A homozygous GABRA2 variant associated with infantile spasms evolving to Lennox-Gastaut syndrome alters receptor gating.

Abstract

Variants in GABAA receptor subunits are increasingly implicated in developmental and epileptic encephalopathies. Although GABRA2 variants have been associated with early-onset epilepsy, the functional consequences of individual variants, particularly those located outside canonical ligand-binding and transmembrane pore-forming regions, remain incompletely understood. We identified a homozygous GABRA2p.A407K variant in a patient with infantile epileptic spasms syndrome (IESS) evolving to Lennox-Gastaut syndrome (LGS). Functional effects were assessed using two-electrode voltage clamp in Xenopus laevis oocytes and whole-cell patch clamp recordings in HEK293T cells expressing α2β3γ2 GABAA receptors. A Gabra2p.A407K/A407K knock-in mouse model was generated to examine neuronal membrane properties, provoked seizure responses, and behavioral phenotypes. The p.A407K variant did not impair receptor trafficking but slowed receptor desensitization. In hippocampal slices from adult knock-in mice, CA1 pyramidal neurons exhibited a more depolarized resting membrane potential and were positioned closer to action potential threshold, while action potential threshold itself was unchanged. In a limited adult EEG cohort of Gabra2p.A407K/A407K mice, no spontaneous seizures or overt epileptiform activity were detected. However, mutant mice showed prolonged seizure duration following 6 Hz corneal stimulation. Behavioral analyses revealed increased locomotor activity and altered exploratory behavior. These findings show that a rare homozygous GABRA2 intracellular loop variant alters α2-containing GABAA receptor gating and produces measurable neuronal, behavioral, and provoked seizure-response effects in a knock-in mouse model. The model does not reproduce the full human developmental epileptic encephalopathy phenotype but supports the conclusion that p.A407K is functionally consequential and provides a platform for studying variant-specific effects of GABRA2 dysfunction.