Myotonia congenita, autosomal dominant
A non-dystrophic skeletal muscle disorder characterized by muscle stiffness and an inability of the muscle to relax after voluntary contraction. Most patients have symptom onset in the legs, which later progresses to the arms, neck, and facial muscles. Many patients show marked hypertrophy of the lower limb muscles. The autosomal dominant form (Thomsen disease) is less common and less severe than the autosomal recessive one (Becker disease). A milder form of autosomal dominant myotonia is characterized by isolated myotonia without muscle weakness, hypotrophy, or hypertrophy (myotonia levior).
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