Clinical, electrophysiologic, and genetic study of non-dystrophic myotonia in French-Canadians

Neuromuscul Disord. 2009 May;19(5):330-4. doi: 10.1016/j.nmd.2008.01.007. Epub 2008 Mar 11.


Thirty-three French-Canadian families with non-dystrophic myotonia were identified. Fifty subjects were recruited and submitted to a complete clinical, electrophysiologic and genetic evaluation. Thirteen mutations were identified in CLCN1 and five mutations were identified in SCN4A. Onset in the lower extremities, presence of tongue myotonia and transient weakness suggested recessive CLCN1 mutations. Lid myotonia, absence of hypertrophy and exacerbation with cold temperature suggested SCN4A mutations. Pain was not a feature of dominant CLCN1 mutations while it could be seen in the others, more frequently in SCN4A mutations. Warm up phenomenon, hand grip myotonia, percussion myotonia, lid lag and hormonal effects were not distinguishing features. Repetitive nerve stimulation and short exercise test showed either a large (>50%) or mild-moderate (10-50%) decrement with recessive CLCN1 mutations while they showed only mild or no decrement with dominant CLCN1 and SCN4A mutations. The French-Canadian population shows wide phenotypic and genotypic heterogeneity in non-dystrophic myotonias.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Chloride Channels / genetics*
  • Cold Temperature / adverse effects
  • DNA Mutational Analysis
  • Exercise Tolerance / genetics
  • Female
  • Genetic Markers / genetics
  • Genetic Predisposition to Disease / genetics*
  • Genetic Testing
  • Genotype
  • Humans
  • Leg / physiopathology
  • Male
  • Middle Aged
  • Muscle Weakness / genetics
  • Muscle Weakness / physiopathology
  • Muscle, Skeletal / metabolism
  • Muscle, Skeletal / pathology
  • Muscle, Skeletal / physiopathology
  • Mutation / genetics*
  • Myotonia / diagnosis
  • Myotonia / genetics*
  • Myotonia / physiopathology*
  • NAV1.4 Voltage-Gated Sodium Channel
  • Quebec / ethnology
  • Sodium Channels / genetics*
  • Tongue / physiopathology
  • Young Adult


  • CLC-1 channel
  • Chloride Channels
  • Genetic Markers
  • NAV1.4 Voltage-Gated Sodium Channel
  • SCN4A protein, human
  • Sodium Channels