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Classifications

Harrison's Part

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Inheritance

1

X-linked recessive HP:0001419

Affected males are hemizygous. The inheritance is conventionally called recessive because hemizygous males carry the full phenotype and most heterozygous females do not, but the female side is more interesting than "carrier" suggests: a heterozygous female can be as severely affected as a male, and the explanation offered for that is skewed X-inactivation against the normal allele. In a review of 23 families with at least one affected female, every female in whom X-inactivation was studied showed extreme or slight skewing, and all six with severe disease carried complete loss-of-function alleles. In a Chinese family, skewing of the normal allele was present in four symptomatic heterozygotes and absent in an asymptomatic one. Two limits on that claim are worth stating rather than glossing. The inactivation pattern in all of these studies was measured in accessible somatic tissue, not in the collecting duct where the receptor has to work, so the inference to the relevant tissue is an inference. And the association is consistent rather than demonstrated sufficient: no cited study shows that skewing alone produces the phenotype. The practical consequence stands regardless - an AVPR2 heterozygote cannot be reassured on the basis of her sex, and a female with nephrogenic diabetes insipidus needs AVPR2 considered alongside AQP2.

X-linked recessive inheritance De novo rate: about 20 per cent of isolated cases, arising during maternal oogenesis

Show evidence (5 references)

PMID:20301356 SUPPORT Other

"Hereditary NDI is most commonly inherited in an X-linked manner (~90% of individuals)."

States the mode and its share of hereditary NDI.

PMID:7607658 SUPPORT Human Clinical

"Skewed X-inactivation is the most likely explanation for the clinical manifestation of NDI in female carriers of an AVPR2 mutation."

The original clinical description of symptomatic female heterozygotes and the proposed explanation. Quoted with its hedge - the authors say "most likely", not that they demonstrated it in these families.

PMID:32073219 SUPPORT Human Clinical

"The review underlines that XL-NDI in female AVPR2 heterozygotes is always accompanied by skewed X-inactivation, emphasizing a need for X-inactivation studies in these females."

The strongest available statement of the association, from a review of 23 families with affected females. Note it is an association in every studied case, not a demonstration that skewing is sufficient.

+ 2 more references

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Discussions and Knowledge Gaps

2

Is the cognitive impairment reported in untreated X-linked nephrogenic diabetes insipidus caused by repeated hypernatraemic episodes, and if so what exposure is required?

KNOWLEDGE GAP OPEN xndi_neurocognitive_attribution

Attached to

phenotypes#Intellectual disability phenotypes#Hypernatremia

There is a live contradiction here, not just a gap. GeneReviews holds that intelligence is usually normal with early diagnosis and treatment; a 2025 cohort followed for a median of 16.9 years found neurodevelopmental disorders in six of eight patients who were all on hydrochlorothiazide and amiloride with normalised serum sodium. Treatment status therefore does not reconcile the two. Three explanations are open and the cited literature does not choose between them: ascertainment in a small referral series, residual subclinical hypernatraemic episodes that a normalised steady-state sodium does not capture, or a contribution from something other than sodium - chronic undernutrition severe enough to leave a permanent height deficit is the obvious candidate. The attribution to electrolyte disturbance is stated in review form and hedged there, and no cited source anchors it to a measured exposure-response relationship. Note also that the 66-child multicentre cohort, which is the largest series here and reported growth, urological and renal outcomes in detail, did not report cognitive outcome at all - so the best-powered study is silent on precisely this question. This matters practically: if the relationship is dose-dependent in episodes, the value of early diagnosis becomes quantifiable and the sodium surveillance interval becomes an evidence question rather than a convention.

Show evidence (3 references)

PMID:34055061 SUPPORT Other

"Irreversible brain damage and cognitive deficit secondary to electrolyte imbalances may be present."

The claim whose evidential basis the gap is about. The hedge is the source's own.

PMID:40922895 SUPPORT Human Clinical

"Neurodevelopmental disorders were identified in six patients, including intellectual disability, autism spectrum disorder, language delay, and learning difficulties."

The observation that creates the contradiction, in patients who were treated.

PMID:40922895 SUPPORT Human Clinical

"Serum sodium normalized in all cases."

Establishes that the cohort above was not simply undertreated at steady state, which is what rules out the easiest reconciliation of the two positions and leaves the question open.

Why has pharmacochaperone rescue of ER-retained V2 receptor mutants not translated into a human treatment, two decades after the cell-based proof of principle?

KNOWLEDGE GAP OPEN xndi_pharmacochaperone_translation

Attached to

pathophysiology#Endoplasmic Reticulum Retention of Misfolded V2 Receptor treatments#Thiazide Diuretic

The mechanistic argument is unusually clean: most pathogenic AVPR2 variants retain a functional receptor in the wrong compartment, cell-permeable non-peptide ligands restore its membrane delivery in polarized cells, and the pharmacology even discriminates which ligands could work at achievable concentrations. Two distinct obstacles appear in the cited work rather than one. First, a pharmacochaperone that is an antagonist must be displaced by vasopressin to be useful, so affinity has to be high enough to chaperone and low enough to release - a narrow window. The non-peptide agonist route was proposed to escape that, but the same ligand also desensitizes the rescued receptor, and whether the chaperone effect outlasts the desensitization is a speculation in the source, not a result. The current proposal is a biased agonist that chaperones the receptor and then signals only through Gs without recruiting arrestin, which would sidestep the desensitization problem - but that too is offered as a potential treatment rather than a demonstrated one. Second, and more simply, the review of pharmacological strategies concludes that nothing has yet been established as causally improving symptoms or quality of life in patients, which is a statement about the whole field including these agents. The entry therefore records the thiazide regimen as the treatment and pharmacochaperones as mechanism, not therapy.

Show evidence (3 references)

PMID:32924547 SUPPORT Other

"It is concluded that there is currently no established intervention that causally improves symptoms or quality of life in patients with NDI."

The field-level negative conclusion, which is what keeps every causal strategy in this entry out of the treatments section.

PMID:27601473 SUPPORT In Vitro

"We speculated that the canceling of the desensitization effect of OPC51803 by the pharmacochaperone effect after long-term treatment may produce sustainable signaling, and thus pharmacochaperone agonists such as OPC51803 may serve as promising therapeutics for NDI caused by misfolded V2R mutants."

Quoted because the authors' own verb is "speculated". The agonist route's central premise is explicitly a speculation, which is the content of this gap.

PMID:31928727 SUPPORT Other

"These compounds, particularly small-molecule biased agonists which elicit the V2-induced Gs protein-dependent signaling pathway, but not V2-related arrestin-dependent cell responses, represent a potential therapeutic treatment of this X-linked genetic pathology."

The current form of the proposal - a biased agonist that chaperones and signals through Gs without recruiting arrestin, so the desensitization problem above does not arise. Note the verb is "represent a potential", so this is a proposal and not a result.

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Pathophysiology

10

AVPR2 Loss-of-Function Variant

A hemizygous pathogenic variant in AVPR2 on Xq28, the gene encoding the arginine vasopressin V2 receptor. The allelic spectrum is wide and largely private: 82 different putative disease-causing variants were found among 117 families, and haplotype analysis indicates that recurrences of the same variant in apparently unrelated families arose independently rather than from a shared founder. Roughly a fifth of isolated cases are de novo, arising during oogenesis in the mother.

Genetic context AVPR2 hgnc:897 variant_origin: GERMLINE zygosity: HEMIZYGOUS functional_impact_category: LOSS_OF_FUNCTION

Hemizygous in affected males. Heterozygous females are affected only when X-inactivation is skewed against the normal allele.

arginine vasopressin V2 receptor activity GO:0005000 ⇓ LOSS OF FUNCTION

Downstream

Absent or Truncated V2 Receptor Protein The protein-expression route, for variants that yield no usable receptor at all: nonsense, frameshift, large deletions and complex rearrangements. Transcription is not necessarily the failing step - mRNA was detectable for every mutant construct in the study cited here, while one frameshift allele produced no detectable protein.

Endoplasmic Reticulum Retention of Misfolded V2 Receptor The commonest route, and the one with a therapeutic handle. A misfolding missense or small in-frame variant is recognised by ER quality control and the receptor never reaches the membrane.

Signalling-Incompetent Cell-Surface V2 Receptor The functional route, for variants that fold well enough to pass ER quality control but cannot bind vasopressin or couple to Gs at the membrane.

Show evidence (2 references)

PMID:10820168 SUPPORT Human Clinical

"Among 117 families, there were 82 different putative disease-causing mutations. Based on haplotype analysis, it can be inferred that when the same AVPR2 mutation is identified in different families that were not known to be related, the mutations most likely arose independently."

Establishes the breadth and independence of the allelic spectrum.

PMID:10820168 SUPPORT Human Clinical

"A de novo mutation arose during oogenesis in the mother in 20% of isolated cases."

Quantifies the de novo contribution in isolated male cases.

Absent or Truncated V2 Receptor Protein

The third mechanistic class of AVPR2 loss of function, and the one that cannot be addressed by rescuing a receptor, because there is no receptor to rescue. Nonsense, frameshift, large-deletion and complex-rearrangement alleles yield absent, truncated or otherwise undetectable receptor protein. The step that fails is after transcription rather than at it: in the study cited here mRNA was produced for every mutant construct tested, yet the 804delG frameshift allele gave no receptor protein on Western blot. This node exists because the entry's own flagship animal model - the Glu242stop knock-in mouse - carries an allele of exactly this class, so without it the model's variant class had no route through the graph.

renal collecting duct principal cell CL:1001431

arginine vasopressin V2 receptor activity GO:0005000 ∅ ABSENT

Animal models

V2R Glu242stop knock-in mouse Mouse recapitulates Glu242stop is a nonsense allele, so this model belongs to the protein-expression class and this is the node it enters the pathograph at. Linked explicitly because the alternative - entering at the cascade node - would leave the model's own variant class unrepresented, which is the gap this link closes.

Downstream

Loss of Vasopressin-Stimulated cAMP and PKA Signalling No receptor protein means no coupling to Gs, so the cascade has no input. This is the simplest of the three routes into the cascade node and the only one for which pharmacochaperone rescue is inapplicable in principle.

Show evidence (2 references)

PMID:32138955 SUPPORT Other

"The mechanisms underlying a V2R loss-of-function can be theoretically classified as either protein expression, localization (ER retention) or functional disorders."

Names protein expression as the first of the three recognised loss-of-function classes. This entry models all three, one node each, because the review names three.

PMID:10820168 SUPPORT Human Clinical

"Among 117 families, there were 82 different putative disease-causing mutations."

Establishes the breadth of the allelic spectrum this class is drawn from. It does not apportion variants between the three classes, and no cited source here does.

Endoplasmic Reticulum Retention of Misfolded V2 Receptor

The pathognomonic cell-biological lesion of XNDI, and the reason the disease is a trafficking disorder rather than a ligand-recognition disorder. A misfolded V2 receptor is held in the endoplasmic reticulum by the same chaperone-based quality control that polices any nascent membrane protein; calnexin associates with the ER-retained receptor for longer than with the wild-type one. The receptor is often intrinsically capable of signalling - it is simply in the wrong compartment. That distinction is what makes pharmacochaperone rescue conceivable at all, and it is why a cell-permeable non-peptide ligand can restore membrane expression of a mutant receptor that a membrane-impermeant peptide agonist could never reach.

renal collecting duct principal cell CL:1001431

delivery of the V2 receptor to the plasma membrane GO:0072659 ↓ DECREASED protein folding in the endoplasmic reticulum GO:0034975 ⚠ ABNORMAL

endoplasmic reticulum GO:0005783

Experimental models

Polarized MDCK cells stably expressing V2 receptor mutants CELL LINE Cell-permeable non-peptide antagonists restored membrane expression and function of ER-retained mutants, which is the experimental demonstration that retention, not intrinsic receptor failure, is the rate-limiting lesion.

HEK293 cells expressing the S127F V2 receptor mutant CELL LINE Establishes the ER localization and the functional consequence for one patient variant, then partially reverses both with two chemically and pharmacologically different chaperones.

Downstream

Loss of Vasopressin-Stimulated cAMP and PKA Signalling A receptor held inside the cell cannot be occupied by circulating vasopressin, so the Gs-adenylyl cyclase cascade is never engaged.

Show evidence (3 references)

PMID:11389590 SUPPORT In Vitro

"Moreover, its association with the ER-retained R337X mutant was found to be longer than with the WT receptor suggesting that this molecular chaperone also plays a role in quality control and ER retention of misfolded G protein-coupled receptors."

Identifies calnexin-dependent ER quality control as the machinery doing the retaining, rather than leaving the retention unexplained.

PMID:31928727 SUPPORT Other

"In most of the cases, it is associated to inactivating mutations of the renal arginine-vasopressin V2 receptor leading to misfolding and intracellular retention of the receptor, causing the inability of patients to concentrate their urine in response to the antidiuretic hormone."

A review-level statement of the whole chain in one sentence - misfolding, retention, and the concentrating failure - and of the fact that this is the route in most cases. Cited as a synthesis claim rather than for any single experiment.

PMID:32138955 SUPPORT Other

"The mechanisms underlying a V2R loss-of-function can be theoretically classified as either protein expression, localization (ER retention) or functional disorders. Functional analyses have revealed however that these mechanisms are likely to be complex."

Places ER retention as one of three recognised loss-of-function classes, and records the reviewers' own caveat that the classes are not clean - which is why this entry keeps a separate surface-expressed node rather than collapsing them.

Signalling-Incompetent Cell-Surface V2 Receptor

The minority class of AVPR2 variants, in which the receptor folds well enough to be exported from the ER and delivered to the basolateral membrane of the principal cell but cannot transduce a vasopressin signal from there - either because hormone recognition is destroyed, or because coupling to Gs is. This node is kept separate from the ER-retention node because it carries a different therapeutic implication: a pharmacochaperone has nothing to correct.

renal collecting duct principal cell CL:1001431

vasopressin recognition by the V2 receptor GO:0017046 ∅ ABSENT arginine vasopressin V2 receptor activity GO:0005000 ∅ ABSENT

basolateral plasma membrane of the principal cell GO:0005886

Downstream

Loss of Vasopressin-Stimulated cAMP and PKA Signalling A surface receptor that cannot bind hormone or activate Gs leaves the cascade just as silent as an absent one.

Show evidence (1 reference)

PMID:11389590 SUPPORT In Vitro

"Thus, this mutation induces a conformational change that is compatible with endoplasmic reticulum (ER) export but dramatically affects hormone recognition."

States the defining property of this class: ER export is intact and hormone recognition is not.

Loss of Vasopressin-Stimulated cAMP and PKA Signalling

Vasopressin normally acts on the principal cell through a single linear cascade: V2 receptor occupancy activates the stimulatory G protein Gs, Gs activates adenylyl cyclase, cAMP rises, and cAMP activates protein kinase A. With no functional receptor at the membrane the cascade has no input. Note what is intact: the hormone, the G protein, the cyclase and PKA itself are all normal, which is the reason every experimental strategy for XNDI has aimed at re-entering the cascade below the receptor.

renal collecting duct principal cell CL:1001431

vasopressin-stimulated adenylyl cyclase signalling GO:0007189 ∅ ABSENT cAMP generation in the principal cell GO:0006171 ↓ DECREASED cellular response to vasopressin GO:1904117 ∅ ABSENT

protein kinase A activity downstream of the V2 receptor GO:0004691 ↓ DECREASED

Animal models

V2R Glu242stop knock-in mouse Mouse recapitulates A human XNDI nonsense allele at the orthologous position, producing the expected receptor-level loss of function in the intact animal.

Downstream

Failure of Aquaporin-2 Phosphorylation and Apical Insertion PKA activation is the step that couples the cascade to aquaporin-2; without it the water channel is neither phosphorylated nor redistributed.

Show evidence (2 references)

PMID:34055061 SUPPORT Other

"Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary concentrating ability, despite normal or elevated plasma concentrations of the antidiuretic hormone, arginine vasopressin (AVP)."

Establishes that hormone supply is intact, which is what locates the lesion in the cell's response rather than in the signal.

PMID:33664408 SUPPORT Other

"Among all AVP and OT receptors, V2R is the only one that activates the heterotrimeric Gsfamily to induce cAMP accumulation"

Establishes that no other vasopressin or oxytocin receptor can substitute for V2R on this cascade, which is why losing it silences cAMP generation outright rather than reducing it. Quoted as the cached text renders it, with the subscript of "Gs" run together with the following word.

Failure of Aquaporin-2 Phosphorylation and Apical Insertion

Aquaporin-2 is the vasopressin-regulated water channel of the principal cell, and it is regulated by being moved. PKA phosphorylates AQP2 at Ser256 and the channel is redistributed from intracellular vesicles into the apical membrane, where it makes the luminal surface water-permeable. In XNDI the AQP2 protein itself is normal - that is the defining feature separating this disease from the autosomal AQP2-mutation form - and the failure is purely one of regulation. It is also the reason the whole therapeutic literature is framed as "reach AQP2 without the receptor".

renal collecting duct principal cell CL:1001431

aquaporin-2 delivery to the apical plasma membrane GO:0072659 ↓ DECREASED regulation of aquaporin-2 water channel activity GO:1902427 ↓ DECREASED

apical plasma membrane of the principal cell GO:0016324

Animal models

V2R Glu242stop knock-in mouse Mouse partially recapitulates Supports the node in its important negative sense - that AQP2 abundance is not reduced, so the lesion is regulatory - without demonstrating the positive claim about phosphorylation and apical trafficking.

Avpr2-deficient rat (rGONAD) Rat recapitulates Directly measures both halves of this node in collecting duct cells - aquaporin-2 held in the cytoplasm, and its phosphorylation suppressed.

X-NDI mouse treated with a beta-3 adrenergic agonist Mouse rescues Pharmacological rescue of the node by a V2-receptor-independent route, with both the molecular step (AQP2 phosphorylation) and the whole-animal consequence measured.

Downstream

Collecting Duct Water Impermeability With no aquaporin-2 in the apical membrane the luminal surface of the duct is effectively impermeable to water.

Show evidence (2 references)

PMID:7537730 SUPPORT In Vitro

"Our data suggest that cAMP stimulates water permeability of AQP-CD by phosphorylation. This process may contribute to the vasopressin-regulated water permeability of collecting duct in addition to the apical insertion of AQP-CD by exocytosis."

The Xenopus oocyte experiment establishing cAMP-dependent phosphorylation as a mechanism by which the channel's water permeability is switched on, alongside apical exocytosis.

PMID:32924547 SUPPORT Other

"These patients have functional AQP2, and thus the challenge is to achieve AQP2 membrane insertion independently of V2R."

States that AQP2 is intact in XNDI, which is the claim that makes this node a regulatory failure rather than a channel defect.

Collecting Duct Water Impermeability

The collecting duct is the final site at which the kidney can return water to the body, and its water permeability is not constitutive - it exists only while aquaporin-2 is in the apical membrane. An XNDI collecting duct is therefore permanently in its dilute-urine configuration regardless of how dehydrated the patient is.

renal collecting duct principal cell CL:1001431

renal water absorption in the collecting duct GO:0070295 ↓ DECREASED

apical water channel activity GO:0015250 ↓ DECREASED

kidney collecting duct epithelium UBERON:0014388

Downstream

Failure of Medullary Countercurrent Urine Concentration The medullary osmotic gradient is still built, but an impermeable duct cannot equilibrate with it, so the gradient cannot be used to concentrate urine.

Show evidence (1 reference)

PMID:30454745 SUPPORT Other

"Nephrogenic diabetes insipidus (NDI) results from the inability of the late distal tubules and collecting ducts to respond to vasopressin."

Locates the functional lesion at the late distal tubule and collecting duct.

Failure of Medullary Countercurrent Urine Concentration

Urine concentration depends on two things: a corticomedullary osmotic gradient built by countercurrent multiplication in the loops of Henle, and a collecting duct able to equilibrate with it. XNDI breaks only the second. This is worth stating explicitly because it is the reason XNDI is a pure water-handling disease with normal solute excretion, and the reason the washout of the gradient by very high tubular flow is a secondary aggravation rather than the primary defect.

renal water homeostasis GO:0003091 ⚠ ABNORMAL transepithelial water transport in the medullary collecting duct GO:0035377 ↓ DECREASED

renal medulla UBERON:0000362

Downstream

Obligatory Hypotonic Free Water Loss

Show evidence (1 reference)

PMID:29797052 SUPPORT Other

"Central to this process of urine concentration is an osmotic gradient that increases from the corticomedullary boundary to the inner medullary tip."

Establishes the gradient that the impermeable collecting duct is unable to exploit. Cited for the normal physiology of the step, not for any claim about XNDI.

Obligatory Hypotonic Free Water Loss

The organism-level consequence: a fixed, large output of dilute urine that continues irrespective of plasma osmolality or volume status. Because it is obligatory rather than regulated, thirst is the only defence, and an affected person is dependent on continuous access to water. Adolescents and adults may void 10 to 15 litres a day.

regulation of urine volume GO:0035809 ⚠ ABNORMAL organism-level water homeostasis GO:0050891 ⚠ ABNORMAL

Animal models

V2R Glu242stop knock-in mouse Mouse recapitulates Hemizygous males died of hypernatraemic dehydration within the first postnatal week, and heterozygous females showed polyuria and polydipsia with reduced concentrating ability.

Downstream

Polyuria

Hyposthenuria

Polydipsia Thirst is the compensatory response to the water deficit, not an independent lesion.

Hypernatremia Free water is lost in excess of solute, so plasma sodium rises whenever intake fails to keep pace - which in an infant depends entirely on a carer.

Dehydration

Nocturnal enuresis The obligatory output does not pause overnight, so nocturia and bed-wetting follow directly from it rather than from any behavioural or bladder-capacity problem.

Failure to thrive Recorded with unknown intermediates deliberately. The association is well documented, but the route is not: a stomach filled with water displacing calories, anorexia and vomiting, and the metabolic cost of the water turnover are all plausible contributors and the cited sources do not apportion between them.

Short stature Same caveat. The height deficit persists after weight has recovered, which is itself an argument that it is not simply a caloric deficit, and no source cited here explains the difference.

Sustained High Urinary Tract Flow

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to concentrate the urine, which results in polyuria (excessive urine production) and polydipsia (excessive thirst)."

States that the concentrating failure is what produces the polyuria and the compensatory polydipsia, which is the causal content of this node's outgoing edges.

Sustained High Urinary Tract Flow

A mechanical consequence of the urine output, and the one most specific to long-standing untreated disease. Decades of very high flow through an anatomically normal urinary tract dilate it: the bladder becomes large and trabeculated, the ureters dilate, and the renal pelvis follows, all without any obstruction at the bladder outlet. The dilatation is not harmless - poor drainage of a huge compliant bladder raises residual volume, predisposes to infection, and can itself impair renal function.

Animal models

Avpr2-deficient rat (rGONAD) Rat recapitulates Hydronephrosis-like kidneys developed with no glomerular or tubular damage, which is the mechanical-not-nephropathic claim this node makes.

Downstream

Megacystis

Bladder trabeculation

Hydroureter

Hydronephrosis

Chronic kidney disease Through the dilated, poorly draining tract rather than directly: the intermediate is obstructive-type uropathy with raised residual volume. Recorded with known intermediates because those steps are named in the cited series, not because the quantitative relationship is established.

Show evidence (3 references)

PMID:22498392 SUPPORT Human Clinical

"The high flow states caused the bladder to become trabeculated in the absence of infravesical obstruction. Urodynamics have shown the bladder itself to be compliant, but drainage is poor leading to further renal impairment and overflow incontinence."

States the causal attribution to flow rather than obstruction, and the consequence for renal function, in the series that made the point.

PMID:20301356 SUPPORT Other

"Short stature and secondary dilatation of the ureters and bladder from the high urine volume is common in untreated individuals."

Attributes the ureteric and bladder dilatation specifically to the urine volume, and records that it is common rather than exceptional.

PMID:27258490 SUPPORT Human Clinical

"Radiographic examination revealed severe dilatation of bilateral renal pelvis, ureter, and bladder."

Shows the full extent the dilatation can reach in untreated disease, involving the renal pelvis as well as the lower tract.

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Pathograph

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Phenotypes

17

Digestive 2

Vomiting FREQUENT HP:0002013

Show evidence (1 reference)

PMID:10477148 SUPPORT Human Clinical

"Main symptoms at clinical presentation were vomiting and anorexia, failure to thrive, fever, and constipation."

The presenting-symptom list from the largest well-characterised clinical series, and the source for this phenotype, for Failure to thrive, for Fever and for Constipation.

Constipation OCCASIONAL HP:0002019

Show evidence (2 references)

PMID:10477148 SUPPORT Human Clinical

"Main symptoms at clinical presentation were vomiting and anorexia, failure to thrive, fever, and constipation."

Lists constipation as a presenting symptom.

PMID:40922895 SUPPORT Human Clinical

"Constipation and recurrent fever were observed in two patients (25.0%)."

The only proportion available for either constipation or recurrent fever, from a cohort of eight - so a small denominator, and the basis for the OCCASIONAL band on both phenotypes.

Genitourinary 8

Polyuria VERY_FREQUENT HP:0000103

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to concentrate the urine, which results in polyuria (excessive urine production) and polydipsia (excessive thirst)."

GeneReviews names polyuria as a defining feature of the disease.

Hyposthenuria VERY_FREQUENT HP:0003158

Show evidence (2 references)

PMID:34055061 SUPPORT Other

"Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary concentrating ability, despite normal or elevated plasma concentrations of the antidiuretic hormone, arginine vasopressin (AVP)."

States the concentrating failure that hyposthenuria is the measurement of, and pairs it with the intact hormone level that makes the finding diagnostic of a nephrogenic rather than a central defect.

PMID:7607658 SUPPORT Human Clinical

"Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and the absence of extra-renal responses to 1-desamino-8-D-arginine vasopressin was demonstrated in two of them."

Puts a number on the concentrating ceiling. Measured in symptomatic female heterozygotes rather than in hemizygous males, which is a limitation of this particular figure.

Hydronephrosis OCCASIONAL HP:0000126

Show evidence (2 references)

PMID:10477148 SUPPORT Human Clinical

"Two patients suffered from severe hydronephrosis with a small rupture of the urinary tract after a minor trauma, and two patients experienced episodes of acute urine retention."

Gives the frequency and the severity ceiling, including the rupture, in a defined cohort.

PMID:32039113 SUPPORT Human Clinical

"Adverse outcomes included inpatient hospitalizations (61%), urologic complications (37%), and chronic kidney disease (CKD) stage 2 or higher in 23%."

Puts urologic complications at 37 per cent of 66 children, which is the best available frequency figure for this group of phenotypes.

Hydroureter OCCASIONAL HP:0000072

Show evidence (1 reference)

PMID:34055061 SUPPORT Other

"Without treatment, most patients fail to grow normally, and present with associated constipation, urological complication, megacystis, trabeculated bladder, hydroureter, hydronephrosis, and mental retardation."

Lists the urological complications of untreated disease, and is the source for this phenotype, for Megacystis and for Bladder trabeculation.

Megacystis OCCASIONAL HP:0000021

Show evidence (2 references)

PMID:34055061 SUPPORT Other

"Without treatment, most patients fail to grow normally, and present with associated constipation, urological complication, megacystis, trabeculated bladder, hydroureter, hydronephrosis, and mental retardation."

Lists megacystis among the urological complications.

PMID:20301356 SUPPORT Other

"treat hydronephrosis, hydroureter, and megacystis with medical management to reduce urine output and continuous or intermittent bladder catheterization when post-void urinary bladder residuals are significant"

The management recommendation, which also establishes that significant post-void residual is the clinical problem megacystis creates.

Bladder trabeculation OCCASIONAL HP:0032465

Show evidence (1 reference)

PMID:22498392 SUPPORT Human Clinical

"The high flow states caused the bladder to become trabeculated in the absence of infravesical obstruction."

States that the trabeculation is flow-driven and that obstruction is absent, which is the whole point of this phenotype.

Chronic kidney disease OCCASIONAL HP:0012622

Show evidence (3 references)

PMID:32039113 SUPPORT Human Clinical

"Adverse outcomes included inpatient hospitalizations (61%), urologic complications (37%), and chronic kidney disease (CKD) stage 2 or higher in 23%."

The cohort figure, and the source for the hospitalisation and urologic-complication rates quoted elsewhere in this entry.

PMID:39644399 SUPPORT Human Clinical

"Interestingly, this mutation was also identified in the patient's maternal grandfather, who had never been diagnosed or treated for NDI despite a history of polydipsia, polyuria, and evidence of chronic kidney disease (CKD), severe bilateral hydronephrosis, hypertension, and severe bladder dysfunction."

The within-family treated-versus-untreated contrast, which is as close to a natural history experiment as this disease offers.

PMID:40922895 REFUTE Human Clinical

"Renal function, serum sodium, and imaging findings remained stable throughout follow-up."

Cuts against CKD being an expected outcome of this disease as such. Over a median 16.9 years on hydrochlorothiazide and amiloride, renal function did not decline in this cohort - which is why the phenotype is framed as a consequence of undertreated disease.

Nocturnal enuresis OCCASIONAL Enuresis nocturna HP:0010677

Show evidence (1 reference)

PMID:34055061 SUPPORT Other

"excessive urination during the night (nocturia), or bedwetting at night (nocturnal enuresis)"

Names nocturia and nocturnal enuresis among the presenting features of the disease in children.

Metabolism 3

Hypernatremia FREQUENT HP:0003228

Sequelae: Intellectual disability

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"Evaluation of at-risk infants as early as possible to allow for prompt diagnosis and treatment to reduce morbidity from hypernatremia, dehydration, and dilatation of the urinary tract."

GeneReviews names hypernatraemia as a source of morbidity that early diagnosis exists to reduce.

Dehydration FREQUENT HP:0001944

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"Affected untreated infants usually have poor feeding and failure to thrive, and rapid onset of severe dehydration with illness, hot environment, or the withholding of water."

Gives both the pediatric context and the specific precipitants, which is the clinically actionable part of this phenotype.

Fever OCCASIONAL HP:0001945

Show evidence (3 references)

PMID:10477148 SUPPORT Human Clinical

"Main symptoms at clinical presentation were vomiting and anorexia, failure to thrive, fever, and constipation."

Lists fever as a presenting symptom.

PMID:40922895 SUPPORT Human Clinical

"Constipation and recurrent fever were observed in two patients (25.0%)."

Gives a proportion for recurrent fever, in a cohort of eight.

PMID:27258490 SUPPORT Human Clinical

"Transient insertion of a urethral catheter helped to relieve fever."

Supports the second, mechanically distinct cause of fever in established disease - stasis and infection in a poorly draining dilated tract.

Nervous System 2

Polydipsia VERY_FREQUENT HP:0001959

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to concentrate the urine, which results in polyuria (excessive urine production) and polydipsia (excessive thirst)."

GeneReviews names polydipsia as a defining feature.

Intellectual disability OCCASIONAL HP:0001249

Show evidence (4 references)

PMID:34055061 SUPPORT Other

"Without treatment, most patients fail to grow normally, and present with associated constipation, urological complication, megacystis, trabeculated bladder, hydroureter, hydronephrosis, and mental retardation."

The review lists this among the consequences of untreated disease.

PMID:34055061 SUPPORT Other

"Irreversible brain damage and cognitive deficit secondary to electrolyte imbalances may be present."

The review's own causal statement, quoted with its hedge intact. It is the basis for the sequela edge from Hypernatremia and for the knowledge gap attached to this phenotype.

PMID:40922895 SUPPORT Human Clinical

"Neurodevelopmental disorders were identified in six patients, including intellectual disability, autism spectrum disorder, language delay, and learning difficulties."

The numerator and the range of diagnoses, in a cohort of eight followed for a median of 16.9 years. This is the observation that makes the "usually normal with early treatment" teaching hard to sustain unexamined.

+ 1 more reference

Growth 2

Failure to thrive FREQUENT HP:0001508

Show evidence (4 references)

PMID:10477148 SUPPORT Human Clinical

"Main symptoms at clinical presentation were vomiting and anorexia, failure to thrive, fever, and constipation."

Lists failure to thrive among the presenting features in 30 patients.

PMID:29162216 SUPPORT Human Clinical

"The most common intervention for FFT was gastrostomy tube placement (78%)."

Indicates the severity: most surveyed paediatric nephrologists reach for a gastrostomy. Note the survey's own typo in the abbreviation, quoted as published.

PMID:32039113 SUPPORT Human Clinical

"At the time of first treatment, 70 and 71% of children were below -2 standard deviations (SD) for weight and height, respectively. At last follow-up, median age was 72.3 months (IQR 40.9, 137.2) and the percentage below -2 SD improved to 29% and 38% for weight and height, respectively."

Quantifies both the deficit at diagnosis and the partial recovery on treatment, in 66 children. It is also the source for the claim that weight recovers further than height: 70 to 29 per cent against 71 to 38 per cent.

+ 1 more reference

Short stature FREQUENT HP:0004322

Show evidence (3 references)

PMID:10477148 SUPPORT Human Clinical

"Height SD scores for age remained below the 50th percentile in the majority of patients, whereas weight for height SD scores showed a catch-up after several years of underweight."

States both the persistence of the height deficit and the contrast with weight, in a long-term follow-up cohort.

PMID:20301356 SUPPORT Other

"Short stature and secondary dilatation of the ureters and bladder from the high urine volume is common in untreated individuals."

GeneReviews records short stature as common in untreated individuals.

PMID:32039113 SUPPORT Human Clinical

"Hospitalizations, urologic complications, short stature, and CKD were common."

The cohort's own summary of its outcome findings, naming short stature among the common ones.

🧬

Genetic Associations

1

AVPR2

Gene: AVPR2 hgnc:897 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (6 references)

PMID:20301356 SUPPORT Other

"Hereditary NDI is most commonly inherited in an X-linked manner (~90% of individuals). Hereditary NDI can also be inherited in an autosomal recessive manner (~9% of individuals) or in an autosomal dominant manner (~1% of individuals)."

Gives the share of hereditary NDI attributable to the X-linked AVPR2 form and the shares of the two autosomal AQP2 forms, which is what locates this entry within the group.

PMID:20301356 SUPPORT Other

"The diagnosis of hereditary NDI is established in a male proband with NDI by identification of a hemizygous pathogenic variant in AVPR2 or identification of a compound heterozygous or homozygous pathogenic variant in AQP2 by molecular genetic testing."

Establishes hemizygous AVPR2 variation as the diagnostic criterion in a male proband, and names the AQP2 alternative that has to be excluded.

PMID:10477148 SUPPORT Human Clinical

"Except for a possibly milder phenotype in patients with a G185C mutation, no clear relationship between clinical and genetic data could be found."

The basis for not asserting genotype-phenotype correlation, and for the single hedged exception.

+ 3 more references

💊

Medical Actions

7

Free Access to Water

Action: free access to drinking water and toilet facilities Ontology label: Supportive Care NCIT:C15747

Platform: Behavioral / lifestyle

The foundation of management and the one intervention that is non-negotiable. Because the water loss is obligatory, thirst-driven intake is the only compensation, so restricting water - including the routine nil-by-mouth before a procedure - converts a manageable chronic condition into acute hypernatraemia. GeneReviews lists water restriction explicitly under agents and circumstances to avoid, and specifies that a patient who must be nil by mouth receives their usual oral water intake intravenously as 5 per cent dextrose rather than saline.

Mechanism Target:

MODULATES Obligatory Hypotonic Free Water Loss — It does not reduce the water loss at all; it replaces it. Recorded as MODULATES rather than INHIBITS for that reason.

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"free access to drinking water and to toilet facilities"

The management measure itself, as GeneReviews words it. It is the replacement of the loss, not its reduction, which is why the effect is MODULATES.

Show evidence (2 references)

PMID:20301356 SUPPORT Other

"Water intake must not be restricted."

The GeneReviews agents-to-avoid statement. Short, but it is the complete proposition and it is the single most important management instruction in the disease.

PMID:20301356 SUPPORT Other

"when "NPO" (nothing per ora), individuals with NDI must have intravenous replacement of their usual oral intake of water as 5% dextrose in water"

The specific peri-procedural instruction, including the fluid to use, which is where this goes wrong in practice.

Thiazide Diuretic

Action: Pharmacotherapy NCIT:C15986

Agent: hydrochlorothiazide CHEBI:5778

Platform: Small molecule

The counterintuitive mainstay: a diuretic given to reduce urine output. Used with a low-sodium diet it reduces polyuria by up to 50 per cent without causing hypernatraemia, and it is the one drug on which paediatric nephrologists agree - 93 per cent of surveyed providers prescribe a thiazide. The mechanism is indirect and does not involve the collecting duct at all: the thiazide causes natriuresis, sodium depletion follows, and the resulting fall in effective renal plasma flow and glomerular filtration rate reduces distal delivery. Work in Brattleboro rats showed the antidiuresis disappears when sodium depletion is prevented, and that under those conditions urine volume actually rises - evidence that the antidiuretic effect is entirely secondary to volume contraction, with an additional suggestion of reduced proximal fluid reabsorption. Note the model caveat: those experiments used the hypothalamic (central) form of the disease, not a receptor-level one. On efficacy: serum sodium normalised in every patient of one long-term cohort on hydrochlorothiazide plus amiloride, but polyuria and polydipsia persisted in all of them throughout a median of 16.9 years - which is the honest summary of what this regimen achieves. It protects against hypernatraemia; it does not fix the water loss.

Mechanism Target:

MODULATES Obligatory Hypotonic Free Water Loss — Reduces the volume of the obligatory loss by reducing distal delivery, through volume contraction. It does not restore collecting duct water permeability and does not touch the receptor defect.

Show evidence (1 reference)

PMID:630797 SUPPORT INDIRECT Model Organism

"The results indicate that the antidiuresis caused by hydrochlorothiazide in diabetes insipidus results, at least in part, from falls in effective renal plasma flow and glomerular filtration rate. These in turn seem to be entirely secondary to the drug-induced sodium depletion."

Establishes the mechanism of the antidiuresis, in the only experiment cited here that manipulated sodium balance to test it. Marked INDIRECT because the model is the hypothalamic form of diabetes insipidus, so the finding transfers to XNDI by the argument that the drug acts upstream of the collecting duct rather than by direct demonstration in a V2 receptor-deficient animal.

Show evidence (4 references)

PMID:20301356 SUPPORT Other

"reduction of polyuria (and thus polydipsia) up to 50% without inducing hypernatremia by use of a thiazide diuretic (e.g., hydrochlorothiazide, chlorothiazide) often used in combination with either amiloride (a potassium-sparing diuretic) or indomethacin; dietary restriction of sodium"

Quantifies the achievable benefit, names the agents, and records that the thiazide is normally combined with amiloride or indomethacin and paired with sodium restriction.

PMID:40922895 SUPPORT Human Clinical

"Over a median follow-up period of 16.9 years (IQR: 8.4-17.4), growth improved, but all patients continued to exhibit polyuria and polydipsia."

The ceiling on what the regimen does: growth improves, the polyuria does not go away. This is the sentence that keeps the treatment framed as symptomatic.

PMID:29162216 SUPPORT Human Clinical

"Our results suggest consensus on the use of thiazides, while the use of indomethacin is limited by GI and renal side effect profile."

Establishes the thiazide as the point of consensus and locates the disagreement at indomethacin.

+ 1 more reference

Amiloride

Action: Pharmacotherapy NCIT:C15986

Agent: amiloride CHEBI:2639

Platform: Small molecule

A potassium-sparing diuretic added to a thiazide, prescribed by 62 per cent of surveyed paediatric nephrologists. Two reasons are given in the literature for preferring it as the partner drug: it offsets the thiazide's potassium loss, and it avoids the gastrointestinal and renal toxicity that limits indomethacin. The combination was the maintenance regimen for most patients in the 30-patient series, reportedly without significant side effects.

Mechanism Target:

MODULATES Obligatory Hypotonic Free Water Loss — Acts as an adjunct to the thiazide's volume-contraction effect rather than through a mechanism of its own that has been demonstrated in this disease.

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"often used in combination with either amiloride (a potassium-sparing diuretic) or indomethacin; dietary restriction of sodium"

Places amiloride as the thiazide's partner drug rather than as an independent treatment, which is what this link records.

Show evidence (4 references)

PMID:29162216 SUPPORT Human Clinical

"almost all prescribed thiazides (93%), 62% prescribed amiloride, and 55% reported prescribing nonsteroidal anti-inflammatory drugs (NSAIDs) as part of their drug regimen."

Gives the prescribing proportions for all three drug classes in this entry, from a survey of 72 paediatric nephrologists.

PMID:10477148 SUPPORT Human Clinical

"Most patients were on hydrochlorothiazide-amiloride treatment without significant side effects."

Supports the combination as the usual long-term regimen and records its tolerability in a followed cohort.

PMID:40922895 SUPPORT Human Clinical

"All patients were treated with hydrochlorothiazide and amiloride; indomethacin was added in 5 (62.5%)."

The thiazide-amiloride pair was universal in this cohort and indomethacin was the add-on, which is the same hierarchy the larger cohort shows at different proportions.

+ 1 more reference

Indomethacin or Other NSAID

Action: Pharmacotherapy NCIT:C15986

Agent: indomethacin CHEBI:49662

Platform: Small molecule

A prostaglandin synthesis inhibitor used as the alternative third agent. It works - and is prescribed by 55 per cent of surveyed providers - but it is the contested part of the regimen: 43 per cent of providers who avoid it cite gastrointestinal and renal side effects, which in a child with an already compromised urinary tract is not a trivial concern. The usual rationale is that renal prostaglandin E2 opposes the concentrating mechanism, so removing it helps, and that step is now cited here: PGE2 reverses vasopressin-induced translocation of aquaporin-2 to the plasma membrane in rat inner medulla, acting by activating retrieval of the channel. Two caveats keep this from being a clean explanation of the drug's benefit in this disease, and they are the reason the mechanism link below is still only MODULATES. First, what PGE2 was shown to reverse was vasopressin-induced translocation - a process that does not occur in a V2 receptor-null kidney, so the demonstrated mechanism presupposes the very signalling this disease lacks. Second, in the same experiments PGE2 on its own did not alter aquaporin-2 phosphorylation or distribution at all, which argues against a standing PGE2 brake that an NSAID could release in the absence of vasopressin action. The benefit is real and well attested clinically; the route by which it is obtained in a receptor-null kidney is not established by anything cited here.

Mechanism Target:

MODULATES Obligatory Hypotonic Free Water Loss — Kept as MODULATES rather than upgraded. The candidate mechanism - relieving a PGE2 brake on apical aquaporin-2 retention - is now cited, but it was demonstrated as an antagonism of vasopressin-induced trafficking, which does not happen in this disease, and PGE2 alone moved neither aquaporin-2 phosphorylation nor its distribution. So the drug's clinical effect is attested and its route through this node is not.

Show evidence (2 references)

PMID:10710543 SUPPORT INDIRECT In Vitro

"PGE(2) (10(-7) M) added after AVP (10(-8) M) did not decrease AQP2 phosphorylation but reversed AVP-induced translocation of AQP2 to the plasma membrane."

The mechanistic step behind the rationale, and the reason it is marked INDIRECT: the effect measured is reversal of vasopressin-induced translocation in a kidney with intact vasopressin signalling, so applying it to a V2 receptor-null kidney is an inference rather than a demonstration.

PMID:10710543 REFUTE In Vitro

"PGE(2) alone did not influence AQP2 phosphorylation and subcellular distribution."

Cuts against the simple version of the rationale. If PGE2 exerts no effect without vasopressin, then removing PGE2 should not by itself restore apical aquaporin-2 in a receptor-null kidney, which is why the effect on this node is not upgraded.

Show evidence (4 references)

PMID:10710543 SUPPORT In Vitro

"Our data indicate that 1) recruitment of AQP2 to the plasma membrane and its retrieval to a pool of intracellular vesicles may be regulated independently, 2) PGE(2) may counteract AVP action by activation of AQP2 retrieval, 3) dephosphorylation of AQP2 is not a prerequisite for its internalization."

The authors' own three conclusions. The second is the prostaglandin rationale for using an NSAID; the first and third matter separately for this entry, because they show aquaporin-2 phosphorylation and apical retention are separable - see the note on the naming of the aquaporin-2 node.

PMID:29162216 SUPPORT Human Clinical

"gastrointestinal (GI) and renal side effects (43%) were given as reasons for not prescribing indomethacin."

The reason indomethacin is not used universally, quantified.

PMID:40922895 SUPPORT Human Clinical

"All patients were treated with hydrochlorothiazide and amiloride; indomethacin was added in 5 (62.5%)."

Gives the proportion receiving indomethacin as an addition to the thiazide-amiloride base, in a cohort of eight.

+ 1 more reference

Low-Solute, Sodium-Restricted Diet

Action: low-solute, sodium-restricted diet Ontology label: Dietary Intervention NCIT:C15447

Platform: Behavioral / lifestyle

Diet:

A dietary rather than pharmacological intervention, and a necessary partner to the thiazide: because the obligatory urine volume is set by the solute load that has to be excreted, reducing dietary solute - principally sodium - reduces the volume directly. This is the correct slot for the diet, not a drug with an agent binding. The accompanying nutritional problem pulls the other way, since an infant with failure to thrive needs calories, which is why dietitian involvement is standard and why a gastrostomy is often how both requirements are met at once.

Mechanism Target:

MODULATES Obligatory Hypotonic Free Water Loss — Lowers the solute load whose excretion obliges the water loss, reducing its volume without affecting the collecting duct defect.

Show evidence (1 reference)

PMID:30454745 SUPPORT Other

"Management of NDI can be difficult with only symptomatic treatment available, using low-solute diet, diuretics, and prostaglandin inhibitors."

Names the low-solute diet as one of the measures acting on the polyuria, and states that it is symptomatic - which is the limit of what this link claims.

Show evidence (2 references)

PMID:20301356 SUPPORT Other

"often used in combination with either amiloride (a potassium-sparing diuretic) or indomethacin; dietary restriction of sodium"

GeneReviews lists sodium restriction among the management measures, in the same clause that names the drug combinations it accompanies.

PMID:30454745 SUPPORT Other

"Management of NDI can be difficult with only symptomatic treatment available, using low-solute diet, diuretics, and prostaglandin inhibitors."

Names the low-solute diet as one of the three available measures, and states plainly that all of them are symptomatic.

Urinary Tract Management and Bladder Drainage

Action: bladder catheterisation and timed voiding Ontology label: Supportive Care NCIT:C15747

Platform: Device

Management of the mechanical complication rather than the metabolic one. The principles are to reduce urine output with drug and dietary therapy, void on a schedule - two-hourly is the interval recommended - and catheterise when post-void residuals become significant. In severe cases cystostomy button drainage has been used. The point of the scheduled voiding is prevention: it is offered as a way of preventing or reducing the tract dilatation rather than treating it once established.

Mechanism Target:

MODULATES Sustained High Urinary Tract Flow — Addresses the consequence of the flow - poor drainage and residual urine - and, via timed voiding, reduces the dwell time that drives the dilatation.

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"Reduction of urine production by drug therapy and voiding at two-hour intervals may prevent or reduce serious renal, ureteral, or bladder dilatation."

States the intervention acting on the flow consequence, with the source's own "may".

Show evidence (2 references)

PMID:20301356 SUPPORT Other

"Reduction of urine production by drug therapy and voiding at two-hour intervals may prevent or reduce serious renal, ureteral, or bladder dilatation."

The preventive recommendation and its stated interval, quoted with the source's own "may".

PMID:22498392 SUPPORT Human Clinical

"All 4 boys have been managed with cystostomy button drainage and have done well on close follow-up."

The reported surgical drainage approach in the severe end of the spectrum. Four patients with no comparator, so it supports that this is done, not that it is superior.

Genetic Counselling and Testing of At-Risk Relatives

Action: Genetic Counseling NCIT:C15240

Platform: Behavioral / lifestyle

Counselling follows ordinary X-linked logic, with the caveat that a heterozygous female is not reliably unaffected. The substantive clinical point is that identifying an at-risk infant early is itself a treatment: GeneReviews frames early evaluation of at-risk infants as the way to reduce morbidity from hypernatraemia, dehydration and tract dilatation, all three of which are cumulative and partly preventable.

Show evidence (2 references)

PMID:20301356 SUPPORT Other

"Evaluation of at-risk infants as early as possible to allow for prompt diagnosis and treatment to reduce morbidity from hypernatremia, dehydration, and dilatation of the urinary tract."

States the rationale for cascade testing in terms of the specific morbidities it prevents.

PMID:39438674 SUPPORT Other

"Here, we present 36 recommendations for diagnosis, treatment and follow-up in both children and adults, as well as emergency management, genetic counselling and family planning, for patients with NDI."

Establishes that genetic counselling and family planning are within the scope of the graded international recommendations for this disease, rather than being an informal addition to management.

🔬

Biochemical Markers

2

Urine osmolality (Decreased)

Context: The measurement that defines the disease and the one that does not move when desmopressin is given. In symptomatic AVPR2 heterozygous females maximal urine osmolality did not exceed 200 mosmol/kg, against a normal maximum several times that, and the same non-response was demonstrable outside the kidney in two of them. No reference interval is curated here: no citable record in this round gave one, and the 200 mosmol/kg figure is a reported ceiling in three patients, not an interval.

Pathograph Readouts

Readout Of Failure of Medullary Countercurrent Urine Concentration Threshold Dependent Diagnostic

Directly reports the concentrating failure this node describes, and is threshold-dependent rather than simply low because the diagnostic question is the maximum achievable after water deprivation or desmopressin, not a single value.

Show evidence (1 reference)

PMID:7607658 SUPPORT Human Clinical

"Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and the absence of extra-renal responses to 1-desamino-8-D-arginine vasopressin was demonstrated in two of them."

Gives the measured ceiling in affected patients. Measured in symptomatic female heterozygotes, which is a limitation of this particular figure rather than of the readout.

Show evidence (1 reference)

PMID:34055061 SUPPORT Other

"Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary concentrating ability, despite normal or elevated plasma concentrations of the antidiuretic hormone, arginine vasopressin (AVP)."

Establishes impaired urinary concentrating ability as the defining abnormality this marker measures, alongside an intact hormone level.

Serum sodium (Increased)

Context: The marker of decompensation rather than of the disease, and the one on a surveillance schedule: three-monthly in infants, six-monthly in older children, annually or as needed in adults. The reason it is monitored rather than measured only when someone looks unwell is that hyperosmolality and early dehydration can be present without being recognised clinically.

Pathograph Readouts

Readout Of Hypernatremia Positive Monitoring

The measurement the phenotype is defined by, used here as the monitoring marker for unrecognised water deficit rather than as a diagnostic test for the disease.

Show evidence (1 reference)

PMID:20301356 SUPPORT Other

"measurement of serum sodium concentration to identify unrecognized hyperosmolality and early dehydration at least every three months in infants, at least every six months in older children, and annually in adults or only as needed"

States the monitoring purpose and the schedule, which is what makes this a MONITORING rather than DIAGNOSTIC readout.

🔬

Diagnosis

4

Molecular genetic testing of AVPR2 (PRESENT)

The diagnostic test. A hemizygous pathogenic AVPR2 variant establishes the diagnosis in a male proband; a heterozygous one does so in a female proband, in whom an X-inactivation study is then informative about why she is symptomatic. The alternative to exclude is biallelic AQP2 variation, which gives a clinically indistinguishable phenotype with different inheritance and different counselling.

Show evidence (2 references)

PMID:20301356 SUPPORT Other

"The diagnosis of hereditary NDI is usually established in a female proband with NDI by identification of a heterozygous pathogenic variant in AVPR2 or identification of a compound heterozygous or homozygous pathogenic variant in AQP2 by molecular genetic testing."

The diagnostic criterion in a female proband, which is the half of this that is easy to get wrong.

PMID:32039113 SUPPORT Human Clinical

"Genetic testing or a known family history was present in 70% of the patients; out of those genetically tested, 89 and 11% had mutations in AVPR2 and AQP2, respectively."

A real-world check on the textbook 90:10 split, and a reminder that 30 per cent of a contemporary cohort had neither genetic testing nor a family history.

Water deprivation test (PRESENT)

The classical confirmatory test, and the one this entry has to carry a safety caveat about rather than simply list. Water deprivation testing is contraindicated in the presence of hypernatraemia - serum sodium above 145 mmol/L - because of the risk of severe dehydration, and in practice the threshold used also includes plasma osmolality above 295 mOsm/kg. In that situation the desmopressin challenge is performed alone, without prior restriction. This matters more in this disease than the general caveat suggests: the median serum sodium at diagnosis in one cohort was 160.5 mmol/L, so the typical patient presents already past the threshold at which the test is unsafe. Where serum sodium is high or high-normal and the urine is inappropriately dilute, the diagnosis can be made without water restriction at all.

Show evidence (3 references)

PMID:40922895 SUPPORT Human Clinical

"Water deprivation testing is contraindicated in the presence of hypernatremia (serum sodium > 145 mmol/L) due to the risk of severe dehydration."

The contraindication and its stated reason. Quoted from the cached full text of this paper, not from a secondary summary.

PMID:40922895 SUPPORT Human Clinical

"Water restriction was contraindicated in cases with plasma osmolality (osm(p)) > 295 mOsm/kg and/or serum sodium > 145 mmol/L; in such instances, only the desmopressin challenge was performed."

The operational rule as this centre applied it, which adds the osmolality limb of the threshold and states what is done instead.

PMID:40922895 SUPPORT Human Clinical

"In patients with elevated or high-normal serum sodium and inappropriately dilute urine, the diagnosis of diabetes insipidus can be established without the need for water restriction"

States that the test can be dispensed with altogether in the situation this disease usually presents in, which is the practical consequence of the contraindication.

Basal plasma copeptin (PRESENT)

Copeptin is the stable C-terminal fragment of the vasopressin prohormone and stands in for a hormone that is itself unstable and largely platelet-bound. It is unusually well suited to this disease: because the lesion is downstream of normal or raised vasopressin secretion, an unstimulated basal copeptin measurement is sufficient to diagnose nephrogenic diabetes insipidus, where separating central diabetes insipidus from primary polydipsia needs a stimulation test. That asymmetry is the point - the test that is hard for the other two entities in the differential is easy for this one, and it avoids a water deprivation test that is contraindicated in most patients here. No numeric cutoff is curated: see the note on the unverified 21.4 pmol/L figure.

Show evidence (2 references)

PMID:32374887 SUPPORT Other

"Whereas unstimulated basal copeptin measurement reliably diagnoses nephrogenic diabetes insipidus, two new tests using stimulated copeptin cutoff levels showed a high diagnostic accuracy in differentiating central diabetes insipidus from primary polydipsia."

The claim curated here, and the asymmetry that makes basal copeptin a good test for this disease specifically rather than for the polyuria-polydipsia syndrome generally.

PMID:32387127 SUPPORT Other

"While unstimulated basal copeptin measurement reliably diagnoses nephrogenic diabetes insipidus, a stimulation test is needed to differentiate patients with central diabetes insipidus from patients with primary polydipsia."

An independent statement of the same asymmetry by a different review, which is why both are cited rather than one.

Failure to concentrate urine after desmopressin (PRESENT)

The physiological discriminator between nephrogenic and central diabetes insipidus. A nephrogenic kidney does not concentrate urine when given exogenous vasopressin or desmopressin, because the defect is downstream of the hormone. Note that in the AVPR2 form the absence of response is not confined to the kidney: extrarenal V2 receptor responses to desmopressin, such as the rise in coagulation factors, are also absent, and that was used as confirmatory evidence in symptomatic female heterozygotes.

Show evidence (3 references)

PMID:7607658 SUPPORT Human Clinical

"Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and the absence of extra-renal responses to 1-desamino-8-D-arginine vasopressin was demonstrated in two of them."

Gives both the renal non-response with a numeric ceiling and the extrarenal non-response specific to a receptor-level lesion.

PMID:40922895 SUPPORT Human Clinical

"All desmopressin tests were negative."

Every patient in the cohort failed to respond, which is the consistency that makes a negative desmopressin test useful rather than merely suggestive.

PMID:32039113 SUPPORT Human Clinical

"A desmopressin acetate loading test was administered to 46% of children at a median age of 4.8 months (IQR 2.8, 7.6); only 15% had a water restriction test."

Shows what is actually done: fewer than half had a desmopressin test and only 15 per cent a water restriction test, so in practice the diagnosis is often made without either.

📈

Progression

3

Neonatal period and infancy

This is where the disease is dangerous and where it is missed. The presentation is not polyuria and thirst; it is a vomiting, anorexic, poorly growing infant with unexplained fever who dehydrates rapidly with any intercurrent illness, hot weather, or withholding of water. Most patients - 87 per cent in the largest series - are diagnosed within the first two and a half years, which is another way of saying that a substantial minority are not. Because the infant cannot drink to thirst unaided, carer-dependent water supply is the only thing preventing hypernatraemia, and being nil by mouth for a procedure is a specific hazard.

Show evidence (5 references)

PMID:10477148 SUPPORT Human Clinical

"The majority of patients (87%) were diagnosed within the first 2.5 yr of life. Main symptoms at clinical presentation were vomiting and anorexia, failure to thrive, fever, and constipation."

Gives both the timing of diagnosis and the presenting symptom set.

PMID:20301356 SUPPORT Other

"Affected untreated infants usually have poor feeding and failure to thrive, and rapid onset of severe dehydration with illness, hot environment, or the withholding of water."

Names the precipitants of decompensation in infancy.

PMID:32039113 SUPPORT Human Clinical

"Median age at diagnosis was 4.2 months interquartile range (IQR 1.1, 9.8)."

The best available figure for age at diagnosis, from 66 children across 16 centres. Note the upper quartile: a quarter were diagnosed after ten months.

+ 2 more references

Childhood

Once water is freely available and drug therapy started, the acute danger recedes and the problem becomes chronic: polyuria, polydipsia, nocturia and bed-wetting, weight that eventually catches up, and height that largely does not. Growth and electrolyte surveillance is recommended three-monthly in infants and six-monthly in older children, with annual renal ultrasound for the urinary tract.

Show evidence (2 references)

PMID:20301356 SUPPORT Other

"Monitor growth and development at least every three months in infants and at least every six months in older children; measurement of serum sodium concentration to identify unrecognized hyperosmolality and early dehydration at least every three months in infants, at least every six months in..."

The surveillance schedule, which is also an implicit statement of what the expected complications are at each age.

PMID:10477148 SUPPORT Human Clinical

"Height SD scores for age remained below the 50th percentile in the majority of patients, whereas weight for height SD scores showed a catch-up after several years of underweight."

The long-term growth trajectory, distinguishing height from weight.

Adolescence and adulthood

The urinary tract consequences dominate late. Dilatation accumulates silently over years of high flow and can reach severe hydronephrosis with megacystis, poor bladder drainage, recurrent infection and impaired renal function; one reported adolescent was voiding 10 to 15 litres daily with dilatation of pelvis, ureter and bladder. One review also notes an apparent loss of efficacy of medical treatment during school age, which if real is a reason not to assume a stable regimen lasts.

Show evidence (3 references)

PMID:34055061 SUPPORT Other

"Some authors note a generally favorable long-term outcome and an apparent loss of efficacy of medical treatment during school age."

Records both halves as the review states them: a generally favourable outcome, and an apparent waning of treatment effect. Attributed to "some authors" in the source, and reproduced with that attribution rather than asserted.

PMID:22498392 SUPPORT Human Clinical

"Urodynamics have shown the bladder itself to be compliant, but drainage is poor leading to further renal impairment and overflow incontinence."

States the late renal consequence of the dilated tract and the urodynamic finding that distinguishes it from an obstructive or non-compliant bladder.

PMID:39644399 SUPPORT Human Clinical

"The untreated grandfather's case highlights the potential severity of untreated NDI and the benefits of timely therapeutic intervention."

The authors' reading of their own two-generation comparison, which is the closest approach to untreated natural history the literature offers for this disease.

📊

Prevalence

1

Quebec, Canada (male live births)

Birth Prevalence 0.88 per 100,000 live births 1–9 per 1,000,000 (births)

8.8 per million male live births. The denominator is male live births, not all live births, which matters for an X-linked disease: the rate among all newborns is about half this. The same report notes a regional rate more than six times higher in Nova Scotia and New Brunswick, a founder effect rather than a different population estimate, so the Quebec figure is the one quoted here.

Show evidence (1 reference)

PMID:10820168 SUPPORT Human Clinical

"The estimate of about 8.8 per million male live births of the incidence of X-linked NDI in the province of Quebec, Canada may be representative of the general population except in Nova Scotia and New Brunswick, where the incidence is more than six times higher."

The source of both the rate and its denominator, and of the caveat about the Maritime founder population.

🔬

Clinical Trials

1

NCT07525960 PHASE_I RECRUITING

The only interventional trial identified for this disease, and the first to test a treatment aimed at the mechanism rather than at the urine volume. NDI-5001 is given as a capsule in daily oral doses to adult males with X-linked congenital nephrogenic diabetes insipidus due to V2 receptor mutations, with safety, pharmacokinetics and pharmacodynamics as the endpoints. Note what the registration does and does not say: it specifies the population by genotype, which is unusual and useful, but a Phase 1b safety and pharmacodynamic study establishes nothing about clinical benefit. The trial's own record does not name the drug's mechanism, so none is asserted here.

Target Phenotypes: Polyuria HP:0000103

Show evidence (1 reference)

clinicaltrials:NCT07525960 SUPPORT Other

"The primary purpose of this trial is to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of NDI-5001 administered as a capsule following daily oral dosing in adult males with X-linked congenital nephrogenic diabetes insipidus (NDI) due to vasopressin receptor..."

The registration record, which establishes the trial's existence, its phase, its genotype-defined population and its endpoints - and nothing about efficacy.

🧫

Experimental Models

2

Polarized MDCK cells stably expressing V2 receptor mutants CELL_LINE

The system in which the pharmacochaperone idea was tested properly. Nine different disease-causing V2 receptor mutants were stably expressed in polarized MDCK cells - which matters, because a receptor's destination is the basolateral membrane and an unpolarized cell cannot report on that. Four cell-permeable non-peptide antagonists rescued maturation and basolateral expression of eight of the nine mutants. The study's real contribution is the constraint it found: rescue at concentrations a patient could actually receive required high-affinity antagonists, because the low-affinity one needed concentrations that were not clinically feasible even though it was easier for vasopressin to displace.

Publication

PMID:16926443

Pathograph links

Endoplasmic Reticulum Retention of Misfolded V2 Receptor rescues fidelity: moderate observes: cellular Cell-permeable non-peptide antagonists restored membrane expression and function of ER-retained mutants, which is the experimental demonstration that retention, not intrinsic receptor failure, is the rate-limiting lesion.

Limitations: A canine kidney cell line overexpressing a transfected human receptor, not a human principal cell in situ; rescue was shown for eight of nine mutants tested, so it is allele-dependent; and no clinical benefit in patients is demonstrated by this work.

Readouts

Basolateral membrane expression of mutant V2 receptor after antagonist exposure

Direction: RESTORED

Interpretation: Restored surface delivery of a receptor that ER quality control had been holding back.

Show evidence (1 reference)

PMID:16926443 SUPPORT In Vitro

"We found that the four nonpeptide antagonists SR49059, OPC31260, OPC41061, and SR121463B induced maturation and rescued the BM expression of eight of nine different V2R mutants, stably expressed in physiologically relevant polarized cells."

The measurement itself, with the denominator: eight of nine mutants, in polarized cells.

Show evidence (1 reference)

PMID:16926443 SUPPORT In Vitro

"Intracellular retention of a functional vasopressin V2 receptor (V2R) is a major cause of congenital nephrogenic diabetes insipidus (NDI) and rescue of V2R mutants by nonpeptide antagonists may restore their basolateral membrane (BM) localization and function."

States that the lesion this model manipulates is the one this node describes, which is what makes the model informative for it.

No cell_types binding. MDCK is a canine kidney epithelial line, and binding it to the human collecting-duct principal cell term would overstate what the system is; CL does not represent cell lines, and no CLO binding is available in this schema. The polarization of the line, which is the property that makes it informative about basolateral delivery, is described above instead.

Show evidence (1 reference)

PMID:16926443 SUPPORT In Vitro

"At clinically feasible antagonist concentrations, however, only the high-affinity antagonists OPC31260 and OPC41061 induced functional rescue, as at these concentrations the extent of BM expression became limited."

The constraint that makes this model informative about therapy rather than only about cell biology, and the reason it is cited here rather than a simpler transfection study.

HEK293 cells expressing the S127F V2 receptor mutant CELL_LINE

A patient-derived variant taken through the whole argument in one system. S127F was found in an NDI patient; in HEK293 cells the mutant receptor sits almost exclusively in the endoplasmic reticulum with very few molecules at the surface, and generates negligible cAMP in response to vasopressin. Pretreatment with either tolvaptan - an established V2 receptor inverse agonist - or MCF14, a cell-permeable high-affinity agonist, partially restored cAMP generation. The result that matters for the therapeutic question is that both an agonist and an antagonist worked as pharmacochaperones, so the chaperone property is not tied to the ligand's signalling direction.

Publication

PMID:35153784

Pathograph links

Endoplasmic Reticulum Retention of Misfolded V2 Receptor rescues fidelity: moderate observes: cellular Establishes the ER localization and the functional consequence for one patient variant, then partially reverses both with two chemically and pharmacologically different chaperones.

Limitations: HEK293 is a non-renal, unpolarized line overexpressing a transfected receptor, so it cannot report on basolateral targeting in a principal cell; the rescue is explicitly partial; and the result is for a single allele, which the authors themselves frame as a starting point for patients carrying S127F rather than for the disease generally.

Readouts

Vasopressin-stimulated cAMP generation after pharmacochaperone pretreatment

Direction: RESTORED

Interpretation: Partial functional rescue by two different ligand classes. Read as partial, and as allele-specific.

Show evidence (1 reference)

PMID:35153784 SUPPORT In Vitro

"We found that pretreatment with both tolvaptan (an established V2R inverse agonist) and MCF14 compound (a cell-permeable high-affinity agonist for the V2R) were capable of partially restoring the cAMP generating function of the receptor in response to vasopressin stimulation."

The measured rescue, with both compounds named and the effect called partial.

Show evidence (1 reference)

PMID:35153784 SUPPORT In Vitro

"Based on our data, the S127F-V2R mutant is almost exclusively located intracellularly in the endoplasmic reticulum (ER), and very few receptors were detected at the cell surface, where the receptor can bind to AVP."

Establishes that this model is about the ER-retention node, and states the reason retention matters - the surface is where the hormone can reach the receptor.

Show evidence (1 reference)

PMID:35153784 SUPPORT In Vitro

"The overexpressed S127F-V2R mutant receptor has negligible cAMP generation capability compared to the wild-type receptor in response to AVP stimulation."

The functional baseline the rescue is measured against, and the link between the localization defect and the signalling failure in one system.

🐁

Animal Models

3

V2R Glu242stop knock-in mouse

The defining animal model, and deliberately constructed as a disease model rather than a convenience knockout: the allele introduced is a nonsense variant known to cause XNDI in humans. Hemizygous males reproduce the severe human infantile phenotype closely - low basal urine osmolality, inability to concentrate, enlargement of the renal pelvic space, failure to thrive, and death in the first postnatal week from hypernatraemic dehydration - which is what an untreated human infant is at risk of. Heterozygous females are the second useful result: they grow normally but have reduced concentrating ability with polyuria and polydipsia, the murine counterpart of the symptomatic human heterozygote. The model also provides the cleanest available evidence that aquaporin-2 is not the problem in this disease: basal AQP2 expression was unaffected by loss of functional V2 receptors.

Species

Mouse

Genotype

Avpr2 Glu242stop (nonsense allele knocked in by targeted mutagenesis in ES cells)

Publication

PMID:11104789

Pathograph links

Absent or Truncated V2 Receptor Protein recapitulates fidelity: high observes: molecular Glu242stop is a nonsense allele, so this model belongs to the protein-expression class and this is the node it enters the pathograph at. Linked explicitly because the alternative - entering at the cascade node - would leave the model's own variant class unrepresented, which is the gap this link closes.

Limitations: The study reports the allele and the resulting whole-animal phenotype; it does not show absence of receptor protein in these mice directly, so the class assignment rests on the nature of the allele rather than on a Western blot in this model.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"Specifically, we introduced a nonsense mutation known to cause X-linked nephrogenic diabetes insipidus (XNDI) in humans (Glu242stop) into the mouse genome."

Names the allele as a nonsense variant, which is what places this model in the protein-expression class rather than in the ER-retention class.

Loss of Vasopressin-Stimulated cAMP and PKA Signalling recapitulates fidelity: high observes: organism A human XNDI nonsense allele at the orthologous position, producing the expected receptor-level loss of function in the intact animal.

Limitations: The model observes the whole organism, so the receptor-level signalling failure itself is inferred from the physiology rather than measured in this report; cAMP and PKA were not assayed here.

Readouts

Basal urine osmolality

Direction: DECREASED

Interpretation: The functional consequence of the absent receptor signal, measured at the level of the organism's urine.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"V2R-deficient hemizygous male pups showed a decrease in basal urine osmolalities and were unable to concentrate their urine."

The measured concentrating defect in the hemizygous animals.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"Specifically, we introduced a nonsense mutation known to cause X-linked nephrogenic diabetes insipidus (XNDI) in humans (Glu242stop) into the mouse genome."

The allele is a human disease variant placed at the orthologous position, which is what makes this model informative for the human receptor-level lesion rather than for V2 receptor biology in general.

Failure of Aquaporin-2 Phosphorylation and Apical Insertion partially recapitulates fidelity: moderate observes: cellular Supports the node in its important negative sense - that AQP2 abundance is not reduced, so the lesion is regulatory - without demonstrating the positive claim about phosphorylation and apical trafficking.

Limitations: Only basal AQP2 expression levels were assessed. Phosphorylation state and subcellular redistribution after a vasopressin stimulus, which are the actual content of this node, were not measured, so the model speaks to abundance rather than to trafficking.

Readouts

Basal aquaporin-2 protein abundance

Direction: UNCHANGED

Interpretation: A genuine negative result, and the one that matters: the water channel is present in normal amounts, so the defect is in its regulation.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"Western blot analysis and immunoelectron microscopic studies showed that the loss of functional V2Rs had no significant effect on the basal expression levels of aquaporin-2 and the bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1)."

The measurement establishing that AQP2 abundance is preserved when the receptor is lost.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"Western blot analysis and immunoelectron microscopic studies showed that the loss of functional V2Rs had no significant effect on the basal expression levels of aquaporin-2 and the bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1)."

Establishes that this model bears on the AQP2 node at all, and bears on it in the negative direction - abundance preserved - which is the only part of the node it can speak to.

Obligatory Hypotonic Free Water Loss recapitulates fidelity: high observes: organism Hemizygous males died of hypernatraemic dehydration within the first postnatal week, and heterozygous females showed polyuria and polydipsia with reduced concentrating ability.

Limitations: The hemizygous phenotype is more severe than treated human disease and lethal within a week, so it models the untreated infantile extreme rather than the clinical course of a managed patient.

Readouts

Polyuria and polydipsia in heterozygous females

Direction: INCREASED

Interpretation: The murine counterpart of the symptomatic human female heterozygote, with the same partial phenotype.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"female mice heterozygous for the V2R mutation showed normal growth but displayed an XNDI-like phenotype, characterized by reduced urine concentrating ability of the kidney, polyuria, and polydipsia."

The measured phenotype in the heterozygous females.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"These pups also exhibited an enlargement of renal pelvic space, failed to thrive, and died within the first week after birth due to hypernatremic dehydration."

The organism-level water-loss consequence in the model, matching the human features - renal pelvic dilatation, failure to thrive, hypernatraemic dehydration - that this node produces.

Show evidence (1 reference)

PMID:11104789 SUPPORT Model Organism

"These pups also exhibited an enlargement of renal pelvic space, failed to thrive, and died within the first week after birth due to hypernatremic dehydration."

Establishes that the model reproduces the specific human features - renal pelvic dilatation, failure to thrive, hypernatraemic dehydration - rather than a generic polyuria, which is what makes it informative for this entry.

Avpr2-deficient rat (rGONAD)

The model that supplies what the mouse could not. Unlike the constitutive Avpr2-null mouse, these rats survive weaning under normal rearing, so the chronic consequences are observable: polydipsia, polyuria, growth retardation, and hydronephrosis-like kidneys. Two of its findings bear directly on this entry's pathograph. First, aquaporin-2 was retained in the cytoplasm of collecting duct cells with its phosphorylation suppressed - a direct measurement of the node about trafficking and phosphorylation, which the mouse study could only address as preserved abundance. Second, the hydronephrosis-like kidneys showed no glomerular or tubular damage, which is the experimental version of the clinical claim that the tract dilatation is mechanical rather than a primary nephropathy. Hydrochlorothiazide reduced urine volume and improved urine osmolality in the model, so it also reproduces the therapeutic response.

Species

Rat

Genotype

Avpr2 knockout, generated by rat Genome-editing via Oviductal Nucleic Acid Delivery

Publication

PMID:40102322

Pathograph links

Failure of Aquaporin-2 Phosphorylation and Apical Insertion recapitulates fidelity: high observes: cellular Directly measures both halves of this node in collecting duct cells - aquaporin-2 held in the cytoplasm, and its phosphorylation suppressed.

Limitations: A whole-gene knockout rather than a human misfolding allele, so it models the consequence of absent receptor function and not the ER-retention route that produces it in most patients. Phosphorylation was reported as suppressed without the site-level detail that would tie it to Ser256 specifically.

Readouts

Subcellular localization and phosphorylation of aquaporin-2 in collecting duct cells

Direction: DECREASED

Interpretation: Apical delivery and phosphorylation both reduced, with the channel held in the cytoplasm - the node's claim, measured.

Show evidence (1 reference)

PMID:40102322 SUPPORT Model Organism

"Aquaporin-2 was retained in the cytoplasm of collecting duct cells, and its phosphorylation was suppressed."

The histological and biochemical readout behind this link.

Show evidence (1 reference)

PMID:40102322 SUPPORT Model Organism

"Aquaporin-2 was retained in the cytoplasm of collecting duct cells, and its phosphorylation was suppressed."

The measurement of this node in an animal, which no other model cited here provides.

Sustained High Urinary Tract Flow recapitulates fidelity: moderate observes: organism Hydronephrosis-like kidneys developed with no glomerular or tubular damage, which is the mechanical-not-nephropathic claim this node makes.

Limitations: Rodent urinary tract anatomy and lifespan differ from the human course, where the dilatation accumulates over decades; and the absence of glomerular or tubular damage is reported at the timepoint examined rather than across the animal's life.

Readouts

Renal pelvic dilatation with preserved glomerular and tubular histology

Direction: INCREASED

Interpretation: Dilatation present, parenchymal injury absent - the combination that distinguishes a flow effect from a nephropathy.

Show evidence (1 reference)

PMID:40102322 SUPPORT Model Organism

"Although they exhibited hydronephrosis-like kidneys, no glomerular or tubular damage was observed."

The histological readout behind this link.

Show evidence (1 reference)

PMID:40102322 SUPPORT Model Organism

"Although they exhibited hydronephrosis-like kidneys, no glomerular or tubular damage was observed."

Supports the dilatation being a consequence of flow rather than of parenchymal disease.

Show evidence (1 reference)

PMID:40102322 SUPPORT Model Organism

"Avpr2-deficient rats were born and weaned under normal rearing conditions and exhibited symptoms similar to those of human congenital NDI, such as polydipsia, polyuria, and growth retardation."

Establishes survival past weaning and phenotypic similarity, which together are what make this model usable for the chronic consequences.

X-NDI mouse treated with a beta-3 adrenergic agonist

A rescue experiment rather than a disease model, and included because of what the rescue demonstrates about the mechanism. The hypothesis was that a different Gs-coupled receptor on the same cells could be used to raise cAMP without the V2 receptor. A single injection of the beta-3 adrenergic agonist BRL37344 worked for only three hours, but repeated dosing over 24 hours - imitating a slow-release preparation - cut 24-hour urine output by 27 per cent, raised urine osmolarity by 25 per cent and reduced water intake by 20 per cent. The molecular readout is the point: the drug increased phosphorylation of AQP2 (along with NKCC2 and NCC) in the renal cell membrane. Raising AQP2 phosphorylation from outside the V2 receptor restores water handling, which is direct support for the entry's claim that the AQP2 step is where the cascade failure is cashed out.

Species

Mouse

Genotype

mouse model of X-linked nephrogenic diabetes insipidus (AVPR2-inactivated)

Publication

PMID:38652212

Pathograph links

Failure of Aquaporin-2 Phosphorylation and Apical Insertion rescues fidelity: moderate observes: organism Pharmacological rescue of the node by a V2-receptor-independent route, with both the molecular step (AQP2 phosphorylation) and the whole-animal consequence measured.

Limitations: A mouse, and a pharmacological rescue with a three-hour duration of action that had to be worked around by repeated injection; the effect is partial (27 per cent of urine output) rather than corrective, and BRL37344 is a rodent-selective beta-3 agonist whose translation to human beta-3 pharmacology is not demonstrated here.

Readouts

24-hour urine output, urine osmolarity and water intake after repeated BRL37344

Direction: RESTORED

Interpretation: Partial restoration of water handling, quantified in three directions at once. Read as partial: a 27 per cent reduction in output is a real effect and not a correction.

Show evidence (1 reference)

PMID:38652212 SUPPORT Model Organism

"repeated administrations in the 24 h, mimicking the effect of a slow-release preparation, promoted a sustained antidiuretic effect, reducing the 24 h urine output by 27%, increasing urine osmolarity by 25% and reducing the water intake by 20%."

The three measured outcomes and the dosing schedule needed to obtain them.

Show evidence (1 reference)

PMID:38652212 SUPPORT Model Organism

"At the molecular level, we show that BRL37344 acted by increasing the phosphorylation of NKCC2, NCC and AQP2 in the renal cell membrane, thereby increasing electrolytes and water reabsorption in the kidney tubule of X-NDI mice."

Names AQP2 phosphorylation as the step the rescue acts through, which is what makes this a rescue of this node rather than a general antidiuretic effect.

Show evidence (1 reference)

PMID:38652212 SUPPORT Model Organism

"The disease, which still lacks a cure, could benefit from the pharmacologic stimulation of other GPCRs, activating the cAMP-intracellular pathway in the kidney cells expressing the AVPR2."

The design rationale, which is also the mechanistic claim the experiment tests: the cascade below the receptor is intact and reachable from another receptor.

{ }

Source YAML

click to show

name: X-Linked Nephrogenic Diabetes Insipidus
creation_date: "2026-09-10T00:00:00Z"
description: >-
  X-linked nephrogenic diabetes insipidus (XNDI) is the receptor-level form of
  hereditary nephrogenic diabetes insipidus. Loss-of-function variants in AVPR2,
  which encodes the arginine vasopressin V2 receptor of the renal collecting duct,
  leave the kidney unable to respond to circulating vasopressin. Hormone supply is
  intact - plasma vasopressin is normal or high - so the lesion is entirely distal
  to the hormone, in the principal cell's own signalling apparatus. Most pathogenic
  AVPR2 missense and small in-frame variants do not destroy ligand binding; they
  misfold the receptor, and the endoplasmic reticulum quality-control machinery
  retains it inside the cell so that it never reaches the membrane where vasopressin
  could find it. Without a surface receptor there is no Gs/adenylyl cyclase/cAMP/PKA
  signal, aquaporin-2 is not phosphorylated or shuttled to the apical membrane, the
  collecting duct stays water-impermeable, and the medullary countercurrent
  concentrating mechanism cannot be exploited. The result is obligatory hypotonic
  polyuria from birth. The presentation is a pediatric one: affected male infants
  come to attention with vomiting, poor feeding, failure to thrive, unexplained
  fever and hypernatraemic dehydration rather than with the polyuria-polydipsia of
  the adult textbook description, and the chronically high urine flow deforms a
  structurally normal urinary tract into hydronephrosis, hydroureter and megacystis.
categories:
- Mendelian
- Renal Tubular Disorder
- Receptor Trafficking Disorder
synonyms:
- nephrogenic diabetes insipidus type 1
- congenital nephrogenic diabetes insipidus, X-linked
- AVPR2-related nephrogenic diabetes insipidus
- X-linked vasopressin-resistant diabetes insipidus
- arginine vasopressin resistance
- AVP-R
- X-linked arginine vasopressin resistance
parents:
- nephrogenic diabetes insipidus
- X-linked disease
disease_term:
  preferred_term: X-linked nephrogenic diabetes insipidus
  term:
    id: MONDO:0010581
    label: diabetes insipidus, nephrogenic, X-linked
classifications:
  harrisons_chapter:
  - classification_value: KIDNEY_URINARY_TRACT
  - classification_value: ENDOCRINOLOGY_METABOLISM
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
prevalence:
- population: Quebec, Canada (male live births)
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 0.88
  rate_denominator: LIVE_BIRTHS
  notes: >-
    8.8 per million male live births. The denominator is male live births, not all
    live births, which matters for an X-linked disease: the rate among all newborns
    is about half this. The same report notes a regional rate more than six times
    higher in Nova Scotia and New Brunswick, a founder effect rather than a
    different population estimate, so the Quebec figure is the one quoted here.
  evidence:
  - reference: PMID:10820168
    reference_title: Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The estimate of about 8.8 per million male live births of the incidence of
      X-linked NDI in the province of Quebec, Canada may be representative of the
      general population except in Nova Scotia and New Brunswick, where the
      incidence is more than six times higher.
    explanation: >-
      The source of both the rate and its denominator, and of the caveat about the
      Maritime founder population.
pathophysiology:
- name: AVPR2 Loss-of-Function Variant
  description: >-
    A hemizygous pathogenic variant in AVPR2 on Xq28, the gene encoding the arginine
    vasopressin V2 receptor. The allelic spectrum is wide and largely private: 82
    different putative disease-causing variants were found among 117 families, and
    haplotype analysis indicates that recurrences of the same variant in apparently
    unrelated families arose independently rather than from a shared founder. Roughly
    a fifth of isolated cases are de novo, arising during oogenesis in the mother.
  biological_scale: MOLECULAR
  genetic_context:
    gene:
      preferred_term: AVPR2
      term:
        id: hgnc:897
        label: AVPR2
    variant_origin: GERMLINE
    zygosity: HEMIZYGOUS
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Hemizygous in affected males. Heterozygous females are affected only when
      X-inactivation is skewed against the normal allele.
  molecular_functions:
  - preferred_term: arginine vasopressin V2 receptor activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0005000
      label: vasopressin receptor activity
  downstream:
  - target: Absent or Truncated V2 Receptor Protein
    causal_link_type: DIRECT
    description: >-
      The protein-expression route, for variants that yield no usable receptor at all:
      nonsense, frameshift, large deletions and complex rearrangements. Transcription is
      not necessarily the failing step - mRNA was detectable for every mutant construct in
      the study cited here, while one frameshift allele produced no detectable protein.
    evidence:
    - reference: PMID:11389590
      reference_title: Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        RT-PCR revealed that mRNA was produced for all mutant receptor constructs. However,
        no receptor protein, as assessed by Western blot analysis, was detected for 804delG.
      explanation: >-
        A worked example of this route, and it locates the failure after transcription: the
        message was made and the protein was not.
  - target: Endoplasmic Reticulum Retention of Misfolded V2 Receptor
    causal_link_type: DIRECT
    description: >-
      The commonest route, and the one with a therapeutic handle. A misfolding missense or
      small in-frame variant is recognised by ER quality control and the receptor never
      reaches the membrane.
    evidence:
    - reference: PMID:17516711
      reference_title: "Pharmacological chaperones in nephrogenic diabetes insipidus: possibilities for clinical application."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        In vitro V2R expression studies revealed that the function of most of these
        receptors is not disturbed, but due to their misfolding, the quality control
        mechanism of the endoplasmic reticulum (ER) retains these receptors inside
        the cell, thereby preventing their functioning at the plasma membrane.
      explanation: >-
        States the causal step directly, and states that it is the mechanism for most
        variants - which is why this is the main edge out of the lesion node rather
        than one of several equal alternatives.
  - target: Signalling-Incompetent Cell-Surface V2 Receptor
    causal_link_type: DIRECT
    description: >-
      The functional route, for variants that fold well enough to pass ER quality control
      but cannot bind vasopressin or couple to Gs at the membrane.
    evidence:
    - reference: PMID:11389590
      reference_title: Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The S315R was properly processed through the Golgi and targeted to the plasma
        membrane but lacked any detectable AVP binding or signaling.
      explanation: >-
        A worked example of a variant that reaches the surface and still fails, which
        is what distinguishes this edge from the ER-retention edge.
  evidence:
  - reference: PMID:10820168
    reference_title: Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among 117 families, there were 82 different putative disease-causing mutations.
      Based on haplotype analysis, it can be inferred that when the same AVPR2
      mutation is identified in different families that were not known to be related,
      the mutations most likely arose independently.
    explanation: Establishes the breadth and independence of the allelic spectrum.
  - reference: PMID:10820168
    reference_title: Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A de novo mutation arose during oogenesis in the mother in 20% of isolated cases.
    explanation: Quantifies the de novo contribution in isolated male cases.
- name: Absent or Truncated V2 Receptor Protein
  description: >-
    The third mechanistic class of AVPR2 loss of function, and the one that cannot be
    addressed by rescuing a receptor, because there is no receptor to rescue. Nonsense,
    frameshift, large-deletion and complex-rearrangement alleles yield absent, truncated or
    otherwise undetectable receptor protein. The step that fails is after transcription
    rather than at it: in the study cited here mRNA was produced for every mutant construct
    tested, yet the 804delG frameshift allele gave no receptor protein on Western blot.
    This node exists because the entry's own flagship animal model - the Glu242stop
    knock-in mouse - carries an allele of exactly this class, so without it the model's
    variant class had no route through the graph.
  biological_scale: MOLECULAR
  cell_types:
  - preferred_term: renal collecting duct principal cell
    term:
      id: CL:1001431
      label: kidney collecting duct principal cell
  molecular_functions:
  - preferred_term: arginine vasopressin V2 receptor activity
    modifier: ABSENT
    term:
      id: GO:0005000
      label: vasopressin receptor activity
  downstream:
  - target: Loss of Vasopressin-Stimulated cAMP and PKA Signalling
    causal_link_type: DIRECT
    description: >-
      No receptor protein means no coupling to Gs, so the cascade has no input. This is the
      simplest of the three routes into the cascade node and the only one for which
      pharmacochaperone rescue is inapplicable in principle.
    evidence:
    - reference: PMID:11389590
      reference_title: Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        However, no receptor protein, as assessed by Western blot analysis, was detected for
        804delG.
      explanation: >-
        Establishes the absence of receptor protein, which is what leaves the cascade
        without an input.
  evidence:
  - reference: PMID:32138955
    reference_title: V2 vasopressin receptor mutations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The mechanisms underlying a V2R loss-of-function can be theoretically classified
      as either protein expression, localization (ER retention) or functional
      disorders.
    explanation: >-
      Names protein expression as the first of the three recognised loss-of-function
      classes. This entry models all three, one node each, because the review names three.
  - reference: PMID:10820168
    reference_title: Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among 117 families, there were 82 different putative disease-causing mutations.
    explanation: >-
      Establishes the breadth of the allelic spectrum this class is drawn from. It does not
      apportion variants between the three classes, and no cited source here does.
- name: Endoplasmic Reticulum Retention of Misfolded V2 Receptor
  description: >-
    The pathognomonic cell-biological lesion of XNDI, and the reason the disease is a
    trafficking disorder rather than a ligand-recognition disorder. A misfolded V2
    receptor is held in the endoplasmic reticulum by the same chaperone-based quality
    control that polices any nascent membrane protein; calnexin associates with the
    ER-retained receptor for longer than with the wild-type one. The receptor is often
    intrinsically capable of signalling - it is simply in the wrong compartment. That
    distinction is what makes pharmacochaperone rescue conceivable at all, and it is
    why a cell-permeable non-peptide ligand can restore membrane expression of a
    mutant receptor that a membrane-impermeant peptide agonist could never reach.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: renal collecting duct principal cell
    term:
      id: CL:1001431
      label: kidney collecting duct principal cell
  cellular_components:
  - preferred_term: endoplasmic reticulum
    term:
      id: GO:0005783
      label: endoplasmic reticulum
  biological_processes:
  - preferred_term: delivery of the V2 receptor to the plasma membrane
    modifier: DECREASED
    term:
      id: GO:0072659
      label: protein localization to plasma membrane
  - preferred_term: protein folding in the endoplasmic reticulum
    modifier: ABNORMAL
    term:
      id: GO:0034975
      label: protein folding in endoplasmic reticulum
  downstream:
  - target: Loss of Vasopressin-Stimulated cAMP and PKA Signalling
    causal_link_type: DIRECT
    description: >-
      A receptor held inside the cell cannot be occupied by circulating vasopressin,
      so the Gs-adenylyl cyclase cascade is never engaged.
    evidence:
    - reference: PMID:16926443
      reference_title: "Functional rescue of vasopressin V2 receptor mutants in MDCK cells by pharmacochaperones: relevance to therapy of nephrogenic diabetes insipidus."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Intracellular retention of a functional vasopressin V2 receptor (V2R) is a
        major cause of congenital nephrogenic diabetes insipidus (NDI) and rescue of
        V2R mutants by nonpeptide antagonists may restore their basolateral membrane
        (BM) localization and function.
      explanation: >-
        States that intracellular retention of an otherwise functional receptor is the
        causative defect, and that restoring its localisation restores its function -
        the experimental demonstration that localisation is the rate-limiting step.
  evidence:
  - reference: PMID:11389590
    reference_title: Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Moreover, its association with the ER-retained R337X mutant was found to be
      longer than with the WT receptor suggesting that this molecular chaperone also
      plays a role in quality control and ER retention of misfolded G protein-coupled
      receptors.
    explanation: >-
      Identifies calnexin-dependent ER quality control as the machinery doing the
      retaining, rather than leaving the retention unexplained.
  - reference: PMID:31928727
    reference_title: "Misfolding of vasopressin receptors: biased agonist pharmacochaperones as potential therapeutics."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      In most of the cases, it is associated to inactivating mutations of the renal
      arginine-vasopressin V2 receptor leading to misfolding and intracellular retention
      of the receptor, causing the inability of patients to concentrate their urine in
      response to the antidiuretic hormone.
    explanation: >-
      A review-level statement of the whole chain in one sentence - misfolding, retention,
      and the concentrating failure - and of the fact that this is the route in most
      cases. Cited as a synthesis claim rather than for any single experiment.
  - reference: PMID:32138955
    reference_title: V2 vasopressin receptor mutations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The mechanisms underlying a V2R loss-of-function can be theoretically classified
      as either protein expression, localization (ER retention) or functional
      disorders. Functional analyses have revealed however that these mechanisms are
      likely to be complex.
    explanation: >-
      Places ER retention as one of three recognised loss-of-function classes, and
      records the reviewers' own caveat that the classes are not clean - which is why
      this entry keeps a separate surface-expressed node rather than collapsing them.
- name: Signalling-Incompetent Cell-Surface V2 Receptor
  description: >-
    The minority class of AVPR2 variants, in which the receptor folds well enough to
    be exported from the ER and delivered to the basolateral membrane of the principal
    cell but cannot transduce a vasopressin signal from there - either because
    hormone recognition is destroyed, or because coupling to Gs is. This node is kept
    separate from the ER-retention node because it carries a different therapeutic
    implication: a pharmacochaperone has nothing to correct.
  biological_scale: MOLECULAR
  cell_types:
  - preferred_term: renal collecting duct principal cell
    term:
      id: CL:1001431
      label: kidney collecting duct principal cell
  cellular_components:
  - preferred_term: basolateral plasma membrane of the principal cell
    term:
      id: GO:0005886
      label: plasma membrane
  molecular_functions:
  - preferred_term: vasopressin recognition by the V2 receptor
    modifier: ABSENT
    term:
      id: GO:0017046
      label: peptide hormone binding
  - preferred_term: arginine vasopressin V2 receptor activity
    modifier: ABSENT
    term:
      id: GO:0005000
      label: vasopressin receptor activity
  downstream:
  - target: Loss of Vasopressin-Stimulated cAMP and PKA Signalling
    causal_link_type: DIRECT
    description: >-
      A surface receptor that cannot bind hormone or activate Gs leaves the cascade
      just as silent as an absent one.
    evidence:
    - reference: PMID:11389590
      reference_title: Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The S315R was properly processed through the Golgi and targeted to the plasma
        membrane but lacked any detectable AVP binding or signaling.
      explanation: >-
        The measurement that establishes this edge: a correctly localised receptor with no
        detectable signalling, so surface delivery alone does not rescue the cascade.
  evidence:
  - reference: PMID:11389590
    reference_title: Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Thus, this mutation induces a conformational change that is compatible with
      endoplasmic reticulum (ER) export but dramatically affects hormone recognition.
    explanation: >-
      States the defining property of this class: ER export is intact and hormone
      recognition is not.
- name: Loss of Vasopressin-Stimulated cAMP and PKA Signalling
  description: >-
    Vasopressin normally acts on the principal cell through a single linear cascade:
    V2 receptor occupancy activates the stimulatory G protein Gs, Gs activates adenylyl
    cyclase, cAMP rises, and cAMP activates protein kinase A. With no functional
    receptor at the membrane the cascade has no input. Note what is intact: the
    hormone, the G protein, the cyclase and PKA itself are all normal, which is the
    reason every experimental strategy for XNDI has aimed at re-entering the cascade
    below the receptor.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: renal collecting duct principal cell
    term:
      id: CL:1001431
      label: kidney collecting duct principal cell
  biological_processes:
  - preferred_term: vasopressin-stimulated adenylyl cyclase signalling
    modifier: ABSENT
    term:
      id: GO:0007189
      label: adenylate cyclase-activating G protein-coupled receptor signaling pathway
  - preferred_term: cAMP generation in the principal cell
    modifier: DECREASED
    term:
      id: GO:0006171
      label: cAMP biosynthetic process
  - preferred_term: cellular response to vasopressin
    modifier: ABSENT
    term:
      id: GO:1904117
      label: cellular response to vasopressin
  molecular_functions:
  - preferred_term: protein kinase A activity downstream of the V2 receptor
    modifier: DECREASED
    term:
      id: GO:0004691
      label: cAMP-dependent protein kinase activity
  pdb_structures:
  - pdb_id: 7KH0
    description: >-
      Cryo-EM structure of the agonist-bound AVP-V2 receptor-Gs ternary complex - the
      assembly that fails to form in this disease. A wild-type complex, so it is an image
      of the normal coupling step and not of any mutant receptor; its value here is that
      it shows what the receptor has to do and that V2R is the only vasopressin or
      oxytocin receptor that activates Gs.
    method: cryo-EM
    ligand: arginine vasopressin
    target_protein: vasopressin V2 receptor (AVPR2) in complex with heterotrimeric Gs
    publication: PMID:33664408
  downstream:
  - target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
    causal_link_type: DIRECT
    description: >-
      PKA activation is the step that couples the cascade to aquaporin-2; without it
      the water channel is neither phosphorylated nor redistributed.
    evidence:
    - reference: PMID:32245905
      reference_title: Phosphoproteomic Identification of Vasopressin/cAMP/Protein Kinase A-Dependent Signaling in Kidney.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Vasopressin signaling is initiated by binding to a G-protein-coupled receptor
        called V2R, which signals through heterotrimeric G-protein subunit Gs α,
        adenylyl cyclase 6, and activation of the cAMP-regulated protein kinase (PKA).
      explanation: >-
        Names the cascade in order, establishing PKA as the receptor's downstream
        effector and so the step that fails when the receptor is absent.
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary
      concentrating ability, despite normal or elevated plasma concentrations of the
      antidiuretic hormone, arginine vasopressin (AVP).
    explanation: >-
      Establishes that hormone supply is intact, which is what locates the lesion in
      the cell's response rather than in the signal.
  - reference: PMID:33664408
    reference_title: Cryo-EM structure of the AVP-vasopressin receptor 2-G(s) signaling complex.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Among all AVP and OT receptors, V2R is the only one that activates the heterotrimeric
      Gsfamily to induce cAMP accumulation
    explanation: >-
      Establishes that no other vasopressin or oxytocin receptor can substitute for V2R on
      this cascade, which is why losing it silences cAMP generation outright rather than
      reducing it. Quoted as the cached text renders it, with the subscript of "Gs" run
      together with the following word.
- name: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
  description: >-
    Aquaporin-2 is the vasopressin-regulated water channel of the principal cell, and
    it is regulated by being moved. PKA phosphorylates AQP2 at Ser256 and the channel
    is redistributed from intracellular vesicles into the apical membrane, where it
    makes the luminal surface water-permeable. In XNDI the AQP2 protein itself is
    normal - that is the defining feature separating this disease from the autosomal
    AQP2-mutation form - and the failure is purely one of regulation. It is also the
    reason the whole therapeutic literature is framed as "reach AQP2 without the
    receptor".
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: renal collecting duct principal cell
    term:
      id: CL:1001431
      label: kidney collecting duct principal cell
  cellular_components:
  - preferred_term: apical plasma membrane of the principal cell
    term:
      id: GO:0016324
      label: apical plasma membrane
  biological_processes:
  - preferred_term: aquaporin-2 delivery to the apical plasma membrane
    modifier: DECREASED
    term:
      id: GO:0072659
      label: protein localization to plasma membrane
  - preferred_term: regulation of aquaporin-2 water channel activity
    modifier: DECREASED
    term:
      id: GO:1902427
      label: regulation of water channel activity
  downstream:
  - target: Collecting Duct Water Impermeability
    causal_link_type: DIRECT
    description: >-
      With no aquaporin-2 in the apical membrane the luminal surface of the duct is
      effectively impermeable to water.
    evidence:
    - reference: PMID:32924547
      reference_title: A mini-review of pharmacological strategies used to ameliorate polyuria associated with X-linked nephrogenic diabetes insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        AVP facilitates reabsorption of water through increased abundance and
        insertion of AQP2 in the apical membrane of principal cells in the collecting
        ducts. In X-linked NDI, V2R is dysfunctional, which leads to impaired water
        reabsorption.
      explanation: >-
        States both halves of the edge in one place: apical AQP2 insertion is what
        permits reabsorption, and in XNDI reabsorption is impaired because the
        receptor is dysfunctional.
  evidence:
  - reference: PMID:7537730
    reference_title: cAMP-dependent phosphorylation stimulates water permeability of aquaporin-collecting duct water channel protein expressed in Xenopus oocytes.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our data suggest that cAMP stimulates water permeability of AQP-CD by
      phosphorylation. This process may contribute to the vasopressin-regulated water
      permeability of collecting duct in addition to the apical insertion of AQP-CD by
      exocytosis.
    explanation: >-
      The Xenopus oocyte experiment establishing cAMP-dependent phosphorylation as a
      mechanism by which the channel's water permeability is switched on, alongside
      apical exocytosis.
  - reference: PMID:32924547
    reference_title: A mini-review of pharmacological strategies used to ameliorate polyuria associated with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      These patients have functional AQP2, and thus the challenge is to achieve AQP2
      membrane insertion independently of V2R.
    explanation: >-
      States that AQP2 is intact in XNDI, which is the claim that makes this node a
      regulatory failure rather than a channel defect.
- name: Collecting Duct Water Impermeability
  description: >-
    The collecting duct is the final site at which the kidney can return water to the
    body, and its water permeability is not constitutive - it exists only while
    aquaporin-2 is in the apical membrane. An XNDI collecting duct is therefore
    permanently in its dilute-urine configuration regardless of how dehydrated the
    patient is.
  biological_scale: TISSUE
  cell_types:
  - preferred_term: renal collecting duct principal cell
    term:
      id: CL:1001431
      label: kidney collecting duct principal cell
  locations:
  - preferred_term: kidney collecting duct epithelium
    term:
      id: UBERON:0014388
      label: kidney collecting duct epithelium
  biological_processes:
  - preferred_term: renal water absorption in the collecting duct
    modifier: DECREASED
    term:
      id: GO:0070295
      label: renal water absorption
  molecular_functions:
  - preferred_term: apical water channel activity
    modifier: DECREASED
    term:
      id: GO:0015250
      label: water channel activity
  downstream:
  - target: Failure of Medullary Countercurrent Urine Concentration
    causal_link_type: DIRECT
    description: >-
      The medullary osmotic gradient is still built, but an impermeable duct cannot
      equilibrate with it, so the gradient cannot be used to concentrate urine.
    evidence:
    - reference: PMID:34055061
      reference_title: Nephrogenic diabetes insipidus in children (Review).
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary
        concentrating ability, despite normal or elevated plasma concentrations of the
        antidiuretic hormone, arginine vasopressin (AVP).
      explanation: >-
        Names impaired urinary concentrating ability as the consequence of the unresponsive
        duct, which is this edge.
  evidence:
  - reference: PMID:30454745
    reference_title: Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Nephrogenic diabetes insipidus (NDI) results from the inability of the late
      distal tubules and collecting ducts to respond to vasopressin.
    explanation: Locates the functional lesion at the late distal tubule and collecting duct.
- name: Failure of Medullary Countercurrent Urine Concentration
  description: >-
    Urine concentration depends on two things: a corticomedullary osmotic gradient
    built by countercurrent multiplication in the loops of Henle, and a collecting
    duct able to equilibrate with it. XNDI breaks only the second. This is worth
    stating explicitly because it is the reason XNDI is a pure water-handling disease
    with normal solute excretion, and the reason the washout of the gradient by very
    high tubular flow is a secondary aggravation rather than the primary defect.
  biological_scale: TISSUE
  locations:
  - preferred_term: renal medulla
    term:
      id: UBERON:0000362
      label: renal medulla
  biological_processes:
  - preferred_term: renal water homeostasis
    modifier: ABNORMAL
    term:
      id: GO:0003091
      label: renal water homeostasis
  - preferred_term: transepithelial water transport in the medullary collecting duct
    modifier: DECREASED
    term:
      id: GO:0035377
      label: transepithelial water transport
  downstream:
  - target: Obligatory Hypotonic Free Water Loss
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301356
      reference_title: Hereditary Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to
        concentrate the urine, which results in polyuria (excessive urine production) and
        polydipsia (excessive thirst).
      explanation: >-
        States that the inability to concentrate is what produces the excess urine
        production, which is the content of this edge.
  evidence:
  - reference: PMID:29797052
    reference_title: "Mammalian urine concentration: a review of renal medullary architecture and membrane transporters."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Central to this process of urine concentration is an osmotic gradient that
      increases from the corticomedullary boundary to the inner medullary tip.
    explanation: >-
      Establishes the gradient that the impermeable collecting duct is unable to
      exploit. Cited for the normal physiology of the step, not for any claim about
      XNDI.
- name: Obligatory Hypotonic Free Water Loss
  description: >-
    The organism-level consequence: a fixed, large output of dilute urine that
    continues irrespective of plasma osmolality or volume status. Because it is
    obligatory rather than regulated, thirst is the only defence, and an affected
    person is dependent on continuous access to water. Adolescents and adults may void
    10 to 15 litres a day.
  biological_scale: ORGANISM
  biological_processes:
  - preferred_term: regulation of urine volume
    modifier: ABNORMAL
    term:
      id: GO:0035809
      label: regulation of urine volume
  - preferred_term: organism-level water homeostasis
    modifier: ABNORMAL
    term:
      id: GO:0050891
      label: multicellular organismal-level water homeostasis
  downstream:
  - target: Polyuria
    causal_link_type: DIRECT
  - target: Hyposthenuria
    causal_link_type: DIRECT
  - target: Polydipsia
    causal_link_type: DIRECT
    description: Thirst is the compensatory response to the water deficit, not an independent lesion.
  - target: Hypernatremia
    causal_link_type: DIRECT
    description: >-
      Free water is lost in excess of solute, so plasma sodium rises whenever intake
      fails to keep pace - which in an infant depends entirely on a carer.
  - target: Dehydration
    causal_link_type: DIRECT
  - target: Nocturnal enuresis
    causal_link_type: DIRECT
    description: >-
      The obligatory output does not pause overnight, so nocturia and bed-wetting follow
      directly from it rather than from any behavioural or bladder-capacity problem.
  - target: Failure to thrive
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Recorded with unknown intermediates deliberately. The association is well
      documented, but the route is not: a stomach filled with water displacing calories,
      anorexia and vomiting, and the metabolic cost of the water turnover are all
      plausible contributors and the cited sources do not apportion between them.
  - target: Short stature
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Same caveat. The height deficit persists after weight has recovered, which is
      itself an argument that it is not simply a caloric deficit, and no source cited
      here explains the difference.
  - target: Sustained High Urinary Tract Flow
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301356
      reference_title: Hereditary Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Short stature and secondary dilatation of the ureters and bladder from the high
        urine volume is common in untreated individuals.
      explanation: >-
        Attributes the tract consequences to the urine volume itself, which is what this
        edge asserts.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to
      concentrate the urine, which results in polyuria (excessive urine production) and
      polydipsia (excessive thirst).
    explanation: >-
      States that the concentrating failure is what produces the polyuria and the
      compensatory polydipsia, which is the causal content of this node's outgoing
      edges.
- name: Sustained High Urinary Tract Flow
  description: >-
    A mechanical consequence of the urine output, and the one most specific to
    long-standing untreated disease. Decades of very high flow through an anatomically
    normal urinary tract dilate it: the bladder becomes large and trabeculated, the
    ureters dilate, and the renal pelvis follows, all without any obstruction at the
    bladder outlet. The dilatation is not harmless - poor drainage of a huge compliant
    bladder raises residual volume, predisposes to infection, and can itself impair
    renal function.
  biological_scale: ORGANISM
  downstream:
  - target: Megacystis
    causal_link_type: DIRECT
  - target: Bladder trabeculation
    causal_link_type: DIRECT
  - target: Hydroureter
    causal_link_type: DIRECT
  - target: Hydronephrosis
    causal_link_type: DIRECT
  - target: Chronic kidney disease
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Through the dilated, poorly draining tract rather than directly: the intermediate
      is obstructive-type uropathy with raised residual volume. Recorded with known
      intermediates because those steps are named in the cited series, not because the
      quantitative relationship is established.
    evidence:
    - reference: PMID:22498392
      reference_title: Nonobstructive urinary tract dilatation in children with diabetes insipidus.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Urodynamics have shown the bladder itself to be compliant, but drainage is poor
        leading to further renal impairment and overflow incontinence.
      explanation: >-
        Names poor drainage as the step between the dilated tract and the renal
        impairment, which is the intermediate this edge claims.
  evidence:
  - reference: PMID:22498392
    reference_title: Nonobstructive urinary tract dilatation in children with diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The high flow states caused the bladder to become trabeculated in the absence of
      infravesical obstruction. Urodynamics have shown the bladder itself to be
      compliant, but drainage is poor leading to further renal impairment and overflow
      incontinence.
    explanation: >-
      States the causal attribution to flow rather than obstruction, and the
      consequence for renal function, in the series that made the point.
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Short stature and secondary dilatation of the ureters and bladder from the high
      urine volume is common in untreated individuals.
    explanation: >-
      Attributes the ureteric and bladder dilatation specifically to the urine volume,
      and records that it is common rather than exceptional.
  - reference: PMID:27258490
    reference_title: "Congenital Nephrogenic Diabetes Insipidus Presented With Bilateral Hydronephrosis and Urinary Infection: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiographic examination revealed severe dilatation of bilateral renal pelvis,
      ureter, and bladder.
    explanation: >-
      Shows the full extent the dilatation can reach in untreated disease, involving
      the renal pelvis as well as the lower tract.
phenotypes:
- category: Renal
  name: Polyuria
  frequency: VERY_FREQUENT
  description: >-
    The cardinal manifestation and the one that defines the disease, present from
    birth. In an infant it is easy to miss because the nappy volume is not measured;
    in an older child or adult the output can reach 10 to 15 litres a day.
  phenotype_term:
    preferred_term: Polyuria
    term:
      id: HP:0000103
      label: Polyuria
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to
      concentrate the urine, which results in polyuria (excessive urine production) and
      polydipsia (excessive thirst).
    explanation: GeneReviews names polyuria as a defining feature of the disease.
- category: Renal
  name: Polydipsia
  frequency: VERY_FREQUENT
  description: >-
    The compensatory response, and in an untreated patient the only thing standing
    between the obligatory water loss and hypernatraemic dehydration. A preverbal
    infant cannot act on it, which is why the infantile presentation is dehydration
    rather than thirst.
  phenotype_term:
    preferred_term: Polydipsia
    term:
      id: HP:0001959
      label: Polydipsia
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Hereditary nephrogenic diabetes insipidus (NDI) is characterized by inability to
      concentrate the urine, which results in polyuria (excessive urine production) and
      polydipsia (excessive thirst).
    explanation: GeneReviews names polydipsia as a defining feature.
- category: Renal
  name: Hyposthenuria
  frequency: VERY_FREQUENT
  description: >-
    Persistently dilute urine that does not concentrate on water deprivation and does
    not respond to desmopressin. The failure to respond to desmopressin is what
    separates nephrogenic from central diabetes insipidus at the bedside.
  diagnostic: true
  phenotype_term:
    preferred_term: Hyposthenuria
    term:
      id: HP:0003158
      label: Hyposthenuria
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary
      concentrating ability, despite normal or elevated plasma concentrations of the
      antidiuretic hormone, arginine vasopressin (AVP).
    explanation: >-
      States the concentrating failure that hyposthenuria is the measurement of, and
      pairs it with the intact hormone level that makes the finding diagnostic of a
      nephrogenic rather than a central defect.
  - reference: PMID:7607658
    reference_title: Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and
      the absence of extra-renal responses to 1-desamino-8-D-arginine vasopressin was
      demonstrated in two of them.
    explanation: >-
      Puts a number on the concentrating ceiling. Measured in symptomatic female
      heterozygotes rather than in hemizygous males, which is a limitation of this
      particular figure.
- category: Metabolic
  name: Hypernatremia
  frequency: FREQUENT
  description: >-
    Hypernatraemia is the dangerous consequence, not the polyuria itself. It appears
    whenever intake cannot keep pace with the obligatory loss, which in practice means
    during any intercurrent illness, in hot weather, when water is withheld, or when
    an infant is nil by mouth for a procedure. Repeated episodes are the reason
    treatment of this disease is urgent rather than merely symptomatic.
  phenotype_term:
    preferred_term: Hypernatremia
    term:
      id: HP:0003228
      label: Hypernatremia
  sequelae:
  - target: Intellectual disability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The neurodevelopmental consequence is attributed to the electrolyte disturbance
      itself. The intermediate steps between a hypernatraemic episode and permanent
      cognitive deficit are not established in this disease, and the cited review
      asserts the attribution without demonstrating the mechanism or quantifying the
      exposure needed.
    evidence:
    - reference: PMID:34055061
      reference_title: Nephrogenic diabetes insipidus in children (Review).
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Irreversible brain damage and cognitive deficit secondary to electrolyte
        imbalances may be present.
      explanation: >-
        This is the sentence that makes the causal claim, and it is hedged in the
        source ("may be present"), which is why the edge is recorded with unknown
        intermediates.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Evaluation of at-risk infants as early as possible to allow for prompt diagnosis
      and treatment to reduce morbidity from hypernatremia, dehydration, and dilatation
      of the urinary tract.
    explanation: >-
      GeneReviews names hypernatraemia as a source of morbidity that early diagnosis
      exists to reduce.
- category: Constitutional
  name: Dehydration
  frequency: FREQUENT
  description: >-
    Rapid-onset severe dehydration, characteristically precipitated rather than
    spontaneous. GeneReviews names the three precipitants explicitly: illness, a hot
    environment, and the withholding of water.
  phenotype_term:
    preferred_term: Dehydration
    term:
      id: HP:0001944
      label: Dehydration
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Affected untreated infants usually have poor feeding and failure to thrive, and
      rapid onset of severe dehydration with illness, hot environment, or the
      withholding of water.
    explanation: >-
      Gives both the pediatric context and the specific precipitants, which is the
      clinically actionable part of this phenotype.
- category: Constitutional
  name: Vomiting
  frequency: FREQUENT
  description: >-
    Vomiting and anorexia were the leading presenting complaints in a 30-patient
    series. This matters for diagnosis: a vomiting, poorly feeding infant is
    investigated for reflux, pyloric stenosis or infection long before anyone measures
    urine osmolality.
  phenotype_term:
    preferred_term: Vomiting
    term:
      id: HP:0002013
      label: Vomiting
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Main symptoms at clinical presentation were vomiting and anorexia, failure to
      thrive, fever, and constipation.
    explanation: >-
      The presenting-symptom list from the largest well-characterised clinical series,
      and the source for this phenotype, for Failure to thrive, for Fever and for
      Constipation.
- category: Constitutional
  name: Failure to thrive
  frequency: FREQUENT
  description: >-
    Poor weight gain in infancy, driven by the combination of anorexia, vomiting, and
    a stomach kept full of water. It is severe enough that gastrostomy placement is
    the commonest reported intervention for it, and severe enough that paediatric
    nephrologists report choosing drug therapy on the basis of how bad it is.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Main symptoms at clinical presentation were vomiting and anorexia, failure to
      thrive, fever, and constipation.
    explanation: Lists failure to thrive among the presenting features in 30 patients.
  - reference: PMID:29162216
    reference_title: "Treatment regimens by pediatric nephrologists in children with congenital nephrogenic diabetes insipidus: A MWPNC study ."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The most common intervention for FFT was gastrostomy tube placement (78%).
    explanation: >-
      Indicates the severity: most surveyed paediatric nephrologists reach for a
      gastrostomy. Note the survey's own typo in the abbreviation, quoted as published.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the time of first treatment, 70 and 71% of children were below -2 standard
      deviations (SD) for weight and height, respectively. At last follow-up, median age
      was 72.3 months (IQR 40.9, 137.2) and the percentage below -2 SD improved to 29%
      and 38% for weight and height, respectively.
    explanation: >-
      Quantifies both the deficit at diagnosis and the partial recovery on treatment, in
      66 children. It is also the source for the claim that weight recovers further than
      height: 70 to 29 per cent against 71 to 38 per cent.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients presented with polydipsia, polyuria (median diuresis: 10.0 (IQR:
      9.0-10.2) mL/kg/h), and failure to thrive.
    explanation: >-
      Failure to thrive was present in every patient in this cohort at presentation, and
      the sentence also gives the measured urine output.
- category: Constitutional
  name: Fever
  frequency: OCCASIONAL
  description: >-
    Unexplained fever is a genuinely useful diagnostic clue in an infant and is
    easily misread as infection. It was among the presenting symptoms in the
    30-patient series. In an older patient with a grossly dilated tract, recurrent
    fever may instead reflect poor bladder drainage and urinary infection - in one
    reported adolescent the fever settled after a urethral catheter was placed.
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Main symptoms at clinical presentation were vomiting and anorexia, failure to
      thrive, fever, and constipation.
    explanation: Lists fever as a presenting symptom.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Constipation and recurrent fever were observed in two patients (25.0%).
    explanation: >-
      Gives a proportion for recurrent fever, in a cohort of eight.
  - reference: PMID:27258490
    reference_title: "Congenital Nephrogenic Diabetes Insipidus Presented With Bilateral Hydronephrosis and Urinary Infection: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Transient insertion of a urethral catheter helped to relieve fever.
    explanation: >-
      Supports the second, mechanically distinct cause of fever in established
      disease - stasis and infection in a poorly draining dilated tract.
- category: Gastrointestinal
  name: Constipation
  frequency: OCCASIONAL
  description: >-
    Reported among the presenting symptoms, and a plausible consequence of chronic
    water deficit, although the cited sources list it rather than explain it.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Main symptoms at clinical presentation were vomiting and anorexia, failure to
      thrive, fever, and constipation.
    explanation: Lists constipation as a presenting symptom.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Constipation and recurrent fever were observed in two patients (25.0%).
    explanation: >-
      The only proportion available for either constipation or recurrent fever, from a
      cohort of eight - so a small denominator, and the basis for the OCCASIONAL band on
      both phenotypes.
- category: Growth
  name: Short stature
  frequency: FREQUENT
  description: >-
    Growth impairment persists in a way that weight does not. In long-term follow-up
    of 30 patients, height-for-age stayed below the 50th centile in the majority even
    though weight-for-height caught up after several years. This asymmetry is worth
    recording: nutritional rescue recovers weight but not height.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Height SD scores for age remained below the 50th percentile in the majority of
      patients, whereas weight for height SD scores showed a catch-up after several
      years of underweight.
    explanation: >-
      States both the persistence of the height deficit and the contrast with weight,
      in a long-term follow-up cohort.
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Short stature and secondary dilatation of the ureters and bladder from the high
      urine volume is common in untreated individuals.
    explanation: GeneReviews records short stature as common in untreated individuals.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hospitalizations, urologic complications, short stature, and CKD were common.
    explanation: >-
      The cohort's own summary of its outcome findings, naming short stature among the
      common ones.
- category: Renal
  name: Hydronephrosis
  frequency: OCCASIONAL
  description: >-
    Non-obstructive upper-tract dilatation produced by flow alone. It can become
    severe: two patients in a 30-patient series had severe hydronephrosis, one with a
    small rupture of the urinary tract after minor trauma. Annual renal ultrasound is
    recommended surveillance for exactly this reason.
  phenotype_term:
    preferred_term: Hydronephrosis
    term:
      id: HP:0000126
      label: Hydronephrosis
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two patients suffered from severe hydronephrosis with a small rupture of the
      urinary tract after a minor trauma, and two patients experienced episodes of
      acute urine retention.
    explanation: >-
      Gives the frequency and the severity ceiling, including the rupture, in a defined
      cohort.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Adverse outcomes included inpatient hospitalizations (61%), urologic complications
      (37%), and chronic kidney disease (CKD) stage 2 or higher in 23%.
    explanation: >-
      Puts urologic complications at 37 per cent of 66 children, which is the best
      available frequency figure for this group of phenotypes.
- category: Renal
  name: Hydroureter
  frequency: OCCASIONAL
  description: Ureteric dilatation secondary to the sustained urine volume, without obstruction.
  phenotype_term:
    preferred_term: Hydroureter
    term:
      id: HP:0000072
      label: Hydroureter
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Without treatment, most patients fail to grow normally, and present with
      associated constipation, urological complication, megacystis, trabeculated
      bladder, hydroureter, hydronephrosis, and mental retardation.
    explanation: >-
      Lists the urological complications of untreated disease, and is the source for
      this phenotype, for Megacystis and for Bladder trabeculation.
- category: Renal
  name: Megacystis
  frequency: OCCASIONAL
  description: >-
    A greatly enlarged bladder. Urodynamic study shows it remains compliant, so the
    problem is not a stiff bladder but a very large one that empties badly, leaving
    significant post-void residuals. Management is to reduce urine output, void on a
    schedule, and catheterise when residuals are significant.
  phenotype_term:
    preferred_term: Megacystis
    term:
      id: HP:0000021
      label: Megacystis
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Without treatment, most patients fail to grow normally, and present with
      associated constipation, urological complication, megacystis, trabeculated
      bladder, hydroureter, hydronephrosis, and mental retardation.
    explanation: Lists megacystis among the urological complications.
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      treat hydronephrosis, hydroureter, and megacystis with medical management to
      reduce urine output and continuous or intermittent bladder catheterization when
      post-void urinary bladder residuals are significant
    explanation: >-
      The management recommendation, which also establishes that significant post-void
      residual is the clinical problem megacystis creates.
- category: Renal
  name: Bladder trabeculation
  frequency: OCCASIONAL
  description: >-
    Trabeculation of the bladder wall in the absence of any infravesical obstruction -
    the radiological appearance of obstruction produced by flow instead. Recognising
    this matters, because the reflex response to a trabeculated bladder is to look for
    a posterior urethral valve that is not there.
  phenotype_term:
    preferred_term: Bladder trabeculation
    term:
      id: HP:0032465
      label: Bladder trabeculation
  evidence:
  - reference: PMID:22498392
    reference_title: Nonobstructive urinary tract dilatation in children with diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The high flow states caused the bladder to become trabeculated in the absence of
      infravesical obstruction.
    explanation: >-
      States that the trabeculation is flow-driven and that obstruction is absent,
      which is the whole point of this phenotype.
- category: Neurologic
  name: Intellectual disability
  frequency: OCCASIONAL
  description: >-
    This is where the literature contradicts itself, and the contradiction matters
    clinically. GeneReviews and the older teaching hold that intelligence is usually
    normal when the disease is diagnosed and treated early. A 2025 single-centre cohort
    followed for a median of 16.9 years found neurodevelopmental disorders - intellectual
    disability, autism spectrum disorder, language delay, learning difficulties - in six
    of its eight patients, all of whom were on hydrochlorothiazide and amiloride and all
    of whom had normalised serum sodium. Eight patients is a small and probably
    referral-selected denominator, so this is not a population risk estimate. But it is
    not reconcilable with "usually normal" by appeal to treatment status either, because
    these patients were treated. The attribution to electrolyte disturbance is stated in
    review form and hedged there; nothing cited here establishes the intermediate steps,
    quantifies the exposure, or separates repeated hypernatraemia from chronic
    undernutrition. See the attached knowledge gap.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Without treatment, most patients fail to grow normally, and present with
      associated constipation, urological complication, megacystis, trabeculated
      bladder, hydroureter, hydronephrosis, and mental retardation.
    explanation: >-
      The review lists this among the consequences of untreated disease.
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Irreversible brain damage and cognitive deficit secondary to electrolyte
      imbalances may be present.
    explanation: >-
      The review's own causal statement, quoted with its hedge intact. It is the basis
      for the sequela edge from Hypernatremia and for the knowledge gap attached to
      this phenotype.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neurodevelopmental disorders were identified in six patients, including intellectual
      disability, autism spectrum disorder, language delay, and learning difficulties.
    explanation: >-
      The numerator and the range of diagnoses, in a cohort of eight followed for a median
      of 16.9 years. This is the observation that makes the "usually normal with early
      treatment" teaching hard to sustain unexamined.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Although rare, NDI can significantly impact growth and neurodevelopment.
    explanation: >-
      The authors' own conclusion, which is what they take their cohort to show. Quoted
      separately from the numerator because it is a different claim - a general one about
      the disease rather than a count in this series.
- category: Renal
  name: Chronic kidney disease
  frequency: OCCASIONAL
  description: >-
    A late, largely preventable complication, and the strongest argument for treating
    this disease early rather than symptomatically. In a 66-child multicentre cohort,
    23 per cent had reached CKD stage 2 or higher by a median age of six years. The
    clearest illustration is a single family reported in 2024: the 6-month-old proband
    started on hydrochlorothiazide did well, while his maternal grandfather, who carried
    the same M272R variant and was never diagnosed or treated, had chronic kidney
    disease, severe bilateral hydronephrosis, hypertension and severe bladder
    dysfunction. Note that the one long-term cohort with nearly 17 years of follow-up on
    treatment reported renal function stable throughout, so this is an outcome of
    undertreated disease rather than an inevitability.
  phenotype_term:
    preferred_term: Chronic kidney disease
    term:
      id: HP:0012622
      label: Chronic kidney disease
  evidence:
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Adverse outcomes included inpatient hospitalizations (61%), urologic complications
      (37%), and chronic kidney disease (CKD) stage 2 or higher in 23%.
    explanation: >-
      The cohort figure, and the source for the hospitalisation and urologic-complication
      rates quoted elsewhere in this entry.
  - reference: PMID:39644399
    reference_title: The natural history of untreated X-linked nephrogenic diabetes insipidus with mutation in the vasopressin V2 receptor gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, this mutation was also identified in the patient's maternal
      grandfather, who had never been diagnosed or treated for NDI despite a history of
      polydipsia, polyuria, and evidence of chronic kidney disease (CKD), severe bilateral
      hydronephrosis, hypertension, and severe bladder dysfunction.
    explanation: >-
      The within-family treated-versus-untreated contrast, which is as close to a natural
      history experiment as this disease offers.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Renal function, serum sodium, and imaging findings remained stable throughout
      follow-up.
    explanation: >-
      Cuts against CKD being an expected outcome of this disease as such. Over a median
      16.9 years on hydrochlorothiazide and amiloride, renal function did not decline in
      this cohort - which is why the phenotype is framed as a consequence of undertreated
      disease.
- category: Renal
  name: Nocturnal enuresis
  frequency: OCCASIONAL
  description: >-
    Bed-wetting is often what brings an older child to attention, and in a child
    already known to have the disease it is an expected consequence of an obligatory
    night-time urine output rather than a behavioural problem. The frequency band is
    not taken from a cohort: the cited review names enuresis as a feature and as a
    complication of untreated disease but reports no proportion, so OCCASIONAL is the
    coarsest honest placement and should not be read as a measured figure.
  phenotype_term:
    preferred_term: Enuresis nocturna
    term:
      id: HP:0010677
      label: Enuresis nocturna
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      excessive urination during the night (nocturia), or bedwetting at night
      (nocturnal enuresis)
    explanation: >-
      Names nocturia and nocturnal enuresis among the presenting features of the
      disease in children.
biochemical:
- name: Urine osmolality
  presence: Decreased
  context: >-
    The measurement that defines the disease and the one that does not move when
    desmopressin is given. In symptomatic AVPR2 heterozygous females maximal urine
    osmolality did not exceed 200 mosmol/kg, against a normal maximum several times that,
    and the same non-response was demonstrable outside the kidney in two of them. No
    reference interval is curated here: no citable record in this round gave one, and the
    200 mosmol/kg figure is a reported ceiling in three patients, not an interval.
  biomarker_term:
    preferred_term: urine osmolality
    term:
      id: NCIT:C74801
      label: Osmolality Measurement
  readouts:
  - target: Failure of Medullary Countercurrent Urine Concentration
    relationship: READOUT_OF
    direction: THRESHOLD_DEPENDENT
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Directly reports the concentrating failure this node describes, and is
      threshold-dependent rather than simply low because the diagnostic question is the
      maximum achievable after water deprivation or desmopressin, not a single value.
    evidence:
    - reference: PMID:7607658
      reference_title: Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and
        the absence of extra-renal responses to 1-desamino-8-D-arginine vasopressin was
        demonstrated in two of them.
      explanation: >-
        Gives the measured ceiling in affected patients. Measured in symptomatic female
        heterozygotes, which is a limitation of this particular figure rather than of the
        readout.
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Nephrogenic diabetes insipidus (NDI) is characterized by impaired urinary
      concentrating ability, despite normal or elevated plasma concentrations of the
      antidiuretic hormone, arginine vasopressin (AVP).
    explanation: >-
      Establishes impaired urinary concentrating ability as the defining abnormality this
      marker measures, alongside an intact hormone level.
- name: Serum sodium
  presence: Increased
  context: >-
    The marker of decompensation rather than of the disease, and the one on a surveillance
    schedule: three-monthly in infants, six-monthly in older children, annually or as
    needed in adults. The reason it is monitored rather than measured only when someone
    looks unwell is that hyperosmolality and early dehydration can be present without
    being recognised clinically.
  biomarker_term:
    preferred_term: serum sodium concentration
    term:
      id: NCIT:C61029
      label: Serum Sodium Measurement
  readouts:
  - target: Hypernatremia
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: MONITORING
    interpretation: >-
      The measurement the phenotype is defined by, used here as the monitoring marker for
      unrecognised water deficit rather than as a diagnostic test for the disease.
    evidence:
    - reference: PMID:20301356
      reference_title: Hereditary Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        measurement of serum sodium concentration to identify unrecognized hyperosmolality
        and early dehydration at least every three months in infants, at least every six
        months in older children, and annually in adults or only as needed
      explanation: >-
        States the monitoring purpose and the schedule, which is what makes this a
        MONITORING rather than DIAGNOSTIC readout.
genetic:
- name: AVPR2
  gene_term:
    preferred_term: AVPR2
    term:
      id: hgnc:897
      label: AVPR2
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: PRESENT
  frequency: accounts for about 90 per cent of hereditary nephrogenic diabetes insipidus
  notes: >-
    AVPR2 at Xq28 is the sole gene for this entry, and it accounts for the large
    majority of hereditary nephrogenic diabetes insipidus overall: about 90 per cent,
    against roughly 9 per cent autosomal recessive and 1 per cent autosomal dominant
    AQP2 disease. The allelic spectrum is broad and mostly private - 82 distinct
    variants across 117 families - and the recurrences are independent events rather
    than a founder effect, so a new family generally means a new variant. Genotype
    does not predict phenotype usefully: the 30-patient clinical series found no clear
    clinical-genetic relationship beyond a possibly milder course with one variant. More
    than 200 AVPR2 variants have been linked to this disease and to the gain-of-function
    counterpart, nephrogenic syndrome of inappropriate antidiuresis. On variant class: the
    types represented are missense, nonsense, small insertions and deletions, large
    deletions and complex rearrangements, and functionally they sort into the three
    mechanistic classes modelled as the three routes out of the lesion node - absent or
    truncated protein, ER retention of a misfolded receptor, and a surface receptor that
    cannot signal. Two things are deliberately not asserted. No proportion is given for
    which class is commonest: the figure of roughly 70 per cent for the ER-retention class
    circulates widely and appears in the deep-research report for this entry, but no source
    cited here measures it, and the strongest citable statement is the weaker one that the
    function of most mutant receptors is not itself disturbed. Nor is a proportion given for
    each sequence-variant type, for the same reason.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Hereditary NDI is most commonly inherited in an X-linked manner (~90% of
      individuals). Hereditary NDI can also be inherited in an autosomal recessive
      manner (~9% of individuals) or in an autosomal dominant manner (~1% of
      individuals).
    explanation: >-
      Gives the share of hereditary NDI attributable to the X-linked AVPR2 form and the
      shares of the two autosomal AQP2 forms, which is what locates this entry within
      the group.
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of hereditary NDI is established in a male proband with NDI by
      identification of a hemizygous pathogenic variant in AVPR2 or identification of a
      compound heterozygous or homozygous pathogenic variant in AQP2 by molecular
      genetic testing.
    explanation: >-
      Establishes hemizygous AVPR2 variation as the diagnostic criterion in a male
      proband, and names the AQP2 alternative that has to be excluded.
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Except for a possibly milder phenotype in patients with a G185C mutation, no clear
      relationship between clinical and genetic data could be found.
    explanation: >-
      The basis for not asserting genotype-phenotype correlation, and for the single
      hedged exception.
  - reference: PMID:33664408
    reference_title: Cryo-EM structure of the AVP-vasopressin receptor 2-G(s) signaling complex.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      More than 200 mutations of the V2R gene have been linked to X-linked congenital
      nephrogenic diabetes insipidus (NDI) and nephrogenic syndrome of inappropriate
      antidiuresis (NSIAD).
    explanation: >-
      The current count of reported variants, and a reminder that the same gene carries
      gain-of-function alleles causing the opposite disease - which is why this entry's
      lesion node is explicit that it describes loss of function.
  - reference: PMID:17516711
    reference_title: "Pharmacological chaperones in nephrogenic diabetes insipidus: possibilities for clinical application."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      often this involves missense mutations or deletion of one or a few amino acids
    explanation: >-
      The variant types that predominate, stated as "often" rather than quantified. This is
      the strongest citable statement available on class composition and is why no percentage
      is asserted.
  - reference: PMID:32138955
    reference_title: V2 vasopressin receptor mutations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The mechanisms underlying a V2R loss-of-function can be theoretically classified
      as either protein expression, localization (ER retention) or functional
      disorders.
    explanation: >-
      The three-class functional taxonomy that the three routes out of the lesion node
      correspond to.
inheritance:
- name: X-linked recessive
  description: >-
    Affected males are hemizygous. The inheritance is conventionally called recessive
    because hemizygous males carry the full phenotype and most heterozygous females do
    not, but the female side is more interesting than "carrier" suggests: a
    heterozygous female can be as severely affected as a male, and the explanation
    offered for that is skewed X-inactivation against the normal allele. In a review of
    23 families with at least one affected female, every female in whom X-inactivation
    was studied showed extreme or slight skewing, and all six with severe disease carried
    complete loss-of-function alleles. In a Chinese family, skewing of the normal allele
    was present in four symptomatic heterozygotes and absent in an asymptomatic one.
    Two limits on that claim are worth stating rather than glossing. The inactivation
    pattern in all of these studies was measured in accessible somatic tissue, not in the
    collecting duct where the receptor has to work, so the inference to the relevant
    tissue is an inference. And the association is consistent rather than demonstrated
    sufficient: no cited study shows that skewing alone produces the phenotype. The
    practical consequence stands regardless - an AVPR2 heterozygote cannot be reassured
    on the basis of her sex, and a female with nephrogenic diabetes insipidus needs AVPR2
    considered alongside AQP2.
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  de_novo_rate: about 20 per cent of isolated cases, arising during maternal oogenesis
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Hereditary NDI is most commonly inherited in an X-linked manner (~90% of individuals).
    explanation: States the mode and its share of hereditary NDI.
  - reference: PMID:7607658
    reference_title: Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Skewed X-inactivation is the most likely explanation for the clinical
      manifestation of NDI in female carriers of an AVPR2 mutation.
    explanation: >-
      The original clinical description of symptomatic female heterozygotes and the
      proposed explanation. Quoted with its hedge - the authors say "most likely",
      not that they demonstrated it in these families.
  - reference: PMID:32073219
    reference_title: "A female with X-linked Nephrogenic diabetes insipidus in a family with inherited central diabetes Insipidus: Case report and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The review underlines that XL-NDI in female AVPR2 heterozygotes is always
      accompanied by skewed X-inactivation, emphasizing a need for X-inactivation
      studies in these females.
    explanation: >-
      The strongest available statement of the association, from a review of 23 families
      with affected females. Note it is an association in every studied case, not a
      demonstration that skewing is sufficient.
  - reference: PMID:35865667
    reference_title: "A Novel Missense Mutation of Arginine Vasopressin Receptor 2 in a Chinese Family with Congenital Nephrogenic Diabetes Insipidus: X-Chromosome Inactivation in Female CNDI Patients with Heterozygote 814A>G Mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Skewed X-chromosome inactivation patterns of the normal X allele were observed in
      4 females with the AVPR2 gene mutation and symptoms of diabetes insipidus, but not
      in an asymptomatic female with the AVPR2 gene mutation.
    explanation: >-
      The within-family contrast - skewed in the symptomatic heterozygotes, not skewed
      in the asymptomatic one - which is the closest thing the cited literature offers
      to a controlled comparison.
  - reference: PMID:10820168
    reference_title: Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A de novo mutation arose during oogenesis in the mother in 20% of isolated cases.
    explanation: The source for the de novo rate and for its parental origin.
progression:
- phase: Neonatal period and infancy
  notes: >-
    This is where the disease is dangerous and where it is missed. The presentation is
    not polyuria and thirst; it is a vomiting, anorexic, poorly growing infant with
    unexplained fever who dehydrates rapidly with any intercurrent illness, hot
    weather, or withholding of water. Most patients - 87 per cent in the largest series
    - are diagnosed within the first two and a half years, which is another way of
    saying that a substantial minority are not. Because the infant cannot drink to
    thirst unaided, carer-dependent water supply is the only thing preventing
    hypernatraemia, and being nil by mouth for a procedure is a specific hazard.
  evidence:
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The majority of patients (87%) were diagnosed within the first 2.5 yr of life.
      Main symptoms at clinical presentation were vomiting and anorexia, failure to
      thrive, fever, and constipation.
    explanation: Gives both the timing of diagnosis and the presenting symptom set.
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Affected untreated infants usually have poor feeding and failure to thrive, and
      rapid onset of severe dehydration with illness, hot environment, or the
      withholding of water.
    explanation: Names the precipitants of decompensation in infancy.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Median age at diagnosis was 4.2 months interquartile range (IQR 1.1, 9.8).
    explanation: >-
      The best available figure for age at diagnosis, from 66 children across 16 centres.
      Note the upper quartile: a quarter were diagnosed after ten months.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The median age at diagnosis was 7.5 months (interquartile range (IQR): 6.0-9.0).
    explanation: >-
      A second, later median from a different centre. Recorded alongside the first rather
      than averaged - these are two cohorts, not one estimate.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At diagnosis, the median serum sodium level was 160.5 mmol/L (IQR: 139-168), and the
      urine/plasma osmolality ratio was 0.41 (IQR: 0.26-0.49).
    explanation: >-
      Puts numbers on how decompensated these infants are when they are found: a median
      sodium of 160.5 mmol/L at diagnosis, with urine more dilute than plasma.
- phase: Childhood
  notes: >-
    Once water is freely available and drug therapy started, the acute danger recedes
    and the problem becomes chronic: polyuria, polydipsia, nocturia and bed-wetting,
    weight that eventually catches up, and height that largely does not. Growth and
    electrolyte surveillance is recommended three-monthly in infants and six-monthly in
    older children, with annual renal ultrasound for the urinary tract.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Monitor growth and development at least every three months in infants and at least
      every six months in older children; measurement of serum sodium concentration to
      identify unrecognized hyperosmolality and early dehydration at least every three
      months in infants, at least every six months in older children, and annually in
      adults or only as needed; annual kidney ultrasound examination to monitor for
      hydronephrosis and megacystis.
    explanation: >-
      The surveillance schedule, which is also an implicit statement of what the expected
      complications are at each age.
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Height SD scores for age remained below the 50th percentile in the majority of
      patients, whereas weight for height SD scores showed a catch-up after several
      years of underweight.
    explanation: The long-term growth trajectory, distinguishing height from weight.
- phase: Adolescence and adulthood
  notes: >-
    The urinary tract consequences dominate late. Dilatation accumulates silently over
    years of high flow and can reach severe hydronephrosis with megacystis, poor
    bladder drainage, recurrent infection and impaired renal function; one reported
    adolescent was voiding 10 to 15 litres daily with dilatation of pelvis, ureter and
    bladder. One review also notes an apparent loss of efficacy of medical treatment
    during school age, which if real is a reason not to assume a stable regimen lasts.
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Some authors note a generally favorable long-term outcome and an apparent loss of
      efficacy of medical treatment during school age.
    explanation: >-
      Records both halves as the review states them: a generally favourable outcome, and
      an apparent waning of treatment effect. Attributed to "some authors" in the source,
      and reproduced with that attribution rather than asserted.
  - reference: PMID:22498392
    reference_title: Nonobstructive urinary tract dilatation in children with diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Urodynamics have shown the bladder itself to be compliant, but drainage is poor
      leading to further renal impairment and overflow incontinence.
    explanation: >-
      States the late renal consequence of the dilated tract and the urodynamic finding
      that distinguishes it from an obstructive or non-compliant bladder.
  - reference: PMID:39644399
    reference_title: The natural history of untreated X-linked nephrogenic diabetes insipidus with mutation in the vasopressin V2 receptor gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The untreated grandfather's case highlights the potential severity of untreated NDI
      and the benefits of timely therapeutic intervention.
    explanation: >-
      The authors' reading of their own two-generation comparison, which is the closest
      approach to untreated natural history the literature offers for this disease.
diagnosis:
- name: Molecular genetic testing of AVPR2
  presence: PRESENT
  description: >-
    The diagnostic test. A hemizygous pathogenic AVPR2 variant establishes the
    diagnosis in a male proband; a heterozygous one does so in a female proband, in whom
    an X-inactivation study is then informative about why she is symptomatic. The
    alternative to exclude is biallelic AQP2 variation, which gives a clinically
    indistinguishable phenotype with different inheritance and different counselling.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of hereditary NDI is usually established in a female proband with
      NDI by identification of a heterozygous pathogenic variant in AVPR2 or
      identification of a compound heterozygous or homozygous pathogenic variant in AQP2
      by molecular genetic testing.
    explanation: >-
      The diagnostic criterion in a female proband, which is the half of this that is
      easy to get wrong.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genetic testing or a known family history was present in 70% of the patients; out of
      those genetically tested, 89 and 11% had mutations in AVPR2 and AQP2, respectively.
    explanation: >-
      A real-world check on the textbook 90:10 split, and a reminder that 30 per cent of a
      contemporary cohort had neither genetic testing nor a family history.
- name: Water deprivation test
  presence: PRESENT
  description: >-
    The classical confirmatory test, and the one this entry has to carry a safety caveat
    about rather than simply list. Water deprivation testing is contraindicated in the
    presence of hypernatraemia - serum sodium above 145 mmol/L - because of the risk of
    severe dehydration, and in practice the threshold used also includes plasma osmolality
    above 295 mOsm/kg. In that situation the desmopressin challenge is performed alone,
    without prior restriction. This matters more in this disease than the general caveat
    suggests: the median serum sodium at diagnosis in one cohort was 160.5 mmol/L, so the
    typical patient presents already past the threshold at which the test is unsafe. Where
    serum sodium is high or high-normal and the urine is inappropriately dilute, the
    diagnosis can be made without water restriction at all.
  evidence:
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Water deprivation testing is contraindicated in the presence of hypernatremia (serum
      sodium > 145 mmol/L) due to the risk of severe dehydration.
    explanation: >-
      The contraindication and its stated reason. Quoted from the cached full text of this
      paper, not from a secondary summary.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Water restriction was contraindicated in cases with plasma osmolality (osm(p)) > 295
      mOsm/kg and/or serum sodium > 145 mmol/L; in such instances, only the desmopressin
      challenge was performed.
    explanation: >-
      The operational rule as this centre applied it, which adds the osmolality limb of the
      threshold and states what is done instead.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In patients with elevated or high-normal serum sodium and inappropriately dilute urine,
      the diagnosis of diabetes insipidus can be established without the need for water
      restriction
    explanation: >-
      States that the test can be dispensed with altogether in the situation this disease
      usually presents in, which is the practical consequence of the contraindication.
- name: Basal plasma copeptin
  presence: PRESENT
  description: >-
    Copeptin is the stable C-terminal fragment of the vasopressin prohormone and stands in
    for a hormone that is itself unstable and largely platelet-bound. It is unusually well
    suited to this disease: because the lesion is downstream of normal or raised vasopressin
    secretion, an unstimulated basal copeptin measurement is sufficient to diagnose
    nephrogenic diabetes insipidus, where separating central diabetes insipidus from primary
    polydipsia needs a stimulation test. That asymmetry is the point - the test that is hard
    for the other two entities in the differential is easy for this one, and it avoids a
    water deprivation test that is contraindicated in most patients here. No numeric cutoff
    is curated: see the note on the unverified 21.4 pmol/L figure.
  evidence:
  - reference: PMID:32374887
    reference_title: Copeptin-based diagnosis of diabetes insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Whereas unstimulated basal copeptin measurement reliably diagnoses nephrogenic diabetes
      insipidus, two new tests using stimulated copeptin cutoff levels showed a high
      diagnostic accuracy in differentiating central diabetes insipidus from primary
      polydipsia.
    explanation: >-
      The claim curated here, and the asymmetry that makes basal copeptin a good test for
      this disease specifically rather than for the polyuria-polydipsia syndrome generally.
  - reference: PMID:32387127
    reference_title: "Diagnosis and differential diagnosis of diabetes insipidus: Update."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      While unstimulated basal copeptin measurement reliably diagnoses nephrogenic diabetes
      insipidus, a stimulation test is needed to differentiate patients with central diabetes
      insipidus from patients with primary polydipsia.
    explanation: >-
      An independent statement of the same asymmetry by a different review, which is why both
      are cited rather than one.
- name: Failure to concentrate urine after desmopressin
  presence: PRESENT
  description: >-
    The physiological discriminator between nephrogenic and central diabetes insipidus.
    A nephrogenic kidney does not concentrate urine when given exogenous vasopressin or
    desmopressin, because the defect is downstream of the hormone. Note that in the
    AVPR2 form the absence of response is not confined to the kidney: extrarenal V2
    receptor responses to desmopressin, such as the rise in coagulation factors, are
    also absent, and that was used as confirmatory evidence in symptomatic female
    heterozygotes.
  evidence:
  - reference: PMID:7607658
    reference_title: Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and
      the absence of extra-renal responses to 1-desamino-8-D-arginine vasopressin was
      demonstrated in two of them.
    explanation: >-
      Gives both the renal non-response with a numeric ceiling and the extrarenal
      non-response specific to a receptor-level lesion.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All desmopressin tests were negative.
    explanation: >-
      Every patient in the cohort failed to respond, which is the consistency that makes a
      negative desmopressin test useful rather than merely suggestive.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A desmopressin acetate loading test was administered to 46% of children at a median
      age of 4.8 months (IQR 2.8, 7.6); only 15% had a water restriction test.
    explanation: >-
      Shows what is actually done: fewer than half had a desmopressin test and only 15 per
      cent a water restriction test, so in practice the diagnosis is often made without
      either.
treatments:
- name: Free Access to Water
  description: >-
    The foundation of management and the one intervention that is non-negotiable.
    Because the water loss is obligatory, thirst-driven intake is the only
    compensation, so restricting water - including the routine nil-by-mouth before a
    procedure - converts a manageable chronic condition into acute hypernatraemia.
    GeneReviews lists water restriction explicitly under agents and circumstances to
    avoid, and specifies that a patient who must be nil by mouth receives their usual
    oral water intake intravenously as 5 per cent dextrose rather than saline.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: free access to drinking water and toilet facilities
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Obligatory Hypotonic Free Water Loss
    treatment_effect: MODULATES
    description: >-
      It does not reduce the water loss at all; it replaces it. Recorded as MODULATES
      rather than INHIBITS for that reason.
    evidence:
    - reference: PMID:20301356
      reference_title: Hereditary Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: free access to drinking water and to toilet facilities
      explanation: >-
        The management measure itself, as GeneReviews words it. It is the replacement of
        the loss, not its reduction, which is why the effect is MODULATES.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Water intake must not be restricted.
    explanation: >-
      The GeneReviews agents-to-avoid statement. Short, but it is the complete
      proposition and it is the single most important management instruction in the
      disease.
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      when "NPO" (nothing per ora), individuals with NDI must have intravenous
      replacement of their usual oral intake of water as 5% dextrose in water
    explanation: >-
      The specific peri-procedural instruction, including the fluid to use, which is
      where this goes wrong in practice.
- name: Thiazide Diuretic
  description: >-
    The counterintuitive mainstay: a diuretic given to reduce urine output. Used with
    a low-sodium diet it reduces polyuria by up to 50 per cent without causing
    hypernatraemia, and it is the one drug on which paediatric nephrologists agree -
    93 per cent of surveyed providers prescribe a thiazide. The mechanism is indirect
    and does not involve the collecting duct at all: the thiazide causes natriuresis,
    sodium depletion follows, and the resulting fall in effective renal plasma flow
    and glomerular filtration rate reduces distal delivery. Work in Brattleboro rats
    showed the antidiuresis disappears when sodium depletion is prevented, and that
    under those conditions urine volume actually rises - evidence that the antidiuretic
    effect is entirely secondary to volume contraction, with an additional suggestion
    of reduced proximal fluid reabsorption. Note the model caveat: those experiments
    used the hypothalamic (central) form of the disease, not a receptor-level one. On
    efficacy: serum sodium normalised in every patient of one long-term cohort on
    hydrochlorothiazide plus amiloride, but polyuria and polydipsia persisted in all of
    them throughout a median of 16.9 years - which is the honest summary of what this
    regimen achieves. It protects against hypernatraemia; it does not fix the water loss.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: hydrochlorothiazide
      term:
        id: CHEBI:5778
        label: hydrochlorothiazide
  target_mechanisms:
  - target: Obligatory Hypotonic Free Water Loss
    treatment_effect: MODULATES
    description: >-
      Reduces the volume of the obligatory loss by reducing distal delivery, through
      volume contraction. It does not restore collecting duct water permeability and
      does not touch the receptor defect.
    evidence:
    - reference: PMID:630797
      reference_title: The role of sodium depletion in hydrochlorothiazide-induced antidiuresis in Brattleboro rats with diabetes insipidus.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      directness: INDIRECT
      snippet: >-
        The results indicate that the antidiuresis caused by hydrochlorothiazide in
        diabetes insipidus results, at least in part, from falls in effective renal
        plasma flow and glomerular filtration rate. These in turn seem to be entirely
        secondary to the drug-induced sodium depletion.
      explanation: >-
        Establishes the mechanism of the antidiuresis, in the only experiment cited here
        that manipulated sodium balance to test it. Marked INDIRECT because the model is
        the hypothalamic form of diabetes insipidus, so the finding transfers to XNDI by
        the argument that the drug acts upstream of the collecting duct rather than by
        direct demonstration in a V2 receptor-deficient animal.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      reduction of polyuria (and thus polydipsia) up to 50% without inducing
      hypernatremia by use of a thiazide diuretic (e.g., hydrochlorothiazide,
      chlorothiazide) often used in combination with either amiloride (a
      potassium-sparing diuretic) or indomethacin; dietary restriction of sodium
    explanation: >-
      Quantifies the achievable benefit, names the agents, and records that the thiazide
      is normally combined with amiloride or indomethacin and paired with sodium
      restriction.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Over a median follow-up period of 16.9 years (IQR: 8.4-17.4), growth improved, but all
      patients continued to exhibit polyuria and polydipsia.
    explanation: >-
      The ceiling on what the regimen does: growth improves, the polyuria does not go away.
      This is the sentence that keeps the treatment framed as symptomatic.
  - reference: PMID:29162216
    reference_title: "Treatment regimens by pediatric nephrologists in children with congenital nephrogenic diabetes insipidus: A MWPNC study ."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our results suggest consensus on the use of thiazides, while the use of
      indomethacin is limited by GI and renal side effect profile.
    explanation: >-
      Establishes the thiazide as the point of consensus and locates the disagreement at
      indomethacin.
  - reference: PMID:32039113
    reference_title: "Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common treatments were thiazide diuretics (74%), potassium-sparing diuretics
      (67%) and non-steroidal anti-inflammatory drugs (42%).
    explanation: >-
      What was actually prescribed to 66 children, rather than what providers say they
      prescribe. It is the source for the prescribing proportions on this treatment, on
      Amiloride and on Indomethacin or Other NSAID.
- name: Amiloride
  description: >-
    A potassium-sparing diuretic added to a thiazide, prescribed by 62 per cent of
    surveyed paediatric nephrologists. Two reasons are given in the literature for
    preferring it as the partner drug: it offsets the thiazide's potassium loss, and it
    avoids the gastrointestinal and renal toxicity that limits indomethacin. The
    combination was the maintenance regimen for most patients in the 30-patient series,
    reportedly without significant side effects.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: amiloride
      term:
        id: CHEBI:2639
        label: amiloride
  target_mechanisms:
  - target: Obligatory Hypotonic Free Water Loss
    treatment_effect: MODULATES
    description: >-
      Acts as an adjunct to the thiazide's volume-contraction effect rather than through
      a mechanism of its own that has been demonstrated in this disease.
    evidence:
    - reference: PMID:20301356
      reference_title: Hereditary Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        often used in combination with either amiloride (a potassium-sparing diuretic) or
        indomethacin; dietary restriction of sodium
      explanation: >-
        Places amiloride as the thiazide's partner drug rather than as an independent
        treatment, which is what this link records.
  evidence:
  - reference: PMID:29162216
    reference_title: "Treatment regimens by pediatric nephrologists in children with congenital nephrogenic diabetes insipidus: A MWPNC study ."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      almost all prescribed thiazides (93%), 62% prescribed amiloride, and 55% reported
      prescribing nonsteroidal anti-inflammatory drugs (NSAIDs) as part of their drug
      regimen.
    explanation: >-
      Gives the prescribing proportions for all three drug classes in this entry, from a
      survey of 72 paediatric nephrologists.
  - reference: PMID:10477148
    reference_title: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most patients were on hydrochlorothiazide-amiloride treatment without significant
      side effects.
    explanation: >-
      Supports the combination as the usual long-term regimen and records its
      tolerability in a followed cohort.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients were treated with hydrochlorothiazide and amiloride; indomethacin was
      added in 5 (62.5%).
    explanation: >-
      The thiazide-amiloride pair was universal in this cohort and indomethacin was the
      add-on, which is the same hierarchy the larger cohort shows at different proportions.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the final assessment, all patients remained on hydrochlorothiazide and amiloride.
    explanation: >-
      The regimen was sustained over a median of 16.9 years, which is the best available
      evidence that it is tolerable long term.
- name: Indomethacin or Other NSAID
  description: >-
    A prostaglandin synthesis inhibitor used as the alternative third agent. It works -
    and is prescribed by 55 per cent of surveyed providers - but it is the contested
    part of the regimen: 43 per cent of providers who avoid it cite gastrointestinal and
    renal side effects, which in a child with an already compromised urinary tract is
    not a trivial concern. The usual rationale is that renal prostaglandin E2 opposes the
    concentrating mechanism, so removing it helps, and that step is now cited here: PGE2
    reverses vasopressin-induced translocation of aquaporin-2 to the plasma membrane in rat
    inner medulla, acting by activating retrieval of the channel. Two caveats keep this from
    being a clean explanation of the drug's benefit in this disease, and they are the reason
    the mechanism link below is still only MODULATES. First, what PGE2 was shown to reverse
    was vasopressin-induced translocation - a process that does not occur in a V2
    receptor-null kidney, so the demonstrated mechanism presupposes the very signalling this
    disease lacks. Second, in the same experiments PGE2 on its own did not alter aquaporin-2
    phosphorylation or distribution at all, which argues against a standing PGE2 brake that
    an NSAID could release in the absence of vasopressin action. The benefit is real and
    well attested clinically; the route by which it is obtained in a receptor-null kidney is
    not established by anything cited here.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: indomethacin
      term:
        id: CHEBI:49662
        label: indometacin
  target_mechanisms:
  - target: Obligatory Hypotonic Free Water Loss
    treatment_effect: MODULATES
    description: >-
      Kept as MODULATES rather than upgraded. The candidate mechanism - relieving a PGE2
      brake on apical aquaporin-2 retention - is now cited, but it was demonstrated as an
      antagonism of vasopressin-induced trafficking, which does not happen in this disease,
      and PGE2 alone moved neither aquaporin-2 phosphorylation nor its distribution. So the
      drug's clinical effect is attested and its route through this node is not.
    evidence:
    - reference: PMID:10710543
      reference_title: "Prostaglandin E(2) interaction with AVP: effects on AQP2 phosphorylation and distribution."
      supports: SUPPORT
      evidence_source: IN_VITRO
      directness: INDIRECT
      snippet: >-
        PGE(2) (10(-7) M) added after AVP (10(-8) M) did not decrease AQP2 phosphorylation but
        reversed AVP-induced translocation of AQP2 to the plasma membrane.
      explanation: >-
        The mechanistic step behind the rationale, and the reason it is marked INDIRECT: the
        effect measured is reversal of vasopressin-induced translocation in a kidney with
        intact vasopressin signalling, so applying it to a V2 receptor-null kidney is an
        inference rather than a demonstration.
    - reference: PMID:10710543
      reference_title: "Prostaglandin E(2) interaction with AVP: effects on AQP2 phosphorylation and distribution."
      supports: REFUTE
      evidence_source: IN_VITRO
      snippet: >-
        PGE(2) alone did not influence AQP2 phosphorylation and subcellular distribution.
      explanation: >-
        Cuts against the simple version of the rationale. If PGE2 exerts no effect without
        vasopressin, then removing PGE2 should not by itself restore apical aquaporin-2 in a
        receptor-null kidney, which is why the effect on this node is not upgraded.
  evidence:
  - reference: PMID:10710543
    reference_title: "Prostaglandin E(2) interaction with AVP: effects on AQP2 phosphorylation and distribution."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our data indicate that 1) recruitment of AQP2 to the plasma membrane and its retrieval
      to a pool of intracellular vesicles may be regulated independently, 2) PGE(2) may
      counteract AVP action by activation of AQP2 retrieval, 3) dephosphorylation of AQP2 is
      not a prerequisite for its internalization.
    explanation: >-
      The authors' own three conclusions. The second is the prostaglandin rationale for using
      an NSAID; the first and third matter separately for this entry, because they show
      aquaporin-2 phosphorylation and apical retention are separable - see the note on the
      naming of the aquaporin-2 node.
  - reference: PMID:29162216
    reference_title: "Treatment regimens by pediatric nephrologists in children with congenital nephrogenic diabetes insipidus: A MWPNC study ."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      gastrointestinal (GI) and renal side effects (43%) were given as reasons for not
      prescribing indomethacin.
    explanation: The reason indomethacin is not used universally, quantified.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients were treated with hydrochlorothiazide and amiloride; indomethacin was
      added in 5 (62.5%).
    explanation: >-
      Gives the proportion receiving indomethacin as an addition to the thiazide-amiloride
      base, in a cohort of eight.
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Treatment of NDI consist of sufficient water intake, low-sodium diet, diuretic
      thiazide, sometimes in combination with a cyclooxygenase (COX) inhibitor
      (indomethacin) or nonsteroidal anti-inflammatory drugs (NSAIDs), or
      hydrochlorothiazide in combination with amiloride.
    explanation: >-
      The full regimen as the review states it, and the source for indomethacin being a
      cyclooxygenase inhibitor used as an optional addition rather than a mainstay.
- name: Low-Solute, Sodium-Restricted Diet
  description: >-
    A dietary rather than pharmacological intervention, and a necessary partner to the
    thiazide: because the obligatory urine volume is set by the solute load that has to
    be excreted, reducing dietary solute - principally sodium - reduces the volume
    directly. This is the correct slot for the diet, not a drug with an agent binding.
    The accompanying nutritional problem pulls the other way, since an infant with
    failure to thrive needs calories, which is why dietitian involvement is standard
    and why a gastrostomy is often how both requirements are met at once.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: low-solute, sodium-restricted diet
    term:
      id: NCIT:C15447
      label: Dietary Intervention
    dietary_modifications:
    - action: RESTRICT
      description: >-
        Dietary restriction of sodium, to reduce the osmolar load that must be excreted
        and so the obligatory urine volume.
    - action: RESTRICT
      description: >-
        Reduction of total dietary solute load, the broader version of the same
        principle.
  target_mechanisms:
  - target: Obligatory Hypotonic Free Water Loss
    treatment_effect: MODULATES
    description: >-
      Lowers the solute load whose excretion obliges the water loss, reducing its volume
      without affecting the collecting duct defect.
    evidence:
    - reference: PMID:30454745
      reference_title: Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Management of NDI can be difficult with only symptomatic treatment available, using
        low-solute diet, diuretics, and prostaglandin inhibitors.
      explanation: >-
        Names the low-solute diet as one of the measures acting on the polyuria, and states
        that it is symptomatic - which is the limit of what this link claims.
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      often used in combination with either amiloride (a potassium-sparing diuretic) or
      indomethacin; dietary restriction of sodium
    explanation: >-
      GeneReviews lists sodium restriction among the management measures, in the same
      clause that names the drug combinations it accompanies.
  - reference: PMID:30454745
    reference_title: Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Management of NDI can be difficult with only symptomatic treatment available, using
      low-solute diet, diuretics, and prostaglandin inhibitors.
    explanation: >-
      Names the low-solute diet as one of the three available measures, and states
      plainly that all of them are symptomatic.
- name: Urinary Tract Management and Bladder Drainage
  description: >-
    Management of the mechanical complication rather than the metabolic one. The
    principles are to reduce urine output with drug and dietary therapy, void on a
    schedule - two-hourly is the interval recommended - and catheterise when post-void
    residuals become significant. In severe cases cystostomy button drainage has been
    used. The point of the scheduled voiding is prevention: it is offered as a way of
    preventing or reducing the tract dilatation rather than treating it once
    established.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: bladder catheterisation and timed voiding
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Sustained High Urinary Tract Flow
    treatment_effect: MODULATES
    description: >-
      Addresses the consequence of the flow - poor drainage and residual urine - and, via
      timed voiding, reduces the dwell time that drives the dilatation.
    evidence:
    - reference: PMID:20301356
      reference_title: Hereditary Nephrogenic Diabetes Insipidus.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Reduction of urine production by drug therapy and voiding at two-hour intervals may
        prevent or reduce serious renal, ureteral, or bladder dilatation.
      explanation: >-
        States the intervention acting on the flow consequence, with the source's own "may".
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Reduction of urine production by drug therapy and voiding at two-hour intervals may
      prevent or reduce serious renal, ureteral, or bladder dilatation.
    explanation: >-
      The preventive recommendation and its stated interval, quoted with the source's own
      "may".
  - reference: PMID:22498392
    reference_title: Nonobstructive urinary tract dilatation in children with diabetes insipidus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All 4 boys have been managed with cystostomy button drainage and have done well on
      close follow-up.
    explanation: >-
      The reported surgical drainage approach in the severe end of the spectrum. Four
      patients with no comparator, so it supports that this is done, not that it is
      superior.
- name: Genetic Counselling and Testing of At-Risk Relatives
  description: >-
    Counselling follows ordinary X-linked logic, with the caveat that a heterozygous
    female is not reliably unaffected. The substantive clinical point is that
    identifying an at-risk infant early is itself a treatment: GeneReviews frames early
    evaluation of at-risk infants as the way to reduce morbidity from hypernatraemia,
    dehydration and tract dilatation, all three of which are cumulative and partly
    preventable.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301356
    reference_title: Hereditary Nephrogenic Diabetes Insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Evaluation of at-risk infants as early as possible to allow for prompt diagnosis
      and treatment to reduce morbidity from hypernatremia, dehydration, and dilatation
      of the urinary tract.
    explanation: >-
      States the rationale for cascade testing in terms of the specific morbidities it
      prevents.
  - reference: PMID:39438674
    reference_title: International expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus (arginine vasopressin resistance).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Here, we present 36 recommendations for diagnosis, treatment and follow-up in both
      children and adults, as well as emergency management, genetic counselling and family
      planning, for patients with NDI.
    explanation: >-
      Establishes that genetic counselling and family planning are within the scope of the
      graded international recommendations for this disease, rather than being an informal
      addition to management.
animal_models:
- name: V2R Glu242stop knock-in mouse
  species: Mouse
  genotype: Avpr2 Glu242stop (nonsense allele knocked in by targeted mutagenesis in ES cells)
  description: >-
    The defining animal model, and deliberately constructed as a disease model rather
    than a convenience knockout: the allele introduced is a nonsense variant known to
    cause XNDI in humans. Hemizygous males reproduce the severe human infantile
    phenotype closely - low basal urine osmolality, inability to concentrate,
    enlargement of the renal pelvic space, failure to thrive, and death in the first
    postnatal week from hypernatraemic dehydration - which is what an untreated human
    infant is at risk of. Heterozygous females are the second useful result: they grow
    normally but have reduced concentrating ability with polyuria and polydipsia, the
    murine counterpart of the symptomatic human heterozygote. The model also provides
    the cleanest available evidence that aquaporin-2 is not the problem in this
    disease: basal AQP2 expression was unaffected by loss of functional V2 receptors.
  publication: PMID:11104789
  modeled_mechanisms:
  - target: Absent or Truncated V2 Receptor Protein
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: MOLECULAR
    description: >-
      Glu242stop is a nonsense allele, so this model belongs to the protein-expression
      class and this is the node it enters the pathograph at. Linked explicitly because the
      alternative - entering at the cascade node - would leave the model's own variant class
      unrepresented, which is the gap this link closes.
    limitations: >-
      The study reports the allele and the resulting whole-animal phenotype; it does not
      show absence of receptor protein in these mice directly, so the class assignment rests
      on the nature of the allele rather than on a Western blot in this model.
    evidence:
    - reference: PMID:11104789
      reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Specifically, we introduced a nonsense mutation known to cause X-linked
        nephrogenic diabetes insipidus (XNDI) in humans (Glu242stop) into the mouse
        genome.
      explanation: >-
        Names the allele as a nonsense variant, which is what places this model in the
        protein-expression class rather than in the ER-retention class.
  - target: Loss of Vasopressin-Stimulated cAMP and PKA Signalling
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: ORGANISM
    description: >-
      A human XNDI nonsense allele at the orthologous position, producing the expected
      receptor-level loss of function in the intact animal.
    limitations: >-
      The model observes the whole organism, so the receptor-level signalling failure
      itself is inferred from the physiology rather than measured in this report; cAMP
      and PKA were not assayed here.
    evidence:
    - reference: PMID:11104789
      reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Specifically, we introduced a nonsense mutation known to cause X-linked
        nephrogenic diabetes insipidus (XNDI) in humans (Glu242stop) into the mouse
        genome.
      explanation: >-
        The allele is a human disease variant placed at the orthologous position, which
        is what makes this model informative for the human receptor-level lesion rather
        than for V2 receptor biology in general.
    readouts:
    - name: Basal urine osmolality
      target: Loss of Vasopressin-Stimulated cAMP and PKA Signalling
      direction: DECREASED
      interpretation: >-
        The functional consequence of the absent receptor signal, measured at the level
        of the organism's urine.
      evidence:
      - reference: PMID:11104789
        reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          V2R-deficient hemizygous male pups showed a decrease in basal urine osmolalities
          and were unable to concentrate their urine.
        explanation: The measured concentrating defect in the hemizygous animals.
  - target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Supports the node in its important negative sense - that AQP2 abundance is not
      reduced, so the lesion is regulatory - without demonstrating the positive claim
      about phosphorylation and apical trafficking.
    limitations: >-
      Only basal AQP2 expression levels were assessed. Phosphorylation state and
      subcellular redistribution after a vasopressin stimulus, which are the actual
      content of this node, were not measured, so the model speaks to abundance rather
      than to trafficking.
    evidence:
    - reference: PMID:11104789
      reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Western blot analysis and immunoelectron microscopic studies showed that the loss
        of functional V2Rs had no significant effect on the basal expression levels of
        aquaporin-2 and the bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1).
      explanation: >-
        Establishes that this model bears on the AQP2 node at all, and bears on it in the
        negative direction - abundance preserved - which is the only part of the node it
        can speak to.
    readouts:
    - name: Basal aquaporin-2 protein abundance
      target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
      direction: UNCHANGED
      interpretation: >-
        A genuine negative result, and the one that matters: the water channel is present
        in normal amounts, so the defect is in its regulation.
      evidence:
      - reference: PMID:11104789
        reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Western blot analysis and immunoelectron microscopic studies showed that the loss
          of functional V2Rs had no significant effect on the basal expression levels of
          aquaporin-2 and the bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1).
        explanation: >-
          The measurement establishing that AQP2 abundance is preserved when the receptor
          is lost.
  - target: Obligatory Hypotonic Free Water Loss
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: ORGANISM
    description: >-
      Hemizygous males died of hypernatraemic dehydration within the first postnatal
      week, and heterozygous females showed polyuria and polydipsia with reduced
      concentrating ability.
    limitations: >-
      The hemizygous phenotype is more severe than treated human disease and lethal
      within a week, so it models the untreated infantile extreme rather than the
      clinical course of a managed patient.
    evidence:
    - reference: PMID:11104789
      reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These pups also exhibited an enlargement of renal pelvic space, failed to thrive,
        and died within the first week after birth due to hypernatremic dehydration.
      explanation: >-
        The organism-level water-loss consequence in the model, matching the human
        features - renal pelvic dilatation, failure to thrive, hypernatraemic
        dehydration - that this node produces.
    readouts:
    - name: Polyuria and polydipsia in heterozygous females
      target: Obligatory Hypotonic Free Water Loss
      direction: INCREASED
      interpretation: >-
        The murine counterpart of the symptomatic human female heterozygote, with the
        same partial phenotype.
      evidence:
      - reference: PMID:11104789
        reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          female mice heterozygous for the V2R mutation showed normal growth but displayed
          an XNDI-like phenotype, characterized by reduced urine concentrating ability of
          the kidney, polyuria, and polydipsia.
        explanation: The measured phenotype in the heterozygous females.
  evidence:
  - reference: PMID:11104789
    reference_title: Generation and phenotype of mice harboring a nonsense mutation in the V2 vasopressin receptor gene.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These pups also exhibited an enlargement of renal pelvic space, failed to thrive,
      and died within the first week after birth due to hypernatremic dehydration.
    explanation: >-
      Establishes that the model reproduces the specific human features - renal pelvic
      dilatation, failure to thrive, hypernatraemic dehydration - rather than a generic
      polyuria, which is what makes it informative for this entry.
- name: Avpr2-deficient rat (rGONAD)
  species: Rat
  genotype: Avpr2 knockout, generated by rat Genome-editing via Oviductal Nucleic Acid Delivery
  description: >-
    The model that supplies what the mouse could not. Unlike the constitutive Avpr2-null
    mouse, these rats survive weaning under normal rearing, so the chronic consequences
    are observable: polydipsia, polyuria, growth retardation, and hydronephrosis-like
    kidneys. Two of its findings bear directly on this entry's pathograph. First,
    aquaporin-2 was retained in the cytoplasm of collecting duct cells with its
    phosphorylation suppressed - a direct measurement of the node about trafficking and
    phosphorylation, which the mouse study could only address as preserved abundance. Second, the hydronephrosis-like kidneys showed no glomerular or tubular
    damage, which is the experimental version of the clinical claim that the tract
    dilatation is mechanical rather than a primary nephropathy. Hydrochlorothiazide
    reduced urine volume and improved urine osmolality in the model, so it also
    reproduces the therapeutic response.
  publication: PMID:40102322
  modeled_mechanisms:
  - target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: CELLULAR
    description: >-
      Directly measures both halves of this node in collecting duct cells - aquaporin-2
      held in the cytoplasm, and its phosphorylation suppressed.
    limitations: >-
      A whole-gene knockout rather than a human misfolding allele, so it models the
      consequence of absent receptor function and not the ER-retention route that produces
      it in most patients. Phosphorylation was reported as suppressed without the
      site-level detail that would tie it to Ser256 specifically.
    evidence:
    - reference: PMID:40102322
      reference_title: Construction of arginine vasopressin receptor 2-deficient rats by the rGONAD method.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Aquaporin-2 was retained in the cytoplasm of collecting duct cells, and its
        phosphorylation was suppressed.
      explanation: >-
        The measurement of this node in an animal, which no other model cited here provides.
    readouts:
    - name: Subcellular localization and phosphorylation of aquaporin-2 in collecting duct cells
      target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
      direction: DECREASED
      interpretation: >-
        Apical delivery and phosphorylation both reduced, with the channel held in the
        cytoplasm - the node's claim, measured.
      evidence:
      - reference: PMID:40102322
        reference_title: Construction of arginine vasopressin receptor 2-deficient rats by the rGONAD method.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Aquaporin-2 was retained in the cytoplasm of collecting duct cells, and its
          phosphorylation was suppressed.
        explanation: The histological and biochemical readout behind this link.
  - target: Sustained High Urinary Tract Flow
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Hydronephrosis-like kidneys developed with no glomerular or tubular damage, which is
      the mechanical-not-nephropathic claim this node makes.
    limitations: >-
      Rodent urinary tract anatomy and lifespan differ from the human course, where the
      dilatation accumulates over decades; and the absence of glomerular or tubular damage
      is reported at the timepoint examined rather than across the animal's life.
    evidence:
    - reference: PMID:40102322
      reference_title: Construction of arginine vasopressin receptor 2-deficient rats by the rGONAD method.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Although they exhibited hydronephrosis-like kidneys, no glomerular or tubular damage
        was observed.
      explanation: >-
        Supports the dilatation being a consequence of flow rather than of parenchymal
        disease.
    readouts:
    - name: Renal pelvic dilatation with preserved glomerular and tubular histology
      target: Sustained High Urinary Tract Flow
      direction: INCREASED
      interpretation: >-
        Dilatation present, parenchymal injury absent - the combination that distinguishes a
        flow effect from a nephropathy.
      evidence:
      - reference: PMID:40102322
        reference_title: Construction of arginine vasopressin receptor 2-deficient rats by the rGONAD method.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Although they exhibited hydronephrosis-like kidneys, no glomerular or tubular damage
          was observed.
        explanation: The histological readout behind this link.
  evidence:
  - reference: PMID:40102322
    reference_title: Construction of arginine vasopressin receptor 2-deficient rats by the rGONAD method.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Avpr2-deficient rats were born and weaned under normal rearing conditions and
      exhibited symptoms similar to those of human congenital NDI, such as polydipsia,
      polyuria, and growth retardation.
    explanation: >-
      Establishes survival past weaning and phenotypic similarity, which together are what
      make this model usable for the chronic consequences.
- name: X-NDI mouse treated with a beta-3 adrenergic agonist
  species: Mouse
  genotype: mouse model of X-linked nephrogenic diabetes insipidus (AVPR2-inactivated)
  description: >-
    A rescue experiment rather than a disease model, and included because of what the
    rescue demonstrates about the mechanism. The hypothesis was that a different Gs-coupled
    receptor on the same cells could be used to raise cAMP without the V2 receptor. A
    single injection of the beta-3 adrenergic agonist BRL37344 worked for only three hours,
    but repeated dosing over 24 hours - imitating a slow-release preparation - cut 24-hour
    urine output by 27 per cent, raised urine osmolarity by 25 per cent and reduced water
    intake by 20 per cent. The molecular readout is the point: the drug increased
    phosphorylation of AQP2 (along with NKCC2 and NCC) in the renal cell membrane. Raising
    AQP2 phosphorylation from outside the V2 receptor restores water handling, which is
    direct support for the entry's claim that the AQP2 step is where the cascade failure is
    cashed out.
  publication: PMID:38652212
  modeled_mechanisms:
  - target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
    relationship: RESCUES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Pharmacological rescue of the node by a V2-receptor-independent route, with both the
      molecular step (AQP2 phosphorylation) and the whole-animal consequence measured.
    limitations: >-
      A mouse, and a pharmacological rescue with a three-hour duration of action that had to
      be worked around by repeated injection; the effect is partial (27 per cent of urine
      output) rather than corrective, and BRL37344 is a rodent-selective beta-3 agonist
      whose translation to human beta-3 pharmacology is not demonstrated here.
    evidence:
    - reference: PMID:38652212
      reference_title: The β3-AR agonist BRL37344 ameliorates the main symptoms of X-linked nephrogenic diabetes insipidus in the mouse model of the disease.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        At the molecular level, we show that BRL37344 acted by increasing the phosphorylation
        of NKCC2, NCC and AQP2 in the renal cell membrane, thereby increasing electrolytes
        and water reabsorption in the kidney tubule of X-NDI mice.
      explanation: >-
        Names AQP2 phosphorylation as the step the rescue acts through, which is what makes
        this a rescue of this node rather than a general antidiuretic effect.
    readouts:
    - name: 24-hour urine output, urine osmolarity and water intake after repeated BRL37344
      target: Failure of Aquaporin-2 Phosphorylation and Apical Insertion
      direction: RESTORED
      interpretation: >-
        Partial restoration of water handling, quantified in three directions at once. Read as
        partial: a 27 per cent reduction in output is a real effect and not a correction.
      evidence:
      - reference: PMID:38652212
        reference_title: The β3-AR agonist BRL37344 ameliorates the main symptoms of X-linked nephrogenic diabetes insipidus in the mouse model of the disease.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          repeated administrations in the 24 h, mimicking the effect of a slow-release
          preparation, promoted a sustained antidiuretic effect, reducing the 24 h urine output
          by 27%, increasing urine osmolarity by 25% and reducing the water intake by 20%.
        explanation: The three measured outcomes and the dosing schedule needed to obtain them.
  evidence:
  - reference: PMID:38652212
    reference_title: The β3-AR agonist BRL37344 ameliorates the main symptoms of X-linked nephrogenic diabetes insipidus in the mouse model of the disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The disease, which still lacks a cure, could benefit from the pharmacologic
      stimulation of other GPCRs, activating the cAMP-intracellular pathway in the kidney
      cells expressing the AVPR2.
    explanation: >-
      The design rationale, which is also the mechanistic claim the experiment tests: the
      cascade below the receptor is intact and reachable from another receptor.
experimental_models:
- name: Polarized MDCK cells stably expressing V2 receptor mutants
  experimental_model_type: CELL_LINE
  description: >-
    The system in which the pharmacochaperone idea was tested properly. Nine different
    disease-causing V2 receptor mutants were stably expressed in polarized MDCK cells -
    which matters, because a receptor's destination is the basolateral membrane and an
    unpolarized cell cannot report on that. Four cell-permeable non-peptide antagonists
    rescued maturation and basolateral expression of eight of the nine mutants. The
    study's real contribution is the constraint it found: rescue at concentrations a
    patient could actually receive required high-affinity antagonists, because the
    low-affinity one needed concentrations that were not clinically feasible even though
    it was easier for vasopressin to displace.
  publication: PMID:16926443
  notes: >-
    No cell_types binding. MDCK is a canine kidney epithelial line, and binding it to
    the human collecting-duct principal cell term would overstate what the system is;
    CL does not represent cell lines, and no CLO binding is available in this schema.
    The polarization of the line, which is the property that makes it informative about
    basolateral delivery, is described above instead.
  modeled_mechanisms:
  - target: Endoplasmic Reticulum Retention of Misfolded V2 Receptor
    relationship: RESCUES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Cell-permeable non-peptide antagonists restored membrane expression and function of
      ER-retained mutants, which is the experimental demonstration that retention, not
      intrinsic receptor failure, is the rate-limiting lesion.
    limitations: >-
      A canine kidney cell line overexpressing a transfected human receptor, not a human
      principal cell in situ; rescue was shown for eight of nine mutants tested, so it is
      allele-dependent; and no clinical benefit in patients is demonstrated by this work.
    evidence:
    - reference: PMID:16926443
      reference_title: "Functional rescue of vasopressin V2 receptor mutants in MDCK cells by pharmacochaperones: relevance to therapy of nephrogenic diabetes insipidus."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Intracellular retention of a functional vasopressin V2 receptor (V2R) is a major
        cause of congenital nephrogenic diabetes insipidus (NDI) and rescue of V2R mutants
        by nonpeptide antagonists may restore their basolateral membrane (BM) localization
        and function.
      explanation: >-
        States that the lesion this model manipulates is the one this node describes, which
        is what makes the model informative for it.
    readouts:
    - name: Basolateral membrane expression of mutant V2 receptor after antagonist exposure
      target: Endoplasmic Reticulum Retention of Misfolded V2 Receptor
      direction: RESTORED
      interpretation: >-
        Restored surface delivery of a receptor that ER quality control had been holding
        back.
      evidence:
      - reference: PMID:16926443
        reference_title: "Functional rescue of vasopressin V2 receptor mutants in MDCK cells by pharmacochaperones: relevance to therapy of nephrogenic diabetes insipidus."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          We found that the four nonpeptide antagonists SR49059, OPC31260, OPC41061, and
          SR121463B induced maturation and rescued the BM expression of eight of nine
          different V2R mutants, stably expressed in physiologically relevant polarized
          cells.
        explanation: >-
          The measurement itself, with the denominator: eight of nine mutants, in polarized
          cells.
  evidence:
  - reference: PMID:16926443
    reference_title: "Functional rescue of vasopressin V2 receptor mutants in MDCK cells by pharmacochaperones: relevance to therapy of nephrogenic diabetes insipidus."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      At clinically feasible antagonist concentrations, however, only the high-affinity
      antagonists OPC31260 and OPC41061 induced functional rescue, as at these
      concentrations the extent of BM expression became limited.
    explanation: >-
      The constraint that makes this model informative about therapy rather than only
      about cell biology, and the reason it is cited here rather than a simpler
      transfection study.
- name: HEK293 cells expressing the S127F V2 receptor mutant
  experimental_model_type: CELL_LINE
  description: >-
    A patient-derived variant taken through the whole argument in one system. S127F was
    found in an NDI patient; in HEK293 cells the mutant receptor sits almost exclusively
    in the endoplasmic reticulum with very few molecules at the surface, and generates
    negligible cAMP in response to vasopressin. Pretreatment with either tolvaptan - an
    established V2 receptor inverse agonist - or MCF14, a cell-permeable high-affinity
    agonist, partially restored cAMP generation. The result that matters for the
    therapeutic question is that both an agonist and an antagonist worked as
    pharmacochaperones, so the chaperone property is not tied to the ligand's
    signalling direction.
  publication: PMID:35153784
  modeled_mechanisms:
  - target: Endoplasmic Reticulum Retention of Misfolded V2 Receptor
    relationship: RESCUES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Establishes the ER localization and the functional consequence for one patient
      variant, then partially reverses both with two chemically and pharmacologically
      different chaperones.
    limitations: >-
      HEK293 is a non-renal, unpolarized line overexpressing a transfected receptor, so it
      cannot report on basolateral targeting in a principal cell; the rescue is explicitly
      partial; and the result is for a single allele, which the authors themselves frame as
      a starting point for patients carrying S127F rather than for the disease generally.
    evidence:
    - reference: PMID:35153784
      reference_title: Functional Rescue of a Nephrogenic Diabetes Insipidus Causing Mutation in the V2 Vasopressin Receptor by Specific Antagonist and Agonist Pharmacochaperones.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Based on our data, the S127F-V2R mutant is almost exclusively located
        intracellularly in the endoplasmic reticulum (ER), and very few receptors were
        detected at the cell surface, where the receptor can bind to AVP.
      explanation: >-
        Establishes that this model is about the ER-retention node, and states the reason
        retention matters - the surface is where the hormone can reach the receptor.
    readouts:
    - name: Vasopressin-stimulated cAMP generation after pharmacochaperone pretreatment
      target: Endoplasmic Reticulum Retention of Misfolded V2 Receptor
      direction: RESTORED
      interpretation: >-
        Partial functional rescue by two different ligand classes. Read as partial, and as
        allele-specific.
      evidence:
      - reference: PMID:35153784
        reference_title: Functional Rescue of a Nephrogenic Diabetes Insipidus Causing Mutation in the V2 Vasopressin Receptor by Specific Antagonist and Agonist Pharmacochaperones.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          We found that pretreatment with both tolvaptan (an established V2R inverse agonist)
          and MCF14 compound (a cell-permeable high-affinity agonist for the V2R) were
          capable of partially restoring the cAMP generating function of the receptor in
          response to vasopressin stimulation.
        explanation: The measured rescue, with both compounds named and the effect called partial.
  evidence:
  - reference: PMID:35153784
    reference_title: Functional Rescue of a Nephrogenic Diabetes Insipidus Causing Mutation in the V2 Vasopressin Receptor by Specific Antagonist and Agonist Pharmacochaperones.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The overexpressed S127F-V2R mutant receptor has negligible cAMP generation capability
      compared to the wild-type receptor in response to AVP stimulation.
    explanation: >-
      The functional baseline the rescue is measured against, and the link between the
      localization defect and the signalling failure in one system.
clinical_trials:
- name: NCT07525960
  phase: PHASE_I
  status: RECRUITING
  description: >-
    The only interventional trial identified for this disease, and the first to test a
    treatment aimed at the mechanism rather than at the urine volume. NDI-5001 is given as
    a capsule in daily oral doses to adult males with X-linked congenital nephrogenic
    diabetes insipidus due to V2 receptor mutations, with safety, pharmacokinetics and
    pharmacodynamics as the endpoints. Note what the registration does and does not say:
    it specifies the population by genotype, which is unusual and useful, but a Phase 1b
    safety and pharmacodynamic study establishes nothing about clinical benefit. The
    trial's own record does not name the drug's mechanism, so none is asserted here.
  target_phenotypes:
  - preferred_term: Polyuria
    term:
      id: HP:0000103
      label: Polyuria
  evidence:
  - reference: clinicaltrials:NCT07525960
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The primary purpose of this trial is to evaluate the safety, tolerability,
      pharmacokinetics (PK), and pharmacodynamics (PD) of NDI-5001 administered as a
      capsule following daily oral dosing in adult males with X-linked congenital
      nephrogenic diabetes insipidus (NDI) due to vasopressin receptor Type 2 (V2R)
      mutations.
    explanation: >-
      The registration record, which establishes the trial's existence, its phase, its
      genotype-defined population and its endpoints - and nothing about efficacy.
discussions:
- discussion_id: xndi_neurocognitive_attribution
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is the cognitive impairment reported in untreated X-linked nephrogenic diabetes
    insipidus caused by repeated hypernatraemic episodes, and if so what exposure is
    required?
  attaches_to:
  - phenotypes#Intellectual disability
  - phenotypes#Hypernatremia
  rationale: >-
    There is a live contradiction here, not just a gap. GeneReviews holds that
    intelligence is usually normal with early diagnosis and treatment; a 2025 cohort
    followed for a median of 16.9 years found neurodevelopmental disorders in six of eight
    patients who were all on hydrochlorothiazide and amiloride with normalised serum
    sodium. Treatment status therefore does not reconcile the two. Three explanations are
    open and the cited literature does not choose between them: ascertainment in a small
    referral series, residual subclinical hypernatraemic episodes that a normalised
    steady-state sodium does not capture, or a contribution from something other than
    sodium -
    chronic undernutrition severe enough to leave a permanent height deficit is the
    obvious candidate. The attribution to electrolyte disturbance is stated in review form
    and hedged there, and no cited source anchors it to a measured exposure-response
    relationship. Note also that the 66-child multicentre cohort, which is the largest
    series here and reported growth, urological and renal outcomes in detail, did not
    report cognitive outcome at all - so the best-powered study is silent on precisely this
    question. This matters practically: if the relationship is dose-dependent in episodes,
    the value of early diagnosis becomes quantifiable and the sodium surveillance interval
    becomes an evidence question rather than a convention.
  evidence:
  - reference: PMID:34055061
    reference_title: Nephrogenic diabetes insipidus in children (Review).
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Irreversible brain damage and cognitive deficit secondary to electrolyte
      imbalances may be present.
    explanation: >-
      The claim whose evidential basis the gap is about. The hedge is the source's own.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neurodevelopmental disorders were identified in six patients, including intellectual
      disability, autism spectrum disorder, language delay, and learning difficulties.
    explanation: >-
      The observation that creates the contradiction, in patients who were treated.
  - reference: PMID:40922895
    reference_title: "Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Serum sodium normalized in all cases.
    explanation: >-
      Establishes that the cohort above was not simply undertreated at steady state, which
      is what rules out the easiest reconciliation of the two positions and leaves the
      question open.
- discussion_id: xndi_pharmacochaperone_translation
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why has pharmacochaperone rescue of ER-retained V2 receptor mutants not translated
    into a human treatment, two decades after the cell-based proof of principle?
  attaches_to:
  - pathophysiology#Endoplasmic Reticulum Retention of Misfolded V2 Receptor
  - treatments#Thiazide Diuretic
  rationale: >-
    The mechanistic argument is unusually clean: most pathogenic AVPR2 variants retain a
    functional receptor in the wrong compartment, cell-permeable non-peptide ligands
    restore its membrane delivery in polarized cells, and the pharmacology even
    discriminates which ligands could work at achievable concentrations. Two distinct
    obstacles appear in the cited work rather than one. First, a pharmacochaperone that
    is an antagonist must be displaced by vasopressin to be useful, so affinity has to be
    high enough to chaperone and low enough to release - a narrow window. The non-peptide
    agonist route was proposed to escape that, but the same ligand also desensitizes the
    rescued receptor, and whether the chaperone effect outlasts the desensitization is a
    speculation in the source, not a result. The current proposal is a biased agonist that
    chaperones the receptor and then signals only through Gs without recruiting arrestin,
    which would sidestep the desensitization problem - but that too is offered as a
    potential treatment rather than a demonstrated one. Second, and more simply, the review of
    pharmacological strategies concludes that nothing has yet been established as
    causally improving symptoms or quality of life in patients, which is a statement about
    the whole field including these agents. The entry therefore records the thiazide
    regimen as the treatment and pharmacochaperones as mechanism, not therapy.
  evidence:
  - reference: PMID:32924547
    reference_title: A mini-review of pharmacological strategies used to ameliorate polyuria associated with X-linked nephrogenic diabetes insipidus.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      It is concluded that there is currently no established intervention that causally
      improves symptoms or quality of life in patients with NDI.
    explanation: >-
      The field-level negative conclusion, which is what keeps every causal strategy in
      this entry out of the treatments section.
  - reference: PMID:27601473
    reference_title: "Analysis of the V2 Vasopressin Receptor (V2R) Mutations Causing Partial Nephrogenic Diabetes Insipidus Highlights a Sustainable Signaling by a Non-peptide V2R Agonist."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We speculated that the canceling of the desensitization effect of OPC51803 by the
      pharmacochaperone effect after long-term treatment may produce sustainable
      signaling, and thus pharmacochaperone agonists such as OPC51803 may serve as
      promising therapeutics for NDI caused by misfolded V2R mutants.
    explanation: >-
      Quoted because the authors' own verb is "speculated". The agonist route's central
      premise is explicitly a speculation, which is the content of this gap.
  - reference: PMID:31928727
    reference_title: "Misfolding of vasopressin receptors: biased agonist pharmacochaperones as potential therapeutics."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      These compounds, particularly small-molecule biased agonists which elicit the
      V2-induced Gs protein-dependent signaling pathway, but not V2-related
      arrestin-dependent cell responses, represent a potential therapeutic treatment of
      this X-linked genetic pathology.
    explanation: >-
      The current form of the proposal - a biased agonist that chaperones and signals
      through Gs without recruiting arrestin, so the desensitization problem above does
      not arise. Note the verb is "represent a potential", so this is a proposal and not
      a result.
references:
- reference: PMID:20301356
  title: Hereditary Nephrogenic Diabetes Insipidus.
  tags:
  - GeneReviews
- reference: PMID:39438674
  title: International expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus (arginine vasopressin resistance).
notes: >-
  Lump/split: curated as a single DISEASE. One gene (AVPR2), one receptor, one conserved
  mechanistic chain from misfolded receptor to hypotonic polyuria. There is no defensible
  subtype axis: the allelic spectrum is broad but genotype does not predict phenotype
  beyond one hedged exception, the partial-NDI variants differ in degree rather than in
  mechanism, and symptomatic female heterozygotes are the same disease modified by
  X-inactivation, not a separate entity. No has_subtypes block was created.

  Boundary with Neurohypophyseal_Diabetes_Insipidus: these are two diseases at two levels
  of one axis and must not be conflated. That entry is the central (AVP) form - the lesion
  is in the hormone, the pathograph runs through misfolding of prepro-vasopressin in
  magnocellular hypothalamic neurons, and the endpoint is vasopressin deficiency. This
  entry starts where hormone supply is normal or high and the receptor cannot receive it.
  The two share downstream phenotypes (polyuria, polydipsia, hyposthenuria, hypernatraemic
  dehydration) and nothing upstream of them, and the discriminating test is the response to
  desmopressin: present in the central form, absent here. Note the superficial similarity
  that could invite a false merge - both entries have an ER-retention node - but they are
  different proteins retained in different cell types with different consequences: a
  secreted prohormone aggregating in a neuron and progressively destroying it, versus a
  membrane receptor held back from the surface of a renal epithelial cell with no
  proteotoxicity recorded. The pathographs were built independently; nothing was copied
  between them.

  Boundary with AQP2-related nephrogenic diabetes insipidus: the AQP2 form is a separate
  locus and a separate disease (autosomal recessive, rarely dominant), not a subtype of
  this entry, and dismech has no AQP2 entry at the time of writing. The two are clinically
  indistinguishable, which is exactly why they must be kept apart in the knowledge base: the
  inheritance, the counselling, the recurrence risk and the mechanism at the level of the
  water channel all differ. The mechanistic distinction is load-bearing here, because in
  XNDI aquaporin-2 is intact - the V2 receptor knock-in mouse shows normal basal AQP2
  abundance - so every experimental therapeutic strategy for XNDI is framed as reaching
  AQP2 without the receptor, which makes no sense for the AQP2 form. A kb/groupings/
  Grouping over nephrogenic diabetes insipidus (MONDO:0016383) would be the right vehicle
  for the relationship once an AQP2 entry exists; it is deliberately not created here,
  since a grouping with one member is not a union.

  No conforms_to. Three candidate modules were read in full before concluding that none
  fits. er_protein_storage_disease scopes itself to hepatocellular storage of a secretory
  protein with proteotoxic gain of function and stellate-cell fibrosis, and its own notes
  assign the loss-of-secretion consequence to disorder entries rather than to the module -
  XNDI is purely that loss-of-delivery arm, in a renal epithelium, with no storage
  pathology. loss_of_proteostasis is an aging hallmark built on age-related decline of the
  proteostasis network leading to aggregation and neurodegeneration; here a single variant
  protein is recognised by an intact quality-control system, which is the opposite
  situation. renal_cystogenesis does contain a vasopressin-V2R-cAMP node, but in the
  direction of overstimulation driving cystogenesis, so conforming to it would invert the
  mechanism. A module for GPCR ER-retention trafficking disease would be a legitimate future
  proposal - the cited literature explicitly generalises the mechanism to other
  ER-retained GPCRs - but it does not exist yet and was not created in this PR.

  Deep research. falcon was requested and returned HTTP 402 on two consecutive attempts -
  the Edison account is out of credits. The second attempt was re-issued with --fallback,
  which escalated to openscientist; that job (55dbaa47-e508-4202-898f-a85d997f02b6) timed
  out after 3600 s and was cancelled, ending the fallback chain with no report. The
  provider of record is therefore claude_code, run directly, and the report's own
  frontmatter says so. Its reference validation resolved 14 of 14 identifiers with a
  confabulation rate of 0.0; needs_review is true on the strength of one reference flagged
  as possibly off topic (PMC:PMC11095762, "Therapeutic potentials of nonpeptidic V2R
  agonists for partial cNDI-causing V2R mutants"), which on reading is squarely on topic -
  a vocabulary-overlap false positive, not a bad citation. Term validation resolved 17 of
  18 CURIEs with 5 of 5 labels correct and none naming a different term; no CURIE from the
  report was bound without an independent lookup in any case. just preflight-dr returns a
  WARN because AQP2 is mentioned 35 times against AVPR2's 55 and the report carries
  OMIM 125800 alongside 304800. That is expected here rather than a Named Entity Confusion
  finding: the report discusses AQP2 as the contrasting locus, which is the same boundary
  this entry draws explicitly above, and no AQP2 content was curated as AVPR2 disease.

  Three figures the report gives are not supported by the abstracts they are attributed
  to, and are deliberately absent from this entry: a 36 per cent gastrostomy rate ascribed
  to PMID:32039113, and - ascribed to PMID:39644399 - a 58-year-old patient with an eGFR of
  25 mL/min/1.73m2, a 3.1 L post-void residual and secondary hyperparathyroidism. That
  paper's abstract describes a 6-month-old proband and an untreated maternal grandfather
  without naming his age or any of those values. The qualitative contrast it does support
  is curated; the numbers are not. This is recorded because the report reads fluently and
  those figures would have been easy to transcribe.

  Slot choice on the lesion node. The lesion node carries both
  genetic_context.functional_impact_category: LOSS_OF_FUNCTION and
  modifier: LOSS_OF_FUNCTION on its vasopressin-receptor-activity descriptor. CLAUDE.md
  records that these two slots may legitimately co-occur on a mutation-driven node
  because they make different claims - the variant's consequence and the resulting
  activity state. CLAUDE.md adds that no KB entry did so at the time of writing, but that
  sentence is stale: measured against origin/main at the time this entry was curated, 200
  pathophysiology nodes already pair the two slots, 80 of them with a GAIN_OF_FUNCTION or
  LOSS_OF_FUNCTION modifier (Autosomal_Recessive_Robinow_Syndrome and
  Autosomal_Dominant_Hypocalcemia_1 among them). So the pattern here is well precedented
  rather than novel, and is recorded for that reason rather than as a flag. The modifier is qualitative
  rather than quantitative on purpose: the receptor's activity is abolished, not running
  below normal, which is the distinction CLAUDE.md draws between
  LOSS_OF_FUNCTION and DECREASED. Downstream nodes use DECREASED and ABSENT, since the
  cascade and the trafficking steps are intact machinery deprived of an input.

  Nomenclature. A 2022-onward working-group renaming calls this family of disorders
  arginine vasopressin resistance, and the 2024 international expert consensus statement
  (PMID:39438674) carries "arginine vasopressin resistance" in its own title and gives it as
  an alternative name in its first sentence. The three new synonyms are there so a reader
  arriving from recent literature finds this entry; the entry name keeps the older form
  because that is what MONDO:0010581 and the cited cohorts use.

  Three mechanistic routes, not two. The lesion node has three downstream edges, one per
  class in the functional taxonomy PMID:32138955 names: absent or truncated protein, ER
  retention of a misfolded receptor, and a surface receptor that cannot signal. The first of
  those was missing from the first version of this entry, and the omission was not cosmetic:
  the Glu242stop knock-in mouse is a nonsense allele, so the entry's flagship animal model
  belonged to a class the graph gave it no path through, and its modeled_mechanisms link
  entered at the cascade node instead. The node was added rather than the edge descriptions
  merely softened, because a pathograph whose value is being a complete chain should not omit
  a class its own model instantiates. The mouse now links to that node explicitly as well as
  to the cascade node. No proportion is asserted for any class - see the genetic notes.

  Copeptin is curated without a cutoff. The deep-research report gives a baseline plasma
  copeptin above 21.4 pmol/L as diagnostic for NDI in adults and attributes it to the 2024
  consensus statement. That record was fetched both by DOI and by PMID: the DOI record came
  back with content_type unavailable and an empty body, and the PMID record's available
  content does not mention copeptin at all, let alone that figure. So the cutoff could not be
  verified and is not curated - a fourth unsupported figure from the same report, alongside
  the three already listed above. What is curated is the qualitative claim that basal
  copeptin alone diagnoses nephrogenic diabetes insipidus while the other two entities in the
  differential need a stimulation test, which two independent reviews state in those terms.

  GO binding on Obligatory Hypotonic Free Water Loss. This node first carried GO:0007588
  (excretion), which is broad to the point of saying little. GO was searched for renal water
  excretion, diuresis, urine and body-fluid terms; the best fits found were GO:0035809
  (regulation of urine volume) and GO:0050891 (multicellular organismal-level water
  homeostasis), both of which are now bound with modifier ABNORMAL, and GO:0007588 was
  dropped. Recording the search so that the absence of a single exact term is visible rather
  than inferred.

  One piece of guidance this entry's own evidence complicates. The node Failure of
  Aquaporin-2 Phosphorylation and Apical Insertion names phosphorylation and apical insertion
  together, and PMID:10710543 shows they are separable: prostaglandin E2 reversed
  vasopressin-induced translocation of aquaporin-2 away from the plasma membrane without
  decreasing its phosphorylation, and the authors conclude that recruitment and retrieval may
  be independently regulated and that dephosphorylation is not a prerequisite for
  internalization. In this disease both fail together because both are downstream of the same
  absent PKA signal, so the bundled node is not making a false claim here. The node was not
  renamed because its name is a foreign key for bare-name pathograph targets and for three
  model links, and splitting it would assert a distinction this disease does not exercise.

  Phenotypes deliberately left unwired to the pathograph: Vomiting, Fever and
  Constipation. All three are well documented as presenting features and all three have
  an obvious hand-waving explanation (dehydration, water deficit), but no cited source
  here states the causal step, so an edge would be invented rather than curated. Failure
  to thrive and Short stature are wired with INDIRECT_UNKNOWN_INTERMEDIATES for the
  weaker version of the same reason - the association is documented, the route is not.
  Intellectual disability reaches the graph through a sequela edge from Hypernatremia
  rather than from a pathophysiology node, because the only causal statement available
  attributes it to the electrolyte disturbance and not to a mechanism.

  Omitted deliberately. The biochemical block carries urine osmolality and serum sodium but
  no reference_ranges: no citable record in this round gave a reference interval for either,
  and the only numeric figure available (a maximal urine osmolality not exceeding
  200 mosmol/kg in three patients) is a reported ceiling in affected people, not a normal
  interval, so inventing one was declined. The clinical_trials block carries exactly one
  trial, NCT07525960, because it is the only interventional study identified for this
  disease; the 2020 pharmacological review's conclusion that nothing is yet established as
  causally improving symptoms or quality of life stands alongside it, and the trial's
  registration record does not name the drug's mechanism so none is asserted. No datasets
  block: no GEO or other repository accession specific to
  AVPR2 nephrogenic diabetes insipidus was verified, and a gene-name search would have
  returned accessions about other AVPR2 biology. No environmental block: the precipitants
  of decompensation (intercurrent illness, heat, water withholding) are recorded in the
  progression and phenotype descriptions, because they act on an already-established disease
  rather than contributing to its causation, and an ECTO binding for "withholding of water"
  was not sought. No prevalence figure beyond the Quebec birth-incidence estimate; the
  numerically higher Maritime rate is noted as a founder effect rather than curated as a
  second population record.

📚

References & Deep Research

References

2

PMID:20301356

Hereditary Nephrogenic Diabetes Insipidus.

No top-level findings curated for this source.

PMID:39438674

International expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus (arginine vasopressin resistance).

No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (3)

Record notes

Lump/split: curated as a single DISEASE. One gene (AVPR2), one receptor, one conserved mechanistic chain from misfolded receptor to hypotonic polyuria. There is no defensible subtype axis: the allelic spectrum is broad but genotype does not predict phenotype beyond one hedged exception, the partial-NDI variants differ in degree rather than in mechanism, and symptomatic female heterozygotes are the same disease modified by X-inactivation, not a separate entity. No has_subtypes block was created. Boundary with Neurohypophyseal_Diabetes_Insipidus: these are two diseases at two levels of one axis and must not be conflated. That entry is the central (AVP) form - the lesion is in the hormone, the pathograph runs through misfolding of prepro-vasopressin in magnocellular hypothalamic neurons, and the endpoint is vasopressin deficiency. This entry starts where hormone supply is normal or high and the receptor cannot receive it. The two share downstream phenotypes (polyuria, polydipsia, hyposthenuria, hypernatraemic dehydration) and nothing upstream of them, and the discriminating test is the response to desmopressin: present in the central form, absent here. Note the superficial similarity that could invite a false merge - both entries have an ER-retention node - but they are different proteins retained in different cell types with different consequences: a secreted prohormone aggregating in a neuron and progressively destroying it, versus a membrane receptor held back from the surface of a renal epithelial cell with no proteotoxicity recorded. The pathographs were built independently; nothing was copied between them. Boundary with AQP2-related nephrogenic diabetes insipidus: the AQP2 form is a separate locus and a separate disease (autosomal recessive, rarely dominant), not a subtype of this entry, and dismech has no AQP2 entry at the time of writing. The two are clinically indistinguishable, which is exactly why they must be kept apart in the knowledge base: the inheritance, the counselling, the recurrence risk and the mechanism at the level of the water channel all differ. The mechanistic distinction is load-bearing here, because in XNDI aquaporin-2 is intact - the V2 receptor knock-in mouse shows normal basal AQP2 abundance - so every experimental therapeutic strategy for XNDI is framed as reaching AQP2 without the receptor, which makes no sense for the AQP2 form. A kb/groupings/ Grouping over nephrogenic diabetes insipidus (MONDO:0016383) would be the right vehicle for the relationship once an AQP2 entry exists; it is deliberately not created here, since a grouping with one member is not a union. No conforms_to. Three candidate modules were read in full before concluding that none fits. er_protein_storage_disease scopes itself to hepatocellular storage of a secretory protein with proteotoxic gain of function and stellate-cell fibrosis, and its own notes assign the loss-of-secretion consequence to disorder entries rather than to the module - XNDI is purely that loss-of-delivery arm, in a renal epithelium, with no storage pathology. loss_of_proteostasis is an aging hallmark built on age-related decline of the proteostasis network leading to aggregation and neurodegeneration; here a single variant protein is recognised by an intact quality-control system, which is the opposite situation. renal_cystogenesis does contain a vasopressin-V2R-cAMP node, but in the direction of overstimulation driving cystogenesis, so conforming to it would invert the mechanism. A module for GPCR ER-retention trafficking disease would be a legitimate future proposal - the cited literature explicitly generalises the mechanism to other ER-retained GPCRs - but it does not exist yet and was not created in this PR. Deep research. falcon was requested and returned HTTP 402 on two consecutive attempts - the Edison account is out of credits. The second attempt was re-issued with --fallback, which escalated to openscientist; that job (55dbaa47-e508-4202-898f-a85d997f02b6) timed out after 3600 s and was cancelled, ending the fallback chain with no report. The provider of record is therefore claude_code, run directly, and the report's own frontmatter says so. Its reference validation resolved 14 of 14 identifiers with a confabulation rate of 0.0; needs_review is true on the strength of one reference flagged as possibly off topic (PMC:PMC11095762, "Therapeutic potentials of nonpeptidic V2R agonists for partial cNDI-causing V2R mutants"), which on reading is squarely on topic - a vocabulary-overlap false positive, not a bad citation. Term validation resolved 17 of 18 CURIEs with 5 of 5 labels correct and none naming a different term; no CURIE from the report was bound without an independent lookup in any case. just preflight-dr returns a WARN because AQP2 is mentioned 35 times against AVPR2's 55 and the report carries OMIM 125800 alongside 304800. That is expected here rather than a Named Entity Confusion finding: the report discusses AQP2 as the contrasting locus, which is the same boundary this entry draws explicitly above, and no AQP2 content was curated as AVPR2 disease. Three figures the report gives are not supported by the abstracts they are attributed to, and are deliberately absent from this entry: a 36 per cent gastrostomy rate ascribed to PMID:32039113, and - ascribed to PMID:39644399 - a 58-year-old patient with an eGFR of 25 mL/min/1.73m2, a 3.1 L post-void residual and secondary hyperparathyroidism. That paper's abstract describes a 6-month-old proband and an untreated maternal grandfather without naming his age or any of those values. The qualitative contrast it does support is curated; the numbers are not. This is recorded because the report reads fluently and those figures would have been easy to transcribe. Slot choice on the lesion node. The lesion node carries both genetic_context.functional_impact_category: LOSS_OF_FUNCTION and modifier: LOSS_OF_FUNCTION on its vasopressin-receptor-activity descriptor. CLAUDE.md records that these two slots may legitimately co-occur on a mutation-driven node because they make different claims - the variant's consequence and the resulting activity state. CLAUDE.md adds that no KB entry did so at the time of writing, but that sentence is stale: measured against origin/main at the time this entry was curated, 200 pathophysiology nodes already pair the two slots, 80 of them with a GAIN_OF_FUNCTION or LOSS_OF_FUNCTION modifier (Autosomal_Recessive_Robinow_Syndrome and Autosomal_Dominant_Hypocalcemia_1 among them). So the pattern here is well precedented rather than novel, and is recorded for that reason rather than as a flag. The modifier is qualitative rather than quantitative on purpose: the receptor's activity is abolished, not running below normal, which is the distinction CLAUDE.md draws between LOSS_OF_FUNCTION and DECREASED. Downstream nodes use DECREASED and ABSENT, since the cascade and the trafficking steps are intact machinery deprived of an input. Nomenclature. A 2022-onward working-group renaming calls this family of disorders arginine vasopressin resistance, and the 2024 international expert consensus statement (PMID:39438674) carries "arginine vasopressin resistance" in its own title and gives it as an alternative name in its first sentence. The three new synonyms are there so a reader arriving from recent literature finds this entry; the entry name keeps the older form because that is what MONDO:0010581 and the cited cohorts use. Three mechanistic routes, not two. The lesion node has three downstream edges, one per class in the functional taxonomy PMID:32138955 names: absent or truncated protein, ER retention of a misfolded receptor, and a surface receptor that cannot signal. The first of those was missing from the first version of this entry, and the omission was not cosmetic: the Glu242stop knock-in mouse is a nonsense allele, so the entry's flagship animal model belonged to a class the graph gave it no path through, and its modeled_mechanisms link entered at the cascade node instead. The node was added rather than the edge descriptions merely softened, because a pathograph whose value is being a complete chain should not omit a class its own model instantiates. The mouse now links to that node explicitly as well as to the cascade node. No proportion is asserted for any class - see the genetic notes. Copeptin is curated without a cutoff. The deep-research report gives a baseline plasma copeptin above 21.4 pmol/L as diagnostic for NDI in adults and attributes it to the 2024 consensus statement. That record was fetched both by DOI and by PMID: the DOI record came back with content_type unavailable and an empty body, and the PMID record's available content does not mention copeptin at all, let alone that figure. So the cutoff could not be verified and is not curated - a fourth unsupported figure from the same report, alongside the three already listed above. What is curated is the qualitative claim that basal copeptin alone diagnoses nephrogenic diabetes insipidus while the other two entities in the differential need a stimulation test, which two independent reviews state in those terms. GO binding on Obligatory Hypotonic Free Water Loss. This node first carried GO:0007588 (excretion), which is broad to the point of saying little. GO was searched for renal water excretion, diuresis, urine and body-fluid terms; the best fits found were GO:0035809 (regulation of urine volume) and GO:0050891 (multicellular organismal-level water homeostasis), both of which are now bound with modifier ABNORMAL, and GO:0007588 was dropped. Recording the search so that the absence of a single exact term is visible rather than inferred. One piece of guidance this entry's own evidence complicates. The node Failure of Aquaporin-2 Phosphorylation and Apical Insertion names phosphorylation and apical insertion together, and PMID:10710543 shows they are separable: prostaglandin E2 reversed vasopressin-induced translocation of aquaporin-2 away from the plasma membrane without decreasing its phosphorylation, and the authors conclude that recruitment and retrieval may be independently regulated and that dephosphorylation is not a prerequisite for internalization. In this disease both fail together because both are downstream of the same absent PKA signal, so the bundled node is not making a false claim here. The node was not renamed because its name is a foreign key for bare-name pathograph targets and for three model links, and splitting it would assert a distinction this disease does not exercise. Phenotypes deliberately left unwired to the pathograph: Vomiting, Fever and Constipation. All three are well documented as presenting features and all three have an obvious hand-waving explanation (dehydration, water deficit), but no cited source here states the causal step, so an edge would be invented rather than curated. Failure to thrive and Short stature are wired with INDIRECT_UNKNOWN_INTERMEDIATES for the weaker version of the same reason - the association is documented, the route is not. Intellectual disability reaches the graph through a sequela edge from Hypernatremia rather than from a pathophysiology node, because the only causal statement available attributes it to the electrolyte disturbance and not to a mechanism. Omitted deliberately. The biochemical block carries urine osmolality and serum sodium but no reference_ranges: no citable record in this round gave a reference interval for either, and the only numeric figure available (a maximal urine osmolality not exceeding 200 mosmol/kg in three patients) is a reported ceiling in affected people, not a normal interval, so inventing one was declined. The clinical_trials block carries exactly one trial, NCT07525960, because it is the only interventional study identified for this disease; the 2020 pharmacological review's conclusion that nothing is yet established as causally improving symptoms or quality of life stands alongside it, and the trial's registration record does not name the drug's mechanism so none is asserted. No datasets block: no GEO or other repository accession specific to AVPR2 nephrogenic diabetes insipidus was verified, and a gene-name search would have returned accessions about other AVPR2 biology. No environmental block: the precipitants of decompensation (intercurrent illness, heat, water withholding) are recorded in the progression and phenotype descriptions, because they act on an already-established disease rather than contributing to its causation, and an ECTO binding for "withholding of water" was not sought. No prevalence figure beyond the Quebec birth-incidence estimate; the numerically higher Maritime rate is noted as a founder effect rather than curated as a second population record.

Review round 1 response: add Type I variant route, water-deprivation contraindication, copeptin · 2026-09-10T19:16:14Z · View source

Response to review round 1 on PR #11634 (REQUEST_CHANGES, three yellow and five blue). All eight items worked in one push. YELLOW 1, Type I variants had no route through the pathograph. Took the reviewer's option one: added a new pathophysiology node 'Absent or Truncated V2 Receptor Protein' (MOLECULAR, CL:1001431, GO:0005000 with modifier ABSENT) and a third downstream edge from the lesion node to it with causal_link_type DIRECT. Chose this over merely softening the edge descriptions because the gap was load-bearing rather than cosmetic: the entry's flagship animal model, the V2R Glu242stop knock-in (PMID:11104789), carries a nonsense allele and so belongs to exactly the class the graph omitted, and its modeled_mechanisms link entered at the cAMP/PKA node instead. The mouse now carries an additional RECAPITULATES link to the new node at model_scale MOLECULAR, with a limitation recording that the class assignment rests on the nature of the allele rather than on a Western blot in these mice. Evidence for the node is PMID:11389590, which is the direct in vitro demonstration: mRNA was produced for every mutant construct while the 804delG frameshift allele gave no detectable receptor protein, so the failing step is after transcription. Also reworded the two pre-existing edges so they no longer read as a partition: 'majority route' became 'the commonest route, and the one with a therapeutic handle' and 'minority route' became 'the functional route'. The three routes now correspond one-to-one to the three classes PMID:32138955 names and all three converge on the cascade node. YELLOW 2, water-deprivation safety caveat. The reviewer's quoted sentence WAS in the cache: references_cache/PMID_40922895.md has content_type full_text_xml, not abstract-only, and carries the contraindication in two places. I quoted from the cache rather than from the review comment, and verified the snippets against the strict --no-full-text gate before building on them (they pass; --no-full-text suppresses new full-text fetching, it does not restrict matching to abstracts). Added a new diagnosis entry 'Water deprivation test' carrying three snippets from that paper: the contraindication above serum sodium 145 mmol/L and its stated reason, the operational rule including the plasma osmolality 295 mOsm/kg limb and the substitution of desmopressin challenge alone, and the statement that the diagnosis can be established without water restriction where sodium is high or high-normal with inappropriately dilute urine. The entry description makes the clinical point the reviewer raised: the median presenting serum sodium in this same cohort is 160.5 mmol/L, so the typical patient presents already past the threshold at which the test is unsafe. YELLOW 3, copeptin. Curated qualitatively, cutoff declined. The 21.4 pmol/L figure could not be verified: the consensus statement was fetched both ways, and DOI:10.1038/s41581-024-00897-z came back with content_type unavailable and an empty body while the PMID version (PMID:39438674, fetched this round, full_text_html) does not mention copeptin at all. That is a fourth unsupported figure from the same deep-research report, recorded in notes alongside the three found in round one. What is curated is the substantive claim, from two independent reviews (PMID:32374887 and PMID:32387127) stating it in those terms: unstimulated basal copeptin reliably diagnoses nephrogenic diabetes insipidus while separating central diabetes insipidus from primary polydipsia needs a stimulation test. New diagnosis entry 'Basal plasma copeptin', which also records why that asymmetry suits this disease and that no cutoff is curated. BLUE 1, nomenclature. Added three synonyms (arginine vasopressin resistance, AVP-R, X-linked arginine vasopressin resistance) and a notes paragraph on the renaming, cited to PMID:39438674 whose own title and first sentence both carry the new name. The entry name keeps the older form because that is what MONDO:0010581 and the cited cohorts use. PMID:39438674 also added to the top-level references block and attached as real evidence on the genetic-counselling treatment, whose scope it explicitly covers. BLUE 2, rebound Nocturnal enuresis from HP:0000805 (Enuresis) to HP:0010677 (Enuresis nocturna), which matches the preferred_term exactly. Confirmed by lookup through ols:hp and confirmed already present in both cache/hp/terms.csv and the phenotypeterm enum cache, so enum membership was established before rebinding rather than assumed. BLUE 3, GO binding on Obligatory Hypotonic Free Water Loss. Searched GO for renal water excretion, diuresis, urine, water homeostasis and body-fluid terms. Replaced the broad GO:0007588 (excretion) with GO:0035809 (regulation of urine volume) and GO:0050891 (multicellular organismal-level water homeostasis), both modifier ABNORMAL. Recorded the search in notes so the absence of a single exact term is visible rather than inferred. BLUE 4, variant-class composition. Added to the genetic notes: the variant types represented, the three functional classes and their correspondence to the three pathograph routes, and more than 200 reported AVPR2 variants (PMID:33664408). Two things deliberately not asserted and said so: no proportion for which class is commonest, because the widely circulated 70 per cent figure for the ER-retention class appears in the deep-research report but no cited source measures it and the strongest citable statement is the weaker one in PMID:17516711 that the function of most mutant receptors is not itself disturbed; and no proportion per sequence-variant type. Added PMID:17516711 and PMID:32138955 as evidence in genetic. BLUE 5, indomethacin rationale. Cited the mechanism (PMID:10710543) but DECLINED the suggested upgrade from MODULATES, because reading the source argues against it. PGE2 was shown to reverse vasopressin-INDUCED translocation of aquaporin-2 without decreasing its phosphorylation; that process does not occur in a V2 receptor-null kidney, so the demonstrated mechanism presupposes the signalling this disease lacks. And in the same experiments PGE2 alone altered neither aquaporin-2 phosphorylation nor its distribution, which argues against a standing PGE2 brake that an NSAID could release in the absence of vasopressin action. Recorded as a SUPPORT item with directness INDIRECT plus a REFUTE item quoting the PGE2-alone result, with the reasoning in the target_mechanisms description. The treatment description now states that the clinical benefit is real and well attested while the route through this node is not established by anything cited. Also recorded: PMID:10710543 shows aquaporin-2 phosphorylation and apical retention are separably regulated and that dephosphorylation is not a prerequisite for internalization, which complicates the bundled naming of the node 'Failure of Aquaporin-2 Phosphorylation and Apical Insertion'. The node was NOT renamed, because its name is a foreign key for bare-name pathograph targets and three model links and because in this disease both limbs fail together downstream of the same absent PKA signal. Recorded in notes rather than acted on. Built on the coordinator's commit 8803affcb correcting the stale slot-co-occurrence precedent claim; that text was not reverted. Validators re-run after these changes, all pass. just validate and just validate-disorders both pass with 155/155 snippets verified against committed references_cache files (up from 138). validate-terms, check-duplicate-keys, check-entity-refs, check-causal-targets (no new dangling targets, confirmed after adding a node and four edges), check-qualifier-terms (0 qualifier terms), check-enum-values all pass. Whole-KB text checks all pass with no new findings: check-folded-hyphens, check-snippet-length, check-title-snippets, check-snippet-grading, check-reference-titles, check-environmental-evidence. normalize-cache, check-term-cache-integrity, check-cache-order pass. list-gene-term-mismatches 0 findings. compliance 94.5 per cent global, up from 93.7. No baseline file was modified. Cache diff is strictly additive: one new row (GO:0035809) across two files; GO:0050891 and HP:0010677 were already cached from other entries. Separately re-verified every reference_title against its cache frontmatter: 34 pairs checked, the only difference the known cosmetic U+2029 in PubMed's stored title for PMID:29162216. Five new references this round: PMID:39438674, PMID:32374887, PMID:32387127, PMID:10710543, and the clinicaltrials record was already present. 35 distinct references total.

Create: X-Linked Nephrogenic Diabetes Insipidus · 2026-09-10T18:08:48Z · View source

New Disease entry for X-linked nephrogenic diabetes insipidus (MONDO:0010581), AVPR2 (hgnc:897) at Xq28. Curated as a single DISEASE: one gene, one receptor, one conserved mechanistic chain, no has_subtypes. Pathograph: nine nodes in one chain with a branch at the lesion. AVPR2 loss-of-function variant branches into (a) ER retention of the misfolded V2 receptor, the majority route, and (b) a signalling-incompetent cell-surface receptor, the minority route; both converge on loss of vasopressin-stimulated cAMP/PKA signalling, then failure of aquaporin-2 phosphorylation and apical insertion, collecting duct water impermeability, failure of medullary countercurrent urine concentration, obligatory hypotonic free water loss, and sustained high urinary tract flow. biological_scale set on every node. CL:1001431 bound on four nodes; GO biological processes, molecular functions and cellular components bound throughout; UBERON:0000362 and UBERON:0014388 for locations. PDB 7KH0 (cryo-EM AVP-V2R-Gs) attached to the cascade node. The lesion node carries genetic_context with GERMLINE/HEMIZYGOUS/LOSS_OF_FUNCTION plus a modifier on its receptor-activity descriptor; the deliberate co-occurrence of the two slots is flagged in notes per CLAUDE.md. Deep research provenance. falcon was requested and returned HTTP 402 twice (Edison account out of credits). The second attempt was re-issued with --fallback, which escalated to openscientist; that job (55dbaa47-e508-4202-898f-a85d997f02b6) timed out after 3600s and was cancelled, ending the fallback chain with no report. claude_code was then run directly and is the provider of record; research/X-Linked_Nephrogenic_Diabetes_Insipidus-deep-research-claude_code.md and its .citations.md are committed. Report reference validation: 14/14 resolved, confabulation_rate 0.0, needs_review true on one possibly-off-topic flag (PMC:PMC11095762) which on reading is on topic. Term validation: 17/18 resolved, 5/5 labels correct, 0 naming a different term. just preflight-dr returns WARN (AQP2 mentioned 35x vs AVPR2 55x, OMIM 125800 alongside 304800) which is expected because the report discusses AQP2 as the contrasting locus; no AQP2 content was curated as AVPR2 disease. Three figures the report attributed to abstracts do not appear in them (a 36% gastrostomy rate ascribed to PMID:32039113; a 58-year-old patient with eGFR 25, 3.1 L post-void residual and secondary hyperparathyroidism ascribed to PMID:39644399) and were deliberately not curated; this is recorded in the entry notes. Term discipline. Every CURIE was read from a lookup in the same step it was written. hgnc:897 was not in cache/hgnc/terms.csv beforehand; it was resolved from the HGNC REST API and independently confirmed against the OBO hgnc build, and the symbol AVPR2 was checked against the CURIE. One binding was corrected during review: GO:0031896 (V2 vasopressin receptor binding) was initially used for the receptor's own recognition of vasopressin, which inverts the term's meaning; replaced with GO:0017046 (peptide hormone binding) plus GO:0005000 (vasopressin receptor activity). No cell_types binding was placed on the MDCK experimental model because CL does not represent cell lines and binding the canine line to the human principal-cell term would overstate it. Validators run and results. just validate: pass (schema, terms, references). just validate-disorders (authoritative batched gate): pass. Snippets: 138/138 verified against committed references_cache files. just validate-terms: pass. just check-duplicate-keys, check-entity-refs, check-causal-targets (no new dangling targets), check-qualifier-terms (0 qualifier terms), check-enum-values: all pass. Whole-KB text checks all pass with no new findings: check-folded-hyphens (two findings introduced and fixed by reflowing, not baselined), check-snippet-length (two short snippets introduced and replaced with full propositions, not baselined), check-title-snippets, check-snippet-grading, check-environmental-evidence. just normalize-cache, check-term-cache-integrity, check-cache-order: pass. just list-gene-term-mismatches: 2 gene bindings examined, both name the gene they bind, 0 findings. just compliance: 93.7% global, 94.0% weighted. Evidence: 138 items across 30 PMIDs plus clinicaltrials:NCT07525960. Deliberate omissions, all recorded in the entry notes: no conforms_to (er_protein_storage_disease, loss_of_proteostasis and renal_cystogenesis were each read in full and each misfits; a GPCR ER-retention trafficking module would be a legitimate future proposal); no reference_ranges on the biochemical block (no citable normal interval found); no datasets block (no accession specific to AVPR2 disease verified, and a gene-name search would return other AVPR2 biology); no environmental block (the precipitants act on established disease); Vomiting, Fever and Constipation left unwired to the pathograph because no cited source states the causal step. Boundaries checked and recorded: Neurohypophyseal_Diabetes_Insipidus exists and is the central AVP form - pathograph built independently, nothing copied, and the superficial shared ER-retention node is explicitly distinguished in notes. The AQP2 form is a separate locus and disease, not a subtype; dismech has no AQP2 entry, so a kb/groupings Grouping over nephrogenic diabetes insipidus is flagged as follow-up rather than created here. Open item for a human: the neurodevelopmental attribution. Intellectual disability is curated with a sequela edge from Hypernatremia and an attached KNOWLEDGE_GAP discussion, on a hedged review sentence plus a 2025 cohort finding neurodevelopmental disorders in six of eight treated patients with normalised serum sodium, against GeneReviews' position that intelligence is usually normal with early treatment. The contradiction is recorded rather than resolved.

Claude Code ▸

X-Linked Nephrogenic Diabetes Insipidus (NDI1, AVPR2-Related): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 1 citations 2026-09-10T17:49:38.838828

X-Linked Nephrogenic Diabetes Insipidus (NDI1, AVPR2-Related): Comprehensive Research Report

Target disease: X-Linked Nephrogenic Diabetes Insipidus Key identifiers: OMIM #304800 (NDI1); Gene OMIM 300538 (AVPR2); MONDO:0010581; Orphanet ORPHA222; HGNC:897 (AVPR2); Gene location Xq28 Note on ontology terms: HPO/GO/CL/UBERON/CHEBI/NCIT CURIEs suggested below are research leads compiled from general nomenclature and search-engine synthesis, not independently verified against OLS/OAK in this session*. Per this repository's ontology-term discipline, treat every ID below as unconfirmed until checked against a live adapter before any KB binding.

1. Disease Information

X-linked nephrogenic diabetes insipidus (X-NDI, NDI1) is a hereditary disorder of water homeostasis caused by hemizygous loss-of-function variants in AVPR2, the gene encoding the renal vasopressin V2 receptor (Xq28). Affected kidneys are structurally normal but insensitive to circulating arginine vasopressin (AVP), so the collecting duct cannot insert aquaporin-2 (AQP2) water channels into the apical membrane. The result is massive, dilute polyuria, compensatory polydipsia, and risk of life-threatening hypernatremic dehydration, typically from birth.

About 90% of hereditary congenital NDI cases are X-linked (AVPR2); the remaining ~10% are autosomal (AQP2-related, OMIM #125800, both dominant ~9% and recessive ~1% of the inherited total) (search synthesis of PMC articles, this session). NDI must be distinguished from far more common acquired NDI (lithium, hypercalcemia, hypokalemia, obstructive uropathy) and from central diabetes insipidus and primary polydipsia, which share the polyuria-polydipsia phenotype but have different mechanisms and treatments.

Key identifiers: - OMIM #304800 — DIABETES INSIPIDUS, NEPHROGENIC, 1, X-LINKED; NDI1 (omim.org/entry/304800) - OMIM 300538 — ARGININE VASOPRESSIN RECEPTOR 2; AVPR2 - MONDO:0010581 (per search synthesis; verify before KB use) - Related: OMIM #125800 (NDI2, autosomal, AQP2) and OMIM 107777 (AQP2 gene) — the genocopy to distinguish from NDI1 - Orphanet: "Nephrogenic diabetes insipidus" (X-linked form as a subtype) - ICD-10: N25.1 (Nephrogenic diabetes insipidus)

Synonyms: Vasopressin-resistant diabetes insipidus; X-linked recessive nephrogenic diabetes insipidus; congenital NDI (X-linked form); AVPR2-related NDI; DI, nephrogenic, X-linked.

Evidence basis: This report draws on aggregated disease-level resources (OMIM, GeneReviews, Orphanet-type structured sources) and primary literature — case series, pediatric cohort studies, and functional/mechanistic studies — rather than individual unpublished EHR data.

2. Etiology

Disease causal factor

The sole cause of X-NDI (NDI1) is a hemizygous loss-of-function pathogenic variant in AVPR2 (Xq28), encoding the V2 vasopressin receptor expressed on the basolateral membrane of renal collecting-duct principal cells. Over 200 distinct disease-causing AVPR2 variants have been published — missense, nonsense, small insertions/deletions, large deletions, and complex rearrangements (search synthesis, this session, corroborating GeneReviews NBK1177/PMID:20301356).

Genetic risk factors

Causal variant class: hemizygous AVPR2 variant in a male, or — less commonly — a heterozygous variant in a manifesting female carrier.
Partial-NDI variants: at least 18 AVPR2 variants (e.g., p.Asp85Asn, p.Val88Met, p.Asn317Lys) produce a partial phenotype with later onset and residual DDAVP responsiveness, via mechanisms such as reduced (but not absent) surface expression or impaired G-protein coupling rather than complete intracellular retention (GeneReviews NBK1177/PMID:20301356).
Modifier: degree of X-inactivation skewing in heterozygous females is the principal modifier of female phenotype severity (see below).
Founder variants: regional founder effects elevate local incidence — see Epidemiology (§9).

Environmental risk factors

There are no known environmental causal or risk factors for the X-linked hereditary form — it is a fully penetrant monogenic disorder in hemizygous males. (Environmental/acquired causes of NDI — lithium, hypercalcemia, hypokalemia, obstructive uropathy — are a mechanistically related but etiologically distinct secondary phenomenon; see §5 and §6.) Sex is itself the principal "risk factor": because AVPR2 is X-linked, males are at far higher risk of a full, early-onset phenotype than females.

Protective factors

No genetic or environmental protective factor against the X-linked inherited form is described in the literature surveyed. The nearest analogue is favorable X-inactivation skewing in a female carrier, which can render her phenotypically normal rather than a "protective" factor in the population-genetics sense.

Gene-environment interaction

The clearest gene-environment interaction is with water access: the AVPR2 defect is unmasked and made dangerous specifically when free water intake is restricted (illness, vomiting, reduced access in infancy, anesthesia/surgery, hot weather) — each of these is a described precipitant of acute hypernatremic crisis in case reports reviewed this session (e.g., Capasso et al., natural-history case report, PMID:39644399). There is no described interaction with diet, toxins, or infection altering the AVPR2 genotype-phenotype relationship beyond the acquired-NDI mechanisms listed in §5, which can compound the inherited defect (e.g., superimposed lithium exposure in an AVPR2 hemizygote, not directly documented but mechanistically plausible from the independent acquired-NDI literature).

3. Phenotypes

Phenotype type and characteristics

The cardinal phenotype triad is polyuria, polydipsia, and failure to thrive, present from birth but typically recognized once nonspecific infant symptoms prompt laboratory evaluation.

Phenotype	Type	Onset	Frequency / notes	Suggested HPO term (unverified)
Polyuria (often >10–20 L/day in adults; median 10.0 mL/kg/h in one pediatric cohort)	Clinical sign / lab	Birth–infancy	Universal	HP:0000103 Polyuria
Polydipsia (compensatory)	Symptom	Infancy onward	Universal (in verbal children/adults)	HP:0001959 (per search synthesis; verify — commonly cited for Polydipsia)
Hypernatremia (median 160.5 mmol/L in one cohort at presentation)	Lab abnormality	Neonatal/infancy crisis	Common at diagnosis	HP:0003228 Hypernatremia (verify)
Hyposthenuria / low urine osmolality, failure to concentrate urine after DDAVP	Lab abnormality	From birth	Universal, diagnostic	—
Poor feeding, irritability, vomiting	Symptom	First days–weeks of life	Common presenting complaint	HP:0011968 Feeding difficulties (verify)
Failure to thrive / growth retardation	Physical sign	Infancy–childhood	70–71% below −2 SD for weight/height at initial treatment in a 66-subject cohort (PMID:32039113)	HP:0001508 Failure to thrive
Fever (unexplained)	Symptom	Infancy	Recurrent, noted in multiple case series	HP:0001945 Fever (verify)
Hydronephrosis / hydroureter / megacystis (secondary urinary tract dilatation from chronic high urine flow and bladder overdistension)	Structural/radiologic	Childhood–adulthood, progressive if untreated	37% urologic complications in pediatric cohort (PMID:32039113); severe in untreated adults (PMID:39644399)	HP:0000126 Hydronephrosis
Nocturia / nocturnal enuresis	Symptom	Childhood	44% at final follow-up in pediatric cohort	HP:0000017 Nocturia
Chronic kidney disease (secondary, from chronic obstructive uropathy)	Lab/clinical	Later childhood–adulthood	23–30% CKD stage ≥2 in pediatric cohort (PMID:32039113); eGFR 25 mL/min/1.73m² in an untreated 58-year-old (PMID:39644399)	HP:0012622 Chronic kidney disease
Neurodevelopmental disorder (intellectual disability, ASD, language delay)	Behavioral/cognitive	Variable	75% (6/8) in one long-term pediatric follow-up cohort (PMID:40922895) — notably higher than the oft-quoted "normal intelligence with early treatment" figure, reflecting either ascertainment in a severe-case series, subclinical dehydration episodes, or both	HP:0001249 Intellectual disability
Secondary hyperparathyroidism	Lab	Adulthood (untreated/CKD)	Described in a severe untreated case (PMID:39644399)	—
Hypertension	Clinical sign	Adulthood (CKD-associated)	Described in untreated case	HP:0000822 Hypertension

Heterozygous (carrier) females: clinical expression ranges from asymptomatic to a full NDI phenotype indistinguishable from affected males. This variability is attributed to skewed X-chromosome inactivation; one AVPR2-mutation-positive female in a recent cohort had overt NDI despite the "typically asymptomatic carrier" expectation (PMID:40922895).

Quality-of-life impact

Chronic polyuria/polydipsia in school-age children and adults causes significant social and functional burden: need for constant water access, disrupted sleep from nocturia, school/work disruption, and psychological burden of a rare chronic disease. The pediatric cohort above documented high health-system burden directly attributable to the phenotype: 61% required inpatient hospitalization and 36% required gastrostomy tube placement for fluid/caloric management (PMID:32039113). No disease-specific quality-of-life instrument validation was identified in this search; QoL is inferred from these morbidity proxies rather than from EQ-5D/SF-36/PROMIS studies specific to NDI.

4. Genetic/Molecular Information

Causal gene

AVPR2 (HGNC:897; OMIM 300538), Xq28, 2.2 kb, 3 exons, encoding a 371-amino-acid, ~40.3 kDa class-A (rhodopsin-like) G protein-coupled receptor with 7 transmembrane domains (search synthesis, this session, consistent with OMIM 300538).

Pathogenic variants

Variant spectrum: >200 published disease-causing AVPR2 variants — missense (the largest class), nonsense, small insertions/deletions, large deletions, and complex rearrangements.
ACMG/AMP classification: individual variants are classified via ClinVar/ClinGen on a case-by-case basis; e.g., ClinVar RCV000011591 classifies AVPR2 c.1009C>T (p.Arg337Ter) as pathogenic for X-linked NDI, and RCV000011599 classifies c.137T>A (p.Ile46Lys) likewise (search synthesis, this session — verify exact ClinVar classification labels before citing in a KB entry).
Allele frequency: AVPR2 pathogenic variants are individually rare/private (frequent de novo occurrence and many unique familial variants); no single recurrent common allele dominates globally, though regional founder variants exist (§9). No gnomAD constraint metric (LOEUF/pLI) for AVPR2 was retrieved with confidence in this session — recommend a direct gnomAD query before citing a specific constraint value.
Origin: germline (inherited X-linked or de novo); no somatic AVPR2 NDI mechanism is described.
Functional consequence — three recognized mechanistic classes of mutant V2 receptor (search synthesis, consistent with the functional-rescue literature reviewed, e.g., PMID:35153784, and Sci Rep 2020, doi:10.1038/s41598-020-73089-x):
Type I (protein-expression disorder): decreased, truncated, or null protein expression from transcription/mRNA-processing/translation defects.
Type II (localization/trafficking disorder) — the most common class, ~70% of NDI-causing AVPR2 variants: the receptor misfolds, is retained in the endoplasmic reticulum by ER quality control, and never reaches the plasma membrane (e.g., variants at W164S, A165D, A165P, S167T, Q174R fail to exit the ER). One Danish case documents ER retention with subsequent lysosomal degradation of the mutant receptor (academic.oup.com/ckj, this session).
Type III (functional disorder): the receptor reaches the cell surface normally but has defective ligand binding, defective Gs-coupling, or constitutive endocytosis, so it cannot generate a normal cAMP response despite correct trafficking.
Partial-NDI variants (§2) typically behave as attenuated Type II/III defects retaining residual function.

Modifier genes

No AVPR2-independent modifier gene for X-NDI severity is established in the literature surveyed; the principal "modifier" of phenotype in heterozygotes is X-inactivation skewing (an epigenetic, not genic, modifier — see below) rather than a second locus.

Epigenetic information

The dominant epigenetic determinant of disease expression in heterozygous females is the pattern of X-chromosome inactivation (XCI): skewing toward preferential inactivation of the wild-type allele yields a manifesting carrier with an overt (sometimes full) phenotype, while skewing toward the mutant allele yields an asymptomatic carrier. No disease-specific DNA methylation or histone-modification signature of the AVPR2 locus itself (beyond XCI) was identified in this search.

Chromosomal abnormalities

Some AVPR2-causing lesions are large deletions spanning the gene (e.g., a novel large AVPR2 deletion reported in an infant, PMC article reviewed this session) rather than point mutations; complex rearrangements are also reported. No recurrent translocation or aneuploidy mechanism is described for NDI1.

5. Environmental Information

Environmental factors

For the inherited X-linked form, there is no environmental causal factor — the lesion is a germline AVPR2 variant. However, environmental exposures precipitate the clinical emergencies of the disease (dehydration, hypernatremic crisis) and can be superimposed to worsen the renal concentrating defect:

Water restriction / reduced access — the single most important modifiable precipitant of crisis in an AVPR2 hemizygote (documented repeatedly in case series, this session).
Illness with vomiting/reduced intake — a recurring precipitant of acute decompensation in infants (GeneReviews NBK1177/PMID:20301356).
Heat/high ambient temperature and exercise — increase insensible losses on top of an already maximal obligate renal water loss (general clinical inference; not independently verified by a specific citation in this session).

Environmental factors relevant to the acquired/secondary NDI phenocopy (important differential, and mechanistically informative even though genetically distinct from X-NDI):

Lithium therapy — downregulates renal AQP2 via chronic collecting-duct toxicity (search synthesis, this session).
Hypercalcemia — induces targeted autophagic degradation of AQP2 (ScienceDirect article reviewed, this session).
Hypokalemia — likewise triggers autophagic AQP2 degradation.
Increased renal prostaglandin E2 (PGE2) production, seen in both human and animal acquired-NDI, antagonizes AVP-stimulated water permeability by promoting AQP2 internalization from the apical membrane — this is the documented mechanistic basis for indomethacin's (a PGE2-synthesis inhibitor) therapeutic benefit even in the genetic, receptor-null form of NDI.

Lifestyle factors

No specific lifestyle (smoking, alcohol, exercise pattern) risk-modifying factor for X-NDI onset or severity was identified; lifestyle management (ensured free water access, avoidance of salt/protein-overload diet) is a treatment, not a primary risk factor (§12).

Infectious agents

X-NDI itself has no infectious etiology. Note for differential diagnosis: acquired NDI has been documented secondary to leptospirosis in a dog (PMC4005616, this session) and can occur secondary to pyelonephritis/obstructive uropathy in humans — mechanistically informative as a phenocopy, not a cause of the inherited disorder.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical phenotype)

A hemizygous loss-of-function AVPR2 variant (Xq28) is inherited or arises de novo, producing a mutant V2 vasopressin receptor — demonstrated, not inferred, by the >200 characterized pathogenic variants and associated functional studies reviewed above.
This leads to one of three receptor defects (demonstrated by functional/trafficking studies): (a) deficient/absent receptor protein synthesis (Type I), (b) ER misfolding with failure to traffic to the basolateral plasma membrane of the collecting-duct principal cell, followed by ER-associated degradation/lysosomal degradation (Type II, ~70% of cases — the dominant branch), or (c) normal surface expression but defective ligand binding or Gs-coupling (Type III).
Each defect results in failure of arginine vasopressin (AVP), released from the posterior pituitary in response to rising plasma osmolality, to productively engage a functional V2 receptor on the principal cell's basolateral membrane — demonstrated by radioligand-binding and signaling assays in the mutant-receptor literature.
This leads to failure to activate the Gs–adenylyl cyclase–cAMP–protein kinase A (PKA) cascade inside the principal cell — the canonical V2R signal-transduction pathway, now resolved at near-atomic resolution by cryo-EM structures of the AVP–V2R–Gs ternary complex (PMID:33664408, Cell Research 2021; companion structures in Science Advances, PMID:34020960, 2021, and a 2022 V2R–β-arrestin1 ternary-complex structure).
Without PKA activation, AQP2 is not phosphorylated at its regulatory serine residues (notably Ser256) — demonstrated biochemically — so AQP2-containing subapical vesicles fail to fuse with the apical plasma membrane of the principal cell.
This results in a structurally intact but functionally "closed" collecting duct: the apical membrane lacks water channels despite an intact basolateral-to-lumen osmotic gradient, so free water cannot be reabsorbed regardless of how high circulating AVP rises (demonstrated — NDI patients have elevated, not deficient, plasma AVP, which is the defining diagnostic distinction from central DI).
Impaired water reabsorption leads to the inability to concentrate urine above ~200 mOsm/kg despite maximal physiologic AVP stimulation (demonstrated diagnostically by the water-deprivation/DDAVP test) and produces massive hyposthenuric polyuria.
Polyuria triggers a compensatory increase in thirst drive and polydipsia; when water intake cannot keep pace with obligate renal free-water loss (illness, restricted access, infancy when thirst cannot be behaviorally expressed), this leads to hypernatremic dehydration, which in turn can cause CNS injury (inferred from clinical outcome literature — seizures, brain injury, and neurodevelopmental impairment are reported sequelae of recurrent hypernatremic episodes, PMID:40922895, rather than of the AVPR2 defect directly).
Chronic high urine flow leads to, over years, progressive dilatation of the collecting system — hydronephrosis, hydroureter, and megacystis with bladder-wall trabeculation and voiding dysfunction — demonstrated longitudinally in both pediatric cohorts (PMID:32039113) and an extreme untreated adult case (post-void residual 3.1 L; PMID:39644399).
Chronic obstructive uropathy from branch 9 results in slowly progressive chronic kidney disease, which can in turn cause secondary hyperparathyroidism and hypertension, as documented in the untreated 58-year-old case above — this is a downstream, largely preventable consequence of delayed diagnosis/treatment rather than a direct effect of the AVPR2 defect on nephron mass.
Separately and in parallel, chronic caloric expenditure on excessive urine production plus reduced oral intake during feeding-limited infancy contributes to failure to thrive and growth impairment (documented: 70–71% of a pediatric cohort below −2 SD for weight/height at presentation, PMID:32039113) — partially reversible with treatment (29–38% still below −2 SD at follow-up).

Molecular pathway

Gs–adenylyl cyclase–cAMP–PKA signaling downstream of the V2 receptor is the central, and in the inherited disease the exclusively disrupted, pathway (KEGG/Reactome-type annotation: "vasopressin-regulated water reabsorption" pathway). A cAMP-independent rescue pathway has been identified pharmacologically: AMPK activation (e.g., by metformin) can phosphorylate AQP2 (and UT-A1) and increase apical AQP2 trafficking even in V2R-null cells/mice, providing an alternate kinase route to the same vesicle-trafficking endpoint (search synthesis, this session; mechanistic basis for the NDI-5001 candidate drug, §12).

Cellular processes

The principal cellular lesion is a protein-trafficking/quality-control defect (ER retention, ERAD, lysosomal degradation of misfolded V2R) rather than apoptosis, classical inflammation, or cell-cycle dysregulation. Secondary cellular consequences of chronic obstruction (tubular atrophy, interstitial fibrosis) presumably occur in long-standing untreated disease but were not separately characterized in the sources reviewed.

Protein dysfunction

Loss-of-function via misfolding dominates (Type II, ~70%); a minority of variants alter catalytic/signaling function without misfolding (Type III); a further subset abolish expression outright (Type I). This is a receptor-level loss-of-function disorder, not a gain-of-function or dominant-negative mechanism in the X-linked hemizygous male (dominant-negative mechanisms are instead characteristic of some autosomal dominant AQP2 NDI variants, a genocopy — see §4/§9 comparison).

Metabolic changes

No primary metabolic pathway defect is described; secondary electrolyte derangement (hypernatremia) and, in chronic disease, CKD-associated metabolic bone disease (secondary hyperparathyroidism, documented in the untreated adult case above) are downstream consequences rather than primary mechanisms.

Immune system involvement

Not implicated; X-NDI is not an immune-mediated or inflammatory disorder.

Tissue damage mechanisms

The principal tissue-damage mechanism is mechanical/obstructive — chronic high urine flow leading to collecting-system dilatation, bladder-wall trabeculation, and secondary CKD — rather than oxidative, ischemic, or fibrotic injury at the cellular level (though fibrosis likely supervenes in long-standing obstructive nephropathy by general nephrology principles, not separately documented here for X-NDI specifically).

Biochemical abnormalities

Defective GPCR function (V2 receptor) is the core biochemical lesion; AQP2 itself is structurally normal in X-NDI (distinguishing it from the AQP2-mutant autosomal form, where AQP2 itself is the defective protein/channel).

Molecular profiling

No disease-specific transcriptomic, proteomic, metabolomic, lipidomic, single-cell, or spatial-transcriptomic dataset for human X-NDI kidney tissue was identified in this search (unsurprising given inaccessibility of human collecting-duct tissue and the kidney's structural normalcy). The closest analogues are the Avpr2-deficient rat model generated by the rGONAD gene-editing method (PMID:40102322, Clin Exp Nephrol 2025) and inducible Avpr2-knockout mice (Avpr2^fl/y^;Esr1-Cre, tamoxifen-inducible, used because constitutive Avpr2-null male pups die within the first week of life), which support molecular/histological characterization (§15).

7. Anatomical Structures Affected

Organ level

Primary organ: kidney — specifically the renal collecting duct (cortical and medullary segments) and, to a lesser extent, the distal convoluted tubule, where V2 receptor expression is concentrated.
Secondary organ involvement: urinary bladder (chronic overdistension, trabeculation, diverticulum formation in severe/untreated disease) and ureters (hydroureter from chronically high urine flow and, later, outflow dysfunction); CNS (secondary injury from hypernatremic episodes, not primary involvement).
Body systems involved: renal/urinary (primary), endocrine (vasopressin axis — pituitary AVP secretion is normal/elevated, not primarily affected), and secondarily cardiovascular (hypertension in CKD) and skeletal/parathyroid (secondary hyperparathyroidism in CKD).

Tissue and cell level

Cell population targeted: renal collecting-duct principal cells (the AQP2- and V2R-expressing epithelial cell type); suggested Cell Ontology term: CL:1001431 (kidney collecting duct principal cell) — unverified, confirm via OAK/CL before KB use.
Tissue type: simple cuboidal epithelium of the collecting duct.

Subcellular level

Endoplasmic reticulum — site of V2 receptor misfolding and retention for Type II variants; candidate GO Cellular Component term GO:0005783 (endoplasmic reticulum) — unverified.
Apical plasma membrane of the principal cell — the destination AQP2 fails to reach; candidate GO:0016324 (apical plasma membrane) — unverified.
Subapical storage vesicles — site of AQP2 sequestration absent PKA-mediated trafficking signal.
Lysosome — site of degradation of ER-retained misfolded V2 receptor in at least one documented case (academic.oup.com/ckj, this session).

Localization

Bilateral, symmetric — there is no described lateralization, consistent with a systemic/genetic (not focal/structural) renal defect. Suggested UBERON term: UBERON:0001232 (collecting duct) — unverified.

8. Temporal Development

Onset

The renal concentrating defect is present from birth (congenital). Clinical recognition, however, is typically delayed to early infancy: median age at diagnosis was 4.2 months (IQR 1.1–9.8) in a 66-subject multicenter pediatric cohort (PMID:32039113), and 7.5 months in a smaller long-term single-center cohort (PMID:40922895). Onset pattern is insidious/subacute in presentation (nonspecific feeding/irritability symptoms) punctuated by acute hypernatremic crises.

Progression

Disease course pattern is best described as chronic and stable at the renal-tubular level (the receptor defect itself does not worsen over time) but progressive at the level of secondary complications when inadequately treated — hydronephrosis, bladder dysfunction, and CKD accumulate over years to decades (documented trajectory from infancy to a severely affected 58-year-old in PMID:39644399).
Rate: slow/progressive for secondary urologic and renal complications; rapid/acute for hypernatremic decompensation episodes.
Duration: lifelong (no spontaneous remission described; this is a structural receptor null state, not a transient or reversible lesion as in some acquired NDI).

Patterns

Remission: none spontaneous; substantial symptomatic improvement (but not cure) with treatment — thiazide/amiloride/NSAID combination therapy reduces polyuria by up to ~50% (GeneReviews NBK1177/PMID:20301356) and normalized serum sodium in all treated patients in one cohort (PMID:40922895), though the underlying receptor defect persists lifelong.
Critical period: infancy is the period of highest vulnerability — thirst cannot be behaviorally satisfied by a pre-verbal infant, so undiagnosed infants are at greatest risk of recurrent hypernatremic injury and of the failure-to-thrive/developmental sequelae documented above. Early diagnosis and treatment within this window is repeatedly identified in the literature as the single most important determinant of long-term neurodevelopmental and renal outcome.

9. Inheritance and Population

Epidemiology

Prevalence (Quebec, Canada): 8.8 per 1,000,000 males — the most frequently cited population estimate, assumed to be broadly representative worldwide (GeneReviews NBK1177/PMID:20301356; corroborated independently by search synthesis).
Regional founder-effect elevation: incidence is six times higher in Nova Scotia/New Brunswick than the Quebec baseline, and is also elevated in Utah, due to population-specific founder AVPR2 variants.
Rarity context: one long-term single-center cohort identified only 8 pediatric patients over a 34-year period (1991–2024) (PMID:40922895), illustrating the disease's rarity even at a referral center.

Inheritance pattern

X-linked recessive (note: one automated extraction in this session's research mislabeled this "X-linked dominant" — that is incorrect terminology for this disorder and is not adopted here). The canonical pattern is: hemizygous males are affected; heterozygous female carriers are classically described as asymptomatic but can manifest a partial-to-full phenotype through skewed X-inactivation (a manifesting-carrier phenomenon, not X-linked dominance in the Mendelian sense). At least one AVPR2-positive female in the literature reviewed had an overt, non-partial NDI phenotype (PMID:40922895).

Penetrance: complete in hemizygous males; variable/incomplete in heterozygous females depending on XCI skewing.
Expressivity: variable, most clearly illustrated by the partial-NDI variant class (§2, §4), which produces a milder, later-onset phenotype than the typical full loss-of-function variant.
Genetic anticipation: not described (not a repeat-expansion disorder).
Germline mosaicism: GeneReviews notes that for apparent de novo cases, recurrence risk in future offspring of the mother is low (<1%) but not zero, because of the possibility of maternal germline mosaicism (GeneReviews NBK1177/PMID:20301356).
Founder effects: documented in Quebec/Nova Scotia/New Brunswick (Canada) and Utah (USA) populations (see Epidemiology above).
Consanguinity: more relevant to the autosomal recessive AQP2 form (NDI2) than to X-linked NDI1, which does not require biallelic inheritance in males.
Carrier frequency: not separately quantified in the sources reviewed beyond the prevalence figures above; would require a dedicated population-genetics study (e.g., gnomAD hemizygote counts), not retrieved with confidence in this session.

Population demographics

Sex ratio: strongly male-predominant by mechanism; one pediatric cohort was 89% male (PMID:32039113), and 7 of 8 patients in another long-term cohort were male (PMID:40922895) — the residual female cases are manifesting heterozygous carriers, not a second inheritance mechanism.
Ethnic/geographic distribution: documented cases worldwide (Chinese, Turkish, Danish, Asian, and North American pedigrees all cited in this session's sources), with founder-variant clustering in parts of Canada and Utah as above; one cohort was 67% white (PMID:32039113), though this likely reflects referral-center ascertainment rather than a biological ethnic predisposition.
Age distribution: overwhelmingly diagnosed in infancy; adult presentations in the literature largely represent either undiagnosed/untreated childhood-onset disease recognized late (e.g., the 58-year-old case, PMID:39644399) or partial-NDI variants with delayed clinical recognition.

10. Diagnostics

Clinical tests

Water-deprivation test with DDAVP (desmopressin) challenge: the classic confirmatory test — affected individuals fail to concentrate urine above ~200 mOsm/kg H2O despite desmopressin administration, distinguishing NDI from central DI (which responds to DDAVP) (GeneReviews NBK1177/PMID:20301356). Important safety caveat documented in a recent case series: water-deprivation testing is contraindicated once serum sodium exceeds 145 mmol/L; in that setting, a desmopressin challenge alone (without prior deprivation) should be used, and "all desmopressin tests were negative" across all NDI1 cases in one cohort (PMID:40922895).
Copeptin-based diagnosis (a major recent diagnostic advance, supplanting/complementing the water-deprivation test): copeptin is the stable C-terminal fragment of the AVP prohormone and is a reliable surrogate for plasma AVP. Unstimulated basal copeptin reliably diagnoses nephrogenic DI (high basal copeptin unequivocally indicates NDI, since the defect is downstream of normal/elevated AVP secretion), whereas a stimulation test (hypertonic saline or arginine infusion) is needed to separate central DI from primary polydipsia. A stimulated copeptin level of 4.9 pmol/L after hypertonic saline infusion differentiates central DI from primary polydipsia with high accuracy, superior to the classical water-deprivation test (search synthesis referencing the landmark NEJM copeptin studies, e.g., Fenske et al., N Engl J Med 2018 — PMID not independently verified in this session). The 2024 international consensus statement additionally reports a baseline plasma copeptin cutoff >21.4 pmol/L as diagnostic for NDI in adults (Levtchenko et al., Nat Rev Nephrol 2024, DOI:10.1038/s41581-024-00897-z — PMID not captured; cite by DOI).
Laboratory findings: hypernatremia (serum Na+ often >145–160 mmol/L at presentation), low urine specific gravity/osmolality, normal-to-elevated plasma AVP.
Imaging: renal/bladder ultrasound to detect and monitor secondary hydronephrosis, hydroureter, and megacystis (recommended periodic surveillance per GeneReviews — annual in adults).

Genetic testing

First-tier: AVPR2 single-gene sequence analysis, detecting ~90% of pathogenic variants.
Second-tier (if sequencing negative): gene-targeted deletion/duplication analysis (MLPA or equivalent) for the remaining large-rearrangement cases.
Alternative: multigene renal-tubulopathy or polyuria/DI panel including AVPR2, AQP2, and AVP.
In the Pediatric Nephrology Research Consortium cohort, genetic testing or family history was obtained in 70% of subjects; among those tested, 89% had AVPR2 variants and 11% had AQP2 (PMID:32039113) — a useful real-world confirmation of the textbook 90:10 split.
Whole-exome/genome sequencing is appropriate when single-gene/panel testing is negative or the phenotype is atypical, per general rare-disease diagnostic practice (not separately validated for NDI specifically in the sources reviewed).

Differential diagnosis

The core differential is the polyuria-polydipsia syndrome triad: 1. Central (neurogenic) diabetes insipidus — deficient AVP secretion; responds to desmopressin (the key distinguishing response). 2. Primary (dipsogenic) polydipsia — excessive water intake from a primary thirst-drive abnormality, with intact AVP axis. 3. Nephrogenic diabetes insipidus — AVP resistance at the kidney (this disease). Additional mimics/secondary causes to exclude: acquired NDI (lithium, hypercalcemia, hypokalemia, obstructive uropathy); Bartter syndrome (can present with hypernatremia-hyperchloremia mimicking NDI, and refractory hypokalemia should prompt evaluation for Bartter syndrome rather than primary NDI); sickle cell disease/trait-associated renal medullary injury; other inherited tubulopathies.

Screening

No population-based newborn screening program for X-NDI exists (it is not detected by standard metabolic newborn screening panels). Cascade/carrier testing in at-risk female relatives and prenatal/preimplantation genetic testing become available once the family's causal AVPR2 variant is identified (GeneReviews NBK1177/PMID:20301356).

11. Outcome/Prognosis

Survival and mortality

No disease-specific mortality or survival-rate statistic (5-year/10-year) was identified in the literature surveyed; NDI1 is not generally described as a life-shortening condition when diagnosed and treated, though recurrent severe hypernatremic crises in undiagnosed infants carry acute mortality/morbidity risk (general clinical inference, consistent with but not separately quantified by the sources reviewed).

Morbidity and function

With early diagnosis and appropriate management, intelligence and lifespan are "usually normal" per GeneReviews (NBK1177/PMID:20301356) — but a more recent long-term single-center cohort (median follow-up 16.9 years) found 75% (6 of 8) patients developed a neurodevelopmental disorder (intellectual disability, ASD, or language delay) despite treatment (PMID:40922895), a substantially more concerning figure that should be weighed against the classic "normal outcome with early treatment" teaching — the discrepancy may reflect residual subclinical dehydration episodes, cohort/ascertainment differences, or genuine evolving understanding of long-term neurodevelopmental risk; this is flagged as an open tension in the literature rather than resolved here.
Growth: severe growth impairment is common at diagnosis (70–71% below −2 SD weight/height) and improves but often does not normalize with treatment (29–38% still below −2 SD at follow-up) (PMID:32039113).
Renal function: 23–30% of a pediatric cohort had CKD stage ≥2 at follow-up (PMID:32039113); an untreated adult case showed eGFR 25 mL/min/1.73m² after decades of disease (PMID:39644399) — illustrating a clear treatment-dependent divergence in renal prognosis.
Urologic morbidity: 37% urologic complications (hydronephrosis, bladder dysfunction) in the pediatric cohort; severe bladder decompensation (3.1 L post-void residual, trabeculation, diverticulum) in the untreated adult case.

Disease course / complications

Complications cluster into: (1) acute hypernatremic dehydration/CNS injury episodes, (2) chronic urologic tract dilatation and bladder dysfunction, (3) secondary CKD and its sequelae (hypertension, secondary hyperparathyroidism), and (4) growth impairment. Recovery potential for the renal-tubular defect itself is nil (it is a fixed genetic lesion), but recovery/stabilization of the secondary complications is substantial with early, sustained treatment.

Prognostic factors

Age at diagnosis/treatment initiation is the dominant prognostic factor identified across every source reviewed — earlier diagnosis and treatment correlates with better growth, renal, and (per the classic teaching, though contested by the more recent cohort above) neurodevelopmental outcomes. Variant class (full vs. partial loss-of-function) is a secondary prognostic determinant, with partial-NDI variants generally producing a milder course.

12. Treatment

There is no curative therapy for X-NDI; management is lifelong and directed at minimizing polyuria, preventing dehydration, and averting secondary complications (GeneReviews NBK1177/PMID:20301356; search synthesis this session).

Pharmacotherapy

Thiazide diuretics (hydrochlorothiazide, chlorothiazide) — first-line; paradoxically reduce urine output in NDI by inducing mild volume contraction that increases proximal tubular sodium/water reabsorption, thereby reducing delivery of filtrate to the unresponsive collecting duct. Used in 74% of one pediatric cohort (PMID:32039113) and in all patients of another cohort, combined with amiloride (PMID:40922895). Suggested NCIT clinical-action term: NCIT:C15986 (Pharmacotherapy) for the generic action, with the specific agent as therapeutic_agent — e.g., CHEBI (hydrochlorothiazide) — unverified CURIEs, confirm before KB use.
Potassium-sparing diuretics (amiloride) — frequently combined with thiazide (33% of one cohort used this combination specifically; PMID:32039113) both for additive antidiuretic effect and to offset thiazide-induced hypokalemia.
NSAIDs (indomethacin) — added in 42% of one cohort (PMID:32039113) and 62.5% of another (PMID:40922895); mechanistically reduces renal PGE2 synthesis, and PGE2 independently promotes AQP2 internalization (§6), so indomethacin provides an AQP2-membrane-stabilizing effect independent of the V2R defect. Use requires monitoring for renal/GI NSAID toxicity with prolonged use.
Pharmacogenomics: no AVPR2-genotype-specific drug-dosing guidance (e.g., PharmGKB/CPIC guideline) was identified; dosing is empiric/weight-based per general pediatric nephrology practice.

Emergency/acute management

Critical point emphasized in GeneReviews: IV normal saline is contraindicated in acute hypernatremic crisis in NDI, as it can worsen hypernatremia; free-water-deficit replacement with 5% dextrose in water is the correct emergency fluid strategy (NBK1177/PMID:20301356).

Supportive care

Unrestricted free access to water is mandatory and is itself the most important "treatment" — water restriction is explicitly contraindicated. Dietary measures: exclusive breastfeeding in infancy where feasible, and a high-calorie, low-sodium, low-protein diet to reduce the obligate solute load the nephron must excrete (search synthesis, this session).

Experimental / emerging therapeutics (recent developments, 2024–2026)

Pharmacological chaperones targeting the mutant V2 receptor directly: tolvaptan (a clinically approved V2R inverse agonist/antagonist used for other indications) can, counter-intuitively, act as a pharmacochaperone for certain misfolded (Type II) AVPR2 variants — aiding correct folding in the ER and escape from ER quality control so the mutant receptor reaches the membrane, where endogenous AVP can then activate it. The M272R V2R mutant specifically responded to tolvaptan with improved maturation, membrane trafficking, and DDAVP responsiveness (Sci Rep 2020, doi:10.1038/s41598-020-73089-x). A related study using both the antagonist tolvaptan and a novel high-affinity agonist pharmacochaperone (MCF14) showed partial functional rescue of a different NDI-causing V2R mutant (PMID:35153784, Frontiers in Pharmacology 2022). This is inherently a mutation-specific / personalized-medicine approach — not all variant classes are rescuable (Type II ER-retained variants are the best candidates; Type I null-expression variants are not).
Nonpeptide V2R agonists (e.g., SR121463) have similarly been shown to act as chaperones, partially rescuing trafficking-defective mutants such as L57R in experimental systems, particularly relevant for partial cNDI-causing variants (PMC11095762, this session).
β3-adrenergic receptor (β3-AR) agonism — a V2R-independent rescue strategy, 2024: in the mouse model of X-NDI, the β3-AR agonist BRL37344 produced a sustained antidiuretic effect (24-h urine output reduced 27%, urine osmolality increased 25%, water intake reduced 20%) by increasing phosphorylation of NKCC2, NCC, and AQP2 (notably AQP2 Ser256) and increasing AQP2 apical membrane expression — entirely bypassing the defective V2 receptor (Milano et al., J Cell Mol Med 2024, PMID:38652212). This is proposed as a candidate strategy applicable regardless of AVPR2 variant class, since it does not require receptor rescue at all.
AMPK activation — the basis of an active clinical-stage candidate: AMPK provides a cAMP/PKA-independent route to AQP2 (and UT-A1) phosphorylation and apical trafficking; metformin-mediated AMPK activation improved urine osmolality in V2R-knockout mice (search synthesis, this session). This mechanism underlies NDI-5001, a proprietary small-molecule AMPK activator in active clinical development by NephroDI Therapeutics (partnered with Otsuka's McQuade Center for Strategic Research and Development) as a potential first-in-class therapy. A Phase 1 trial — NCT07525960, "A Study in Adult Males With X-linked Congenital Nephrogenic Diabetes Insipidus to Test the Effects of NDI-5001 Given for Multiple Days and to Test How NDI-5001 is Tolerated and Taken up in the Body" — is registered on ClinicalTrials.gov (sponsor: Otsuka Pharmaceutical Development & Commercialization, Inc.), representing the most advanced V2R-bypass therapeutic approach currently in human testing for this disease.
Gene therapy: no AVPR2 gene-replacement or gene-editing clinical program was identified in this search; this remains a theoretical future direction rather than a current pipeline asset.

Surgical/interventional and rehabilitative

Surgical intervention is reserved for managing severe secondary urologic complications (e.g., bladder decompression/augmentation in cases of severe chronic overdistension) rather than as a primary disease treatment; no NDI-specific surgical protocol was identified. No physical/occupational/speech therapy protocol specific to NDI beyond standard management of any associated neurodevelopmental comorbidity.

Treatment strategy / algorithm

The de facto algorithm from the sources reviewed is: (1) ensure unrestricted water access and correct any acute hypernatremia with D5W (never isotonic/hypertonic saline); (2) initiate thiazide + amiloride combination as first-line chronic therapy; (3) add indomethacin/NSAID if polyuria remains inadequately controlled, with renal-function monitoring; (4) for select, genotyped Type II "rescuable" variants, pharmacochaperone approaches (tolvaptan, investigational agonist chaperones) are an emerging personalized option rather than standard of care; (5) structured surveillance (growth, serum sodium, renal ultrasound) per the schedule in §10/GeneReviews.

Treatment outcomes

In the most detailed long-term cohort reviewed, combination hydrochlorothiazide + amiloride (± indomethacin in 62.5%) normalized serum sodium in all patients and preserved renal function throughout follow-up (PMID:40922895) — even though neurodevelopmental outcomes in that same cohort were less favorable than classically taught (§11), underscoring that biochemical/renal control does not guarantee freedom from neurodevelopmental sequelae, possibly reflecting the cumulative impact of pre-treatment and breakthrough dehydration episodes.

13. Prevention

Primary prevention

There is no way to prevent the underlying genetic lesion; "primary prevention" in this disease is effectively genetic counseling and reproductive options (below) rather than risk-factor modification, since there is no modifiable environmental cause of the inherited disorder itself.

Secondary prevention (early detection)

High index of suspicion in male infants with unexplained fever, poor feeding, irritability, or failure to thrive — the literature consistently identifies delayed recognition (median diagnosis age 4.2–7.5 months, well after birth) as a remediable gap, since the renal defect is congenital.
Family-history-triggered testing: once an index case's AVPR2 variant is known, at-risk male relatives can be tested in the neonatal period, pre-empting the diagnostic delay seen in sporadic/index presentations.

Tertiary prevention (preventing complications in those already affected)

Consistent thiazide/amiloride (±NSAID) therapy and unrestricted water access to prevent recurrent hypernatremic crises (which drive neurodevelopmental risk) and to blunt the progression to hydronephrosis/CKD (§6, §11).
Scheduled surveillance: growth every 3 months (infants) to every 6–12 months (older children/adults); serum sodium on the same cadence; annual renal/bladder ultrasound to catch early structural complications (GeneReviews NBK1177/PMID:20301356).
Emergency-preparedness education for families (recognizing early dehydration signs, avoiding inappropriate isotonic IV fluids) given the specific and counter-intuitive emergency-management pitfall noted in §12.

Genetic counseling / family planning

Once the family's causal AVPR2 variant is identified, carrier testing in at-risk female relatives, prenatal diagnosis, and preimplantation genetic testing are all available (GeneReviews NBK1177/PMID:20301356). The 2024 international consensus statement explicitly includes "genetic counselling and family planning" as one of its 36 formal recommendation domains (Levtchenko et al., Nat Rev Nephrol 2024, DOI:10.1038/s41581-024-00897-z), reflecting current expert consensus that this is now a standard, guideline-level component of care — not an ad hoc addition.

Immunization / public health / prophylaxis

Not applicable — this is a non-infectious, non-communicable monogenic disorder.

14. Other Species / Natural Disease

Taxonomy and naturally occurring disease

Dogs and cats: primary (familial) congenital NDI is recognized in veterinary medicine as a rare disorder involving impaired AQP2 membrane insertion, mechanistically analogous to the human disease, though the search did not return a confirmed naturally-occurring AVPR2-mutant canine/feline pedigree specifically (as opposed to the human-orthologous mechanism generally) — this should be treated as a mechanistic analogy pending a specific OMIA entry, not a confirmed AVPR2 ortholog defect in a companion-animal breed.
Secondary/acquired NDI in companion animals is well documented and far more common than primary/congenital veterinary NDI — e.g., a case of acquired NDI secondary to leptospirosis in a dog (PMC4005616, this session), and secondary NDI as "the most common cause of polyuria/polydipsia in small animals," usually from bacterial infection or hypercalcemia rather than an inherited AVPR2 defect.
No specific OMIA (Online Mendelian Inheritance in Animals) entry for a naturally occurring AVPR2-mutant breed-specific disease was retrieved with confidence in this session; this gap should be treated as "not found," not as evidence of absence, and would merit a direct OMIA database query before a definitive claim in a KB entry.

Comparative biology / orthologous gene

AVPR2 and its downstream AQP2/cAMP/PKA pathway are highly conserved across mammals — this conservation is precisely what makes rodent models (mouse, rat) informative surrogates for human mechanism and drug testing (§15). No NCBI Gene ortholog ID or cross-species evolutionary-conservation statistic specific to AVPR2 was independently verified in this session.

Transmission

Not applicable — this is a non-transmissible monogenic disorder with no zoonotic potential.

15. Model Organisms

Mouse models

Constitutive Avpr2-null mice are embryonic/perinatally compromised: male pups lacking Avpr2 die within the first week after birth, precluding study of the adult phenotype with a simple knockout — a significant modeling limitation directly analogous to, but more severe than, the human disease (search synthesis, this session).
Inducible conditional knockout (Avpr2^fl/y^; Esr1-Cre, tamoxifen-inducible): developed specifically to circumvent the neonatal-lethality problem, allowing Avpr2 ablation after survival to adulthood, and used as the platform for the 2024 β3-AR agonist rescue study (PMID:38652212) — this is the current standard mouse model for adult-phenotype X-NDI pharmacology.
Floxed Aqp2 inducible deletion mouse (PMID:16434568) — models the downstream/genocopy AQP2 lesion rather than AVPR2 itself, but recapitulates the shared distal phenotype (inability to concentrate urine) and is useful for dissecting AQP2-specific versus receptor-specific contributions.
Aqp2 point-mutation mouse (PLOS Genetics; URL retrieved, PMID not independently confirmed this session) — a genocopy model of the autosomal AQP2 form, useful comparator.
Limitations common to all current mouse models: the neonatal lethality of the true null genotype means available models either require an inducible/conditional strategy (introducing a "when was the gene lost" confound relative to the congenital human disease) or model the AQP2 genocopy rather than the AVPR2 lesion itself — a translational caveat to flag explicitly if these models are cited as supporting evidence for an X-NDI (AVPR2) pathophysiology node in a KB entry, since strict fidelity to the congenital AVPR2-null phenotype is not fully captured by the inducible-adult model.

Rat models

Avpr2-deficient rat, generated by the rGONAD (rat Genome-editing via Oviductal Nucleic Acid Delivery) method (PMID:40102322, Clin Exp Nephrol 2025) — a novel, recently published (2025) gene-edited rat model explicitly developed as "a reliable model of congenital NDI for elucidating the underlying mechanisms and identifying therapeutic targets," with phenotyping by biological, molecular, and histological examination, and pharmacologic testing of hydrochlorothiazide (40 mg/kg/d) effects on water intake, urine volume, and urine osmolality in metabolic cages. This is the most recent (2025) and most directly AVPR2-relevant whole-animal model identified in this research.

Applications and research use

These rodent models support: (1) mechanistic dissection of receptor-trafficking defects and downstream AQP2 regulation, (2) preclinical testing of V2R-bypass pharmacology (β3-AR agonism, AMPK activators such as the NDI-5001 candidate, metformin) — directly informing the current human Phase 1 program (NCT07525960), and (3) testing of pharmacochaperone rescue strategies for specific trafficking-defective receptor variants, though pharmacochaperone rescue studies to date have relied predominantly on heterologous cell-expression systems (e.g., HEK293, COS-7 — standard in the functional-characterization literature cited throughout §4/§6/§12) rather than whole-animal models, since chaperone rescue is inherently variant-specific and not easily modeled in a single knockout/knock-in animal.

Resources

No dedicated NDI-specific model registry was identified; relevant models would be catalogued through standard resources — MGI (mouse), RGD (rat) — though specific strain/allele designations for the Avpr2 conditional-knockout and rGONAD rat lines were not independently cross-referenced against MGI/RGD accession numbers in this session.

Summary of Key Sources Cited

Source	PMID/DOI	Use in report
Bichet/Knoers, Hereditary Nephrogenic Diabetes Insipidus, GeneReviews	PMID:20301356 (NBK1177)	Clinical description, genetics, management, surveillance
Levtchenko E, et al. International expert consensus statement on cNDI. Nat Rev Nephrol. 2024	DOI:10.1038/s41581-024-00897-z	Classification, copeptin diagnostic threshold, 36-recommendation framework, genetic counseling
Pediatric Nephrology Research Consortium cohort study	PMID:32039113	Genetic-testing yield, treatment patterns, growth/urologic/CKD outcomes (n=66)
"Nephrogenic Diabetes Insipidus: Three Decades of Clinical Reality"	PMID:40922895	Long-term cohort (n=8, 34 years), neurodevelopmental outcome, diagnostic/treatment detail
Capasso et al., natural history of untreated X-NDI	PMID:39644399	Severe untreated-adult complication profile (hydronephrosis, CKD, bladder failure)
rGONAD Avpr2-deficient rat model	PMID:40102322	2025 whole-animal model
Milano et al., β3-AR agonist BRL37344 mouse study	PMID:38652212	2024 V2R-independent rescue mechanism/therapeutic lead
Cryo-EM AVP–V2R–Gs structure	PMID:33664408; companion PMID:34020960	Structural basis of signal transduction
Pharmacochaperone rescue (tolvaptan/MCF14)	PMID:35153784	Mutation-specific rescue strategy
ClinicalTrials.gov NCT07525960 (NDI-5001)	NCT07525960	Active 2025–2027 Phase 1 AMPK-activator trial

Verification note: several identifiers in this report (specific HPO/GO/CL/UBERON/CHEBI term IDs, the exact ClinVar classification labels, the MONDO ID, and a small number of PMIDs recalled from general domain knowledge rather than directly confirmed by a fetched source this session — notably the copeptin NEJM paper) are flagged inline as unverified leads. Per this repository's term- and reference-validation discipline, each should be confirmed against its authoritative source (OLS/OAK lookup, ClinVar record, or PubMed) before being written into a KB YAML entry.

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	14
Resolved	14
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	14
On topic	7
Off topic	1

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

PMC:PMC11095762 (1 mention) - Therapeutic potentials of nonpeptidic V2R agonists for partial cNDI-causing V2R mutants.
shared terms: receptor, genetic

Weighed against this report's own most characteristic terms: avpr2, disease, session, variant, renal, ndi, secondary, aqp2, cohort, water, defect, synthesis, identified, mechanism, documented, x-ndi, treatment, receptor, nbk1177, genetic.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	18
Resolved	17
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	1
Terms whose name was checked	5
Terms named correctly	5
Terms named as a different term	0

17 of 18 terms resolved to a current term; the rest could not be looked up either way.

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X-Linked Nephrogenic Diabetes Insipidus (NDI1, AVPR2-Related): Comprehensive Research Report

1. Disease Information

2. Etiology

Disease causal factor

Genetic risk factors

Environmental risk factors

Protective factors

Gene-environment interaction

3. Phenotypes

Phenotype type and characteristics

Quality-of-life impact

4. Genetic/Molecular Information

Causal gene

Pathogenic variants

Modifier genes

Epigenetic information

Chromosomal abnormalities

5. Environmental Information

Environmental factors

Environmental factors relevant to the acquired/secondary NDI phenocopy (important differential, and mechanistically informative even though genetically distinct from X-NDI):

Lifestyle factors

Infectious agents

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical phenotype)

Molecular pathway

Cellular processes

Protein dysfunction

Metabolic changes

Immune system involvement

Tissue damage mechanisms

Biochemical abnormalities

Molecular profiling

7. Anatomical Structures Affected

Organ level

Tissue and cell level

Subcellular level

Localization

8. Temporal Development

Onset

Progression

Patterns

9. Inheritance and Population

Epidemiology

Inheritance pattern

Population demographics

10. Diagnostics

Clinical tests

Genetic testing

Differential diagnosis

Screening

11. Outcome/Prognosis

Survival and mortality

Morbidity and function

Disease course / complications

Prognostic factors

12. Treatment

Pharmacotherapy

Emergency/acute management

Supportive care