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.

Paramyotonia congenita and hypokalemic periodic paralysis in a family with mutation p.R1448H in α-subunit type Ⅳ of voltage gated sodium channel gene / 中华神经科杂志

Objective Through description of the clinical,electrophysiological,pathological and gene sequencing characteristics of a family diagnosed as paramyotonia congenita and hypokalemic periodic paralysis to broaden the understanding of skeletal muscle channel disease and provide the reference for clinical diagnosis.Methods The clinical manifestation,electromyography,muscle pathology and gene sequencing of a family diagnosed as paramyotonia congenita and hypokalemic periodic paralysis in the First Hospital of Shanxi Medical University in October 2017 were collected.Results The proband represented myotonia and episodic muscle weakness,and the manifestations of different patients of the family were varied,including myotonia,episodic muscle weakness or myotonia and episodic muscle weakness.The electromyography of the proband showed myotonic potential,and the compound muscle action potential decreased by 36％ in 40 minutes after exercise in the long exercise test in cold environment (11 ℃).The gene sequencing showed α-subunit type Ⅳ of voltage gated sodium channel (SCN4A) gene p.R1448H mutation.Conclusions The proband presented with paramyotonia congenita and hypokalemic periodic paralysis.Family clinical manifestations suggested phenotypic heterogeneity.The long exercise text in cold environment (11 ℃) confirmed the diagnosis of the proband as paramyotonia congenita and hypokalemic periodic paralysis.Family gene sequencing showed that the mutation of p.R1448H in SCN4A gene was the pathogenic gene mutation site of paramyotonia congenita and hypokalemic periodic paralysis.

Epidural anesthesia for a lumbar discectomy in a patient with paramyotonia congenita: A case report

Paramyotonia congenita is a rare hereditary skeletal muscle disease characterized by exercise- or cold-induced myotonia. Anesthesiologists should make any efforts to prevent perioperative myotonic attack and muscle weakness in patients with this kind of disorder. Specifically, the administration of depolarizing muscle relaxants should be avoided and serum potassium level as well as body temperature should be carefully managed. The present report describes our experiences with successful epidural anesthesia in a patient with paramyotonia congenita who underwent a lumbar discectomy.