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Detailed information of THOMSEN'S DISEASE (MYOTONIA CONGENITA)
THOMSEN'S DISEASE (MYOTONIA CONGENITA)
DEFINITION:
A nonprogressive disorder characterized by a chloride channel
dysfunction resulting in muscle stiffness and myotonia (delayed
muscle relaxation).
EPIDEMIOLOGY:
- incidence: ?
- age of onset:
- risk factors:
- familial - autosomal dominant with complete penetrance
- chrom.#: 7q35
- gene: human skeletal muscle chloride channel gene
- M = F
PATHOGENESIS:
- first described by Julius Thomsen a Dutch physician in 1876
in his own family
- there are two forms of Myotonia Congenita:
- both forms are characterized by defects in the gene coding
for the human skeletal muscle chloride channel (HUMCLC)
resulting phenotypically in muscle stiffness and delayed muscle
relaxation
- it seems that the location and type of mutation in the
HUMCLC gene determines whether the phenotype is dominant or
recessive
- Thomsen's Disease is the less severe form with later age of
onset and nonprogressive nature
2. Genetic Defect
- genetic defect -> skeletal muscle chloride channel defect ->
decreased muscle membrane chloride conductance -> instability of
the membrane resting potential -> accumulation of potassium
during the repolarization phase -> depolorizing after-potential
-> repetitive action potential generation -> muscle stiffness
and delayed muscle relaxation (myotonia)
- point mutation in the human skeletal muscle chloride channel
gene first identified in patients with Thomsen's Disease in
April 1993 (George et al., Nature Genetics 3:305; 1993)
CLINICAL FEATURES:
- slow, stiff muscle movements
- delayed muscle contraction
- onset may be in infancy
- males more severely affected than females
- does not progress
- marked variation in severity amoung family members
- aggravating factors:
- cold, voluntary contractions, sudden emotional
stimulation, prolonged rest
- relieving factors:
- muscle groups affected:
- hands, legs, eyelids
- laryngeal (speech)
- pharyngeal (chewing and swallowing)
- ocular (transient double vision)
- percussion myotonia elicited in many muscle groups, hands,
and tongue
2. Others
- generalized muscle hypertrophy with normal muscle strength
or minimal weakness
INVESTIGATIONS:
2. Muscle Biopsy
- minimal pathologic changes
MANAGEMENT:
- no treatment for underlying disorder
- multidisciplinary approach:
- Paediatrics, Neurology
- genetic counselling
2. Prognosis
- excellent with normal life span
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Pediatric Database - THOMSEN'S DISEASE (MYOTONIA CONGENITA)
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