A form of nondystrophic myotonia
Synonyms:
a.k.a. Thomsen’s disease
Clinical features:
1st and 2nd decade
When infant: inability to open eyes after face is washed, peculiar cry
Muscular hypertrophy (generalized), myotonia (worse in cold),
No weakness
Warm up phenomenon: improved strength and movement after warm up
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.
Findings on investigations:
EMG:
- Myotonia