Purpose: Mutations in SCN2A, the gene encoding the brain voltage-gated sodium channel α-subunit NaV1.2, are associated with inherited epilepsies including benign familial neonatal-infantile seizures (BFNIS). Functional characterization of three BFNIS mutations was performed to identify defects in channel function that underlie this disease.
Methods: We examined three BFNIS mutations (R1319Q, L1330F, and L1563V) using whole-cell patch-clamp recording of heterologously expressed human NaV1.2. Membrane biotinylation was employed to examine the cell surface protein expression of the four NaV1.2 alleles.
Results: R1319Q displayed mixed effects on activation and fast inactivation gating, consistent with a net loss of channel function. L1563V exhibited impaired fast inactivation predicting a net gain of channel function. The L1330F mutation significantly decreased overall channel availability during repetitive stimulation. Patch-clamp analysis also revealed that cells expressing BFNIS mutants exhibited lower levels of sodium current compared to wild type (WT) NaV1.2. Biochemical experiments demonstrated that all three BFNIS mutations exhibited a significant reduction in cell surface expression compared to WT.
Discussion: Our findings indicate that BFNIS is associated with a range of biophysical defects accompanied by reduced levels of channel protein at the plasma membrane.