GRIN2D Recurrent De Novo Dominant Mutation Causes a Severe Epileptic Encephalopathy Treatable with NMDA Receptor Channel Blockers

Am J Hum Genet. 2016 Oct 6;99(4):802-816. doi: 10.1016/j.ajhg.2016.07.013.

Dong Li ¹, Hongjie Yuan ², Xilma R Ortiz-Gonzalez ³, Eric D Marsh ³, Lifeng Tian ¹, Elizabeth M McCormick ⁴, Gabrielle J Kosobucki ⁵, Wenjuan Chen ², Anthony J Schulien ⁵, Rosetta Chiavacci ¹, Anel Tankovic ², Claudia Naase ⁶, Frieder Brueckner ⁷, Celina von Stülpnagel-Steinbeis ⁸, Chun Hu ², Hirofumi Kusumoto ², Ulrike B S Hedrich ⁹, Gina Elsen ⁹, Konstanze Hörtnagel ¹⁰, Elias Aizenman ⁵, Johannes R Lemke ¹¹, Hakon Hakonarson ¹², Stephen F Traynelis ², Marni J Falk ¹³

Affiliations

1 Center for Applied Genomics, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
2 Department of Pharmacology and Center for Functional Evaluation of Rare Variant (CFERV), Emory University School of Medicine, Rollins Research Center, Atlanta, GA 30322, USA.
3 Division of Neurology, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA; University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA.
4 Center for Applied Genomics, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA; Division of Human Genetics, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
5 Department of Neurobiology, Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
6 Children's Hospital Bayreuth, 95445 Bayreuth, Germany.
7 Institute for Neuropediatrics and Social Pediatrics Hamburg East, 22111 Hamburg, Germany.
8 Hospital for Neuropediatrics and Neurological Rehabilitation, Epilepsy Center for Children and Adolescents, 83569 Vogtareuth, Germany; Institute for Transition, Rehabilitation and Palliation in Children and Adolescents, Paracelsus Medical University Salzburg, 5020 Salzburg, Austria.
9 Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, 72076 Tübingen, Germany.
10 CeGaT GmbH, 72076 Tübingen, Germany.
11 Institute of Human Genetics, University of Leipzig Hospitals and Clinics, 04103 Leipzig, Germany.
12 Center for Applied Genomics, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA; University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Division of Human Genetics, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
13 University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Division of Human Genetics, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA. Electronic address: falkm@email.chop.edu.

PMID: 27616483 DOI: 10.1016/j.ajhg.2016.07.013

Abstract

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated cation channels that mediate excitatory synaptic transmission. Genetic mutations in multiple NMDAR subunits cause various childhood epilepsy syndromes. Here, we report a de novo recurrent heterozygous missense mutation-c.1999G>A (p.Val667Ile)-in a NMDAR gene previously unrecognized to harbor disease-causing mutations, GRIN2D, identified by exome and candidate panel Sequencing in two unrelated children with epileptic encephalopathy. The resulting GluN2D p.Val667Ile exchange occurs in the M3 transmembrane domain involved in channel gating. This gain-of-function mutation increases glutamate and glycine potency by 2-fold, increases channel open probability by 6-fold, and reduces receptor sensitivity to endogenous negative modulators such as extracellular protons. Moreover, this mutation prolongs the deactivation time course after glutamate removal, which controls the synaptic time course. Transfection of cultured neurons with human GRIN2D cDNA harboring c.1999G>A leads to dendritic swelling and neuronal cell death, suggestive of excitotoxicity mediated by NMDAR over-activation. Because both individuals' seizures had proven refractory to conventional antiepileptic medications, the sensitivity of mutant NMDARs to FDA-approved NMDAR antagonists was evaluated. Based on these results, oral memantine was administered to both children, with resulting mild to moderate improvement in seizure burden and development. The older proband subsequently developed refractory status epilepticus, with dramatic electroclinical improvement upon treatment with ketamine and magnesium. Overall, these results suggest that NMDAR antagonists can be useful as Adjuvant epilepsy therapy in individuals with GRIN2D gain-of-function mutations. This work further demonstrates the value of functionally evaluating a mutation, enabling mechanistic understanding and therapeutic modeling to realize precision medicine for epilepsy.

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