title: Somatic Mutations in the MTOR gene cause focal cortical dysplasia type IIb.
abstract: OBJECTIVE
  Focal cortical dysplasia (FCD) type IIb is a cortical malformation characterized by cortical architectural abnormalities, dysmorphic neurons, and balloon cells. It has been suggested that FCDs are caused by somatic mutations in cells in the developing brain. Here, we explore the possible involvement of somatic mutations in FCD type IIb.
  
  
  METHODS
  We collected a total of 24 blood-brain paired samples with FCD, including 13 individuals with FCD type IIb, 5 with type IIa, and 6 with type I. We performed whole-exome sequencing using paired samples from 9 of the FCD type IIb subjects. Somatic MTOR mutations were identified and further investigated using all 24 paired samples by deep sequencing of the entire gene's coding region. Somatic MTOR mutations were confirmed by droplet digital polymerase chain reaction. The effect of MTOR mutations on mammalian target of rapamycin (mTOR) kinase signaling was evaluated by immunohistochemistry and Western blotting analyses of brain samples and by in vitro transfection experiments.
  
  
  RESULTS
  We identified four lesion-specific somatic MTOR mutations in 6 of 13 (46%) individuals with FCD type IIb showing mutant allele rates of 1.11% to 9.31%. Functional analyses showed that phosphorylation of ribosomal protein S6 in FCD type IIb brain tissues with MTOR mutations was clearly elevated, compared to control samples. Transfection of any of the four MTOR mutants into HEK293T cells led to elevated phosphorylation of 4EBP, the direct target of mTOR kinase.
  
  
  CONCLUSIONS
  We found low-prevalence somatic mutations in MTOR in FCD type IIb, indicating that activating somatic mutations in MTOR cause FCD type IIb.
authors.affiliation: Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Nakashima
authors.affiliation: Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Hirotomo
authors.initials: H
authors.lastname: Saitsu
authors.affiliation: Department of Molecular Neurobiology, Brain Research Institute, Niigata University, Niigata, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Takei
authors.affiliation: Department of Child Neurology, Nishi-Niigata Chuo National Hospital, Niigata, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Tohyama
authors.affiliation: Department of Pediatrics, Showa University School of Medicine, Tokyo, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Kato
authors.affiliation: Department of Pathology, Brain Research Institute, University of Niigata, Niigata, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kitaura
authors.affiliation: Department of Biochemistry, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Shiina
authors.affiliation: Department of Functional Neurosurgery, Epilepsy Center, Nishi-Niigata Chuo National Hospital, Niigata, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shirozu
authors.affiliation: Department of Functional Neurosurgery, Epilepsy Center, Nishi-Niigata Chuo National Hospital, Niigata, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Masuda
authors.affiliation: Division of Neurobiology and Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Ohba
authors.affiliation: Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Tsurusaki
authors.affiliation: Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Miyake
authors.affiliation: Department of Pathology, Brain Research Institute, University of Niigata, Niigata, Japan.
authors.forename: Yingjun
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: Division of Biochemistry, School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan.
authors.forename: Tatsuhiro
authors.initials: T
authors.lastname: Sato
authors.affiliation: Division of Neurobiology and Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan.
authors.forename: Hirohide
authors.initials: H
authors.lastname: Takebayashi
authors.affiliation: Department of Biochemistry, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Ogata
authors.affiliation: Department of Functional Neurosurgery, Epilepsy Center, Nishi-Niigata Chuo National Hospital, Niigata, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kameyama
authors.affiliation: Department of Pathology, Brain Research Institute, University of Niigata, Niigata, Japan.
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Kakita
authors.affiliation: Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
authors.forename: Naomichi
authors.initials: N
authors.lastname: Matsumoto
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000473:pathology*; D002648:Child; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D054220:Malformations of Cortical Development / Q000175:diagnosis / Q000235:genetics; D054081:Malformations of Cortical Development, Group II / Q000175:diagnosis / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics*
chemical_list: C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases