De novo variant in SCN4A causes neonatal sodium channel myotonia with general muscle stiffness and respiratory failure.

Variants of the skeletal muscle sodium channel gene SCN4A are associated with different neuromuscular disorders including sodium channel myotonia. Here, we report an infant with a de novo variant in SCN4A presenting with neonatal onset of severe muscle stiffness with involvement of facial and eyelid muscles, and life-threatening events with respiratory failure due to severe apnoea and thorax rigidity. The boy dramatically improved in both respiratory and motor function under carbamazepine therapy.

[Diagnosis and treatment of congenital myopaties]. / Diagnóstico y tratamiento de las miopatías congénitas.

Important advances have been made in the field of congenital myopathies in recent years, forcing clinicians to constantly review and update this group of diseases. The increasing identification of new genes and phenotypes associated with already known genes has been possible to a great extent thanks to the development accomplished in next generation sequencing techniques, which are increasingly accessible. Knowing better the phenotypic spectrum of these entities allows to establish a phenotype/genotype correlation in some subgroups. The best understanding of the pathophysiology and natural history of these diseases are fundamental to design new therapies. The first clinical trials in the field of gene therapy are already a reality and are showing positive results, creating a new expectation for patients, families and specialists, which will be reflected in the need to adapt the protocols of care, diagnosis and treatment of some of these entities. It is essential that pediatric neurologists, pediatricians, physiotherapists and other professionals involved in the care of these patients are informed and updated on the advances in this group of diseases.

Existen importantes avances en el campo de las miopatías congénitas en los últimos años que obligan a la revisión y actualización constante de este grupo de enfermedades. La identificación creciente de nuevos genes y fenotipos asociados a genes ya conocidos, fue posible en gran medida gracias al avance de las técnicas de secuenciación de nueva generación, cada vez más accesibles. El conocer mejor el espectro fenotípico de estas entidades, permite establecer una correlación fenotipo/genotipo en algunos subgrupos. La mejor compresión de la fisiopatología e historia natural de estas enfermedades, son fundamentales para el desarrollo de nuevas terapias. Los primeros ensayos clínicos en el campo de la terapia génica ya son una realidad y están mostrando resultados positivos, creando una nueva expectativa en paciente, familiares y especialistas, lo que se verá reflejado en la necesidad de adaptar los protocolos de atención, diagnóstico y tratamiento de algunas de estas entidades. Es fundamental que los neuropediatras, pediatras, fisioterapeutas y otros profesionales involucrados en el cuidado de estos pacientes, estén informados y actualizados de los avances en este grupo de enfermedades.

Diagnóstico y tratamiento de las miopatías congénitas / Diagnosis and treatment of congenital myopaties

Existen importantes avances en el campo de las miopatías congénitas en los últimos años que obligan a la revisión y actualización constante de este grupo de enfermedades. La identificación creciente de nuevos genes y fenotipos asociados a genes ya conocidos, fue posible en gran medida gracias al avance de las técnicas de secuenciación de nueva generación, cada vez más accesibles. El conocer mejor el espectro fenotípico de estas entidades, permite establecer una correlación fenotipo/genotipo en algunos subgrupos. La mejor compresión de la fisiopatología e historia natural de estas enfermedades, son fundamentales para el desarrollo de nuevas terapias. Los primeros ensayos clínicos en el campo de la terapia génica ya son una realidad y están mostrando resultados positivos, creando una nueva expectativa en paciente, familiares y especialistas, lo que se verá reflejado en la necesidad de adaptar los protocolos de atención, diagnóstico y tratamiento de algunas de estas entidades. Es fundamental que los neuropediatras, pediatras, fisioterapeutas y otros profesionales involucrados en el cuidado de estos pacientes, estén informados y actualizados de los avances en este grupo de enfermedades.

Important advances have been made in the field of congenital myopathies in recent years, forcing clinicians to constantly review and update this group of diseases. The increasing identification of new genes and phenotypes associated with already known genes has been possible to a great extent thanks to the development accomplished in next generation sequencing techniques, which are increasingly accessible. Knowing better the phenotypic spectrum of these entities allows to establish a phenotype/genotype correlation in some subgroups. The best understanding of the pathophysiology and natural history of these diseases are fundamental to design new therapies. The first clinical trials in the field of gene therapy are already a reality and are showing positive results, creating a new expectation for patients, families and specialists, which will be reflected in the need to adapt the protocols of care, diagnosis and treatment of some of these entities. It is essential that pediatric neurologists, pediatricians, physiotherapists and other professionals involved in the care of these patients are informed and updated on the advances in this group of diseases.

Aerobic training in myotonia congenita: Effect on myotonia and fitness.

INTRODUCTION: Exercise has not been investigated in myotonia congenita (MC). We investigated whether regular aerobic training can reduce myotonia and improve fitness. METHODS: Untrained patients with MC (age: 24-62 years; n = 6) completed 28 ± 3 sessions of 30-minute cycle ergometer training at 75% of maximal capacity for 11 ± 1 weeks. Fitness was evaluated by maximal oxygen uptake. The level of myotonia was assessed by the Myotonia Behavior Scale, 14 step stair test, timed up and go test, and hand and eye closure-open tests. RESULTS: Training increased fitness by 9% (95% confidence interval [CI], 1-17%; P = 0.02) and maximal workload by 10% (95% CI, 3-18%; P = 0.03). None of the myotonia tests changed in a clinically meaningful way. CONCLUSIONS: Regular endurance training improves fitness and maximal workload performance in patients with MC. The lack of creatine kinase elevations indicates that muscle damage did not occur. Improved fitness, however, did not change myotonic symptoms in this small cohort. Muscle Nerve 56: 696-699, 2017.

Current and future therapeutic approaches to the congenital myopathies.

The congenital myopathies - including Central Core Disease (CCD), Multi-minicore Disease (MmD), Centronuclear Myopathy (CNM), Nemaline Myopathy (NM) and Congenital Fibre Type Disproportion (CFTD) - are a genetically heterogeneous group of early-onset neuromuscular conditions characterized by distinct histopathological features, and associated with a substantial individual and societal disease burden. Appropriate supportive management has substantially improved patient morbidity and mortality but there is currently no cure. Recent years have seen an exponential increase in the genetic and molecular understanding of these conditions, leading to the identification of underlying defects in proteins involved in calcium homeostasis and excitation-contraction coupling, thick/thin filament assembly and function, redox regulation, membrane trafficking and/or autophagic pathways. Based on these findings, specific therapies are currently being developed, or are already approaching the clinical trial stage. Despite undeniable progress, therapy development faces considerable challenges, considering the rarity and diversity of specific conditions, and the size and complexity of some of the genes and proteins involved. The present review will summarize the key genetic, histopathological and clinical features of specific congenital myopathies, and outline therapies already available or currently being developed in the context of known pathogenic mechanisms. The relevance of newly discovered molecular mechanisms and novel gene editing strategies for future therapy development will be discussed.

Diagnóstico y tratamiento de las miotonías congénitas menos frecuentes / Diagnosis and treatment of less common myotonia congenita

Las miotonías no-distróficas son un grupo importante de canalopatías del músculo esquelético caracterizadas por excitabilidad alterada de la membrana celular. Hoy día se reconocen muchos fenotipos clínicos distintos con un rango de severidad que oscila desde la miotonía neonatal severa con compromiso respiratorio hasta el ataque miotónico ligero que producen las Parálisis Periódicas.Objetivo: analizar y discutir la fisiopatología, cuadro clínico y criterios diagnósticos de las miotonías no distróficas menos frecuentes de la práctica clínica.Desarrollo: las mutaciones genéticas específicas en los canales de voltaje del cloruro y de sodio son la causa en la mayoría de los pacientes. Estudios recientes han permitido las correlaciones más precisas entre el genotipo, patrón electrofisiológico y fenotipo clínico. Se comenta además el criterio diagnóstico de cada canalopatía en particular.Conclusiones: a pesar de los adelantos significativos en la clínica, genética molecular y fisiopatología de estos desórdenes existen problemas importantes no resueltos, tales como la utilidad de los estudios neurofisiológicos para identificar el posible genotipo, la ausencia de una historia natural de las canalopatías actualmente, aun cuando está disponible el estudio de genética molecular, la asociación de las miotonías congénitas con los cambios miopáticos, la relación de las miopatías congénitas con las miotonías congénitas y por último la posibilidad de un tratamiento más especifico y adecuado en ausencia de ensayos clínicos farmacológicos aleatorizados que permitan en el futuro tratar y prevenir el daño de los canales iónicos

Myotonia non-dystrophica is an important group of skeletal muscle channelopathies characterized by altered excitability of cell membrane. Nowadays are recognized many different clinical phenotypes with a severity level, ranging from severe neonatal myotonia with respiratory compromise to mild myotonic attack produced by periodical paralysis. Objective: to analyze and discuss the physiopathology, clinical picture and diagnostic criteria of myotonia non-dystrophica less frequent in clinical practice.Development: the specific genetic mutations in the chloride and sodium voltage channels are the cause in the majority of patients. Recent studies have allowed more precise correlations between genotype, electrophysiologic pattern and clinical phenotype. In addition each channelopathy diagnosis criterion is discussed.Conclusions: despite significant advances in the clinic, molecular genetics and physiopathology of these disorders, there are important unresolved issues, such as the usefulness of neurophysiologic studies to identify possible genotype, the absence of a natural history on channelopathy currently, even when is available the study of molecular genetics, the association of myotonia congenita with myopathic changes, the relationship of myotonia congenita with congenital myopathies and finally the possibility of a more specific and appropriate treatment in the absence of randomized pharmacologic clinical trials to enable in the future treating and preventing ionic channels damage

Myotonia congenita.

Myotonia is a symptom of many different acquired and genetic muscular conditions that impair the relaxation phase of muscular contraction. Myotonia congenita is a specific inherited disorder of muscle membrane hyperexcitability caused by reduced sarcolemmal chloride conductance due to mutations in CLCN1, the gene coding for the main skeletal muscle chloride channel ClC-1. The disorder may be transmitted as either an autosomal-dominant or recessive trait with close to 130 currently known mutations. Although this is a rare disorder, elucidation of the pathophysiology underlying myotonia congenita established the importance of sarcolemmal chloride conductance in the control of muscle excitability and demonstrated the first example of human disease associated with the ClC family of chloride transporting proteins.

Phenotypic variability of autosomal dominant myotonia congenita in a Taiwanese family with muscle chloride channel (CLCN1) mutation.

BACKGROUND: Myotonia congenita (MC), whether inherited in autosomal dominant or recessive form, is caused by mutation of CLCN1 on chromosome 7 and associated with impaired skeletal muscle relaxation after contraction. The basic pathophysiology is the reduction of chloride conductance in skeletal muscles caused by various molecular mechanisms. The cause of the wide phenotypic variability in both dominant and recessive MC remains unclear. METHODS: A family clinically diagnosed with autosomal dominant myotonia congenita was enrolled. Three family members underwent a detailed neurological examination, eletromyography, and genetic analysis. RESULTS: A G230E mutation of CLCN1 was confirmed in these three family members. One of them was completely asymptomatic and the electromyographic studies were normal. A great variability of clinical presentation was found in these family members with MC. CONCLUSIONS: We report the first autosomal dominant MC family with G230E mutation in oriental countries. Most of the previously reported MC families with G230E mutation were autosomal dominant pedigrees, and only 1 out of 20 heterozygous family members was asymptomatic. The reduced penetrance in this family indicates a less "dominant negative effect" of the G230E mutation.

Quantification of mobility impairment and self-assessment of stiffness in patients with myotonia congenita by the physiotherapist.

We investigated test-retest reliability and responsiveness in two functional measuring instruments, Timed Up&Go (TUG) and Timed-Stands Test (TST), and in three self-assessment scales, Visual Analogue Scale (VAS), Borg's Category-Ratio Scale (BorgCR10) and Myotonia Behaviour Scale (MBS) when quantifying myotonic stiffness and mobility impairment. These methods were used in the assessment of treatment efficacy of mexiletine. Six male patients with myotonia congenita followed a standardised protocol with time scoring and rest on two occasions, with and without mexiletine. Time scoring of TUG and TST and self-assessments of stiffness were performed. A 14-day stiffness diary was used at home. Timed Up&Go and TST showed very good test-retest agreement (ICC=0.87-0.95) and significant to change (P=0.005 and 0.001, respectively). All self-assessment scales revealed excellent responsiveness and good test-retest reliability. The measurement instruments possess great capacity to detect functional impairment in the myotonia congenita patient group, and sensibility to identify true changes due to treatment. When considering the results, three instruments are favoured; Timed Up&Go and BorgCR10 for short, and MBS for long-term evaluations.

[The genetic basis of muscle disease]. / Arvelige muskelsykdommer.

BACKGROUND: Our understanding of the genetic basis of muscle disease has grown dramatically over the last few years. Gene tests are now available for the diagnosis of several conditions and molecular research is providing greater understanding of pathogenesis. MATERIAL AND METHODS: This article reviews some of these advances. RESULTS: Duchenne and Becker muscular dystrophies are allelic disorders that differ in age of onset and severity. This can be explained at the genetic level by different types of mutations, one giving total protein loss (Duchenne) whereas the other results in a less severe deficiency (Becker). Facioscapulohumeral muscular dystrophy is associated with deletion involving repeated DNA in the sub-telomeric region of chromosome 4. No single gene responsible for this disorder has been identified, but we know that deletion size correlates with disease severity. Interestingly, complete removal of this region does not result in disease. Limb girdle muscular dystrophies share a similar phenotype, but genetic and protein studies show that this can be the result of mutation in very different types of protein including a protease. There are now two forms of myotonic dystrophy, both caused by what are called expansions, an increased number of triplet repeats. Both forms demonstrate multisystem involvement and in both cases more than one genetic mechanism has been shown to be active. Certain muscle diseases appear more common in Scandinavia. Amongst these are the distal myopathies in which one type prevalent in Finland has been linked to defects in the titin protein. INTERPRETATION: The challenge is now to translate the advances in our understanding of genetic mechanism into potential forms of treatment. Unfortunately, while much research is focused on techniques such as gene therapy, myoblast transplantation and the use of stem cells, these have not yet born fruit.

Carrell-Krusen Symposium Invited Lecture-1997. Myotonic disorders in childhood: diagnosis and treatment.

The recent discoveries that mutations in the genes for the skeletal muscle sodium and chloride channels are responsible, respectively, for paramyotonia/hyperkalemic periodic paralysis and for myotonia congenita of Thomsen have made the classification, diagnosis, and treatment of these disorders much easier. The discovery that myotonic dystrophy results from an unstable [CTG]n trinucleotide expansion has permitted the accurate diagnosis of both symptomatic and asymptomatic individuals, and has led to major advances in preventive treatment, including prenatal and genetic counseling. Diseases that resemble the inherited myotonic disorders are now easier to identify, and as a result of genetic testing a new clinical disorder that is similar to but distinct from myotonic dystrophy has emerged. This new disorder, proximal myotonic myopathy, does not appear to be linked to the genes for the sodium or chloride channels, and has cataracts, myotonia, weakness, and no abnormal expansion of the [CTG]n repeat in the gene for myotonic dystrophy. This review discusses the diagnosis and treatment of these myotonic disorders.

Autosomal recessive nondystrophic myotonia. Report of a case with unusual clinical course.

We describe the case of a girl with a probable autosomal recessive form of nondystrophic hereditary myotonia whose clinical findings are more compatible with the dominant ones mainly myotonia congenita of Thomsen or myotonia fluctuans. Besides the clinical aspects of the atypical form presented by our patient, the efficacy of the more available drugs employed for the treatment of myotonia congenita is briefly discussed.

Autosomal recessive nondystrophic myotonia: report of a case with unusual clinical course

As miotonias näo distróficas hereditárias podem ser divididas em um grupo mais heterogêneo, de herança autossômica dominante, que inclui a miotonia congênita de Thomsen, a paramiotonia congênita, a miotonia fluctuans e paralisia periódica hipercaliêmica; e em uma forma mais rara, de herança autossômica recessiva, que é a miotonia congênita de Becker. É descrito o caso de uma adolescente com uma forma de miotonia de herança provavelmente autossômica recessiva, cujos achados clínicos, entretanto, säo mais compatíveis com as formas de herança autossômica dominante, principalmente a miotonia congênita de Thomsen ou a miotonia fluctuans. Além do quadro clínico atípico apresentado pela paciente, säo discutidos os aspectos principais do tratamento medicanmentoso mais empregado atualmente para aliviar o fenômeno miotônico

[Myotonia with muscular weakness corrected by exercise. The therapeutic effect of mexiletine]. / Myotonie avec faiblesse musculaire corrigée par l'exercice. Effet thérapeutique de la mexilétine.

A case of generalized myotonia with autosomal recessive transmission related to Becker's type is reported. A muscular weakness improved by exercise was combined to myotonia. In addition to abundant myotonic discharges, electromyography showed alteration of the voluntary pattern during sustained contraction. The repetitive stimulation showed a marked decrement of the motor potential amplitude with high frequency stimulation. Carbamazepine (800 mg/day) and diphenylhydantoin (300 mg/day) were without effect while myotonia and muscular weakness were considerably and quickly improved by mexiletine (400 mg/day). Tests on ergometric bicycle allowed to quantify this improvement. The physiopathological mechanism of muscular weakness is considered as a depolarization block due to the cumulative depolarization which occurs during myotonic discharge. Most antimyotonic drugs belong to the group of local anesthetics. One of their characteristics is a blocking potency depending on the frequency of membrane activity. Their action is predominant on fibers with repetitive discharges; thus they block the myotonic discharge and prevent the membrane block due to cumulative depolarization. All local anesthetics do not have the same antimyotonic effect. The low molecular weight of mexiletine entails a faster time constant for the block recovery of the sodium channel. It follows that the drug block mainly depends on the frequency of membrane activity and this characteristic could explain the remarkable antimyotonic effect of mexiletine.

[A case of familial muscle weakness corrected by exercise (author's transl)]. / Un nouveau cas de faiblesse musculaire corrigée par l'exercice (forme familiale).

The symptom described as muscle weakness corrected by exercise appears to be part of the recessive form of congenital myotonia, of which it can constitute the dominant clinical manifestation in some cases. This symptom coincides with decrements of the action of potentials to repetitive stimulations in the electromyogram, which may be particularly severe in these same cases. These observations contribute to the modification and precision of the description of the recessive form of Thomsen's disease, but their pathogenicity remains unclear.