title: Clinical Diversity of SCN4A-Mutation-Associated Skeletal Muscle Sodium Channelopathy.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Neurology, Dong-Eui Hospital, Busan, Korea.
authors.forename: Sang-Chan
authors.initials: SC
authors.lastname: Lee
authors.forename: Hyang-Sook
authors.initials: HS
authors.lastname: Kim
authors.forename: Yeong-Eun
authors.initials: YE
authors.lastname: Park
authors.forename: Young-Chul
authors.initials: YC
authors.lastname: Choi
authors.forename: Kyu-Hyun
authors.initials: KH
authors.lastname: Park
authors.forename: Dae-Seong
authors.initials: DS
authors.lastname: Kim