title: Mutations in APOPT1, encoding a mitochondrial protein, cause cavitating leukoencephalopathy with cytochrome c oxidase deficiency.
abstract: Cytochrome c oxidase (COX) deficiency is a frequent biochemical abnormality in mitochondrial disorders, but a large fraction of cases remains genetically undetermined. Whole-exome sequencing led to the identification of APOPT1 mutations in two Italian sisters and in a third Turkish individual presenting severe COX deficiency. All three subjects presented a distinctive brain MRI pattern characterized by cavitating leukodystrophy, predominantly in the posterior region of the cerebral hemispheres. We then found APOPT1 mutations in three additional unrelated children, selected on the basis of these particular MRI features. All identified mutations predicted the synthesis of severely damaged protein variants. The clinical features of the six subjects varied widely from acute neurometabolic decompensation in late infancy to subtle neurological signs, which appeared in adolescence; all presented a chronic, long-surviving clinical course. We showed that APOPT1 is targeted to and localized within mitochondria by an N-terminal mitochondrial targeting sequence that is eventually cleaved off from the mature protein. We then showed that APOPT1 is virtually absent in fibroblasts cultured in standard conditions, but its levels increase by inhibiting the proteasome or after oxidative challenge. Mutant fibroblasts showed reduced amount of COX holocomplex and higher levels of reactive oxygen species, which both shifted toward control values by expressing a recombinant, wild-type APOPT1 cDNA. The shRNA-mediated knockdown of APOPT1 in myoblasts and fibroblasts caused dramatic decrease in cell viability. APOPT1 mutations are responsible for infantile or childhood-onset mitochondrial disease, hallmarked by the combination of profound COX deficiency with a distinctive neuroimaging presentation.
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Melchionda
authors.affiliation: Institute of Human Genetics, Technische Universität München, Munich 81675, Germany; Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg 85764, Germany.
authors.forename: Tobias B
authors.initials: TB
authors.lastname: Haack
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Hardy
authors.affiliation: Departments of Child Neurology and Functional Genomics, Neuroscience Campus Amsterdam, VU University and VU University Medical Center, Amsterdam 1081 HV, the Netherlands.
authors.forename: Truus E M
authors.initials: TE
authors.lastname: Abbink
authors.affiliation: MRC Mitochondrial Biology Unit, Cambridge CB2 0XY, UK.
authors.forename: Erika
authors.initials: E
authors.lastname: Fernandez-Vizarra
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Lamantea
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Marchet
authors.affiliation: Neuromuscular Diseases and Neuroimmunology Unit, Foundation IRCCS Institute of Neurology Besta, 20133 Milan, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Morandi
authors.affiliation: Neuromuscular Unit, Department of Neurology, Centro Dino Ferrari, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, University of Milan, 20122 Milan, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Moggio
authors.affiliation: Unit of Neuromuscular Disorders, Laboratory of Molecular Medicine, Bambino Gesu' Children's Research Hospital, 00165 Rome, Italy.
authors.forename: Rosalba
authors.initials: R
authors.lastname: Carrozzo
authors.affiliation: Unit of Neuromuscular Disorders, Laboratory of Molecular Medicine, Bambino Gesu' Children's Research Hospital, 00165 Rome, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Torraco
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy; Unit of Neuromuscular Disorders, Laboratory of Molecular Medicine, Bambino Gesu' Children's Research Hospital, 00165 Rome, Italy.
authors.forename: Daria
authors.initials: D
authors.lastname: Diodato
authors.affiliation: Institute of Human Genetics, Technische Universität München, Munich 81675, Germany; Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg 85764, Germany.
authors.forename: Tim M
authors.initials: TM
authors.lastname: Strom
authors.affiliation: Institute of Human Genetics, Technische Universität München, Munich 81675, Germany; Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg 85764, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Meitinger
authors.affiliation: Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, 34098 Istanbul, Turkey.
authors.forename: Pinar
authors.initials: P
authors.lastname: Tekturk
authors.affiliation: Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, 34098 Istanbul, Turkey.
authors.forename: Zuhal
authors.initials: Z
authors.lastname: Yapici
authors.affiliation: Genetic and Developmental Medicine Clinic, Sultan Qaboos University Hospital, Muscat 123, Oman.
authors.forename: Fathiya
authors.initials: F
authors.lastname: Al-Murshedi
authors.affiliation: Department of Paediatrics, CHC Clinique de l'Espérance at Liège, Liège 4000, Belgium.
authors.forename: René
authors.initials: R
authors.lastname: Stevens
authors.affiliation: Nijmegen Center for Mitochondrial Disorders, Laboratory for Genetic, Endocrine, and Metabolic Disorders, Department of Pediatrics, Radboud University Medical Center, 9101 Nijmegen, the Netherlands.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Rodenburg
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy.
authors.forename: Costanza
authors.initials: C
authors.lastname: Lamperti
authors.affiliation: Department of Child Neurology, Foundation IRCCS Institute of Neurology Besta, 20133 Milan, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Ardissone
authors.affiliation: Department of Child Neurology, Foundation IRCCS Institute of Neurology Besta, 20133 Milan, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Moroni
authors.affiliation: Department of Child Neurology, Foundation IRCCS Institute of Neurology Besta, 20133 Milan, Italy.
authors.forename: Graziella
authors.initials: G
authors.lastname: Uziel
authors.affiliation: Institute of Human Genetics, Technische Universität München, Munich 81675, Germany; Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg 85764, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Prokisch
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Taylor
authors.affiliation: Unit of Neuromuscular Disorders, Laboratory of Molecular Medicine, Bambino Gesu' Children's Research Hospital, 00165 Rome, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Bertini
authors.affiliation: Departments of Child Neurology and Functional Genomics, Neuroscience Campus Amsterdam, VU University and VU University Medical Center, Amsterdam 1081 HV, the Netherlands.
authors.forename: Marjo S
authors.initials: MS
authors.lastname: van der Knaap
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy. Electronic address: dghezzi@instituto-besta.it.
authors.forename: Daniele
authors.initials: D
authors.lastname: Ghezzi
authors.affiliation: Unit of Molecular Neurogenetics, Foundation IRCCS Institute of Neurology Besta, 20126 Milan, Italy; MRC Mitochondrial Biology Unit, Cambridge CB2 0XY, UK. Electronic address: mdz21@mrc-mbu.cam.ac.uk.
authors.forename: Massimo
authors.initials: M
authors.lastname: Zeviani
mesh_terms: D000293:Adolescent; D000328:Adult; D051017:Apoptosis Regulatory Proteins / Q000235:genetics*; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D030401:Cytochrome-c Oxidase Deficiency; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007223:Infant; D056784:Leukoencephalopathies / Q000201:enzymology / Q000235:genetics* / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D032446:Myoblasts / Q000378:metabolism / Q000473:pathology
chemical_list: D051017:Apoptosis Regulatory Proteins; D024101:Mitochondrial Proteins; D003576:Electron Transport Complex IV