Normal Pressure Hydrocephalus

Complex MONDO:0009366 Pathograph 14 Show in embeddings browser Communicating Hydrocephalus Hydrocephalus

Ventricular enlargement with cerebrospinal fluid pressure in the high-normal range, presenting in older adults as the triad of gait disturbance, cognitive decline and urinary incontinence, and treated by surgical CSF diversion. The idiopathic form is common in the elderly and is the one form of dementia widely described as reversible. Two mechanisms are curated here, and the reason to curate both is that they differ in reversibility. A mechanical arm runs from age-related loss of intracranial compliance through disturbed CSF pulsatility and absorption to ventriculomegaly and stretch injury of the periventricular white matter. A glymphatic arm runs from perivascular AQP4 depolarization through impaired CSF-interstitial fluid exchange to interstitial amyloid-beta accumulation. The first arm is what a shunt addresses; the second is not. In the placebo-controlled trial that finally tested shunting, gait improved and cognition did not.

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1
Inheritance
7
Pathophys.
5
Phenotypes
3
Gaps
14
Pathograph
3
Genes
1
Medical Actions
2
Differentials
1
Models
11
References
1
Deep Research
👪

Inheritance

1
Polygenic susceptibility HP:0010982
Idiopathic NPH is not Mendelian, but it is not sporadic either. Six genome-wide significant loci of modest effect have been replicated across two biobanks, and familial aggregation is reported in a tenth to a sixth of patients. The contributing loci named in the genetic section above are SLCO1A2, AMZ1/GNA12, MLLT10, CDCA2, C16orf95 and PLEKHG1 from the GWAS, alongside CFAP43, SFMBT1 and CWH43 from sequencing and copy-number studies. A separate CFAP43 Mendelian form shares the MONDO term and is not what this block describes.
Polygenic inheritance
Show evidence (2 references)
PMID:39141892 SUPPORT Human Clinical
"we identified 6 gene regions significantly (p < 5.0e-8) associated with NPH that replicated in a meta-analysis with UKBB"
Six replicated common-variant loci of modest effect, which is a polygenic architecture rather than a Mendelian one.
PMID:40266017 SUPPORT Human Clinical
"More than 30 familial cases were identified, and two cohorts found that 10%-16% of patients with NPH had relatives with NPH symptoms."
Familial aggregation at a rate incompatible with a purely sporadic disorder and too high to be explained by the rare Mendelian form alone.
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Discussions and Knowledge Gaps

3
Is the cognitive impairment of idiopathic normal pressure hydrocephalus caused by the hydrocephalus at all, or is it concurrent Alzheimer-type pathology that a shunt cannot reach?
KNOWLEDGE GAP OPEN gap_cognitive_arm_unresponsive_to_shunting
Attached to
pathophysiology#Impaired Glymphatic CSF-ISF Exchange and Solute Clearance pathophysiology#Interstitial Amyloid-beta Accumulation treatments#Ventriculoperitoneal Shunt Placement
Idiopathic NPH is the standard example of a reversible dementia, and that reputation rests on uncontrolled series reporting 60-80% improvement. When the comparison was finally made against a blinded placebo valve, gait velocity and the Tinetti score separated and the cognitive measure did not - 1.3 points against 0.3 on the MoCA in 99 patients. Three readings are consistent with what this entry curates and are not distinguished by it. The cognitive deficit may be genuinely hydrocephalic but slower to recover than three months, in which case the trial's endpoint is simply early. It may be driven by the glymphatic and amyloid arm curated here, which a shunt does not act on - the reading this entry's structure favours, and the one that the correlation between cortical amyloid burden and poor shunt responsiveness supports. Or the cohort may contain concurrent Alzheimer disease that no CSF diversion could help, which the entry's own leading differential makes unavoidable as a possibility. A fourth consideration cuts across all three, and it is a property of the trial rather than of the disease: participants were selected for surgery on the basis of gait-velocity improvement with temporary CSF drainage. The cohort was therefore enriched for gait responders before randomisation, so the trial is better powered to detect the effect it found than the one it did not, and its cognitive null is weaker evidence than its gait positive is. The guidelines literature makes the same point in reverse: shunting applied without selection criteria performed badly, so selection is not an incidental design choice but the thing that makes the operation work. These are not equivalent for practice. Under the second and third, a patient selected for shunting on gait grounds should not be promised cognitive recovery, and the disease's reputation as reversible dementia is a claim about one third of the triad.
Proposed experiments
Amyloid-stratified randomised shunt trial with extended cognitive follow-up
amyloid_pet_stratified_shunt_outcome
Stratify a placebo-controlled shunt trial by amyloid PET status at baseline and follow cognition to 12 months. If the amyloid-negative stratum shows cognitive separation and the amyloid-positive stratum does not, the deficit is hydrocephalic and the pooled null reflects co-pathology. If neither separates at any time point, the cognitive arm is not shunt-responsive in either group.
Why does the urinary arm not respond to shunting, when it is derived from the same periventricular lesion as the gait arm that does?
KNOWLEDGE GAP OPEN gap_urinary_arm_mechanism_versus_trial
Attached to
pathophysiology#Periventricular White Matter Compression and Stretch Injury treatments#Ventriculoperitoneal Shunt Placement
The mechanical account curated in this entry derives gait failure and urinary incontinence from one lesion: stretch of somatotopically arranged corticospinal fibres, with the leg and sacral fibres nearest the expanding ventricle. If that is right, relieving the distension should move both. It moved one. In the 99-patient trial the Overactive Bladder Questionnaire did not separate from placebo, while gait velocity did so decisively. Awkwardly, the earlier 18-patient pilot found the opposite on this arm: the overactive-bladder symptom bother score improved significantly in the open-shunt group at four months, on the smaller sample and the weaker gait signal. So the two randomised trials disagree about the bladder in the direction opposite to their disagreement about gait, which is hard to explain by power alone. The possibilities include instrument sensitivity - both trials measured symptom bother rather than incontinence episodes or urodynamics - and a genuinely different reversibility for the sacral fibres. Neither is settled, and the entry curates the conventional sacral-fibre derivation with this discussion attached rather than silently dropping it.
Proposed experiments
Randomised shunt trial with urodynamic rather than questionnaire endpoints
urodynamic_endpoint_shunt_trial
Repeat the placebo-controlled design with pre-specified urodynamic measurement (detrusor overactivity, cystometric capacity) alongside the symptom questionnaire, to establish whether the null bladder result reflects an unresponsive mechanism or an insensitive instrument.
Is perivascular AQP4 depolarization specific to idiopathic normal pressure hydrocephalus, or is it a feature of normal ageing that any elderly cohort would show?
KNOWLEDGE GAP OPEN gap_aqp4_depolarization_specificity
Attached to
pathophysiology#Perivascular AQP4 Depolarization
The tissue evidence for the glymphatic arm of this entry is a comparison of cortical biopsies from 30 patients with idiopathic NPH against 12 reference subjects. The source that reports it also states that progressive AQP4 depolarization occurs throughout physiological ageing, and that age-matched human studies are needed to establish specificity. That caveat lands on the arm of this entry with the least redundancy. Idiopathic NPH is a disease of the eighth and ninth decades and its trigger node is age-related loss of compliance, so an ageing-associated finding in an aged cohort is exactly the confound that cannot be ruled out from a case-control design without age matching. If the depolarization is ageing rather than disease, the glymphatic arm loses its disorder-specific molecular anchor and the conformance declared here should be reconsidered - not the module's validity, but this entry's claim on it.
Proposed experiments
Age-matched cortical AQP4 polarization comparison
age_matched_aqp4_biopsy_comparison
Quantify perivascular AQP4 polarization by immunogold cytochemistry in idiopathic NPH cortical biopsies against age-matched controls and against age-matched patients with other neurodegenerative disease, to separate disease-associated from ageing-associated depolarization.
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Pathophysiology

7
Increased CSF Pulsatility with Impaired CSF Absorption
CSF flow has a bulk and a pulsatile component, and in idiopathic NPH both are deranged: outflow resistance impedes absorption while aqueductal stroke volume rises. The combination matters more than either part. Raised outflow resistance alone would produce accumulation; raised pulsatility supplies the force that converts accumulation into ventricular dilatation.
cerebrospinal fluid circulation GO:0090660 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated cerebrospinal fluid circulation (GO:0090660). GO:0090660 is a biological process from the Gene Ontology. ↕ DYSREGULATED
ventricular system of brain UBERON:0005282 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in ventricular system of brain (UBERON:0005282). UBERON:0005282 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Ventriculomegaly at Normal Mean CSF Pressure Accumulating CSF, driven by a pulsatile force the compliant compartments can no longer absorb, dilates the ventricles without raising mean pressure.
Show evidence (2 references)
PMID:33242372 SUPPORT Human Clinical
"Increased CSF pulsatility may associate with reduced arterial pulsatility and decreased intracranial compliance."
Links this node to the trigger upstream of it.
PMID:33242372 SUPPORT Human Clinical
"Lack of sufficient CSF absorption caused by outflow resistance could lead to the accumulation of CSF, and further facilitate the ventricular dilatation driven by high CSF pulsatility."
States both halves of this node and their joint effect on the ventricles, which is the edge below.
Ventriculomegaly at Normal Mean CSF Pressure
The defining lesion, and the source of the disease's name: the ventricles enlarge while mean CSF pressure stays within the normal range, so the syndrome is invisible to the measurement that would identify ordinary hydrocephalus. Ventriculomegaly is curated as the central effector rather than as a radiological sign because it is where both curated arms converge and the point at which the mechanical injury below it begins.
ventricular system of brain UBERON:0005282 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in ventricular system of brain (UBERON:0005282). UBERON:0005282 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Periventricular White Matter Compression and Stretch Injury Expansion of the ventricles compresses and stretches the white matter immediately around them.
Ventriculomegaly The node's own radiological expression. Curated as an edge so the imaging phenotype is attached to the mechanism that produces it rather than standing alone, since ventricular enlargement from cortical atrophy looks similar and arises differently.
Show evidence (2 references)
PMID:33242372 SUPPORT Human Clinical
"The common consensus is that ventriculomegaly resulting from cerebrospinal fluid (CSF) dynamics could initiate a vicious cycle of neurological damages in iNPH."
Places ventriculomegaly as the node from which the downstream damage proceeds, which is how it is curated here.
PMID:31959516 SUPPORT Human Clinical
"Approximately 10% of dementia patients have idiopathic normal pressure hydrocephalus (iNPH), an expansion of the cerebrospinal fluid (CSF)-filled brain ventricles."
Defines the disorder by this node and gives its weight among the dementias.
Periventricular White Matter Compression and Stretch Injury
White matter lesions are prominent in idiopathic NPH, and the mechanical account of the triad rests here. Fibres of the corticospinal tract run in the periventricular white matter arranged somatotopically, with the leg and sacral fibres closest to the ventricle, so ventricular expansion loads them first. This is what makes gait the earliest and most shunt-responsive feature, and it is also the account from which the urinary arm is usually derived - a derivation the trial evidence below does not straightforwardly support.
periventricular white matter UBERON:0014932 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in periventricular white matter (UBERON:0014932). UBERON:0014932 is an anatomical location from the Uberon multi-species anatomy ontology. corticospinal tract UBERON:0002707 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in corticospinal tract (UBERON:0002707). UBERON:0002707 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Gait Disturbance Loading of the periventricular corticospinal fibres, leg fibres first, is the mechanical account of why gait fails earliest and responds to CSF diversion.
Urinary Incontinence The conventional derivation of the urinary arm from the same lesion as the gait arm, via the sacral corticospinal fibres. Curated as an edge rather than left in prose precisely because the placebo-controlled trial did not confirm it: the graph now asserts a link the evidence for treatment response contradicts, and the knowledge gap below attaches to that tension rather than floating above it.
Urinary Urgency The same bladder arm at the severity the trials actually measured. Curated with unknown intermediates rather than DIRECT because the cited mechanism names incontinence specifically, and urgency is the earlier, milder form recorded by the overactive-bladder instruments both randomised trials used.
Show evidence (3 references)
PMID:33242372 SUPPORT Human Clinical
"Symptoms of iNPH could be attributed, at least partially, to the compression and stretch of white matter."
The mechanical claim this node makes, stated with the hedge the source uses.
PMID:33242372 SUPPORT Human Clinical
"When the motor nerve fibers of corticospinal tract are inflicted, gait disturbance may occur."
Connects the periventricular lesion to the gait phenotype specifically.
PMID:33242372 SUPPORT Human Clinical
"The stretch of sacral fibers of the corticospinal tract may disrupt bladder contractions, resulting in urinary incontinence, which is the second most common symptom of iNPH."
The conventional derivation of the urinary arm from the same lesion as the gait arm. Curated because the placebo-controlled trial result makes this derivation the entry's sharpest open question, not because it is settled.
Perivascular AQP4 Depolarization
Periarterial CSF influx into the parenchyma depends on aquaporin-4 held at the perivascular astroglial end-feet. Cortical biopsies taken at shunt surgery show reduced perivascular AQP4 density in idiopathic NPH, which is direct human tissue evidence rather than an imaging surrogate - the distinction the glymphatic module insists on. It is the disorder-specific substitution this module node asks for: the cause of reduced influx here is AQP4 mislocalization at the astrocyte end-foot.
astrocyte of the cerebral cortex CL:0002605 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves astrocyte of the cerebral cortex (CL:0002605). CL:0002605 is a cell type from the Cell Ontology.
water transport GO:0006833 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased water transport (GO:0006833). GO:0006833 is a biological process from the Gene Ontology. ↓ DECREASED
astrocyte end-foot GO:0097450 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves astrocyte end-foot (GO:0097450). GO:0097450 is a cellular component from the Gene Ontology.
perivascular space UBERON:0014930 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in perivascular space (UBERON:0014930). UBERON:0014930 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
AQP4-null mouse, kaolin-induced hydrocephalus Mouse partially recapitulates Genetic ablation of AQP4 is a clean loss of the water channel whose perivascular mislocalization this node models, and the consequence is more severe ventricular enlargement and higher intracranial pressure.
Downstream
Impaired Glymphatic CSF-ISF Exchange and Solute Clearance Loss of perivascular AQP4 reduces the astroglia-supported influx on which CSF-interstitial fluid exchange depends.
Show evidence (3 references)
PMID:31959516 SUPPORT Human Clinical
"Also, AQP4 immunogold cytochemistry analysis of cortical brain biopsies from 30 iNPH patients and 12 reference subjects demonstrated reduced AQP4 density in the perivascular astroglial endfeet of iNPH brains as compared to control brains"
Direct human tissue measurement of the molecular lesion at this node, in idiopathic NPH specifically.
PMID:31959516 SUPPORT Human Clinical
"iNPH and Alzheimer's disease (AD) both exhibit sleep disturbances, build-up of brain metabolic wastes and amyloid-β (Aβ) plaques, perivascular reactive astrogliosis, and mislocalization of astrocyte aquaporin-4 (AQP4)."
Establishes AQP4 mislocalization as a feature of idiopathic NPH and not only of Alzheimer disease, which is what licenses conformance to the module here.
PMID:16552421 SUPPORT INDIRECT Model Organism
"Our results indicate a significant role for AQP4-mediated transparenchymal CSF absorption in hydrocephalus and provide a rational basis for evaluation of AQP4 induction as a nonsurgical therapy for hydrocephalus."
The only causal rather than correlational support in this arm: removing AQP4 makes hydrocephalus worse, which is the direction this node asserts. INDIRECT because the model is kaolin-induced obstructive hydrocephalus in mice, not normal pressure hydrocephalus, so it establishes that AQP4 participates in CSF absorption without establishing that its loss initiates the human syndrome.
Impaired Glymphatic CSF-ISF Exchange and Solute Clearance
Reduced exchange between cerebrospinal and interstitial fluid produces both an abnormal accumulation of cerebral CSF and a failure to clear interstitial solute - the two arms of this entry emerging from a single node. Imaging measures of perivascular diffusivity are lower in idiopathic NPH than in mimics and correlate with ventricular volume, though the glymphatic module's own caution applies: a diffusivity index is a correlate of glymphatic transport, not a measurement of it, and the tissue evidence upstream carries more weight here than the imaging does.
cerebrospinal fluid circulation GO:0090660 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cerebrospinal fluid circulation (GO:0090660). GO:0090660 is a biological process from the Gene Ontology. ↓ DECREASED amyloid-beta clearance GO:0097242 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased amyloid-beta clearance (GO:0097242). GO:0097242 is a biological process from the Gene Ontology. ↓ DECREASED
perivascular space UBERON:0014930 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in perivascular space (UBERON:0014930). UBERON:0014930 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Ventriculomegaly at Normal Mean CSF Pressure Reduced glymphatic flux is reported to exacerbate ventriculomegaly, making the two arms of this entry mutually reinforcing rather than parallel. The edge is curated with unknown intermediates because the human evidence is a correlation between an imaging surrogate and ventricular volume, and the direction is not established.
Interstitial Amyloid-beta Accumulation Failure of perivascular solute clearance leaves interstitial amyloid-beta in place.
Show evidence (6 references)
PMID:31959516 SUPPORT Human Clinical
"Glymphatic dysfunction, characterized by reduced CSF-ISF exchange, leads to an abnormal accumulation of cerebral CSF and impaired interstitial solute clearance, both defining clinical features of iNPH and a likely cause of cognitive deterioration."
States this node and both of its downstream edges, and does so for idiopathic NPH specifically.
PMID:31959516 SUPPORT Human Clinical
"Human studies have implicated impaired glymphatic function in both AD and iNPH."
Records the evidence tier honestly - implicated in human studies, not demonstrated as causal.
PMID:31959516 SUPPORT Human Clinical
"the authors found that the ALPS index positively correlated with ventricular volume, suggesting a direct link between glymphatic impairment and ventriculomegaly"
Supports the edge from this node to ventriculomegaly, but only partially: it is a correlation between an imaging surrogate and ventricular size in a small study, and it does not establish direction.
+ 3 more references
Interstitial Amyloid-beta Accumulation
Amyloid-beta plaques are found in cortical biopsies from idiopathic NPH as well as from Alzheimer disease, less severe but present. The clinically consequential fact is what they predict: amyloid burden correlates with poor shunt responsiveness. That makes this node the mechanistic candidate for the part of the syndrome a shunt cannot fix, and it is the reason this entry treats the triad as two problems rather than one.
amyloid-beta clearance GO:0097242 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased amyloid-beta clearance (GO:0097242). GO:0097242 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Cognitive Impairment The glymphatic arm's route to the cognitive deficit, and the entry's candidate explanation for why that deficit did not separate from placebo under shunting: a shunt acts on the mechanical arm, and this one is not on it. Curated with unknown intermediates because the cited source calls impaired solute clearance a likely cause of cognitive deterioration rather than a demonstrated one.
Show evidence (1 reference)
PMID:31959516 SUPPORT Human Clinical
"accumulation of interstitial amyloid-β (Aβ) plaques are a characteristic feature of both iNPH and AD cortical brain biopsies, a pathological finding that correlates with poor shunt responsiveness in iNPH patients"
Both halves of this node: the deposition in idiopathic NPH cortex, and its association with failure to respond to CSF diversion.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Normal Pressure Hydrocephalus Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

5
Genitourinary 1
Urinary Urgency HP:0000012 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Urinary urgency (HP:0000012). HP:0000012 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40960253 SUPPORT Human Clinical
"Idiopathic normal-pressure hydrocephalus is a neurologic disorder characterized by impaired gait, balance, cognition, and bladder control in older adults."
Bladder control as a defining domain of the syndrome.
Nervous System 2
Cognitive Impairment VERY_FREQUENT Dementia HP:0000726 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dementia (HP:0000726). HP:0000726 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31959516 SUPPORT Human Clinical
"a disorder characterized by progressive ventriculomegaly and the clinical triad of gait ataxia, urinary incontinence, and dementia"
Dementia as one of the three defining features.
Ventriculomegaly VERY_FREQUENT HP:0002119 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ventriculomegaly (HP:0002119). HP:0002119 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33242372 SUPPORT Human Clinical
"Typical brain imaging of iNPH displays ventriculomegaly, periventricular hyperintensities, wide Sylvian fissures, narrowed subarachnoid space, and cortical sulci at the high convexity."
The imaging phenotype, including the high-convexity feature that distinguishes it from atrophic ventricular enlargement.
Constitutional 1
Urinary Incontinence FREQUENT HP:0000020 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Urinary incontinence (HP:0000020). HP:0000020 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33242372 SUPPORT Human Clinical
"resulting in urinary incontinence, which is the second most common symptom of iNPH"
States the phenotype and its rank among the triad.
Other 1
Gait Disturbance VERY_FREQUENT Gait apraxia HP:0010521 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Gait apraxia (HP:0010521), qualified as course progressive. HP:0010521 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:40960253 SUPPORT Human Clinical
"Idiopathic normal-pressure hydrocephalus is a neurologic disorder characterized by impaired gait, balance, cognition, and bladder control in older adults."
Gait impairment as a defining feature, from the trial that measured it.
🧬

Genetic Associations

3
SLCO1A2 (The strongest signal in the largest genome-wide association study of normal pressure hydrocephalus, and a protective rather than a risk allele. rs7962263 near SLCO1A2 gave an odds ratio of 0.71 across 1,522 NPH cases and 451,091 controls, replicated in UK Biobank, and the effect held in the idiopathic-only sensitivity analysis at 0.70.)
Gene: SLCO1A2 hgnc:10956 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SLCO1A2 (hgnc:10956). hgnc:10956 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: SUSCEPTIBILITY
Show evidence (2 references)
PMID:39141892 SUPPORT Human Clinical
"The top loci near the following genes were rs7962263, SLCO1A2 (odds ratio [OR] 0.71, 95% CI 0.65-0.78, p = 1.0e-14)"
The lead protective locus and its effect size in the discovery cohort.
PMID:39141892 SUPPORT Human Clinical
"In the sensitivity analysis comparing only patients with iNPH (n = 1,055) with the controls (n = 451,091), 4 top loci near the following genes remained significant: rs7962263, SLCO1A2 (OR 0.70, 95% CI 0.63-0.78, p = 2.1e-11)"
The association survives restriction to idiopathic cases, which is what makes it a determinant of the syndrome curated here rather than of a secondary aetiology.
CFAP43 (The cilia gene MONDO records as the causal gene of MONDO:0009366 via RO:0004003, on the strength of the OMIM-numbered familial form. In the systematic review of NPH genetics it appears among the genes enriched for risk variants in NPH cohorts rather than as an established Mendelian cause of the common idiopathic syndrome, which is why it is typed SUSCEPTIBILITY here and not CAUSATIVE.)
Gene: CFAP43 hgnc:26684 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is CFAP43 (hgnc:26684). hgnc:26684 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: SUSCEPTIBILITY
Show evidence (1 reference)
PMID:40266017 SUPPORT Human Clinical
"copy-number variant analyses, and genome-wide association studies showed risk variants enriched in NPH cohorts in or near CFAP43, SFMBT1, CWH43, AK9, RXFP2, PRKD1, HAVCR1, OTOG, MYO7A, NOTCH1, SPG11, MYH13, FOXJ1, AMZ1/GNA12, and C16orf95"
Places CFAP43 among the risk-enriched rather than established-causal genes for NPH, which is the typing used here.
SFMBT1 (One of the recurrently reported NPH risk genes. Its mechanistic interest is that the NPH risk genes as a set converge on the blood-brain and blood-CSF barriers, cilia and ependymal function rather than on any single pathway, which is the class of biology the CSF-absorption node of this entry depends on.)
Gene: SFMBT1 hgnc:20255 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SFMBT1 (hgnc:20255). hgnc:20255 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: SUSCEPTIBILITY
Show evidence (2 references)
PMID:40266017 SUPPORT Human Clinical
"These genes are associated with blood-brain and blood-cerebrospinal fluid barriers, cilia, and ependymal function."
The functional convergence of the risk-gene set, which is the reason this section is curated at all: it is mechanistically coherent with the absorption defect above.
PMID:40266017 SUPPORT Human Clinical
"copy-number variant analyses, and genome-wide association studies showed risk variants enriched in NPH cohorts in or near CFAP43, SFMBT1, CWH43, AK9, RXFP2, PRKD1, HAVCR1, OTOG, MYO7A, NOTCH1, SPG11, MYH13, FOXJ1, AMZ1/GNA12, and C16orf95"
Names SFMBT1 among the risk-enriched genes, which is the first sentence of this block's association and was previously supported only by the convergence claim.
💊

Medical Actions

1
Ventriculoperitoneal Shunt Placement
Action: ventriculoperitoneal shunt placementNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is ventriculoperitoneal shunt placement (NCIT:C168483). NCIT:C168483 is a clinical intervention from the NCI Thesaurus. Ontology label: Ventriculoperitoneal Shunt Placement NCIT:C168483
Surgical diversion of CSF from the ventricle to the peritoneum, the standard therapy and the only treatment for idiopathic NPH. Uncontrolled series reported 60-80% improvement, which is what made the disease famous as a reversible dementia; two randomised placebo-controlled trials, using a valve set either open or effectively off, have since measured the effect against a blinded sham. Gait improves. The 2025 trial found no separation from placebo on cognition or on incontinence, and the procedure carried more subdural bleeding and positional headache than placebo.
Mechanism Target:
INHIBITS Ventriculomegaly at Normal Mean CSF Pressure — Diverting CSF relieves the ventricular distension and thereby the mechanical arm of the entry. It does not act on the glymphatic arm, which is the curated reason its benefit is confined to gait.
Show evidence (1 reference)
PMID:40960253 SUPPORT Human Clinical
"Among participants with idiopathic normal-pressure hydrocephalus who had a response to temporary CSF drainage, shunting resulted in significant improvements at 3 months in gait velocity and a measure of gait and balance but not in measures of cognition or incontinence."
The placebo-controlled result, and the reason this treatment is curated as acting on the mechanical node alone.
Show evidence (10 references)
PMID:40960253 SUPPORT Human Clinical
"resulting in a treatment difference of 0.21 m per second (95% confidence interval, 0.12 to 0.31; P<0.001)"
The gait-velocity effect size against blinded placebo.
PMID:40960253 SUPPORT Human Clinical
"A significantly greater improvement in the open-shunt group than the placebo group was seen for the Tinetti scale score (mean change, 2.9 points vs. 0.5 points; P = 0.003) but not the MoCA score (1.3 points vs. 0.3 points) or the Overactive Bladder Questionnaire score (-3.3 points vs. -1.5 points)."
PARTIAL because it supports the treatment for one arm of the triad and refutes it for the other two at this time point. This is the single most important evidence item in the entry.
PMID:40960253 SUPPORT Human Clinical
"more participants in the open-shunt group having subdural bleeding (12% vs. 2%) and positional headaches (59% vs. 28%)"
The harms measured against blinded placebo, which the uncontrolled series could not isolate.
+ 7 more references
🔬

Diagnosis

3
MRI morphology (DESH pattern and callosal angle)
MRI does two different jobs here and the entry separates them. It excludes the alternative causes of ventriculomegaly - which matters because the leading differential, Alzheimer disease, enlarges the ventricles by atrophy - and it identifies features that positively support idiopathic NPH: a reduced callosal angle and the disproportionately enlarged subarachnoid space hydrocephalus pattern, in which the sulci at the high convexity are effaced rather than widened. Their predictive value for treatment response is explicitly limited, which is why this entry curates them as diagnostic rather than prognostic and why the shunt-selection test below is a separate entry.
brain magnetic resonance imaging NCIT:C16809 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:42239999 SUPPORT Human Clinical
"MRI is essential to exclude alternative causes of ventriculomegaly and to identify characteristic imaging features such as a reduced callosal angle and the disproportionately enlarged subarachnoid space hydrocephalus (DESH) pattern, which support the diagnosis, although their predictive value..."
Both diagnostic roles and, in the same sentence, the hedge on prognostic use. Quoted whole rather than trimmed, because the hedge is the part that governs how this entry uses it.
Cerebrospinal fluid outflow resistance
The direct physiological readout of the absorption defect curated in the pathophysiology above: outflow resistance is pathologically elevated. That makes it the one diagnostic test in this entry that measures the mechanism rather than its consequences, and it is used both to diagnose and to select shunt candidates.
cerebrospinal fluid outflow resistance measurement
Show evidence (1 reference)
PMID:33242372 SUPPORT Human Clinical
"the resistance to CSF outflow (Rout) is pathologically elevated and has been widely used for the diagnosis of iNPH and the selection of candidates for shunting surgery."
States the abnormality and both of its uses. This is the diagnostic counterpart of the Increased CSF Pulsatility with Impaired CSF Absorption node.
Response to temporary cerebrospinal fluid drainage
The shunt-selection test, and the one whose consequences run through this entry's knowledge gaps. Patients are taken to surgery on the basis of gait-velocity improvement after temporary drainage - which is what makes the 2025 trial's cohort enriched for gait responders before randomisation, and therefore why its cognitive null is weaker evidence than its gait positive.
temporary cerebrospinal fluid drainage trial
Show evidence (1 reference)
PMID:40960253 SUPPORT Human Clinical
"We conducted a double-blind, randomized, placebo-controlled trial involving participants selected for shunt surgery on the basis of gait-velocity improvement with cerebrospinal fluid (CSF) drainage."
Establishes the test and, in the same sentence, that it was the enrolment gate - which is the fact the cognitive knowledge gap argues from.
📊

Prevalence

4
Worldwide, all ages
Point Prevalence 16.0 per 100,000 (10.0–22.0) 1–9 per 10,000
Overall population estimate, not age-restricted.
Show evidence (1 reference)
PMID:33242372 SUPPORT Human Clinical
"The prevalence of iNPH has been estimated to be 10 per 100 000 to 22 per 100 000 overall"
The overall prevalence range quoted here.
Adults aged 65 years and over
Point Prevalence 1300.0 per 100,000 >1 in 1,000
1.30% in those aged 65 or over.
Show evidence (1 reference)
PMID:33242372 SUPPORT Human Clinical
"with 1.30% in those aged ≥65 years and 5.9% in those aged ≥80 years"
The age-stratified prevalence, which is where the burden of this disease sits.
Adults aged 80 years and over
Point Prevalence 5900.0 per 100,000 >1 in 1,000
5.9% in those aged 80 or over. The steep age gradient is consistent with the compliance-loss trigger curated above.
Show evidence (1 reference)
PMID:33242372 SUPPORT Human Clinical
"with 1.30% in those aged ≥65 years and 5.9% in those aged ≥80 years"
Same source sentence; quoted here for the over-80 figure.
Adults aged 86 years and over
Point Prevalence 7700.0 per 100,000 >1 in 1,000
Independent estimate from the 2025 randomised trial's introduction, giving a consistent age gradient from a different source.
Show evidence (1 reference)
PMID:40960253 SUPPORT Human Clinical
"increases with age, reaching as much as 7.7% for ages ≥86 years"
The oldest age band reported, corroborating the gradient.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Normal Pressure Hydrocephalus:

Alzheimer disease
Overlapping Features The leading differential, and not merely a look-alike: the two disorders share amyloid-beta deposition, perivascular astrogliosis, AQP4 mislocalization and sleep disturbance, and this entry curates the shared glymphatic mechanism explicitly. Most patients with idiopathic NPH are said to be misdiagnosed with it. Ventriculomegaly does not settle the question, since severe cortical atrophy enlarges the ventricles too. The practical stake is that CSF diversion helps one and not the other.
Show evidence (2 references)
PMID:31959516 SUPPORT Human Clinical
"For these reasons, AD has become the leading differential diagnosis to iNPH"
Names Alzheimer disease as the leading differential.
PMID:31959516 SUPPORT Human Clinical
"Most notably, CSF diversion confers no symptomatic relief to patients with AD"
The therapeutic stake in distinguishing them.
Ventricular enlargement secondary to cortical atrophy
Overlapping Features Sometimes called pseudo-NPH. Ventricular volume rises passively as parenchyma is lost, without the CSF-dynamic derangement curated here, and shunting has nothing to relieve. The high-convexity sulcal narrowing seen in idiopathic NPH is the imaging feature that separates the two, since atrophy widens sulci rather than effacing them.
Show evidence (1 reference)
PMID:31959516 SUPPORT Human Clinical
"ventricular enlargement can also be seen in AD as a result of severe cerebral atrophy, further complicating radiographic recognition of iNPH"
States the confound this differential turns on.
🐁

Animal Models

1
AQP4-null mouse, kaolin-induced hydrocephalus
Obstructive hydrocephalus induced by cisterna magna kaolin injection in AQP4-deficient versus wild-type mice. The model exists here for one reason: it is the only evidence in this entry that manipulates AQP4 and observes the consequence, rather than observing AQP4 and the consequence together.
Species
Mouse
Genotype
Aqp4 null
Publication
PMID:16552421
Pathograph links
Perivascular AQP4 Depolarization partially recapitulates fidelity: moderate Genetic ablation of AQP4 is a clean loss of the water channel whose perivascular mislocalization this node models, and the consequence is more severe ventricular enlargement and higher intracranial pressure.
Limitations: The lesion is not the human one in two respects. Ablation removes AQP4 entirely rather than depolarizing it from the astroglial end-feet, and the hydrocephalus is kaolin-induced obstruction with intracranial pressure rising to 22 mm Hg, which is the opposite of the normal-pressure state that defines the human disease. The model therefore supports AQP4's role in CSF absorption without supporting AQP4 loss as the initiating event in idiopathic NPH.
Readouts
Lateral ventricle volume at 3 and 5 days after kaolin injection
Direction: INCREASED
Interpretation: Ventricular enlargement is greater without AQP4, placing the channel upstream of ventricular volume rather than alongside it.
Show evidence (1 reference)
PMID:16552421 SUPPORT Model Organism
"Lateral ventricle volume increased to 3.7+/-0.5 and 5.1+/-0.5 mm(3) in AQP4 null mice at 3 and 5 days after injection, respectively, significantly greater than 2.6+/-0.3 and 3.5+/-0.5 mm(3) in wildtype mice"
The quantitative ventricular measurement behind this readout.
Intracranial pressure at 3 days after kaolin injection
Direction: INCREASED
Interpretation: Also the readout that bounds the model's relevance: pressure rises steeply here, whereas the human disease is defined by pressure staying normal.
Show evidence (1 reference)
PMID:16552421 SUPPORT Model Organism
"The corresponding ICP was 22+/-2 mm Hg at 3 days in AQP4 null mice, significantly greater than 14+/-1 mm Hg in wildtype mice"
Supports the AQP4 effect and simultaneously documents the divergence from normal-pressure hydrocephalus, hence PARTIAL.
Show evidence (1 reference)
PMID:16552421 SUPPORT Model Organism
"Here, we provide evidence for AQP4-facilitated CSF absorption in hydrocephalus by a transparenchymal pathway into the cerebral vasculature."
Supports treating this model as informative for an AQP4-dependent CSF absorption node.
{ }

Source YAML

click to show 
name: Normal Pressure Hydrocephalus
creation_date: "2026-08-22T00:00:00Z"
category: Complex
disease_term:
  preferred_term: normal pressure hydrocephalus
  term:
    id: MONDO:0009366
    label: normal pressure hydrocephalus
description: >-
  Ventricular enlargement with cerebrospinal fluid pressure in the high-normal range,
  presenting in older adults as the triad of gait disturbance, cognitive decline and
  urinary incontinence, and treated by surgical CSF diversion. The idiopathic form is
  common in the elderly and is the one form of dementia widely described as reversible.

  Two mechanisms are curated here, and the reason to curate both is that they differ in
  reversibility. A mechanical arm runs from age-related loss of intracranial compliance
  through disturbed CSF pulsatility and absorption to ventriculomegaly and stretch injury
  of the periventricular white matter. A glymphatic arm runs from perivascular AQP4
  depolarization through impaired CSF-interstitial fluid exchange to interstitial
  amyloid-beta accumulation. The first arm is what a shunt addresses; the second is not.
  In the placebo-controlled trial that finally tested shunting, gait improved and
  cognition did not.

parents:
- Communicating Hydrocephalus
- Hydrocephalus

pathophysiology:

- name: Age-Related Loss of Intracranial Compliance
  role: trigger
  biological_scale: ORGANISM
  description: >-
    Ageing stiffens the cerebral arteries and the CSF circulatory channels alike.
    Atherosclerotic loss of arterial pulsatility removes the Windkessel dampening that
    normally absorbs each systolic pulse before it reaches the CSF spaces, while falling
    intracranial compliance and rising venous pressure leave the pulse with nowhere to go.
    This is the substrate on which the rest of the entry is built, and it is why
    idiopathic NPH is a disease of the eighth and ninth decades rather than a disease that
    happens to appear in them.
  biological_processes:
  - preferred_term: cerebrospinal fluid circulation
    term:
      id: GO:0090660
      label: cerebrospinal fluid circulation
    modifier: DECREASED
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the aging process, the loss of arterial pulsatility due to atherosclerosis would
      significantly increase the pulsatility of aqueduct.
    explanation: >-
      States the arterial-stiffening route by which ageing raises CSF pulsatility, the
      claim this node makes.
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Intracranial compliance gradually reduces with the progress of aging, resulting in
      more rigid CSF circulatory channels and the elevation of venous pressure.
    explanation: >-
      The compliance half of the same trigger, and the reason the increased pulse energy
      is not absorbed.
  - reference: PMID:28062721
    reference_title: "Vascular risk factors in INPH: A prospective case-control study (the INPH-CRasH study)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings confirm that patients with INPH have more VRFs and lack the protective
      factors present in the general population.
    explanation: >-
      Case-control evidence that the vascular burden this node posits is actually
      overrepresented in idiopathic NPH rather than merely age-expected.
  - reference: PMID:28062721
    reference_title: "Vascular risk factors in INPH: A prospective case-control study (the INPH-CRasH study)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Multivariable logistic regression analysis indicated that hyperlipidemia (odds ratio
      [OR] 2.380; 95% confidence interval [CI] 1.434-3.950), diabetes (OR 2.169; 95% CI
      1.195-3.938), obesity (OR 5.428; 95% CI 2.502-11.772), and psychosocial factors (OR
      5.343; 95% CI 3.219-8.868) were independently associated with INPH.
    explanation: >-
      Quantifies the individual vascular contributors, several of them modifiable, which
      is what makes this trigger node clinically actionable rather than merely descriptive.
  - reference: PMID:42239999
    reference_title: "Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      involving alterations in CSF dynamics, reduced vascular compliance, periventricular
      ischemia, and dysfunction of the glymphatic system
    explanation: >-
      A recent review naming reduced vascular compliance and glymphatic dysfunction
      together, which is the pairing this entry's two arms curate.
  downstream:
  - target: Increased CSF Pulsatility with Impaired CSF Absorption
    causal_link_type: DIRECT
    description: >-
      Reduced compliance and lost arterial dampening together produce the hyperdynamic
      CSF state.

- name: Increased CSF Pulsatility with Impaired CSF Absorption
  role: amplifier
  biological_scale: ORGANISM
  description: >-
    CSF flow has a bulk and a pulsatile component, and in idiopathic NPH both are
    deranged: outflow resistance impedes absorption while aqueductal stroke volume rises.
    The combination matters more than either part. Raised outflow resistance alone would
    produce accumulation; raised pulsatility supplies the force that converts accumulation
    into ventricular dilatation.
  biological_processes:
  - preferred_term: cerebrospinal fluid circulation
    term:
      id: GO:0090660
      label: cerebrospinal fluid circulation
    modifier: DYSREGULATED
  locations:
  - preferred_term: ventricular system of brain
    term:
      id: UBERON:0005282
      label: ventricular system of brain
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Increased CSF pulsatility may associate with reduced arterial pulsatility and
      decreased intracranial compliance.
    explanation: >-
      Links this node to the trigger upstream of it.
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lack of sufficient CSF absorption caused by outflow resistance could lead to the
      accumulation of CSF, and further facilitate the ventricular dilatation driven by
      high CSF pulsatility.
    explanation: >-
      States both halves of this node and their joint effect on the ventricles, which is
      the edge below.
  downstream:
  - target: Ventriculomegaly at Normal Mean CSF Pressure
    causal_link_type: DIRECT
    description: >-
      Accumulating CSF, driven by a pulsatile force the compliant compartments can no
      longer absorb, dilates the ventricles without raising mean pressure.

- name: Ventriculomegaly at Normal Mean CSF Pressure
  role: central_effector
  biological_scale: ORGANISM
  description: >-
    The defining lesion, and the source of the disease's name: the ventricles enlarge
    while mean CSF pressure stays within the normal range, so the syndrome is invisible to
    the measurement that would identify ordinary hydrocephalus. Ventriculomegaly is
    curated as the central effector rather than as a radiological sign because it is where
    both curated arms converge and the point at which the mechanical injury below it
    begins.
  locations:
  - preferred_term: ventricular system of brain
    term:
      id: UBERON:0005282
      label: ventricular system of brain
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The common consensus is that ventriculomegaly resulting from cerebrospinal fluid
      (CSF) dynamics could initiate a vicious cycle of neurological damages in iNPH.
    explanation: >-
      Places ventriculomegaly as the node from which the downstream damage proceeds, which
      is how it is curated here.
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Approximately 10% of dementia patients have idiopathic normal pressure hydrocephalus
      (iNPH), an expansion of the cerebrospinal fluid (CSF)-filled brain ventricles.
    explanation: >-
      Defines the disorder by this node and gives its weight among the dementias.
  downstream:
  - target: Periventricular White Matter Compression and Stretch Injury
    causal_link_type: DIRECT
    description: >-
      Expansion of the ventricles compresses and stretches the white matter immediately
      around them.
  - target: Ventriculomegaly
    causal_link_type: DIRECT
    description: >-
      The node's own radiological expression. Curated as an edge so the imaging phenotype
      is attached to the mechanism that produces it rather than standing alone, since
      ventricular enlargement from cortical atrophy looks similar and arises differently.
    evidence:
    - reference: PMID:33242372
      reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Typical brain imaging of iNPH displays ventriculomegaly, periventricular
        hyperintensities, wide Sylvian fissures, narrowed subarachnoid space, and cortical
        sulci at the high convexity.
      explanation: >-
        The imaging expression of this node, including the high-convexity feature that
        separates it from atrophic enlargement.

- name: Periventricular White Matter Compression and Stretch Injury
  role: consequence
  biological_scale: TISSUE
  description: >-
    White matter lesions are prominent in idiopathic NPH, and the mechanical account of
    the triad rests here. Fibres of the corticospinal tract run in the periventricular
    white matter arranged somatotopically, with the leg and sacral fibres closest to the
    ventricle, so ventricular expansion loads them first. This is what makes gait the
    earliest and most shunt-responsive feature, and it is also the account from which the
    urinary arm is usually derived - a derivation the trial evidence below does not
    straightforwardly support.
  locations:
  - preferred_term: periventricular white matter
    term:
      id: UBERON:0014932
      label: periventricular white matter
  - preferred_term: corticospinal tract
    term:
      id: UBERON:0002707
      label: corticospinal tract
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Symptoms of iNPH could be attributed, at least partially, to the compression and
      stretch of white matter.
    explanation: >-
      The mechanical claim this node makes, stated with the hedge the source uses.
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      When the motor nerve fibers of corticospinal tract are inflicted, gait disturbance
      may occur.
    explanation: >-
      Connects the periventricular lesion to the gait phenotype specifically.
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The stretch of sacral fibers of the corticospinal tract may disrupt bladder
      contractions, resulting in urinary incontinence, which is the second most common
      symptom of iNPH.
    explanation: >-
      The conventional derivation of the urinary arm from the same lesion as the gait arm.
      Curated because the placebo-controlled trial result makes this derivation the
      entry's sharpest open question, not because it is settled.
  downstream:
  - target: Gait Disturbance
    causal_link_type: DIRECT
    description: >-
      Loading of the periventricular corticospinal fibres, leg fibres first, is the
      mechanical account of why gait fails earliest and responds to CSF diversion.
    evidence:
    - reference: PMID:33242372
      reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        When the motor nerve fibers of corticospinal tract are inflicted, gait disturbance
        may occur.
      explanation: >-
        States this edge directly.
  - target: Urinary Incontinence
    causal_link_type: DIRECT
    description: >-
      The conventional derivation of the urinary arm from the same lesion as the gait arm,
      via the sacral corticospinal fibres. Curated as an edge rather than left in prose
      precisely because the placebo-controlled trial did not confirm it: the graph now
      asserts a link the evidence for treatment response contradicts, and the knowledge
      gap below attaches to that tension rather than floating above it.
    evidence:
    - reference: PMID:33242372
      reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The stretch of sacral fibers of the corticospinal tract may disrupt bladder
        contractions, resulting in urinary incontinence, which is the second most common
        symptom of iNPH.
      explanation: >-
        The mechanistic claim this edge makes. Note it is a claim about pathogenesis, not
        about reversibility - which is exactly the distinction the trial exposed.
  - target: Urinary Urgency
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The same bladder arm at the severity the trials actually measured. Curated with
      unknown intermediates rather than DIRECT because the cited mechanism names
      incontinence specifically, and urgency is the earlier, milder form recorded by the
      overactive-bladder instruments both randomised trials used.
    evidence:
    - reference: PMID:40960253
      reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Idiopathic normal-pressure hydrocephalus is a neurologic disorder characterized by
        impaired gait, balance, cognition, and bladder control in older adults.
      explanation: >-
        Establishes bladder control as a defining domain of the syndrome. PARTIAL because
        it does not itself attribute the bladder arm to the periventricular lesion; that
        attribution comes from the incontinence edge above.

- name: Perivascular AQP4 Depolarization
  role: amplifier
  biological_scale: CELLULAR
  conforms_to: "glymphatic_dysfunction#Perivascular AQP4 Depolarization and Reduced Periarterial CSF Influx"
  description: >-
    Periarterial CSF influx into the parenchyma depends on aquaporin-4 held at the
    perivascular astroglial end-feet. Cortical biopsies taken at shunt surgery show
    reduced perivascular AQP4 density in idiopathic NPH, which is direct human tissue
    evidence rather than an imaging surrogate - the distinction the glymphatic module
    insists on. It is the disorder-specific substitution this module node asks for: the
    cause of reduced influx here is AQP4 mislocalization at the astrocyte end-foot.
  cell_types:
  - preferred_term: astrocyte of the cerebral cortex
    term:
      id: CL:0002605
      label: astrocyte of the cerebral cortex
  cellular_components:
  - preferred_term: astrocyte end-foot
    term:
      id: GO:0097450
      label: astrocyte end-foot
  biological_processes:
  - preferred_term: water transport
    term:
      id: GO:0006833
      label: water transport
    modifier: DECREASED
  locations:
  - preferred_term: perivascular space
    term:
      id: UBERON:0014930
      label: perivascular space
  evidence:
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Also, AQP4 immunogold cytochemistry analysis of cortical brain biopsies from 30 iNPH
      patients and 12 reference subjects demonstrated reduced AQP4 density in the
      perivascular astroglial endfeet of iNPH brains as compared to control brains
    explanation: >-
      Direct human tissue measurement of the molecular lesion at this node, in idiopathic
      NPH specifically.
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      iNPH and Alzheimer's disease (AD) both exhibit sleep disturbances, build-up of brain
      metabolic wastes and amyloid-β (Aβ) plaques, perivascular reactive astrogliosis, and
      mislocalization of astrocyte aquaporin-4 (AQP4).
    explanation: >-
      Establishes AQP4 mislocalization as a feature of idiopathic NPH and not only of
      Alzheimer disease, which is what licenses conformance to the module here.
  - reference: PMID:16552421
    reference_title: "Accelerated progression of kaolin-induced hydrocephalus in aquaporin-4-deficient mice."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Our results indicate a significant role for AQP4-mediated transparenchymal CSF
      absorption in hydrocephalus and provide a rational basis for evaluation of AQP4
      induction as a nonsurgical therapy for hydrocephalus.
    explanation: >-
      The only causal rather than correlational support in this arm: removing AQP4 makes
      hydrocephalus worse, which is the direction this node asserts. INDIRECT because the
      model is kaolin-induced obstructive hydrocephalus in mice, not normal pressure
      hydrocephalus, so it establishes that AQP4 participates in CSF absorption without
      establishing that its loss initiates the human syndrome.
  downstream:
  - target: Impaired Glymphatic CSF-ISF Exchange and Solute Clearance
    causal_link_type: DIRECT
    description: >-
      Loss of perivascular AQP4 reduces the astroglia-supported influx on which
      CSF-interstitial fluid exchange depends.

- name: Impaired Glymphatic CSF-ISF Exchange and Solute Clearance
  role: central_effector
  biological_scale: ORGANISM
  conforms_to: "glymphatic_dysfunction#Impaired Perivascular CSF-ISF Exchange and Solute Clearance"
  description: >-
    Reduced exchange between cerebrospinal and interstitial fluid produces both an
    abnormal accumulation of cerebral CSF and a failure to clear interstitial solute - the
    two arms of this entry emerging from a single node. Imaging measures of perivascular
    diffusivity are lower in idiopathic NPH than in mimics and correlate with ventricular
    volume, though the glymphatic module's own caution applies: a diffusivity index is a
    correlate of glymphatic transport, not a measurement of it, and the tissue evidence
    upstream carries more weight here than the imaging does.
  biological_processes:
  - preferred_term: cerebrospinal fluid circulation
    term:
      id: GO:0090660
      label: cerebrospinal fluid circulation
    modifier: DECREASED
  - preferred_term: amyloid-beta clearance
    term:
      id: GO:0097242
      label: amyloid-beta clearance
    modifier: DECREASED
  locations:
  - preferred_term: perivascular space
    term:
      id: UBERON:0014930
      label: perivascular space
  evidence:
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Glymphatic dysfunction, characterized by reduced CSF-ISF exchange, leads to an
      abnormal accumulation of cerebral CSF and impaired interstitial solute clearance,
      both defining clinical features of iNPH and a likely cause of cognitive
      deterioration.
    explanation: >-
      States this node and both of its downstream edges, and does so for idiopathic NPH
      specifically.
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Human studies have implicated impaired glymphatic function in both AD and iNPH.
    explanation: >-
      Records the evidence tier honestly - implicated in human studies, not demonstrated
      as causal.
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the authors found that the ALPS index positively correlated with ventricular volume,
      suggesting a direct link between glymphatic impairment and ventriculomegaly
    explanation: >-
      Supports the edge from this node to ventriculomegaly, but only partially: it is a
      correlation between an imaging surrogate and ventricular size in a small study, and
      it does not establish direction.
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ALPS indices of the iNPH patients were also lower than those of the pseudo-iNPH
      group
    explanation: >-
      The comparison against mimics asserted in this node's description, which was
      previously uncited. PARTIAL for the same reason as the item above - a small study,
      and an imaging surrogate rather than a measurement of transport.
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pathophysiological factors including hypoperfusion, glymphatic impairment,
      disturbance of metabolism, astrogliosis, neuroinflammation, and blood-brain barrier
      disruption jointly cause white matter and gray matter lesions, and eventually lead
      to various iNPH symptoms.
    explanation: >-
      Places glymphatic impairment among the accepted pathophysiological factors in
      idiopathic NPH, alongside several this entry does not curate.
  - reference: PMID:42239999
    reference_title: "Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recent MRI advances have introduced biomarkers of glymphatic dysfunction, such as
      diffusion tensor imaging along perivascular spaces (DTI-ALPS), which may improve
      understanding of disease mechanisms and refine patient selection.
    explanation: >-
      Cited for the hedge as much as the claim. DTI-ALPS is described as a biomarker that
      may improve understanding, not as an established measurement of transport, which is
      the same caution the glymphatic module records and the reason the imaging evidence
      here is curated as PARTIAL throughout.
  downstream:
  - target: Ventriculomegaly at Normal Mean CSF Pressure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced glymphatic flux is reported to exacerbate ventriculomegaly, making the two
      arms of this entry mutually reinforcing rather than parallel. The edge is curated with
      unknown intermediates because the human evidence is a correlation between an imaging surrogate
      and ventricular volume, and the direction is not established.
    evidence:
    - reference: PMID:31959516
      reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This correlation may indicate a role of inflammation-induced depolarization of
        AQP4 in iNPH pathogenesis, such that attenuated perivascular AQP4 expression
        reduces glymphatic fluid flux, subsequently exacerbating Aβ accumulation and
        ventriculomegaly.
      explanation: >-
        Proposes exactly this edge, in the source's own hypothetical register, which is
        why the edge is INDIRECT and the evidence PARTIAL.
  - target: Interstitial Amyloid-beta Accumulation
    causal_link_type: DIRECT
    description: >-
      Failure of perivascular solute clearance leaves interstitial amyloid-beta in place.

- name: Interstitial Amyloid-beta Accumulation
  role: consequence
  biological_scale: TISSUE
  conforms_to: "glymphatic_dysfunction#Accumulation of Aggregation-Prone Interstitial Proteins"
  description: >-
    Amyloid-beta plaques are found in cortical biopsies from idiopathic NPH as well as
    from Alzheimer disease, less severe but present. The clinically consequential fact is
    what they predict: amyloid burden correlates with poor shunt responsiveness. That
    makes this node the mechanistic candidate for the part of the syndrome a shunt cannot
    fix, and it is the reason this entry treats the triad as two problems rather than one.
  biological_processes:
  - preferred_term: amyloid-beta clearance
    term:
      id: GO:0097242
      label: amyloid-beta clearance
    modifier: DECREASED
  evidence:
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      accumulation of interstitial amyloid-β (Aβ) plaques are a characteristic feature of
      both iNPH and AD cortical brain biopsies, a pathological finding that correlates
      with poor shunt responsiveness in iNPH patients
    explanation: >-
      Both halves of this node: the deposition in idiopathic NPH cortex, and its
      association with failure to respond to CSF diversion.
  downstream:
  - target: Cognitive Impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The glymphatic arm's route to the cognitive deficit, and the entry's candidate
      explanation for why that deficit did not separate from placebo under shunting: a
      shunt acts on the mechanical arm, and this one is not on it. Curated with unknown
      intermediates because the cited source calls impaired solute clearance a likely
      cause of cognitive deterioration rather than a demonstrated one.
    evidence:
    - reference: PMID:31959516
      reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Glymphatic dysfunction, characterized by reduced CSF-ISF exchange, leads to an
        abnormal accumulation of cerebral CSF and impaired interstitial solute clearance,
        both defining clinical features of iNPH and a likely cause of cognitive
        deterioration.
      explanation: >-
        PARTIAL because the source says "a likely cause", which is the strength this edge
        is curated at.
    - reference: PMID:31959516
      reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        accumulation of interstitial amyloid-β (Aβ) plaques are a characteristic feature of
        both iNPH and AD cortical brain biopsies, a pathological finding that correlates
        with poor shunt responsiveness in iNPH patients
      explanation: >-
        Ties this edge to treatment response: the burden at its source node predicts
        failure of the intervention that acts on the other arm.

phenotypes:

- category: Neurological
  name: Gait Disturbance
  description: >-
    A slowly progressive apraxic gait, typically the earliest feature and the only arm of
    the triad with placebo-controlled evidence of reversibility.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Gait apraxia
    term:
      id: HP:0010521
      label: Gait apraxia
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic normal-pressure hydrocephalus is a neurologic disorder characterized by
      impaired gait, balance, cognition, and bladder control in older adults.
    explanation: >-
      Gait impairment as a defining feature, from the trial that measured it.

- category: Neurological
  name: Cognitive Impairment
  description: >-
    Subcortical-frontal cognitive decline. Idiopathic NPH is widely described as a
    reversible dementia, but in the placebo-controlled trial the cognitive measure did not
    separate from placebo at three months.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Dementia
    term:
      id: HP:0000726
      label: Dementia
  evidence:
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a disorder characterized by progressive ventriculomegaly and the clinical triad of
      gait ataxia, urinary incontinence, and dementia
    explanation: >-
      Dementia as one of the three defining features.

- category: Genitourinary
  name: Urinary Incontinence
  description: >-
    Urinary urgency progressing to incontinence, conventionally attributed to stretch of
    the sacral corticospinal fibres. Described as the second most common symptom.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Urinary incontinence
    term:
      id: HP:0000020
      label: Urinary incontinence
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      resulting in urinary incontinence, which is the second most common symptom of iNPH
    explanation: >-
      States the phenotype and its rank among the triad.

- category: Genitourinary
  name: Urinary Urgency
  description: >-
    The bladder symptom measured in both randomised shunt trials, via overactive-bladder
    instruments rather than incontinence episodes.
  phenotype_term:
    preferred_term: Urinary urgency
    term:
      id: HP:0000012
      label: Urinary urgency
  evidence:
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic normal-pressure hydrocephalus is a neurologic disorder characterized by
      impaired gait, balance, cognition, and bladder control in older adults.
    explanation: >-
      Bladder control as a defining domain of the syndrome.

- category: Neuroimaging
  name: Ventriculomegaly
  description: >-
    Disproportionate ventricular enlargement with narrowed high-convexity sulci, present
    with CSF pressure in the normal range.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Ventriculomegaly
    term:
      id: HP:0002119
      label: Ventriculomegaly
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Typical brain imaging of iNPH displays ventriculomegaly, periventricular
      hyperintensities, wide Sylvian fissures, narrowed subarachnoid space, and cortical
      sulci at the high convexity.
    explanation: >-
      The imaging phenotype, including the high-convexity feature that distinguishes it
      from atrophic ventricular enlargement.

genetic:

- name: SLCO1A2
  relationship_type: SUSCEPTIBILITY
  gene_term:
    preferred_term: SLCO1A2
    term:
      id: hgnc:10956
      label: SLCO1A2
  association: >-
    The strongest signal in the largest genome-wide association study of normal pressure
    hydrocephalus, and a protective rather than a risk allele. rs7962263 near SLCO1A2 gave
    an odds ratio of 0.71 across 1,522 NPH cases and 451,091 controls, replicated in UK
    Biobank, and the effect held in the idiopathic-only sensitivity analysis at 0.70.
  evidence:
  - reference: PMID:39141892
    reference_title: "Risk Variants Associated With Normal Pressure Hydrocephalus: Genome-Wide Association Study in the FinnGen Cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The top loci near the following genes were rs7962263, SLCO1A2 (odds ratio [OR] 0.71,
      95% CI 0.65-0.78, p = 1.0e-14)
    explanation: >-
      The lead protective locus and its effect size in the discovery cohort.
  - reference: PMID:39141892
    reference_title: "Risk Variants Associated With Normal Pressure Hydrocephalus: Genome-Wide Association Study in the FinnGen Cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the sensitivity analysis comparing only patients with iNPH (n = 1,055) with the
      controls (n = 451,091), 4 top loci near the following genes remained significant:
      rs7962263, SLCO1A2 (OR 0.70, 95% CI 0.63-0.78, p = 2.1e-11)
    explanation: >-
      The association survives restriction to idiopathic cases, which is what makes it a
      determinant of the syndrome curated here rather than of a secondary aetiology.

- name: CFAP43
  relationship_type: SUSCEPTIBILITY
  gene_term:
    preferred_term: CFAP43
    term:
      id: hgnc:26684
      label: CFAP43
  association: >-
    The cilia gene MONDO records as the causal gene of MONDO:0009366 via RO:0004003, on
    the strength of the OMIM-numbered familial form. In the systematic review of NPH
    genetics it appears among the genes enriched for risk variants in NPH cohorts rather
    than as an established Mendelian cause of the common idiopathic syndrome, which is why
    it is typed SUSCEPTIBILITY here and not CAUSATIVE.
  evidence:
  - reference: PMID:40266017
    reference_title: "Genetic Risk Factors in Normal Pressure Hydrocephalus: What We Know and What Is Next."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      copy-number variant analyses, and genome-wide association studies showed risk
      variants enriched in NPH cohorts in or near CFAP43, SFMBT1, CWH43, AK9, RXFP2,
      PRKD1, HAVCR1, OTOG, MYO7A, NOTCH1, SPG11, MYH13, FOXJ1, AMZ1/GNA12, and C16orf95
    explanation: >-
      Places CFAP43 among the risk-enriched rather than established-causal genes for NPH,
      which is the typing used here.

- name: SFMBT1
  relationship_type: SUSCEPTIBILITY
  gene_term:
    preferred_term: SFMBT1
    term:
      id: hgnc:20255
      label: SFMBT1
  association: >-
    One of the recurrently reported NPH risk genes. Its mechanistic interest is that the
    NPH risk genes as a set converge on the blood-brain and blood-CSF barriers, cilia and
    ependymal function rather than on any single pathway, which is the class of biology
    the CSF-absorption node of this entry depends on.
  evidence:
  - reference: PMID:40266017
    reference_title: "Genetic Risk Factors in Normal Pressure Hydrocephalus: What We Know and What Is Next."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These genes are associated with blood-brain and blood-cerebrospinal fluid barriers,
      cilia, and ependymal function.
    explanation: >-
      The functional convergence of the risk-gene set, which is the reason this section is
      curated at all: it is mechanistically coherent with the absorption defect above.
  - reference: PMID:40266017
    reference_title: "Genetic Risk Factors in Normal Pressure Hydrocephalus: What We Know and What Is Next."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      copy-number variant analyses, and genome-wide association studies showed risk
      variants enriched in NPH cohorts in or near CFAP43, SFMBT1, CWH43, AK9, RXFP2,
      PRKD1, HAVCR1, OTOG, MYO7A, NOTCH1, SPG11, MYH13, FOXJ1, AMZ1/GNA12, and C16orf95
    explanation: >-
      Names SFMBT1 among the risk-enriched genes, which is the first sentence of this
      block's association and was previously supported only by the convergence claim.

inheritance:

- name: Polygenic susceptibility
  inheritance_term:
    preferred_term: Polygenic inheritance
    term:
      id: HP:0010982
      label: Polygenic inheritance
  description: >-
    Idiopathic NPH is not Mendelian, but it is not sporadic either. Six genome-wide
    significant loci of modest effect have been replicated across two biobanks, and
    familial aggregation is reported in a tenth to a sixth of patients. The contributing
    loci named in the genetic section above are SLCO1A2, AMZ1/GNA12, MLLT10, CDCA2,
    C16orf95 and PLEKHG1 from the GWAS, alongside CFAP43, SFMBT1 and CWH43 from sequencing
    and copy-number studies. A separate CFAP43 Mendelian form shares the MONDO term and is
    not what this block describes.
  evidence:
  - reference: PMID:39141892
    reference_title: "Risk Variants Associated With Normal Pressure Hydrocephalus: Genome-Wide Association Study in the FinnGen Cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified 6 gene regions significantly (p < 5.0e-8) associated with NPH that
      replicated in a meta-analysis with UKBB
    explanation: >-
      Six replicated common-variant loci of modest effect, which is a polygenic
      architecture rather than a Mendelian one.
  - reference: PMID:40266017
    reference_title: "Genetic Risk Factors in Normal Pressure Hydrocephalus: What We Know and What Is Next."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      More than 30 familial cases were identified, and two cohorts found that 10%-16% of
      patients with NPH had relatives with NPH symptoms.
    explanation: >-
      Familial aggregation at a rate incompatible with a purely sporadic disorder and too
      high to be explained by the rare Mendelian form alone.

animal_models:

- name: AQP4-null mouse, kaolin-induced hydrocephalus
  species: Mouse
  genotype: Aqp4 null
  publication: PMID:16552421
  description: >-
    Obstructive hydrocephalus induced by cisterna magna kaolin injection in AQP4-deficient
    versus wild-type mice. The model exists here for one reason: it is the only evidence
    in this entry that manipulates AQP4 and observes the consequence, rather than
    observing AQP4 and the consequence together.
  modeled_mechanisms:
  - target: Perivascular AQP4 Depolarization
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Genetic ablation of AQP4 is a clean loss of the water channel whose perivascular
      mislocalization this node models, and the consequence is more severe ventricular
      enlargement and higher intracranial pressure.
    limitations: >-
      The lesion is not the human one in two respects. Ablation removes AQP4 entirely
      rather than depolarizing it from the astroglial end-feet, and the hydrocephalus is
      kaolin-induced obstruction with intracranial pressure rising to 22 mm Hg, which is
      the opposite of the normal-pressure state that defines the human disease. The model
      therefore supports AQP4's role in CSF absorption without supporting AQP4 loss as the
      initiating event in idiopathic NPH.
    readouts:
    - name: Lateral ventricle volume at 3 and 5 days after kaolin injection
      target: Perivascular AQP4 Depolarization
      direction: INCREASED
      interpretation: >-
        Ventricular enlargement is greater without AQP4, placing the channel upstream of
        ventricular volume rather than alongside it.
      evidence:
      - reference: PMID:16552421
        reference_title: "Accelerated progression of kaolin-induced hydrocephalus in aquaporin-4-deficient mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Lateral ventricle volume increased to 3.7+/-0.5 and 5.1+/-0.5 mm(3) in AQP4 null
          mice at 3 and 5 days after injection, respectively, significantly greater than
          2.6+/-0.3 and 3.5+/-0.5 mm(3) in wildtype mice
        explanation: >-
          The quantitative ventricular measurement behind this readout.
    - name: Intracranial pressure at 3 days after kaolin injection
      target: Perivascular AQP4 Depolarization
      direction: INCREASED
      interpretation: >-
        Also the readout that bounds the model's relevance: pressure rises steeply here,
        whereas the human disease is defined by pressure staying normal.
      evidence:
      - reference: PMID:16552421
        reference_title: "Accelerated progression of kaolin-induced hydrocephalus in aquaporin-4-deficient mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          The corresponding ICP was 22+/-2 mm Hg at 3 days in AQP4 null mice,
          significantly greater than 14+/-1 mm Hg in wildtype mice
        explanation: >-
          Supports the AQP4 effect and simultaneously documents the divergence from
          normal-pressure hydrocephalus, hence PARTIAL.
    evidence:
    - reference: PMID:16552421
      reference_title: "Accelerated progression of kaolin-induced hydrocephalus in aquaporin-4-deficient mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Here, we provide evidence for AQP4-facilitated CSF absorption in hydrocephalus by
        a transparenchymal pathway into the cerebral vasculature.
      explanation: >-
        Supports treating this model as informative for an AQP4-dependent CSF absorption
        node.

prevalence:

- population: Worldwide, all ages
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_5_PER_10000
  rate_per_100000: 16.0
  rate_low: 10.0
  rate_high: 22.0
  notes: Overall population estimate, not age-restricted.
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The prevalence of iNPH has been estimated to be 10 per 100 000 to 22 per 100 000
      overall
    explanation: >-
      The overall prevalence range quoted here.

- population: Adults aged 65 years and over
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 1300.0
  notes: 1.30% in those aged 65 or over.
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      with 1.30% in those aged ≥65 years and 5.9% in those aged ≥80 years
    explanation: >-
      The age-stratified prevalence, which is where the burden of this disease sits.

- population: Adults aged 80 years and over
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 5900.0
  notes: >-
    5.9% in those aged 80 or over. The steep age gradient is consistent with the
    compliance-loss trigger curated above.
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      with 1.30% in those aged ≥65 years and 5.9% in those aged ≥80 years
    explanation: >-
      Same source sentence; quoted here for the over-80 figure.

- population: Adults aged 86 years and over
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 7700.0
  notes: >-
    Independent estimate from the 2025 randomised trial's introduction, giving a
    consistent age gradient from a different source.
  evidence:
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      increases with age, reaching as much as 7.7% for ages ≥86 years
    explanation: >-
      The oldest age band reported, corroborating the gradient.

diagnosis:

- name: MRI morphology (DESH pattern and callosal angle)
  description: >-
    MRI does two different jobs here and the entry separates them. It excludes the
    alternative causes of ventriculomegaly - which matters because the leading
    differential, Alzheimer disease, enlarges the ventricles by atrophy - and it
    identifies features that positively support idiopathic NPH: a reduced callosal angle
    and the disproportionately enlarged subarachnoid space hydrocephalus pattern, in which
    the sulci at the high convexity are effaced rather than widened.

    Their predictive value for treatment response is explicitly limited, which is why this
    entry curates them as diagnostic rather than prognostic and why the shunt-selection
    test below is a separate entry.
  diagnosis_term:
    preferred_term: brain magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  evidence:
  - reference: PMID:42239999
    reference_title: "Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MRI is essential to exclude alternative causes of ventriculomegaly and to identify
      characteristic imaging features such as a reduced callosal angle and the
      disproportionately enlarged subarachnoid space hydrocephalus (DESH) pattern, which
      support the diagnosis, although their predictive value for treatment response
      remains limited
    explanation: >-
      Both diagnostic roles and, in the same sentence, the hedge on prognostic use. Quoted
      whole rather than trimmed, because the hedge is the part that governs how this entry
      uses it.

- name: Cerebrospinal fluid outflow resistance
  description: >-
    The direct physiological readout of the absorption defect curated in the
    pathophysiology above: outflow resistance is pathologically elevated. That makes it
    the one diagnostic test in this entry that measures the mechanism rather than its
    consequences, and it is used both to diagnose and to select shunt candidates.
  diagnosis_term:
    preferred_term: cerebrospinal fluid outflow resistance measurement
  evidence:
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the resistance to CSF outflow (Rout) is pathologically elevated and has been widely
      used for the diagnosis of iNPH and the selection of candidates for shunting surgery.
    explanation: >-
      States the abnormality and both of its uses. This is the diagnostic counterpart of
      the Increased CSF Pulsatility with Impaired CSF Absorption node.

- name: Response to temporary cerebrospinal fluid drainage
  description: >-
    The shunt-selection test, and the one whose consequences run through this entry's
    knowledge gaps. Patients are taken to surgery on the basis of gait-velocity
    improvement after temporary drainage - which is what makes the 2025 trial's cohort
    enriched for gait responders before randomisation, and therefore why its cognitive
    null is weaker evidence than its gait positive.
  diagnosis_term:
    preferred_term: temporary cerebrospinal fluid drainage trial
  evidence:
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We conducted a double-blind, randomized, placebo-controlled trial involving
      participants selected for shunt surgery on the basis of gait-velocity improvement
      with cerebrospinal fluid (CSF) drainage.
    explanation: >-
      Establishes the test and, in the same sentence, that it was the enrolment gate -
      which is the fact the cognitive knowledge gap argues from.

treatments:

- name: Ventriculoperitoneal Shunt Placement
  description: >-
    Surgical diversion of CSF from the ventricle to the peritoneum, the standard therapy
    and the only treatment for idiopathic NPH. Uncontrolled series reported 60-80%
    improvement, which is what made the disease famous as a reversible dementia; two
    randomised placebo-controlled trials, using a valve set either open or effectively
    off, have since measured the effect against a blinded sham. Gait improves. The
    2025 trial found no separation from placebo on cognition or on incontinence, and the
    procedure carried more subdural bleeding and positional headache than placebo.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: ventriculoperitoneal shunt placement
    term:
      id: NCIT:C168483
      label: Ventriculoperitoneal Shunt Placement
  target_mechanisms:
  - target: Ventriculomegaly at Normal Mean CSF Pressure
    treatment_effect: INHIBITS
    description: >-
      Diverting CSF relieves the ventricular distension and thereby the mechanical arm of
      the entry. It does not act on the glymphatic arm, which is the curated reason its
      benefit is confined to gait.
    evidence:
    - reference: PMID:40960253
      reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Among participants with idiopathic normal-pressure hydrocephalus who had a
        response to temporary CSF drainage, shunting resulted in significant improvements
        at 3 months in gait velocity and a measure of gait and balance but not in measures
        of cognition or incontinence.
      explanation: >-
        The placebo-controlled result, and the reason this treatment is curated as acting
        on the mechanical node alone.
  evidence:
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      resulting in a treatment difference of 0.21 m per second (95% confidence interval,
      0.12 to 0.31; P<0.001)
    explanation: >-
      The gait-velocity effect size against blinded placebo.
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A significantly greater improvement in the open-shunt group than the placebo group
      was seen for the Tinetti scale score (mean change, 2.9 points vs. 0.5 points; P =
      0.003) but not the MoCA score (1.3 points vs. 0.3 points) or the Overactive Bladder
      Questionnaire score (-3.3 points vs. -1.5 points).
    explanation: >-
      PARTIAL because it supports the treatment for one arm of the triad and refutes it
      for the other two at this time point. This is the single most important evidence
      item in the entry.
  - reference: PMID:40960253
    reference_title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      more participants in the open-shunt group having subdural bleeding (12% vs. 2%) and
      positional headaches (59% vs. 28%)
    explanation: >-
      The harms measured against blinded placebo, which the uncontrolled series could not
      isolate.
  - reference: PMID:36700738
    reference_title: "Placebo-Controlled Effectiveness of Idiopathic Normal Pressure Hydrocephalus Shunting: A Randomized Pilot Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The estimated treatment difference was 0.22 m/s
    explanation: >-
      The earlier pilot found a gait effect of almost identical magnitude but did not
      reach significance in 18 patients, which is why it is PARTIAL and why the larger
      trial was needed.
  - reference: PMID:36700738
    reference_title: "Placebo-Controlled Effectiveness of Idiopathic Normal Pressure Hydrocephalus Shunting: A Randomized Pilot Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The 4-month treatment delay did not reduce the subsequent response to active
      shunting, nor did it increase the adverse advents rate at 12 months.
    explanation: >-
      Establishes that the placebo arm was not harmed by the delay, which is what made the
      larger placebo-controlled trial ethically tractable.
  - reference: PMID:33242372
    reference_title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment of ventricular shunting, mostly the ventriculoperitoneal shunting, was
      proved to be successful in alleviating symptoms in approximately 60%‐80% patients.
    explanation: >-
      The uncontrolled figure that the placebo-controlled trials were designed to test.
  - reference: PMID:40054973
    reference_title: "Guidelines for Diagnosis and Management of Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Afterward the adoption of shunt treatment without clear diagnostic criteria and
      surgical techniques resulted in poor outcomes with significant complications.
    explanation: >-
      Why this treatment's effect is inseparable from patient selection: shunting applied
      without selection criteria performed badly.
  - reference: PMID:40054973
    reference_title: "Guidelines for Diagnosis and Management of Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both guidelines led to diagnosis and treatment algorithms and significantly improved
      outcomes, along with decreased surgical risk.
    explanation: >-
      Establishes that the reported success of shunting is a property of the selected
      population, which is the caveat carried into the discussions below.
  - reference: PMID:37004132
    reference_title: "The impact of cerebrospinal fluid shunting on quality of life in idiopathic normal pressure hydrocephalus: a long-term analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      QOL improved in 103/130 (79%) patients through 5 years after shunt surgery, although
      it remained lower than that of the control group
    explanation: >-
      Benefit on a patient-centred measure, and its ceiling: shunted patients improved but
      did not reach the control group.
  - reference: PMID:37004132
    reference_title: "The impact of cerebrospinal fluid shunting on quality of life in idiopathic normal pressure hydrocephalus: a long-term analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The SF-36 score reduced progressively, reaching baseline at 5-7 years of follow-up
      and decreased to below baseline at 7-11 years of follow-up
    explanation: >-
      The durability limit. Quality of life returns to baseline within five to seven years
      and falls below it thereafter, so reversibility in this disease is a statement about
      a time window, not a cure. Curated as PARTIAL for the same reason.

differential_diagnoses:

- name: Alzheimer disease
  description: >-
    The leading differential, and not merely a look-alike: the two disorders share
    amyloid-beta deposition, perivascular astrogliosis, AQP4 mislocalization and sleep
    disturbance, and this entry curates the shared glymphatic mechanism explicitly. Most
    patients with idiopathic NPH are said to be misdiagnosed with it. Ventriculomegaly
    does not settle the question, since severe cortical atrophy enlarges the ventricles
    too. The practical stake is that CSF diversion helps one and not the other.
  evidence:
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For these reasons, AD has become the leading differential diagnosis to iNPH
    explanation: >-
      Names Alzheimer disease as the leading differential.
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most notably, CSF diversion confers no symptomatic relief to patients with AD
    explanation: >-
      The therapeutic stake in distinguishing them.

- name: Ventricular enlargement secondary to cortical atrophy
  description: >-
    Sometimes called pseudo-NPH. Ventricular volume rises passively as parenchyma is lost,
    without the CSF-dynamic derangement curated here, and shunting has nothing to relieve.
    The high-convexity sulcal narrowing seen in idiopathic NPH is the imaging feature that
    separates the two, since atrophy widens sulci rather than effacing them.
  evidence:
  - reference: PMID:31959516
    reference_title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ventricular enlargement can also be seen in AD as a result of severe cerebral
      atrophy, further complicating radiographic recognition of iNPH
    explanation: >-
      States the confound this differential turns on.

discussions:

- discussion_id: gap_cognitive_arm_unresponsive_to_shunting
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is the cognitive impairment of idiopathic normal pressure hydrocephalus caused by the
    hydrocephalus at all, or is it concurrent Alzheimer-type pathology that a shunt cannot
    reach?
  attaches_to:
  - pathophysiology#Impaired Glymphatic CSF-ISF Exchange and Solute Clearance
  - pathophysiology#Interstitial Amyloid-beta Accumulation
  - treatments#Ventriculoperitoneal Shunt Placement
  rationale: >-
    Idiopathic NPH is the standard example of a reversible dementia, and that reputation
    rests on uncontrolled series reporting 60-80% improvement. When the comparison was
    finally made against a blinded placebo valve, gait velocity and the Tinetti score
    separated and the cognitive measure did not - 1.3 points against 0.3 on the MoCA in 99
    patients.

    Three readings are consistent with what this entry curates and are not distinguished
    by it. The cognitive deficit may be genuinely hydrocephalic but slower to recover than
    three months, in which case the trial's endpoint is simply early. It may be driven by
    the glymphatic and amyloid arm curated here, which a shunt does not act on - the
    reading this entry's structure favours, and the one that the correlation between
    cortical amyloid burden and poor shunt responsiveness supports. Or the cohort may
    contain concurrent Alzheimer disease that no CSF diversion could help, which the
    entry's own leading differential makes unavoidable as a possibility.

    A fourth consideration cuts across all three, and it is a property of the trial rather
    than of the disease: participants were selected for surgery on the basis of
    gait-velocity improvement with temporary CSF drainage. The cohort was therefore
    enriched for gait responders before randomisation, so the trial is better powered to
    detect the effect it found than the one it did not, and its cognitive null is weaker
    evidence than its gait positive is. The guidelines literature makes the same point in
    reverse: shunting applied without selection criteria performed badly, so selection is
    not an incidental design choice but the thing that makes the operation work.

    These are not equivalent for practice. Under the second and third, a patient selected
    for shunting on gait grounds should not be promised cognitive recovery, and the
    disease's reputation as reversible dementia is a claim about one third of the triad.
  proposed_experiments:
  - experiment_id: amyloid_pet_stratified_shunt_outcome
    name: Amyloid-stratified randomised shunt trial with extended cognitive follow-up
    description: >-
      Stratify a placebo-controlled shunt trial by amyloid PET status at baseline and
      follow cognition to 12 months. If the amyloid-negative stratum shows cognitive
      separation and the amyloid-positive stratum does not, the deficit is hydrocephalic
      and the pooled null reflects co-pathology. If neither separates at any time point,
      the cognitive arm is not shunt-responsive in either group.

- discussion_id: gap_urinary_arm_mechanism_versus_trial
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why does the urinary arm not respond to shunting, when it is derived from the same
    periventricular lesion as the gait arm that does?
  attaches_to:
  - pathophysiology#Periventricular White Matter Compression and Stretch Injury
  - treatments#Ventriculoperitoneal Shunt Placement
  rationale: >-
    The mechanical account curated in this entry derives gait failure and urinary
    incontinence from one lesion: stretch of somatotopically arranged corticospinal
    fibres, with the leg and sacral fibres nearest the expanding ventricle. If that is
    right, relieving the distension should move both.

    It moved one. In the 99-patient trial the Overactive Bladder Questionnaire did not
    separate from placebo, while gait velocity did so decisively. Awkwardly, the earlier
    18-patient pilot found the opposite on this arm: the overactive-bladder symptom bother
    score improved significantly in the open-shunt group at four months, on the smaller
    sample and the weaker gait signal.

    So the two randomised trials disagree about the bladder in the direction opposite to
    their disagreement about gait, which is hard to explain by power alone. The
    possibilities include instrument sensitivity - both trials measured symptom bother
    rather than incontinence episodes or urodynamics - and a genuinely different
    reversibility for the sacral fibres. Neither is settled, and the entry curates the
    conventional sacral-fibre derivation with this discussion attached rather than
    silently dropping it.
  proposed_experiments:
  - experiment_id: urodynamic_endpoint_shunt_trial
    name: Randomised shunt trial with urodynamic rather than questionnaire endpoints
    description: >-
      Repeat the placebo-controlled design with pre-specified urodynamic measurement
      (detrusor overactivity, cystometric capacity) alongside the symptom questionnaire,
      to establish whether the null bladder result reflects an unresponsive mechanism or
      an insensitive instrument.

- discussion_id: gap_aqp4_depolarization_specificity
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is perivascular AQP4 depolarization specific to idiopathic normal pressure
    hydrocephalus, or is it a feature of normal ageing that any elderly cohort would show?
  attaches_to:
  - pathophysiology#Perivascular AQP4 Depolarization
  rationale: >-
    The tissue evidence for the glymphatic arm of this entry is a comparison of cortical
    biopsies from 30 patients with idiopathic NPH against 12 reference subjects. The
    source that reports it also states that progressive AQP4 depolarization occurs
    throughout physiological ageing, and that age-matched human studies are needed to
    establish specificity.

    That caveat lands on the arm of this entry with the least redundancy. Idiopathic NPH
    is a disease of the eighth and ninth decades and its trigger node is age-related loss
    of compliance, so an ageing-associated finding in an aged cohort is exactly the
    confound that cannot be ruled out from a case-control design without age matching. If
    the depolarization is ageing rather than disease, the glymphatic arm loses its
    disorder-specific molecular anchor and the conformance declared here should be
    reconsidered - not the module's validity, but this entry's claim on it.
  proposed_experiments:
  - experiment_id: age_matched_aqp4_biopsy_comparison
    name: Age-matched cortical AQP4 polarization comparison
    description: >-
      Quantify perivascular AQP4 polarization by immunogold cytochemistry in idiopathic
      NPH cortical biopsies against age-matched controls and against age-matched patients
      with other neurodegenerative disease, to separate disease-associated from
      ageing-associated depolarization.

notes: >-
  Scope. This entry curates idiopathic normal pressure hydrocephalus, the form in which
  the CSF-dynamic derangement has no identified antecedent. Secondary normal pressure
  hydrocephalus following haemorrhage, meningitis or trauma shares the ventriculomegaly
  and much of the mechanical arm but has a known cause, and is not curated here.

  Pathograph shape, stated precisely. Seven pathophysiology nodes and five phenotypes are
  joined by eleven `downstream` edges into one connected component; counting the shunt's
  `target_mechanisms` link and the AQP4-null mouse's `modeled_mechanisms` link, that
  component is fourteen nodes and thirteen edges. An earlier version of this sentence said
  twelve edges, which is neither count. The five phenotypes are attached to the arm
  that produces them, which is the point of the entry: gait and the bladder arm hang off
  the periventricular lesion, cognition off the amyloid node, and the imaging phenotype
  off ventriculomegaly itself. An earlier version left them unattached, so the entry's
  central claim - which arm each element of the triad belongs to - lived only in prose and
  was invisible to anything reading the graph.

  The three `genetic:` entries are deliberately not part of that component, and the reason
  is a curation judgement rather than a schema limitation. An earlier version of this note
  claimed the latter and was wrong. `Genetic` has no `downstream` slot, but that is not the
  only route into the pathograph: graph.py indexes pathophysiology nodes by the genes named
  in their descriptors and emits a contributes_to edge whenever a `genetic:` entry's gene
  matches, and SUSCEPTIBILITY is not among the relationship types excluded from that
  inference. Wiring these loci in would take one `genes:` descriptor on a node.

  They are left unwired because the mechanistic step is not established. The GWAS gives
  replicated loci at the population level, and the systematic review gives a functional
  convergence for the risk-gene set as a whole - barriers, cilia, ependymal function - but
  neither says that SLCO1A2, CFAP43 or SFMBT1 acts on CSF absorption in particular.
  Attaching them to that node would assert a per-gene mechanism the sources do not make,
  and the convergence claim is already curated where it belongs, on the SFMBT1 entry.

  Reversibility is a time window. The disease's reputation rests on symptom reversal after
  shunting, and that reversal is real on the gait arm against blinded placebo. On a
  patient-centred measure it is also finite: quality of life improves in about four fifths
  of shunted patients, never reaches that of controls, returns to baseline at five to
  seven years and falls below it thereafter. The entry curates that trajectory rather than
  the headline, because the headline is what makes idiopathic NPH the standard example of
  reversible dementia.

  Why two arms. The mechanical and glymphatic chains are curated as one connected
  pathograph rather than as competing accounts because the sources treat them as
  mutually reinforcing, and because separating them is what makes the trial result
  legible: shunting acts on the mechanical arm and the mechanical arm is where gait sits.
  The reinforcing edge from glymphatic impairment back to ventriculomegaly is curated as
  indirect with unknown intermediates and PARTIAL evidence, because the human support for it is a correlation
  between an imaging surrogate and ventricular volume in a small study and the direction
  is not established.

  Glymphatic conformance. Three nodes declare conformance to the glymphatic_dysfunction
  module. The decision was argued from evidence rather than from topic adjacency: the
  anchor is the AQP4 immunogold measurement in idiopathic NPH cortical biopsies, which is
  human tissue rather than an imaging index. The module carries an explicit knowledge gap
  warning that a low perivascular-diffusivity index is not a measurement of glymphatic
  dysfunction, and that caution is honoured here - the ALPS findings are curated as
  PARTIAL support for a correlation, never as a measurement of transport. Conformance is
  not declared for the module's sleep node, because no sleep measurement in idiopathic
  NPH is cited in the sources used here; the sleep disturbance is mentioned only as a
  feature shared with Alzheimer disease.

  Clinical trial record. The 2025 randomised trial is registered as NCT05081128 (PENS).
  No clinical_trials entry is curated for it because the ClinicalTrials.gov fetch failed
  in this environment on TLS certificate verification, and reference cache files must
  never be hand-created. The trial's design and results are fully covered by
  PMID:40960253, which is cached and quoted throughout. The trial entry should be added
  once the identifier can be fetched.

  Terminology. HP:0002343 (Normal pressure hydrocephalus) exists alongside
  MONDO:0009366, so this is one of the disease-like phenotypes that carries both. It is
  not annotated as a phenotype of itself here. Whether the mechanism curated above should
  eventually be lifted into a module in the manner of the other dual-identifier entries
  is left open; there is currently one disorder to conform to it.

  MONDO:0009366 covers two entities. Its definition is the acquired clinical syndrome,
  attributing the absorption defect to antecedents such as subarachnoid haemorrhage and
  chronic meningitis. The same term nevertheless carries the synonym "hydrocephalus,
  normal pressure, 1", the xref OMIM:236690, an is_a edge to hereditary neurological
  disease, and a causal-gene relation RO:0004003 to CFAP43. So the term simultaneously
  names the common idiopathic syndrome curated here and the OMIM-numbered CFAP43
  Mendelian form, which is a distinct entity with a distinct mechanism. This entry curates
  the idiopathic syndrome; the CFAP43 Mendelian form is not curated here.

  The genetic section is typed SUSCEPTIBILITY throughout, deliberately. Idiopathic NPH has
  a real and replicated common-variant architecture - six genome-wide significant loci
  across two biobanks, with familial aggregation in a tenth to a sixth of patients - and
  the risk-gene set converges on the blood-brain and blood-CSF barriers, cilia and
  ependymal function, which is the biology the absorption node above depends on. None of
  that makes any of these genes causative for the common syndrome. CFAP43 in particular is
  typed SUSCEPTIBILITY here even though MONDO records it as the causal gene of this term,
  because the term's causal-gene relation belongs to the Mendelian entity discussed above
  and the systematic review places CFAP43 among risk-enriched rather than
  established-causal genes for NPH. Curating the CFAP43 Mendelian form properly is
  separate work and, given the term's dual character, probably belongs in a separate entry.
  That cannot be queued as a stub, because a stub needs its own mondo_id and the only
  available one is this term, which is now curated - the absence of a distinct identifier
  is the problem rather than an obstacle to recording it. Tracked as issue #9225 instead.

  Only three of the reported risk genes are curated as structured entries. The remaining
  GWAS loci (AMZ1/GNA12, MLLT10, CDCA2, C16orf95, PLEKHG1) and sequencing hits (CWH43 and
  the longer list in the review) are named in the inheritance block rather than given
  their own entries, because the evidence for each is a single locus-level association
  and expanding them would multiply structure without adding a mechanistic claim the
  entry can act on.

  Not used. A PubMed All Fields search for GeneReviews coverage returned chapters on
  unrelated Mendelian disorders; the idiopathic syndrome curated here is not Mendelian and
  has no GeneReviews chapter, so no GeneReviews baseline applies.

  Deep-research provenance and its limits. The candidate reference set was drawn from a
  claude_code deep-research report, which was used as a lead generator only: every claim
  in this entry was written from the cached primary reference after reading it, not from
  the report's summary of it. The report-level reference validation could not be run in
  this environment - both `just validate-research-reference` and the ClinicalTrials.gov
  fetch fail on TLS certificate verification through the outbound proxy - so that report
  carries no Reference Validation section. The KB-level checks, which are the ones that
  govern what is asserted here, were all run: all eleven cited references were fetched
  individually into the cache and all 54 evidence snippets verify against it.

  The NEC preflight against MONDO:0009366 returns WARN rather than PASS, and the reason
  is worth recording because it is a false positive of a check worth keeping. The tool
  compares gene-mention frequency against MONDO's canonical causal gene, finds CFAP43 at
  6 mentions against AQP4 at 16, and warns that a second disease entity may be mixed in.
  AQP4 here is not a rival disease's gene but the astroglial water channel that is the
  molecular substrate of the glymphatic arm curated above, and the next most frequent
  symbols (SFMBT1, CWH43, DNAH14) are all reported idiopathic-NPH candidate genes rather
  than another disease's. The report mentions iNPH 67 times and neuromyelitis optica, the
  disease AQP4 is otherwise famous for, not once. The asymmetry the check detected is
  real; it reflects a mechanism gene dominating a mechanism report about a
  non-Mendelian disease, compounded by MONDO recording a causal gene for the Mendelian
  entity that shares the term.

references:
- reference: PMID:33242372
  title: "Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus."
- reference: PMID:31959516
  title: "Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus."
- reference: PMID:40960253
  title: "A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus."
- reference: PMID:36700738
  title: "Placebo-Controlled Effectiveness of Idiopathic Normal Pressure Hydrocephalus Shunting: A Randomized Pilot Trial."
- reference: PMID:40054973
  title: "Guidelines for Diagnosis and Management of Idiopathic Normal Pressure Hydrocephalus."
- reference: PMID:39141892
  title: "Risk Variants Associated With Normal Pressure Hydrocephalus: Genome-Wide Association Study in the FinnGen Cohort."
- reference: PMID:40266017
  title: "Genetic Risk Factors in Normal Pressure Hydrocephalus: What We Know and What Is Next."
- reference: PMID:16552421
  title: "Accelerated progression of kaolin-induced hydrocephalus in aquaporin-4-deficient mice."
- reference: PMID:28062721
  title: "Vascular risk factors in INPH: A prospective case-control study (the INPH-CRasH study)."
- reference: PMID:37004132
  title: "The impact of cerebrospinal fluid shunting on quality of life in idiopathic normal pressure hydrocephalus: a long-term analysis."
- reference: PMID:42239999
  title: "Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review."
📚

References & Deep Research

References

11
PMID:33242372
Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus.
No top-level findings curated for this source.
PMID:31959516
Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus.
No top-level findings curated for this source.
PMID:40960253
A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus.
No top-level findings curated for this source.
PMID:36700738
Placebo-Controlled Effectiveness of Idiopathic Normal Pressure Hydrocephalus Shunting: A Randomized Pilot Trial.
No top-level findings curated for this source.
PMID:40054973
Guidelines for Diagnosis and Management of Idiopathic Normal Pressure Hydrocephalus.
No top-level findings curated for this source.
PMID:39141892
Risk Variants Associated With Normal Pressure Hydrocephalus: Genome-Wide Association Study in the FinnGen Cohort.
No top-level findings curated for this source.
PMID:40266017
Genetic Risk Factors in Normal Pressure Hydrocephalus: What We Know and What Is Next.
No top-level findings curated for this source.
PMID:16552421
Accelerated progression of kaolin-induced hydrocephalus in aquaporin-4-deficient mice.
No top-level findings curated for this source.
PMID:28062721
Vascular risk factors in INPH: A prospective case-control study (the INPH-CRasH study).
No top-level findings curated for this source.
PMID:37004132
The impact of cerebrospinal fluid shunting on quality of life in idiopathic normal pressure hydrocephalus: a long-term analysis.
No top-level findings curated for this source.
PMID:42239999
Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
Normal Pressure Hydrocephalus: Comprehensive Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 32 citations 2026-08-22T00:09:42.579009

Normal Pressure Hydrocephalus: Comprehensive Research Report

1. Disease Information

Overview. Normal pressure hydrocephalus (NPH) is a chronic communicating hydrocephalus syndrome characterized by ventriculomegaly with cerebrospinal fluid (CSF) opening pressure that is normal or only mildly elevated (typically 80–200 mmH₂O) on lumbar puncture, occurring in the absence of papilledema. Clinically it presents with the classic Hakim–Adams triad: gait/balance disturbance (usually the earliest and most prominent feature — a broad-based, short-stepped, "magnetic" or shuffling gait), cognitive impairment (subcortical/frontal-executive pattern: psychomotor slowing, impaired attention and executive function, later memory involvement), and urinary dysfunction (urgency progressing to incontinence). Not all three features need be present, especially early in the disease course. NPH is classified as: - Idiopathic NPH (iNPH) — no identifiable antecedent cause, typically affecting adults >60 years; the dominant form discussed in most modern literature. - Secondary NPH (sNPH) — arising after a defined CNS insult (subarachnoid hemorrhage, meningitis, traumatic brain injury, intracranial hemorrhage, tumor, prior neurosurgery) that impairs CSF absorption at the arachnoid granulations, typically presenting at a younger age with a more clearly defined temporal relationship to the inciting event.

iNPH is potentially reversible with CSF diversion (shunt surgery), which distinguishes it clinically from most neurodegenerative dementias and motivates aggressive diagnostic pursuit in elderly patients presenting with gait decline and cognitive slowing (Rovira et al., Neuroradiology 2026, PMID:42239999; Johnson & Williams, NEJM 2025, DOI:10.1056/NEJMra2306506).

Key identifiers: - MONDO: MONDO:0004909 (normal pressure hydrocephalus) — idiopathic and secondary forms have related but distinct MONDO terms in some releases; verify current mapping via OAK before curation. - OMIM: No single-gene Mendelian OMIM phenotype entry exists for typical iNPH (multifactorial/complex trait); familial/genetic risk loci are catalogued separately (see §4). - Orphanet: ORPHA:98644 (Idiopathic normal pressure hydrocephalus). - ICD-10-CM: G91.2 (Idiopathic normal pressure hydrocephalus); G91.0 (Communicating hydrocephalus, used for some secondary/congenital forms); G91.1 (Obstructive hydrocephalus, distinct entity). - ICD-11: 8A05.2 or the hydrocephalus stem code in the "Diseases of the nervous system" chapter (verify exact code at curation time). - MeSH: D065886 (Hydrocephalus, Normal Pressure). - HPO (as a phenotype, for use when NPH itself is an HPO-coded feature of another disease): HP:0007099 (Normal pressure hydrocephalus, if present in the current HPO release) or component terms (see §3).

Synonyms: Hakim–Adams syndrome; Hakim syndrome; occult hydrocephalus; normotensive hydrocephalus; chronic communicating hydrocephalus of adults; symptomatic hydrocephalus with normal CSF pressure.

Evidence basis. The literature on NPH derives from a mix of individual case series/cohorts (single- and multi-center surgical outcome studies), national registry/claims analyses (e.g., the German Federal Statistical Office database), large population-based epidemiological cohorts (e.g., the Western Sweden population study), and a national biobank-linked GWAS (FinnGen). This is a disease where aggregated registry/claims data substantially undercount true prevalence because of underdiagnosis (see §9), so population-based neuroimaging screening cohorts are considered more authoritative for prevalence than administrative coding data (PMC10661316).

2. Etiology

Disease Causal Factors

iNPH's root cause remains incompletely defined and is considered multifactorial, converging on a final common pathway of disturbed CSF dynamics, reduced intracranial compliance, and impaired glymphatic clearance (see §6). Proposed contributing mechanisms include: - Altered CSF hydrodynamics — a shift in balance between CSF pulsatile bulk flow, reduced ventricular compliance and cerebral arterial pulsatility transmission to periventricular tissue. - Impaired CSF absorption/outflow resistance — increased resistance to CSF outflow (Rout) at the arachnoid granulations and along perivascular/glymphatic-lymphatic exit routes. - Glymphatic-lymphatic clearance failure — reduced perivascular AQP4-dependent CSF-interstitial fluid exchange, causing solute/metabolite accumulation (see §6 and the glymphatic scoping review, J Neurosurg 2025, DOI:10.3171/2024.12.JNS2420). - Cerebrovascular/small-vessel pathology — chronic vascular risk factor burden producing periventricular ischemia and reduced vascular/venous compliance.

sNPH has an unambiguous causal chain: an antecedent insult (SAH, meningitis, trauma, tumor, intraventricular hemorrhage) triggers subarachnoid space fibrosis/inflammation, obliterating arachnoid granulation CSF absorption pathways.

Risk Factors

Genetic risk factors (see §4 for detail): copy-number loss in SFMBT1; missense/loss-of-function variants in cilia-related genes (CFAP43, DNAH14); CWH43 variants; and, per the 2024 FinnGen GWAS, 6 genome-wide significant loci near genes implicated in blood–brain-barrier/blood–CSF-barrier function (Kaprio et al./Jyrkkänen et al., Neurology 2024, PMID:39141892). A positive family history and possible autosomal-dominant-like clustering has been described in some kindreds, though iNPH is predominantly sporadic/complex.

Environmental/demographic risk factors: - Age — the single strongest risk factor; incidence and prevalence rise steeply after age 65–70 and again after 80 (PMC11666604). - Vascular risk factor burden — hypertension (described as "perhaps the most important" modifiable VRF), diabetes mellitus (OR ≈2.17), hyperlipidemia (OR ≈2.38), obesity (OR ≈5.43), and psychosocial stress factors (OR ≈5.34) were each independently associated with iNPH in the INPH-CRasH case-control study; the authors estimate that up to ~25% of iNPH cases may be attributable to modifiable vascular risk factors (PMID:28062721; PMC5304464). A subsequent Mendelian randomization study (J Neurol 2023, DOI:10.1007/s00415-023-11604-6) examined the causal relationship between vascular risk factors and iNPH. - Cerebral small vessel disease / white matter hyperintensity burden — frequently comorbid, sharing risk factors with iNPH (hypertension, diabetes, hyperlipidemia, smoking). - Prior neurosurgical/CNS insult — for sNPH specifically: subarachnoid hemorrhage (most common precipitant), bacterial/tuberculous/rheumatoid meningitis, traumatic brain injury, intracerebral/intraventricular hemorrhage, posterior fossa or intraventricular tumors, and prior cranial surgery. - Diabetes/obesity/metabolic syndrome as above. - Male sex — some but not all cohorts report a modest male predominance among iNPH cases.

Protective factors: No robust genetic protective variants or alleles have been established for NPH. Management of modifiable vascular risk factors (blood pressure control, glycemic control, weight management) is proposed as a plausible protective/preventive strategy given the vascular risk factor association data, though this remains largely inferential rather than proven by interventional trials.

Gene–environment interactions: Not well characterized for iNPH specifically; the cilia/choroid-plexus/ependymal gene signal (SFMBT1, CFAP43, DNAH14) plausibly interacts with vascular and CSF-outflow environmental stressors to determine whether ventriculomegaly and clinical symptoms manifest, but formal GxE studies are lacking.

3. Phenotypes

Core Triad (symptoms/clinical signs)

Phenotype HPO term (suggested) Onset/course Frequency
Gait disturbance (broad-based, magnetic, shuffling, short-stepped) HP:0002317 (Unsteady gait) / HP:0002378 (Difficulty walking) / HP:0002355 (Difficulty walking, more specific gait terms as available: HP:0031936 Delayed gait or HP:0100269 Cerebellar-type gait not appropriate — best fit HP:0002317 or a magnetic-gait-specific descendant if present) Typically the first and most consistent symptom; insidious onset, chronic progressive Most frequent triad component (~90%+ of diagnosed cases have gait involvement)
Cognitive impairment (subcortical-frontal pattern: bradyphrenia, impaired executive function, attention, psychomotor slowing; memory relatively preserved early) HP:0100543 (Cognitive impairment) / HP:0002354 (Memory impairment) / HP:0000733 (Psychomotor slowing, if coded) Insidious, progressive; may precede or follow gait symptoms Common (~60–80% of diagnosed cases)
Urinary dysfunction (urgency, frequency, progressing to urge incontinence) HP:0000012 (Urinary incontinence) / HP:0100519 (Urinary urgency) / HP:0100515 (Urinary urgency, alt) Typically the last of the triad to appear; progressive Less consistently present (~50–75%)

Additional recognized phenotypes: - Neuropsychiatric features — apathy, depression, and less commonly psychosis, are increasingly recognized (systematic review/meta-analysis, PMC12879024). Suggested HPO: HP:0000739 (Anxiety), HP:0000723 (Restlessness), HP:0000741 (Apathy, if present in current HPO), HP:0000716 (Depression). - Falls — a frequent and clinically significant consequence of the gait disorder. HPO: HP:0002527 (Falls). - Postural instability — HP:0002172.

Phenotype Characteristics

  • Age of onset: Adult-onset, overwhelmingly ≥60 years for iNPH (diagnostic criteria commonly require age >60); sNPH can occur at any age depending on the inciting event.
  • Severity: Variable; graded clinically with instruments such as the iNPH Grading Scale (iNPHGS) and modified Rankin Scale (mRS).
  • Progression: Classically insidious and slowly progressive over months to years if untreated; can plateau or, less commonly, progress more rapidly. Some component symptoms (especially gait) are reported to show partial/complete reversibility after shunting if intervention occurs before irreversible axonal/white-matter injury sets in.
  • Frequency among affected individuals: Gait disturbance is near-universal at diagnosis; the full triad is present in a minority at initial presentation, with many patients evolving to the complete triad over time.

Quality of Life Impact

Gait impairment and falls are major drivers of loss of independence, institutionalization risk, and caregiver burden. Cognitive impairment compounds functional decline and can be misattributed to "normal aging" or another dementia, delaying diagnosis. Urinary incontinence carries substantial psychosocial and QoL impact and is an independent predictor of nursing-home placement. Long-term shunting studies report sustained QoL improvement in shunt responders (PMID:37004132, "The impact of cerebrospinal fluid shunting on quality of life in idiopathic normal pressure hydrocephalus: a long-term analysis").

4. Genetic/Molecular Information

iNPH is best understood as a complex, multifactorial trait rather than a single-gene Mendelian disorder, though several candidate genes and one genome-wide significant locus set have emerged.

Causal/candidate genes: - SFMBT1 (chromosome 3p21) — a segmental copy-number loss within intron 2 was found in 26.0% of shunt-responsive definite iNPH patients vs 4.2% of healthy elderly controls and 6.3% of Parkinson's disease patients in a Japanese case-control study, and replicated in Finnish and Norwegian cohorts (Kato et al., PLOS ONE 2016, PMID via PMC5115754). SFMBT1 protein localizes to arterial walls, ependymal cells, and choroid plexus epithelium — tissues directly involved in CSF secretion, flow, and absorption. - CFAP43 — a nonsense mutation was identified in one family with NPH and ciliary abnormalities, implicating ependymal ciliary dysfunction in impaired CSF flow/mixing. - DNAH14 — another cilia-associated gene reported among candidate NPH-associated loci. - CWH43 — variants associated with both disease risk and clinical phenotypic severity measures in NPH patients (Neurology Genetics, DOI:10.1212/NXG.0000000000200086). - 2024 FinnGen GWAS (Jyrkkänen et al., Neurology 2024, PMID:39141892) — the largest GWAS in chronic hydrocephalus to date (473,691 Finns with genotype and nationwide health-record linkage), identifying 6 genome-wide significant loci associated with NPH, with genes near the top loci previously implicated in blood–brain-barrier and blood–CSF-barrier function — supporting a barrier-integrity mechanism distinct from purely mechanical CSF-flow obstruction.

Gene-level pattern: Multiple implicated genes (SFMBT1, DNAH14, CFAP43, CWH43) are highly expressed in choroid plexus and ependymal cells, and several are linked to ciliary function — a convergent theme suggesting impaired ependymal ciliary beating/CSF flow-mixing as a contributing mechanism, analogous to mechanisms in congenital hydrocephalus and primary ciliary dyskinesia (Piccinin et al., "Genetic Risk Factors in Normal Pressure Hydrocephalus," Movement Disorders 2025, PMID:40266017; review in J Neurosurg 2024, DOI:10.3171/... "Genetics and molecular pathophysiology of normal pressure hydrocephalus").

Variant classification / population frequency: No ClinVar-curated pathogenic/likely-pathogenic variant set exists comparable to monogenic disease; SFMBT1 copy-number loss frequency in general elderly populations (~4–6%) versus iNPH cases (~26%) suggests it functions as a susceptibility/risk allele rather than a fully penetrant causal variant — appropriate relationship_type: SUSCEPTIBILITY in dismech terms, with HP:0010982-style polygenic/complex inheritance framing rather than classic Mendelian inheritance.

Somatic vs. germline: All reported variants are germline; no somatic mosaicism data reported for iNPH.

Epigenetics / chromosomal abnormalities: No systematic epigenome-wide association study or chromosomal-abnormality series specific to iNPH was identified in current literature; this remains an evidence gap.

Functional consequence: The SFMBT1/CFAP43/DNAH14/CWH43 gene set suggests a mechanism of partial loss of function in genes governing choroid plexus/ependymal barrier integrity and ciliary CSF propulsion, predisposing to the CSF-dynamics disturbance that culminates in ventriculomegaly — a susceptibility/modifier rather than sole-causal genetic architecture, consistent with the multifactorial (vascular + genetic + glymphatic) model.

5. Environmental Information

  • Vascular/metabolic environmental exposures: hypertension, diabetes, hyperlipidemia, obesity — see §2 for effect sizes (INPH-CRasH study).
  • Psychosocial stress factors: independently associated with iNPH risk in case-control analysis (OR ≈5.3), though the mechanism is unclear and may reflect confounding or reverse causation.
  • Infectious agents: Bacterial meningitis, tuberculous meningitis, and rheumatoid/aseptic meningitis are established precipitants of secondary NPH via arachnoiditis/fibrosis of the CSF absorptive pathways (case report of rheumatoid meningitis-associated secondary NPH, PMC8299371). Meningoencephalitis accounted for ~5% of cases in a large secondary-NPH case review (n=1,208 cases).
  • Trauma/hemorrhage exposures: subarachnoid hemorrhage (the best-studied precipitant of sNPH, with shunt-dependent hydrocephalus complicating a substantial minority of aneurysmal SAH survivors — see PMC11319414 systematic review/meta-analysis of risk factors for shunt-dependent hydrocephalus after SAH), traumatic brain injury, and intraventricular/intracerebral hemorrhage.
  • Iatrogenic exposures: prior cranial neurosurgery (tumor resection, posterior fossa surgery) is a recognized precipitant of secondary NPH.
  • No specific occupational toxin, pollutant, or dietary exposure has been robustly linked to iNPH risk; nutritional/lifestyle risk factor data remain limited and largely inferential (see the Nutritional and Lifestyle Risk Factors chapter, ScienceDirect B9780124078246000100).

6. Mechanism / Pathophysiology

The pathophysiology of iNPH is best framed as a convergence of three interacting mechanistic axes: (1) disturbed CSF hydrodynamics/compliance, (2) glymphatic-lymphatic clearance failure, and (3) periventricular vascular/ischemic injury — culminating in white matter and cortical dysfunction.

Causal chain (upstream → downstream)

  1. Trigger/predisposition: genetic susceptibility (choroid plexus/ependymal ciliary and barrier genes) + vascular risk factor burden + (for sNPH) an antecedent CNS insult causing arachnoid granulation fibrosis.
  2. CSF outflow resistance increases and/or ventricular/vascular compliance is reduced — normal pulsatile arterial-driven CSF/interstitial fluid exchange is impaired.
  3. Glymphatic-lymphatic clearance dysfunction: AQP4 water channels on perivascular astrocytic endfeet, which normally drive convective glymphatic CSF-ISF exchange, show reduced expression and perivascular mislocalization, together with reactive perivascular astrogliosis, in iNPH brain tissue and CSF studies (glymphatic scoping review, J Neurosurg 2025, DOI:10.3171/2024.12.JNS2420; AQP4 CSF evaluation study, PMC8486078).
  4. Impaired clearance of interstitial waste/metabolites (including amyloid-beta and other neurotoxic solutes) accumulates in periventricular white matter and CSF.
  5. Ventricular enlargement develops as CSF preferentially expands the low-resistance ventricular compartment, producing periventricular white-matter stretch injury, transependymal CSF flow, and periventricular ischemia from compression of penetrating medullary arterioles.
  6. Downstream clinical manifestation: disruption of periventricular white matter tracts serving frontal-subcortical circuits (corticospinal tracts controlling gait, frontal-executive circuits, and pontine/periventricular pathways involved in bladder control) produces the gait–cognition–urinary triad.

Molecular/cellular detail

  • Molecular pathways: Disturbed AQP4-dependent glymphatic convective flow (analogous mechanistically to the glymphatic_dysfunction module framework used for Alzheimer's disease — perivascular AQP4 depolarization/mislocalization reducing periarterial CSF influx and paravenous efflux).
  • Cellular processes: reactive astrogliosis (elevated CSF YKL-40/chitinase-3-like protein 1, a marker of activated astrocytes, is significantly higher in CSF tap-test non-responders than responders — PMC11399724), ependymal ciliary dysfunction, and choroid plexus epithelial dysfunction (impacting CSF secretion).
  • Protein dysfunction: AQP4 mislocalization from perivascular endfeet to a more diffuse astrocytic membrane distribution — a functional redistribution rather than a loss-of-expression phenomenon in most studies, though net reduction has also been reported.
  • Tissue damage mechanisms: periventricular ischemia from compression/stretch of penetrating arterioles; chronic mechanical stretch injury to periventricular white matter (corpus callosum, corona radiata); transependymal CSF absorption causing periventricular white matter edema/gliosis (visible as periventricular hyperintensity on MRI).
  • Biochemical/CSF proteomic abnormalities: Unbiased CSF proteomics (Neurology, DOI:10.1212/WNL.0000000000213375) identified decreases in numerous CSF proteins in iNPH consistent with impaired efflux from interstitial fluid into CSF — a proteomic signature directly supporting the glymphatic-failure model. Elevated leucine-rich alpha-2-glycoprotein (LRG) and decreased classic Alzheimer's-type biomarkers have also been reported (PMC7961420).
  • Immune involvement: chronic low-grade neuroinflammation and reactive astrogliosis (YKL-40) rather than primary autoimmunity, except in secondary NPH caused by inflammatory/autoimmune meningitis (e.g., rheumatoid meningitis).

Molecular profiling

  • CSF proteomics: decreased protein efflux signature (2024 Neurology study above).
  • Neuroimaging-correlate "omics": DESH (disproportionately enlarged subarachnoid space hydrocephalus) pattern reflects regional CSF compliance mismatch — tight high-convexity/medial subarachnoid spaces with enlarged Sylvian fissures and ventricles — used increasingly as a structural/morphometric biomarker (see §10).
  • Single-cell/spatial transcriptomic and multi-omic data specific to human iNPH brain tissue remain sparse; most molecular-mechanism data derive from CSF biomarker studies and animal models rather than human single-cell atlases.

Suggested ontology terms

  • GO (biological process): GO:0007420 (brain development, upstream context), GO:0003094 (glomerular filtration analogy not applicable); more precisely: GO:0055082 (cellular chemical homeostasis), GO:0072488 (ammonium transmembrane transport, N/A); best fits: GO:0007605 (N/A), and specifically GO:0035378 (carbon dioxide transmembrane transport via aquaporin channel), GO:0003094 not relevant — most precise GO terms are GO:0035378 and GO:0006833 (water transport), plus GO:0050893 (sensory processing, N/A). Recommend: GO:0006833 (water transport, AQP4 function), GO:0007420 (brain development — ependymal/ciliary genes), GO:0003341 (cilium movement, for ependymal ciliary dysfunction), GO:0034976 (response to endoplasmic reticulum stress, N/A).
  • GO (cellular component): GO:0016327 (apicolateral plasma membrane, astrocyte endfeet context), GO:0043209 (myelin sheath, periventricular white matter injury), GO:0005929 (cilium, ependymal).
  • CL (cell types): CL:0000127 (astrocyte), CL:0000067 (ciliated cell), CL:1001602 (choroid plexus epithelial cell) or CL:0000710 (choroid plexus cell), CL:0011005 (ependymal cell / GO alt CL:0000065 ependymal cell).
  • CHEBI: CHEBI:15377 (water, AQP4 substrate); CHEBI:81571 (amyloid beta, comorbid pathology context).

7. Anatomical Structures Affected

Organ level: - Primary: brain (ventricular system, periventricular white matter, subarachnoid space). - Secondary/complications: bladder (neurogenic urinary dysfunction), musculoskeletal system (falls-related injury), and — after shunt placement — abdominal peritoneal cavity (site of distal shunt catheter and occasional complications). - Body systems: nervous system (primary), genitourinary system (secondary), musculoskeletal system (secondary, gait/falls).

Tissue/cell level: - Ventricular ependyma (CL:0000065 ependymal cell) — ciliary dysfunction. - Choroid plexus epithelium (CL:1001602 / choroid plexus epithelial cell) — CSF secretion. - Perivascular astrocytes (CL:0000127 astrocyte) — AQP4-mediated glymphatic function. - Periventricular white matter oligodendrocytes/axons (CL:0000128 oligodendrocyte) — stretch/ischemic injury. - Arachnoid granulation cells — CSF absorption (particularly relevant to secondary NPH fibrosis).

Subcellular level: - Astrocytic endfeet plasma membrane — AQP4 water channel localization (GO:0043195 terminal bouton not applicable; better: GO:0097449 astrocyte projection). - Ependymal cell cilia (GO:0005929 cilium). - Perivascular (Virchow-Robin) space — the anatomical conduit for glymphatic CSF-ISF exchange.

Localization (UBERON terms): - UBERON:0002037 (cerebellum, N/A unless cerebellar involvement noted); primary relevant terms: UBERON:0002450 (lateral ventricle), UBERON:0002316 (white matter of cerebrum / periventricular white matter), UBERON:0002078 (right cerebral hemisphere, bilateral involvement typical), UBERON:0002298 (brainstem, less directly involved), UBERON:0001893 (cerebral cortex — frontal-subcortical circuit disruption), UBERON:0000955 (brain, general), UBERON:0002037 for cerebellum not primary. Also UBERON:0035328 (subarachnoid space) and UBERON:0002440 (choroid plexus). - Lateralization: bilateral and symmetric ventriculomegaly is typical of iNPH; asymmetric ventriculomegaly should prompt consideration of secondary/obstructive causes.

8. Temporal Development

  • Onset: Adult-onset, insidious, typically ≥60 years for iNPH (diagnostic criteria commonly specify age >60); sNPH onset is anchored to the timing of the antecedent insult (days to years post-SAH/meningitis/trauma), with shunt-dependent hydrocephalus after SAH often manifesting within the first weeks to months.
  • Onset pattern: Chronic/insidious for iNPH; can be subacute for some secondary forms (post-hemorrhagic).
  • Progression: Slowly progressive without treatment; gait disturbance often progresses first and most reliably, with cognitive and urinary symptoms accruing over months to a few years. Disease duration prior to diagnosis is frequently prolonged (often years), contributing to underdiagnosis (§9).
  • Disease course pattern: Generally progressive rather than relapsing-remitting; no well-described spontaneous remission pattern, though very slow plateaus are reported.
  • Reversibility: A defining and clinically critical feature — early, appropriately selected patients can show substantial or complete reversal of gait, and partial reversal of cognitive/urinary symptoms, after CSF shunting; delayed diagnosis is associated with reduced reversibility due to accumulating irreversible periventricular white-matter injury.
  • Critical periods: Earlier intervention (shorter duration of preoperative symptoms) is repeatedly identified as a positive prognostic factor for shunt responsiveness, underscoring a "window of opportunity" before fixed structural injury occurs.

9. Inheritance and Population

Epidemiology

  • Incidence (Germany, national claims data, 2005–2022): rose 48%, from 5.4 to 8.0 cases per 100,000 population, peaking in 2018, with the largest increases in the 80–89 age group (PMC11666604).
  • Incidence (population-based cohort): ~4.8 cases per 1,000 person-years among older adults in longitudinal follow-up.
  • Prevalence: In the largest population-based study (Western Sweden), 0.2% of individuals aged 70–79 and 5.9% of those ≥80 years met guideline criteria for probable iNPH — figures substantially higher than earlier clinic-based estimates, reflecting how underdiagnosed the condition is. A separate cohort found prevalence of "possible iNPH" doubling from 1.5% to 2.9% over the follow-up period.
  • Proportion of dementia burden: iNPH is estimated to account for roughly 6% of all dementia cases, notable because it is one of the few potentially reversible dementia causes.
  • Underdiagnosis: widely emphasized as a major public-health and economic issue — "possibly enormous underdiagnosis" (PMC10661316) — with substantial social and economic burden from unrecognized, treatable disability.

Inheritance Pattern

iNPH does not follow classic Mendelian inheritance; it is best modeled as a complex/multifactorial trait with contributing common-variant risk loci (FinnGen GWAS, 6 genome-wide significant loci) and rarer higher-effect susceptibility variants/copy-number changes (SFMBT1 intron-2 CNV, CFAP43, DNAH14, CWH43). No formal penetrance/expressivity estimates analogous to monogenic disease exist; genetic anticipation, germline mosaicism, and founder-effect data specific to iNPH have not been robustly reported, though SFMBT1 CNV enrichment in Finnish and Norwegian cohorts hints at possible population-specific enrichment worth further study (a Nordic founder-effect hypothesis has been raised but not definitively established).

Population Demographics

  • Age distribution: overwhelmingly elderly (≥65, with steep increase ≥80).
  • Sex ratio: some cohorts report a modest male predominance, though this varies by study population; not as strongly skewed as many other neurodegenerative conditions.
  • Geographic/ancestry patterns: Most large genetic and epidemiologic studies derive from Nordic/European populations (FinnGen, Swedish, Norwegian, German cohorts, Japanese cohorts for SFMBT1); population-specific prevalence and genetic architecture in other ancestries is comparatively understudied — a notable evidence gap.

10. Diagnostics

Clinical Diagnostic Criteria

The most widely used framework derives from the Japanese iNPH Treatment Guidelines (currently in a third edition) and analogous international consensus criteria, requiring: 1. Age typically >60 years. 2. Presence of ≥1 of the triad: gait disturbance, cognitive impairment, urinary dysfunction (gait is usually required/most heavily weighted). 3. Radiological ventriculomegaly, classically Evans Index >0.3 (ratio of maximal frontal horn width to maximal internal skull diameter on axial CT/MRI). 4. Normal/near-normal CSF opening pressure (80–200 mmH₂O) on lumbar puncture, without papilledema. 5. Symptoms not fully explained by another condition.

Imaging Biomarkers

  • Evans Index (EI): meta-analytic sensitivity 96%, specificity 83% for iNPH; cutoff >0.3 (some frameworks use >0.32).
  • DESH (Disproportionately Enlarged Subarachnoid-space Hydrocephalus) — tight high-convexity sulci with enlarged Sylvian fissures and ventriculomegaly; considered highly specific, and interobserver reliability of the DESH score has been a recent subject of study (ScienceDirect, 2025).
  • Callosal angle (CA): meta-analytic sensitivity 91%, specificity 93%.
  • Emerging AI-based automated 3D T1 MRI volumetric analysis for iNPH diagnosis (AJNR 2025, DOI in article 46/1/33).
  • Cortical thickness combined with ventricular morphometry improves diagnostic accuracy (Front Aging Neurosci 2024).

CSF Dynamic/Provocative Testing

  • CSF tap test (Miller Fisher / large-volume lumbar puncture or tap test): positivity defined as ≥20% improvement in timed 10-meter walk test time/steps, and/or ≥10% improvement in MMSE, and/or ≥1-point improvement in a urinary incontinence score; meeting any one criterion is considered positive.
  • External lumbar drainage (ELD) and CSF infusion testing (measuring outflow resistance, Rout) are more invasive but higher-sensitivity predictors of shunt responsiveness, discussed in "Invasive Preoperative Investigations in iNPH: A Comprehensive Review" (ScienceDirect S1878875023015474).

CSF Biomarkers

  • AD-type biomarkers (Aβ42, Aβ40, total-tau, phospho-tau): iNPH classically shows low Aβ42 (similar to Alzheimer's disease) but normal t-tau and p-tau, producing a distinctive but sometimes confounding profile; a positive Aβ42/Aβ40 ratio together with elevated p-tau raises suspicion of coexistent Alzheimer's pathology, which may influence shunt outcome.
  • YKL-40 (chitinase-3-like protein 1): elevated in CSF tap-test non-responders, proposed as a marker of reactive astrogliosis/AQP4 dysregulation predicting poor shunt response.
  • AQP4: reduced/mislocalized in iNPH CSF and tissue studies (§6).
  • Emerging unbiased CSF proteomics: broad decreases in CSF protein efflux signatures, a molecular fingerprint of glymphatic failure (Neurology 2024/2025, DOI:10.1212/WNL.0000000000213375).
  • In vivo amyloid-PET studies show a substantial prevalence of concomitant beta-amyloid pathology in iNPH cohorts, associated with distinct neuropsychological profiles (PMC11351685).

Genetic Testing

No clinically validated genetic test panel currently guides routine iNPH diagnosis or management; genetic findings (SFMBT1 CNV, GWAS loci) remain research-stage rather than diagnostic-stage. Whole-genome/exome sequencing, gene panels, and chromosomal microarray have no established clinical indication for typical iNPH but may be considered in atypical, familial, or early-onset presentations, or when a syndromic ciliopathy is suspected.

Differential Diagnosis

Alzheimer's disease and other dementias (frontotemporal dementia — notably, a 10-year retrospective study found increased prevalence of NPH in both FTD variants, PMC10508318), Parkinson's disease and other parkinsonian/gait disorders, cerebral small vessel disease/vascular dementia, and other causes of ventriculomegaly (ex vacuo dilation from atrophy, obstructive hydrocephalus).

Screening

No population-wide screening program exists; opportunistic case-finding relies on clinical suspicion in elderly patients presenting with the triad, supported by incidental radiological ventriculomegaly noted on imaging obtained for other indications.

11. Outcome/Prognosis

  • Mortality/life expectancy: iNPH itself is not typically directly fatal, but untreated disease contributes substantially to morbidity (falls, immobility, institutionalization) that can shorten life expectancy indirectly; formal disease-specific mortality statistics are not well standardized across studies.
  • Shunt-responder outcomes: Ventriculoperitoneal (VP) shunting produces significant improvement in modified Rankin Scale and iNPH Grading Scale (iNPHGS) scores at 1, 2, and 3 years post-surgery, with MMSE improvement significant at 1 and 3 years in some cohorts (PMC11992790, long-term VP shunt outcomes study). Long-term (multi-year) quality-of-life benefit is documented (PMID:37004132).
  • Endoscopic third ventriculostomy (ETV) vs VPS: a retrospective cohort comparison found differences in surgical management outcomes between the two approaches for iNPH (PMC11875132) — VPS remains the more established/first-line approach for communicating (non-obstructive) iNPH, while ETV is generally reserved for obstructive hydrocephalus variants.
  • Complications: Subdural hematoma/hygroma occurs in ~9–10.4% of shunted patients, related to over- or under-drainage; shunt malfunction, infection, and the need for revision surgery are recognized risks.
  • Prognostic factors for shunt response: shorter duration of preoperative symptoms, absence of significant comorbid vascular/neurodegenerative pathology, higher education level, non-smoking status, and fewer postoperative complications are associated with better outcomes; multiple concurrent comorbidities predict worse outcomes and should be weighed before shunt insertion.
  • Prognostic biomarkers: CSF Aβ42/Aβ40 and p-tau positivity (suggesting comorbid AD pathology) may predict attenuated or less durable shunt response; elevated CSF YKL-40 is associated with tap-test non-response. Preoperative imaging biomarkers (DESH, callosal angle, ventricular morphometry) combined with tap test improve prediction of shunt surgery outcome (PMC11903477).
  • A recent placebo-controlled randomized trial ("A Randomized Trial of Shunting for Idiopathic Normal-Pressure Hydrocephalus," NEJM, DOI:10.1056/NEJMoa2503109 — the PENS trial, NCT03350750) provides higher-tier randomized evidence for shunting effectiveness versus the historically observational/uncontrolled evidence base — a major methodological advance for the field.

12. Treatment

Surgical (mainstay of definitive therapy)

  • Ventriculoperitoneal (VP) shunting — the established first-line definitive treatment for both iNPH and most sNPH; a programmable/adjustable-valve shunt diverts CSF from the lateral ventricle to the peritoneal cavity. NCIT: treatment_term NCIT:C15329 (Surgical Procedure) or a more specific shunt-placement term if available in NCIT; therapeutic_modality: SURGERY/DEVICE.
  • Ventriculoatrial or ventriculopleural shunting — alternative distal sites used when peritoneal shunting is contraindicated.
  • Endoscopic third ventriculostomy (ETV) — an alternative in select patients, more established for obstructive hydrocephalus but studied comparatively against VPS in iNPH (PMC11875132).
  • Lumboperitoneal shunting — an alternative extracranial approach avoiding ventricular catheterization, used in some centers for communicating NPH.

Pharmacotherapy

No disease-modifying pharmacologic therapy exists for iNPH; pharmacologic management is largely supportive (e.g., anticholinergic or beta-3 agonist agents for residual urinary urgency post-shunt — NCIT:C15986 Pharmacotherapy) and management of comorbid vascular risk factors (antihypertensives, statins, glycemic control agents) as an adjunctive/preventive strategy given the vascular risk factor association data.

Supportive/Rehabilitative

  • Physical therapy/gait rehabilitation (NCIT:C15302 Physical Therapy) — used both pre- and post-shunt to maximize functional gait recovery.
  • Fall-prevention programs and assistive devices.
  • Genetic counseling (NCIT:C15240) — of limited current applicability given the absence of validated single-gene testing, but relevant in rare suspected familial/syndromic cases.
  • Supportive care (NCIT:C15747) for advanced/non-responsive disease.

Experimental / Investigational

  • Ongoing trials characterizing the prodromal phase of iNPH (European Study of Prodromal iNPH, NCT05910944), aiming to define earlier intervention windows.
  • The PENS trial (NCT03350750) provides the first placebo-controlled randomized evidence base for shunting effectiveness.
  • No gene therapy, cell therapy, or RNA-based therapeutics are in development specific to iNPH given its complex/multifactorial and largely mechanical pathophysiology; the primary "molecular" therapeutic frontier is biomarker-guided patient selection (CSF/glymphatic biomarkers to predict shunt responsiveness) rather than a distinct disease-modifying drug target.

Treatment Outcomes / Adverse Events

See §11 for response rates and complications (subdural hematoma/hygroma 9–10.4%, shunt malfunction/infection, over/under-drainage).

Treatment Algorithm

Standard pathway: clinical suspicion → imaging (Evans Index, DESH, callosal angle) → CSF tap test (± infusion study/ELD in equivocal cases) → shunt surgery in tap-test/ELD responders → postoperative gait/cognitive/urinary reassessment and shunt-valve adjustment as needed. A proposed algorithm for managing secondary post-shunt deterioration in iNPH patients is described in PMC7055114.

13. Prevention

  • Primary prevention: No established primary prevention strategy for iNPH exists given its multifactorial, poorly understood etiology; modifiable vascular risk factor control (blood pressure, glycemic control, weight management, lipid management) is a plausible but not rigorously trial-proven preventive approach, extrapolated from the INPH-CRasH association data.
  • Secondary prevention (for sNPH): Prompt and adequate treatment of subarachnoid hemorrhage, bacterial/tuberculous/other meningitis, and traumatic brain injury, along with vigilant post-insult monitoring for evolving hydrocephalus (serial imaging, ICP monitoring where indicated), aims to detect and treat secondary hydrocephalus before irreversible neurological injury occurs. Early recognition and shunting/ETV in at-risk post-SAH patients reduces morbidity from shunt-dependent hydrocephalus (see the SAH shunt-dependence risk-factor meta-analysis, PMC11319414).
  • Screening/early detection: No population-based screening program exists; earlier clinical recognition of the prodromal triad (motivating current prodromal-iNPH research, NCT05910944) and opportunistic radiological flagging of ventriculomegaly on incidental imaging are the most actionable current strategies to shorten the diagnosis-to-treatment interval, which is itself a major modifiable prognostic factor (§8, §11).
  • Genetic counseling: Not currently a mainstream component of iNPH prevention given the absence of validated predictive genetic testing, though this could become more relevant as GWAS/candidate-gene findings mature.
  • Public health/behavioral interventions: General cardiovascular risk factor modification (as for cerebral small vessel disease prevention broadly) is the most plausible population-level lever, though iNPH-specific outcome trials of such interventions are lacking.

14. Other Species / Natural Disease

  • Taxonomy: NCBITaxon:9606 (Homo sapiens) is the primary species of clinical interest; naturally occurring NPH-like syndromes in companion animals are not well established as a distinct clinical entity comparable to human iNPH (unlike, e.g., congenital hydrocephalus, which is well described in toy-breed dogs).
  • Comparative note: Congenital/obstructive hydrocephalus is naturally occurring and well documented in several companion-animal breeds (e.g., Chihuahuas, English Bulldogs — OMIA entries exist for canine hydrocephalus), but these are developmental/obstructive rather than adult-onset communicating NPH phenocopies, so cross-species natural-disease relevance to iNPH specifically is limited.
  • Zoonotic potential: Not applicable — NPH is not an infectious/transmissible disease itself (though secondary NPH can follow an infectious meningitis, the hydrocephalus sequela itself is not zoonotic).

15. Model Organisms

Rodent (primary model system)

  • Kaolin-induced hydrocephalus (rat, and some mouse studies) — the dominant experimental model, first introduced by Dixon (1932). Kaolin injected into the cisterna magna or basal cisterns produces an obstructive hydrocephalus (OHC) model with elevated intracranial pressure that subsides toward normal range within about a week, useful for studying acute/subacute CSF dynamics.
  • Cortical subarachnoid space kaolin injection — produces a slower-onset, initially asymptomatic communicating hydrocephalus considered more representative of late-adult-onset NPH specifically, via an inflammatory/fibrotic subarachnoid response impairing CSF absorption (a mechanistic parallel to human secondary NPH pathogenesis).
  • AQP4-deficient mice with kaolin-induced hydrocephalus — show accelerated progression of hydrocephalus compared to wild-type, directly supporting AQP4's protective/compensatory role in glymphatic CSF clearance and providing causal (not just correlative) evidence for the glymphatic-failure mechanism (PMID:16552421).
  • Kaolin-induced chronic hydrocephalus in transgenic rats expressing human APP — accelerates amyloid deposition and vascular disease, modeling the mechanistic link between impaired CSF/glymphatic clearance and amyloid pathology relevant to the iNPH–Alzheimer's comorbidity axis (PMC4328504).
  • Optic disc/ICP changes in rat obstructive hydrocephalus models — used to study secondary consequences of elevated ICP (PMC9128145).
  • CSF outflow resistance / lymphatic CSF absorption studies in kaolin-induced communicating hydrocephalus rats demonstrate elevated CSF outflow resistance linked to impaired lymphatic (not just arachnoid granulation) CSF absorption — broadening the mechanistic model beyond the classical arachnoid-villi-only absorption paradigm (PMC2831828).

Model Characteristics

  • Phenotype recapitulation: Kaolin models recapitulate ventriculomegaly, elevated/altered ICP dynamics, and periventricular white matter injury reasonably well, and the cortical-subarachnoid variant specifically models the communicating, slow-onset phenotype relevant to adult NPH.
  • Limitations: Kaolin models are inflammatory/chemically induced rather than spontaneous/age-related, so they do not capture the genetic susceptibility architecture (SFMBT1, ciliary genes) or the decades-long human aging process; they also do not naturally reproduce the full human clinical triad (gait/cognition/urinary function) with behavioral readouts of comparable specificity, limiting translational fidelity for cognitive/psychiatric endpoints. Rodent CSF dynamics and cranial compliance also differ substantially in scale from human CSF physiology, and AQP4-knockout findings, while mechanistically informative, represent an extreme genetic perturbation rather than the partial/complex genetic risk architecture seen in human iNPH — an appropriate HUMAN_MODEL_MISMATCH framing if curated in dismech.

Applications

Rodent kaolin models are primarily used to study: CSF outflow resistance and absorption pathways (including the lymphatic contribution), the role of AQP4/glymphatic function in disease progression, periventricular white matter/ischemic injury mechanisms, and the mechanistic interaction between impaired CSF clearance and amyloid pathology (APP-transgenic + kaolin combination models).

Resources

No single organism-specific hydrocephalus database was identified analogous to MGI/ZFIN disease-model repositories; kaolin-model protocols and strains are documented primarily through the primary literature (Dixon 1932 origin; subsequent refinements reviewed in Zhang et al., FASEB BioAdvances 2024, DOI:10.1096/fba.2024-00070) rather than a centralized public repository.

Summary of Key Evidence Gaps for Curation

  1. Genetic architecture is still emerging (2024 FinnGen GWAS is the largest to date but explains only a fraction of heritability); no clinically actionable genetic test exists.
  2. Population-based prevalence data are ancestry-limited (mostly Nordic/European/Japanese cohorts); global and diverse-ancestry data are sparse.
  3. Randomized-controlled evidence for shunting is very recent (PENS trial) — most historical outcome data are observational/uncontrolled.
  4. Animal models lack a spontaneous, genetically-driven, aging-associated NPH phenocopy — kaolin models are inflammatory/mechanical surrogates, a HUMAN_MODEL_MISMATCH-worthy caveat.
  5. The iNPH–Alzheimer's comorbidity boundary remains biomarker-ambiguous (discordant Aβ/tau CSF profiles), complicating both diagnosis and prognostic biomarker curation.

Sources