Potassium-aggravated myotonia

Potassium-aggravated myotonia
Classification and external resources
OMIM	608390

Potassium-aggravated myotonia is a rare genetic disorder that affects skeletal muscle. Beginning in childhood or adolescence, people with this condition experience bouts of sustained muscle tensing (myotonia) that prevent muscles from relaxing normally. Myotonia causes muscle stiffness, often painful, that worsens after exercise and may be aggravated by eating potassium-rich foods such as bananas and potatoes. Stiffness occurs in skeletal muscles throughout the body. Potassium-aggravated myotonia ranges in severity from mild episodes of muscle stiffness to severe, disabling disease with frequent attacks. Potassium-aggravated myotonia may, in some cases, also cause paradoxical myotonia, in which myotonia becomes more severe at the time of movement instead of after movement has ceased. Unlike some other forms of myotonia, potassium-aggravated myotonia is not associated with episodes of muscle weakness.

Mutations in the SCN4A gene cause potassium-aggravated myotonia. The SCN4A gene provides instructions for making a protein that is critical for the normal function of skeletal muscle cells. For the body to move normally, skeletal muscles contract and relax in a coordinated way. Muscle contractions are triggered by the flow of positively charged ions, including sodium, into skeletal muscle cells. The SCN4A protein forms channels that control the flow of sodium ions into these cells. Mutations in the SCN4A gene alter the usual structure and function of sodium channels. The altered channels cannot properly regulate ion flow, increasing the movement of sodium ions into skeletal muscle cells. The influx of extra sodium ions triggers prolonged muscle contractions, which are the hallmark of myotonia.

Potassium-aggravated myotonia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits a mutation in the SCN4A gene from one affected parent. Other cases result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.

References

U.S. National Library of Medicine. Potassium-aggravated myotonia

Diseases of ion channels

Calcium channel

Voltage-gated	CACNA1A Familial hemiplegic migraine 1 Episodic ataxia 2 Spinocerebellar ataxia type-6 CACNA1C Timothy syndrome Brugada syndrome 3 Long QT syndrome 8 CACNA1F Ocular albinism 2 CSNB2A CACNA1S Hypokalemic periodic paralysis 1 Thyrotoxic periodic paralysis 1 CACNB2 Brugada syndrome 4

Ligand gated	RYR1 Malignant hyperthermia Central core disease RYR2 CPVT1 ARVD2

Sodium channel

Voltage-gated	SCN1A Familial hemiplegic migraine 3 GEFS+ 2 Febrile seizure 3A SCN1B Brugada syndrome 6 GEFS+ 1 SCN4A Hypokalemic periodic paralysis 2 Hyperkalemic periodic paralysis Paramyotonia congenita Potassium-aggravated myotonia SCN4B Long QT syndrome 10 SCN5A Brugada syndrome 1 Long QT syndrome 3 SCN9A Erythromelalgia Febrile seizure 3B Paroxysmal extreme pain disorder Congenital insensitivity to pain

Constitutively active	SCNN1B/SCNN1G Liddle's syndrome SCNN1A/SCNN1B/SCNN1G Pseudohypoaldosteronism 1AR

Potassium channel

Voltage-gated	KCNA1 Episodic ataxia 1 KCNA5 Familial atrial fibrillation 7 KCNC3 Spinocerebellar ataxia type-13 KCNE1 Jervell and Lange-Nielsen syndrome Long QT syndrome 5 KCNE2 Long QT syndrome 6 KCNE3 Brugada syndrome 5 KCNH2 Short QT syndrome KCNQ1 Jervell and Lange-Nielsen syndrome Romano–Ward syndrome Short QT syndrome Long QT syndrome 1 Familial atrial fibrillation 3 KCNQ2 BFNS1

Inward-rectifier	KCNJ1 Bartter syndrome 2 KCNJ2 Andersen–Tawil syndrome Long QT syndrome 7 Short QT syndrome) KCNJ11 TNDM3 KCNJ18 Thyrotoxic periodic paralysis 2

Chloride channel

TRP channel

TRPC6
- FSGS2
TRPML1
- Mucolipidosis type IV

Connexin

Porin

AQP2
- Nephrogenic diabetes insipidus 2

See also: ion channels

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