Store-operated calcium entry dysfunction in CRAC channelopathy: Insights from a novel STIM1 mutation.

Store-operated calcium entry (SOCE) plays a crucial role in maintaining cellular calcium homeostasis. This mechanism involves proteins, such as stromal interaction molecule 1 (STIM1) and ORAI1. Mutations in the genes encoding these proteins, especially STIM1, can lead to various diseases, including CRAC channelopathies associated with severe combined immunodeficiency. Herein, we describe a novel homozygous mutation, NM_003156 c.792-3C > G, in STIM1 in a patient with a clinical profile of CRAC channelopathy, including immune system deficiencies and muscle weakness. Functional analyses revealed three distinct spliced forms in the patient cells: wild-type, exon 7 skipping, and intronic retention. Calcium influx analysis revealed impaired SOCE in the patient cells, indicating a loss of STIM1 function. We developed an antisense oligonucleotide treatment that improves STIM1 splicing and highlighted its potential as a therapeutic approach. Our findings provide insights into the complex effects of STIM1 mutations and shed light on the multifaceted clinical presentation of the patient.

Objective Evaluation of Clinical Actionability for Genes Involved in Myopathies: 63 Genes with a Medical Value for Patient Care.

The implementation of high-throughput diagnostic sequencing has led to the generation of large amounts of mutational data, making their interpretation more complex and responsible for long delays. It has been important to prioritize certain analyses, particularly those of "actionable" genes in diagnostic situations, involving specific treatment and/or management. In our project, we carried out an objective assessment of the clinical actionability of genes involved in myopathies, for which only few data obtained methodologically exist to date. Using the ClinGen Actionability criteria, we scored the clinical actionability of all 199 genes implicated in myopathies published by FILNEMUS for the "National French consensus on gene Lists for the diagnosis of myopathies using next generation sequencing". We objectified that 63 myopathy genes were actionable with the currently available data. Among the 36 myopathy genes with the highest actionability scores, only 8 had been scored to date by ClinGen. The data obtained through these methodological tools are an important resource for strategic choices in diagnostic approaches and the management of genetic myopathies. The clinical actionability of genes has to be considered as an evolving concept, in relation to progresses in disease knowledge and therapeutic approaches.

Retrospective analysis and reclassification of DYSF variants in a large French series of dysferlinopathy patients.

PURPOSE: Recent evolution of sequencing technologies and the development of international standards in variant interpretation have profoundly changed the diagnostic approaches in clinical genetics. As a consequence, many variants that were initially claimed to be disease-causing can be now reclassified as benign or uncertain in light of the new data available. Unfortunately, the misclassified variants are still present in the scientific literature and variant databases, greatly interfering with interpretation of diagnostic sequencing results. Despite the urgent need, large-scale efforts to update the classifications of these variants are still not sufficient. METHODS: We retrospectively analyzed 176 DYSF gene variants that were identified in dysferlinopathy patients referred to the Marseille Medical Genetics Department for diagnostic sequencing since 2001. RESULTS: We reclassified all variants into five-tier American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) pathogenicity classes, revealing changed pathogenicity for 17 variants. We then updated the information for the variants that have been previously published in the variant database and submitted 46 additional DYSF variants. CONCLUSION: Besides direct benefit for dysferlinopathy diagnostics, our study contributes to the much needed effort to reanalyze variants from previously published cohorts and to work with curators of variant databases to update the entries for erroneously classified variants.

Motor axonal neuropathy associated with GNE mutations.

BACKGROUND: Mutations in the GNE gene have been so far described as predominantly associated with distal lower-limb myopathies. Recent reports describe mutations in this gene in patients with peripheral neuropathy and motor neuron disease. METHODS: We describe three patients displaying motor neuropathy in association with GNE mutations. Clinical, electrophysiological, imaging, pathological, and genetic data are presented in a retrospective manner. RESULTS: The three patients had different phenotypes, ranging from mildly progressive lower limb weakness to a rapidly progressive 4-limb weakness. Genetic testing revealed GNE gene mutations in all patients; of those mutations, p.(His186Arg) has not been previously reported. All patients showed evidence of axonal motor nerve involvement on electrodiagnostic examination and/or muscle biopsy. CONCLUSIONS: Nerve involvement associated with GNE gene mutations may be an underdiagnosed pathology and may influence clinical presentation and disease progression.

Deep phenotyping of an international series of patients with late-onset dysferlinopathy.

BACKGROUND: To describe the clinical, pathological, and molecular characteristics of late-onset (LO) dysferlinopathy patients. METHODS: Retrospective series of patients with LO dysferlinopathy, defined by an age at onset of symptoms ≥30 years, from neuromuscular centers in France and the International Clinical Outcome Study for dysferlinopathy (COS). Patients with early-onset (EO) dysferlinopathy (<30 years) were randomly selected from the COS study as a control group, and the North Star Assessment for Dysferlinopathy (NSAD) and Activity Limitation (ACTIVLIM) scores were used to assess functionality. Muscle biopsies obtained from 11 LO and 11 EO patients were revisited. RESULTS: Forty-eight patients with LO dysferlinopathy were included (28 females). Median age at onset of symptoms was 37 (range 30-57) years and most patients showed a limb-girdle (n = 26) or distal (n = 10) phenotype. However, compared with EO dysferlinopathy patients (n = 48), LO patients more frequently showed atypical phenotypes (7 vs. 1; p = 0.014), including camptocormia, lower creatine kinase levels (2855 vs. 4394 U/L; p = 0.01), and higher NSAD (p = 0.008) and ACTIVLIM scores (p = 0.016). Loss of ambulation in LO patients tended to occur later (23 ± 4.4 years after disease onset vs. 16.3 ± 6.8 years; p = 0.064). Muscle biopsy of LO patients more frequently showed an atypical pattern (unspecific myopathic changes) as well as significantly less necrosis regeneration and inflammation. Although LO patients more frequently showed missense variants (39.8% vs. 23.9%; p = 0.021), no differences in dysferlin protein expression were found on Western blot. CONCLUSIONS: Late-onset dysferlinopathy patients show a higher frequency of atypical presentations, are less severely affected, and show milder dystrophic changes in muscle biopsy.

First characterization of congenital myasthenic syndrome type 5 in North Africa.

BACKGROUND: Congenital myasthenic syndromes (CMS) are associated with defects in the structure and the function of neuromuscular junctions. These rare disorders can result from mutations in the collagenic tail of endplate acetylcholinesterase (COLQ) essentially associated with autosomal recessive inheritance. With the lowered cost of genetic testing and increased access to next-generation sequencing, many mutations have been reported to date. METHODS AND RESULTS: In this study we identified the first COLQ homozygous mutation c.1193T>A in the North African population. This study outlines the genetic and phenotypic features of a CMS patient in a Moroccan family. It also describes a novel COLQ missense mutation associated with CMS-5. CONCLUSION: COLQ mutations are probably underdiagnosed in these North African populations, this is an issue as CMS-5 may be treated with ephedrine, and albuterol. Indeed, patients can seriously benefit and even recover after the treatment that should be planned according to genetic tests and clinical findings.

Splicing impact of deep exonic missense variants in CAPN3 explored systematically by minigene functional assay.

Improving the accuracy of variant interpretation during diagnostic sequencing is a major goal for genomic medicine. To explore an often-overlooked splicing effect of missense variants, we developed the functional assay ("minigene") for the majority of exons of CAPN3, the gene responsible for limb girdle muscular dystrophy. By systematically screening 21 missense variants distributed along the gene, we found that eight clinically relevant missense variants located at a certain distance from the exon-intron borders (deep exonic missense variants) disrupted normal splicing of CAPN3 exons. Several recent machine learning-based computational tools failed to predict splicing impact for the majority of these deep exonic missense variants, highlighting the importance of including variants of this type in the training sets during the future algorithm development. Overall, 24 variants in CAPN3 gene were explored, leading to the change in the American College of Medical Genetics and Genomics classification of seven of them when results of the "minigene" functional assay were considered. Our findings reveal previously unknown splicing impact of several clinically important variants in CAPN3 and draw attention to the existence of deep exonic variants with a disruptive effect on gene splicing that could be overlooked by the current approaches in clinical genetics.

VarAFT: a variant annotation and filtration system for human next generation sequencing data.

With the rapidly developing high-throughput sequencing technologies known as next generation sequencing or NGS, our approach to gene hunting and diagnosis has drastically changed. In <10 years, these technologies have moved from gene panel to whole genome sequencing and from an exclusively research context to clinical practice. Today, the limit is not the sequencing of one, many or all genes but rather the data analysis. Consequently, the challenge is to rapidly and efficiently identify disease-causing mutations within millions of variants. To do so, we developed the VarAFT software to annotate and pinpoint human disease-causing mutations through access to multiple layers of information. VarAFT was designed both for research and clinical contexts and is accessible to all scientists, regardless of bioinformatics training. Data from multiple samples may be combined to address all Mendelian inheritance modes, cancers or population genetics. Optimized filtration parameters can be stored and re-applied to large datasets. In addition to classical annotations from dbNSFP, VarAFT contains unique features at the disease (OMIM), phenotypic (HPO), gene (Gene Ontology, pathways) and variation levels (predictions from UMD-Predictor and Human Splicing Finder) that can be combined to optimally select candidate pathogenic mutations. VarAFT is freely available at: http://varaft.eu.

Genetic Characterization of a French Cohort of GNE-mutation negative inclusion body myopathy patients with exome sequencing.

INTRODUCTION: Hereditary inclusion body myopathy (hIBM) refers to a group of clinically and genetically heterogeneous diseases. The overlapping histochemical features of hIBM with other genetic disorders lead to low diagnostic rates with targeted single-gene sequencing. This is true for the most prevalent form of hIBM, GNEpathy. Therefore, we used whole-exome sequencing (WES) to determine whether a cohort of clinically suspected GNEpathy patients undiagnosed by targeted GNE analysis could be genetically characterized. METHODS: Twenty patients with hIBM but undiagnosed by targeted GNE sequencing were analyzed by WES before data filtering on 306 genes associated with neuromuscular disorders. RESULTS: Seven patients out of 20 were found to have disease-causing mutations in genes associated with hIBM or genes allowing for hIBM in the differential diagnosis or associated with unexpected diagnosis. DISCUSSION: Next-generation sequencing is an efficient strategy in the context of hIBM, resulting in a molecular diagnosis for 35% of the patients initially undiagnosed by targeted GNE analysis. Muscle Nerve 56: 993-997, 2017.

Actionable Genes, Core Databases, and Locus-Specific Databases.

Adoption of next-generation sequencing (NGS) in a diagnostic context raises numerous questions with regard to identification and reports of secondary variants (SVs) in actionable genes. To better understand the whys and wherefores of these questioning, it is necessary to understand how they are selected during the filtering process and how their proportion can be estimated. It is likely that SVs are underestimated and that our capacity to label all true SVs can be improved. In this context, Locus-specific databases (LSDBs) can be key by providing a wealth of information and enabling classifying variants. We illustrate this issue by analyzing 318 SVs in 23 actionable genes involved in cancer susceptibility syndromes identified through sequencing of 572 participants selected for a range of atherosclerosis phenotypes. Among these 318 SVs, only 43.4% are reported in Human Gene Mutation Database (HGMD) Professional versus 71.4% in LSDB. In addition, 23.9% of HGMD Professional variants are reported as pathogenic versus 4.8% for LSDB. These data underline the benefits of LSDBs to annotate SVs and minimize overinterpretation of mutations thanks to their efficient curation process and collection of unpublished data.

Constitutive activation of the calcium sensor STIM1 causes tubular-aggregate myopathy.

Tubular aggregates are regular arrays of membrane tubules accumulating in muscle with age. They are found as secondary features in several muscle disorders, including alcohol- and drug-induced myopathies, exercise-induced cramps, and inherited myasthenia, but also exist as a pure genetic form characterized by slowly progressive muscle weakness. We identified dominant STIM1 mutations as a genetic cause of tubular-aggregate myopathy (TAM). Stromal interaction molecule 1 (STIM1) is the main Ca(2+) sensor in the endoplasmic reticulum, and all mutations were found in the highly conserved intraluminal Ca(2+)-binding EF hands. Ca(2+) stores are refilled through a process called store-operated Ca(2+) entry (SOCE). Upon Ca(2+)-store depletion, wild-type STIM1 oligomerizes and thereby triggers extracellular Ca(2+) entry. In contrast, the missense mutations found in our four TAM-affected families induced constitutive STIM1 clustering, indicating that Ca(2+) sensing was impaired. By monitoring the calcium response of TAM myoblasts to SOCE, we found a significantly higher basal Ca(2+) level in TAM cells and a dysregulation of intracellular Ca(2+) homeostasis. Because recessive STIM1 loss-of-function mutations were associated with immunodeficiency, we conclude that the tissue-specific impact of STIM1 loss or constitutive activation is different and that a tight regulation of STIM1-dependent SOCE is fundamental for normal skeletal-muscle structure and function.

Respiratory and cardiac function in japanese patients with dysferlinopathy.

INTRODUCTION: We retrospectively reviewed respiratory and cardiac function in patients with dysferlinopathy, including 2 autopsy cases with respiratory dysfunction. METHODS: Subjects included 48 patients who underwent respiratory evaluation (n = 47), electrocardiography (n = 46), and echocardiography (n = 23). RESULTS: Of the 47 patients, 10 had reduced percent forced vital capacity (%FVC), and 4 required non-invasive positive pressure ventilation. %FVC was significantly correlated with disease duration, and mean %FVC was significantly lower in non-ambulatory patients, as well as in those aged ≥65 years with normal creatine kinase levels. On electrocardiography, QRS complex duration was prolonged in 19 patients, although no significant association with age, disease duration, or respiratory function was found. Echocardiography indicated no left ventricular dysfunction in any patient. Histopathology of autopsied cases revealed mild cardiomyopathy and moderate diaphragm involvement. CONCLUSION: Patients with dysferlinopathy may develop severe respiratory failure and latent cardiac dysfunction. Both respiratory and cardiac function should be monitored diligently.

Toward an objective measure of functional disability in dysferlinopathy.

INTRODUCTION: Understanding the natural history of dysferlinopathy is essential to design and quantify novel therapeutic protocols. Our aim in this study was to assess, clinically and functionally, a cohort of patients with dysferlinopathy, using validated scales. METHODS: Thirty-one patients with genetically confirmed dysferlinopathy were assessed using the motor function measure (MFM), Modified Rankin Scale (MRS), Muscle Research Council (MRC) scale, serum creatine kinase (CK) assessment, baseline spirometry data, and echocardiographic and electrophysiologic studies. RESULTS: MFM and MRC scores showed a significant negative correlation with disease duration and inverse correlation with MRS, but not with onset age, clinical phenotype, or CK levels. Percent forced vital capacity (%FVC) correlated negatively with disease duration and onset age. Eight known pathogenic mutations were identified recurrently, 4 of which accounted for 79% of the total. CONCLUSIONS: The results suggest that MFM is a reliable outcome measure that may be useful for longitudinal follow-up in dysferlinopathy. Recurrent mutations suggest a founder effect in the Chilean population.

Identification of variants in the 4q35 gene FAT1 in patients with a facioscapulohumeral dystrophy-like phenotype.

Facioscapulohumeralmuscular dystrophy (FSHD) is linked to copy-number reduction (N < 10) of the 4q D4Z4 subtelomeric array, in association with DUX4-permissive haplotypes. This main form is indicated as FSHD1. FSHD-like phenotypes may also appear in the absence of D4Z4 copy-number reduction. Variants of the SMCHD1 gene have been reported to associate with D4Z4 hypomethylation in DUX4-compatible haplotypes, thus defining FSHD2. Recently, mice carrying a muscle-specific knock-out of the protocadherin gene Fat1 or its constitutive hypomorphic allele were shown to develop muscular and nonmuscular defects mimicking human FSHD. Here, we report FAT1 variants in a group of patients presenting with neuromuscular symptoms reminiscent of FSHD. The patients do not carry D4Z4 copy-number reduction, 4q hypomethylation, or SMCHD1 variants. However, abnormal splicing of the FAT1 transcript is predicted for all identified variants. To determine their pathogenicity, we elaborated a minigene approach coupled to an antisense oligonucleotide (AON) assay. In vitro, four out of five selected variants induced partial or complete alteration of splicing by creating new splice sites or modifying splicing regulators. AONs confirmed these effects. Altered transcripts may affect FAT1 protein interactions or stability. Altogether, our data suggest that defective FAT1 is associated with an FSHD-like phenotype.

Identification of splicing defects caused by mutations in the dysferlin gene.

Missense, iso-semantic, and intronic mutations are challenging for interpretation, in particular for their impact in mRNA. Various tools such as the Human Splicing Finder (HSF) system could be used to predict the impact on splicing; however, no diagnosis result could rely on predictions alone, but requires functional testing. Here, we report an in vitro approach to study the impact of DYSF mutations on splicing. It was evaluated on a series of 45 DYSF mutations, both intronic and exonic. We confirmed splicing alterations for all intronic mutations localized in 5' or 3' splice sites. Then, we showed that DYSF missense mutations could also result in splicing defects: mutations c.463G>A and c.2641A>C abolished ESEs and led to exon skipping; mutations c.565C>G and c.1555G>A disrupted Exonic Splicing Enhancer (ESE), while concomitantly creating new 5' or 3' splice site leading to exonic out of frame deletions. We demonstrated that 20% of DYSF missense mutations have a strong impact on splicing. This minigene strategy is an efficient tool for the detection of splicing defects in dysferlinopathies, which could allow for a better comprehension of splicing defects due to mutations and could improve prediction tools evaluating splicing defects.

Entire CAPN3 gene deletion in a patient with limb-girdle muscular dystrophy type 2A.

Limb-girdle muscular dystrophy type 2A (LGMD2A) due to mutations in the CAPN3 gene is one of the most common of autosomal recessive limb-girdle muscular dystrophies. We describe a patient who had a typical LGMD2A phenotype and posterior compartment involvement on MRI. Different genetic analyses were performed, including microarray analysis. There was an apparently homozygous mutation in exon 24, c.2465G>T, p.(*822Leuext62*), and a lack of correlation in the disease segregation analyses. This suggested the presence of a genomic rearrangement. In fact, a heterozygous deletion of the entire CAPN3 gene was found. This novel deletion comprised the terminal region of the GANC gene and the entire CAPN3 gene. This finding points out the need to reconsider and adapt our current strategy of molecular diagnosis in order to detect these types of genomic rearrangements that escape standard mutation screening procedures.

Clinical heterogeneity and a high proportion of novel mutations in a Chinese cohort of patients with dysferlinopathy.

BACKGROUND AND AIMS: Dysferlinopathies are a group of autosomal recessive muscular dystrophies caused by mutations in the dysferlin gene. This study presents clinical features and the mutational spectrum in the largest cohort of Chinese patients analyzed to date. PATIENTS AND METHODS: A total of 36 unrelated Chinese patients with diagnostic suspicion of dysferlinopathy were clinically and genetically characterized. RESULTS: Patients were divided into five phenotypes: 19 patients with limb girdle muscular dystrophy (LGMD) type 2B, 10 with Miyoshi myopathy (MM), 1 with distal anterior compartment myopathy (DACM), 3 with exercise intolerance, and 3 with asymptomatic hypercreatine phosphokinasemia (hyperCPKemia). Thirty-one patients showed an absence or drastic reduction of dysferlin expression by Westernblot. Forty-three mutations were identified in DYSF, including 31 novel. CONCLUSION: Our study underlines clinical heterogeneity and a high proportion of novel mutations in Chinese patients affected with dysferlinopathy.

Phenotype variability and natural history of X-linked myopathy with excessive autophagy.

OBJECTIVE: X-linked myopathy with excessive autophagy (XMEA) linked to the VMA21 gene leads to autophagy failure with progressive vacuolation and atrophy of skeletal muscles. Current knowledge of this rare disease is limited. Our objective was to define the clinical, radiological, and natural history of XMEA. METHODS: We conducted a retrospective study collecting clinical, genetic, muscle imaging, and biopsy data of XMEA patients followed in France and reviewed the literature for additional cases. RESULTS: Eighteen males had genetically confirmed XMEA in France, carrying four different VMA21 variants. Mean age at disease onset was 9.4 ± 9.9 (range 1-40) years. In 14/18 patients (77.8%), onset occurred during childhood (< 15 years); however in four patients, the disease started in adulthood. Patients had anterior and medial compartment thigh muscle weakness, distal contractures (56.3%), elevated CK levels (1287.9 ± 757.8 U/l) and autophagic vacuoles with sarcolemmal features on muscle histopathology. Muscle MRI (n = 10) showed a characteristic pattern of lower limb muscle involvement. In 11 patients, outcome measures were available for an average follow-up period of 10.6 ± 9.8 years and six of them show disease progression. Mean change of functional outcomes was 0.5 ± 1.2 points for Brooke and 2.2 ± 2.5 points for Vignos score, 7/16 patients (43.8%) needed a walking aid and 3/16 (18.8%) were wheelchair-bound (median age of 40 years old, range 39-48). The variant c.164-7 T > G was associated with a later onset of symptoms. Respiratory insufficiency was common (57.1%) but cardiac involvement rare (12.5%). INTERPRETATION: XMEA has variable age of onset, but a characteristic clinical, histopathological, and muscle imaging presentation, guiding the diagnosis. Although slowly, motor disability progresses with time, and relevant genotype-phenotype correlations will help design future clinical trials.

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.