Idiopathic epilepsy of childhood and potassium ion channels.

The etiology of common idiopathic epileptic syndromes is genetically determined, but the complex pattern of inheritance suggests an epistatic interaction of several susceptibility genes. Mutations in over 70 genes now define biological pathways leading to rare monogenic forms of epilepsy in humans and animals. Recognizing the molecular basis of an ion-channel disease has provided new opportunities for screening, early diagnosis, and therapy of these conditions. Potassium can affect the development of common seizure type and can be defined seizure susceptibility allele. The existence of inward-rectifying potassium (Kir) channels was first recognized half a century ago. The biophysical fingerprint of Kir channels is inward rectification in the current-voltage relationship , which limits potassium efflux at depolarizing membrane potentials. Kir channels are essential in the control of resting membrane potential, coupling of the metabolic cellular state with membrane excitability, and maintenance of potassium homeostasis. The critical interval contains several candidate genes, one of which, KCNJ1O, exhibits a potentially important polymorphism with regard to fundamental aspects of seizure susceptibility. Deletion of KCNJ1O as a seizure susceptibility gene that code for inward rectifier potassium ion channels imparts protection against seizures results in spontaneous seizures and increased seizure susceptibility. The unique role of Kir channels in membrane physiology coupled with previous strong association between ion channel gene mutations and seizure phenotypes puts even greater focus on KCNJ1O. The major challenge of the future will be to recognize the molecular basis of a Kir-mediated channelopathy in order to screen, diagnose and treat these ion channel diseases.