Humans ; Myotonia Congenita/genetics* ; Mutation ; NAV1.4 Voltage-Gated Sodium Channel/genetics*

No abstract available.
Dyskinesias ; Myotonia Congenita ; Myotonia

Myotonia congenita (MC) is a genetic disease that displays impaired relaxation of skeletal muscle and muscle hypertrophy. This disease is mainly caused by mutations of CLCN1 that encodes human skeletal muscle chloride channel (CLC-1). CLC-1 is a voltage gated chloride channel that activates upon depolarizing potentials and play a major role in stabilization of resting membrane potentials in skeletal muscle. In this study, we report 4 unrelated Korean patients diagnosed with myotonia congenita and their clinical features. Sequence analysis of all coding regions of the patients was performed and mutation, R47W and A298T, was commonly identified. The patients commonly displayed transient muscle weakness and only one patient was diagnosed with autosomal dominant type of myotonia congenita. To investigate the pathological role of the mutation, electrophysiological analysis was also performed in HEK 293 cells transiently expressing homo- or heterodimeric mutant channels. The mutant channels displayed reduced chloride current density and altered channel gating. However, the effect of A298T on channel gating was reduced with the presence of R47W in the same allele. This analysis suggests that impaired CLC-1 channel function can cause myotonia congenita and that R47W has a protective effect on A298T in relation to channel gating. Our results provide clinical features of Korean myotonia congenita patients who have the heterozygous mutation and reveal underlying pathophyological consequences of the mutants by taking electrophysiological approach.
Alleles ; Chloride Channels ; Clinical Coding ; Electrophysiology ; HEK293 Cells ; Humans ; Hypertrophy ; Membrane Potentials ; Muscle Weakness ; Muscle, Skeletal ; Myotonia Congenita* ; Myotonia* ; Relaxation ; Sequence Analysis

No abstract available.
Humans ; Myotonia Congenita* ; Myotonia*

Myotonia congenita (MC) is a hereditary disease of the chloride channels of skeletal muscle caused by mutation of CLCN1. It characteristically manifests as delayed relaxation of the skeletal muscle or myotonia. It has a wide phenotypic variability, ranging from asymptomatic to severe disability. However, it is uncommon for a phenotypic difference to appear within a family. We report the first Korean family with the p.A313T mutation exhibiting marked phenotypic variability.
Chloride Channels ; Genetic Diseases, Inborn ; Humans ; Muscle, Skeletal ; Myotonia Congenita* ; Myotonia* ; Relaxation

BACKGROUNDParoxysmal kinesigenic dyskinesia (PKD) is the most common subtype of paroxysmal dyskinesias and is caused by mutations in PRRT2 gene. The majority of familial PKD was identified to harbor PRRT2 mutations. However, over two-third of sporadic PKD patients did not carry anyPRRT2 mutation, suggesting an existence of additional genetic mutations or possible misdiagnosis due to clinical overlap.

METHODSA cohort of 28 Chinese patients clinically diagnosed with sporadic PKD and excluded PRRT2 mutations were recruited. Clinical features were evaluated, and all subjects were screened for MR-1, SLC2A1, and CLCN1 genes, which are the causative genes of paroxysmal nonkinesigenic dyskinesia (PNKD), paroxysmal exertion-induced dyskinesia, and myotonia congenita (MC), respectively. In addition, 200 genetically matched healthy individuals were recruited as controls.

RESULTSA total of 16 genetic variants including 4 in MR-1 gene, 8 in SLC2A1 gene, and 4 in CLCN1 gene were detected. Among them, SLC2A1 c.363G>A mutation was detected in one case, and CLCN1 c.1205C>T mutation was detected in other two cases. Neither of them was found in 200 controls as well as 1000 Genomes database and ExAC database. Both mutations were predicted to be pathogenic by SIFT and PolyPhen2. The SLC2A1 c.363G>A mutation was novel.

CONCLUSIONSThe phenotypic overlap may lead to the difficulty in distinguishing PKD from PNKD and MC. For those PRRT2- negative PKD cases, screening of SLC2A1 and CLCN1 genes are useful in confirming the diagnosis.

Adolescent ; Adult ; Child ; Chloride Channels ; genetics ; Chorea ; genetics ; Dystonia ; diagnosis ; genetics ; Female ; Glucose Transporter Type 1 ; genetics ; Humans ; Male ; Membrane Proteins ; genetics ; Muscle Proteins ; genetics ; Mutation ; Myotonia Congenita ; genetics ; Nerve Tissue Proteins ; genetics

BACKGROUND: Fibromyalgia syndrome (FMS) is a complex disorder characterized by chronic widespread pain (CWP), multiple areas of tenderness, sleep disturbance, fatigue, and mood or cognitive dysfunction. Myotonia congenita (MC) is an inherited myopathic disorder that is caused by mutations in the gene encoding the skeletal muscle chloride channel, which can infrequently manifest as generalized muscle cramps or myalgia. CASE REPORT: The first case was a 33-year-old woman who complained of CWP and chronic headache occurring during pregnancy, and the second case was a 37-year-old man with CWP and depression who suffered from cold-induced muscle cramps. These two patients were initially diagnosed with FMS by rheumatologists, based on CWP of longer than 3 months duration and mechanical tenderness in specific body regions. However, these two FMS patients were subsequently also diagnosed with MC. CONCLUSIONS: These two cases are the first report of an overlap of CWP between FMS and MC.
Adult ; Body Regions ; Chloride Channels ; Chronic Pain ; Depression ; Fatigue ; Female ; Fibromyalgia* ; Headache Disorders ; Humans ; Muscle Cramp ; Muscle, Skeletal ; Myalgia ; Myotonia Congenita* ; Pregnancy

OBJECTIVETo investigate chloride channel 1 (CLCN1) gene mutation and clinical features of 2 Chinese patients with myotonia congenita.

METHODSClinical data of a patient from a family affected with myotonia congenita in addition with a sporadic patient from Fujian province were analyzed. Exons of CLCN1 gene were amplified and sequenced.

RESULTSThe proband from the affected family was found to carry a c.1024G>A heterozygous missense mutation in exon 8, whilst the sporadic patient has carried a c.1292C>T heterozygous missense mutation in exon 11.

CONCLUSIONDetection of CLCN1 gene mutation is an effective method for the diagnosis of myotonia congenita. Exon 8 of CLCN1 gene may be a mutational hotspot in Chinese patients with myotonia congenita.

Adolescent ; Base Sequence ; Chloride Channels ; genetics ; Exons ; Heterozygote ; Humans ; Male ; Mutation ; Myotonia Congenita ; diagnosis ; genetics ; Pedigree

BACKGROUND AND PURPOSE: While the etiology and clinical features of "EMG disease" - which is characterized by diffusely increased insertional activity on needle electromyography (EMG) in the absence of neuromuscular disease - are not well known, some authorities believe it may be a form of myotonia congenita (MC). The aims of this study were to determine the clinical features of EMG disease and its relationship with CLCN1 mutations in patients. METHODS: The detailed clinical and electrophysiological features of EMG disease were evaluated in six patients. All 23 coding exons and exon-intron boundaries in CLCN1 gene were analyzed by direct sequencing to detect nucleotide changes. RESULTS: The common clinical symptoms of EMG disease were chronic muscle stiffness or generalized myalgia, which were aggravated in a cold environment. Four patients complained of action myotonia several times a year. Short trains of provoked positive sharp waves were documented on needle EMG, but myotonic discharges, fibrillation potentials, and fasciculations were not. Increased insertional activity was identified at the asymptomatic muscles studied. One novel heterozygous mutation was identified in one patient following genetic testing for CLCN1 mutations (c.1679T>C, p.Met560Thr). CONCLUSIONS: The clinical features of EMG disease might be quite similar to those of MC, but CLCN1 mutation was found in only one subject. It is thus difficult to accept that EMG disease lies within the phenotypic spectrum of MC. Additional testing is needed to verify the pathogenetic cause of the diffusely increased insertional activity associated with this condition.
Chloride Channels ; Clinical Coding ; Cold Temperature ; Electromyography ; Exons ; Fasciculation ; Genetic Testing ; Humans ; Muscles ; Myotonia ; Myotonia Congenita ; Needles ; Neuromuscular Diseases

BACKGROUND AND PURPOSE: Mutations of the skeletal muscle sodium channel gene SCN4A, which is located on chromosome 17q23-25, are associated with various neuromuscular disorders that are labeled collectively as skeletal muscle sodium channelopathy. These disorders include hyperkalemic periodic paralysis (HYPP), hypokalemic periodic paralysis, paramyotonia congenita (PMC), potassium-aggravated myotonia, and congenital myasthenic syndrome. This study analyzed the clinical and mutational spectra of skeletal muscle sodium channelopathy in Korean subjects. METHODS: Six unrelated Korean patients with periodic paralysis or nondystrophic myotonia associated with SCN4A mutations were included in the study. For the mutational analysis of SCN4A, we performed a full sequence analysis of the gene using the patients' DNA. We also analyzed the patients' clinical history, physical findings, laboratory tests, and responses to treatment. RESULTS: We identified four different mutations (one of which was novel) in all of the patients examined. The novel heterozygous missense mutation, p.R225W, was found in one patient with mild nonpainful myotonia. Our patients exhibited various clinical phenotypes: pure myotonia in four, and PMC in one, and HYPP in one. The four patients with pure myotonia were initially diagnosed as having myotonia congenita (MC), but a previous analysis revealed no CLCN1 mutation. CONCLUSIONS: Clinical differentiating between sodium-channel myotonia (SCM) and MC is not easy, and it is suggested that a mutational analysis of both SCN4A and CLCN1 is essential for the differential diagnosis of SCM and MC.
Channelopathies ; Diagnosis, Differential ; DNA ; Humans ; Hypokalemic Periodic Paralysis ; Muscle, Skeletal ; Mutation, Missense ; Myasthenic Syndromes, Congenital ; Myotonia ; Myotonia Congenita ; Myotonic Disorders ; Paralyses, Familial Periodic ; Paralysis ; Paralysis, Hyperkalemic Periodic ; Sequence Analysis ; Sodium ; Sodium Channels