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At least 19 recordsLinked to original sources
PubMed1996

Mutations in the human skeletal muscle chloride channel gene (CLCN1) associated with dominant and recessive myotonia congenita.

Myotonia, defined as delayed relaxation of muscle after contraction, is seen in a group of genetic disorders that includes autosomal dominant myotonia congenita (Thomsen's disease) and autosomal recessive myotonia congenita (Becker's disease). Both disorders are characterized electrophysiologically by increased excitability of muscle fibers, reflected in clinical myotonia. These diseases are similar except that transient weakness is seen in patients with Becker's, but not Thomsen's disease. Becker's and Thomsen's diseases are caused by mutations in the skeletal muscle voltage-gated chloride channel gene (CLCN1). Genetic screening of a panel of 18 consecutive myotonia congenita (MC) probands for mutation in CLCN1 revealed that a novel Gln-68-Stop nonsense mutation predicts premature truncation of the chloride channel protein. Four previously reported mutations, Arg-894-stop, Arg-338-Gln, Gly-230-Glu, and del 1437-1450, were also noted in our sample set. The Arg-338-Gln and Gly-230-Glu mutations were found in patients with different phenotypes from those of previous reports. Further study of the Arg-338-Gln and Gln-230-Glu alleles may shed light on variable modes of transmission (dominant versus recessive) in different families. Physiologic study of these mutations may lead to better understanding of the pathophysiology of myotonia in these patients and of voltage-gated chloride channel structure/function relationships in skeletal muscles.

Chloride Channels↗
PubMed2005

Phenotypic variability in myotonia congenita.

Myotonia congenita is a hereditary chloride channel disorder characterized by delayed relaxation of skeletal muscle (myotonia). It is caused by mutations in the skeletal muscle chloride channel gene CLCN1 on chromosome 7. The phenotypic spectrum of myotonia congenita ranges from mild myotonia disclosed only by clinical examination to severe and disabling myotonia with transient weakness and myopathy. The most severe phenotypes are seen in patients with two mutated alleles. Heterozygotes are often asymptomatic but for some mutations heterozygosity is sufficient to cause pronounced myotonia, although without weakness and myopathy. Thus, the phenotype depends on the mutation type to some extent, but this does not explain the fact that severity varies greatly between heterozygous family members and may even vary with time in the individual patient. In this review, existing knowledge about phenotypic variability is summarized, and the possible contributing factors are discussed.

Chloride Channels↗
PubMed1999

Identification of three novel mutations in the major human skeletal muscle chloride channel gene (CLCN1), causing myotonia congenita.

Myotonia congenita (MC) is a genetic disease characterized by mutations in the CLCN1 gene (OMIM*118425) encoding the skeletal muscle voltage-gated chloride channel (ClC-1). Autosomal dominant and recessive forms are observed, characterized by impaired muscle relaxation after forceful contraction (myotonia), which is more pronounced after inactivity and improves with exercise. We report three novel and one known mutations of the CLCN1 gene in four unrelated MC families. In two families the mutations were missense: 803C>T (T268M) and 1272C>G (I424M) in exons 7 and 12, respectively. The third was a splice mutation in intron 5 (696+2T>A), which induced a frame shift with a stop codon in exon 6 (fs213X). In the fourth family the previously-reported missense mutation 689G>A (G230E) was found. We also report two known polymorphisms: 261C>T (T87T) and 2154T>C (D718D) in exons 2 and 17 of two MC families; also found in 14 (33%) and 28 (67%) of 42 healthy controls, respectively. These findings expand our knowledge of mutations responsible for myotonia congenita, reducing the proportion of MC patients in whom genetic alterations have not been found.

Chloride Channels↗
PubMed1983

Distinguishing paramyotonia congenita and myotonia congenita by electromyography.

Compound muscle action potential (CMAP) amplitudes, response to 2 Hz nerve stimulation, response to exercise and electromyographic needle electrode examination findings from the thenar muscles of two patients with paramyotonia congenita were compared with those from two patients with dominantly inherited myotonia congenita in warm (34 degrees C) and cold (20 degrees C) states. Cold induced a significant fall in CMAP amplitude, induced/worsened a significant decremental response to 2 Hz stimulation, and virtually abolished myotonia and voluntary recruitment of motor unit potentials in patients with paramyotonia congenita; none of these occurred in myotonia congenita. Though exercise induced a mild fall in CMAP amplitude in both groups, postexercise fibrillations occurred only in patients with paramyotonia congenita. These findings serve to distinguish these two entities in the clinical electromyography laboratory.

Adult↗
PubMed1982

Electromyographic distinction between paramyotonia congenita and myotonia congenita: effect of cold.

We studied three patients with paramyotonia congenita and three with myotonia congenita. At room temperature myotonic bursts in the EMG were similar in the two disorders. After repetitive maximal contractions, patients with paramyotonia showed decreasing recruitment pattern and increasing after-activity, while myotonia patients showed unchanged recruitment pattern, and after-activity tended to decrease, but these differences were not consistent. However, immersion of the hand in ice water for 10 minutes caused unambiguous differences: In paramyotonia, the myotonic discharges disappeared and the muscles went into stiff, electrically silent, contracture; in myotonia patients, the myotonic activity increased and muscle contraction patterns remained normal.

Action Potentials↗
PubMed1975

A family with dominant hereditary myotonia, muscular hypertrophy, and increased muscular irritability, distinct from myotonia congenita thomsen.

Myotonia is a symptom, which occurs in a series of hereditary diseases, and it is also seen in less frequently occurring syndromes. A summary is given of conditions with myotonia. Five cases are reported from a family with a dominant hereditary disease presenting myotonia, muscular hypertrophy and increased muscle irritability as the only symptoms. In the most affected patient, some unusual rolling muscle contractions are seen. Apart from a moderate increase of creatin kinase, supplementary examinations are normal. The clinical picture resembles myotonia congenita Thomsen, but differs from this in significant respects. Other diagnostic possibilities are also considered. It is concluded that the clinical picture is different from all previously described conditions.

Adolescent↗
PubMed2006

Novel mutations at carboxyl terminus of CIC-1 channel in myotonia congenita.

OBJECTIVES: Myotonia congenita (MC), caused by mutations in the muscle chloride channel (CLCN1) gene, can be inherited dominantly or recessively. The mutations at the carboxyl terminus of the CLCN1 gene have been identified in MC patients, but the functional implication of these mutations is unknown. MATERIAL AND METHODS: Direct sequencing of polymerase chain reaction products covering the whole coding region of the CLCN1 gene was performed in a MC family. This study was designed to investigate the clinical manifestations and genetic analysis of the CLCN1 gene. RESULTS: We identified two novel mutations, 2330delG and 1892C>T, from a genetic screening of the CLCN1 gene in the MC family. The 2330delG mutant allele producing a fs793X truncated protein was identified in a heterozygous state in all the patients. The 1892C>T nucleotide change induced a missense mutation (T631I) found in several asymptomatic individuals, indicating that it may not be associated with MC. Intriguingly, the 2330delG mutation was also found in an asymptomatic subject who also carried the 1892C>T mutation. CONCLUSION: The data indicate that the fs793X mutant protein causes dominantly inherited MC. Because the mutation has been found in a recessive pedigree, the fs793X mutation may have a dual inheritance pattern.

Adult↗
PubMed2000

Dental and craniofacial findings in eight miniature schnauzer dogs affected by myotonia congenita: preliminary results.

Myotonia is a clinical sign characterized by the delay of skeletal muscle relaxation following the cessation of a voluntary activity or the termination of an electrical or mechanical stimulus. Recently, Miniature Schnauzers with myotonia congenita associated with defective chloride ion conductance across the skeletal muscle membrane were identified. Congenital myotonia in these dogs appears to follow an autosomal recessive mode of inheritance. Craniofacial and dental findings of eight Miniature Schnauzer dogs with myotonia congenita are described in the present paper. These findings include: delayed dental eruption of both deciduous and permanent dentition: persistent deciduous dentition; unerupted or partially erupted permanent teeth: crowding and rotation of premolar and or incisor teeth: missing teeth: increased interproximal space between the maxillary fourth premolar and first molar teeth: decreased interproximal space between the maxillary canine and lateral incisor teeth: inability to fully close the mouth due to malocclusion: distoclusion: and, decreased mandibular range of motion. A long narrow skull with a flattened zygomatic arch and greater mandibular body curvature were also consistent findings in the affected dogs. The small number of dogs studied prevents conclusive statements about the origin of these abnormalities, however it is interesting that only 1 of 45 unaffected Miniature Schnauzer dogs showed similar traits.

Animals↗
PubMed2001

Spectrum of CLCN1 mutations in patients with myotonia congenita in Northern Scandinavia.

Myotonia congenita is a non-dystrophic muscle disorder affecting the excitability of the skeletal muscle membrane. It can be inherited either as an autosomal dominant (Thomsen's myotonia) or an autosomal recessive (Becker's myotonia) trait. Both types are characterised by myotonia (muscle stiffness) and muscular hypertrophy, and are caused by mutations in the muscle chloride channel gene, CLCN1. At least 50 different CLCN1 mutations have been described worldwide, but in many studies only about half of the patients showed mutations in CLCN1. Limitations in the mutation detection methods and genetic heterogeneity might be explanations. In the current study, we sequenced the entire CLCN1 gene in 15 Northern Norwegian and three Northern Swedish MC families. Our data show a high prevalence of myotonia congenita in Northern Norway similar to Northern Finland, but with a much higher degree of mutation heterogeneity. In total, eight different mutations and three polymorphisms (T87T, D718D, and P727L) were detected. Three mutations (F287S, A331T, and 2284+5C>T) were novel while the others (IVS1+3A>T, 979G>A, F413C, A531V, and R894X) have been reported previously. The mutations F413C, A531V, and R894X predominated in our patient material. Compound heterozygosity for A531V/R894X was the predominant genotype. In two probands, three mutations cosegregated with myotonia. No CLCN1 mutations were identified in two families. Our data support the presence of genetic heterogeneity and additional modifying factors in myotonia congenita.

Amino Acid Sequence↗
PubMed1999

A missense mutation in canine C1C-1 causes recessive myotonia congenita in the dog.

Myotonia congenita is an inherited disorder of sarcolemmal excitation leading to delayed relaxation of skeletal muscle following contractions. Mutations in a skeletal muscle voltage-dependent chloride channel, CIC-1, have been identified as the molecular genetic basis for the syndrome in humans, and in two well characterized animal models of the disease: the myotonic goat, and the arrested development of righting (adr) mouse. We now report the molecular genetic and electrophysiological characterization of a canine CIC-1 mutation that causes autosomal recessive myotonia congenita in miniature Schnauzers. The mutation results in replacement of a threonine residue in the D5 transmembrane segment with methionine. Functional characterization of the mutation introduced into a recombinant CIC-1 and heterologously expressed in a cultured mammalian cell line demonstrates a profound effect on the voltage-dependence of activation such that mutant channels have a greatly reduced open probability at voltages near the resting membrane potential of skeletal muscle. The degree of this dysfunction is greatly diminished when heterodimeric channels containing a wild-type and mutant subunit are expressed together as a covalent concatemer strongly supporting the observed recessive inheritance in affected dog pedigrees. Genetic and electrophysiological characterization of the myotonic dog provides a new and potentially valuable animal model of an inherited skeletal muscle disease that has advantages over existing models of myotonia congenita.

Amino Acid Sequence↗
PubMed1984

Respiratory muscle dysfunction in myotonia congenita.

A patient with myotonia congenita (Thomsen's disease) presented with unpleasant sensations of tightness in the chest and dyspnea, which were maximal at the beginning of exercise and gradually improved as exercise progressed. Lung function tests and maximal static respiratory pressures were within normal limits. Precise electromyographic (EMG) and mechanical studies, however, demonstrated the increased excitability, impaired relaxation, and transient weakness of the respiratory muscles. These studies thus indicate that myotonia congenita may involve the respiratory muscles to the same extent as any other skeletal muscle, and that precise EMG studies are occasionally useful in determining the organic basis of respiratory symptoms.

Adolescent↗
PubMed2000

Functional consequences of chloride channel gene (CLCN1) mutations causing myotonia congenita.

OBJECTIVE: To determine the functional consequences of missense mutations within the skeletal muscle chloride channel gene CLCN1 that cause myotonia congenita. BACKGROUND: Myotonia congenita is a genetic muscle disease associated with abnormalities in the skeletal muscle voltage-gated chloride (ClC-1) channel. In order to understand the molecular basis of this inherited disease, it is important to determine the physiologic consequences of mutations found in patients affected by it. METHODS: The authors used a mammalian cell (human embryonic kidney 293) expression system and the whole-cell voltage-clamp technique to functionally express and physiologically characterize five CLCN1 mutations. RESULTS: The I329T mutation shifted the voltage dependence of open probability of ClC-1 channels to the right by 192 mV, and the R338Q mutation shifted it to the right by 38 mV. In addition, the I329T ClC-1 channels deactivated to a lesser extent than normal at negative potentials. The V165G, F167L, and F413C ClC-1 channels also shifted the voltage dependence of open probability, but only by +14 to +20 mV. CONCLUSIONS: The functional consequences of these mutations form the physiologic argument that these are disease-causing mutations and could lead to myotonia congenita by impairing the ability of the skeletal muscle voltage-gated chloride channels to maintain normal muscle excitability. Understanding of genetic and physiologic defects may ultimately lead to better diagnosis and treatment of patients with myotonia congenita.

Chloride Channels↗
PubMed1991

Response to treatment with antihistamines in a family with myotonia congenita.

In a family in which myotonia congenita was found in five generations, both great-grandparents of the index case were affected. In subsequent generations mild and severely affected cases were clearly segregated down parallel lines of this family. The grandmother of the index case had noted improvement with an antihistamine. When the index case was prescribed trimeprazine, she showed a striking reduction in severity of symptoms. Antihistamines seem to deserve further evaluation as a safe and effective treatment for myotonia congenita.

Adult↗