NON-SYNDROMIC AUTISM–ASSOCIATED <EM>SCN2A</EM> VARIANTS SELECTIVELY EXERT DOMINANT-NEGATIVE EFFECTS ON NA<SUB>V</SUB>1.2 SODIUM CHANNELS

Pathogenic variants of the SCN2A gene, coding for the Na_V1.2 voltage gated sodium channel alpha subunit, can cause a wide phenotypic spectrum, including different types of developmental epileptic encephalopathies (DEEs) and of neurodevelopmental disorders without epilepsy. Functional studies have shown that variants implicated in infantile-childhood onset DEEs or neurodevelopmental disorders cause loss of function (LoF), but genotype-phenotype relationships within these variants are not clear yet.
We have investigated functional effects of 14 of these variants (7 of them not published yet) associated with non-syndromic autism spectrum disorder (ASD), ASD with epileptiform activity, DEEs or schizophrenia. We transfected cell lines and neurons in primary culture, either expressing the mutant in isolation or co-expressing mutant and wild-type Na_V1.2, to reproduce the conditions of heterozygosis.
Only non-syndromic ASD‑associated variants produced a complete loss of Na_V1.2 function in both cell lines and cultured neocortical neurons, which was observed for most of these ASD mutants, accompanied by abolition of plasma‑membrane targeting quantified by radioligand binding. When co‑expressed with wild‑type Na_V1.2, ASD variants exerted a dominant‑negative effect that strongly diminished wild‑type channel activity and surface expression. Perturbing domains previously implicated in α‑subunit interactions eliminated the dominant‑negative effect, consistent with a mechanism involving α‑subunit dimerization.
These findings identify a mechanistically distinct class of SCN2A variants defined by dominant‑negative loss of Na_V1.2 function, with potential utility as an in vitro biomarker for genetic counseling, patient stratification, and the development of precision therapeutic strategies.