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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 ]
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]
[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 ...
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.
NMT is a diverse disorder. As a result of muscular hyperactivity, patients may present with muscle cramps, stiffness, myotonia-like symptoms (slow relaxation), associated walking difficulties, hyperhidrosis (excessive sweating), myokymia (quivering of a muscle), fasciculations (muscle twitching), fatigue, exercise intolerance, myoclonic jerks and other related symptoms.
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]
Paramyotonia congenita (PC) is a rare congenital autosomal dominant neuromuscular disorder characterized by "paradoxical" myotonia. [2] This type of myotonia has been termed paradoxical because it becomes worse with exercise whereas classical myotonia, as seen in myotonia congenita , is alleviated by exercise.
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 .