title: Brain white matter oedema due to ClC-2 chloride channel deficiency: an observational analytical study.
abstract: BACKGROUND
  Mutant mouse models suggest that the chloride channel ClC-2 has functions in ion and water homoeostasis, but this has not been confirmed in human beings. We aimed to define novel disorders characterised by distinct patterns of MRI abnormalities in patients with leukoencephalopathies of unknown origin, and to identify the genes mutated in these disorders. We were specifically interested in leukoencephalopathies characterised by white matter oedema, suggesting a defect in ion and water homoeostasis.
  
  
  METHODS
  In this observational analytical study, we recruited patients with leukoencephalopathies characterised by MRI signal abnormalities in the posterior limbs of the internal capsules, midbrain cerebral peduncles, and middle cerebellar peduncles from our databases of patients with leukoencephalopathies of unknown origin. We used exome sequencing to identify the gene involved. We screened the candidate gene in additional patients by Sanger sequencing and mRNA analysis, and investigated the functional effects of the mutations. We assessed the localisation of ClC-2 with immunohistochemistry and electron microscopy in post-mortem human brains of individuals without neurological disorders.
  
  
  RESULTS
  Seven patients met our inclusion criteria, three with adult-onset disease and four with childhood-onset disease. We identified homozygous or compound-heterozygous mutations in CLCN2 in three adult and three paediatric patients. We found evidence that the CLCN2 mutations result in loss of function of ClC-2. The remaining paediatric patient had an X-linked family history and a mutation in GJB1, encoding connexin 32. Clinical features were variable and included cerebellar ataxia, spasticity, chorioretinopathy with visual field defects, optic neuropathy, cognitive defects, and headaches. MRI showed restricted diffusion suggesting myelin vacuolation that was confined to the specified white matter structures in adult patients, and more diffusely involved the brain white matter in paediatric patients. We detected ClC-2 in all components of the panglial syncytium, enriched in astrocytic endfeet at the perivascular basal lamina, in the glia limitans, and in ependymal cells.
  
  
  CONCLUSIONS
  Our observations substantiate the concept that ClC-2 is involved in brain ion and water homoeostasis. Autosomal-recessive CLCN2 mutations cause a leukoencephalopathy that belongs to an emerging group of disorders affecting brain ion and water homoeostasis and characterised by intramyelinic oedema.
  
  
  BACKGROUND
  European Leukodystrophies Association, INSERM and Assistance Publique-Hôpitaux de Paris, Dutch Organisation for Scientific Research (ZonMw), E-Rare, Hersenstichting, Optimix Foundation for Scientific Research, Myelin Disorders Bioregistry Project, National Institute of Neurological Disorders and Stroke, and Genetic and Epigenetic Networks in Cognitive Dysfunction (GENCODYS) Project (funded by the European Union Framework Programme 7).
authors.affiliation: INSERM, U975-CRICM, Hôpital Pitié-Salpêtrière, Paris, France. christel.depienne@upmc.fr
authors.forename: Christel
authors.initials: C
authors.lastname: Depienne
authors.forename: Marianna
authors.initials: M
authors.lastname: Bugiani
authors.forename: Céline
authors.initials: C
authors.lastname: Dupuits
authors.forename: Damien
authors.initials: D
authors.lastname: Galanaud
authors.forename: Valérie
authors.initials: V
authors.lastname: Touitou
authors.forename: Nienke
authors.initials: N
authors.lastname: Postma
authors.forename: Carola
authors.initials: C
authors.lastname: van Berkel
authors.forename: Emiel
authors.initials: E
authors.lastname: Polder
authors.forename: Eleonore
authors.initials: E
authors.lastname: Tollard
authors.forename: Frédéric
authors.initials: F
authors.lastname: Darios
authors.forename: Alexis
authors.initials: A
authors.lastname: Brice
authors.forename: Christine E
authors.initials: CE
authors.lastname: de Die-Smulders
authors.forename: Johannes S
authors.initials: JS
authors.lastname: Vles
authors.forename: Adeline
authors.initials: A
authors.lastname: Vanderver
authors.forename: Graziella
authors.initials: G
authors.lastname: Uziel
authors.forename: Cengiz
authors.initials: C
authors.lastname: Yalcinkaya
authors.forename: Suzanna G
authors.initials: SG
authors.lastname: Frints
authors.forename: Vera M
authors.initials: VM
authors.lastname: Kalscheuer
authors.forename: Jan
authors.initials: J
authors.lastname: Klooster
authors.forename: Maarten
authors.initials: M
authors.lastname: Kamermans
authors.forename: Truus Em
authors.initials: TE
authors.lastname: Abbink
authors.forename: Nicole I
authors.initials: NI
authors.lastname: Wolf
authors.forename: Frédéric
authors.initials: F
authors.lastname: Sedel
authors.forename: Marjo S
authors.initials: MS
authors.lastname: van der Knaap
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D001921:Brain / Q000473:pathology; D001929:Brain Edema / Q000209:etiology* / Q000235:genetics* / Q000473:pathology; D000090007:CLC-2 Chloride Channels; D002524:Cerebellar Ataxia / Q000235:genetics / Q000473:pathology; D002648:Child; D018118:Chloride Channels / Q000172:deficiency* / Q000648:ultrastructure; D059472:Exome / Q000235:genetics; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D040181:Genetic Diseases, X-Linked; D006720:Homozygote; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D056784:Leukoencephalopathies / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000473:pathology; D009460:Neurologic Examination; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; C000715428:Clcn2 protein, mouse; D012333:RNA, Messenger