@article {984,
	title = {Gain-of-function  variants identified in vigabatrin-hypersensitive epileptic encephalopathies.},
	journal = {Brain Commun},
	volume = {2},
	year = {2020},
	month = {2020},
	pages = {fcaa162},
	abstract = {<p>Variants in the  gene encoding the β3-subunit of the γ-aminobutyric acid type A ( receptor are associated with various developmental and epileptic encephalopathies. Typically, these variants cause a loss-of-function molecular phenotype whereby γ-aminobutyric acid has reduced inhibitory effectiveness leading to seizures. Drugs that potentiate inhibitory GABAergic activity, such as nitrazepam, phenobarbital or vigabatrin, are expected to compensate for this and thereby reduce seizure frequency. However, vigabatrin, a drug that inhibits γ-aminobutyric acid transaminase to increase tonic γ-aminobutyric acid currents, has mixed success in treating seizures in patients with  variants: some patients experience seizure cessation, but there is hypersensitivity in some patients associated with hypotonia, sedation and respiratory suppression. A  variant that responds well to vigabatrin involves a truncation variant (p.Arg194*) resulting in a clear loss-of-function. We hypothesized that patients with a hypersensitive response to vigabatrin may exhibit a different γ-aminobutyric acid A receptor phenotype. To test this hypothesis, we evaluated the phenotype of  variants in  (p.Glu77Lys and p.Thr287Ile) associated with patients who are clinically hypersensitive to vigabatrin. We introduced the  p.Glu77Lys and p.Thr287Ile variants into a concatenated synaptic and extrasynaptic γ-aminobutyric acid A receptor construct, to resemble the γ-aminobutyric acid A receptor expression by a patient heterozygous for the  variant. The mRNA of these constructs was injected into  oocytes and activation properties of each receptor measured by two-electrode voltage clamp electrophysiology. Results showed an atypical gain-of-function molecular phenotype in the  p.Glu77Lys and p.Thr287Ile variants characterized by increased potency of γ-aminobutyric acid A without change to the estimated maximum open channel probability, deactivation kinetics or absolute currents. Modelling of the activation properties of the receptors indicated that either variant caused increased chloride flux in response to low concentrations of γ-aminobutyric acid that mediate tonic currents. We therefore propose that the hypersensitivity reaction to vigabatrin is a result of  variants that exacerbate GABAergic tonic currents and caution is required when prescribing vigabatrin. In contrast, drug strategies increasing tonic currents in loss-of-function variants are likely to be a safe and effective therapy. This study demonstrates that functional genomics can explain beneficial and adverse anti-epileptic drug effects, and propose that vigabatrin should be considered in patients with clear loss-of-function  variants.</p>},
	issn = {2632-1297},
	doi = {10.1093/braincomms/fcaa162},
	author = {Absalom, Nathan L and Liao, Vivian W Y and Kothur, Kavitha and Indurthi, Dinesh C and Bennetts, Bruce and Troedson, Christopher and Mohammad, Shekeeb S and Gupta, Sachin and McGregor, Iain S and Bowen, Michael T and Lederer, Damien and Mary, Sandrine and De Waele, Liesbeth and Jansen, Katrien and Gill, Deepak and Kurian, Manju A and McTague, Amy and M{\o}ller, Rikke S and Ahring, Philip K and Dale, Russell C and Chebib, Mary}
}
