myotonia congenita

myotonia con·gen·i·ta -kän-'jen-ə-tə n an inherited condition that is characterized by delay in the ability to relax muscles after forceful contractions but not by wasting of muscle called also Thomsen's disease

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tonic spasm and rigidity of certain muscles when an attempt is made to move them after a period of rest or when mechanically stimulated; the stiffness disappears as the muscles are used. There are autosomal dominant and autosomal recessive forms; both are due to mutation in the CLCN1 gene (locus: 7q35), which encodes a skeletal muscle chloride channel. The autosomal dominant form is called also Thomsen disease; the autosomal recessive form, which is more severe, appears later in childhood, and is often also characterized by muscle weakness, is called also Becker disease.