National Organization for Rare Disorders, Inc.
It is possible that the main title of the report Myotonia Congenita is not the name you expected.
- Thomsen Disease (THD); Myotonia Congenita, Autosomal Dominant
- Becker Disease; Myotonia Congenita, Autosomal Recessive (MCR); Generalized
Myotonia congenita is a rare genetic disorder in which an abnormality of voluntary (skeletal) muscle fiber membranes causes an unusually exaggerated response to stimulation (hyperexcitability). As a result, affected individuals have difficulty relaxing certain muscles after contracting them (myotonia), muscle stiffness (rigidity), and associated symptoms. Such symptoms tend to occur when attempting to move certain muscles after rest. In many cases, individuals with myotonia congenita also have abnormal enlargement of the muscles (hypertrophy), resulting in a "herculean" or "body-builder like" appearance.
Two main forms of myotonia congenita have been described: Thomsen disease and Becker disease. In individuals with Thomsen disease, symptoms and findings such as myotonia, associated muscle rigidity, and abnormal muscle enlargement may become apparent from infancy to approximately two to three years of age. In many cases, muscles of the eyelids, hands, and legs may be most affected. Thomsen disease is transmitted as an autosomal dominant trait.
In those with Becker disease, symptoms most commonly become apparent between the ages of four and 12 years. As in Thomsen type myotonia congenita, affected individuals develop myotonia, associated muscle rigidity, and abnormal muscle enlargement (hypertrophy). The symptoms tend to remain constant, with little progression. Becker disease is inherited as an autosomal recessive trait.
Malignant Hyperthermia Association of the United States
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Muscular Dystrophy Association
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NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases
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NIH/National Institute of Neurological Disorders and Stroke
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Genetic and Rare Diseases (GARD) Information Center
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Child Neurology Foundation
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Last Updated: 9/17/2007
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