Exonic microdeletions of the gephyrin gene impair GABAergic synaptic inhibition in patients with idiopathic generalized epilepsy.

Gephyrin is a postsynaptic scaffolding protein, essential for the clustering of glycine and γ-aminobutyric acid type-A receptors (GABAARs) at inhibitory synapses. An impairment of GABAergic synaptic inhibition represents a key pathway of epileptogenesis. Recently, exonic microdeletions in the gephyrin (GPHN) gene have been associated with neurodevelopmental disorders including autism spectrum disorder, schizophrenia and epileptic seizures. Here we report the identification of novel exonic GPHN microdeletions in two patients with idiopathic generalized epilepsy (IGE), representing the most common group of genetically determined epilepsies. The identified GPHN microdeletions involve exons 5-9 (Δ5-9) and 2-3 (Δ2-3), both affecting the gephyrin G-domain. Molecular characterization of the GPHN Δ5-9 variant demonstrated that it perturbs the clustering of regular gephyrin at inhibitory synapses in cultured mouse hippocampal neurons in a dominant-negative manner, resulting in a significant loss of γ2-subunit containing GABAARs. GPHN Δ2-3 causes a frameshift resulting in a premature stop codon (p.V22Gfs*7) leading to haplo-insufficiency of the gene. Our results demonstrate that structural exonic microdeletions affecting the GPHN gene constitute a rare genetic risk factor for IGE and other neuropsychiatric disorders by an impairment of the GABAergic inhibitory synaptic transmission.

Dejanovic B ，Lal D ，Catarino CB ，Arjune S ，Belaidi AA ，Trucks H ，Vollmar C ，Surges R ，Kunz WS ，Motameny S ，Altmüller J ，Köhler A ，Neubauer BA ，Epicure Consortium ，Nürnberg P ，Noachtar S ，Schwarz G ，Sander T ... -  《-》

Rare exonic deletions implicate the synaptic organizer Gephyrin (GPHN) in risk for autism, schizophrenia and seizures.

Lionel AC ，Vaags AK ，Sato D ，Gazzellone MJ ，Mitchell EB ，Chen HY ，Costain G ，Walker S ，Egger G ，Thiruvahindrapuram B ，Merico D ，Prasad A ，Anagnostou E ，Fombonne E ，Zwaigenbaum L ，Roberts W ，Szatmari P ，Fernandez BA ，Georgieva L ，Brzustowicz LM ，Roetzer K ，Kaschnitz W ，Vincent JB ，Windpassinger C ，Marshall CR ，Trifiletti RR ，Kirmani S ，Kirov G ，Petek E ，Hodge JC ，Bassett AS ，Scherer SW ... -  《-》

Gephyrin: a central GABAergic synapse organizer.

Choii G ，Ko J 《-》

Biallelic gephyrin variants lead to impaired GABAergic inhibition in a patient with developmental and epileptic encephalopathy.

Synaptic inhibition is essential for shaping the dynamics of neuronal networks, and aberrant inhibition is linked to epilepsy. Gephyrin (Geph) is the principal scaffolding protein at inhibitory synapses and is essential for postsynaptic clustering of glycine (GlyRs) and GABA type A receptors. Consequently, gephyrin is crucial for maintaining the relationship between excitation and inhibition in normal brain function and mutations in the gephyrin gene (GPHN) are associated with neurodevelopmental disorders and epilepsy. We identified bi-allelic variants in the GPHN gene, namely the missense mutation c.1264G > A and splice acceptor variant c.1315-2A > G, in a patient with developmental and epileptic encephalopathy. We demonstrate that the splice acceptor variant leads to nonsense-mediated mRNA decay. Furthermore, the missense variant (D422N) alters gephyrin structure, as examined by analytical size exclusion chromatography and circular dichroism-spectroscopy, thus leading to reduced receptor clustering and sensitivity towards calpain-mediated cleavage. In addition, both alterations contribute to an observed reduction of inhibitory signal transmission in neurons, which likely contributes to the pathological encephalopathy.

Macha A ，Liebsch F ，Fricke S ，Hetsch F ，Neuser F ，Johannes L ，Kress V ，Djémié T ，Santamaria-Araujo JA ，Vilain C ，Aeby A ，Van Bogaert P ，Dejanovic B ，Weckhuysen S ，Meier JC ，Schwarz G ... -  《-》

Isoform heterogeneity of the human gephyrin gene (GPHN), binding domains to the glycine receptor, and mutation analysis in hyperekplexia.

Rees MI ，Harvey K ，Ward H ，White JH ，Evans L ，Duguid IC ，Hsu CC ，Coleman SL ，Miller J ，Baer K ，Waldvogel HJ ，Gibbon F ，Smart TG ，Owen MJ ，Harvey RJ ，Snell RG ... -  《-》