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Myotonia congenita is a congenital neuromuscular channelopathy that affects skeletal muscles (muscles used for movement). It is a genetic disorder.The hallmark of the disease is the failure of initiated contraction to terminate, often referred to as delayed relaxation of the muscles and rigidity. [1]
Myotonia congenita is caused by an inherited disorder of a chloride channel in the muscles of the skeleton (skeletal muscle chloride channel 1, CLCN1). [14] Congenital myotonia can be inherited as an autosomal dominant trait (with incomplete penetrance) or a recessive trait, resulting in the varying severity of the condition.
Myotonia is the defining symptom of many channelopathies (diseases of ion channel transport) such as myotonia congenita, paramyotonia congenita and myotonic dystrophy. [3] [4] Brody disease (a disease of ion pump transport) has symptoms similar to myotonia congenita, however, the delayed muscle relaxation is pseudo-myotonia as the EMG is normal ...
Potassium-aggravated myotonia is a rare genetic disorder that affects skeletal muscle. [2] Beginning in childhood or adolescence, people with this condition experience bouts of sustained muscle tensing ( myotonia ) that prevent muscles from relaxing normally.
Mutations in this gene cause two forms of inherited human muscle disorders: recessive generalized myotonia congenita (Becker) and dominant myotonia (Thomsen). [5] Chloride channel protein, skeletal muscle (CLCN1) is a protein that in humans is encoded by the CLCN1 gene. [6] Mutations in this protein cause congenital myotonia.
Isolated case reports of myotonia had been published previously, including reports by Frederick Eustace Batten and Hans Curschmann, and type 1 myotonic dystrophy is therefore sometimes known as Curschmann-Batten-Steinert syndrome. [35] The underlying cause of type 1 myotonic dystrophy was determined in 1992. [2]
Limb–girdle muscular dystrophy (LGMD) is a genetically heterogeneous group of rare muscular dystrophies that share a set of clinical characteristics. [7] It is characterised by progressive muscle wasting which affects predominantly hip and shoulder muscles. [8]
Schwartz–Jampel syndrome (SJS, also known as chondrodystrophic myotonia) is a rare genetic disease caused by a mutation in the perlecan gene (HSPG2) [1] which causes osteochondrodysplasia associated with myotonia. [2] Most people with Schwartz–Jampel syndrome have a nearly normal life expectancy. [3]