Abstracts

The majority of children with epilepsy have cortical seizures, yet underlying mechanisms at the cellular level are poorly understood in humans. In familial epilepsies, most mutations occur in ion-channel and transporter genes, and in model systems, subunit expression levels critically impact channel and neuronal network function. We have identified aberrant sodium currents within surgically resected cortical seizure foci using electrophysiology. We hypothesize that altered expression of ion channel subunit genes may be accountable, and critical for the expression of cortical epileptogenesis. Neocortical tissue classified as [ldquo]focal[rdquo]or [ldquo]control[rdquo] by source localization methods was recovered from patients with medically intractable epilepsy. Expression analysis was performed on mRNA amplified from sectioned, oxygenated tissue, by 32P-hybridization onto commercial cDNA arrays for multi-gene profiling, or by Quantitative RT-PCR amplification for single gene confirmation. Expression was normalized using total-blot hybridization efficiency, or HPRT expression (QRT-PCR). Relative gene expression was calculated as the ratio of [quot]focal[quot] to [quot]control[quot] signal, using within-patient[apos]s samples or non-epileptic post-mortem cortex (external control). By cDNA array, over half of measurable ion-channel/neurotransmitter genes exhibited [gt]1.4-fold expression change between focal and control tissue; similar results were obtained for most genes whether the [apos]control[apos] was derived from an internal patient sample/frozen age-matched tissue, or from matched/mis-matched (parietal:temporal) cortical regions. Quantitative RT-PCR analysis of genes with low-level expression identified similar amplitudes of expression changes, and analysis of representative genes confirmed array hybridization measurements of over 1.3-fold difference, regardless of direction of change. Surprisingly, patients with separate etiologies shared over a third of expression changes; it would be expected that [lt] 1 in 10 genes would arbitrarily show common expression changes in a three-way comparison (p[lt]0.01). An unusually large number of gene expression changes were also observed within idiopathic epilepsy (p[lt]0.007). Furthermore, expression differences were confirmed between separate foci removed from a patient with encephalopathy: [gt]30% of genes in the second focus differed in the direction of change from the common pattern. Our findings suggest that there may be common causal and/or compensatory mechanisms underlying cortical epilepsies with differing etiologies. Further studies are ongoing to determine whether expression changes are consistent between individual neurons within cortical sections, and whether uniquely affected genes or amplitude of change are specific to patient, etiology or focal localization. (Supported by Falk Fdn (LBKH, WvD, KEH, CJM), IRSA (LBKH), Children[apos]s Research Fdn (LBKH, CJM).)