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What are ion channel disorders?

Ion channel disorders are a heterogeneous group of rare inherited disorders. They are clinically characterised by episodic recurrence of functional defects of the skeletal or heart musculature, the central nervous system or other tissues specific for the respective disorder.
During an attack hyper- or hypoexcitability of the affected tissue occur spontaneously leading to cardiac arrhythmia, muscle stiffness or weakness, paralysis, ataxia, migraine, or epileptic seizures.

Among so far identified ion channel disorders are skeletal disorders (myotonias, periodic paralyses, and malign hyperthermia), disturbances in conduction within the central nervous system (episodic ataxias, familial hemiplegic migraine, and three forms of dominant inherited epilepsies) and cardiac arrhythmias (long QT syndrome and idiopathic ventricular fibrillation).

Symptoms can commonly be provoked by triggers like physical activity or uptake of carbohydrate-rich food. During attack-free intervals, patients are often inconspicuous. However, it is possible that degeneration of the affected tissue can occur in the course of some disorders. This could lead to slowly progressing muscular atrophies, ataxia or nystagmus. Apart from the described symptoms, evidence for the existence of such a disorder is a positive family history.

Characteristics of ion channel disorders are:
  • in most cases disturbances in the excitability of neuron or muscle cells
  • occurrence of attacks or episodic symptoms
  • often provoked by certain triggers
  • often inconspicuous findings between attacks
  • positive family history

Disorders are caused by mutation of genes coding for different tissue-specific ion channels. Ion channels are membrane-spanning proteins forming selective pores for Na+-, K+-, Cl-- , or Ca2+ ions and allow for electric excitability of neuron and muscle cells. They translate sensory stimuli into receptor potentials thereby mediating communication with the environment and transmitting information within the body.

Ref.: Dt Ärztebl 2000; 97: A-1826–1831[Heft 26]

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