Potassium-aggravated myotonia

Other names| PAM[1]
This condition is inherited in an autosomal dominant manner
myotonia figure.png

Potassium-aggravated myotonia is a rare genetic disorder that affects skeletal muscle.[2] 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.[citation needed]

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.[citation needed]

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

1. ↑ RESERVED, INSERM US14-- ALL RIGHTS. "Orphanet: Potassium aggravated myotonia" (in en). https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=612. Retrieved 30 September 2019.
2. ↑ Reference, Genetics Home. "Potassium-aggravated myotonia" (in en). https://ghr.nlm.nih.gov/condition/potassium-aggravated-myotonia. Retrieved 30 September 2019.

## External links

Classification|

* ICD-10: G71.1
* OMIM: 608390
* MeSH: C538353

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External resources|

* Orphanet: 612

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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|

* CFTR
* Cystic fibrosis
* Congenital absence of the vas deferens
* CLCN1
* Thomsen disease
* Myotonia congenita
* CLCN5
* Dent's disease
* CLCN7
* Osteopetrosis A2, B4
* BEST1
* Vitelliform macular dystrophy
* CLCNKB
* Bartter syndrome 3

TRP channel|

* TRPC6
* FSGS2
* TRPML1
* Mucolipidosis type IV

Connexin|

* GJA1
* Oculodentodigital dysplasia
* Hallermann–Streiff syndrome
* Hypoplastic left heart syndrome
* GJB1
* Charcot–Marie–Tooth disease X1
* GJB2
* Keratitis–ichthyosis–deafness syndrome
* Ichthyosis hystrix
* Bart–Pumphrey syndrome
* Vohwinkel syndrome)
* GJB3/GJB4
* Erythrokeratodermia variabilis
* Progressive symmetric erythrokeratodermia
* GJB6
* Clouston's hidrotic ectodermal dysplasia

Porin|

* AQP2
* Nephrogenic diabetes insipidus 2

See also: ion channels

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