Myotonia Fluctuans

Watchlist

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Retrieved

2021-01-23

Source

Orphanet

Trials

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Genes

SCN4A, AKT1, TNF, INTS2, TRBV5-7, INTS1, TCIRG1, USP14, CXCR4, WNT1, VEGFA, CXCL12, FGF3, MMP1, JAK2, IRF4, IL10, IL6, IL4, IL1B, QTRT1

Drugs

Mexiletine hydrochloride ( NAMUSCLA )

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Myotonia fluctuans (MF) is a form of potassium-aggravated myotonia (PAM, see this term) which is cold insensitive, dramatically fluctuating and profoundly worsened by potassium ingestion.

Epidemiology

Prevalence is unknown.

Clinical description

Fluctuating myotonia develops during childhood or adolescence and involves the extraocular, bulbar and limb muscles. Eyelid myotonia is often the first sign of the disease. Episodes of stiffness vary in severity and frequency and may be separated by prolonged periods of normality. Myotonia is aggravated by potassium ingestion and appears with a delayed onset (10-30 min) after exercise (exercise-induced delayed-onset myotonia). Cold has no effect on myotonia. Paralysis is never observed. Episodic weakness is rare.

Etiology

Myotonia fluctuans is a sodium muscle channelopathy due to missense mutations of the SCN4A gene encoding the alpha subunit of the skeletal muscle voltage-gated sodium channel Nav1.4.

Genetic counseling

Transmission is autosomal dominant.