Association of nonsense mutation in GABRG2 with abnormal trafficking of GABAA receptors in severe epilepsy.
Mutations in GABRG2, which encodes the γ2 subunit of GABAA receptors, can cause both genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome. Most GABRG2 truncating mutations associated with Dravet syndrome result in premature termination codons (PTCs) and are stably translated into mutant proteins with potential dominant-negative effects. This study involved search for mutations in candidate genes for Dravet syndrome, namely SCN1A, 2A, 1B, 2B, GABRA1, B2, and G2. A heterozygous nonsense mutation (c.118C>T, p.Q40X) in GABRG2 was identified in dizygotic twin girls with Dravet syndrome and their apparently healthy father. Electrophysiological studies with the reconstituted GABAA receptors in HEK cells showed reduced GABA-induced currents when mutated γ2 DNA was cotransfected with wild-type α1 and β2 subunits. In this case, immunohistochemistry using antibodies to the α1 and γ2 subunits of GABAA receptor showed granular staining in the soma. In addition, microinjection of mutated γ2 subunit cDNA into HEK cells severely inhibited intracellular trafficking of GABAA receptor subunits α1 and β2, and retention of these proteins in the endoplasmic reticulum. The mutated γ2 subunit-expressing neurons also showed impaired axonal transport of the α1 and β2 subunits. Our findings suggested that different phenotypes of epilepsy, e.g., GEFS+ and Dravet syndrome (which share similar abnormalities in causative genes) are likely due to impaired axonal transport associated with the dominant-negative effects of GABRG2.
Department of Pediatrics, Fukuoka University, Fukuoka, Japan; Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka, Japan.
Atsushi
A
Ishii
Department of Pediatrics, Fukuoka University, Fukuoka, Japan; Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka, Japan.
Takeshi
T
Kanaumi
Division of Oral Biochemistry, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
Miwa
M
Sohda
Department of Cell Biology, Fukuoka University, Fukuoka, Japan.
Yoshio
Y
Misumi
Department of Biochemistry, Fukuoka University, Fukuoka, Japan.
Bo
B
Zhang
Department of Anatomy and Cell Biology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Japan.
Naoto
N
Kakinuma
Department of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Yoshiko
Y
Haga
Faculty of Health and Medical Sciences, Aichi Shukutoku University, Nagakute, Japan.
Kazuyoshi
K
Watanabe
Department of Anatomy and Cell Biology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Japan.
Sen
S
Takeda
Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu, Japan.
Motohiro
M
Okada
Rehabilitation Medicine, Institute of Brain Science, Japan.
Shinya
S
Ueno
Department of Neuropsychiatry, Hirosaki University, Hirosaki, Japan; North Tohoku Epilepsy Center, Minato Hospital, Hachinohe, Japan.
Sunao
S
Kaneko
Yanagawa Institute for Developmental Disabilities, Child Neurology, International University of Health and Welfare, Yanagawa, Japan.
Sachio
S
Takashima
Department of Pediatrics, Fukuoka University, Fukuoka, Japan; Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka, Japan. Electronic address: hirose@fukuoka-u.ac.jp.
Shinichi
S
Hirose
D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D002675:Child, Preschool; D018389:Codon, Nonsense / Q000235:genetics*; D004831:Epilepsies, Myoclonic / Q000235:genetics / Q000473:pathology; D004827:Epilepsy / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D007223:Infant; D007564:Japan; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008958:Models, Molecular; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D011963:Receptors, GABA-A / Q000235:genetics* / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism / Q000648:ultrastructure; D014429:Twins, Dizygotic
D018389:Codon, Nonsense; C546279:GABRG2 protein, human; D021122:Protein Subunits; D011963:Receptors, GABA-A
Channelopathy; ER stress; Sorting; Trafficking; Unfolded protein response