Pathogenic SCN2A variants cause early-stage dysfunction in patient-derived neurons.

Area of Science:

• Neuroscience
• Genetics
• Cell Biology

Background:

• Pathogenic SCN2A variants, encoding the NaV1.2 sodium channel, are linked to epilepsy and intellectual disability (ID)/autism.
• Gain-of-function variants typically cause epilepsy, while loss-of-function variants are associated with ID/autism.
• The translation of altered NaV1.2 biophysics into patient-derived neurons remains largely unknown.

Purpose of the Study:

• To investigate the cellular and molecular consequences of pathogenic SCN2A variants in patient-derived neurons.
• To compare NaV1.2 channel function and molecular pathways in neurons from patients with ID versus epileptic encephalopathy (EE).

Main Methods:

• Utilized induced pluripotent stem cell (iPSC)-derived early-stage cortical neurons from ID and EE patients with distinct SCN2A variants.
• Performed electrophysiological analyses to assess sodium current density and action potential firing.
• Employed single-cell transcriptomics to identify dysregulated molecular pathways.

Main Results:

• ID neurons consistently showed reduced NaV1.2 protein levels, with some exhibiting reduced mRNA, suggesting haploinsufficiency or instability.
• Electrophysiology revealed decreased sodium current density and impaired action potential firing in ID neurons.
• EE neurons displayed normal NaV1.2 levels and current density but impaired sodium channel inactivation; transcriptomics showed distinct pathway dysregulation in both ID and EE neurons.

Conclusions:

• Patient iPSC-derived neurons recapitulate SCN2A variant-specific channel dysfunction, linking reduced NaV1.2 levels to ID and impaired firing.
• Epilepsy-associated variants impair sodium channel inactivation, distinct from the mechanisms in ID.
• Identified dysregulated molecular pathways (e.g., oxidative phosphorylation, calcium signaling) that may represent homeostatic responses to NaV1.2 dysfunction.