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Hyperkalemic Periodic Paralysis Type 1.

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GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014.
2003 Jul 18 [updated 2011 May 31].

Excerpt

DISEASE CHARACTERISTICS:

Hyperkalemic periodic paralysis type 1 (hyperPP1) is characterized by attacks of flaccid limb weakness (which may also include weakness of the muscles of the eyes, throat, and trunk), hyperkalemia (serum potassium concentration >5 mmol/L) or an increase of serum potassium concentration of at least 1.5 mmol/L during an attack of weakness and/or provoking/worsening of an attack by oral potassium intake, normal serum potassium and muscle strength between attacks, onset before age 20 years, and absence of paramyotonia (muscle stiffness aggravated by cold and exercise). The attacks of flaccid muscle weakness usually begin in the first decade of life. Initially infrequent, the attacks then increase in frequency and severity over time until approximately age 50 years, after which the frequency of attacks declines considerably. Potassium-rich food or rest after exercise may precipitate an attack. A cold environment and emotional stress provoke or worsen the attacks. A spontaneous attack commonly starts in the morning before breakfast, lasts for 15 minutes to one hour, and then disappears. Cardiac arrhythmia or respiratory insufficiency usually does not occur during attacks. Between attacks, hyperPP1 is usually associated with mild myotonia (muscle stiffness) that does not impede voluntary movements. Many older affected individuals develop a chronic progressive myopathy.

DIAGNOSIS/TESTING:

Diagnosis is based on clinical findings. In case of diagnostic uncertainty, one of three provocative tests can be employed. HyperPP1 is caused by point mutations in SCN4A encoding the voltage-gated skeletal muscle sodium channel. Targeted mutation analysis for nine common mutations detects a mutation in approximately 55% of affected individuals.

MANAGEMENT:

Treatment of manifestations: At the onset of weakness, attacks may be prevented or aborted with mild exercise and/or oral ingestion of carbohydrates, inhalation of salbutamol, or intravenous calcium gluconate. Prevention of primary manifestations: Hyperkalemic attacks of weakness can be prevented by frequent meals rich in carbohydrates, continuous use of a thiazide diuretic or acetazolamide, and avoidance of potassium-rich medications and foods, fasting, strenuous work, and exposure to cold. Prevention of secondary complications: During surgery, avoid use of depolarizing anesthetic agents including potassium, suxamethonium, and anticholinesterases that aggravate myotonia and can result in masseter spasm and stiffness of respiratory and other skeletal muscles, interfering with intubation and mechanical ventilation. Surveillance: During prophylactic treatment, determination of serum potassium concentration twice per year to avoid severe diuretic-induced hypokalemia; assessment of neurologic status and MRI of proximal leg muscles every three years. Agents/circumstances to avoid: Potassium-rich medications and foods, fasting, strenuous work, exposure to cold. Evaluation of relatives at risk: It is appropriate to test asymptomatic at-risk family members for the disease-causing mutation identified in an affected relative in order to institute preventive measures prior to surgery.

GENETIC COUNSELING:

HyperPP1 is inherited in an autosomal dominant manner. Most individuals with hyperPP1 have an affected parent; the proportion of cases caused by de novo mutations is unknown. Each child of an individual with hyperPP1 has a 50% chance of inheriting the mutation. Prenatal diagnosis for pregnancies at increased risk is possible if the disease-causing mutation in the family has been identified; however, requests for prenatal testing for conditions such as hyperPP1 that do not affect intellect and have some treatment available are not common.

Copyright © 1993-2014, University of Washington, Seattle. All rights reserved.

PMID:
20301669
[PubMed]
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