Myotonia congenita: mutation spectrum of CLCN1 in Spanish patients.

Myotonia congenita (MC) is a Mendelian inherited genetic disease caused by the mutations in the CLCN1 gene, encoding the main skeletal muscle ion chloride channel (ClC-1). The clinical diagnosis of MC should be suspected in patients presenting myotonia, warm-up phenomenon, a characteristic electromyographic pattern, and/or family history. Here, we describe the largest cohort of MC Spanish patients including their relatives (up to 102 individuals). Genetic testing was performed by CLCN1 sequencing and multiplex ligation-dependent probe amplification (MLPA). Analysis of selected exons of the SCN4A gene, causing paramyotonia congenita, was also performed. Mutation spectrum and analysis of a likely founder effect of c.180+3A>T was achieved by haplotype analysis and association tests. Twenty-eight different pathogenic variants were found in the CLCN1 gene, of which 21 were known mutations and seven not described. Gross deletions/duplications were not detected. Four probands had a pathogenic variant in SCN4A. Two main haplotypes were detected in c.180+3A>T carriers and no statistically significant differences were detected between case and control groups regarding the type of haplotype and its frequencies. A diagnostic yield of 51% was achieved; of which 88% had pathogenic variants in CLCN1 and 12% in SCN4A. The existence of a c.180+3A>T founder effect remains unsolved.

Directional coupling of oligodendrocyte connexin-47 and astrocyte connexin-43 gap junctions.

Intercellular communication via gap junction channels between oligodendrocytes and between astrocytes as well as between these cell types is essential to maintain the integrity of myelin in the central nervous system. Oligodendrocyte gap junction connexin-47 (Cx47) is a key element in this crosstalk and indeed, mutations in human Cx47 cause severe myelin disorders. However, the permeation properties of channels of Cx47 alone and in heterotypic combination with astrocyte Cx43 remain unclear. We show here that Cx47 contains three extra residues at 5' amino-terminus that play a critical role in the channel pore structure and account for relative low ionic conductivity, cationic permselectivity and voltage-gating properties of oligodendrocyte-oligodendrocyte Cx47 channels. Regarding oligodendrocyte-astrocyte coupling, heterotypic channels formed by Cx47 with Cx43 exhibit ionic and chemical rectification, which creates a directional diffusion barrier for the movement of ions and larger negatively charged molecules from cells expressing Cx47 to those with Cx43. The restrictive permeability of Cx47 channels and the diffusion barrier of Cx47-Cx43 channels was abolished by a mutation associated with leukodystrophy, the Cx47P90S, suggesting a novel pathogenic mechanism underlying myelin disorders that involves alterations in the panglial permeation.

A SCN4A mutation causing paramyotonia congenita.

Paramyotonia congenita (OMIM 168300) is a non-dystrophic myopathy caused by mutations in the SCN4A gene that sometimes can be confused with myotonia congenita. Another disease also caused by mutations in the gene SCN4A is called myotonia aggravated by potassium (OMIM 170500, 613345). It is estimated that more than 20% of patients with suspected myotonia congenita suffer paramyotonia congenita. The two related SCN4A phenotypes exhibit an autosomal dominant inheritance and are the result of mutations that cause an increase in the function of the protein coded by this gene. In this study we present a case of paramyotonia congenita in a family with several affected members and in which a mutation in the SCN4A gene was identified. Evolutionary conservation data and predictive algorithms of pathogenicity allow us to conclude that this DNA variant is the cause of the disease in this family.

Miotonía congénita, una miopatía no distrófica / Myotonia congenita, a non-dystrophic myopathy

La miotonía congénita es la forma más común de miotonía no distrófica. Esta miopatía está causada por mutaciones en el gen CLCN1, codificante del principal canal de iones cloruro del músculo esquelético (ClC-1); la alteración de la función de este canal, regulado por voltaje, da lugar al fenómeno de miotonía. La enfermedad se puede heredar con un tipo de herencia dominante (enfermedad de Thomsen) o recesiva (enfermedad de Becker o miotonía congénita generalizada). El fenotipo clínico de ambas formas de la enfermedad es similar aunque la forma recesiva se caracteriza por una mayor gravedad de los síntomas. El diagnóstico clínico de miotonía congénita debe sospecharse cuando encontramos en un paciente episodios de rigidez muscular (miotonía), remisión o alivio de la rigidez con el ejercicio (fenómeno warm-up), miotonía clínica, un patrón electromiográfico característico y/o historia familiar. El diagnóstico molecular de miotonía congénita consiste en el análisis por secuenciación del gen CLCN1 (AU)

Myotonia congenita is the most common form of non-dystrophic myotonia. This myopathy is caused by mutations in the CLCN1 gene, encoding the main skeletal muscle chloride ion channel (ClC-1). Altering the function of this voltage-gated channel, leads to the phenomenon of myotonia. The disease can be inherited with a dominant (Thomsen disease) or recessive type (Becker disease or congenital generalised myotonia). The clinical phenotype of both forms of the disease is similar, although the recessive form is characterised by more severe symptoms. The clinical diagnosis of congenital myotonia should be suspected in a patient who presents with episodes of muscle stiffness (myotonia), remission or relief from stiffness with exercise (warm-up phenomenon), and a characteristic electromyography pattern, and/or family history. Sequencing the CLCN1 gene is the present approach for molecular diagnosis of myotonia congenita (AU)

Fast skeletal myofibers of mdx mouse, model of Duchenne muscular dystrophy, express connexin hemichannels that lead to apoptosis.

Skeletal muscles of patients with Duchenne muscular dystrophy (DMD) show numerous alterations including inflammation, apoptosis, and necrosis of myofibers. However, the molecular mechanism that explains these changes remains largely unknown. Here, the involvement of hemichannels formed by connexins (Cx HCs) was evaluated in skeletal muscle of mdx mouse model of DMD. Fast myofibers of mdx mice were found to express three connexins (39, 43 and 45) and high sarcolemma permeability, which was absent in myofibers of mdx Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice (deficient in skeletal muscle Cx43/Cx45 expression). These myofibers did not show elevated basal intracellular free Ca(2+) levels, immunoreactivity to phosphorylated p65 (active NF-κB), eNOS and annexin V/active Caspase 3 (marker of apoptosis) but presented dystrophin immunoreactivity. Moreover, muscles of mdx Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice exhibited partial decrease of necrotic features (big cells and high creatine kinase levels). Accordingly, these muscles showed similar macrophage infiltration as control mdx muscles. Nonetheless, the hanging test performance of mdx Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice was significantly better than that of control mdx Cx43(fl/fl)Cx45(fl/fl) mice. All three Cxs found in skeletal muscles of mdx mice were also detected in fast myofibers of biopsy specimens from patients with muscular dystrophy. Thus, reduction of Cx expression and/or function of Cx HCs may be potential therapeutic approaches to abrogate myofiber apoptosis in DMD.

Diagnóstico genético de fibrosis quística mediante la técnica de desnaturalización de ADN a alta resolución (HRM) / Genetic diagnosis of cystic fibrosis by high resolution melting of DNA (HRM)

La fibrosis quística es la enfermedad grave de herencia autosómica recesiva más frecuente en la raza caucásica, con una incidencia estimada entre 1/2.000 y 1/6.000 nacidos vivos y causada por mutaciones en el gen CFTR. La casi totalidad de los pacientes desarrollan una enfermedad pulmonar crónica y progresiva, que es la causa más frecuente de la morbimortalidad. En el 85% de los casos existe disfunción pancreática (exocrina o endocrina). El diagnóstico de la fibrosis quística se basa esencialmente en la historia clínica, aunque el diagnóstico etiológico es el diagnóstico molecular, con la identificación de las mutaciones en el gen CFTR. Para ello, existen técnicas de rastreo de mutaciones que identifican patrones anormales en la secuencia que necesitan ser confirmadas por secuenciación del ADN. Actualmente se acepta que el HRM es la técnica de rastreo más sensible en la búsqueda de variantes en la secuencia de ADN. Alternativamente, existen baterías diagnósticas actualmente disponibles comercialmente, que identifican las mutaciones más frecuentes en fibrosis quística con una sensibilidad superior al 75%. En este trabajo hemos hecho un análisis del gen CFTR en pacientes con fibrosis quística mediante la técnica de rastreo de mutaciones basada en la desnaturalización a alta resolución del ADN (High Resolution Melting [HRM]). En paralelo, en los mismos pacientes, hemos hecho un estudio comparativo de la sensibilidad del HRM con dos test comerciales y de estos dos test entre sí. Uno de los test, Devyser, incluye una batería complementaria para la identificación de mutaciones específicas de la población española. Los resultados de este trabajo indican que el HRM tiene una sensibilidad cercana al 100% en la detección de mutaciones y polimorfismos en el gen CFTR. Además la técnica de HRM es también más sensible que los test comerciales en el diagnóstico molecular de pacientes de fibrosis quística (AU)

Cystic fibrosis is the severe disease of autosomal recessive inheritance most common in caucasians, with an estimated incidence between 1/2,000 and 1/6,000 live births. This disease is caused by mutations in the CFTR gene. Almost all patients develop a chronic, progressive lung disease, which is the most common cause of morbidity and mortality. In 85% of cases there is also pancreatic dysfunction (exocrine and endocrine). The diagnosis of cystic fibrosis is essentially based on clinical history, although the etiologic diagnosis is the diagnosis at molecular level, with the identification of mutations in the CFTR gene. For this purpose, there are screening techniques that identify abnormal patterns that need to be confirmed by DNA sequencing. It is now accepted that the HRM is the most sensitive screening technique in the search for variants in the DNA sequence. Alternatively, there are diagnostic batteries currently available commercially, which identify the most common cystic fibrosis mutations with sensitivity greater than 75%. In this work we have done an analysis of the CFTR gene in cystic fibrosis patients by the screening technique based on denatured DNA at high resolution (High Resolution Melting [HRM]). In parallel, in the same patients, we have made a comparative study of the sensitivity of the HRM with two commercial test. One of the test, Devyser includes an additional battery for identification of specific mutations in the Spanish population. Results obtained indicated that HRM has a sensibility closed to 100% for the detection of mutations and polymorphisms in CFTR gene. Furthermore, HRM presented higher sensitivity than the commercial tests for molecular diagnosis of cystic fibrosis patients (AU)

Regulation of connexin hemichannel activity by membrane potential and the extracellular calcium in health and disease.

Connexins are thought to solely mediate cell-to-cell communication by forming gap junction channels composed of two membrane-spanning hemichannels positioned end-to-end. However, many if not all connexin isoforms also form functional hemichannels (i.e., the precursors of complete channels) that mediate the rapid exchange of ions, second messengers and metabolites between the cell interior and the interstitial space. Electrical and molecular signaling via connexin hemichannels is now widely recognized to be important in many physiological scenarios and pathological conditions. Indeed, mutations in connexins that alter hemichannel function have been implicated in several diseases. Here, we present a comprehensive overview of how hemichannel activity is tightly regulated by membrane potential and the external calcium concentration. In addition, we discuss the genetic mutations known to alter hemichannel function and their deleterious effects, of which a better understanding is necessary to develop novel therapeutic approaches for diseases caused by hemichannel dysfunction. This article is part of the Special Issue Section entitled 'Current Pharmacology of Gap Junction Channels and Hemichannels'.