title: Painful cramps and giant myotonic discharges in a family with the Nav1.4-G1306A mutation.
abstract: BACKGROUND
  Two previously reported Norwegian patients with painful muscle cramps and giant myotonic discharges were genotyped and compared with those of members of 21 families harboring the same mutation.
  
  
  METHODS
  Using primers specific for SCN4A and CLCN1, the DNA of the Norwegian family members was amplified and bidirectionally sequenced. Clinical and neurophysiological features of other families harboring the same mutation were studied.
  
  
  RESULTS
  A G1306A mutation in the Nav1.4 voltage-gated sodium channel of skeletal muscle was identified. This mutation is known to cause myotonia fluctuans. No giant myotonic discharges or painful muscle cramps were found in the other G1306A families.
  
  
  CONCLUSIONS
  Ephaptic transmission between neighboring muscle fibers may not only cause the unusual size of the myotonic discharges in this family, but also a more severe type of potassium-aggravated myotonia than myotonia fluctuans.
authors.affiliation: Department of Clinical Neurophysiology, University Hospital of North Norway, Tromsö, Norway.
authors.forename: Torberg
authors.initials: T
authors.lastname: Torbergsen
authors.affiliation: Division of Neurophysiology and Neuromuscular Center, University of Ulm, Ulm, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Jurkat-Rott
authors.affiliation: Department of Clinical Neurophysiology, Institute of Neurosciences, Uppsala University, Uppsala, Sweden.
authors.forename: Erik V
authors.initials: EV
authors.lastname: Stålberg
authors.affiliation: Department of Clinical Neurophysiology, University Hospital of North Norway, Tromsö, Norway.
authors.forename: Sissel
authors.initials: S
authors.lastname: Løseth
authors.affiliation: Department of Neurology, Vestfold County Hospital, Tønsberg, Norway.
authors.forename: Anne
authors.initials: A
authors.lastname: Hødneø
authors.affiliation: Division of Neurophysiology and Neuromuscular Center, University of Ulm, Ulm, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Lehmann-Horn
mesh_terms: D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000235:genetics*; D005192:Family Health; D005260:Female; D006801:Humans; D008875:Middle Aged; D009120:Muscle Cramp / Q000150:complications* / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000235:genetics*
chemical_list: D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human
keywords: G1306A; ephaptic transmission; muscle pain; mutation; myotonia; positive waves