Myotonia is a clinical sign, which is present on a heterogeneous group of neuromuscular diseases.
Is a muscle disorder that causes muscle relaxation late, after making a voluntary contraction or after subjecting it to an electrical stimulus. Therefore, the patient presents serious difficulties for muscle relaxation. Other different organs may also be affected in varying degrees. The disorder may be caused by alterations in ion channels or in the membrane muscle.
Myotonia can be classified into dystrophic and non-dystrophic myotonia.
SCN4A (17q23.3), CACNA1S (1q32.1) and CLCN1 (7q34) gene alterations, are associated with myotonia.
SCN4A gene encodes the voltage-sensitive sodium channel α-subunit. Mutations in it are associated with: hyperkalemic periodic paralysis type 2 (PPHC2) (# 170500), hypokalemic periodic paralysis (# 613345), myasthenic syndrome with acetazolamide response (# 614198), atypical myotonia congenita acetazolamide sensitive (# 608390) paramyotonia congenita (# 168300).
CLCN1 gene encodes the chloride channel protein, skeletal muscle. Mutations in this gene are associated with autosomal dominant myotonia congenita or Thomsen disease (# 160800), as well as myotonia congenita autosomal recessive or disease Becker (# 255700).
Also have been reported CACNA1S gene alterations. CACNA1S encodes the α-1 subunit of a slowly inactivating L-type voltage-dependent calcium channel in skeletal muscle cells. CACNA1S mutations are associated with hypokalemic periodic paralysis type 1 (# 170400), malignant hyperthermia susceptibility type 5 (# 601887), susceptibility to thyrotoxic periodic paralysis type 1 (# 188580), and myotonic dystrophy as a result of deregulation in alternative splicing processes.
Bioarray offers a complete NGS panel for the detection of myotonia, through SCN4A, CLCN1, and CACNA1S gene sequencing.