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

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

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

Myotonia congenita (MC) is a form of nondystrophic myotonia caused by a mutation of CLCN1, which encodes human skeletal muscle chloride channel (CLC-1). We performed sequence analysis of all coding regions of CLCN1 in patients clinically diagnosed with MC, and identified 10 unrelated Korean patients harboring mutations. Detailed clinical analysis was performed in these patients to identify their clinical characteristics in relation to their genotypes. The CLCN1 mutational analyses revealed nine different point mutations. Of these, six (p.M128I, p.S189C, p.M373L, p.P480S, p.G523D, and p.M609K) were novel and could be unique among Koreans. While some features including predominant lower extremity involvement and normal to slightly elevated creatine kinase levels were consistently observed, general clinical features were highly variable in terms of age of onset, clinical severity, aggravating factors, and response to treatment. Our study is the first systematic study of MC in Korea, and shows its expanding clinical and genetic spectrums.
Adult ; Amino Acid Sequence ; Asian Continental Ancestry Group/*genetics ; Base Sequence ; Child, Preschool ; Chloride Channels/*genetics ; DNA Mutational Analysis ; Exons ; Humans ; Infant ; Korea ; Male ; Molecular Sequence Data ; Myotonia Congenita/*genetics ; *Point Mutation ; Protein Conformation ; Young Adult