title: Association of MTOR Mutations With Developmental Brain Disorders, Including Megalencephaly, Focal Cortical Dysplasia, and Pigmentary Mosaicism.
abstract: Focal cortical dysplasia (FCD), hemimegalencephaly, and megalencephaly constitute a spectrum of malformations of cortical development with shared neuropathologic features. These disorders are associated with significant childhood morbidity and mortality.
  
  
  
  To identify the underlying molecular cause of FCD, hemimegalencephaly, and diffuse megalencephaly.
  
  
  
  Patients with FCD, hemimegalencephaly, or megalencephaly (mean age, 11.7 years; range, 2-32 years) were recruited from Pediatric Hospital A. Meyer, the University of Hong Kong, and Seattle Children's Research Institute from June 2012 to June 2014. Whole-exome sequencing (WES) was performed on 8 children with FCD or hemimegalencephaly using standard-depth (50-60X) sequencing in peripheral samples (blood, saliva, or skin) from the affected child and their parents and deep (150-180X) sequencing in affected brain tissue. Targeted sequencing and WES were used to screen 93 children with molecularly unexplained diffuse or focal brain overgrowth. Histopathologic and functional assays of phosphatidylinositol 3-kinase-AKT (serine/threonine kinase)-mammalian target of rapamycin (mTOR) pathway activity in resected brain tissue and cultured neurons were performed to validate mutations.
  
  
  
  Whole-exome sequencing and targeted sequencing identified variants associated with this spectrum of developmental brain disorders.
  
  
  
  Low-level mosaic mutations of MTOR were identified in brain tissue in 4 children with FCD type 2a with alternative allele fractions ranging from 0.012 to 0.086. Intermediate-level mosaic mutation of MTOR (p.Thr1977Ile) was also identified in 3 unrelated children with diffuse megalencephaly and pigmentary mosaicism in skin. Finally, a constitutional de novo mutation of MTOR (p.Glu1799Lys) was identified in 3 unrelated children with diffuse megalencephaly and intellectual disability. Molecular and functional analysis in 2 children with FCD2a from whom multiple affected brain tissue samples were available revealed a mutation gradient with an epicenter in the most epileptogenic area. When expressed in cultured neurons, all MTOR mutations identified here drive constitutive activation of mTOR complex 1 and enlarged neuronal size.
  
  
  
  In this study, mutations of MTOR were associated with a spectrum of brain overgrowth phenotypes extending from FCD type 2a to diffuse megalencephaly, distinguished by different mutations and levels of mosaicism. These mutations may be sufficient to cause cellular hypertrophy in cultured neurons and may provide a demonstration of the pattern of mosaicism in brain and substantiate the link between mosaic mutations of MTOR and pigmentary mosaicism in skin.
authors.affiliation: Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, Washington, USA.|Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA.
authors.forename: Ghayda M
authors.initials: GM
authors.lastname: Mirzaa
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Catarina D
authors.initials: CD
authors.lastname: Campbell
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Nadia
authors.initials: N
authors.lastname: Solovieff
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Carleton
authors.initials: C
authors.lastname: Goold
authors.affiliation: Department of Neurology, University of Virginia, Charlottesville, VA, USA.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Jansen
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Suchithra
authors.initials: S
authors.lastname: Menon
authors.affiliation: Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, Washington, USA.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Timms
authors.affiliation: Paediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, A. Meyer Children's Hospital, and Department of Neuroscience, Pharmacology and Child Health, University of Florence, Florence, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Conti
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Biag
authors.affiliation: Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA.
authors.forename: Carissa
authors.initials: C
authors.lastname: Adams
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Evan August
authors.initials: EA
authors.lastname: Boyle
authors.affiliation: Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Collins
authors.affiliation: Department of Radiology, Seattle Children's Hospital, Seattle, Washington, USA.
authors.forename: Gisele
authors.initials: G
authors.lastname: Ishak
authors.affiliation: Department of Radiology, Seattle Children's Hospital, Seattle, Washington, USA.
authors.forename: Sandra
authors.initials: S
authors.lastname: Poliachik
authors.affiliation: Department of Medical Genetics, Kasturba Medical College, Manipal University, Manipal, Karnataka, India.
authors.forename: Katta M
authors.initials: KM
authors.lastname: Girisha
authors.affiliation: Department of Pediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Kit San
authors.initials: KS
authors.lastname: Yeung
authors.affiliation: Department of Pediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Brian Hon Yin
authors.initials: BHY
authors.lastname: Chung
authors.affiliation: PEDEGO Research Group and Medical Research Center Oulu, University of Oulu and Department of Clinical Genetics, Oulu University Hospital, Finland.
authors.forename: Elisa
authors.initials: E
authors.lastname: Rahikkala
authors.affiliation: Department of Neurology, University of Virginia, Charlottesville, VA, USA.
authors.forename: Sonya A
authors.initials: SA
authors.lastname: Gunter
authors.affiliation: Pediatric Neurology and Epilepsy, Kaiser Permanente San Francisco Medical Center, San Francisco, California, USA.
authors.forename: Sharon S
authors.initials: SS
authors.lastname: McDaniel
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, Stanford University, Stanford, California, USA.
authors.forename: Colleen Forsyth
authors.initials: CF
authors.lastname: Macmurdo
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, Stanford University, Stanford, California, USA.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Bernstein
authors.affiliation: Department of Genome Sciences, University of Washington, Seattle, Washington, USA.
authors.forename: Beth
authors.initials: B
authors.lastname: Martin
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Leary
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Scott
authors.initials: S
authors.lastname: Mahan
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Shanming
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Pathology, University of Washington, Seattle, Washington, USA.
authors.forename: Molly
authors.initials: M
authors.lastname: Weaver
authors.affiliation: Department of Pathology, University of Washington, Seattle, Washington, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Doerschner
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA.|Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Shalini
authors.initials: S
authors.lastname: Jhangiani
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA.|Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Donna M
authors.initials: DM
authors.lastname: Muzny
authors.affiliation: Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, USA.|Human Genetics Center, University of Texas Health Science Center at Houston, Houston, Texas, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Boerwinkle
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA.|Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Gibbs
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA.|Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, USA.|Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA.|Texas Children's Hospital, Houston, Texas, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Lupski
authors.affiliation: Department of Genome Sciences, University of Washington, Seattle, Washington, USA.
authors.forename: Jay
authors.initials: J
authors.lastname: Shendure
authors.affiliation: Division of Pediatric Neurology, University of Washington, Seattle, Washington, USA.|Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle Washington, USA.
authors.forename: Russell P
authors.initials: RP
authors.lastname: Saneto
authors.affiliation: Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA.|Division of Pediatric Neurology, University of Washington, Seattle, Washington, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Novotny
authors.affiliation: Editas Medicine, Cambridge, Massachusetts, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Wilson
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: William R
authors.initials: WR
authors.lastname: Sellers
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Michael
authors.initials: M
authors.lastname: Morrissey
authors.affiliation: Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA.|Department of Neurosurgery, University of Washington, Seattle, Washington, USA.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Hevner
authors.affiliation: Department of Neurosurgery, University of Washington, Seattle, Washington, USA.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Ojemann
authors.affiliation: Paediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, A. Meyer Children's Hospital, and Department of Neuroscience, Pharmacology and Child Health, University of Florence, Florence, Italy.|IRCCS Stella Maris Foundation, Pisa, Italy.
authors.forename: Renzo
authors.initials: R
authors.lastname: Guerrini
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Leon O
authors.initials: LO
authors.lastname: Murphy
authors.affiliation: Novartis Institutes for BioMedical Research, Inc., Cambridge, MA.
authors.forename: Wendy
authors.initials: W
authors.lastname: Winckler
authors.affiliation: Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, Washington, USA.|Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA.
authors.forename: William B
authors.initials: WB
authors.lastname: Dobyns
mesh_terms: D000293:Adolescent; D000328:Adult; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D002648:Child; D002675:Child, Preschool; D002658:Developmental Disabilities / Q000000981:diagnostic imaging / Q000235:genetics; D004622:Embryo, Mammalian; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D056726:Genetic Association Studies; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency; D008297:Male; D054220:Malformations of Cortical Development / Q000000981:diagnostic imaging / Q000235:genetics*; D000076222:Mechanistic Target of Rapamycin Complex 1; D058627:Megalencephaly / Q000000981:diagnostic imaging / Q000235:genetics*; D009030:Mosaicism; D046912:Multiprotein Complexes / Q000494:pharmacology; D009154:Mutation / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000187:drug effects; D051381:Rats; D012189:Retrospective Studies; D058570:TOR Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D055815:Young Adult
chemical_list: D000596:Amino Acids; D036341:Intercellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases