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Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth.
Thomsen's disease; Becker's disease
Myotonia congenita is caused by a genetic change (mutation). It is passed down from either one or both parents to their children (inherited).
Myotonia congenita is caused by a problem in the part of the muscle cells that are needed for muscles to relax. Abnormal repeated electrical signals occur in the muscles, causing a stiffness called myotonia.
The hallmark of this condition is myotonia -- the muscles are unable to quickly relax after contracting. For example, after a handshake, the person is only very slowly able to open and pull away his hand.
Early symptoms may include:
Children with myotonia congenita often look muscular and well-developed. They may not have symptoms of myotonia congenita until age 2 or 3.
The doctor may ask if there is a family history of myotonia congenita.
Mexiletine is a medication that treats symptoms of myotonia congenita. Other treatments include:
People with this condition can do well. Symptoms only occur when a movement is first started. After a few repetitions, the muscle relaxes and the movement becomes normal. Symptoms may improve later in life.
Call your health care provider if your child has symptoms of myotonia congenita.
Couples who want to have children and who have a family history of myotonia congenita should consider genetic counseling.
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Kerchner GA, Lenz RA, Ptacek LJ. Channelopathies: Episodic and electrical disorders of the nervous system. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice. 5th ed. Philadelphia, Pa: Butterworth-Heinemann: 2008:chap 68.