paramyotonia congenita

a rare constitutional disorder in which prolonged contraction of muscle fibres (see myotonia) develops when the patient is exposed to cold. This may be due to a disorder of potassium channels.

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an autosomal dominant disorder clinically similar to myotonia congenita, except that the precipitating factor is exposure to cold and the myotonia is aggravated by activity. Like myotonia fluctuans and myotonia permanens and several other disorders, it is due to mutation in the SCNA4A gene (locus: 17q23.1-q25.3), which encodes a subunit of a voltage-gated sodium channel. Called also Eulenburg disease.