Human Epilepsy Can Be Linked to a Defective Calcium Channel.

Abstract

Human Epilepsy Associated with Dysfunction of the Brain P/Q-type Calcium Channel Jouvenceau A, Eunson LH, Spauschus A, Ramesh V, Zuberi SM, Kullmann DM, Hanna MG Lancet 2001;358:801–807 Background The genetic basis of most common forms of human paroxysmal disorders of the central nervous system, such as epilepsy, remains unidentified. Several animal models of absence epilepsy, commonly accompanied by ataxia, are caused by mutations in the brain P/Q-type voltage-gated calcium (Ca2+) channel. We aimed to determine whether the P/Q-type Ca2+ channel is associated with both epilepsy and episodic ataxia type 2 in human beings. Methods We identified an 11-year-old boy with a complex phenotype comprising primary generalised epilepsy, episodic and progressive ataxia, and mild learning difficulties. We sequenced the entire coding region of the gene encoding the voltage-gated P/Q-type Ca2+ channel (CACNA1A) on chromosome 19. We then introduced the newly identified heterozygous mutation into the full-length rabbit cDNA and did detailed electrophysiologic expression studies of mutant and wild-type Ca2+ channels. Results We identified a previously undescribed heterozygous point mutation (C5733T) in CACNA1A. This mutation introduces a premature stop codon (R1820stop), resulting in complete loss of the C terminal region of the pore-forming subunit of this Ca2+ channel. Expression studies provided direct evidence that this mutation impairs Ca2+ channel function. Mutant/wild-type coexpression studies indicated a dominant negative effect. Conclusions Human absence epilepsy can be associated with dysfunction of the brain P/Q-type voltage-gated Ca2+ channel. The phenotype in this patient has striking parallels with the mouse absence epilepsy models.