Two zebrafish cacna1s loss-of-function variants provide models of mild and severe CACNA1S-related myopathy.

CACNA1S-related myopathy, due to pathogenic variants in the CACNA1S gene, is a recently described congenital muscle disease. Disease associated variants result in loss of gene expression and/or reduction of Cav1.1 protein stability. There is an incomplete understanding of the underlying disease pathomechanisms and no effective therapies are currently available. A barrier to the study of this myopathy is the lack of a suitable animal model that phenocopies key aspects of the disease. To address this barrier, we generated knockouts of the two zebrafish CACNA1S paralogs, cacna1sa and cacna1sb. Double knockout fish exhibit severe weakness and early death, and are characterized by the absence of Cav1.1 α1 subunit expression, abnormal triad structure, and impaired excitation-contraction coupling, thus mirroring the severe form of human CACNA1S-related myopathy. A double mutant (cacna1sa homozygous, cacna1sb heterozygote) exhibits normal development, but displays reduced body size, abnormal facial structure, and cores on muscle pathologic examination, thus phenocopying the mild form of human CACNA1S-related myopathy. In summary, we generated and characterized the first cacna1s zebrafish loss-of-function mutants, and show them to be faithful models of severe and mild forms of human CACNA1S-related myopathy suitable for future mechanistic studies and therapy development.

Mechanochemical consequences of myopathy-linked mutations in Tpm2.2 on striated muscle contractility.

Tropomyosin (Tpm) is an actin-binding protein central to muscle contraction regulation. The Tpm sequence consists of periodic repeats corresponding to seven actin-binding sites, further divided in two functionally distinct halves. To clarify the importance of the first and second halves of the actin-binding periods in regulating the interaction of myosin with actin, we introduced hypercontractile mutations D20H, E181K located in the N-terminal halves of periods 1 and 5 and hypocontractile mutations E41K, N202K located in the C-terminal halves of periods 1 and 5 of the skeletal muscle Tpm isoform Tpm2.2. Wild-type and mutant Tpms displayed similar actin-binding properties, however, as revealed by FRET experiments, the hypercontractile mutations affected the binding geometry and orientation of Tpm2.2 on actin, causing a stimulation of myosin motor performance. Contrary, the hypocontractile mutations led to an inhibition of both, actin activation of the myosin ATPase and motor activity, that was more pronounced than with wild-type Tpm2.2. Single ATP turnover kinetic experiments indicate that the introduced mutations have opposite effects on product release kinetics. While the hypercontractile Tpm2.2 mutants accelerated product release, the hypocontractile mutants decelerated product release from myosin, thus having either an activating or inhibitory influence on myosin motor performance, which agrees with the muscle disease phenotypes caused by these mutations.

BIN1 modulation in vivo rescues dynamin-related myopathy.

The mechanoenzyme dynamin 2 (DNM2) is crucial for intracellular organization and trafficking. DNM2 is mutated in dominant centronuclear myopathy (DNM2-CNM), a muscle disease characterized by defects in organelle positioning in myofibers. It remains unclear how the in vivo functions of DNM2 are regulated in muscle. Moreover, there is no therapy for DNM2-CNM to date. Here, we overexpressed human amphiphysin 2 (BIN1), a membrane remodeling protein mutated in other CNM forms, in Dnm2RW/+ and Dnm2RW/RW mice modeling mild and severe DNM2-CNM, through transgenesis or with adeno-associated virus (AAV). Increasing BIN1 improved muscle atrophy and main histopathological features of Dnm2RW/+ mice and rescued the perinatal lethality and survival of Dnm2RW/RW mice. In vitro experiments showed that BIN1 binds and recruits DNM2 to membrane tubules, and that the BIN1-DNM2 complex regulates tubules fission. Overall, BIN1 is a potential therapeutic target for dominant centronuclear myopathy linked to DNM2 mutations.

MTM1 overexpression prevents and reverts BIN1-related centronuclear myopathy.

Centronuclear and myotubular myopathies (CNM) are rare and severe genetic diseases associated with muscle weakness and atrophy as well as intracellular disorganization of myofibres. The main mutated proteins control lipid and membrane dynamics and are the lipid phosphatase myotubularin (MTM1), and the membrane remodelling proteins amphiphysin 2 (BIN1) and dynamin 2 (DNM2). There is no available therapy. Here, to validate a novel therapeutic strategy for BIN1- and DNM2-CNM, we evaluated adeno-associated virus-mediated MTM1 (AAV-MTM1 ) overexpression in relevant mouse models. Early systemic MTM1 overexpression prevented the development of the CNM pathology in Bin1mck-/- mice, while late intramuscular MTM1 expression partially reverted the established phenotypes after only 4 weeks of treatment. However, AAV-MTM1 injection did not change the DNM2-CNM mouse phenotypes. We investigated the mechanism of the rescue of the myopathy in BIN1-CNM and found that the lipid phosphatase activity of MTM1 was essential for the rescue of muscle atrophy and myofibre hypotrophy but dispensable for the rescue of myofibre disorganization including organelle mis-position and T-tubule defects. Furthermore, the improvement of T-tubule organization correlated with normalization of key regulators of T-tubule morphogenesis, dysferlin and caveolin. Overall, these data support the inclusion of BIN1-CNM patients in an AAV-MTM1 clinical trial.

Tamoxifen improves muscle structure and function of Bin1- and Dnm2-related centronuclear myopathies.

Congenital myopathies define a genetically heterogeneous group of disorders associated with severe muscle weakness, for which no therapies are currently available. Here we investigated the repurposing of tamoxifen in mouse models of mild or severe forms of centronuclear myopathies due to mutations in BIN1 (encoding amphiphysin 2) or DNM2 (encoding dynamin 2), respectively. Exposure to a tamoxifen-enriched diet from 3 weeks of age resulted in significant improvement in muscle contractility without increase in fibre size in both models, underlying an increase in the capacity of the muscle fibres to produce more force. In addition, the histological alterations were fully rescued in the BIN1-centronuclear myopathies mouse model. To assess the mechanism of the rescue, transcriptome analyses and targeted protein studies were performed. Although tamoxifen is known to modulate the transcriptional activity of the oestrogen receptors, correction of the disease transcriptomic signature was marginal on tamoxifen treatment. Conversely, tamoxifen lowered the abnormal increase in dynamin 2 protein level in both centronuclear myopathies models. Of note, it was previously reported that dynamin 2 increase is a main pathological cause of centronuclear myopathies. The Akt/mTOR muscle hypertrophic pathway and protein markers of the ubiquitin-proteasome system (the E3 ubiquitin ligase cullin 3) and autophagy (p62) were increased in both models of centronuclear myopathies. Normalization of dynamin 2 level mainly correlated with the normalization of cullin 3 protein level on tamoxifen treatment, supporting the idea that the ubiquitin-proteasome system is a main target for the tamoxifen effect in the amelioration of these diseases. Overall, our data suggest that tamoxifen antagonizes disease development probably through dynamin 2 level regulation. In conclusion, the beneficial effect of tamoxifen on muscle function supports the suggestion that tamoxifen may serve as a common therapy for several autosomal forms of centronuclear myopathies.

The emerging spectrum of fetal acetylcholine receptor antibody-related disorders (FARAD).

In utero exposure to maternal antibodies targeting the fetal acetylcholine receptor isoform (fAChR) can impair fetal movement, leading to arthrogryposis multiplex congenita (AMC). Fetal AChR antibodies have also been implicated in apparently rare, milder myopathic presentations termed fetal acetylcholine receptor inactivation syndrome (FARIS). The full spectrum associated with fAChR antibodies is still poorly understood. Moreover, since some mothers have no myasthenic symptoms, the condition is likely underreported, resulting in failure to implement effective preventive strategies. Here we report clinical and immunological data from a multicentre cohort (n = 46 cases) associated with maternal fAChR antibodies, including 29 novel and 17 previously reported with novel follow-up data. Remarkably, in 50% of mothers there was no previously established myasthenia gravis (MG) diagnosis. All mothers (n = 30) had AChR antibodies and, when tested, binding to fAChR was often much greater than that to the adult AChR isoform. Offspring death occurred in 11/46 (23.9%) cases, mainly antenatally due to termination of pregnancy prompted by severe AMC (7/46, 15.2%), or during early infancy, mainly from respiratory failure (4/46, 8.7%). Weakness, contractures, bulbar and respiratory involvement were prominent early in life, but improved gradually over time. Facial (25/34; 73.5%) and variable peripheral weakness (14/32; 43.8%), velopharyngeal insufficiency (18/24; 75%) and feeding difficulties (16/36; 44.4%) were the most common sequelae in long-term survivors. Other unexpected features included hearing loss (12/32; 37.5%), diaphragmatic paresis (5/35; 14.3%), CNS involvement (7/40; 17.5%) and pyloric stenosis (3/37; 8.1%). Oral salbutamol used empirically in 16/37 (43.2%) offspring resulted in symptom improvement in 13/16 (81.3%). Combining our series with all previously published cases, we identified 21/85 mothers treated with variable combinations of immunotherapies (corticosteroids/intravenous immunoglobulin/plasmapheresis) during pregnancy either for maternal MG symptom control (12/21 cases) or for fetal protection (9/21 cases). Compared to untreated pregnancies (64/85), maternal treatment resulted in a significant reduction in offspring deaths (P < 0.05) and other complications, with treatment approaches involving intravenous immunoglobulin/ plasmapheresis administered early in pregnancy most effective. We conclude that presentations due to in utero exposure to maternal (fetal) AChR antibodies are more common than currently recognized and may mimic a wide range of neuromuscular disorders. Considering the wide clinical spectrum and likely diversity of underlying mechanisms, we propose 'fetal acetylcholine receptor antibody-related disorders' (FARAD) as the most accurate term for these presentations. FARAD is vitally important to recognize, to institute appropriate management strategies for affected offspring and to improve outcomes in future pregnancies. Oral salbutamol is a symptomatic treatment option in survivors.

Marked neuropsychiatric involvement and dysmorphic features in nemaline myopathy.

BACKGROUND: Inherited nemaline myopathy is one of the most common congenital myopathies. This genetically heterogeneous disease is defined by the presence of nemaline bodies in muscle biopsy. The phenotypic spectrum is wide and cognitive involvement has been reported, although not extensively evaluated. METHODS: We report two nemaline myopathy patients presenting pronounced central nervous system involvement leading to functional compromise and novel facial and skeletal dysmorphic findings, possibly expanding the disease phenotype. RESULTS: One patient had two likely pathogenic NEB variants, c.2943G > A and c.8889 + 1G > A, and presented cognitive impairment and dysmorphic features, and the other had one pathogenic variant in ACTA1, c.169G > C (p.Gly57Arg), presenting autism spectrum disorder and corpus callosum atrophy. Both patients had severe cognitive involvement despite milder motor dysfunction. CONCLUSION: We raise the need for further studies regarding the role of thin filament proteins in the central nervous system and for a systematic cognitive assessment of congenital myopathy patients.

Myosin post-translational modifications and function in the presence of myopathy-linked truncating MYH2 mutations.

Congenital myopathies are a vast group of genetic muscle diseases. Among the causes are mutations in the MYH2 gene resulting in truncated type IIa myosin heavy chains (MyHCs). The precise cellular and molecular mechanisms by which these mutations induce skeletal muscle symptoms remain obscure. Hence, in the present study, we aimed to explore whether such genetic defects would alter the presence as well as the post-translational modifications of MyHCs and the functionality of myosin molecules. For this, we dissected muscle fibers from four myopathic patients with MYH2 truncating mutations and from five human healthy controls. We then assessed 1) MyHCs presence/post-translational modifications using LC/MS; 2) relaxed myosin conformation and concomitant ATP consumption with a loaded Mant-ATP chase setup; 3) myosin activation with an unloaded in vitro motility assay; and 4) cellular force production with a myofiber mechanical setup. Interestingly, the type IIa MyHC with one additional acetylated lysine (Lys35-Ac) was present in the patients. This was accompanied by 1) a higher ATP demand of myosin heads in the disordered-relaxed conformation; 2) faster actomyosin kinetics; and 3) reduced muscle fiber force. Overall, our findings indicate that MYH2 truncating mutations impact myosin presence/functionality in human adult mature myofibers by disrupting the ATPase activity and actomyosin complex. These are likely important molecular pathological disturbances leading to the myopathic phenotype in patients.

Loss of function variants in DNAJB4 cause a myopathy with early respiratory failure.

DNAJ/HSP40 co-chaperones are integral to the chaperone network, bind client proteins and recruit them to HSP70 for folding. We performed exome sequencing on patients with a presumed hereditary muscle disease and no genetic diagnosis. This identified four individuals from three unrelated families carrying an unreported homozygous stop gain (c.856A > T; p.Lys286Ter), or homozygous missense variants (c.74G > A; p.Arg25Gln and c.785 T > C; p.Leu262Ser) in DNAJB4. Affected patients presented with axial rigidity and early respiratory failure requiring ventilator support between the 1st and 4th decade of life. Selective involvement of the semitendinosus and biceps femoris muscles was seen on MRI scans of the thigh. On biopsy, muscle was myopathic with angular fibers, protein inclusions and occasional rimmed vacuoles. DNAJB4 normally localizes to the Z-disc and was absent from muscle and fibroblasts of affected patients supporting a loss of function. Functional studies confirmed that the p.Lys286Ter and p.Leu262Ser mutant proteins are rapidly degraded in cells. In contrast, the p.Arg25Gln mutant protein is stable but failed to complement for DNAJB function in yeast, disaggregate client proteins or protect from heat shock-induced cell death consistent with its loss of function. DNAJB4 knockout mice had muscle weakness and fiber atrophy with prominent diaphragm involvement and kyphosis. DNAJB4 knockout muscle and myotubes had myofibrillar disorganization and accumulated Z-disc proteins and protein chaperones. These data demonstrate a novel chaperonopathy associated with DNAJB4 causing a myopathy with early respiratory failure. DNAJB4 loss of function variants may lead to the accumulation of DNAJB4 client proteins resulting in muscle dysfunction and degeneration.

A novel variant in the tropomyosin 3 gene presenting as an adult-onset distal myopathy - a case report.

BACKGROUND: We report a patient with a novel c.737 C > T variant (p.Ser246Leu) of the TPM3 gene presenting with adult-onset distal myopathy. CASE PRESENTATION: A 35-year-old Chinese male patient presented with a history of progressive finger weakness. Physical examination revealed differential finger extension weakness, together with predominant finger abduction, elbow flexion, ankle dorsiflexion and toe extension weakness. Muscle MRI showed disproportionate fatty infiltration of the glutei, sartorius and extensor digitorum longus muscles without significant wasting. Muscle biopsy and ultrastructural examination showed a non-specific myopathic pattern without nemaline or cap inclusions. Genetic sequencing revealed a novel heterozygous p.Ser246Leu variant (c.737C>T) of the TPM3 gene which is predicted to be pathogenic. This variant is located in the area of the TPM3 gene where the protein product interacts with actin at position Asp25 of actin. Mutations of TPM3 in these loci have been shown to alter the sensitivity of thin filaments to the influx of calcium ions. CONCLUSION: This report further expands the phenotypic spectrum of myopathies associated with TPM3 mutations, as mutations in TPM3 had not previously been reported with adult-onset distal myopathy. We also discuss the interpretation of variants of unknown significance in patients with TPM3 mutations and summarise the typical muscle MRI findings of patients with TPM3 mutations.

Defining and identifying satellite cell-opathies within muscular dystrophies and myopathies.

Muscular dystrophies and congenital myopathies arise from specific genetic mutations causing skeletal muscle weakness that reduces quality of life. Muscle health relies on resident muscle stem cells called satellite cells, which enable life-course muscle growth, maintenance, repair and regeneration. Such tuned plasticity gradually diminishes in muscle diseases, suggesting compromised satellite cell function. A central issue however, is whether the pathogenic mutation perturbs satellite cell function directly and/or indirectly via an increasingly hostile microenvironment as disease progresses. Here, we explore the effects on satellite cell function of pathogenic mutations in genes (myopathogenes) that associate with muscle disorders, to evaluate clinical and muscle pathological hallmarks that define dysfunctional satellite cells. We deploy transcriptomic analysis and comparison between muscular dystrophies and myopathies to determine the contribution of satellite cell dysfunction using literature, expression dynamics of myopathogenes and their response to the satellite cell regulator PAX7. Our multimodal approach extends current pathological classifications to define Satellite Cell-opathies: muscle disorders in which satellite cell dysfunction contributes to pathology. Primary Satellite Cell-opathies are conditions where mutations in a myopathogene directly affect satellite cell function, such as in Progressive Congenital Myopathy with Scoliosis (MYOSCO) and Carey-Fineman-Ziter Syndrome (CFZS). Primary satellite cell-opathies are generally characterised as being congenital with general hypotonia, and specific involvement of respiratory, trunk and facial muscles, although serum CK levels are usually within the normal range. Secondary Satellite Cell-opathies have mutations in myopathogenes that affect both satellite cells and muscle fibres. Such classification aids diagnosis and predicting probable disease course, as well as informing on treatment and therapeutic development.

X-Linked Myotubular Myopathy in a Female Patient with a Pathogenic Variant in the MTM1 Gene.

X-linked centronuclear myopathy is caused by pathogenic variants in the MTM1 gene, which encodes myotubularin, a phosphatidylinositol 3-phosphate (PI3P) phosphatase. This form of congenital myopathy predominantly affects males. This study presents a case of X-linked myotubular myopathy in a female carrier of a pathogenic c.1261-10A>G variant in the MTM1 gene.

Molecular Mechanisms of Deregulation of Muscle Contractility Caused by the R168H Mutation in TPM3 and Its Attenuation by Therapeutic Agents.

The substitution for Arg168His (R168H) in γ-tropomyosin (TPM3 gene, Tpm3.12 isoform) is associated with congenital muscle fiber type disproportion (CFTD) and muscle weakness. It is still unclear what molecular mechanisms underlie the muscle dysfunction seen in CFTD. The aim of this work was to study the effect of the R168H mutation in Tpm3.12 on the critical conformational changes that myosin, actin, troponin, and tropomyosin undergo during the ATPase cycle. We used polarized fluorescence microscopy and ghost muscle fibers containing regulated thin filaments and myosin heads (myosin subfragment-1) modified with the 1,5-IAEDANS fluorescent probe. Analysis of the data obtained revealed that a sequential interdependent conformational-functional rearrangement of tropomyosin, actin and myosin heads takes place when modeling the ATPase cycle in the presence of wild-type tropomyosin. A multistep shift of the tropomyosin strands from the outer to the inner domain of actin occurs during the transition from weak to strong binding of myosin to actin. Each tropomyosin position determines the corresponding balance between switched-on and switched-off actin monomers and between the strongly and weakly bound myosin heads. At low Ca2+, the R168H mutation was shown to switch some extra actin monomers on and increase the persistence length of tropomyosin, demonstrating the freezing of the R168HTpm strands close to the open position and disruption of the regulatory function of troponin. Instead of reducing the formation of strong bonds between myosin heads and F-actin, troponin activated it. However, at high Ca2+, troponin decreased the amount of strongly bound myosin heads instead of promoting their formation. Abnormally high sensitivity of thin filaments to Ca2+, inhibition of muscle fiber relaxation due to the appearance of the myosin heads strongly associated with F-actin, and distinct activation of the contractile system at submaximal concentrations of Ca2+ can lead to muscle inefficiency and weakness. Modulators of troponin (tirasemtiv and epigallocatechin-3-gallate) and myosin (omecamtiv mecarbil and 2,3-butanedione monoxime) have been shown to more or less attenuate the negative effects of the tropomyosin R168H mutant. Tirasemtiv and epigallocatechin-3-gallate may be used to prevent muscle dysfunction.

Contribution of muscle MRI for diagnosis of myopathy.

Inherited myopathies are a group of disease, which, although distinct from a genetic and prognostic point of view, can lead to non-specific clinical pictures due to phenotypic overlap. Acquired immuno-mediated myopathies may also pose the problem of clinically accurate etiological orientation. The assessment of fatty infiltration and pathological increase in water volume of the muscle contingent on whole-body muscle MRI is becoming increasingly important in aiding the initial diagnosis of inherited and acquired myopathies. MRI helps orientating the clinical diagnostic hypotheses thanks to the patterns of muscle involved (more or less specific according to the entities), which led to the development of decision-making algorithms proposed in the literature. The aim of this article is to specify the proper MRI protocol for the evaluation of myopathies and the basis of the interpretation and to provide a summary of the most frequently inherited and acquired myopathies described in the literature.

A Possible Case of Centronuclear Myopathy: A Case Report.

Congenital myopathies (CMs) are a group of diseases that primarily affect the muscle fiber, especially the contractile apparatus and the different components that condition its normal functioning. They present as muscle weakness and hypotonia at birth or during the first year of life. Centronuclear CM is characterized by a high incidence of nuclei located centrally and internally in muscle fibers. Clinical case: a 22-year-old male patient with symptoms of muscle weakness since early childhood, with difficulty in performing physical activity according to his age, with the presence of a long face, a waddling gait, and a global decrease in muscle mass. Electromyography was performed, showing a neurogenic pattern and not the expected myopathic one, neuroconduction with reduced amplitude of the motor potential of the peroneal nerve and axonal and myelin damage of the posterior tibial nerves. The microscopic study of the studied striated muscle fragments stained with hematoxylin-eosin and Masson's trichrome showed the presence of fibers with central nuclei, diagnosing CM. The patient meets most of the description for CM, with involvement of all striated muscles, although it is important to note the neurogenic pattern present in this case, due to the denervation of damaged muscle fibers, which contain terminal axonal segments. Neuroconduction shows the involvement of motor nerves, but with normal sensory studies, axonal polyneuropathy is unlikely, due to normal sensory potentials. Different pathological findings have been described depending on the mutated gene in this disease, but all coincide with the presence of fibers with central nuclei for diagnosis by this means, which is so important in institutions where it is not possible to carry out genetic studies, and allowing early specific treatment, according to the stage through which the patient passes.

KBTBD13 is a novel cardiomyopathy gene.

KBTBD13 variants cause nemaline myopathy type 6 (NEM6). The majority of NEM6 patients harbors the Dutch founder variant, c.1222C>T, p.Arg408Cys (KBTBD13 p.R408C). Although KBTBD13 is expressed in cardiac muscle, cardiac involvement in NEM6 is unknown. Here, we constructed pedigrees of three families with the KBTBD13 p.R408C variant. In 65 evaluated patients, 12% presented with left ventricle dilatation, 29% with left ventricular ejection fraction< 50%, 8% with atrial fibrillation, 9% with ventricular tachycardia, and 20% with repolarization abnormalities. Five patients received an implantable cardioverter defibrillator, three cases of sudden cardiac death were reported. Linkage analysis confirmed cosegregation of the KBTBD13 p.R408C variant with the cardiac phenotype. Mouse studies revealed that (1) mice harboring the Kbtbd13 p.R408C variant display mild diastolic dysfunction; (2) Kbtbd13-deficient mice have systolic dysfunction. Hence, (1) KBTBD13 is associated with cardiac dysfunction and cardiomyopathy; (2) KBTBD13 should be added to the cardiomyopathy gene panel; (3) NEM6 patients should be referred to the cardiologist.

Mutation update for the ACTN2 gene.

ACTN2 encodes alpha-actinin-2, a protein expressed in human cardiac and skeletal muscle. The protein, located in the sarcomere Z-disk, functions as a link between the anti-parallel actin filaments. This important structural protein also binds N-terminal titins, and thus contributes to sarcomere stability. Previously, ACTN2 mutations have been solely associated with cardiomyopathy, without skeletal muscle disease. Recently, however, ACTN2 mutations have been associated with novel congenital and distal myopathy. Previously reported variants are in varying locations across the gene, but the potential clustering effect of pathogenic locations is not clearly understood. Further, the genotype-phenotype correlations of these variants remain unclear. Here we review the previously reported ACTN2-related molecular and clinical findings and present an additional variant, c.1840-2A>T, that further expands the mutation and phenotypic spectrum. Our results show a growing body of clinical, genetic, and functional evidence, which underlines the central role of ACTN2 in the muscle tissue and myopathy. However, limited segregation and functional data are available to support the pathogenicity of most previously reported missense variants and clear-cut genotype-phenotype correlations are currently only demonstrated for some ACTN2-related myopathies.

Use of animal models to understand titin physiology and pathology.

In recent years, increasing attention has been paid to titin (TTN) and its mutations. Heterozygous TTN truncating variants (TTNtv) increase the risk of a cardiomyopathy. At the same time, TTNtv and few missense variants have been identified in patients with mainly recessive skeletal muscle diseases. The pathogenic mechanisms underlying titin-related diseases are still partly unknown. Similarly, the titin mechanical and functional role in the muscle contraction are far from being exhaustively clarified. In the last few years, several animal models carrying variants in the titin gene have been developed and characterized to study the structural and mechanical properties of specific titin domains or to mimic patients' mutations. This review describes the main animal models so far characterized, including eight mice models and three fish models (Medaka and Zebrafish) and discusses the useful insights provided by a thorough characterization of the cell-, tissue- and organism-phenotypes in these models.

An infant with congenital respiratory insufficiency and diaphragmatic paralysis: A novel BICD2 phenotype?

Monoallelic pathogenic variants in BICD2 are associated with autosomal dominant Spinal Muscular Atrophy Lower Extremity Predominant 2A and 2B (SMALED2A, SMALED2B). As part of the cellular vesicular transport, complex BICD2 facilitates the flow of constitutive secretory cargoes from the trans-Golgi network, and its dysfunction results in motor neuron loss. The reported phenotypes among patients with SMALED2A and SMALED2B range from a congenital onset disorder of respiratory insufficiency, arthrogryposis, and proximal or distal limb weakness to an adult-onset disorder of limb weakness and contractures. We report an infant with congenital respiratory insufficiency requiring mechanical ventilation, congenital diaphragmatic paralysis, decreased lung volume, and single finger camptodactyly. The infant displayed appropriate antigravity limb movements but had radiological, electrophysiological, and histopathological evidence of myopathy. Exome sequencing and long-read whole-genome sequencing detected a novel de novo BICD2 variant (NM_001003800.1:c.[1543G>A];[=]). This is predicted to encode p.(Glu515Lys); p.Glu515 is located in the coiled-coil 2 mutation hotspot. We hypothesize that this novel phenotype of diaphragmatic paralysis without clear appendicular muscle weakness and contractures of large joints is a presentation of BICD2-related disease.

Congenital myopathies in adults: A diagnosis not to overlook.

BACKGROUND: Congenital myopathies (CM) were traditionally classified according to the muscle histopathological features, but in recent years, molecular diagnosis has become increasingly important. CM may present a wide phenotype variability, and while adult-onset CM have been increasingly recognized, substantial diagnostic delays are still reported. OBJECTIVES: To describe a cohort of adult CM patients, including clinical, genetic, and histopathological features, and further characterize the subgroup of adult-diagnosed patients. MATERIALS AND METHODS: We performed a retrospective observational cohort study to characterize the CM patients evaluated in our adult Neuromuscular outpatient clinic, including the subgroup of adult-diagnosed patients. RESULTS: We identified 19 CM patients with compatible molecular and/or histological diagnoses, of which 14 were diagnosed in adulthood. Eleven adult-diagnosed patients had symptoms since childhood and 9 had a family history of myopathy. The median age of symptoms' onset was 4 years old and the median age at diagnosis was 37 years old. The most common causative gene was RYR1, followed by TTN and MYH7. Three patients had non-specific features on muscle biopsy, all diagnosed during adulthood. CONCLUSIONS: In our cohort, the majority of CM were diagnosed in adulthood, despite most having pediatric-onset symptoms and positive family history. The diagnostic delay may be associated with mild presentation, slow course, atypical muscle histology, and lack of awareness of adult-onset CM. Studies with larger populations are needed.