title: Epileptic encephalopathy de novo GABRB mutations impair γ-aminobutyric acid type A receptor function.
abstract: OBJECTIVE
  The Epi4K Consortium recently identified 4 de novo mutations in the γ-aminobutyric acid type A (GABAA) receptor β3 subunit gene GABRB3 and 1 in the β1 subunit gene GABRB1 in children with one of the epileptic encephalopathies (EEs) Lennox-Gastaut syndrome (LGS) and infantile spasms (IS). Because the etiology of EEs is often unknown, we determined the impact of GABRB mutations on GABAAreceptor function and biogenesis.
  
  
  METHODS
  GABAAreceptor α1 and γ2L subunits were coexpressed with wild-type and/or mutant β3 or β1 subunits in HEK 293T cells. Currents were measured using whole cell and single channel patch clamp techniques. Surface and total expression levels were measured using flow cytometry. Potential structural perturbations in mutant GABAAreceptors were explored using structural modeling.
  
  
  RESULTS
  LGS-associated GABRB3(D120N, E180G, Y302C) mutations located at β+subunit interfaces reduced whole cell currents by decreasing single channel open probability without loss of surface receptors. In contrast, IS-associated GABRB3(N110D) and GABRB1(F246S) mutations at β-subunit interfaces produced minor changes in whole cell current peak amplitude but altered current deactivation by decreasing or increasing single channel burst duration, respectively. GABRB3(E180G) and GABRB1(F246S) mutations also produced spontaneous channel openings.
  
  
  CONCLUSIONS
  All 5 de novo GABRB mutations impaired GABAAreceptor function by rearranging conserved structural domains, supporting their role in EEs. The primary effect of LGS-associated mutations was reduced GABA-evoked peak current amplitudes, whereas the major impact of IS-associated mutations was on current kinetic properties. Despite lack of association with epilepsy syndromes, our results suggest GABRB1 as a candidate human epilepsy gene. Ann Neurol 2016;79:806-825.
authors.affiliation: Graduate Program of Neuroscience, Vanderbilt University, Nashville, TN.
authors.forename: Vaishali S
authors.initials: VS
authors.lastname: Janve
authors.affiliation: Department of Neurology, Vanderbilt University, Nashville, TN.
authors.forename: Ciria C
authors.initials: CC
authors.lastname: Hernandez
authors.affiliation: Department of Neurology, Vanderbilt University, Nashville, TN.
authors.forename: Kelienne M
authors.initials: KM
authors.lastname: Verdier
authors.affiliation: Department of Neurology, Vanderbilt University, Nashville, TN.
authors.forename: Ningning
authors.initials: N
authors.lastname: Hu
authors.affiliation: Department of Neurology, Vanderbilt University, Nashville, TN.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Macdonald