The GABRG2 Mutation, Q351X, Associated with Generalized Epilepsy with Febrile Seizures Plus, Has Both Loss of Function and Dominant-Negative Suppression

Abstract

The GABA A receptor ␥2 subunit mutation, Q351X, associated with generalized epilepsy with febrile seizures plus (GEFSϩ), created a loss of function with homozygous expression. However, heterozygous ␥2(ϩ/Ϫ) gene deletion mice are seizure free, suggesting that the loss of one GABRG2 allele alone in heterozygous patients may not be sufficient to produce epilepsy. Here we show that the mutant ␥2 subunit was immature and retained in the endoplasmic reticulum (ER). With heterozygous coexpression of ␥2S/␥2S(Q351X) subunits and ␣1 and ␤2 subunits, the trafficking deficient mutant ␥2 subunit reduced trafficking of wild-type partnering subunits, which was not seen in the hemizygous gene deletion control. Consequently, the function of the heterozygous receptor channel was reduced to less than the hemizygous control and to less than half of the wild-type receptors with a full gene dose. Pulse-chase experiments demonstrated that in the presence of the mutant ␥2S(Q351X) subunit, wild-type ␣1 subunits degraded more substantially within 1 h of translation. We showed that the basis for this dominant-negative effect on wild-type receptors was due to an interaction between mutant and wild-type subunits. The mutant subunit oligomerized with wild-type subunits and trapped them in the ER, subjecting them to glycosylation arrest and ER-associated degradation (ERAD) through the ubiquitin proteosome system. Thus, we hypothesize that a likely explanation for the GEFSϩ phenotype is a dominant-negative suppression of wild-type receptors by the mutant ␥2S subunit in combination with loss of mutant ␥2S subunit protein function.

The Importance of TM3-4 Loop Subdomains for Functional Reconstitution of Glycine Receptors by Independent Domains

“…A similar hyperekplexia-like phenotype was observed in the GlyR mouse mutant oscillator, resulting from lack of GlyR expression due to introduction of a premature stop codon at amino acid position 355 (21). Loss of receptor proteins has also been found in other channelopathies, such as GEFSϩ (generalized epilepsy with febrile seizures plus) associated with truncated GABA A receptor variants (27).…”

Microglia activation triggers astrocyte-mediated modulation of excitatory neurotransmission

“…For instance, injection of LPS into cortex produces focal epileptiform discharges within 5 min after stimulation (79). Fever, a symptom of inflammation, is known to promote febrile seizures in infants or mice with appropriate genetic backgrounds (80). Our work now provides the basis to understand the molecular and cellular cascades by which inflammation triggers seizures.…”

Association of Gamma-Aminobutyric Acid A Receptor α2 Gene (GABRA2) with Alcohol Use Disorder

“…The GABRG2 gene, covering 87 897 bp, is at 5q31.1-q33.1 and two SNPs that we will consider, rs211014 and rs211013, map to intron 8. This gene has also been associated with epilepsy and febrile seizures (Kang et al, 2009). Linkage and association studies have reported, for example, that the 5q34 GABA A receptor genes were involved in AD risk in Finns (Radel et al, 2005), and the 5q33 GABA A receptor genes were associated with HD in Chinese subjects (Loh et al, 2007).…”