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A form of potassium-aggravated myotonia (PAM) which shows dramatic improvement with the use of acetazolamide (ACZ).
ORPHA:99736Classification level: Disorder
- ACZ-responsive congenital myotonia
- ACZ-responsive myotonia
- Acetazolamide-responsive congenital myotonia
- Myotonia-painful contractions syndrome
- Painful congenital myotonia
- Painful myotonia
- Prevalence: 1-9 / 1 000 000
- Inheritance: Autosomal dominant
- Age of onset: Childhood
- ICD-10: G71.1
- OMIM: 608390
- UMLS: -
- MeSH: -
- GARD: -
- MedDRA: -
Prevalence is unknown.
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.
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.
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.
- Clinical practice guidelines
- Deutsch (2012)