Acetazolamide-Responsive Myotonia

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Retrieved

2021-01-23

Source

Orphanet

Trials

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Genes

SCN4A, SLC34A2, PIK3CG, PIK3CA, PIK3CB, PIK3CD, CLCN1, FGF23, CST12P, CRTAM, CASZ1, PDP1, SLC35A1, EBI3, GAL3ST1, IL18R1, ASS1, CXCR4, PAM, KIT, IRF1, IFNG, GRM5, CCR10, CYP51A1, CTNNB1, LOC110806263

Drugs

Mexiletine hydrochloride ( NAMUSCLA )

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A form of potassium-aggravated myotonia (PAM) which shows dramatic improvement with the use of acetazolamide (ACZ).

Epidemiology

Prevalence is unknown.

Clinical description

Symptoms generally manifest during childhood (before 10 years old), with myotonia of the facial, limbs and/or intercostal muscles that is triggered by potassium ingestion, fasting and mildly by cold exposure and exercise. Muscle stiffness is generally painful. Additional clinical signs include generalized muscle hypertrophy, percussion myotonia of proximal upper extremity muscles, thenar eminence and tongue and myotonia in the eyelids. Paralysis or weakness is never observed.

Etiology

ACZ-responsive myotonia 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.

Management and treatment

Myotonia is dramatically improved with ACZ but when ACZ does not control myotonia or when side-effects occur such as kidney stone formation, mexiletine can be used as replacement therapy.