frameshift variants impair GABAA receptor proteostasis.

The gamma-aminobutyric acid type A receptor (GABA R) is the most common inhibitory neurotransmitter-gated ion channel in the central nervous system. Pathogenic variants in genes encoding GABA R subunits can cause receptor dysfunction and lead to genetic epilepsy. Frameshift variants in these genes can result in a premature termination codon, producing truncated receptor subunit variants.

Modulating Endoplasmic Reticulum Chaperones and Mutant Protein Degradation in GABRG2(Q390X) Associated with Genetic Epilepsy with Febrile Seizures Plus and Dravet Syndrome.

A significant number of patients with genetic epilepsy do not obtain seizure freedom, despite developments in new antiseizure drugs, suggesting a need for novel therapeutic approaches. Many genetic epilepsies are associated with misfolded mutant proteins, including -associated Dravet syndrome, which we have previously shown to result in intracellular accumulation of mutant GABA receptor γ2(Q390X) subunit protein. Thus, a potentially promising therapeutic approach is modulation of proteostasis, such as increasing endoplasmic reticulum (ER)-associated degradation (ERAD).

γ-Aminobutyric acid transporter and GABA receptor mechanisms in and mice associated with developmental and epileptic encephalopathies.

We have previously characterized the molecular mechanisms for variants in γ-aminobutyric acid transporter 1-encoding solute carrier family 6-member 1 () and concluded that a partial or complete loss of γ-aminobutyric acid uptake due to impaired protein trafficking is the primary aetiology. Impairment of γ-aminobutyric acid transporter 1 function could cause compensatory changes in the expression of γ-aminobutyric acid receptors, which, in turn, modify disease pathophysiology and phenotype. Here we used different approaches including radioactive H γ-aminobutyric acid uptake in cells and synaptosomes, immunohistochemistry and confocal microscopy as well as brain slice surface protein biotinylation to characterize and mice, representative of a partial or a complete loss of function of mutations, respectively.

4-Phenylbutyrate promoted wild-type γ-aminobutyric acid type A receptor trafficking, reduced endoplasmic reticulum stress, and mitigated seizures in Gabrg2 mice associated with Dravet syndrome.

Objective: γ-Aminobutyric acid type A (GABA ) receptor subunit gene mutations are major causes of various epilepsy syndromes, including severe kinds such as Dravet syndrome. Although the GABA receptor is a major target for antiseizure medications, treating GABA receptor mutations with receptor channel modulators is ineffective. Here, we determined the effect of a novel treatment with 4-phenylbutyrate (PBA) in Gabrg2 knockin mice associated with Dravet syndrome.

Epilepsy plus blindness in microdeletion of GABRA1 and GABRG2 in mouse and human.

Objective: GABA receptor subunit gene (GABR) mutations are significant causes of epilepsy, including syndromic epilepsy. This report for the first time, describes intractable epilepsy and blindness due to optic atrophy in our patient, who has a microdeletion of the GABRA1 and GABRG2 genes. We then characterized the molecular phenotypes and determined patho-mechanisms underlying the genotype-phenotype correlations in a mouse model who is haploinsufficient for both genes (Gabra1/Gabrg2 mouse).

SLC6A1 variant pathogenicity, molecular function and phenotype: a genetic and clinical analysis.

Genetic variants in the SLC6A1 gene can cause a broad phenotypic disease spectrum by altering the protein function. Thus, systematically curated clinically relevant genotype-phenotype associations are needed to understand the disease mechanism and improve therapeutic decision-making. We aggregated genetic and clinical data from 172 individuals with likely pathogenic/pathogenic (lp/p) SLC6A1 variants and functional data for 184 variants (14.

GABA Receptor β3 Subunit Mutation N328D Heterozygous Knock-in Mice Have Lennox-Gastaut Syndrome.

Lennox-Gastaut Syndrome (LGS) is a developmental and epileptic encephalopathy (DEE) characterized by multiple seizure types, electroencephalogram (EEG) patterns, and cognitive decline. Its etiology has a prominent genetic component, including variants in that encodes the GABA receptor (GABAR) β subunit. LGS has an unknown pathophysiology, and few animal models are available for studying LGS.

Heterozygous GABA receptor β3 subunit N110D knock-in mice have epileptic spasms.

Objective: Infantile spasms is an epileptic encephalopathy of childhood, and its pathophysiology is largely unknown. We generated a heterozygous knock-in mouse with the human infantile spasms-associated de novo mutation GABRB3 (c.A328G, p.

Variable Expression of GABAA Receptor Subunit Gamma 2 Mutation in a Nuclear Family Displaying Developmental and Encephalopathic Phenotype.

Mutations in GABA receptor subunit genes () are a major etiology for developmental and epileptic encephalopathies (DEEs). This article reports a case of a genetic abnormality in and updates the pathophysiology and treatment development for mutations in DEEs based on recent advances. Mutations in , especially in , , , and , impair GABAergic signaling and are frequently associated with DEEs such as Dravet syndrome and Lennox-Gastaut syndrome, as GABAergic signaling is critical for early brain development.

Astrocytic GABA transporter 1 deficit in novel SLC6A1 variants mediated epilepsy: Connected from protein destabilization to seizures in mice and humans.

Objective: Mutations in γ-aminobutyric acid (GABA) transporter 1 (GAT-1)-encoding SLC6A1 have been associated with myoclonic atonic epilepsy and other phenotypes. We determined the patho-mechanisms of the mutant GAT-1, in order to identify treatment targets.

Methods: We conducted whole-exome sequencing of patients with myoclonic atonic epilepsy (MAE) and characterized the seizure phenotypes and EEG patterns.

Disruption of the Ubiquitin-Proteasome System and Elevated Endoplasmic Reticulum Stress in Epilepsy.

The epilepsies are a broad group of conditions characterized by repeated seizures, and together are one of the most common neurological disorders. Additionally, epilepsy is comorbid with many neurological disorders, including lysosomal storage diseases, syndromic intellectual disability, and autism spectrum disorder. Despite the prevalence, treatments are still unsatisfactory: approximately 30% of epileptic patients do not adequately respond to existing therapeutics, which primarily target ion channels.

Epileptic Mechanisms Shared by Alzheimer's Disease: Viewed via the Unique Lens of Genetic Epilepsy.

Our recent work on genetic epilepsy (GE) has identified common mechanisms between GE and neurodegenerative diseases including Alzheimer's disease (AD). Although both disorders are seemingly unrelated and occur at opposite ends of the age spectrum, it is likely there are shared mechanisms and studies on GE could provide unique insights into AD pathogenesis. Neurodegenerative diseases are typically late-onset disorders, but the underlying pathology may have already occurred long before the clinical symptoms emerge.

Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons.

Solute carrier family 6 member 1 (SLC6A1) is abundantly expressed in the developing brain even before the CNS is formed. Its encoded GABA transporter 1 (GAT-1) is responsible for the reuptake of GABA into presynaptic neurons and glia, thereby modulating neurotransmission. GAT-1 is expressed globally in the brain, in both astrocytes and neurons.

Genetic mosaicism, intrafamilial phenotypic heterogeneity, and molecular defects of a novel missense SLC6A1 mutation associated with epilepsy and ADHD.

Background: Mutations in SLC6A1, encoding γ-aminobutyric acid (GABA) transporter 1 (GAT-1), have been recently associated with a spectrum of neurodevelopmental disorders ranging from variable epilepsy syndromes, intellectual disability (ID), autism and others. To date, most identified mutations are de novo. We here report a pedigree of two siblings associated with myoclonic astatic epilepsy, attention deficit hyperactivity disorder (ADHD), and ID.

Current knowledge of SLC6A1-related neurodevelopmental disorders.

Advances in gene discovery have identified genetic variants in the solute carrier family 6 member 1 gene as a monogenic cause of neurodevelopmental disorders, including epilepsy with myoclonic atonic seizures, autism spectrum disorder and intellectual disability. The solute carrier family 6 member 1 gene encodes for the GABA transporter protein type 1, which is responsible for the reuptake of the neurotransmitter GABA, the primary inhibitory neurotransmitter in the central nervous system, from the extracellular space. GABAergic inhibition is essential to counterbalance neuronal excitation, and when significantly disrupted, it negatively impacts brain development leading to developmental differences and seizures.

Endoplasmic reticulum stress increases inflammatory cytokines in an epilepsy mouse model Gabrg2 knockin: A link between genetic and acquired epilepsy?

Objective: Neuroinflammation is a major theme in epilepsy, which has been characterized in acquired epilepsy but is poorly understood in genetic epilepsy. γ-Aminobutyric acid type A receptor subunit gene mutations are significant causes of epilepsy, and we have studied the pathophysiology directly resulting from defective receptor channels. Here, we determined the proinflammatory factors in a genetic mouse model, the Gabrg2 knockin (KI).

Endoplasmic reticulum retention and degradation of a mutation in SLC6A1 associated with epilepsy and autism.

Mutations in SLC6A1, encoding γ-aminobutyric acid (GABA) transporter 1 (GAT-1), have been recently associated with a spectrum of epilepsy syndromes, intellectual disability and autism in clinic. However, the pathophysiology of the gene mutations is far from clear. Here we report a novel SLC6A1 missense mutation in a patient with epilepsy and autism spectrum disorder and characterized the molecular defects of the mutant GAT-1, from transporter protein trafficking to GABA uptake function in heterologous cells and neurons.

Distinct roles of and variants in neurological conditions.

Rapid advances in sequencing technology have led to an explosive increase in the number of genetic variants identified in patients with neurological disease and have also enabled the assembly of a robust database of variants in healthy individuals. A surprising number of variants in the genes that encode -methyl-D-aspartate (NMDA) glutamatergic receptor subunits have been found in patients with various neuropsychiatric disorders, including autism spectrum disorders, epilepsy, intellectual disability, attention-deficit/hyperactivity disorder, and schizophrenia. This review compares and contrasts the available information describing the clinical and functional consequences of genetic variations in and Comparison of clinical phenotypes shows that variants are commonly associated with an epileptic phenotype but that variants are commonly found in patients with neurodevelopmental disorders.

Synaptic clustering differences due to different GABRB3 mutations cause variable epilepsy syndromes.

GABRB3 is highly expressed early in the developing brain, and its encoded β3 subunit is critical for GABAA receptor assembly and trafficking as well as stem cell differentiation in embryonic brain. To date, over 400 mutations or variants have been identified in GABRB3. Mutations in GABRB3 have been increasingly recognized as a major cause for severe paediatric epilepsy syndromes such as Lennox-Gastaut syndrome, Dravet syndrome and infantile spasms with intellectual disability as well as relatively mild epilepsy syndromes such as childhood absence epilepsy.

A missense mutation in SLC6A1 associated with Lennox-Gastaut syndrome impairs GABA transporter 1 protein trafficking and function.

Background: Mutations in SLC6A1 have been associated mainly with myoclonic atonic epilepsy (MAE) and intellectual disability. We identified a novel missense mutation in a patient with Lennox-Gastaut syndrome (LGS) characterized by severe seizures and developmental delay.

Methods: Exome Sequencing was performed in an epilepsy patient cohort.

Molecular basis for and chemogenetic modulation of comorbidities in GABRG2-deficient epilepsies.

Objective: γ-Aminobutyric acid type A (GABA ) receptor subunit gene mutations are significant causes of epilepsy, which are often accompanied by various neuropsychiatric comorbidities, but the underlying mechanisms are unclear. It has been suggested that the comorbidities are caused by seizures, as the comorbidities often present in severe epilepsy syndromes. However, findings from both humans and animal models argue against this conclusion.