This chapter examines how disease mutations alter the function of different muscle ion channels and illustrates how these changes in ion channel properties contribute to the pathophysiological mechanisms underlying muscle disorders. A specific ion channel mutation can contribute to distinct disorders or exhibit different patterns of inheritance in different families. Thus, it is clear that genetic and environmental modifiers play important roles in determining the clinical phenotype. Furthermore, calcium channel mutations, which may cause hypokalemic periodic paralysis (HypoPP) by reducing sodium and potassium current densities, may represent indirect channelopathies. Moreover, some of the inherited muscle disorders, such as the myotonic sodium channel disorders, are treated by agents that largely target symptoms but not the cause of the disease, but others such as malignant hyperthermia (MH) can be treated by agents that specifically target the defective molecule. Though, channelopathies are typically rare, the insights gained from studying these genetic mutations should aid in the development of better treatments for excitability disorders.
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