Ion channel disorders are one of the most challenging areas in neurology and basic neuroscience with more than 27 500 results in a PubMed search and an increasing annual publication rate. They have become of particular relevance in muscle disorders (eg, myotonias), epilepsy (eg, benign familial neonatal epilepsy), paraneoplastic syndromes (eg, antibodies against ion channels as in Isaac's syndrome) cerebellar ataxias (eg, episodic ataxias1) or headache (eg, familial hemiplegic migraine). Mutations can affect voltage-gated channels or ligand-gated channels as, for instance, in congenital myasthenic syndromes. Basically, mutations of ion channel genes can have three consequences: loss-of-function (‘nonsense mutations’) when no functional ion channel protein is expressed (due to heterozygosity there is, however, still one normal channel protein, leading to a reduced density of ion channels and ion currents); a change-of-function (‘missense mutations’) leading to an altered ion channel protein, which can change the activation or inactivation potentials, kinetics of opening or closing of the channel or change the ion selectivity, all of which may have a major impact on the function of the ion channel, leading either to a gain-of-function or a reduction in function; change of the trafficking of the ion channel; or incorporation into the membrane. In summary, all these mutations can increase or decrease the excitability of nerve cells, dendrites or …