sentences via an on-screen keyboard: (i) webcam-based facial feature tracking, (ii) arm movement tracking by laser/camera gaming sensor and modified software. 16 volunteers with simulated tracheostomy and bandaged arms to simulate communication via gross movements of a burned limb, communicated 3 standard messages using each system (total 48 per system) in random sequence. ResultsTen and 13 minor typographical errors occurred with each system respectively, however all messages were comprehensible. Speed of sentence formation ranged from 58 to 120s with the facial feature tracking system, and 60–160s with the arm movement tracking system. The average speed of sentence formation was 81s (range 58–120) and 104s (range 60–160) for facial feature and arm tracking systems respectively, (P<0.001, 2-tailed independent sample t-test). ConclusionBoth devices may be potentially useful communication aids in patients in general and burns critical care units who cannot communicate by conventional means, due to the nature of their injuries.

199th ENMC international workshop: FHL1 related myopathies, June 7–9, 2013, Naarden, The Netherlands

199th ENMC international workshop: FHL1 related myopathies, June 7–9, 2013, Naarden, The Netherlands

Muscle MRI in patients with long‐chain fatty acid oxidation disorders

Muscle magnetic resonance imaging (MRI) is a useful tool for visualizing abnormalities in neuromuscular disorders. The value of muscle MRI has not been studied in long-chain fatty acid oxidation (lcFAO) disorders. LcFAO disorders may present with metabolic myopathy including episodic rhabdomyolysis. To investigate whether lcFAO disorders are associated with muscle MRI abnormalities. Lower body MRI was performed in 20 patients with lcFAO disorders, i.e. three carnitine palmitoyltransferase 2 deficiency (CPT2D), 12 very long-chain acyl-CoA dehydrogenase deficiency (VLCADD), three mitochondrial trifunctional protein deficiency (MTPD) and two isolated long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). At the time of MRI, four patients had muscle weakness, 14 had muscle pain and 13 were exercise intolerant. Median creatine kinase (CK) level of patients at the day of MRI was 398 U/L (range 35-12,483). T1W and STIR signal intensity (SI) were markedly increased in MTPD patients from girdle to lower leg. VLCADD patients showed predominantly proximal T1W SI changes, whereas LCHADD patients mostly showed distal T1W SI changes. Prominent STIR weighted signal intensity increases of almost all muscle groups were observed in patients with VLCADD and LCHADD with very high CK (>11.000) levels. lcFAO disorders are associated with specific patterns of increased T1W and STIR signal intensity. These patterns may reflect lipid accumulation and inflammation secondary to lcFAO defects and progressive muscle damage. Future studies are needed to investigate whether muscle MRI might be a useful tool to monitor disease course and to study pathogenesis of lcFAO related myopathy.

P.15.2 Elucidating the mechanism of disease in BAG3 related myofibrillar myopathy

Myofibrillar myopathies are a group of chronic muscle diseases characterised at the cellular level by failure of the muscle fibre at the Z-disk and accumulation of protein aggregates. The vast majority of these diseases are late onset dominant disorders with symptoms typically evident between 35 and 50 years of age. Patients suffer progressive muscle weakness over many years and have reduced life expectancy due to respiratory muscle failure and cardiac complications. Whilst structural failure of the muscle fibre is a feature of myofibrillar myopathies not all of the proteins associated with myofibrillar myopathy have a structural role. Recently mutations in BAG3, a co-chaperone with no direct role in muscle function, were identified as a cause of this disorder. This discovery opened a new area of investigation into the role of chaperones in myopathies and the mechanism of disease in myofibrillar myopathy. In order to investigate the role of BAG3 in muscle development and disease we examined zebrafish lacking BAG3 and those with ectopic expression of GFP-tagged forms of either wildtype BAG3 or the dominant myofibrillar myopathy mutant form Bag3P209L. Examination of these fish identified both the fibre failure and the formation of protein aggregates characteristic of myofibrillar myopathy. Utilising the advantage of the zebrafish model system to examine the onset and progression of the phenotype in vivo, combined with detailed characterisation by immunolabelling and confocal microscopy, we were able to develop a novel model that explains the mechanism of disease in BAG3 related myofibrillar myopathy. We will present this model and discuss its implications for other forms of myofibrillar myopathy.

Recessive truncating titin gene, TTN , mutations presenting as centronuclear myopathy

To identify causative genes for centronuclear myopathies (CNM), a heterogeneous group of rare inherited muscle disorders that often present in infancy or early life with weakness and hypotonia, using next-generation sequencing of whole exomes and genomes. Whole-exome or -genome sequencing was performed in a cohort of 29 unrelated patients with clinicopathologic diagnoses of CNM or related myopathy depleted for cases with mutations of MTM1, DNM2, and BIN1. Immunofluorescence analyses on muscle biopsies, splicing assays, and gel electrophoresis of patient muscle proteins were performed to determine the molecular consequences of mutations of interest. Autosomal recessive compound heterozygous truncating mutations of the titin gene, TTN, were identified in 5 individuals. Biochemical analyses demonstrated increased titin degradation and truncated titin proteins in patient muscles, establishing the impact of the mutations. Our study identifies truncating TTN mutations as a cause of congenital myopathy that is reported as CNM. Unlike the classic CNM genes that are all involved in excitation-contraction coupling at the triad, TTN encodes the giant sarcomeric protein titin, which forms a myofibrillar backbone for the components of the contractile machinery. This study expands the phenotypic spectrum associated with TTN mutations and indicates that TTN mutation analysis should be considered in cases of possible CNM without mutations in the classic CNM genes.