Skeletal muscle channelopathies are a heterogeneous group of rare neuromuscular disorders caused by mutations in muscle ion channel genes. They include non-dystrophic myotonia and periodic paralysis. Molecular defects have been disclosed in CLCN1, SCN4A, CACNA1S and KCNJ2 genes, encoding for chloride, sodium, calcium and potassium muscle channels, respectively. Non-dystrophic myotonia are characterized by myotonia, muscle stiffness, pain and weakness. The periodic paralyses are characterized by episodes of flaccid paralysis.

NON-DYSTROPHIC MYOTONIA:
–       MYOTONIA CONGENITA:
Thomsen myotonia (autosomal dominant)
Becker myotonia (autosomal recessive)
–       SODIUM CHANNEL MYOTONIA (autosomal dominant)
–       PARAMYOTONIA CONGENITA (autosomal dominant)

PERIODIC PARALYSIS:

–       HYPOKALIEMIC PERIODIC PARALYSIS (autosomal dominant)
–       HYPERKALIEMIC PERIODIC PARALYSIS (autosomal dominant)
–       ANDERSEN-TAWIL SYNDROME (autosomal dominant)

Muscle channelopaties show a wide spectrum of overlapping phenotypes making the diagnosis a challenge. The phenotype can differ for the same mutation even in the same family. Genetic analysis is important to define which gene is involved especially in hypokaliemic periodic paralysis type I and type II that are almost indistinguishable.

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