Non-Dystrophic Myotonias

Diagnosis:

Clinical features: childhood onset of myotonia +muscle hypertrophy
There are multiple forms:

  • Becker myotonia: Autosomal recessive
  • Thomsen disease: (see appropriate section)

Genetics:

  • Autosomal dominant
  • Genetic analysis: chloride channel CLCN1 gene mutations on chromosome 7. Different mutations for each.

Muscle biopsy:

  • Variation in fibre size. Rare centronucleation. Type 2A fibre hypertrophy. Type 2B fibres may be absent.

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