Best Practice & Research Clinical Endocrinology & Metabolism 30 (2016) 263e276

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Genetic forms of nephrogenic diabetes insipidus(NDI): Vasopressin receptor defect (X-linked)and aquaporin defect (autosomal recessive anddominant)

Daniel G. Bichet, MD a, b, c, *, Detlef Bockenhauer, MD, PhD d

a Department of Medicine, Universit�e de Montr�eal, Canadab Department of Molecular and Integrative Physiology, Universit�e de Montr�eal, Canadac Hopital du Sacr�e-Coeur de Montr�eal, 5400 Boul. Gouin Ouest, Montr�eal, QC, Canada H4J 1C5d UCL Institute of Child Health, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK

a r t i c l e i n f o

Article history:Available online 2 March 2016

Keywords:Nephrogenic diabetes insipidusX-linked nephrogenic diabetes insipidusAutosomal recessive nephrogenic diabetesinsipidusAVPR2AQP2DehydrationMisfolded proteinsCyclic AMP

* Corresponding author. Hopital du Sacr�e-Coeur d514 338 2486; Fax: þ1 514 338 2694.

E-mail addresses: daniel.bichet@umontreal.ca (

http://dx.doi.org/10.1016/j.beem.2016.02.0101521-690X/© 2016 Elsevier Ltd. All rights reserved

Nephrogenic diabetes insipidus (NDI), which can be inherited oracquired, is characterized by an inability to concentrate urinedespite normal or elevated plasma concentrations of the antidi-uretic hormone, arginine vasopressin (AVP). Polyuria with hypo-sthenuria and polydipsia are the cardinal clinical manifestations ofthe disease. About 90% of patients with congenital NDI are maleswith X-linked NDI who have mutations in the vasopressin V2 re-ceptor (AVPR2) gene encoding the vasopressin V2 receptor. In lessthan 10% of the families studied, congenital NDI has an autosomalrecessive or autosomal dominant mode of inheritance with mu-tations in the aquaporin-2 (AQP2) gene. When studied in vitro,most AVPR2 and AQP2 mutations lead to proteins trapped in theendoplasmic reticulum and are unable to reach the plasmamembrane. Prior knowledge of AVPR2 or AQP2 mutations in NDIfamilies and perinatal mutation testing is of direct clinical valueand can avert the physical and mental retardation associated withrepeated episodes of dehydration.

© 2016 Elsevier Ltd. All rights reserved.

e Montr�eal, 5400 Boul. Gouin Ouest, Montr�eal, QC, Canada H4J 1C5. Tel.: þ1

D.G. Bichet), d.bockenhauer@ucl.ac.uk (D. Bockenhauer).

.

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Cellular actions of vasopressin

The neurohypophyseal hormone arginine vasopressin (AVP) has multiple actions, including theinhibition of diuresis, contraction of smooth muscle, aggregation of platelets, stimulation of liverglycogenolysis, modulation of adrenocorticotropic hormone release from the pituitary, and centralregulation of comportemental and somatic functions (thirst avoidance, thermoregulation, increasedrenal sympathetic nerve activity, blood pressure) [1e4].These multiple actions of AVP could beexplained by the interaction of AVP with at least three types of G protein-coupled receptors; the V1a(vascular hepatic and various; brain cells including pre-autonomic neurons in the paraventricularnucleus responding to the dentritic release of vasopressin by neighboring magnocellular cells) and V1b(anterior pituitary) receptors act through phosphatidylinositol hydrolysis to; mobilize calcium, and theV2 (kidney) receptor is coupled to adenylate cyclase [5,6].

The transfer of water across the principal cells of the collecting ducts is now known at a verydetailed level and the fact that billions of molecules of water traverse the membrane can be demon-strated as a useful teaching tool (http://www.ks.uiuc.edu/Gallery/Movies/aquaporin-movie-explanation.html). The 2003 Nobel Prize in chemistry was awarded to Peter Agre and RoderickMacKinnon, who solved two complementary problems presented by the cell membrane: How does acell let one type of ion through the lipid membrane with simultaneous exclusion of other ions? Andhow does it permeate water without ions? This generated great momentum and renewed interest inbasic discoveries related to the transport of water and indirectly to diabetes insipidus. The first step inthe action of AVP on water excretion is its binding to arginine vasopressin type 2 receptors (hereafterreferred to as V2 receptors) on the basolateral membrane of the collecting duct cells (Fig.1). The humanAVPR2 gene that codes for the V2 receptor is located on chromosome region Xq28 and has three exonsand two small introns [7,8]. The sequence of the cDNA predicts a polypeptide of 371 amino acids withseven transmembrane, four extracellular, and four cytoplasmic domains. The V2 receptor is one of 701members of the rhodopsin family within the superfamily of guanine-nucleotide (G) protein-coupledreceptors [9,10] The activation of the V2 receptor on renal collecting tubules stimulates adenylylcyclase via the stimulatory G protein (Gsa) and promotes the cyclic adenosine monophosphate (cAMP)-mediated incorporation of water pores into the luminal surface of these cells. This process is themolecular basis of the vasopressin-induced increase in the osmotic water permeability of the apicalmembrane of the collecting tubule [11]. There are two target proteins for cAMP: 1) the classical proteinkinase A (PKA)/cAMP-dependent protein kinase; 2) the recently discovered exchange protein directlyactivated by cAMP (Epac)/cAMP regulated guanine nucleotide exchange factors [12]. Like PKA, Epaccontains an evolutionally conserved cAMP binding domain that acts as a molecular switch for sensingintracellular cAMP levels to control diverse biological functions. PKA and Epac may act indepently onlong-term regulation of AQP2 abundance [13].

The increase in cyclic AMP activates protein kinase A (PKA), which could phosphorylate AQP2channels at five cytoplasmic carboxy-terminal tail residues, Thr 244, Ser256, Ser261, Ser264 andSer269 (Thr269 in human AQP2) [14]. Ser256, Ser264 and Ser269 phosphorylations are increased inabundance upon administration of 1-desamino-8-D-arginine vasopressin (DDAVP). Phosphorylation atSer261 is thought to stabilize AQP2 ubiquitination [15].

An X-ray structure of AQP2 at 2.75 Å resolution has been published in 2014 [16]. The structure of thecarboxy- and amino-termini revealed striking differences between the X-ray structure of AQP2 and allother mammalian AQP structures due to the highly variable position of the short carboxy-terminalhelix with high flexibility likely caused by two consecutive prolines (Pro225 and Pro226) that form ahinge region, whereas only one proline residue is present in the corresponding position in othermammalian AQP structures [16]. The crystal structure of AQP2 provided new structural insights tounderstand nephrogenic diabetes insipidus (NDI) AQP2 mutations affecting folding, the selectivityfilter region, and the cadmium2þ/calcium2þ-binding sites [16].

AVP also increases the water reabsorptive capacity of the kidney by regulating the urea transporterUT-A1 that is present in the inner medullary collecting duct, predominantly in its terminal part [17].AVP also increases the permeability of principal collecting duct cells to sodium [18].

In summary, in the absence of AVP stimulation, collecting duct epithelia exhibit very low perme-abilities to sodium, urea and water. These specialized permeability properties permit the excretion of

Fig. 1. Water transport in the principal cell. Binding of AVP to the AVPR2 receptor expressed on the basolateral side of the principalcell stimulates the release of Gsa, which in turn activates adenylyl cyclase, resulting in increased cAMP production. PKA is activatedby cAMP and phosphorylates several residues in the carboxy-terminus of AQP2. This phosphorylation enables trafficking of AQP2 tothe apical membrane and the formation of homotetrameric AQP2 water channels. AQP2 is constantly retrieved from the membraneby endocytosis, so that ongoing water permeability depends on delivery of AQP2 to the membrane, either by recycling or generationof new channels. Water diffuses via these channels along the concentration gradient from the tubular lumen into the principal celland exits into the interstitium via the constitutively expressed AQP3 and AQP4 water channels. In addition to PKA-mediatedphosphorylation of AQP2, cAMP enhances transcription of AQP2. Some of the changes induced by cAMP are likely mediated byEPAC. The G-protein coupled receptors EP2, EP4 and the secretin receptor are also expressed in principal cells. Targeting of thesereceptors could potentially be used to stimulate membrane insertion of AQP2 in the absence of functional AVPR2. Abbreviations:AQP, aquaporin; AVP, arginine vasopressin; AVPR2, vasopressin V2 receptor; CREB, cAMP responsive element binding protein; EP2,prostaglandin E2 receptor EP2 subtype; EP4, prostaglandin E2 receptor EP4 subtype; EPAC, exchange protein directly activated bycAMP; G, G protein; PKA, protein kinase A.

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large volumes of hypotonic urine formed during intervals of water diuresis. By contrast, AVP stimu-lation of the principal cells of the collecting ducts leads to selective increases in the permeability of theapical membrane to water (Pf), urea (Purea), and Na (PNa).

Four prostaglandin E2 (PGE2) receptors designated EP1e4 are expressed in the collecting duct andcould control urine volume and osmolality independently of vasopressin. Olesen et al. have shown thatboth G-coupled PGE2 receptor EP2 and EP4 agonists increased AQP2membrane accumulation and thatthe EP2 agonist butaprost relieved NDI symptoms in a rat model [19]. Moreover, a selective EP4 agonisthas also been reported to be able to alleviate symptoms in a mouse model of NDI [20]. A recent studydemonstrated a unique role for the EP4 receptor in controlling urine volume independently of vaso-pressin. EP4 activation increased collecting duct AQP2 expression in a cAMP/cAMP-response elementbinding protein (CREB)-dependent manner and promoted its membrane sorting via the cAMP/proteinkinase A and extracellular signal-regulated kinase pathways [21].

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An apical calcium/polycation receptor protein expressed in the terminal portion of the innermedullary collecting duct of the rat has been shown to reduce AVP-elicited osmotic water permeabilitywhen luminal calcium concentration rises [22]. This possible link between calcium and water meta-bolism may play a role in the pathogenesis of renal stone formation [22].

Loss-of-function of AVPR2 and AQP2 are responsible for hereditary NDI

In 1992 the AVPR2 gene encoding the V2 receptor was cloned and mutations identified in patientswith X-linked NDI [23e26]. Shortly thereafter, the AQP2 gene; was cloned [27,28] and in 1994 muta-tions in AQP2were found to underlie autosomal; recessive Diabetes Insipidus (DI) [29]. The discovery ofthese 2 key genes, AVPR2 and AQP2, has allowed genetic testing of affected patients and mutations inone of them are identified in almost all patients with a clear clinical phenotype of congenital NDI[30e32].

Rareness and diversity of AVPR2 AND AQP2 mutations

AVPR2 mutations

X-linked NDI is generally a rare disease inwhich the affected male patients do not concentrate theirurine after administration of AVP [33]. Because this form is a rare, recessive X-linked disease, femalesare unlikely to be affected, but heterozygous females can exhibit variable degrees of polyuria andpolydipsia because of skewed X chromosome inactivation. In Quebec, the incidence of this diseaseamongmales was estimated to be approximately 8.8 in 1000 000male live births [31]. A founder effectof two particular AVPR2 mutations [34], one in Ulster Scot immigrants (the ‘Hopewell’ mutation,W71X) and one in a large Utah kindred (the ‘Cannon’ pedigree bearing the L312X mutation) results inan elevated prevalence of X-linked NDI in their descendants in certain communities in Nova Scotia,Canada, and in Utah, USA [34]. These founder mutations have now spread all over the North-Americancontinent. We know of 98 living affected males of the Hopewell kindred and 20 living affected males ofthe Cannon pedigree. We also determined that the historical case report [35] was related to theHopewell pedigree and had the W71X mutation (Fig. 2). To date, more than 250 putative disease-causing AVPR2 mutations have been published in more than 300 NDI families (Fig. 3) [36,37] andBichet, unpublished data.

Approximately half of the mutations are missense mutations. Frameshift mutations owing tonucleotide deletions or insertions (25%), non-sense mutations (10%), large deletions (10%), in-framedeletions or insertions (4%), splice-site mutations, and one complex mutation account for theremainder of the mutations. Mutations have been identified in every domain, but on a per nucleotidebasis, about twice asmanymutations occur in transmembrane domains comparedwith the extracellularor intracellular domains. We previously identified private mutations, recurrent mutations, and mech-anisms ofmutagenesis [31,38]. The ten recurrentmutations (D85N, V88M, R113W, Y128S, R137H, S167L,R181C, R202C, A294P, and S315R) were found in 35 ancestrally independent families. The occurrence ofthe same mutation on different haplotypes was considered evidence for recurrence. In addition, themost frequent mutations e D85N, V88N, R113W, R137H, S167L, R181C, and R202C e occurred at po-tential mutational hot spots (a C-to-T or G-to-A nucleotide substitution occurred at a CpG dinucleotide).

AQP2 mutations

On the basis of DDAVP infusion studies and measurements of plasma cAMP levels followingpharmacological intravenous doses of DDAVP, a vasopressin V2 synthetic analog, we first suggestedthat X-linked NDI was a pre-cAMP defect [39,40]. Male patients with X-linked NDI did not stimulatetheir coagulation factor release or plasma cAMP level after a pharmacological infusion of DDAVP, asuggestion of a loss of function of both renal and extrarenal vasopressin V2 receptors.

Using DDAVP infusion studies and other families with severe polyuric characteristics in both maleand female individuals, a non-X-linked form of NDI with a post-receptor (post-cAMP) defect wassuggested [41e43]. A patient who presented shortly after birth with typical features of NDI, but who

Fig. 2. A typical ‘historical’ picture of a dehydrated and malnourished infant (a) with nephrogenic diabetes insipidus, looking healthyafter rehydration and improved nutrition (b). This infant died a few years later due to repeated episodes of dehydration. This reportwas published years before the identification of the AVPR2 gene. We were contacted by the mother and sister of this patient and wewere able to reconstruct and link this family to the large Hopewell kindred (Ref. [34] and Bichet and Arthus, unpublished data). Themother and sister both had the W71X mutation. Photograph is Fig. 2 of Perry et al. [35] reproduced with permission from the NewEngland Journal of Medicine, 1967; 276.

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exhibited normal coagulation and normal fibrinolytic and vasodilatory responses to DDAVP, was shownto be a compound heterozygote for two missense mutations (R187C and S217P) in the AQP2 gene [29].Expression of each of these two mutations in Xenopus oocytes revealed nonfunctional water channels.We used the sequencing data provided by Deen et al. to solve themolecular identification of NDI in twoinbred Pakistani girls with non-X-linked NDI originally reported by Langley et al. [43]. They were foundto be homozygous for the AQP2 V71M mutation. This mutation was found in two other Pakistanifamilies living in the UK, said to be unrelated, but they were found to bear the same mutation on thesame AQP2 haplotype suggesting common ancestry. To date, more than 51 putative disease-causingAQP2 mutations have been identified in 59 NDI families (Fig. 4).

Patients bearing dominant mutations have a less severe phenotype compared to patients who arecompound heterozygotes or homozygotes for recessive mutations: the patient and her daughter firstdescribed to bear the AQP2 E258K dominant mutation increased their urine osmolality to 350 mOsm/kg H2O following DDAVP [44]. Also the patient with a detailed phenotype described by Robertson andKopp [45] increased her urine osmolality to 220mOsm/kg H2O during amildly hypertonic dehydration,to 258 mOsm/kg H2O after DDAVP and to 305 mOsm/kg H2O after hydrochlorothiazide and indo-methacin. This patient was found to be heterozygous for the R254Qmutation, possibly interfering withthe S256 phosphorylation site [46].

In the mutant Aqp2 (del 763e772) knock-inmice, Sohara et al. [47] demonstrated a slight increase inurine osmolality following dehydration but a marked increase after the administration of Rolipram, aphosphodiesterase-4 inhibitor.

In patients with hereditary polyuria, an X-linked inheritance will suggest X-linked AVPR2mutationsand autosomal recessive cases will be in favor of AQP2 mutations but we are recommending thesequencing analysis of AVPR2 first and then AQP2 genes in all patients. The coding regions of thesegenes are relatively small and easy to sequence. This genomic information is key to the routine care of

Fig. 3. Schematic representation of the V2 receptor and identification of 193 putative disease-causing AVPR2 mutations. Predictedamino acids are shown as the one-letter amino acid code. A solid symbol indicates a codon with a missense or nonsense mutation; anumber indicates more than one mutation in the same codon; other types of mutations are not indicated on the figure. There are 95missense, 18 nonsense, 46 frameshift deletion or insertion, 7 inframe deletion or insertion, 4 splice-site, and 22 large deletionmutations, and one complex mutation.

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patients with congenital polyuria and, as in other genetic diseases, reduces health care costs andprovides psychological benefits to patients and their families.

Benefits of genetic testing

The natural history of untreated X-linked NDI includes hypernatremia, hyperthermia, mentalretardation, and repeated episodes of dehydration in early infancy [33]. Mental retardation, a conse-quence of repeated episodes of dehydration (Fig. 2), was prevalent in the Crawford and Bode study, inwhich only nine of 82 patients (11%) had normal intelligence [48], however, data from the Nijmegengroup suggest that this complication was overestimated in their group of NDI patients [49]. Earlyrecognition and treatment of X-linked NDI with an abundant intake of water allows a normal lifespanwith normal physical and mental development. Familial occurrence of males andmental retardation inuntreated patients are two characteristics suggestive of X-linked NDI. Skewed X-inactivation is themost likely explanation for clinical symptoms of NDI in female carriers [31].

Identification of the molecular defect underlying X-linked NDI is of immediate clinical significancebecause early diagnosis and treatment of affected infants can avert the physical and mental retardationresulting from repeated episodes of dehydration. Affected males are immediately treated with abun-dant water intake, a low sodium diet, and hydrochlorothiazide. They do not experience severe episodes

Fig. 4. A representation of the AQP2 protein and identification of 46 putative disease-causing AQP2 mutations. A monomer isrepresented with six transmembrane helices. The extracellular, transmembrane, and cytoplasmic domains are defined according toDeen et al., 1994 [29]. Solid symbols indicate the location of the mutations: M1I; L22V; V24A; L28P; G29S; A47V; Q57P; G64R, N68S,A70D; V71M; R85X; G100X; G100V; G100R; I107D; 369delC; T125M; T126M; A147T; D150E; V168M; G175R; G180S; C181W; P185A;R187C; R187H; A190T; G196D; W202C; G215C; S216P; S216F; K228E; R254Q; R254L; E258K; and P262L. GenBank accessionnumbersdAQP2: AF147092, exon 1; AF147093, exons 2 through 4. NPA motifs, the N-glycosylation site, the ubiquitination site (Ub)and phosphorylation sites (P) in the C-terminus are also indicated.

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of dehydration and their physical and mental development remains normal; however, their urinaryoutput is only decreased by 30% and a normal growth curve is still difficult to reach during the first 2e3years of their lives despite the aforementioned treatments and intensive attention. Water should beoffered every 2 h day and night, and temperature, appetite, and growth should be monitored. Hospitaladmission may be necessary for continuous gastric feeding. The voluminous amounts of water kept inthe patients' stomachs will exacerbate physiological gastrointestinal reflux in infants and toddlers, andmany affected boys frequently vomit and often have a gastroesophageal reflux disease (GERD) ifevaluated with esophageal pH measurements (positive Tuttle test). These young patients oftenimprove with the absorption of an H-2 blocker and with metoclopramide (which could induceextrapyramidal symptoms) or with domperidone, which seems to be better tolerated and efficacious.

All polyuric states (whether neurogenic, nephrogenic, or psychogenic) can induce large dilatationsof the urinary tract and bladder [48,50,51] and bladder function impairment has been well docu-mented in patients carrying AVPR2 or AQP2 mutations [52,53]. Chronic renal failure secondary to

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bilateral hydronephrosis has been observed as a long-term complication in some of these patients.Renal and abdominal ultrasound should be done annually and simple recommendations includingfrequent urination and ‘double voiding’ could be important to prevent these consequences.

We propose that all families with hereditary diabetes insipidus should have their molecular defectidentified. The molecular identification underlying X-linked NDI is of immediate clinical significancebecause early diagnosis and treatment of affected infants can avert the physical and mental retardationresulting from repeated episodes of dehydration. Diagnosis of X-linked NDI was accomplished bymutation testing of chorionic villous samples (n ¼ 10), cultured amniotic cells (n ¼ 7), or cord blood(n ¼ 57). Three infants who had mutational analysis done using amniotic cells or chorionic villoussamples also had their diagnosis confirmed by cord blood testing. Of the 74 offspring tested, 35 werefound to be affected males, 22 were unaffected males, and nine were non-carriers (M.-F. Arthus, M.Lonergan, and D.G. Bichet, unpublished data). The affected males were immediately treated withabundant water intake, a low sodium diet, and hydrochlorothiazide. They have not experienced severeepisodes of dehydration and their physical and mental development remains normal. Affected pre-mature males may experience less severe polyuric symptoms and may only need increased hydrationduring their first week without a need for hydrochlorothiazide treatment.

Most mutant V2 receptors and AQP2 water channels mutants are not transported to the cellmembrane and are retained in the intracellular compartment

Misfolded AVPR2 mutants

Classification of the defects of naturally occurring mutant human V2 receptors can be based on asimilar scheme to that used for the low-density lipoprotein receptor. Mutations have been groupedaccording to the function and subcellular localization of the mutant protein whose cDNA has beentransiently transfected in a heterologous expression system [54]. Using this classification, type 1mutant V2 receptors reach the cell surface but display impaired ligand binding and are consequentlyunable to induce normal cAMP production. The presence of mutant V2 receptors on the surface oftransfected cells can be determined pharmacologically. By carrying out saturation binding experimentsusing tritiated AVP, the number of cell surface mutant V2 receptors and their apparent binding affinitycan be compared with that of the wild type receptor. In addition, the presence of cell surface receptorscan be assessed directly by using immunodetection strategies to visualize epitope-tagged receptors inwhole-cell immunofluorescence assays.

Type 2 mutant receptors have a defective intracellular transport. This phenotype is confirmed bycarrying out, in parallel, immunofluorescence experiments on cells that are intact (to demonstrate theabsence of cell surface receptors) or permeabilized (to confirm the presence of intracellular receptorpools). In addition, protein expression is confirmed bywestern blot analysis of membrane preparationsfrom transfected cells. It is likely that these mutant type 2 receptors accumulate in a pre-Golgicompartment, because they are initially glycosylated but fail to undergo glycosyl-trimmingmaturation.

Type 3mutant receptors are ineffectively transcribed and lead to unstable mRNAs which are rapidlydegraded. This subgroup seems to be rare, since Northern blot analysis of cells expressing mutantAVPR2 receptors typically show an mRNA of normal quantity and molecular size.

Most of the AVPR2mutants that we and other investigators have tested are type 2mutant receptors.These mutant receptors do not reach the cell membrane and are trapped in the interior of the cell[55e58]. Other mutant G-protein-coupled receptors [59] and gene products causing genetic disordersare also characterized by protein misfolding. Mutations that affect the folding of secretory proteins,integral plasma membrane proteins, or enzymes destined to the endoplasmic reticulum, Golgi com-plex, and lysosomes result in loss-of-function phenotypes irrespective of their direct impact on proteinfunction because these mutant proteins are prevented from reaching their final destination [60].Folding in the endoplasmic reticulum is the limiting step: mutant proteins which fail to fold correctlyare initially retained in the endoplasmic reticulum and subsequently often degraded. Key proteinsinvolved in the urine countercurrent mechanisms are good examples of this basic mechanism ofmisfolding. AQP2 mutations responsible for autosomal recessive NDI are characterized by misroutingof the misfolded mutant proteins and are trapped in the endoplasmic reticulum [61]. This mechanism

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applies to many mutated membrane proteins and, for example, mutants encoding other renal mem-brane proteins that are responsible for Gitelman's syndrome [62], Bartter's syndrome [63,64], andcystinuria [65] are also retained in the endoplasmic reticulum.

The AVPR2 missense mutations are likely to impair folding and lead to rapid degradation of themisfolded polypeptide and not to the accumulation of toxic aggregates (as is the case for AVPmutants),because the other important functions of the principal cells of the collecting duct (where the V2 re-ceptor is expressed) are entirely normal. These cells express the epithelial sodium channel (ENaC).Decreased function of this channel results in a sodium-losing state [66]. This has not been observed inpatients with AVPR2 mutations. However, recent data showed that DDAVP could not stimulate sodiumreabsorption in male patients with NDI bearing AVPR2 mutations [18]. In contrast, another type ofconformational disease is characterized by the toxic retention of the misfolded protein. The relativelycommon Z mutation in alpha-1-antitrypsin deficiency not only causes retention of the mutant proteinin the endoplasmic reticulum but also affects the secondary structure by insertion of the reactive centerloop of one molecule into a destabilized sheet of a second molecule [67]. These polymers clog up theendoplasmic reticulum of hepatocytes and lead to cell death and juvenile hepatitis, cirrhosis, andhepatocarcinomas in these patients [68].

Misfolded AQP2 mutants

AQP2 mutations in autosomal-recessive NDI, which are located throughout the gene, also result inmisfolded proteins [16] that are retained in the endoplasmic reticulum. In contrast, the dominantmutations are located in the region that codes for the carboxyl terminus of AQP2 [69]. Dominant AQP2mutants form heterotetramers with wild type AQP2 and are misrouted [44,46,70e78].

Nonpeptide vasopressin receptor antagonists act as pharmacological chaperones tofunctionally rescue misfolded mutant V2 receptors responsible for X-linked NDI

If the misfolded protein/traffic problem responsible for so many human genetic diseases can beovercome and themutant protein transported out of the endoplasmic reticulum to its final destination,these mutant proteins could be sufficiently functional [79]. Therefore, the use of pharmacologicalchaperones to promote escape from the endoplasmic reticulum is a possible therapeutic approach[56,60,80]. We used selective non-peptide V2 and V1 receptor antagonists to rescue the cell surfaceexpression and function of naturally occurring misfolded human V2 receptors [55]. Other non-peptideV2 receptor agonists were also found to have positive re-folding and functional effects [81,82]. Inclinical studies, we administered a nonpeptide vasopressin antagonist SR49059 to five adult NDI pa-tients bearing the del62-64, R137H, and W164S mutations. SR49059 significantly decreased urinevolume and water intake and increased urine osmolality while sodium, potassium, and creatinineexcretions and plasma sodium were constant throughout the study (Fig. 5) [83]. This new therapeuticapproach could be applied to the treatment of several hereditary diseases resulting from errors inprotein folding and kinesis [79,80].

Since most human gene therapy experiments using viruses to deliver and integrate DNA into hostcells are potentially dangerous [84], other treatments are being actively pursued. Torsten Sch€onebergand colleagues [85] used aminoglycoside antibiotics because of their ability to suppress prematuretermination codons [86]. They demonstrated that geneticin, a potent aminoglycoside antibiotic,increased AVP-stimulated cAMP in cultured collecting duct cells prepared from E242X mutant mice.The urine-concentrating ability of heterozygous mutant mice was also improved. The ability of EP4 toincrease cellular abundance and AQP2 membrane targeting makes it a potential therapeutic target forthe treatment of clinical disorders including acquired and congenital diabetes insipidus [21].

Genome editing of somatic tissue or embryos to correct mutant genes is a topic of considerableinterest, but the ethics of these approachesdespecially of embryo editingdare controversial [87,88]and no such treatment strategies have reached the clinic. We anticipate that the ethical governance,safety and long-term effects of editing therapies could be determined within the next two decades.Patients with hereditary disorders, including NDI, might then benefit from these curative therapies.

Fig. 5. Urine volume and osmolality before (day 1) and after (days 2 and 3) SR49059 administration to a patient bearing the R137Hmutation. Note that the distances observed between the two lines on days 2 and 3 represent the mirror images of urine volume andosmolality. Urine volume and osmolalities that were obtained during the control, second, and third nights are indicated by roundcircles. These data were obtained from 9:30 p.m. to 8:00 a.m. for the patient described here. Data from Bernier [83] with permissionfrom J Am Soc Nephrol.

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Testing patients with NDI; please avoid dehydration

Over the past few years it has become clear that ‘pure’ (i.e. loss of water only) congenital NDI iscaused by inactivating mutations in the genes that code for the V2 receptor or the AQP2 water channel[89]. The time of onset of the disease (shortly after birth) and the clinical symptoms are similarregardless of the molecular defect. The defective gene can be deduced by clinical testing: DDAVP elicitsextrarenal (coagulation and vasodilatory) responses in male patients with NDI due to AQP2 mutations,

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whereas patients with AVPR2 mutations lack extrarenal responses [39,40,90]. Because this test isdifficult to do in young infants, it has been replaced by mutational analysis of the AVPR2 and AQP2genes. The small sizes of the genomic and coding regions of the involved genes (AVPR2 and AQP2) allowfor relatively easy mutational analysis, thereby allowing for carrier, prenatal and perinatal testing. If adehydration test or an infusion of DDAVP is done, they should be performed only during the day andunder strict medical and nursing supervision.

In our clinical research unit, plasma sodium and plasma and urine osmolalities are measured at thebeginning of each dehydration procedure and at regular intervals (usually hourly) thereafter,depending on the severity of the polyuric syndrome explored. In one case, an 8-year-old patient (31 kgbody weight) with a clinical diagnosis of congenital NDI (later found to bear the de novo AVPR2mutant274insG [38] continued to excrete large volumes of urine (300 ml/h) during a short 4-h dehydrationtest. During this time, the patient was suffering from severe thirst, his plasma sodium was 155 mEq/l,his plasma osmolality was 310 mmol/kg, and his urine osmolality was 85 mmol/kg. The patientreceived 1 mg of desmopressin IV and was allowed to drink water. Repeated urine osmolality mea-surements demonstrated a complete urinary resistance to desmopressin. It would have beendangerous and unnecessary to prolong the dehydration further in this young patient. Thus, the usualprescription of overnight dehydration should not be used in patients, and especially children, withsevere polyuria and polydipsia. Great care should be taken to avoid any severe hypertonic state,arbitrarily defined as a plasma sodium of �155 mEq/l.

Practice points

� We propose that all families with hereditary diabetes insipidus should have their moleculardefect identified

� The usual prescription of overnight dehydration should not be used in patients, and espe-cially children, with severe polyuria and polydipsia. Great care should be taken to avoid anysevere hypertonic state, arbitrarily defined as a plasma sodium of �155 mEq/l.

Research agenda

� There is great hope to use the CRISPR (clustered regularly interspaced short palindromicrepeats) gene editing technology to correct monogenic disorders but “off-target” sites arefeared and it is too early to predict the human use of this promising tool in hereditarynephrogenic diabetes insipidus.

� Bypassing the V2 receptor, that is, stimulation of collecting duct cyclic AMP by other hor-monal systems, is a promising experimental approach to express AQP2 channels at rheluminal membrane and trials are needed to test new and re-purposed compounds to achievethis goal.

Acknowledgments

The author's work cited in this manuscript was supported by the Canadian Institutes of HealthResearch and by the Kidney Foundation of Canada. I thank Ellen Buschman and Danielle Binette forcomputer graphics expertise and secretarial assistance.

References

*[1] Bourque CW. Central mechanisms of osmosensation and systemic osmoregulation. Nat Rev Neurosci Jul 2008;9(7):519e31.

D.G. Bichet, D. Bockenhauer / Best Practice & Research Clinical Endocrinology & Metabolism 30 (2016) 263e276274

*[2] Son SJ, Filosa JA, Potapenko ES, et al. Dendritic peptide release mediates interpopulation crosstalk between neurose-cretory and preautonomic networks. Neuron Jun 19 2013;78(6):1036e49.

[3] Choe KY, Han SY, Gaub P, et al. High salt intake increases blood pressure via BDNF-mediated downregulation of KCC2 andimpaired baroreflex inhibition of vasopressin neurons. Neuron Feb 4 2015;85(3):549e60.

*[4] Oka Y, Ye M, Zuker CS. Thirst driving and suppressing signals encoded by distinct neural populations in the brain. NatureApr 16 2015;520(7547):349e52.

[5] Thibonnier M, Coles P, Thibonnier A, et al. The basic and clinical pharmacology of nonpeptide vasopressin receptorantagonists. Annu Rev Pharmacol Toxicol 2001;41:175e202.

[6] Serradeil-Le Gal C, Wagnon J, Simiand J, et al. Characterization of (2S,4R)-1-[5-chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl) -2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide(SSR149415), a selective and orally active vasopressin V1b receptor antagonist. J Pharmacol Exp Ther Mar 2002;300(3):1122e30.

*[7] Birnbaumer M, Seibold A, Gilbert S, et al. Molecular cloning of the receptor for human antidiuretic hormone. Nature 1992;357:333e5.

[8] Seibold A, Brabet P, Rosenthal W, et al. Structure and chromosomal localization of the human antidiuretic hormonereceptor gene. Am J Hum Genet 1992;51:1078e83.

[9] Fredriksson R, Lagerstrom MC, Lundin LG, et al. The G-protein-coupled receptors in the human genome form five mainfamilies. Phylogenetic analysis, paralogon groups, and fingerprints. Mol Pharmacol Jun 2003;63(6):1256e72.

[10] Flock T, Ravarani CN, Sun D, et al. Universal allosteric mechanism for Ga activation by GPCRs. Nature Aug 13 2015;524(7564):173e9.

[11] Nielsen S, Frokiaer J, Marples D, et al. Aquaporins in the kidney: from molecules to medicine. Physiol Rev Jan 2002;82(1):205e44.

[12] Rehmann H, Wittinghofer A, Bos JL. Capturing cyclic nucleotides in action: snapshots from crystallographic studies. NatRev Mol Cell Biol Jan 2007;8(1):63e73.

[13] Kortenoeven ML, Trimpert C, van den Brand M, et al. In mpkCCD cells, long-term regulation of aquaporin-2 by vaso-pressin occurs independent of protein kinase A and CREB but may involve Epac. Am J Physiol Renal Physiol Jun 1 2012;302(11):F1395e401.

[14] Kortenoeven ML, Fenton RA. Renal aquaporins and water balance disorders. Biochim Biophys Acta May 2014;1840(5):1533e49.

[15] Tamma G, Robben JH, Trimpert C, et al. Regulation of AQP2 localization by S256 and S261 phosphorylation and ubiq-uitination. Am J Physiol Cell Physiol Mar 2011;300(3):C636e46.

*[16] Frick A, Eriksson UK, de Mattia F, et al. X-ray structure of human aquaporin 2 and its implications for nephrogenicdiabetes insipidus and trafficking. Proc Natl Acad Sci U S A Apr 29 2014;111(17):6305e10.

[17] Yang B, Bankir L, Gillespie A, et al. Urea-selective concentrating defect in transgenic mice lacking urea transporter UT-B.J Biol Chem Mar 22 2002;277(12):10633e7.

[18] Bankir L, Fernandes S, Bardoux P, et al. Vasopressin-V2 receptor stimulation reduces sodium excretion in healthy humans.J Am Soc Nephrol Jul 2005;16(7):1920e8.

*[19] Olesen ET, Rutzler MR, Moeller HB, et al. Vasopressin-independent targeting of aquaporin-2 by selective E-prostanoidreceptor agonists alleviates nephrogenic diabetes insipidus. Proc Natl Acad Sci U S A Aug 2 2011;108(31):12949e54.

[20] Li JH, Chou CL, Li B, et al. A selective EP4 PGE2 receptor agonist alleviates disease in a new mouse model of X-linkednephrogenic diabetes insipidus. J Clin Invest Oct 2009;119(10):3115e26.

[21] Gao M, Cao R, Du S, et al. Disruption of prostaglandin E2 receptor EP4 impairs urinary concentration via decreasingaquaporin 2 in renal collecting ducts. Proc Natl Acad Sci U S A Jul 7 2015;112(27):8397e402.

[22] Sands JM, Naruse M, Baum M, et al. Apical extracellular calcium/polyvalent cation-sensing receptor regulatesvasopressin-elicited water permeability in rat kidney inner medullary collecting duct. J Clin Invest Mar 15 1997;99(6):1399e405.

[23] Lolait SJ, O'Carroll A-M, McBride OW, et al. Cloning and characterization of a vasopressin V2 receptor and possible link tonephrogenic diabetes insipidus. Nature 1992;357:336e9.

*[24] Rosenthal W, Seibold A, Antaramian A, et al. Molecular identification of the gene responsible for congenital nephrogenicdiabetes insipidus. Nature 1992;359:233e5.

[25] van den Ouweland AM, Dreesen JC, Verdijk M, et al. Mutations in the vasopressin type 2 receptor gene (AVPR2) associatedwith nephrogenic diabetes insipidus. Nat Genet 1992;2(2):99e102.

[26] Pan Y, Metzenberg A, Das S, et al. Mutations in the V2 vasopressin receptor gene are associated with X-linked neph-rogenic diabetes insipidus. Nat Genet 1992;2(2):103e6.

[27] Fushimi K, Uchida S, Hara Y, et al. Cloning and expression of apical membrane water channel of rat kidney collectingtubule. Nature 1993;361(6412):549e52.

[28] Sasaki S, Fushimi K, Saito H, et al. Cloning, characterization, and chromosomal mapping of human aquaporin of collectingduct. J Clin Invest 1994;93:1250e6.

*[29] Deen PMT, Verdijk MAJ, Knoers NVAM, et al. Requirement of human renal water channel aquaporin-2 for vasopressin-dependent concentration of urine. Science 1994;264:92e5.

[30] Sasaki S, Chiga M, Kikuchi E, et al. Hereditary nephrogenic diabetes insipidus in Japanese patients: analysis of 78 familiesand report of 22 new mutations in AVPR2 and AQP2. Clin Exp Nephrol Jun 2013;17(3):338e44.

[31] Arthus MF, Lonergan M, Crumley MJ, et al. Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linkednephrogenic diabetes insipidus. J Am Soc Nephrol Jun 2000;11(6):1044e54.

*[32] Bockenhauer D, Bichet DG. Pathophysiology, diagnosis and management of nephrogenic diabetes insipidus. Nat RevNephrol 2015 Oct;11(10):576e88.

[33] Bichet DG, Fujiwara TM. Nephrogenic diabetes insipidus. In: Scriver CR, Beaudet AL, Sly WS, editors. The metabolic andmolecular basis of inherited disease. New York: McGraw Hill; 2001. p. 4181e204.

[34] Bichet DG, Arthus M-F, Lonergan M, et al. X-linked nephrogenic diabetes insipidus mutations in North America and theHopewell hypothesis. J Clin Invest 1993;92:1262e8.

D.G. Bichet, D. Bockenhauer / Best Practice & Research Clinical Endocrinology & Metabolism 30 (2016) 263e276 275

[35] Perry TL, Robinson GC, Teasdale JM, et al. Concurrence of cystathioninuria, nephrogenic diabetes insipidus and severeanemia. N Engl J Med Mar 30 1967;276(13):721e5.

[36] Arthus MFLM, Fujiwara TM, Bichet DG. Clinical. Paper presented at: The NDI Foundation 2004 Global Conference. andgenetic approaches to the diagnosis of congenital polyuro-polydipsic syndromes. 2004. Phoenix, Arizona.

[37] Spanakis E, Milord E, Gragnoli C. AVPR2 variants and mutations in nephrogenic diabetes insipidus: review and missensemutation significance. J Cell Physiol Dec 2008;217(3):605e17.

[38] Bichet DG, Birnbaumer M, Lonergan M, et al. Nature and recurrence of AVPR2 mutations in X-linked nephrogenic dia-betes insipidus. Am J Hum Genet 1994;55:278e86.

[39] Bichet DG, Razi M, Lonergan M, et al. Hemodynamic and coagulation responses to 1-desamino[8-D-arginine]vasopressin(dDAVP) infusion in patients with congenital nephrogenic diabetes insipidus. N Engl J Med 1988;318:881e7.

[40] Bichet DG, Razi M, Arthus M-F, et al. Epinephrine and dDAVP administration in patients with congenital nephrogenicdiabetes insipidus. Evidence for a pre-cyclic AMP V2 receptor defective mechanism. Kidney Int 1989;36:859e66.

[41] Brenner B, Seligsohn U, Hochberg Z. Normal response of factor VIII and von Willebrand factor to 1-deamino-8D-argininevasopressin in nephrogenic diabetes insipidus. J Clin Endocrinol Metab Jul 1988;67(1):191e3.

[42] Knoers N, Monnens LA. A variant of nephrogenic diabetes insipidus: V2 receptor abnormality restricted to the kidney. EurJ Pediatr Mar 1991;150(5):370e3.

[43] Langley JM, Balfe JW, Selander T, et al. Autosomal recessive inheritance of vasopressin-resistant diabetes insipidus. Am JMed Genet Jan 1991;38(1):90e4.

[44] Mulders SM, Bichet DG, Rijss JPL, et al. An aquaporin-2 water channel mutant which causes autosomal dominantnephrogenic diabetes insipidus is retained in the golgi complex. J Clin Invest 1998;102:57e66.

[45] Robertson GL, Kopp P. A novel dominant mutation of the aquaporin-2 gene resulting in partial nephrogenic diabetesinsipidus. In: Global conference proceedings. NDI Foundation; April 26e28, 2002. 7A.

[46] de Mattia F, Savelkoul PJ, Bichet DG, et al. A novel mechanism in recessive nephrogenic diabetes insipidus: wild-typeaquaporin-2 rescues the apical membrane expression of intracellularly retained AQP2-P262L. Hum Mol Genet Dec 152004;13(24):3045e56.

[47] Sohara E, Rai T, Yang SS, et al. Pathogenesis and treatment of autosomal-dominant nephrogenic diabetes insipidus causedby an aquaporin 2 mutation. Proc Natl Acad Sci U S A Sep 19 2006;103(38):14217e22.

[48] Crawford JD, Bode HH. Disorders of the posterior pituitary in children. In: Gardner LI, editor. Endocrine and geneticdiseases of childhood and adolescence. 2nd ed. Philadelphia: W.B. Saunders; 1975. p. 126e58.

[49] Hoekstra JA, van Lieburg AF, Monnens LA, et al. Cognitive and psychosocial functioning of patients with congenitalnephrogenic diabetes insipidus. Am J Med Genet Jan 2 1996;61(1):81e8.

[50] Boyd SD, Raz S, Ehrlich RM. Diabetes insipidus and nonobstructive dilatation of urinary tract. Urology 1980;16:266e9.[51] Gautier B, Thieblot P, Steg A. M�egauret�ere, m�egavessie et diab�ete insipide familial. Sem Hop 1981;57:60e1.[52] Shalev H, Romanovsky I, Knoers NV, et al. Bladder function impairment in aquaporin-2 defective nephrogenic diabetes

insipidus. Nephrol Dial Transpl Mar 2004;19(3):608e13.[53] Ulinski T, Grapin C, Forin V, et al. Severe bladder dysfunction in a family with ADH receptor gene mutation responsible for

X-linked nephrogenic diabetes insipidus. Nephrol Dial Transpl Nov 2004;19(11):2928e9.[54] Hobbs HH, Russell DW, Brown MS, et al. The LDL receptor locus in familial hypercholesterolemia: mutational analysis of a

membrane protein. Annu Rev Genet 1990;24:133e70.*[55] Morello JP, Salahpour A, Laperri�ere A, et al. Pharmacological chaperones rescue cell-surface expression and function of

misfolded V2 vasopressin receptor mutants. J Clin Invest 2000;105:887e95.[56] Bernier V, Lagace M, Lonergan M, et al. Functional rescue of the constitutively internalized V2 vasopressin receptor

mutant R137H by the pharmacological chaperone action of SR49059. Mol Endocrinol Aug 2004;18(8):2074e84.[57] Hermosilla R, Oueslati M, Donalies U, et al. Disease-causing V(2) vasopressin receptors are retained in different com-

partments of the early secretory pathway. Traffic Dec 2004;5(12):993e1005.[58] Wuller S, Wiesner B, Loffler A, et al. Pharmacochaperones post-translationally enhance cell surface expression by

increasing conformational stability of wild-type and mutant vasopressin V2 receptors. J Biol Chem Nov 5 2004;279(45):47254e63.

[59] Schoneberg T, Schulz A, Biebermann H, et al. Mutant G-protein-coupled receptors as a cause of human diseases. Phar-macol Ther Dec 2004;104(3):173e206.

[60] Romisch K. A cure for traffic jams: small molecule chaperones in the endoplasmic reticulum. Traffic Nov 2004;5(11):815e20.

[61] Tamarappoo BK, Verkman AS. Defective aquaporin-2 trafficking in nephrogenic diabetes insipidus and correction bychemical chaperones. J Clin Invest 1998;101(10):2257e67.

[62] Kunchaparty S, Palcso M, Berkman J, et al. Defective processing and expression of thiazide-sensitive Na-Cl cotransporteras a cause of Gitelman's syndrome. Am J Physiol Oct 1999;277(4 Pt 2):F643e9.

[63] Hayama A, Rai T, Sasaki S, et al. Molecular mechanisms of Bartter syndrome caused by mutations in the BSND gene.Histochem Cell Biol Jun 2003;119(6):485e93.

[64] Peters M, Ermert S, Jeck N, et al. Classification and rescue of ROMK mutations underlying hyperprostaglandin E syn-drome/antenatal Bartter syndrome. Kidney Int Sep 2003;64(3):923e32.

[65] Chillaron J, Estevez R, Samarzija I, et al. An intracellular trafficking defect in type I cystinuria rBAT mutants M467T andM467K. J Biol Chem 1997;272(14):9543e9.

[66] Bonnardeaux A, Bichet DG. Inherited disorders of the renal tubule. Brenner & Rector's the kidney. 10 ed. USA: ElsevierSaunders Company; 2016. p. 1434e74. chapter 45.

[67] Lomas DA, Evans DL, Finch JT, et al. The mechanism of Z alpha 1-antitrypsin accumulation in the liver. Nature Jun 18 1992;357(6379):605e7.

[68] Lawless MW, Greene CM, Mulgrew A, et al. Activation of endoplasmic reticulum-specific stress responses associated withthe conformational disease Z alpha 1-antitrypsin deficiency. J Immunol May 1 2004;172(9):5722e6.

[69] Loonen AJ, Knoers NV, van Os CH, et al. Aquaporin 2 mutations in nephrogenic diabetes insipidus. Semin Nephrol May2008;28(3):252e65.

D.G. Bichet, D. Bockenhauer / Best Practice & Research Clinical Endocrinology & Metabolism 30 (2016) 263e276276

[70] Marr N, Bichet DG, Hoefs S, et al. Cell-biologic and functional analyses of five new aquaporin-2 missense mutations thatcause recessive nephrogenic diabetes inspidus. J Am Soc Nephrol 2002;13:2267e77.

[71] Kuwahara M. Aquaporin-2, a vasopressin-sensitive water channel, and nephrogenic diabetes insipidus. Intern Med 1998;37:215e7.

[72] Kamsteeg EJ, Wormhoudt TA, Rijss JP, et al. An impaired routing of wild-type aquaporin-2 after tetramerization with anaquaporin-2 mutant explains dominant nephrogenic diabetes insipidus. EMBO J 1999;18(9):2394e400.

[73] Kamsteeg EJ, Deen PM. Importance of aquaporin-2 expression levels in genotype -phenotype studies in nephrogenicdiabetes insipidus. Am J Physiol Renal Physiol Oct 2000;279(4):F778e84.

[74] Kamsteeg EJ, Stoffels M, Tamma G, et al. Repulsion between Lys258 and upstream arginines explains the missorting of theAQP2 mutant p.Glu258Lys in nephrogenic diabetes insipidus. Hum Mutat Oct 2009;30(10):1387e96.

[75] Kuwahara M, Iwai K, Ooeda T, et al. Three families with autosomal dominant nephrogenic diabetes insipidus caused byaquaporin-2 mutations in the C-terminus. Am J Hum Genet 2001;69(4):738e48.

[76] Ohzeki T, Igarashi T, Okamoto A. Familial cases of congenital nephrogenic diabetes insipidus type II: remarkable incre-ment of urinary adenosine 30 ,50-monophosphate in response to antidiuretic hormone. J Pediatr 1984;104(4):593e5.

[77] Marr N, Bichet DG, Lonergan M, et al. Heteroligomerization of an aquaporin-2 mutant with wild-type Aquaporin-2 andtheir misrouting to late endosomes/lysosomes explains dominant nephrogenic diabetes insipidus. Hum Mol Genet 2002;11(7):779e89.

[78] Kamsteeg EJ, Bichet DG, Konings IB, et al. Reversed polarized delivery of an aquaporin-2 mutant causes dominantnephrogenic diabetes insipidus. J Cell Biol Dec 8 2003;163(5):1099e109.

[79] Cohen FE, Kelly JW. Therapeutic approaches to protein-misfolding diseases. Nature Dec 18 2003;426(6968):905e9.[80] Ulloa-Aguirre A, Janovick JA, Brothers SP, et al. Pharmacologic rescue of conformationally-defective proteins: implications

for the treatment of human disease. Traffic Nov 2004;5(11):821e37.[81] Robben JH, Kortenoeven ML, Sze M, et al. Intracellular activation of vasopressin V2 receptor mutants in nephrogenic

diabetes insipidus by nonpeptide agonists. Proc Natl Acad Sci U S A Jul 21 2009;106(29):12195e200.[82] Jean-Alphonse F, Perkovska S, Frantz MC, et al. Biased agonist pharmacochaperones of the AVP V2 receptor may treat

congenital nephrogenic diabetes insipidus. J Am Soc Nephrol Oct 2009;20(10):2190e203.[83] Bernier V, Morello JP, Zarruk A, et al. Pharmacologic chaperones as a potential treatment for X-linked nephrogenic

diabetes insipidus. J Am Soc Nephrol Jan 2006;17(1):232e43.[84] Glover DJ, Lipps HJ, Jans DA. Towards safe, non-viral therapeutic gene expression in humans. Nat Rev Genet Apr 2005;

6(4):299e310.[85] Sangkuhl K, Schulz A, Rompler H, et al. Aminoglycoside-mediated rescue of a disease-causing nonsense mutation in the

V2 vasopressin receptor gene in vitro and in vivo. Hum Mol Genet May 1 2004;13(9):893e903.[86] Mankin AS, Liebman SW. Baby, don't stop! Nat Genet Sep 1999;23(1):8e10.[87] Ran FA, Cong L, Yan WX, et al. In vivo genome editing using Staphylococcus aureus Cas9. Nature Apr 9 2015;520(7546):

186e91.[88] Cyranoski D. Ethics of embryo editing divides scientists. Nature Mar 19 2015;519(7543):272.[89] Fujiwara TM, Bichet DG. Molecular biology of hereditary diabetes insipidus. J Am Soc Nephrol Oct 2005;16(10):2836e46.[90] Lin SH, Bichet DG, Sasaki S, et al. Two novel aquaporin-2 mutations responsible for congenital nephrogenic diabetes

insipidus in Chinese families. J Clin Endocrinol Metab Jun 2002;87(6):2694e700.