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The non-dystrophic myotonias are inherited skeletal muscle disorders characterized by skeletal muscle stiffness after voluntary contraction, without muscle atrophy. Based on their clinical features, non-dystrophic myotonias are classified into myotonia congenita, paramyotonia congenita, and sodium channel myotonia. Using whole-exome next-generation sequencing, we identified a L703P mutation (c.2108TC, p.L703P) in SCN4A in a Chinese family diagnosed with non-dystrophic myotonias. The clinical findings of patients in this family included muscle stiffness and hypertrophy. The biophysical properties of wildtype and mutant channels were investigated using whole-cell patch clamp. L703P causes both gain-of-function and loss-of-function changes in Nav1.4 properties, including decreased current density, impaired recovery, enhanced activation and slow inactivation. Our study demonstrates that L703P is a pathogenic variant for myotonia, and provides additional electrophysiological information for understanding the pathogenic mechanism of SCN4A-associated channelopathies.

This pilot study explored the feasibility and effectiveness of vibration therapy (VT) on muscle and bone health, motor performance, and respiratory function in patients with congenital myopathy (CM). Eleven participants with CM (11.5 ± 2.8 years) underwent 12 weeks of side-alternating VT at 20 Hz for nine minutes per session, four days a week. VT was preceded by a 12-week control period. Assessments included dual-energy X-ray absorptiometry scans, 6-minute walk and 10-meter run tests, muscle function and motor performance assessment, dynamometry, and pulmonary function. VT was well-tolerated, with occasional mild itchiness reported. The median compliance level with VT treatment was 75%. 12 weeks of VT improved the total score of motor function performance by 2.4 units (p=0.006) and velocity rise maximum of the chair rising test by 0.11 m/s (p=0.029). VT was shown to be feasible, safe, and associated with improving motor function performance. Our findings support further exploration of VT's potential health benefits to patients with CM in larger studies involving a longer intervention period.

Jorge Andres Olave-Rodriguez,1 Francisco Javier Bonilla-Escobar,2– 4 Estephania Candelo,5,6 Lisa Ximena Rodriguez-Rojas1,7 1Universidad Icesi, Faculty of Health Sciences, Cali, Colombia; 2Somos Ciencia al Servicio de la Comunidad, Fundación SCISCO/Science to Serve the Community, SCISCO Foundation, Cali, Colombia; 3Universidad del Valle, Cali, Colombia; 4Institute for Clinical Research Education, University of Pittsburgh, Pittsburgh, PA, USA; 5Centro de Investigaciones Clínicas, Fundación Valle del Lili, Cali, Colombia; 6Centro enfermedades raras y malformaciones congenitas (CIACER), Universidad Icesi, Cali, Colombia; 7Human Genetics Department, Fundación Valle del Lili, Cali, ColombiaCorrespondence: Lisa Ximena Rodriguez-Rojas Cra. 98 ## 18-49, Cali, Valle del Cauca, ColombiaEmail lixiro@gmail.com; lisa.rodriguez@fvl.org.coBackground: Becker’s type myotonia congenita is an autosomal recessive nondystrophic skeletal muscle disorder characterized by muscle stiffness and the inability of muscle relaxation after voluntary contraction. It is caused by mutations in the CLCN1 gene, which encodes for a chloride channel mainly expressed in the striated muscle. Most cases have been reported in the European population, and only mexiletine has demonstrated a randomized placebo-controlled, double-blinded effectiveness.Case Presentation: We present two male siblings from Colombia with Latino ancestry, without parental consanguinity, with myotonia during voluntary movements, muscle hypertrophy of lower extremities, transient weakness, and severe muscle fatigue after exercise from three years of age. A genetic panel for dystrophic muscle disorders and a muscle biopsy were both negative. Genetic testing was performed in their second decade of life. Both patients’ exomic sequencing test reported the mutation c.1129C >T (p.Arg377*) affecting exon 10 of the CLCN1, generating a premature stop codon. This mutation was described as pathogenic and observed in only one other patient in the United Kingdom.Conclusion: To our knowledge, these are the first cases of Becker’s type myotonia congenita reported in Colombia. Increasing awareness of healthcare providers for this type of disease in the region could lead to the identification of undiagnosed patients. Limited availability of medical geneticists as well as genetic testing may be the cause of the lack of previous description of cases, in addition to the delay in the diagnosis of the patients. Further epidemiological studies can reveal underdiagnosed myotonias in the country and in the Latin-American region.Keywords: Becker type myotonia congenita, myotonia congenita, Colombia, muscular diseases, siblings case reports

Jorge Andres Olave-Rodriguez,1 Francisco Javier Bonilla-Escobar,2– 4 Estephania Candelo,5,6 Lisa Ximena Rodriguez-Rojas1,7 1Universidad Icesi, Faculty of Health Sciences, Cali, Colombia; 2Somos Ciencia al Servicio de la Comunidad, Fundación SCISCO/Science to Serve the Community, SCISCO Foundation, Cali, Colombia; 3Universidad del Valle, Cali, Colombia; 4Institute for Clinical Research Education, University of Pittsburgh, Pittsburgh, PA, USA; 5Centro de Investigaciones Clínicas, Fundación Valle del Lili, Cali, Colombia; 6Centro enfermedades raras y malformaciones congenitas (CIACER), Universidad Icesi, Cali, Colombia; 7Human Genetics Department, Fundación Valle del Lili, Cali, ColombiaCorrespondence: Lisa Ximena Rodriguez-Rojas Cra. 98 ## 18-49, Cali, Valle del Cauca, ColombiaEmail lixiro@gmail.com; lisa.rodriguez@fvl.org.coBackground: Becker’s type myotonia congenita is an autosomal recessive nondystrophic skeletal muscle disorder characterized by muscle stiffness and the inability of muscle relaxation after voluntary contraction. It is caused by mutations in the CLCN1 gene, which encodes for a chloride channel mainly expressed in the striated muscle. Most cases have been reported in the European population, and only mexiletine has demonstrated a randomized placebo-controlled, double-blinded effectiveness.Case Presentation: We present two male siblings from Colombia with Latino ancestry, without parental consanguinity, with myotonia during voluntary movements, muscle hypertrophy of lower extremities, transient weakness, and severe muscle fatigue after exercise from three years of age. A genetic panel for dystrophic muscle disorders and a muscle biopsy were both negative. Genetic testing was performed in their second decade of life. Both patients’ exomic sequencing test reported the mutation c.1129C >T (p.Arg377*) affecting exon 10 of the CLCN1, generating a premature stop codon. This mutation was described as pathogenic and observed in only one other patient in the United Kingdom.Conclusion: To our knowledge, these are the first cases of Becker’s type myotonia congenita reported in Colombia. Increasing awareness of healthcare providers for this type of disease in the region could lead to the identification of undiagnosed patients. Limited availability of medical geneticists as well as genetic testing may be the cause of the lack of previous description of cases, in addition to the delay in the diagnosis of the patients. Further epidemiological studies can reveal underdiagnosed myotonias in the country and in the Latin-American region.Keywords: Becker type myotonia congenita, myotonia congenita, Colombia, muscular diseases, siblings case reports

High-throughput DNA sequencing is increasingly employed to diagnose single gene neurological and neuromuscular disorders. Large volumes of data present new challenges in data interpretation and its useful translation into clinical and genetic counselling for families. Even when a plausible gene is identified with confidence, interpretation of the clinical significance and inheritance pattern of variants can be challenging. We report our approach to evaluating variants in the skeletal muscle chloride channel ClC-1 identified in 223 probands with myotonia congenita as an example of these challenges. Sequencing of CLCN1, the gene that encodes CLC-1, is central to the diagnosis of myotonia congenita. However, interpreting the pathogenicity and inheritance pattern of novel variants is notoriously difficult as both dominant and recessive mutations are reported throughout the channel sequence, ClC-1 structure-function is poorly understood and significant intra- and interfamilial variability in phenotype is reported. Heterologous expression systems to study functional consequences of CIC-1 variants are widely reported to aid the assessment of pathogenicity and inheritance pattern. However, heterogeneity of reported analyses does not allow for the systematic correlation of available functional and genetic data. We report the systematic evaluation of 95 CIC-1 variants in 223 probands, the largest reported patient cohort, in which we apply standardized functional analyses and correlate this with clinical assessment and inheritance pattern. Such correlation is important to determine whether functional data improves the accuracy of variant interpretation and likely mode of inheritance. Our data provide an evidence-based approach that functional characterization of ClC-1 variants improves clinical interpretation of their pathogenicity and inheritance pattern, and serve as reference for 34 previously unreported and 28 previously uncharacterized CLCN1 variants. In addition, we identify novel pathogenic mechanisms and find that variants that alter voltage dependence of activation cluster in the first half of the transmembrane domains and variants that yield no currents cluster in the second half of the transmembrane domain. None of the variants in the intracellular domains were associated with dominant functional features or dominant inheritance pattern of myotonia congenita. Our data help provide an initial estimate of the anticipated inheritance pattern based on the location of a novel variant and shows that systematic functional characterization can significantly refine the assessment of risk of an associated inheritance pattern and consequently the clinical and genetic counselling.

The aim was to define the clinical and histopathologic findings of infants who underwent muscle biopsy and identify the diagnostic yield of muscle biopsy in this cohort. Infants who underwent muscle biopsy from January 2010 to March 2017 at a tertiary hospital were included in the study (N = 87; 64 boys (73.6%), 23 girls (26.4%); age range 0 - 2 years; mean age 9.73 ± 7.04 months). Clinical and histopathologic data were obtained from medical records. Developmental delay (64.4%) and hypotonia (59.8%) were the most frequent clinical findings, and mitochondrial disease (61%) was the most frequent clinical diagnosis, followed by muscular dystrophy (15.9%) and congenital myopathy (11.5%). Creatine kinase level was normal in 65.9% and > 1,000 U/L in 17.1%. Specific pathologic findings were identified from 38 biopsies (43.7%). The most frequent pathologic findings were features compatible with mitochondrial/metabolic myopathy (14 patients, 16.1%) and muscular dystrophy (12 patients, 13.8%). Myopathic changes were present in 7 biopsy samples (8.0%) and neurogenic changes in 5 (5.7%). The clinical and pathologic diagnoses were compatible in 24 patients (63.2%). The diagnostic yield of muscle biopsy remains significant, especially in this age group. Mitochondrial disease is a major diagnostic challenge, and muscle biopsy helps to support the clinical diagnosis and guide further studies.

ZusammenfassungDie Erkrankung Myotonia congenita wurde als Entität 1876 erstmals durch Julius Thomsen beschrieben. Noch im gleichen Jahr wurde diese Beschreibung von Adolph Seeligmüller kritisch betrachtet und um wesentliche Befunde ergänzt. Bereits Charles Bell, Moritz Benedict und Ernst von Leyden hatten vor 1876 die Symptomatik der Erkrankung beschrieben, ohne jedoch eine neue Entität anzunehmen. Der Vergleich der Publikationen von Thomsen und Seeligmüller von 1876 untereinander und mit Seeligmüllers Lehrbuchkapitel von 1887 sowie mit dem heute genetisch gesicherten Krankheitsbild zeigt, dass Seeligmüller zurecht zwei Aspekte an Thomsens Publikation kritisierte: (i) Die von Thomsen vermutete Pathogenese in „der einen Thätigkeitshälfte des Gehirns, des Willens“ mit „Sitz im Cerebrospinalsysteme“ und (ii) die Annahme einer Koordinationsstörung im Sinne einer Ataxie [1]. Demgegenüber diskutierte Seeligmüller eine „schwerer beweglich Muskelsubstanz“ [2] als Pathogenese mit der er gleichwohl eine angeborene Affection der Seitenstränge des Rückenmarks nicht ausschließen wollte. Es wäre deshalb durchaus gerechtfertigt gewesen, Seeligmüllers Anteil an der Konzeptgeschichte der Myotonia congenita durch die Aufnahme seines Namens in das Eponym zu würdigen [3].

Introduction Myotonic disorders are a group of diseases affecting the muscle, in different ways. Myotonic dystrophy type 1 (DM1) is related to (CTG)n expansion in the 3-untranslated region of the dystrophia myotonica protein kinase (DMPK) gene and is the most frequent and disabling form, causing muscular, visibility, respiratory, and cardiac impairment. Non-dystrophic myotonias (NDMs) affect the skeletal muscle alone. In particular, mutations in the chloride channel (CLCN1) gene cause myotonia congenita (MC), which can have autosomal dominant or recessive inheritance. Case report We describe a patient with a family history of asymptomatic or paucisymptomatic myotonia, who presented handgrip myotonia which sharply reduced after mexiletine administration. Molecular analysis showed both a paternally inherited DMPK expansion and a maternally inherited CLCN1 mutation. Conclusions Only one other similar case was reported so far; however, the segregation of the two mutations and the characteristics of the muscle were not studied. Since our patient lacked the classical phenotypical and muscle histopathological characteristics of DM1 and showed mild splicing alterations despite a pathogenic DMPK expansion and the nuclear accumulation of toxic RNA, we may speculate that the co-occurrence of a CLCN1 mutation could have attenuated the severity of DM1 phenotype.

Introduction Mutations of the skeletal muscle sodium channel gene SCN4A are associated with several neuromuscular disorders including hyper/hypokaliemic periodic paralysis, paramyotonia congenita and sodium channel myotonia. These disorders are distinguished from dystrophic myotonias by the absence of progressive weakness and extramuscular systemic involvement. Methods We present an Italian family with 2 subjects carrying a p.Asn1180Ile mutation in SCN4A gene showing a peculiar clinical picture characterized by the association of myopathic features and myotonia. Results The clinical, electromyographic and histological findings of these patients are reported. The possible pathogenicity of the mutation was tested by three different software, all giving positive results. Discussion This is the first report of a dominant, heterozygous mutation in SCN4A causing a complex phenotype of non-congenital myopathy and myotonic syndrome. We suggest that, in patients with myotonia and myopathy not related to dystrophic myotonias, the sequence analysis of SCN4A gene should be performed.

Myotonia congenita is a rare neuromuscular disorder caused by CLCN1 mutations resulting in delayed muscle relaxation. Extramuscular manifestations are not considered to be present in chloride skeletal channelopathies, although recently some cardiac manifestations have been described. We report a family with autosomal dominant myotonia congenita and Brugada syndrome. Bearing in mind the previously reported cases of cardiac arrhythmias in myotonia congenita patients, we discuss the possible involvement of the CLCN1-gene mutations in primary cardiac arrhythmia.

Early-onset myopathy, areflexia, respiratory distress, and dysphagia (EMARDD) is caused by homozygous or compound heterozygous mutation in the

Myotonia congenita Thomsen is a rare genetic disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1). Although this channelopathy may cause disabling muscle symptoms, patient's daily routine can be almost inconspicuous. Nevertheless, during illness or acute diseases this neuromuscular disease may worsen and get clinically apparent up to severe rhabdomyolysis. Within this case report we describe and discuss the treatment of a patient with Myotonia congenita Thomsen treated at our hospital's intensive care unit. Rhabdomyolysis with acute renal failure and necessity of dialysis during the ICU stay was attributed to the initial reason for emergency hospitalization - an aortic dissection. Nevertheless, in this case the patient's myotonia caused rhabdomyolysis and initially led us on a wrong path. Diagnosis of the real cause of rhabdomyolysis is often difficult, although an early and adequate therapy may prevent complications. This case report demonstrates the importance of a thorough anamnesis with all aspects of the patient's history.

Pathogenic variants in TPM2 have been associated with a variable clinical spectrum, including congenital myopathies and distal arthrogryposis, all but one with dominant inheritance. We report the second case of recessively inherited TPM2-related Escobar variant of multiple pterygium syndrome and congenital myopathy in a patient from a consanguineous family. Ultra-structural examination of the biopsy revealed few cores/mini-cores and sparse nemaline rods. We found a novel homozygous intronic sequence variant, c.564–2A>C in TPM2. This variant is predicted to abolish the consensus acceptor splice site for exon 6b of TPM2 gene. Parents of the proband, both healthy adults with no clinical features, were heterozygous for the variant. Here we establish a homozygous intronic variant in TPM2 as the likely cause of Escobar variant of multiple pterygium syndrome and congenital myopathy, with sparse nemaline rods.

Nemaline myopathy (NM) is a congenital myopathy of great heterogeneity, characterized by the presence of rods in the cytoplasm of muscle fibers. The samples of 16 nemaline myopathy patients diagnosed by characteristically pathological features went through whole exon sequencing. Clinico-pathological and genetic features of the cases were systematically analyzed. According to the classification of nemaline myopathy by ENMC, 8 cases are typical congenital subtype, 6 cases are childhood/juvenile onset subtype and 2 case are adult onset subtype. In histological findings, characteristic purple-colored rods are discovered under modified gömöri trichrome staining (MGT). Electron microscopy revealed the presence of high electron-dense nemaline bodies around the submucosa and the nucleus nine patients (9/16 56.3%) were detected pathogenic causative mutations, among whom mutations in the NEB gene were the most frequent (6 patients, 66.7%). KBTBD13 gene mutation was discovered in two patients and ACTA1 gene mutation was discovered in 1 patient. Nemaline myopathy is a congenital myopathy with highly clinico-pathological and genetic heterogeneity. NEB gene mutation is the most common mutation, in which splicing change c.21522 +3A > G is hotspot mutation in Chinese NM patients.

Myotonia congenita is a genetic disease caused by mutations in the CLCN1 gene, which encodes for the major chloride skeletal channel ClC-1, involved in the normal repolarization of muscle action potentials and consequent relaxation of the muscle after contraction. Two allelic forms are recognized, depending on the phenotype and the inheritance pattern: the autosomal dominant Thomsen disease with milder symptoms and the autosomal recessive Becker disorder with a severe phenotype. Before the recent advances of molecular testing, the diagnosis and genetic counseling of families was a challenge due to the large number of mutations in the CLCN1 gene, found both in homozygous or in heterozygous state. Here, we studied a consanguineous family in which three members presented a variable phenotype of myotonia, associated to a combination of three different mutations in the CLCN1 gene. A pathogenic splicing site mutation which causes the skipping of exon 17 was present in homozygosis in one very severely affected son. This mutation was present in compound heterozygosis in the consanguineous parents, but interestingly it was associated to a different second variant in the other allele: c.1453 A > G in the mother and c.1842 G > C in the father. Both displayed variable, but less severe phenotypes than their homozygous son. These results highlight the importance of analyzing the combination of different variants in the same gene in particular in families with patients displaying different phenotypes. This approach may improve the diagnosis, prognosis, and genetic counseling of the involved families.

Non-dystrophic myotonias (NDM) are rare skeletal muscle channelopathies, mainly linked to two voltage-gated ion channel genes, CLCN1 and SCN4A. The aim of this study is to identify the clinical and genetic features of patients with NDM in Japan. We collected a Japanese nationwide case series of patients with clinical diagnosis of NDM (1999-2021). Among 71 out of 88 pedigrees, using Sanger and next-generation sequencing targeting both CLCN1 and SCN4A genes, variants classified as pathogenic/likely pathogenic/unknown significance were detected from CLCN1 (31 probands), SCN4A (36 probands), or both genes (4 probands), and 11 of them were novel. Pedigrees carrying mono-allelic CLCN1 variants were more commonly seen than that with bi-allelic/double variants (24:7). Compared to patients with CLCN1 variants, patients harboring SCN4A variants showed younger onset age (5.64 ± 4.70 years vs. 9.23 ± 5.21 years), fewer warm-up phenomenon, but more paramyotonia, hyperCKemia, transient muscle weakness, and cold-induced myotonia. Haplotype analysis verified founder effects of the hot spot variants in both CLCN1 (p.T539A) and SCN4A (p.T1313M). This study reveals variants in CLCN1 and SCN4A from 80.7% of our case series, extending genetic spectrum of NDM, and would further our understanding of clinical similarity/diversity between CLCN1- and SCN4A-related NDM, as well as the genetic racial differences.

Consistency of differences between non-dystrophic myotonias over time measured by standardized clinical/patient-reported outcomes is lacking. Evaluation of longitudinal data could establish clinically relevant endpoints for future research.Data from prospective observational study of 95 definite/clinically suspected non-dystrophic myotonia participants (six sites in the United States, United Kingdom, and Canada) between March 2006 and March 2009 were analyzed. Outcomes included: standardized symptom interview/exam, Short Form-36, Individualized Neuromuscular Quality of Life (INQoL), electrophysiological short/prolonged exercise tests, manual muscle testing, quantitative grip strength, modified get-up-and-go test. Patterns were assigned as described by Fournier et al. Comparisons were restricted to confirmed sodium channelopathies (SCN4A, baseline, year 1, year 2: n = 34, 19, 13), chloride channelopathies (CLCN1, n = 32, 26, 18), and myotonic dystrophy type 2 (DM2, n = 9, 6, 2).Muscle stiffness was the most frequent symptom over time (54.7%-64.7%). Eyelid myotonia and paradoxical handgrip/eyelid myotonia were more frequent in SCN4A. Grip strength and combined manual muscle testing remained stable. Modified get-up-and-go showed less warm up in SCN4A but remained stable. Median post short exercise decrement was stable, except for SCN4A (baseline to year 2 decrement difference 16.6% [Q1, Q3: 9.5, 39.2]). Fournier patterns type 2 (CLCN1) and 1 (SCN4A) were most specific; 40.4% of participants had a change in pattern over time. INQoL showed higher impact for SCN4A and DM2 with scores stable over time.Symptom frequency and clinical outcome assessments were stable with defined variability in myotonia measures supporting trial designs like cross over or combined n-of-1 as important for rare disorders.

Introduction Non-dystrophic myotonias (NDM) are heterogeneous diseases caused by mutations in CLCN1 and SCN4A. The study aimed to describe the clinical and genetic spectrum of NDM in a large German cohort. Methods We retrospectively identified all patients with genetically confirmed NDM diagnosed in our center. The following data were analyzed: demographics, family history, muscular features, cardiac involvement, CK, EMG, genotype, other tested genes, treatment perceived efficacy. Results 70 patients (age 40.2 years ± 14.9; 52.8% males) were included in our study (48 NDM-CLCN1, 22 NDM-SCN4A). The most frequent presenting symptoms were myotonia (NDM-CLCN1 83.3%, NDM-SCN4A 72.2%) and myalgia (NDM-CLCN1 57.4%, NDM-SCN4A 52.6%). Besides a more prominent facial involvement in NDM-SCN4A and cold-sensitivity in NDM-CLCN1, no other significant differences were observed between groups. Cardiac arrhythmia or conduction defects were documented in sixNDM-CLCN1 patients (three of them requiring a pacemaker) and one patient with NDM-SCN4A. CK was normal in 40% of patients. Myotonic runs in EMG were detected in 89.1% of CLCN1 and 78.9% of SCN4A. 50% of NDM-CLCN1 patients had the classic c.2680C>T (p.Arg894*) mutation. 12 new genetic variants are reported. About 50% of patients were not taking any anti-myotonic drug at the last follow-up. The anti-myotonic drugs with the best patient’s perceived efficacy were mexiletine and lamotrigine. Conclusion This study highlights the relevant clinical overlap between NDM-CLCN1 and NDM-SCN4A patients and warrants the use of early and broad genetic investigation for the precise identification of the NDM subtype. Besides the clinical and genetic heterogeneity, the limited response to current anti-myotonic drugs constitutes a continuing challenge.

In 1876, two articles appeared in Germany in different medical journals under almost the same title "Tonische Krampfe in willkurlich beweglichen Muskeln in Folge von ererbter psychischer Disposition (Ataxia muscularis?)1" by Julius Thomsen and "Tonische Krampfe in willkurlich beweglichen Muskeln (Muskelhypertrophie?)2" by Adolph Seeligmuller). The first article was by Julius Thomsen (1815-1896) from Kappeln, the second by Adolph Seeligmuller (1837-1912) from Halle (Saale). Both articles dealt with a disease that has later been referred to as myotonia congenita by Adolf Strumpell (1853-1925) in 1881. Carl Westphal (1833-1890), however, ignored the contribution of Seeligmuller and proposed to name the disease Thomsen'sche Krankheit (Thomsen disease). Despite, the temporal priority of Thomsen, the pathogenesis of the disease was more accurately described by Seeligmuller. He recognized the origin of the myotonia in voluntary muscle whereas Thomsen postulated the myotonia as a result of inherited psychological disposition. Thus, Seeligmuller's contribution to myotonia congenita has to be recognized and honored.

Skeletal muscle channelopathies, including non-dystrophic myotonia and periodic paralysis, are rare hereditary disorders caused by mutations of various ion channel genes. To define the frequency of associated mutations of skeletal muscle channelopathies in Japan, clinical and genetic data of two academic institutions, which provides genetic analysis service, were reviewed. Of 105 unrelated pedigrees genetically confirmed, 66 pedigrees were non-dystrophic myotonias [CLCN1 (n = 30) and SCN4A (n = 36)], 11 were hyperkalemic periodic paralysis (SCN4A), and 28 were hypokalemic periodic paralysis [CACNA1S (n = 16) and SCN4A (n = 12)]. Of the 30 families with myotonia congenita, dominant form (Thomsen type) consisted 67%, and unique mutations, A298T, P480T, T539A, and M560T, not found in Western countries, were commonly identified in CLCN1. Hypokalemic periodic paralysis caused by SCN4A mutations consisted 43% in Japan, which was much higher than previous reports. Furthermore, the quality of life of the patients was assessed using the patient-reported outcome measures, SF-36 and INQoL, for 41 patients. This study indicated that the etiology of skeletal muscle channelopathies in Japan was not identical to previous reports from Western countries, and provided crucial information for genetics as well as future therapeutic interventions.

The skeletal muscle channelopathies are a group of rare diseases and include non-dystrophic myotonia and periodic paralysis. Given their rarity, little has been published on the management of anaesthesia and pregnancy in this cohort despite being important aspects of care. We have conducted a large study of over 70 patients who underwent anaesthesia and 87 pregnancies to investigate the problems encountered following anaesthesia or during pregnancy. This was performed via patient surveys sent out to genetically confirmed channelopathy patients seen at the National Hospital for Neurology and Neurosurgery. Most significantly in our cohort, patients frequently experienced a worsening or precipitation of symptoms during pregnancy (75%) or following anaesthetic (31%). None of our patients developed malignant hyperthermia, although there are confirmed reports of this in patients with periodic paralysis and mutations in RYR1. There was a significantly higher number of miscarriages compared to the normal population. There was no significant difference in antenatal or delivery complications compared to the general population. However, three neonates did have complications, all of whom were found to carry mutations in SCN4A. This study highlights the importance of counselling patients and clinicians for the possibility of worsening symptoms during pregnancy or anaesthesia and the careful management of neonates following delivery.

A 10-year-old boy presented with muscle stiffness of all extremities. His symptoms typically began during the second or third period of his hockey games and were intermittent, resolving within minutes of cessation of activity. Otherwise, he was asymptomatic. He was able to play baseball and soccer without similar symptoms, and he and his family denied clear triggers such as cold, heat, or meals with high carbohydrates or potassium. He denied vision problems, facial weakness, dysphagia, dysarthria, dyspnea, orthopnea, cramping, and fasciculations. He also denied sensory changes and bladder or bowel dysfunction. His family history was notable for myotonia congenita in his father, who was genetically heterozygous in 2007 for the pathogenic c.1437_1450del variant in the CLCN1 gene.1 His father reported similar symptoms including stiffness exacerbated by physical exertion. His parents were specifically concerned that the patient had inherited the mutation from his father. On neurologic examination, the patient had eyelid myotonia and trace percussion myotonia in the right thenar eminence. Strength was 5/5 throughout, and deep tendon reflexes were 2+ and symmetrical in all 4 extremities. Muscle bulk and tone were normal, sensory examination was normal, and coordination was intact. The patient's father had grip and eyelid myotonia and muscle hypertrophy.

Brody disease is a rare myopathy characterized by exercise-induced muscle stiffness caused by mutations in the ATP2A1 gene. In the largest cohort of Brody patients to date, Molenaar et al. clarify the phenotype and diagnostic possibilities to help improve understanding and recognition of this distinct myopathy., Brody disease is an autosomal recessive myopathy characterized by exercise-induced muscle stiffness due to mutations in the ATP2A1 gene. Almost 50 years after the initial case presentation, only 18 patients have been reported and many questions regarding the clinical phenotype and results of ancillary investigations remain unanswered, likely leading to incomplete recognition and consequently under-diagnosis. Additionally, little is known about the natural history of the disorder, genotype-phenotype correlations, and the effects of symptomatic treatment. We studied the largest cohort of Brody disease patients to date (n = 40), consisting of 22 new patients (19 novel mutations) and all 18 previously published patients. This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids. Onset begins in childhood and there was no or only mild progression of symptoms over time. Four patients had episodes resembling malignant hyperthermia. The key finding at physical examination was delayed relaxation after repetitive contractions. Additionally, no atrophy was seen, muscle strength was generally preserved, and some patients had a remarkable athletic build. Symptomatic treatment was mostly ineffective or produced unacceptable side effects. EMG showed silent contractures in approximately half of the patients and no myotonia. Creatine kinase was normal or mildly elevated, and muscle biopsy showed mild myopathic changes with selective type II atrophy. Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) activity was reduced and western blot analysis showed decreased or absent SERCA1 protein. Based on this cohort, we conclude that Brody disease should be considered in cases of exercise-induced muscle stiffness. When physical examination shows delayed relaxation, and there are no myotonic discharges at electromyography, we recommend direct sequencing of the ATP2A1 gene or next generation sequencing with a myopathy panel. Aside from clinical features, SERCA activity measurement and SERCA1 western blot can assist in proving the pathogenicity of novel ATP2A1 mutations. Finally, patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended. This study will help improve understanding and recognition of Brody disease as a distinct myopathy in the broader field of calcium-related myopathies.

INTRODUCTION Brody myopathy (BM) is a recessive condition caused by mutations in the ATP2A1 gene and usually induces impaired muscle relaxation during and after exercise. Diagnosis relies on needle electromyography showing electrical silence, muscle biopsy with decreased sarcoplasmic reticulum calcium adenosine triphosphatase activity, and genetic analysis. Electrodiagnostic functional analyses are useful in the diagnosis of channelopathies, and thus may be impaired in BM. METHODS We performed exercise tests and repetitive nerve stimulation (RNS; 10 supramaximal stimuli at 3 Hz) in 10 patients with BM. RESULTS All participants showed incremental responses on RNS. Compound muscle action potential amplitude was increased and duration was decreased, especially in the ulnar nerve (+30.2 ± 7.1% and - 30.3 ± 2.8%, respectively; both P

The Bailey-Bloch congenital myopathy, also known as Native American myopathy (NAM), is an autosomal recessive congenital myopathy first reported in the Lumbee tribe people settled in North Carolina (USA), and characterized by congenital weakness and arthrogryposis, cleft palate, ptosis, short stature, kyphoscoliosis, talipes deformities, and susceptibility to malignant hyperthermia (MH) triggered by anesthesia. NAM is linked to STAC3 gene coding for a component of excitation-contraction coupling in skeletal muscles. A homozygous missense variant (c.851G C; p.Trp284Ser) in STAC3 segregated with NAM in the Lumbee families. Non-Native American patients with STAC3 related congenital myopathy, and with other various variants of STAC3 have been reported. Here, we present seven patients from the Comoros Islands (located in the Mozambique Channel) diagnosed with STAC3 related congenital myopathy and having the recurrent variant identified in the Lumbee people. The series is the second largest series of patients having STAC3 related congenital myopathy with a shared ethnicity after le Lumbee series. Local history and geography may explain the overrepresentation of NAM in the Comorian Archipelago with a founder effect. Further researches would be necessary for the understanding of the onset of the NAM in Comorian population as search of the "classical" STAC3 variant in East African population, and haplotypes comparison between Comorian and Lumbee patients.

In myotonia congenita (MC), activation with exercise or cooling can induce transient changes in compound motor action potential (CMAP) parameters, thus providing a guide to genetic analysis.We performed the short exercise test (SET) and the short exercise test with cooling (SETC) in 30 patients with genetically confirmed Becker disease (BMC) to estimate their utility in the diagnosis of BMC.Although we observed a significant decrease in CMAP amplitude immediately after maximal voluntary effort in both tests in the whole BMC group, in men this decline was significantly smaller than in women, especially in SET. Clinical implications/future directions: In men with a clinical suspicion of BMC, a small decrease in CMAP amplitude in SET together with a typical decline in SETC does not exclude the diagnosis of BMC. Our results show a sex-specific difference in chloride channel function in BMC, which needs further investigation.

Native American Myopathy (NAM) is an inherited, malignant hyperthermia-susceptible myopathy associated with abnormal craniofacial development and neuromuscular scoliosis. There is scant NAM anesthetic literature and, to our knowledge, no existing publications describing the anesthetic management of a NAM parturient. The constellation of symptoms of NAM in the parturient presents a number of challenges to the obstetric anesthesiologist, including difficult airway associated with craniofacial abnormalities and pregnancy, malignant hyperthermia susceptibility, and possible difficult neuraxial block. In this report, we present the anesthetic management of a parturient with NAM and previous extensive posterior spinal fusion undergoing cesarean delivery under general anesthesia.

Inherited channelopathies are a clinically and heritably heterogeneous group of disorders that result from ion channel dysfunction. The aim of this study was to characterize the clinicopathologic features of a Belgian Blue x Holstein crossbred calf with paradoxical myotonia congenita, craniofacial dysmorphism, and myelodysplasia, and to identify the most likely genetic etiology. The calf displayed episodes of exercise-induced generalized myotonic muscle stiffness accompanied by increase in serum potassium. It also showed slight flattening of the splanchnocranium with deviation to the right side. On gross pathology, myelodysplasia (hydrosyringomielia and segmental hypoplasia) in the lumbosacral intumescence region was noticed. Histopathology of the muscle profile revealed loss of the main shape in 5.3% of muscle fibers. Whole-genome sequencing revealed a heterozygous missense variant in KCNG1 affecting an evolutionary conserved residue (p.Trp416Cys). The mutation was predicted to be deleterious and to alter the pore helix of the ion transport domain of the transmembrane protein. The identified variant was present only in the affected calf and not seen in more than 5200 other sequenced bovine genomes. We speculate that the mutation occurred either as a parental germline mutation or post-zygotically in the developing embryo. This study implicates an important role for KCNG1 as a member of the potassium voltage-gated channel group in neurodegeneration. Providing the first possible KCNG1-related disease model, we have, therefore, identified a new potential candidate for related conditions both in animals and in humans. This study illustrates the enormous potential of phenotypically well-studied spontaneous mutants in domestic animals to provide new insights into the function of individual genes.

Congenital myopathies are rare neuromuscular hereditary disorders that manifest at birth or during infancy and usually appear with muscle weakness and hypotonia. One of such disorders, early-onset myopathy, areflexia, respiratory distress, and dysphagia (EMARDD, OMIM: 614399, MIM: 612453), is a rare autosomal recessive disorder caused by biallelic mutations (at homozygous or compound heterozygous status) in MEGF10 (multiple epidermal growth factor-like domains protein family). Here, we report two unrelated patients, who were born to consanguineous parents, having two novel MEGF10 deleterious variants. Interestingly, the presence of MEGF10 associated EMARDD has not been reported in Saudi Arabia, a highly consanguineous population. Moreover, both variants lead to a different phenotypic onset of mild and severe types. Our work expands phenotypic features of the disease and provides an opportunity for genetic counseling to the inflicted families.

Background:CLCN1-related myotonia congenita (MC) is one of the most common forms of non-dystrophic myotonia, in which muscle relaxation is delayed after voluntary or evoked contraction. However, there is limited data of clinical and molecular spectrum of MC patients in China.Patients and Methods: Five patients with myotonia congenita due to mutations in CLCN1 gene were enrolled, which were identified through trio-whole-exome sequencing or panel-based next-generation sequencing test. The clinical presentation, laboratory data, electrophysiological tests, muscular pathology feature, and genetic results were collected and reviewed. We also searched all previously reported cases of MC patients with genetic diagnosis in Chinese populations, and their data were reviewed.Results: The median onset age of five patients was 3.0 years old, ranging from 1.0 to 5.0 years old, while the median age of admit was 5.0 years old, ranging from 3.5 to 8.8 years old. Five patients complained of muscle stiffness when rising from chairs or starting to climb stairs (5/5, 100.0%), four patients complained of delayed relaxation of their hands after forceful grip (4/5, 80.0%), all of which improved with exercise (warm-up phenomenon) (5/5, 100%). Electromyogram was conducted in five patients, which all revealed myotonic change (100%). Genetic tests revealed nine potential disease-causing variants in CLCN1 gene, including two novel variants: c.962T>A (p.V321E) and c.1250A>T (p.E417V). Literature review showed that 43 MC Chinese patients with genetic diagnosis have been reported till now (including our five patients). Forty-seven variants in CLCN1 gene were found, which consisted of 33 missense variants, 6 nonsense variants, 5 frame-shift variants, and 3 splicing variants. Variants in exon 8, 15, 12, and 16 were most prevalent, while the most common variants were c.892G>A (p.A298T) (n = 9), c.139C>T (p.R47W) (n = 3), c.1205C>T(p.A402V) (n = 3), c.1657A>T (p.I553F) (n = 3), c.1679T>C (p.M560T) (n = 3), c.350A>G (p.D117G) (n = 2), c.762C>G (p.C254W) (n = 2), c.782A>G (P.Y261C) (n = 2), and c.1277C>A (p.T426N) (n = 2).Conclusion: Our results reported five CLCN1-related MC patients, which expanded the clinical and genetic spectrum of MC patients in China. Based on literature review, 43MC Chinese patients with genetic diagnosis have been reported till now, and variants in exon eight were most prevalent in Chinese MC patients while c.892G>A (p.A298T) was probably a founder mutation.

Nemaline myopathy (NM), a structural congenital myopathy, presents a significant clinical and genetic heterogeneity. Here, we compiled molecular and clinical data of 30 Brazilian patients from 25 unrelated families. Next-generation sequencing was able to genetically classify all patients: sixteen families (64%) with mutation in NEB, five (20%) in ACTA1, two (8%) in KLHL40, and one in TPM2 (4%) and TPM3 (4%). In the NEB-related families, 25 different variants, 11 of them novel, were identified; splice site (10/25) and frame shift (9/25) mutations were the most common. Mutation c.24579 G>C was recurrent in three unrelated patients from the same region, suggesting a common ancestor. Clinically, the “typical” form was the more frequent and caused by mutations in the different NM genes. Phenotypic heterogeneity was observed among patients with mutations in the same gene. Respiratory involvement was very common and often out of proportion with limb weakness. Muscle MRI patterns showed variability within the forms and genes, which was related to the severity of the weakness. Considering the high frequency of NEB mutations and the complexity of this gene, NGS tools should be combined with CNV identification, especially in patients with a likely non-identified second mutation.

Background Defects in the RYR1 (OMIM#180901) gene lead to Ryanodine receptor type 1‐related myopathies (RYR1‐RM); the most common subgroup of congenital myopathies. Methods Congenital myopathy presents a diagnostic challenge due to the need for multiple testing modalities to identify the many different genetic etiologies. In this case, the patient remained undiagnosed after whole‐exome sequencing (WES), chromosomal microarray, methylation analysis, targeted deletion and duplication studies, and targeted repeat expansion studies. Clinical whole‐genome sequencing (WGS) was then pursued as part of a research study to identify a diagnosis. Results WGS identified compound heterozygous RYR1 intronic variants, RNA sequencing confirmed both variants to be pathogenic causing RYR1‐RM in a phenotype of severe congenital hypotonia with respiratory failure from birth, neonatal brain hemorrhage, and congenital heart disease involving transposition of the great arteries. Conclusion While there is an ongoing debate about the clinical superiority of WGS versus WES for patients with a suspected genetic condition, this scenario highlights a weakness of WES as well as the added cost and delay in diagnosis timing with having WGS follow WES or even ending further genetic testing with a negative WES. While knowledge gaps still exist for many intronic variants, transcriptome analysis provides a way of validating the resulting dysfunction caused by these variants and thus allowing for appropriate pathogenicity classification. This is the second published case report of a patient with pathogenic intronic variants in RYR1‐RM, with clinical RNA testing confirming variant pathogenicity and therefore the diagnosis suggesting that for some patients careful analysis of a patient's genome and transcriptome are required for a complete genetic evaluation. The diagnostic odyssey experienced by this patient highlights the importance of early, rapid WGS.

To date there are no therapies for patients with congenital myopathies, muscle disorders causing poor quality of life of affected individuals. In approximately 30% of the cases, patients with congenital myopathies carry either dominant or recessive mutations in the ryanodine receptor 1 (

Myotonia congenita was first described as an entity in 1876 by Julius Thomsen. Shortly later in the same year it was criticized by Adolph Seeligmüller who extended the clinical findings. Charles Bell, Moritz Benedict and Ernst von Leyden had already partly described the symptoms of the disease before 1876, but did not recognize this as a new entity. A comparison of the publications of Thomsen and Seeligmüller in 1876 and of Seeligmüller's textbook published in 1887, as well as the today's genetically proven disease shows that Seeligmüller correctly criticized two aspects of Thomsen's publication: (i) Thomsen suspected the pathogenesis to be in "one half of the brain's activity, the will" with "seat in the cerebrospinal system" and (ii) he made the assumption of a coordination disorder in the sense of an ataxia [1]. Due to a better understanding of the pathogenesis enabled by Seeligmüller's postulate of a "more difficult mobile muscle substance" [2] without excluding an inborn affection of the lateral cords of the spinal cord, it would have been entirely justified to recognize Seeligmüller's contribution to the conceptual history of Myotonia congenita by including his name in the eponym [3].Die Erkrankung Myotonia congenita wurde als Entität 1876 erstmals durch Julius Thomsen beschrieben. Noch im gleichen Jahr wurde diese Beschreibung von Adolph Seeligmüller kritisch betrachtet und um wesentliche Befunde ergänzt. Bereits Charles Bell, Moritz Benedict und Ernst von Leyden hatten vor 1876 die Symptomatik der Erkrankung beschrieben, ohne jedoch eine neue Entität anzunehmen. Der Vergleich der Publikationen von Thomsen und Seeligmüller von 1876 untereinander und mit Seeligmüllers Lehrbuchkapitel von 1887 sowie mit dem heute genetisch gesicherten Krankheitsbild zeigt, dass Seeligmüller zurecht zwei Aspekte an Thomsens Publikation kritisierte: (i) Die von Thomsen vermutete Pathogenese in „der einen Thätigkeitshälfte des Gehirns, des Willens“ mit „Sitz im Cerebrospinalsysteme“ und (ii) die Annahme einer Koordinationsstörung im Sinne einer Ataxie [1]. Demgegenüber diskutierte Seeligmüller eine „schwerer beweglich Muskelsubstanz“ [2] als Pathogenese mit der er gleichwohl eine angeborene Affection der Seitenstränge des Rückenmarks nicht ausschließen wollte. Es wäre deshalb durchaus gerechtfertigt gewesen, Seeligmüllers Anteil an der Konzeptgeschichte der Myotonia congenita durch die Aufnahme seines Namens in das Eponym zu würdigen [3].

Mouse models of skeletal muscle channelopathies are not phenocopies of human disease. In some cases (e.g. Myotonia Congenita) the phenotype is much more severe, whilst in others (e.g. Hypokalaemic periodic paralysis) rodent physiology is protective. This suggests a species' difference in muscle excitability properties. In humans these can be measured indirectly by the post-impulse changes in conduction velocity, using Muscle Velocity Recovery Cycles (MVRCs). We performed MVRCs in mice and compared their muscle excitability properties with humans. Mouse Tibialis Anterior MVRCs (n = 70) have only one phase of supernormality (increased conduction velocity), which is smaller in magnitude (p = 9 × 10-21), and shorter in duration (p = 3 × 10-24) than human (n = 26). This abbreviated supernormality is followed by a period of late subnormality (reduced velocity) in mice, which overlaps in time with the late supernormality seen in human MVRCs. The period of late subnormality suggests increased t-tubule Na+/K+-pump activity. The subnormal phase in mice was converted to supernormality by blocking ClC-1 chloride channels, suggesting relatively higher chloride conductance in skeletal muscle. Our findings help explain discrepancies in phenotype between mice and humans with skeletal muscle channelopathies and potentially other neuromuscular disorders. MVRCs are a valuable new tool to compare in vivo muscle membrane properties between species and will allow further dissection of the molecular mechanisms regulating muscle excitability.

Myotonia congenita is a rare non-dystrophic skeletal muscle disease characterized by an inability to relax skeletal muscles after abrupt voluntary movements. Patients with this condition have stiff muscles and difficulty with mobility, especially when initiating movement after periods of rest. It is well known that movement disorders are a common side effect of antipsychotics due to their ability to antagonize dopamine 2 receptors in the extrapyramidal part of the basal ganglia. The purpose of this case is to describe the effects antipsychotics had on a 59-year-old Caucasian male with comorbid myotonia congenita and schizophrenia in an inpatient psychiatric hospital setting. Medication trials of ziprasidone, haloperidol and clozapine exacerbated his myotonic symptoms leading to falls and complaints of severe muscle stiffness, which were relieved upon discontinuation of all antipsychotic medications. This suggests that patients with myotonia congenita may have an increased sensitivity to the extrapyramidal side effect profile of antipsychotics. Treatment options for this patient case are discussed with an emphasis on lamotrigine. Keywords: Myotonia congenita; Schizophrenia; Myopathy; Antipsychotics; Extrapyramidal symptoms

Patients with myotonia congenita suffer from muscle stiffness caused by muscle hyperexcitability. Although loss-of-function mutations in the ClC-1 muscle chloride channel have been known for 25 years to cause myotonia congenita, this discovery has led to little progress on development of therapy. Currently, treatment is primarily focused on reducing hyperexcitability by blocking Na+ current. However, other approaches such as increasing K+ currents might also be effective. For example, the K+ channel activator retigabine, which opens KCNQ channels, is effective in treating epilepsy because it causes hyperpolarization of the resting membrane potential in neurons. In this study, we found that retigabine greatly reduced the duration of myotonia in vitro. Detailed study of its mechanism of action revealed that retigabine had no effect on any of the traditional measures of muscle excitability such as resting potential, input resistance or the properties of single action potentials. Instead it appears to shorten myotonia by activating K+ current during trains of action potentials. Retigabine also greatly reduced the severity of myotonia in vivo, which was measured using a muscle force transducer. Despite its efficacy in vivo, retigabine did not improve motor performance of mice with myotonia congenita. There are a number of potential explanations for the lack of motor improvement in vivo including central nervous system side effects. Nonetheless, the striking effectiveness of retigabine on muscle itself suggests that activating potassium currents is an effective method to treat disorders of muscle hyperexcitability.

Objective To report the efficacy and safety of lamotrigine in the treatment of one case of Becker myotonia congenita. Methods and Results A 17-year-old male had muscle stiffness in the limbs as the first symptom, which could be alleviated after repeated exercise. The creatine kinase (CK) level was normal. Genetic testing showed there were two missense mutations c.1205C > T (p.Ala402Val) and c.896T > C (p.Val299Ala) located in exon 11 and 8 of CLCN1 gene respectively in the proband. The missense mutation c.1205C > T (p.Ala402Val) in exon 11 was found out in his mother and c.896T > C (p.Val299Ala) located in exon 8 was found out in his father. The latter, exon 8 c.896T > C of CLCN1 gene has not been reported. The proband was clearly diagnosed as Becker myotonia congenita, and his family was diagnosed as Becker myotonia congenita pedigree. After 5 years' treatment with lamotrigine, the symptom of myotonia was significantly improved and no adverse reactions was observed. Conclusions The missense mutation in exon 8 c.896T > C in this patient further expanded the CLCN1 gene mutation spectrum. Lamotrigine is effective in treating Becker myotonia congenita, providing a new idea for the treatment of myotonia congenita. DOI: 10.3969/j.issn.1672-6731.2019.05.009

The identification of genes implicated in myopathies is essential for diagnosis and for revealing novel therapeutic targets. Here we characterize a novel subclass of congenital myopathy at the morphological, molecular, and functional level. Through exome sequencing, we identified de novo ACTN2 mutations, a missense and a deletion, in two unrelated patients presenting with progressive early-onset muscle weakness and respiratory involvement. Morphological and ultrastructural analyses of muscle biopsies revealed a distinctive pattern with the presence of muscle fibers containing small structured cores and jagged Z-lines. Deeper analysis of the missense mutation revealed mutant alpha-actinin-2 properly localized to the Z-line in differentiating myotubes and its level was not altered in muscle biopsy. Modelling of the disease in zebrafish and mice by exogenous expression of mutated alpha-actinin-2 recapitulated the abnormal muscle function and structure seen in the patients. Motor deficits were noted in zebrafish, and muscle force was impaired in isolated muscles from AAV-transduced mice. In both models, sarcomeric disorganization was evident, while expression of wild-type alpha-actinin-2 did not result in muscle anomalies. The murine muscles injected with mutant ACTN2 displayed cores and Z-line defects. Dominant ACTN2 mutations were previously associated with cardiomyopathies, and our data demonstrate that specific mutations in the well-known Z-line regulator alpha-actinin-2 can cause a skeletal muscle disorder.

International audience; The MYOMEX study was a multicentre, randomised, double-blind, placebo-controlled, cross-over study aimed to compare the effects of mexiletine vs. placebo in patients with myotonia congenita (MC) and paramyotonia congenita (PC). The primary endpoint was the selfreported score of stiffness severity on a 100 mm visual analogic scale (VAS). Mexiletine treatment started at 200 mg/day and was up-titrated by 200 mg increment each three days to reach a maximum dose of 600 mg/day for total treatment duration of 18 days for each cross-over period. The modified intent-to-treat population included 25 patients (13 with MC and 12 with PC; mean age, 43.0 years; male, 68.0%). The median VAS score for mexiletine was 71.0 at baseline and decreased to 16.0 at the end of the treatment while the score did not change for placebo (81.0 at baseline vs. 78.0 at end of treatment). A mixed effects linear model analysis on ranked absolute changes showed a significant effect of treatment (p < 0.001). The overall score of the Individualized Neuromuscular Quality of Life questionnaire (INQoL) was significantly improved (p < 0.001). No clinically significant adverse events were reported. In conclusion, mexiletine improved stiffness and quality of life in patients with nondystrophic myotonia and was well tolerated.

The MYOMEX study was a multicentre, randomised, double-blind, placebo-controlled, cross-over study aimed to compare the effects of mexiletine vs. placebo in patients with myotonia congenita (MC) and paramyotonia congenita (PC). The primary endpoint was the self-reported score of stiffness severity on a 100 mm visual analogic scale (VAS). Mexiletine treatment started at 200 mg/day and was up-titrated by 200 mg increment each three days to reach a maximum dose of 600 mg/day for total treatment duration of 18 days for each cross-over period. The modified intent-to-treat population included 25 patients (13 with MC and 12 with PC; mean age, 43.0 years; male, 68.0%). The median VAS score for mexiletine was 71.0 at baseline and decreased to 16.0 at the end of the treatment while the score did not change for placebo (81.0 at baseline vs. 78.0 at end of treatment). A mixed effects linear model analysis on ranked absolute changes showed a significant effect of treatment (p 0.001). The overall score of the Individualized Neuromuscular Quality of Life questionnaire (INQoL) was significantly improved (p 0.001). No clinically significant adverse events were reported. In conclusion, mexiletine improved stiffness and quality of life in patients with nondystrophic myotonia and was well tolerated.

Background Myotonia congenita (MC) is a common channelopathy affecting skeletal muscle and which is due to pathogenic variants within the CLCN1 gene. Various alterations in the function of the channel have been reported and we here illustrate a novel one. Methods A patient presenting the symptoms of myotonia congenita was shown to bear a new heterozygous missense variant in exon 9 of the CLCN1 gene (c.1010 T > G, p.(Phe337Cys)). Confocal imaging and patch clamp recordings of transiently transfected HEK293 cells were used to functionally analyze the effect of this variant on channel properties. Results Confocal imaging showed that the F337C mutant incorporated as well as the WT channel into the plasma membrane. However, in patch clamp, we observed a smaller conductance for F337C at −80 mV. We also found a marked reduction of the fast gating component in the mutant channels, as well as an overall reduced voltage dependence. Conclusion To our knowledge, this is the first report of a mixed alteration in the biophysical properties of hClC‐1 consisting of a reduced conductance at resting potential and an almost abolished voltage dependence., We describe a rare variant of the CLCN1 gene which was found in one family. Functional analysis demonstrated that the channel inserts normally into the membrane, but has a low conductance at −80 mV and a severely reduced voltage‐dependence.

Non-dystrophic myotonias have been linked to loss-of-function mutations in the ClC-1 chloride channel or gain-of-function mutations in the Nav1.4 sodium channel. Here, we describe a family with members diagnosed with Thomsen’s disease. One novel mutation (p.W322*) in CLCN1 and one undescribed mutation (p.R1463H) in SCN4A are segregating in this family. The CLCN1-p.W322* was also found in an unrelated family, in compound heterozygosity with the known CLCN1-p.G355R mutation. One reported mutation, SCN4A-p.T1313M, was found in a third family. Both CLCN1 mutations exhibited loss-of-function: CLCN1-p.W322* probably leads to a non-viable truncated protein, for CLCN1-p.G355R, we predict structural damage, triggering important steric clashes. The SCN4A-p.R1463H produced a positive shift in the steady-state inactivation increasing window currents and a faster recovery from inactivation. These gain-of-function effects are probably due to a disruption of interaction R1463-D1356, which destabilizes the voltage sensor domain (VSD) IV and increases the flexibility of the S4-S5 linker. Finally, modelling suggested that the p.T1313M induces a strong decrease in protein flexibility on the III-IV linker. This study demonstrates that CLCN1-p.W322* and SCN4A-p.R1463H mutations can act alone or in combination as inducers of myotonia. Their co-segregation highlights the necessity for carrying out deep genetic analysis to provide accurate genetic counseling and management of patients.

El síndrome de Becker es una miotonia congénita de herencia autosómica recesiva que se produce por mutaciones en el gen del canal de cloro de músculo esquelético (CLCN1) conduciento a un defecto de la función de este. Generalmente inicia en la infancia y las miotonías son la principal manifestación clínica, las cuales consisten en sensación de imovilidad luego de la contracción muscular voluntaria que típicamente se acompañan de fenómeno de calentamiento en la que los pacientes presentan mejoría de la miotonía con la contracción muscular repetida. Las miotonías pueden ser dolorosas, asociarse a debilidad transtoria o fija y generalmente se ve un fenotipo atlético desde la infancia. En la actualidad solo puede ofrecerse un tratamiento sintomático de las miotonías dado no existe manejo farmacológico modificador de la enfermedad. Objetivo: Caracterizar los aspectos clínicos y electrofisiológicos de un paciente con miotonía congénita de Becker atendido en la Fundación Santa Fé de Bogotá en el 2021. Metodología: Estudio observacional descriptivo tipo reporte de caso Resultados: Se presenta el reporte de caso de un paciente con miotonía congénita de Becker Conclusiones: un adecuado abordaje diagnóstico guiará a un pronto reconocimiento y manejo de la enfermedad. Becker syndrome is a congenital myotonia of autosomal recessive inheritance that is produced by mutations in the skeletal muscle chlorine gene (CLCN1) leading to a defect in its function. It generally begins in childhood and myotonia is the main clinical manifestation, which consists of a sensation of immobility after voluntary muscle contraction that is usually accompanied by a ‘‘warm-up’’ effect in which patients present an improvement in myotonia with repeated muscle contraction. . Myotonias can be painful, associated with transient or fixed weakness, and an athletic phenotype is generally seen from infancy. At present, only a symptomatic treatment of myotonias can be offered since there is no modifying pharmacological management of the disease. 2022-02-09 15:30:03: Script de automatizacion de embargos. Correo recibido 1 dic 2021: Buenas noches, escribe Laura Peña Guzmán, Fellow de Neurofisiología Clínica- Nervio y músculo. Te escribo porque quiero publicar mi tesis de grado titulada: miotonía congénita: reporte de un caso; estoy decidiendo la revista según requisitos por lo que solicito que por favor mi tesis quede bloqueada para publicación. Gracias. Respuesta 9 feb 2022: Hemos realizado la publicación de su documento: Miotonía congénita: reporte de un caso, el cual puede consultar en el siguiente enlace: https://repository.urosario.edu.co/handle/10336/33430 De acuerdo con su solicitud, el documento ha quedado embargado por 2 años hasta el 9 de febrero de 2024 en concordancia con las Políticas de Acceso Abierto de la Universidad. Si usted desea dejarlo con acceso abierto antes de finalizar dicho periodo o si por el contrario desea extender el embargo al finalizar este tiempo, puede enviar un correo a esta misma dirección realizando la solicitud. Tenga en cuenta que los documentos en acceso abierto propician una mayor visibilidad de su producción académica. De otra parte, dado que desea publicar su obra en una revista de prestigio, queremos invitarla a tomar una asesoría con nuestros asesores de información del CRAI, quienes podrán brindarle orientación en la identificación de una revista adecuada para su obra y acompañamiento en la edición para publicación. La solicitud de asesoría puede agendarla en el siguiente link: https://n9.cl/agendamiento_servicios_crai

Mutations in the sarcomeric protein titin, encoded byTTN, are emerging as a common cause of myopathies. The diagnosis of aTTN-related myopathy is, however, often not straightforward due to clinico-pathological overlap with other myopathies and the prevalence ofTTNvariants in control populations. Here, we present a combined clinico-pathological, genetic and biophysical approach to the diagnosis ofTTN-related myopathies and the pathogenicity ascertainment ofTTNmissense variants. We identified 30 patients with a primaryTTN-related congenital myopathy (CM) and two truncating variants, or one truncating and one missenseTTNvariant, or homozygous for oneTTNmissense variant. We found that TTN-related myopathies show considerable overlap with other myopathies but are strongly suggested by a combination of certain clinico-pathological features. Presentation was typically at birth with the clinical course characterized by variable progression of weakness, contractures, scoliosis and respiratory symptoms but sparing of extraocular muscles. Cardiac involvement depended on the variant position. Our biophysical analyses demonstrated that missense mutations associated with CMs are strongly destabilizing and exert their effect when expressed on a truncating background or in homozygosity. We hypothesise that destabilizingTTNmissense mutations phenocopy truncating variants and are a key pathogenic feature of recessive titinopathies that might be amenable to therapeutic intervention.