Mice harboring the T316N variant in the GABAAR γ2 subunit exhibit sleep-related hypermotor epilepsy phenotypes and hypersynchronization in the thalamocortical pathway.

Sleep-related hypermotor epilepsy (SHE) is a focal epilepsy syndrome characterized by seizures that predominantly occur during sleep. The pathogenesis of these seizures remains unclear. We previously detected rare variants in GABRG2 , which encodes the γ 2 subunit of γ-aminobutyric acid type A receptor (GABA A R), in patients with SHE and demonstrated that these variants impaired GABA A R function in vitro. However, the mechanisms by which GABRG2 variants contribute to seizure attacks during sleep remain unclear. In this study, we designed a knock-in (KI) mouse expressing the mouse Gabrg2 T316N variant, corresponding to human GABRG2 T317N variant, using CRISPR/Cas9. Continuous video-electroencephalogram monitoring and in vivo multichannel electrophysiological recordings were performed to explore seizure susceptibility to pentylenetetrazol (PTZ), alterations in the sleep-wake cycle, spontaneous seizure patterns, and synchronized activity in the motor thalamic nuclei (MoTN) and secondary motor cortex (M2). Circadian variations in the expression of total, membrane-bound, and synaptic GABA A R subunits were also investigated. No obvious changes in gross morphology were detected in Gabrg2 T316N/+ mice compared to their wild-type (Gabrg2 +/+ ) littermates. Gabrg2 T316N/+ mice share key phenotypes with patients, including sleep fragmentation and spontaneous seizures during sleep. Gabrg2 T316N/+ mice showed increased susceptibility to PTZ-induced seizures and higher mortality after seizures. Synchronization of the local field potentials between the MoTN and M2 was abnormally enhanced in Gabrg2 T316N/+ mice during light phase, when sleep dominates, accompanied by increased local activities in the MoTN and M2. Interestingly, in Gabrg2 +/+ mice, GABA A R γ2 subunits showed a circadian increase on the neuronal membrane and synaptosomes in the transition from dark phase to light phase, which was absent in Gabrg2 T316N/+ mice. We generated a new SHE mouse model and provided in vivo evidence that rare variants of GABRG2 contribute to seizure attacks during sleep in SHE. • Mice harboring the T316N variant in GABA A R γ 2 subunit are originally constructed. • Gabrg2 T316N/+ knock-in mice have spontaneous seizures mainly occurring during daytime. • NREM sleep is fragmented by brief awakening events in Gabrg2 T316N/+ knock-in mice. • Gabrg2 T316N/+ knock-in mice have enhanced synchronization between MoTN and M2. • Circadian change in membrane γ 2 subunit is absent in Gabrg2 T316N/+ knock-in mice. [ABSTRACT FROM AUTHOR]