Molecular analysis of the A322D mutation in the GABAA receptor α1-subunit causing juvenile myoclonic epilepsy

Authors

  • Klaus Krampfl,

    1. Neurologische Klinik, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
    2. Center for Systems Neuroscience (ZSN), Hannover, Germany
    Search for more papers by this author
  • Snezana Maljevic,

    1. Neurologische Klinik und Abteilung für Angewandte Physiologie, Universität Ulm, Ulm, Germany
    Search for more papers by this author
  • Patrick Cossette,

    1. Service de Neurologie et Centre de Recherche, Centre Hospitalier de l'Université de Montréal – Hôpital Notre-Dame, Montréal, PQ, Canada
    Search for more papers by this author
  • Elke Ziegler,

    1. Neurologische Klinik, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
    2. Center for Systems Neuroscience (ZSN), Hannover, Germany
    Search for more papers by this author
  • Guy A. Rouleau,

    1. Service de Neurologie et Centre de Recherche, Centre Hospitalier de l'Université de Montréal – Hôpital Notre-Dame, Montréal, PQ, Canada
    Search for more papers by this author
  • Holger Lerche,

    1. Neurologische Klinik und Abteilung für Angewandte Physiologie, Universität Ulm, Ulm, Germany
    Search for more papers by this author
  • Johannes Bufler

    1. Neurologische Klinik, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
    2. Center for Systems Neuroscience (ZSN), Hannover, Germany
    Search for more papers by this author

Dr Klaus Krampfl, 1Neurologische Klinik, or Dr Holger Lerche, 3Neurologische Klinik, as above.
E-mail: krampfl.klaus@mh-hannover.de or holger.lerche@medizin.uni-ulm.de

Abstract

Juvenile myoclonic epilepsy (JME) belongs to the most common forms of hereditary epilepsy, the idiopathic generalized epilepsies. Although the mode of inheritance is usually complex, mutations in single genes have been shown to cause the disease in some families with autosomal dominant inheritance. The first mutation in a multigeneration JME family has been recently found in the α1-subunit of the GABAA receptor (GABRA1), predicting the single amino acid substitution A322D. We further characterized the functional consequences of this mutation by coexpressing α1-, β2- and γ2-subunits in human embryonic kidney (HEK293) cells. By using an ultrafast application system, mutant receptors have shown reduced macroscopic current amplitudes at saturating GABA concentrations and a highly reduced affinity to GABA compared to the wild-type (WT). Dose–response curves for current amplitudes, activation kinetics, and GABA-dependent desensitization parameters showed a parallel shift towards 30- to 40-fold higher GABA concentrations. Both deactivation and resensitization kinetics were considerably accelerated in mutant channels. In addition, mutant receptors labelled with enhanced green fluorescent protein (EGFP) were not integrated in the cell membrane, in contrast to WT receptors. Therefore, the A322D mutation leads to a severe loss-of-function of the human GABAA receptor by several mechanisms, including reduced surface expression, reduced GABA-sensitivity, and accelerated deactivation. These molecular defects could decrease and shorten the resulting inhibitory postsynaptic currents (IPSCs) in vivo, which can induce a hyperexcitability of the postsynaptic membrane and explain the occurrence of epileptic seizures.

Ancillary