Disease Information for Myotonia congenita (Thomsens d.)

Myotonia Congenita; Subdivisions: Becker Disease; Myotonia Congenita, Autosomal Recessive (MCR); Generalized; Thomsen Disease (THD); Myotonia Congenita, Autosomal Dominant; 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 to 12 years; As in Thomsen type myotonia congenita, affected individuals develop myotonia, associated muscle rigidity, and abnormal muscle enlargement (hypertrophy); However, in contrast to Thomsen type, such symptoms are progressive and tend to be more severe; In addition, muscle hypertrophy may be particularly striking, and muscle weakness may be present; Becker disease is inherited as an autosomal recessive trait; [NORD]

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