Abstracts

RATIONALE: Our objectives are to use genetic linkage and association techniques to identify human seizure susceptibility genes. Mapping studies identified the potassium ion channel gene KCNJ10 as an excellent epilepsy candidate gene. KCNJ10 protein plays a critical role in regulating extracellular potassium ion concentration in the CNS. Previous work from our laboratories identified DNA variation in the mouse and human KCNJ10 gene implicating it as a putative seizure susceptibility gene for both focal and generalized epilepsy. To confirm and extend these earlier results we are fine mapping the genomic region surrounding the human KCNJ10 locus to systematically identify those DNA variations that are associated with common forms of epilepsy.
METHODS: We have identified several SNP variations in the human KCNJ10 gene using single stranded conformation electrophoresis and DNA sequencing and found others surrounding the gene locus via database searching (dbSNP at NCBI). We currently use restriction fragment length polymorphism analysis and Pyrosequencing[tm] to genotype single nucleotide polymorphisms (SNPs) in high priority genomic regions thought to contain seizure susceptibility genes such as KCNJ10.
RESULTS: One SNP (C1037T, based on NCBI # NM002241) in the KCNJ10 coding region alters an amino acid (R271C) and shows a statistically significant association with common human seizure disorders such as mesial temporal lobe epilepsy (n=153), childhood absence epilepsy (n=84), juvenile myoclonic epilepsy (n=111) and other forms of idiopathic generalized epilepsy (n=59) ([chi]2 = 5.65, df=1, p= 0.017, n= 407 epilepsy, 284 control individuals). The c allele is common (cc~87%, ct ~12%, tt~1% in controls) and the conversion to a t allele occurs twice as often in controls compared to epilepsy patients. All genotypes are in Hardy Weinberg equilibrium. We are currently genotyping SNP markers at small intervals (2-5KB) both proximal and distal to the C1037T SNP to identify additional seizure susceptibility variations if they exist. Thus far no other SNP marker studied in this region shows a significant association with common human seizure disorder.
CONCLUSIONS: In the absence of any other DNA variation in this region that is statistically associated with common forms of epilepsy, the C1037T SNP in KCNJ10 is likely to constitute the first gene variation discovered that affects risk for both generalized and focal epilepsy subtypes. The variation from a c to t allele seems to be protective as it is associated with a decreased risk for common forms of epielspy. Thus KCNJ10 could be considered a [italic]bona fide[/italic] seizure susceptibility gene.
[Supported by: NIH grants RO1NS40554 & RO1NS39516 to TNF and RO1NS40396 to RJB. The Univ of PA Center for Neurobiology and Behavior. F.W. Lohoff was supported by a scholarship from University Hospital Charité, Humboldt University of Berlin, Germany]