title: Identification, characterization and rescue of a novel vasopressin-2 receptor mutation causing nephrogenic diabetes insipidus.
abstract: OBJECTIVE
  X-linked nephrogenic diabetes insipidus (XNDI), caused by mutations in the V2 vasopressin receptor (V2R), is clinically distinguished from central diabetes insipidus (CDI) by elevated serum vasopressin (AVP) levels and unresponsiveness to 1-desamino-8-d-arginine vasopressin (DDAVP). We report two infants with XNDI, and present the characterization and functional rescue of a novel V2R mutation.
  
  
  METHODS
  Two male infants presented with poor growth and hypernatraemia. Both patients had measurable pretreatment serum AVP and polyuria that did not respond to DDAVP, suggesting NDI. However, both also had absent posterior pituitary bright spot on MRI, which is a finding more typical of CDI.
  
  
  METHODS
  The AVPR2 gene encoding V2R was sequenced. The identified novel missense mutation was re-created by site-directed mutagenesis and expressed in HEK293 cells. V2R activity was assessed by the ability of transfected cells to produce cAMP in response to stimulation with DDAVP. Membrane localization of V2R was assessed by fluorescence microscopy.
  
  
  RESULTS
  Patient 1 had a deletion of AVPR2; patient 2 had the novel mutation L57R. In transiently transfected HEK293 cells, DDAVP induced detectable but severely impaired L57R V2R activity compared to cells expressing wild-type V2R. Fluorescence microscopy showed that myc-tagged wild-type V2R localized to the cell membrane while L57R V2R remained intracellular. A nonpeptide V2R chaperone, SR121463, partially rescued L57R V2R function by allowing it to reach the cell membrane.
  
  
  CONCLUSIONS
  L57R V2R has impaired in vitro activity that can be partially improved by treatment with a V2R chaperone. The posterior pituitary hyperintensity may be absent in infants with XNDI.
authors.affiliation: Department of Pediatrics, Division of Endocrinology, University of California San Francisco, San Francisco, CA 94143, USA.
authors.forename: Sayali A
authors.initials: SA
authors.lastname: Ranadive
authors.forename: Baran
authors.initials: B
authors.lastname: Ersoy
authors.forename: Helene
authors.initials: H
authors.lastname: Favre
authors.forename: Clement C
authors.initials: CC
authors.lastname: Cheung
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Rosenthal
authors.forename: Walter L
authors.initials: WL
authors.lastname: Miller
authors.forename: Christian
authors.initials: C
authors.lastname: Vaisse
mesh_terms: D065092:Antidiuretic Hormone Receptor Antagonists; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018500:Diabetes Insipidus, Nephrogenic / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D040181:Genetic Diseases, X-Linked; D006801:Humans; D007223:Infant; D008297:Male; D009025:Morpholines / Q000627:therapeutic use; D009154:Mutation; D021381:Protein Transport / Q000187:drug effects; D017483:Receptors, Vasopressin / Q000235:genetics* / Q000378:metabolism; D013141:Spiro Compounds / Q000627:therapeutic use
chemical_list: D065092:Antidiuretic Hormone Receptor Antagonists; D009025:Morpholines; D017483:Receptors, Vasopressin; D013141:Spiro Compounds; C103281:satavaptan