title: Aquaporin-2: new mutations responsible for autosomal-recessive nephrogenic diabetes insipidus-update and epidemiology.
abstract: It is clinically useful to distinguish between two types of hereditary nephrogenic diabetes insipidus (NDI): a 'pure' type characterized by loss of water only and a complex type characterized by loss of water and ions. Patients with congenital NDI bearing mutations in the vasopressin 2 receptor gene, AVPR2, or in the aquaporin-2 gene, AQP2, have a pure NDI phenotype with loss of water but normal conservation of sodium, potassium, chloride and calcium. Patients with hereditary hypokalemic salt-losing tubulopathies have a complex phenotype with loss of water and ions. They have polyhydramnios, hypercalciuria and hypo- or isosthenuria and were found to bear KCNJ1 (ROMK) and SLC12A1 (NKCC2) mutations. Patients with polyhydramnios, profound polyuria, hyponatremia, hypochloremia, metabolic alkalosis and sensorineural deafness were found to bear BSND mutations. These clinical phenotypes demonstrate the critical importance of the proteins ROMK, NKCC2 and Barttin to transfer NaCl in the medullary interstitium and thereby to generate, together with urea, a hypertonic milieu. This editorial describes two new developments: (i) the genomic information provided by the sequencing of the AQP2 gene is key to the routine care of these patients, and, as in other genetic diseases, reduces health costs and provides psychological benefits to patients and families and (ii) the expression of AQP2 mutants in Xenopus oocytes and in polarized renal tubular cells recapitulates the clinical phenotypes and reveals a continuum from severe loss of function with urinary osmolalities <150 mOsm/kg H2O to milder defects with urine osmolalities >200 mOsm/kg H2O.
authors.affiliation: Groupe d'Étude des Protéines Membranaires (GÉPROM), Département de Physiologie, Université de Montréal, Montréal, Québec, Canada ; Centre de Recherche, Hôpital du Sacré-Cœur de Montréal, Montréal, Québec, Canada.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Bichet
authors.affiliation: Groupe d'Étude des Protéines Membranaires (GÉPROM), Département de Physiologie, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Abdulah
authors.initials: A
authors.lastname: El Tarazi
authors.affiliation: Groupe d'Étude des Protéines Membranaires (GÉPROM), Département de Physiologie, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Jessica
authors.initials: J
authors.lastname: Matar
authors.affiliation: Groupe d'Étude des Protéines Membranaires (GÉPROM), Département de Physiologie, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Yoann
authors.initials: Y
authors.lastname: Lussier
authors.affiliation: Centre de Recherche, Hôpital du Sacré-Cœur de Montréal, Montréal, Québec, Canada.
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Arthus
authors.affiliation: Centre de Recherche, Hôpital du Sacré-Cœur de Montréal, Montréal, Québec, Canada.
authors.forename: Michèle
authors.initials: M
authors.lastname: Lonergan
authors.affiliation: Institute of Child Health, University College London, Great Ormond Street Hospital for Children, NHS Trust, London, UK.
authors.forename: Detlef
authors.initials: D
authors.lastname: Bockenhauer
authors.affiliation: Groupe d'Étude des Protéines Membranaires (GÉPROM), Département de Physiologie, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Bissonnette
keywords: aquaporin-2 mutations; autosomal-dominant and -recessive nephrogenic diabetes insipidus; genetic testing; hereditary polyuric states