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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 ( myotonia ) 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.
The prevalence of DM1 ranges from 5 to 20 per 100,000 (1:20,000–1:5000). [5] Up to 48 per 100,000 (1:2100) individuals tested positive for the mutation of DM1 in New York, although not all of these individuals would have become symptomatic. [33] Again in New York, premutations for DM1 were found in 191 per 100,000 (1:525). [33]
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.
[1] [2] 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 ...
Congenital fiber type disproportion affects skeletal muscle, typically causing weakness in the shoulders, upper arms, thighs, and hips. Skeletal muscle is made up of two kinds of fiber, type 1 and type 2. In congenital fiber type disproportion, type 1 fibers are not only smaller but often more abundant than type 2 fibers. [12]
Multiple congenital anomalies-hypotonia-seizures syndrome is a rare multi-systemic genetic disorder which is characterized by developmental delay, seizures, hypotonia and heart, urinary, and gastrointestinal abnormalities.
[1] The channelopathies of human skeletal muscle include hyper- and hypokalemic (high and low potassium blood concentrations) periodic paralysis, myotonia congenita and paramyotonia congenita. Channelopathies affecting synaptic function are a type of synaptopathy.