title: Urinary exosomes in the diagnosis of Gitelman and Bartter syndromes.
abstract: BACKGROUND
  Gitelman syndrome (GS) and Bartter syndrome (BS) are hereditary salt-losing tubulopathies (SLTs) resulting from defects of renal proteins involved in electrolyte reabsorption, as for sodium-chloride cotransporter (NCC) and furosemide-sensitive sodium-potassium-chloride cotransporter (NKCC2) cotransporters, affected in GS and BS Type 1 patients, respectively. Currently, definitive diagnosis is obtained through expensive and time-consuming genetic testing. Urinary exosomes (UE), nanovesicles released by every epithelial cell facing the urinary space, represent an ideal source of markers for renal dysfunction and injury, because UE molecular composition stands for the cell of origin. On these assumptions, the aim of this work is to evaluate the relevance of UE for the diagnosis of SLTs.
  
  
  METHODS
  UE were purified from second morning urines collected from 32 patients with genetically proven SLTs (GS, BS1, BS2 and BS3 patients), 4 with unclassified SLTs and 22 control subjects (age and sex matched). The levels of NCC and NKCC2 were evaluated in UE by SDS-PAGE/western blotting with specific antibodies.
  
  
  RESULTS
  Due to their location on the luminal side of tubular cells, NCC and NKCC2 are well represented in UE proteome. The NCC signal is significantly decreased/absent in UE of Gitelman patients compared with control subjects (Mann-Whitney t-test, P < 0.001) and, similarly, the NKCC2 in those of Bartter type 1 (P < 0.001). The difference in the levels of the two proteins allows recognition of Gitelman and Bartter type 1 patients from controls and, combined with clinical data, from other Bartter patients. Moreover, the receiver operating characteristic curve analysis using UE NCC densitometric values showed a good discriminating power of the test comparing GS patients versus controls and BS patients (area under the curve value = 0.92; sensitivity 84.2% and specificity 88.6%).
  
  
  CONCLUSIONS
  UE phenotyping may be useful in the diagnosis of GS and BS, thus providing an alternative/complementary, urine-based diagnostic tool for SLT patient recognition and a diagnostic guidance in complex cases.
authors.affiliation: Department of Health Sciences, University of Milano-Bicocca, Monza, Italy.
authors.forename: Samuele
authors.initials: S
authors.lastname: Corbetta
authors.affiliation: Department of Health Sciences, University of Milano-Bicocca, Monza, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Raimondo
authors.affiliation: Laboratory of Medical Genetics, Fondazione IRCCS Ca' Granda Maggiore Policlinico Hospital, Milan, Italy.
authors.forename: Silvana
authors.initials: S
authors.lastname: Tedeschi
authors.affiliation: Laboratory of Medical Genetics, Fondazione IRCCS Ca' Granda Maggiore Policlinico Hospital, Milan, Italy Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy.
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Syrèn
authors.affiliation: Center of Biostatistics for Clinical Epidemiology, Department of Health Sciences, University of Milano-Bicocca, Monza, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Rebora
authors.affiliation: Department of Health Sciences, University of Milano-Bicocca, Monza, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Savoia
authors.affiliation: Department of Laboratory Medicine, San Leopoldo Mandic Hospital, Merate, Lecco, Italy.
authors.forename: Lorenza
authors.initials: L
authors.lastname: Baldi
authors.affiliation: Department of Pediatrics, San Leopoldo Mandic Hospital, Merate, Lecco, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Bettinelli
authors.affiliation: Department of Health Sciences, University of Milano-Bicocca, Monza, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Pitto
mesh_terms: D000293:Adolescent; D000328:Adult; D001477:Bartter Syndrome / Q000175:diagnosis* / Q000652:urine; D015415:Biomarkers / Q000652:urine*; D015153:Blotting, Western; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D055354:Exosomes / Q000378:metabolism*; D005260:Female; D053579:Gitelman Syndrome / Q000175:diagnosis* / Q000652:urine; D006801:Humans; D008297:Male; D064466:Solute Carrier Family 12, Member 1 / Q000652:urine*; D064486:Solute Carrier Family 12, Member 3 / Q000652:urine; D055815:Young Adult
chemical_list: D015415:Biomarkers; C578714:SLC12A1 protein, human; C578874:SLC12A3 protein, human; D064466:Solute Carrier Family 12, Member 1; D064486:Solute Carrier Family 12, Member 3
keywords: NCC; NKCC2; diagnosis; salt-losing tubulopathies; urinary exosomes