Abstracts

The gene [italic]SCN2A[/italic] encodes the human brain voltage-gated sodium channel [alpha][sub]2[/sub] subunit (Na[sub]V[/sub]1.2). Mutations in [italic]SCN2A[/italic] are associated with inherited forms of epilepsy including febrile seizures (FS) and benign familial neonatal-infantile seizures (BFNIS). The epilepsy syndromes associated with mutations in [italic]SCN2A[/italic] tend to have a mild phenotype. In contrast, mutations in [italic]SCN1A[/italic], another neuronal voltage-gated sodium channel, are sometimes associated with more severe clinical phenotypes. For this gene family in particular, the underlying link between mutation, biophysical characteristics, and disease severity remains unclear. The aim of this project is to determine the functional properties of wildtype (WT) and the L1563V mutant human brain voltage-gated sodium channels encoded by [italic]SCN2A[/italic]. We constructed a recombinant human SCN2A cDNA for heterologous expression, and site-directed mutagenesis was utilized to construct the missense mutation. The constructs were functionally characterized by whole-cell patch clamp recordings of tsA201 cells transiently co-transfected with the recombinant human SCN2A along with the human [beta]1 and [beta]2 sodium channel accessory subunits. The L1563V mutation exhibited similar sodium current density to that of WT SCN2A. However, this mutation shifts the voltage-dependence of activation and the midpoint of steady-state channel availability to more positive potentials. These data suggest that sodium channels encoding the L1563V mutation may have less activity at physiologic potentials compared to WT and may have a decreased capacity to respond and propagate action potentials. We also observed accelerated recovery from fast inactivation in the L1563V allele as compared to the WT SCN2A. Once opened and inactivated, the L1563V mutation enables the channel to recover faster for a subsequent round of activation. In summary, the L1563V mutation in [italic]SCN2A[/italic] associated with BFNIS exhibits significant biophysical defects. Further characterization will aid in establishing a genotype-phenotype correlation. These studies will also help to promote a greater understanding of the molecular basis of epilepsy, lead to improved classification of epilepsy disorders, and enable better targeting of anticonvulsant medications. (Supported by the Epilepsy Foundation, NIH grant NS32387, and T32 GM007347.)