title: Is the brain water channel aquaporin-4 a pathogenetic factor in idiopathic intracranial hypertension? Results from a combined clinical and genetic study in a Norwegian cohort.
abstract: OBJECTIVE
  Idiopathic intracranial hypertension (IIH) is a condition of increased intracranial pressure of unknown aetiology. Patients with IIH usually suffer from headache and visual disturbances. High intracranial pressure despite normal ventricle size and negative MRI indicate perturbed water flux across cellular membranes, which is provided by the brain water channel aquaporin-4 (AQP4). IIH could be associated with malfunctioning intracerebral water homeostasis and cerebrospinal fluid (CSF) reabsorption based on functional or regulatory alterations of AQP4.
  
  
  METHODS
  Clinical data, blood and CSF samples were collected from 28 patients with IIH. Clinical characteristics were assessed, and a genetic association study was performed by sequencing the AQP4 gene on chromosome 18. Genetic data were compared with 52 healthy controls and matched by age, sex and ethnicity. Chi-square test and linear discriminant analysis (LDA) were used in the search of a genotype-phenotype association.
  
  
  RESULTS
  While the majority of patients responded to medical treatment, four required shunt application. All, except one, had a good visual outcome. The 24 AQP4 gene SNPs showed no association with IIH. Full cross-validation of the LDA modelling resulted in only 55.1% correct classification of the cases and controls, with a corresponding estimated p-value 0.37.
  
  
  CONCLUSIONS
  Our genetic case-control study did not indicate an association between AQP4 gene variants and IIH. However, the theory of an etiopathogenic link between IIH and AQP4 is tempting, and discussed in this article. Association studies with large sample size are difficult to perform owing is the rarity of the condition.
authors.affiliation: Department of Neurology, Oslo University Hospital, Rikshospitalet, University of Oslo, Oslo, Norway. emilia.kerty@medisin.uio.no
authors.forename: Emilia
authors.initials: E
authors.lastname: Kerty
authors.forename: Kjell
authors.initials: K
authors.lastname: Heuser
authors.forename: Ulf G
authors.initials: UG
authors.lastname: Indahl
authors.forename: Paul R
authors.initials: PR
authors.lastname: Berg
authors.forename: Sigve
authors.initials: S
authors.lastname: Nakken
authors.forename: Sigbjørn
authors.initials: S
authors.lastname: Lien
authors.forename: Stig W
authors.initials: SW
authors.lastname: Omholt
authors.forename: Ole P
authors.initials: OP
authors.lastname: Ottersen
authors.forename: Erlend A
authors.initials: EA
authors.lastname: Nagelhus
mesh_terms: D000328:Adult; D051401:Aquaporin 4 / Q000235:genetics*; D016022:Case-Control Studies; D002557:Cerebrospinal Fluid Shunts; D002887:Chromosomes, Human, Pair 18 / Q000235:genetics; D004232:Diuretics / Q000627:therapeutic use; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D009664:Norway; D020641:Polymorphism, Single Nucleotide; D011559:Pseudotumor Cerebri / Q000235:genetics* / Q000628:therapy; D017287:Ventriculoperitoneal Shunt; D055815:Young Adult
chemical_list: C496030:AQP4 protein, human; D051401:Aquaporin 4; D004232:Diuretics