CIAO1 loss of function causes a neuromuscular disorder with compromise of nucleocytoplasmic Fe-S enzymes.

Cytoplasmic and nuclear iron-sulfur (Fe-S) enzymes that are essential for genome maintenance and replication depend on the cytoplasmic Fe-S assembly (CIA) machinery for cluster acquisition. The core of the CIA machinery consists of a complex of CIAO1, MMS19 and FAM96B. The physiological consequences of loss of function in the components of the CIA pathway have thus far remained uncharacterized. Our study revealed that patients with biallelic loss of function in CIAO1 developed proximal and axial muscle weakness, fluctuating creatine kinase elevation, and respiratory insufficiency. In addition, they presented with CNS symptoms including learning difficulties and neurobehavioral comorbidities, along with iron deposition in deep brain nuclei, mild normocytic to macrocytic anemia, and gastrointestinal symptoms. Mutational analysis revealed reduced stability of the variants compared with WT CIAO1. Functional assays demonstrated failure of the variants identified in patients to recruit Fe-S recipient proteins, resulting in compromised activities of DNA helicases, polymerases, and repair enzymes that rely on the CIA complex to acquire their Fe-S cofactors. Lentivirus-mediated restoration of CIAO1 expression reversed all patient-derived cellular abnormalities. Our study identifies CIAO1 as a human disease gene and provides insights into the broader implications of the cytosolic Fe-S assembly pathway in human health and disease.

Effects of gene replacement therapy with resamirigene bilparvovec (AT132) on skeletal muscle pathology in X-linked myotubular myopathy: results from a substudy of the ASPIRO open-label clinical trial.

BACKGROUND: X-linked myotubular myopathy (XLMTM) is a rare, life-threatening congenital muscle disease caused by mutations in the MTM1 gene that result in profound muscle weakness, significant respiratory insufficiency, and high infant mortality. There is no approved disease-modifying therapy for XLMTM. Resamirigene bilparvovec (AT132; rAAV8-Des-hMTM1) is an investigational adeno-associated virus (AAV8)-mediated gene replacement therapy designed to deliver MTM1 to skeletal muscle cells and achieve long-term correction of XLMTM-related muscle pathology. The clinical trial ASPIRO (NCT03199469) investigating resamirigene bilparvovec in XLMTM is currently paused while the risk:benefit balance associated with this gene therapy is further investigated. METHODS: Muscle biopsies were taken before treatment and 24 and 48 weeks after treatment from ten boys with XLMTM in a clinical trial of resamirigene bilparvovec (ASPIRO; NCT03199469). Comprehensive histopathological analysis was performed. FINDINGS: Baseline biopsies uniformly showed findings characteristic of XLMTM, including small myofibres, increased internal or central nucleation, and central aggregates of organelles. Biopsies taken at 24 weeks post-treatment showed marked improvement of organelle localisation, without apparent increases in myofibre size in most participants. Biopsies taken at 48 weeks, however, did show statistically significant increases in myofibre size in all nine biopsies evaluated at this timepoint. Histopathological endpoints that did not demonstrate statistically significant changes with treatment included the degree of internal/central nucleation, numbers of triad structures, fibre type distributions, and numbers of satellite cells. Limited (predominantly mild) treatment-associated inflammatory changes were seen in biopsy specimens from five participants. INTERPRETATION: Muscle biopsies from individuals with XLMTM treated with resamirigene bilparvovec display statistically significant improvement in organelle localisation and myofibre size during a period of substantial improvements in muscle strength and respiratory function. This study identifies valuable histological endpoints for tracking treatment-related gains with resamirigene bilparvovec, as well as endpoints that did not show strong correlation with clinical improvement in this human study. FUNDING: Astellas Gene Therapies (formerly Audentes Therapeutics, Inc.).

Loss of Function of the Cytoplasmic Fe-S Assembly Protein CIAO1 Causes a Neuromuscular Disorder with Compromise of Nucleocytoplasmic Fe-S Enzymes.

Cytoplasmic and nuclear iron-sulfur enzymes that are essential for genome maintenance and replication depend on the cytoplasmic iron-sulfur assembly (CIA) machinery for cluster acquisition. Here we report that patients with biallelic loss of function in CIAO1 , a key CIA component, develop proximal and axial muscle weakness, fluctuating creatine kinase elevation and respiratory insufficiency. In addition, they present with CNS symptoms including learning difficulties and neurobehavioral comorbidities, along with iron deposition in deep brain nuclei, macrocytic anemia and gastrointestinal symptoms. Mutational analysis and functional assays revealed reduced stability of the variants compared to wild-type CIAO1. Loss of CIAO1 impaired DNA helicases, polymerases and repair enzymes which rely on the CIA complex to acquire their Fe-S cofactors, with lentiviral restoration reversing all patient-derived cellular abnormalities. Our study identifies CIAO1 as a novel human disease gene and provides insights into the broader implications of the iron-sulfur assembly pathway in human health and disease.

Troponin-T type 1 (TNNT1)-related nemaline myopathy: unique respiratory phenotype and muscle pathology findings.

Biallelic pathogenic variants in the troponin T type 1 (TNNT1) gene cause a severe form of congenital nemaline myopathy. Typical features include severe motor delay, proximal contractures and weakness, pectus carinatum, chest wall rigidity and tremor. If left untreated, respiratory failure leads to early death at a median age of 18 months. Here we report on three non-Amish, unrelated patients harbouring novel TNNT1 variants. The peculiar combination of respiratory muscle weakness and chest wall stiffness caused early severe hypoventilation warranting the use of high pressures on BiPAP ventilator, with subsequent rapid escalation of pressures delivered with limited efficacy secondary to the extreme rib cage stiffness. Severe respiratory impairment occurred despite a relatively milder motor involvement in one patient. Muscle biopsies from two individuals showed predominant involvement of type 1 fibres, abundant nemaline bodies, marked fibrosis and loss of TNNT1 protein. We aim to increase the awareness of the challenges of managing respiratory support in patients with this unique respiratory phenotype.

TRAPPC11-related muscular dystrophy with hypoglycosylation of alpha-dystroglycan in skeletal muscle and brain.

AIMS: TRAPPC11, a subunit of the transport protein particle (TRAPP) complex, is important for complex integrity and anterograde membrane transport from the endoplasmic reticulum (ER) to the ER-Golgi intermediate compartment. Several individuals with TRAPPC11 mutations have been reported with muscle weakness and other features including brain, liver, skeletal and eye involvement. A detailed analysis of brain and muscle pathology will further our understanding of the presentation and aetiology of TRAPPC11 disease. METHODS: We describe five cases of early-onset TRAPPC11-related muscular dystrophy with a systematic review of muscle pathology in all five individuals, post-mortem brain pathology findings in one and membrane trafficking assays in another. RESULTS: All affected individuals presented in infancy with muscle weakness, motor delay and elevated serum creatine kinase (CK). Additional features included cataracts, liver disease, intellectual disability, cardiomyopathy, movement disorder and structural brain abnormalities. Muscle pathology in all five revealed dystrophic changes, universal hypoglycosylation of alpha-dystroglycan and variably reduced dystrophin-associated complex proteins. Membrane trafficking assays showed defective Golgi trafficking in one individual. Neuropathological examination of one individual revealed cerebellar atrophy, granule cell hypoplasia, Purkinje cell (PC) loss, degeneration and dendrite dystrophy, reduced alpha-dystroglycan (IIH6) expression in PC and dentate neurones and absence of neuronal migration defects. CONCLUSIONS: This report suggests that recessive mutations in TRAPPC11 are linked to muscular dystrophies with hypoglycosylation of alpha-dystroglycan. The structural cerebellar involvement that we document for the first time resembles the neuropathology reported in N-linked congenital disorders of glycosylation (CDG) such as PMM2-CDG, suggesting defects in multiple glycosylation pathways in this condition.

Limb girdle muscular dystrophy R12 (LGMD 2L, anoctaminopathy) mimicking idiopathic inflammatory myopathy: key points to prevent misdiagnosis.

OBJECTIVES: Diagnosing the idiopathic inflammatory myopathies (IIMs) can be challenging as several conditions, including genetic myopathies such as limb girdle muscular dystrophy type R12 (LGMD 2 l, anoctaminopathy) mimic the presentation. Here we describe learning points identified from review of four patients with LGMD 2 l who were initially incorrectly diagnosed with IIM. Our aim is to provide clinicians working in adult rheumatology services with a toolkit to help identify non-inflammatory presentations of myopathy. METHODS: We performed retrospective review of medical notes, laboratory results, muscle imaging and histological findings of four patients with LGMD 2 l who were previously misdiagnosed with IIM. We focussed on clinical presentation and progression, therapeutic agents used and events leading to revision of the diagnosis. RESULTS: Three male patients and one female patient with a mean age of 51 years at presentation were reviewed. In each case, treatment with immunosuppressants, in one case for >15 years, was observed without a clear therapeutic response. All patients were negative for anti-nuclear antibodies and available myositis-associated/specific autoantibodies and associated connective tissue disease features were absent. Prominent fatty infiltration and selective muscle involvement on thigh MRI was found in common. CONCLUSIONS: Adult-onset genetic myopathies, particularly LGMD R12, can mimic IIM. Accurate diagnosis is crucial to avoid the use of potentially harmful immunosuppressive therapies, to allow appropriate genetic counselling and to facilitate involvement in research studies.

High-Throughput Digital Image Analysis Reveals Distinct Patterns of Dystrophin Expression in Dystrophinopathy Patients.

Duchenne muscular dystrophy (DMD) is an incurable disease caused by out-of-frame DMD gene deletions while in frame deletions lead to the milder Becker muscular dystrophy (BMD). In the last decade several antisense oligonucleotides drugs have been developed to induce a partially functional internally deleted dystrophin, similar to that produced in BMD, and expected to ameliorate the disease course. The pattern of dystrophin expression and functionality in dystrophinopathy patients is variable due to multiple factors, such as molecular functionality of the dystrophin and its distribution. To benchmark the success of therapeutic intervention, a clear understanding of dystrophin expression patterns in dystrophinopathy patients is vital. Recently, several groups have used innovative techniques to quantify dystrophin in muscle biopsies of children but not in patients with milder BMD. This study reports on dystrophin expression using both Western blotting and an automated, high-throughput, image analysis platform in DMD, BMD, and intermediate DMD/BMD skeletal muscle biopsies. Our results found a significant correlation between Western blot and immunofluorescent quantification indicating consistency between the different methodologies. However, we identified significant inter- and intradisease heterogeneity of patterns of dystrophin expression in patients irrespective of the amount detected on blot, due to variability in both fluorescence intensity and dystrophin sarcolemmal circumference coverage. Our data highlight the heterogeneity of the pattern of dystrophin expression in BMD, which will assist the assessment of dystrophin restoration therapies.

Persistently elevated CK and lysosomal storage myopathy associated with mucolipin 1 defects.

Mucolipidosis type IV is a rare autosomal recessive lysosomal storage disorder caused by bi-allelic pathogenic variants in the gene MCOLN1. This encodes for mucolipin-1 (ML1), an endo-lysosomal transmembrane Ca++ channel involved in vesicular trafficking. Although experimental models suggest that defects in mucolipin-1 can cause muscular dystrophy, putatively due to defective lysosomal-mediated sarcolemma repair, the role of mucolipin-1 in human muscle is still poorly deciphered. Elevation of creatine kinase (CK) had been reported in a few cases in the past but comprehensive descriptions of muscle pathology are lacking. Here we report a 7-year-old boy who underwent muscle biopsy due to persistently elevated CK levels (780-15,000 UI/L). Muscle pathology revealed features of a lysosomal storage myopathy with mild regenerative changes. Next generation sequencing confirmed homozygous nonsense variants in MCOLN1. This is a comprehensive pathological description of ML1-related myopathy, supporting the role of mucolipin-1 in muscle homoeostasis.

The administration of antisense oligonucleotide golodirsen reduces pathological regeneration in patients with Duchenne muscular dystrophy.

During the last decade, multiple clinical trials for Duchenne muscular dystrophy (DMD) have focused on the induction of dystrophin expression using different strategies. Many of these trials have reported a clear increase in dystrophin protein following treatment. However, the low levels of the induced dystrophin protein have raised questions on its functionality. In our present study, using an unbiased, high-throughput digital image analysis platform, we assessed markers of regeneration and levels of dystrophin associated protein via immunofluorescent analysis of whole muscle sections in 25 DMD boys who received 48-weeks treatment with exon 53 skipping morpholino antisense oligonucleotide (PMO) golodirsen. We demonstrate that the de novo dystrophin induced by exon skipping with PMO golodirsen is capable of conferring a histological benefit in treated patients with an increase in dystrophin associated proteins at the dystrophin positive regions of the sarcolemma in post-treatment biopsies. Although 48 weeks treatment with golodirsen did not result in a significant change in the levels of fetal/developmental myosins for the entire cohort, there was a significant negative correlation between the amount of dystrophin and levels of regeneration observed in different biopsy samples. Our results provide, for the first time, evidence of functionality of induced dystrophin following successful therapeutic intervention in the human.

A high-throughput digital script for multiplexed immunofluorescent analysis and quantification of sarcolemmal and sarcomeric proteins in muscular dystrophies.

The primary molecular endpoint for many Duchenne muscular dystrophy (DMD) clinical trials is the induction, or increase in production, of dystrophin protein in striated muscle. For accurate endpoint analysis, it is essential to have reliable, robust and objective quantification methodologies capable of detecting subtle changes in dystrophin expression. In this work, we present further development and optimisation of an automated, digital, high-throughput script for quantitative analysis of multiplexed immunofluorescent (IF) whole slide images (WSI) of dystrophin, dystrophin associated proteins (DAPs) and regenerating myofibres (fetal/developmental myosin-positive) in transverse sections of DMD, Becker muscular dystrophy (BMD) and control skeletal muscle biopsies. The script enables extensive automated assessment of myofibre morphometrics, protein quantification by fluorescence intensity and sarcolemmal circumference coverage, colocalisation data for dystrophin and DAPs and regeneration at the single myofibre and whole section level. Analysis revealed significant variation in dystrophin intensity, percentage coverage and amounts of DAPs between differing DMD and BMD samples. Accurate identification of dystrophin via a novel background subtraction method allowed differential assessment of DAP fluorescence intensity within dystrophin positive compared to dystrophin negative sarcolemma regions. This enabled surrogate quantification of molecular functionality of dystrophin in the assembly of the DAP complex. Overall, the digital script is capable of multiparametric and unbiased analysis of markers of myofibre regeneration and dystrophin in relation to key DAPs and enabled better characterisation of the heterogeneity in dystrophin expression patterns seen in BMD and DMD alongside the surrogate assessment of molecular functionality of dystrophin. Both these aspects will be of significant relevance to ongoing and future DMD and other muscular dystrophies clinical trials to help benchmark therapeutic efficacy.

Nebulin nemaline myopathy recapitulated in a compound heterozygous mouse model with both a missense and a nonsense mutation in Neb.

Nemaline myopathy (NM) caused by mutations in the gene encoding nebulin (NEB) accounts for at least 50% of all NM cases worldwide, representing a significant disease burden. Most NEB-NM patients have autosomal recessive disease due to a compound heterozygous genotype. Of the few murine models developed for NEB-NM, most are Neb knockout models rather than harbouring Neb mutations. Additionally, some models have a very severe phenotype that limits their application for evaluating disease progression and potential therapies. No existing murine models possess compound heterozygous Neb mutations that reflect the genotype and resulting phenotype present in most patients. We aimed to develop a murine model that more closely matched the underlying genetics of NEB-NM, which could assist elucidation of the pathogenetic mechanisms underlying the disease. Here, we have characterised a mouse strain with compound heterozygous Neb mutations; one missense (p.Tyr2303His), affecting a conserved actin-binding site and one nonsense mutation (p.Tyr935*), introducing a premature stop codon early in the protein. Our studies reveal that this compound heterozygous model, NebY2303H, Y935X, has striking skeletal muscle pathology including nemaline bodies. In vitro whole muscle and single myofibre physiology studies also demonstrate functional perturbations. However, no reduction in lifespan was noted. Therefore, NebY2303H,Y935X mice recapitulate human NEB-NM and are a much needed addition to the NEB-NM mouse model collection. The moderate phenotype also makes this an appropriate model for studying NEB-NM pathogenesis, and could potentially be suitable for testing therapeutic applications.

Nesprin-1-alpha2 associates with kinesin at myotube outer nuclear membranes, but is restricted to neuromuscular junction nuclei in adult muscle.

Nesprins, nuclear envelope spectrin-repeat proteins encoded by the SYNE1 and SYNE2 genes, are involved in localization of nuclei. The short isoform, nesprin-1-alpha2, is required for relocation of the microtubule organizer function from centromeres to the nuclear rim during myogenesis. Using specific antibodies, we now show that both nesprin-1-alpha2 and nesprin-1-giant co-localize with kinesin at the junctions of concatenated nuclei and at the outer poles of nuclear chains in human skeletal myotubes. In adult muscle, nesprin-1-alpha2 was found, together with kinesin, only on nuclei associated with neuromuscular junctions, whereas all adult cardiomyocyte nuclei expressed nesprin-1-alpha2. In a proteomics study, kinesin heavy and light chains were the only significant proteins in myotube extracts pulled down by nesprin-1-alpha2, but not by a mutant lacking the highly-conserved STAR domain (18 amino-acids, including the LEWD motif). The results support a function for nesprin-1-alpha2 in the specific localization of skeletal muscle nuclei mediated by kinesins and suggest that its primary role is at the outer nuclear membrane.

Clinical, histological, and genetic characterization of PYROXD1-related myopathy.

Recessive mutations in PYROXD1, encoding an oxidoreductase, were recently reported in families with congenital myopathy or limb-girdle muscular dystrophy. Here we describe three novel PYROXD1 families at the clinical, histological, and genetic level. Histological analyses on muscle biopsies from all families revealed fiber size variability, endomysial fibrosis, and muscle fibers with multiple internal nuclei and cores. Further characterization of the structural muscle defects uncovered aggregations of myofibrillar proteins, and provided evidence for enhanced oxidative stress. Sequencing identified homozygous or compound heterozygous PYROXD1 mutations including the first deep intronic mutation reinforcing a cryptic donor splice site and resulting in mRNA instability through exonisation of an intronic segment. Overall, this work expands the PYROXD1 mutation spectrum, defines and specifies the histopathological hallmarks of the disorder, and indicates that oxidative stress contributes to the pathomechanism. Comparison of all new and published cases uncovered a genotype/phenotype correlation with a more severe and early-onset phenotypic presentation of patients harboring splice mutations resulting in reduced PYROXD1 protein levels compared with patients carrying missense mutations.

Nemaline myopathies: a current view.

Nemaline myopathies are a heterogenous group of congenital myopathies caused by de novo, dominantly or recessively inherited mutations in at least twelve genes. The genes encoding skeletal α-actin (ACTA1) and nebulin (NEB) are the commonest genetic cause. Most patients have congenital onset characterized by muscle weakness and hypotonia, but the spectrum of clinical phenotypes is broad, ranging from severe neonatal presentations to onset of a milder disorder in childhood. Most patients with adult onset have an autoimmune-related myopathy with a progressive course. The wide application of massively parallel sequencing methods is increasing the number of known causative genes and broadening the range of clinical phenotypes. Nemaline myopathies are identified by the presence of structures that are rod-like or ovoid in shape with electron microscopy, and with light microscopy stain red with the modified Gömöri trichrome technique. These rods or nemaline bodies are derived from Z lines (also known as Z discs or Z disks) and have a similar lattice structure and protein content. Their shape in patients with mutations in KLHL40 and LMOD3 is distinctive and can be useful for diagnosis. The number and distribution of nemaline bodies varies between fibres and different muscles but does not correlate with severity or prognosis. Additional pathological features such as caps, cores and fibre type disproportion are associated with the same genes as those known to cause the presence of rods. Animal models are advancing the understanding of the effects of various mutations in different genes and paving the way for the development of therapies, which at present only manage symptoms and are aimed at maintaining muscle strength, joint mobility, ambulation, respiration and independence in the activities of daily living.

Recessive MYH7-related myopathy in two families.

Myopathies due to recessive MYH7 mutations are exceedingly rare, reported in only two families to date. We describe three patients from two families (from Australia and the UK) with a myopathy caused by recessive mutations in MYH7. The Australian family was homozygous for a c.5134C > T, p.Arg1712Trp mutation, whilst the UK patient was compound heterozygous for a truncating (c.4699C > T; p.Gln1567*) and a missense variant (c.4664A > G; p.Glu1555Gly). All three patients shared key clinical features, including infancy/childhood onset, pronounced axial/proximal weakness, spinal rigidity, severe scoliosis, and normal cardiac function. There was progressive respiratory impairment necessitating non-invasive ventilation despite preserved ambulation, a combination of features often seen in SEPN1- or NEB-related myopathies. On biopsy, the Australian proband showed classical myosin storage myopathy features, while the UK patient showed multi-minicore like areas. To establish pathogenicity of the Arg1712Trp mutation, we expressed mutant MYH7 protein in COS-7 cells, observing abnormal mutant myosin aggregation compared to wild-type. We describe skinned myofiber studies of patient muscle and hypertrophy of type II myofibers, which may be a compensatory mechanism. In summary, we have expanded the phenotype of ultra-rare recessive MYH7 disease, and provide novel insights into associated changes in muscle physiology.

Dominantly inherited distal nemaline/cap myopathy caused by a large deletion in the nebulin gene.

We report the first family with a dominantly inherited mutation of the nebulin gene (NEB). This ∼100 kb in-frame deletion encompasses NEB exons 14-89, causing distal nemaline/cap myopathy in a three-generation family. It is the largest deletion characterized in NEB hitherto. The mutated allele was shown to be expressed at the mRNA level and furthermore, for the first time, a deletion was shown to cause the production of a smaller mutant nebulin protein. Thus, we suggest that this novel mutant nebulin protein has a dominant-negative effect, explaining the first documented dominant inheritance of nebulin-caused myopathy. The index patient, a young man, was more severely affected than his mother and grandmother. His first symptom was foot drop at the age of three, followed by distal muscle atrophy, slight hypomimia, high-arched palate, and weakness of the neck and elbow flexors, hands, tibialis anterior and toe extensors. Muscle biopsies showed myopathic features with type 1 fibre predominance in the index patient and nemaline bodies and cap-like structures in biopsies from his mother and grandmother. The muscle biopsy findings constitute a further example of nemaline bodies and cap-like structures being part of the same spectrum of pathological changes.

Electromyography and muscle biopsy in paediatric neuromuscular disorders - Evaluation of current practice and literature review.

The conduct and interpretation of electromyography in children is considered difficult and therefore often avoided. We assessed the diagnostic accuracy of the paediatric electromyography protocol used in our tertiary reference centre and compared it to muscle biopsy results and clinical diagnosis. Electromyography was performed in unsedated children with suspected neuromuscular diseases between January 2010 and September 2017 and was analysed quantitatively. Muscle pathology was classified into seven groups based on existing histopathology reports. The clinical diagnosis, including myopathic, neurogenic and non-neuromuscular categories was used as the gold standard. 171 children between the age of 12 days to 17.4 years were included in the analysis. 41 children (24%) were under the age of 2 years at the time of electromyography. 98 (57%) children were diagnosed with a myopathic disorder, 18 (11%) with a neurogenic disease and 55 (32%) as not having a primary neuromuscular disorder. In detecting myopathic disease, electromyography performed as well as muscle biopsy (sensitivity 87.8% for electromyography vs. 84.5% for muscle biopsy; specificity 75.7% vs. 86.4%). This also applied to children under the age of 2 years (sensitivity 81.8% vs. 86.4%). Quantitative analysis of a limited electromyography protocol performed in unsedated children is a very valuable diagnostic tool.