Impaired NaV1.2 function and reduced cell surface expression in benign familial neonatal-infantile seizures

Purpose: Mutations in SCN2A, the gene encoding the brain voltage‐gated sodium channel α‐subunit Na _V 1.2, 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 Na _V 1.2. Membrane biotinylation was employed to examine the cell surface protein expression of the four Na _V 1.2 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) Na _V 1.2. 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.