Myotonia congenita causes abnormal muscle tension and relaxation, with symptoms including pain, cramps, and mobility issues. It is caused by a defect in the CLCN1 gene, which affects electrical impulses in muscles. There are two forms, Thomsen’s disease and Becker disease, with different inheritance patterns. Treatment may include medication and physical therapy.
Myotonia congenita is a genetic disorder that causes a person’s muscles to tense and relax abnormally. An individual with the disease cannot voluntarily relax some muscles, forcing them to remain in a rigid position. Possible symptoms include pain, frequent cramps, and mobility problems. Myotonia congenita can be present at birth or develop in early childhood and usually persists throughout the patient’s life. Depending on the severity of symptoms, treatment may consist of regular doses of muscle relaxant drugs, anticonvulsant drugs, and ongoing physical therapy.
The muscle movement problems associated with myotonia congenita are caused by abnormalities in the way electrical impulses are transmitted in the body. A gene called CLCN1 normally makes proteins that stabilize electrical activity within muscles, allowing them to contract and relax on command. In the case of myotonia congenita, a defect in the CLCN1 gene results in missing or non-functioning proteins.
There are two forms of myotonia congenita that differ in how they are inherited. The most common form, called Thomsen’s disease, is an autosomal dominant disorder that usually causes symptoms from birth. It can be inherited if only one parent carries a mutated copy of the CLCN1 gene. Becker disease is an autosomal recessive disorder that requires both parents to have defective copies of the gene. It typically appears between the ages of four and 12 and tends to cause more debilitating symptoms than Thomsen’s disease.
Young children with both forms of the disease may experience temporary and sporadic muscle spasms that cause the legs or arms to stiffen. Episodes generally only last a few seconds at a time, and the movements tend to get easier the more they’re repeated. If muscles in the face, throat, and chest are affected, a patient may occasionally experience breathing and eating difficulties. Chronic joint and muscle pain are common with myotonia congenita. Overactive muscles tend to get large and well-defined as you age, which can give you a very muscular appearance.
In most cases, the severity and frequency of muscle contraction problems can be relieved with medication. Patients may be prescribed daily doses of drugs such as phenytoin or mexiletine that reduce the electrical activity in the nerves supplying the skeletal muscles. Physical therapy can help many children, adolescents, and adults with myotonia congenita learn to remain fully mobile despite their condition. Because symptoms tend to improve with repetitive motion, patients can learn exercises to perform before engaging in certain activities to reduce the chances of having symptomatic episodes.
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