MUSCULAR ION CHANNEL DISORDERS
 

Ion channels are integral transmembrane proteins that regulate inner and outer flows of ions through the muscle membrane, as well as generate and propagate action potentials. The proper functioning of the muscle membrane relies on a balanced muscle membrane excitability. Mutations in genes encoding ion channels modify this subtle equilibrium driving the membrane towards states of either hyper- or hypo-excitability. Mechanism linking abnormal channel functioning to membrane excitability are well understood for chloride and sodium channel mutations. They remain however mysterious for some of the sodium and calcium channel mutations. Modifications in the state of excitability of the muscle membrane are the basis of symptoms in patients i.e. stiffness (myotonia) or weakness (paralysis). The better understanding of the pathophysiology of symptoms enables a more rationale therapeutic choice. Progess have been made in the diagnosis of these diseases. Exercise tests coupled to electromyography are sensitive enough to detect abnormal muscle membrane excitability and to predict groups of mutations. Molecular diagnosis can also be obtained on a routine basis. Clinical and paraclinical investigations of these rare disorders have improved through a national collaborative network: Resocanaux.