Detailed Information on Myotonia Congenita

 Myotonia congenita is an inherited condition that affects muscle relaxation. The condition is present since premature childhood, but symptoms can be mild.  Most children will be 2 or 3 years old when parents first notice their muscle stiffness, particularly in the legs, often provoked by sudden activity after rest. The muscle stiffness, which particularly occurs in the leg muscles, may be enhanced by cold and inactivity, and is often relieved by exercise. There are two forms of the disorder:  Becker-type, which is the most common form; and Thomsen’s disease, which is a rare and milder form.

The disorder is reason by mutations in a gene responsible for shutting off electrical excitation in the muscles. In Becker disease, symptoms most generally 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). Myotonia congenita is estimated to affect 1 in 100,000 people worldwide. Myotonia congenita is caused by a change to a gene. The CLCN1 gene provides instructions for making a protein that is critical for the normal function of skeletal muscle cells.

For the body to move normally, skeletal muscles must nervous and rest in a coordinated way. Muscle contraction and relaxation are conducted by the flow of ions into and out of muscle cells. Mutations in the CLCN1 gene alter the usual structure or function of chloride channels. The altered channels cannot properly regulate ion flow, reducing the movement of chloride ions into skeletal muscle cells. This disruption in chloride ion flow triggers prolonged muscle contractions, which are the hallmark of myotonia. It is passed down from either one or both parents to the children.

Myotonia congenita is believed to be caused by a problem in the part of the muscle cells that are needed for muscles to relax. Abnormal recurrence electrical discharges occur in the muscles, causing a stiffness called myotonia. Most people with myotonia congenita don’t need special treatments. The symptoms of myotonia congenita may be relieved with quinine, phenytoin, and mexiletine and other anticonvulsant drugs. Stiff muscles usually resolve with exercise, or light movement, especially after resting. Physical therapy and other rehabilitative measures may also be used to help muscle function.