Abstracts

Rationale: A growing number of the genes responsible for heritable epilepsy syndromes have been identified in recent years. Mutations in voltage-gated ion channels are a common cause of monogenic epilepsies. Families that inherit mutations in these genes frequently exhibit a surprising degree of phenotype heterogeneity. This suggests that genetic modifiers may have a strong influence on the epilepsy phenotype. Identifying genetic modifiers can help elucidate the molecular pathways that are involved in epilepsy, and these pathways may contain novel therapeutic targets that could aid in the treatment of epilepsy. We previously identified Kcnv2 as a genetic modifier of epilepsy in the Scn2a^Q54 (Q54) transgenic mouse model of epilepsy (Bergren et al., Mamm Genome 2009; 20:359-366). Kcnv2 encodes the silent modulatory voltage-gated potassium channel subunit (Kv8.2). A screen of pediatric epilepsy patients revealed two novel KCNV2 variants. Both variants altered potassium current in a heterologous expression system, and neither variant was present in neurologically normal control chromosomes. This suggests that KCNV2 may also contribute to human epilepsy (Jorge et al., PNAS; 20(13):5443-5448). Our data suggests that Kcnv2 is a quantitative modifier of the Q54 phenotype. We hypothesize that regulatory sequence variation in the promoter and/or 3'UTR of Kcnv2 influences seizure susceptibility by altering steady-state expression levels. In order to better understand how Kcnv2 influences seizure susceptibility, we are working to identify and characterize cis-regulatory elements that influence steady-state expression levels of KCNV2 in both mouse and human. This work will advance our knowledge of potassium channel regulation and the mechanisms by which genetic modifiers influence epilepsy susceptibility. Methods: We used rapid amplification of cDNA ends (RACE) and RNase protection assays (RPA) as complementary approaches to identify the Kcnv2 transcription start site (tss) region. Luciferase-based promoter assays are currently in progress to identify the minimal promoter region of Kcnv2. Results: The RACE and RPA results both suggest the use of multiple Kcnv2 transcription start sites that lie within an 100 bp region 130 bp upstream of the Kcnv2 start codon. Conclusions: Our results suggest that the tss region lies ~50 bp upstream of the tss predicted in genomic databases [Ensembl database (NCBI37/mm9), UCSC genome browser (NCBI37/mm9)]. Kcnv2 does not have a TATA box. The use of multiple transcription start sites within a tss region is consistent with what has been observed in other TATA-less genes. Determining the location of the tss region has facilitated the development of promoter assays to determine the minimal promoter region of Kcnv2. These are now in progress.