Description

Thomsen and Becker’s disease (myotonia congenita) is characterized by slow muscle relaxation associated with hyper-excitation of muscle fibers. The prevalence is estimated at 1-10 / 100,000. It has an early onset and very often the affected subjects are recognized by the family from the first months of life. Myotonia improves with movement (heating phenomenon). The mode of transmission may be autosomal dominant (Thomsen myotony) or autosomal recessive (Becker’s myotony). Both forms of the disease are due to the loss of function of the gene that codes for the chlorine channel (CLCN1), appointed to repolarize the muscle cells. The clinical diagnosis can easily be confirmed by electromyography (EMG), which reveals myotonic discharges associated with hyper-excitation of the myocyte membrane. The stress test and the cold stress allow the detailed characterization of myotonia and orient the molecular diagnosis. The identification of mutations in the chlorine channel gene is diagnostic, after verifying the positivity of stress EMG and cold stress. Genetic counseling must be offered and the results of molecular analysis must be interpreted with caution, since the same mutations are associated both with the dominant and recessive transmission forms, depending on the family studied. Treatment is based on sodium channel blocking agents, such as mexiletine, carbamazepine or diphenylhydantoin.

External Information

Click here for more information about the Thomsen and Becker Disease genetic test.