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Congenital myotonia (also myotonia congenita) (''Myo-'' from Greek; muscle, and ''Tonus'' from Latin; tension), is a genetic, neuromuscular channelopathy that affects skeletal muscles (muscles used for movement). The disease was first described by Danish/German physician Julius Thomsen in 1876, who himself suffered from the disease. The hallmark of the disease is the failure of initiated contraction to terminate, often referred to as delayed relaxation of the muscles (myotonia) and rigidity. The disorder is caused by mutations in part of a gene (CLCN1) encoding the ClC-1 Chloride channel, resulting in muscle fiber membranes to have an unusually exaggerated response to stimulation (hyperexcitability). Symptoms include delayed relaxation of the muscles after voluntary contraction (myotonia), and may also include stiffness, hypertrophy (enlargement), transient weakness in some mutations, and cramping. ==Disease== Two types of myotonia congenita exist; autosomal dominant myotonia congenita also called Thomsens disease (OMIM 160800), after Julius Thomsen, and recessive generalized myotonia (RGM) or Becker myotonia (OMIM 255700), after the German professor Peter Emil Becker, who discovered the recessive subtype of patients suffering from myotonia congenita. The term congenital, see Congenital disorder, strictly applies only to Thomsens disease, as the onset of Becker myotonia may be delayed up to the age of 4–6 years,. In Myotonia Congenita, the term reflects that the disease is genetically present from birth, while the onset may be delayed. With the advent of genetic testing, it has recently been found that some recessive mutations may occur in a dominant fashion in some individuals. The reason for this is not known. Because several CLCN1 mutations can cause either Becker disease or Thomsen disease, doctors usually rely on characteristic signs and symptoms to distinguish the two forms of myotonia congenita. However, myotonia caused by CLCN1 mutations can occasionally be clinically indistinguishable from myotonia caused by sodium channel mutations (SCN4A mutations) resulting in the similar disease Paramyotonia Congenita. A so-called Finnish heritage disease, congenital myotonia is more common in Finland and among ethnic Finns. A molecular study of the CLCN1 gene in 24 families in northern Finland, including 46 affected individuals, showed that although the inheritance appeared to be dominant (Thomsen type), in fact it is recessive (Becker type). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Myotonia congenita」の詳細全文を読む スポンサード リンク
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