Paget Disease of Bone

Complex MONDO:0005382 Pathograph 11 Show in embeddings browser Metabolic Bone Disease

Paget disease of bone is a focal disorder of remodelling. Its defining lesion is the osteoclast: in affected sites the osteoclasts are larger, more numerous and carry far more nuclei than normal, and they resorb bone at a rate the skeleton is not built to sustain. Osteoblasts then respond normally to an abnormal stimulus, laying down bone fast and without organisation, so the resorbed site is replaced by a mosaic of woven and lamellar bone that is expanded, hypervascular and mechanically inferior. Two features make it unlike most metabolic bone disease. It is focal - a germline SQSTM1 variant is present in every cell, yet lesions appear at a handful of sites and characteristically do not cross joints - and it is disappearing. UK standardised incidence fell by roughly two thirds between 1999 and 2015, over a period far too short for the gene pool to have changed. Both observations point the same way: the genetics set susceptibility and something environmental, still unidentified, decides where and whether disease occurs. The therapeutic story contains a genuine surprise, and it is the reason this entry separates the biochemical target from the clinical one. A single 5 mg infusion of zoledronic acid suppresses bone turnover more durably than any earlier bisphosphonate - one relapse in 152 patients over 6.5 years. But when normalising turnover was tested directly against treating symptoms in a 502-patient randomised trial, it produced no reduction in fracture, no fewer orthopaedic procedures, and no better quality of life. Excellent control of the biochemistry is achievable and is not, by itself, the point.

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2
Inheritance
6
Pathophys.
7
Phenotypes
3
Gaps
11
Pathograph
4
Genes
3
Medical Actions
2
Subtypes
1
Models
18
References
1
Deep Research
👪

Inheritance

2
Autosomal dominant with incomplete age-dependent penetrance HP:0000006
Familial clustering is common and SQSTM1-linked families segregate the variant dominantly, but penetrance is incomplete and rises with age, and expressivity varies within families. That variable expressivity is itself part of the argument for an environmental co-factor, since relatives sharing the same allele do not share the same disease.
Autosomal dominant inheritance
Show evidence (1 reference)
PMID:30671590 SUPPORT Human Clinical
"the focal nature of lesions, the decline in prevalence rates, and the incomplete penetrance of the disease among family members suggest that one or more environmental triggers may play a role in the pathophysiology of PDB"
States the incomplete penetrance among family members and the inference drawn from it.
Complex polygenic susceptibility
Beyond the monogenic families, common variants at seven loci - CSF1, OPTN, TNFRSF11A, TM7SF4/DCSTAMP, PML, RIN3 and NUP205 - contribute to risk. Most act on osteoclast differentiation or fusion, which is the same pathway the monogenic causes reach by a different route.
Show evidence (1 reference)
PMID:21623375 SUPPORT Human Clinical
"Here we extended this study, identified three new loci and confirmed their association with PDB in 2,215 affected individuals (cases) and 4,370 controls from seven independent populations."
The association study establishing the common-variant contribution to risk.
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Subtypes

2
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Discussions and Knowledge Gaps

3
What is the environmental exposure whose withdrawal is making Paget disease disappear, and is the paramyxovirus hypothesis dead?
KNOWLEDGE GAP pdb_environmental_trigger_unidentified
Attached to
environmental#Unidentified declining environmental exposure pathophysiology#Focal Accelerated Bone Resorption
Three observations demand an environmental co-factor and none identifies it. Incidence has fallen by roughly two thirds in the UK in sixteen years and similarly elsewhere; lesions are focal despite a germline variant in every cell; and penetrance within SQSTM1 families is incomplete. A purely genetic account explains none of these. The candidate that has absorbed most of the effort is chronic paramyxovirus infection of the osteoclast - measles, RSV or canine distemper virus - and it has not held up. Measles RNA was reported in pagetic osteoclasts by in-situ hybridisation, but PCR failed to find paramyxovirus sequence in pagetic bone, pet ownership was not a risk factor, and a serological study of several hundred patients found no elevation of measles, distemper or RSV antibodies. The weight of evidence is against it. Weaker recent candidates - rural residence and breeding-cattle density, historical domestic coal burning - are ecological correlations without a mechanism. This gap is unusually well posed and unusually urgent, because the exposure is disappearing on its own. Whatever it is, the population of people who encountered it is ageing out, and the natural experiment that could identify it is closing.
Proposed experiments
Birth-cohort exposure reconstruction in declining-incidence populations
pdb_birth_cohort_exposure_reconstruction
Use the steep incidence gradient across birth cohorts in populations with good historical exposure records to test candidate exposures - domestic solid-fuel combustion, livestock contact, childhood infection history - against year and place of birth rather than against current residence, since the relevant exposure is likely to be decades before diagnosis.
Would support
environmental#Unidentified declining environmental exposure
Supporting outcome
  • A candidate exposure whose historical prevalence tracks the birth-cohort incidence gradient in more than one country, with a dose-response relationship.
Refuting outcome
  • No candidate exposure tracks the cohort gradient, which would move the explanation toward a change in diagnostic practice or ascertainment rather than a change in biology.
Show evidence (4 references)
PMID:3701300 SUPPORT Human Clinical
"measles virus RNA sequences were detected not only in 80 to 90% of the multinucleated osteoclasts where there is morphological and immunocytological evidence of measles virus activity but also in 30 to 40% of mononucleated bone cells"
The in-situ hybridisation result that established the paramyxovirus hypothesis, quoted here as the case for it rather than against.
PMID:1805546 REFUTE Human Clinical
"we found no evidence of viral products in RNA extracts of affected bone from 10 consecutive patients with Paget's disease"
The PCR study that failed to reproduce it, using a method the authors showed could detect as few as 50 infected cells.
PMID:2376461 REFUTE Human Clinical
"We conclude that past dog (or cat) ownership is not a risk factor for the development of Paget's disease."
The epidemiological test of the canine distemper route, in 433 cases with matched controls.
+ 1 more reference
Why does suppressing bone turnover so effectively fail to improve fractures, orthopaedic outcomes or quality of life?
KNOWLEDGE GAP pdb_biochemical_remission_is_not_clinical_benefit
Attached to
treatments#Zoledronic Acid treatments#Symptom-Directed Rather Than Turnover-Directed Management
Zoledronic acid does what it is supposed to do: it suppresses the osteoclast, normalises ALP in most patients, and holds that for years. If the pagetic burden were caused by ongoing high turnover, that should translate into fewer fractures and better function. In PRISM-EZ it did not, and the point estimates for fracture and orthopaedic procedures moved the wrong way. The most economical explanation is that the damage is architectural and already done. Once a site has been remodelled into expanded mosaic bone, the mechanical deficit is a property of the tissue, not of the rate at which it is turning over, and stopping the turnover does not restore the architecture. If that is right, the interesting question is not whether to suppress turnover but whether there is an earlier window - before a lesion has remodelled - in which suppression would matter. That has never been tested, because trials enrol patients with established disease and asymptomatic early disease is not systematically identified. A second possibility, harder to exclude, is that suppressed turnover impairs repair of microdamage in already-abnormal bone, which would explain the direction of the non-significant fracture excess rather than dismissing it as noise.
The P394L mouse develops pagetic disease with no environmental trigger, while the human epidemiology says a trigger is doing most of the work. Which is right about human disease?
HUMAN MODEL MISMATCH pdb_mouse_needs_no_trigger_but_humans_seem_to
Attached to
environmental#Unidentified declining environmental exposure animal_models#P394L Sqstm1 knock-in mouse pathophysiology#Focal Accelerated Bone Resorption
This entry rests substantially on an environmental co-factor: incidence fell by two thirds in the UK in sixteen years, lesions are focal despite a germline allele in every cell, and penetrance within SQSTM1 families is incomplete. The mouse says the opposite. P394L knock-in animals develop focal, asymmetric, age-accumulating lesions with giant hypernucleated osteoclasts and no trigger of any kind, and the authors state the conclusion plainly - SQSTM1 mutations can cause a PDB-like disorder in the absence of an additional trigger. Both observations are solid, so the interesting question is what the disagreement is made of. Three readings are open. The first is dose. Murine penetrance is 77% in heterozygotes by 12 months; human SQSTM1 heterozygote penetrance is far lower and later. A laboratory mouse may simply sit above a threshold that most human carriers sit below, in which case the environmental factor is a modifier of penetrance rather than a necessary second hit - which would reconcile the two without either being wrong. The second is that the environmental signal is not about susceptibility at all. Incidence here means *clinically diagnosed* incidence, and it has fallen over exactly the period in which routine biochemistry and imaging changed. Some of the decline could be ascertainment. The counter is that severity fell too - deformity 54% to 13%, fracture 36.7% to 6.7% - and ascertainment drift should make a disease look milder without changing what the severe end looks like. The third is that the mouse models the SQSTM1-driven minority and the environmental factor operates on the sporadic majority, who have no SQSTM1 variant at all. This entry's own genetics section supports that split: SQSTM1 explains a minority of sporadic disease, and the GWAS loci together explain only about 13% of familial risk. Nothing published distinguishes these. Recorded as a mismatch rather than resolved, because the entry's environmental claim has been softened from 'required' to 'strongly implicated' on the strength of the mouse, and that is as far as the evidence goes.
Proposed experiments
Genotype-stratified penetrance against candidate exposures in the P394L model
pdb_p394l_penetrance_under_controlled_exposure
Test whether candidate human exposures modify penetrance and lesion burden in P394L heterozygotes, which is the genotype that matches human carriers. A trigger that raises murine heterozygote lesion burden would support the modifier reading; one that does nothing in a model already at 77% penetrance would show the model is saturated and cannot address the question.
Would support
environmental#Unidentified declining environmental exposure
Supporting outcome
  • Candidate exposure raises lesion burden or lowers age at onset in P394L heterozygotes relative to unexposed littermates, establishing the environmental factor as a penetrance modifier rather than a necessary trigger.
Refuting outcome
  • No exposure alters murine lesion burden, leaving the human epidemiological signal unexplained by anything the model can represent and pointing at ascertainment or at the SQSTM1-negative majority instead.
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Pathophysiology

6
SQSTM1 UBA-Domain Variant Impairs Selective Autophagy
p62/sequestosome-1 uses its UBA domain to bind ubiquitinated cargo, which is how it links that cargo both to autophagic degradation and to NF-kB signalling. UBA-domain variants impair ubiquitin binding, so damaged protein is cleared less efficiently and the NF-kB arm loses a regulator. The consequence is a corruption of two coupled housekeeping functions rather than the loss of a single enzyme activity, which is part of why the resulting disease is focal and late rather than congenital and generalised.
osteoclast precursor CL:0000092 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves osteoclast precursor, annotated with osteoclast (CL:0000092). CL:0000092 is a cell type from the Cell Ontology.
Genetic context SQSTM1 hgnc:11280 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns SQSTM1 (hgnc:11280). hgnc:11280 is a gene from the HUGO Gene Nomenclature Committee.
autophagy GO:0006914 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal autophagy (GO:0006914). GO:0006914 is a biological process from the Gene Ontology. ⚠ ABNORMAL positive regulation of canonical NF-kappaB signal transduction GO:0043123 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased positive regulation of canonical NF-kappaB signal transduction (GO:0043123). GO:0043123 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Osteoclast Precursor Hypersensitivity to RANKL
Show evidence (2 references)
PMID:37180975 SUPPORT Human Clinical
"The p62 protein plays a crucial role in autophagy, a process involved in removing damaged cellular components. When this function is compromised, it can lead to the accumulation of damaged proteins in bone cells."
States the autophagic function of p62 and the consequence of losing it in bone cells.
PMID:37180975 SUPPORT Human Clinical
"Mutations affecting the UBA domain of SQSTM1 have been detected in both familial and sporadic PDB cases"
Localises the disease-causing variants to the UBA domain this node is about.
Osteoclast Precursor Hypersensitivity to RANKL
Osteoclast differentiation is governed by the RANK-RANKL-OPG triad: RANKL from osteoblasts and marrow stroma drives differentiation through RANK on precursors, and OPG restrains it as a decoy receptor. Pagetic precursors are hypersensitive to RANKL, and the susceptibility loci that emerged from association studies sit largely in this pathway - RANK itself, CSF1, and DCSTAMP, which mediates precursor fusion. The most direct evidence that this axis is the disease's centre of gravity comes from a different disease: loss of OPG causes juvenile Paget disease, a generalised recessive disorder of the same remodelling machinery.
osteoclast precursor CL:0000092 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves osteoclast precursor, annotated with osteoclast (CL:0000092). CL:0000092 is a cell type from the Cell Ontology.
positive regulation of osteoclast differentiation GO:0045672 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased positive regulation of osteoclast differentiation (GO:0045672). GO:0045672 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
P394L Sqstm1 knock-in mouse Mouse recapitulates Osteoclast precursors from mutant mice are measurably more sensitive to RANKL than wild-type, and the sensitivity increases further with age - which is what makes this model an explanation for the age-dependence of human penetrance rather than only a phenocopy.
Downstream
Giant Hypernucleated Hyperactive Osteoclasts
Show evidence (2 references)
PMID:37180975 SUPPORT Human Clinical
"OPG, a decoy receptor, binds to RANKL to prevent RANK binding. Thereby, OPG suppresses the differentiation of osteoclasts."
Describes the regulatory triad whose balance this node concerns.
PMID:21623375 SUPPORT Human Clinical
"We previously identified variants at the CSF1, OPTN and TNFRSF11A loci as risk factors for PDB by genome-wide association study."
Places the susceptibility loci in the osteoclast differentiation pathway described here.
Giant Hypernucleated Hyperactive Osteoclasts
The cellular signature of the disease, and the finding that makes a pagetic biopsy recognisable. Osteoclasts at affected sites are larger, more numerous and contain many more nuclei than normal, and they carry characteristic nuclear inclusion bodies. Everything downstream is a consequence of what these cells do; nothing about the osteoblast is primarily abnormal.
multinuclear osteoclast CL:0000779 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves multinuclear osteoclast (CL:0000779). CL:0000779 is a cell type from the Cell Ontology.
Animal models
P394L Sqstm1 knock-in mouse Mouse recapitulates Osteoclasts within murine lesions are larger and more nucleated than normal and some carry the nuclear inclusion bodies seen in human pagetic osteoclasts - the cellular signature of the disease reproduced in full.
Downstream
Focal Accelerated Bone Resorption
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"This results in increased bone remodeling and mass, with the osteoclasts being larger in size, number, and with more nuclei compared to normal cells"
The direct description of the abnormal osteoclast morphology this node names.
Focal Accelerated Bone Resorption
Intense, localised resorption produces the early lytic phase - osteoporosis circumscripta in the skull, and in long bones an advancing flame-shaped lytic front that begins at one end and travels along the shaft. The focality is the part that is still unexplained: the genetic lesion is in every cell, but only a few sites are affected, and lesions do not cross joint spaces.
osteoclast CL:0000092 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves osteoclast (CL:0000092). CL:0000092 is a cell type from the Cell Ontology.
bone resorption GO:0045453 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased bone resorption (GO:0045453). GO:0045453 is a biological process from the Gene Ontology. ↑ INCREASED
bone element UBERON:0001474 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in bone element (UBERON:0001474). UBERON:0001474 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
P394L Sqstm1 knock-in mouse Mouse recapitulates Focal lesions accumulate with age - 77% of heterozygotes and 95% of homozygotes by 12 months against none in wild-type littermates - and predominantly affect the lower limbs asymmetrically, reproducing the focality and asymmetry that a germline allele does not obviously explain.
Downstream
Disorganised Compensatory Bone Formation
Show evidence (1 reference)
PMID:30671590 SUPPORT Human Clinical
"characterized by increased osteoclast-mediated bone resorption and a subsequent compensatory increase in bone formation"
States the resorption step and its temporal relationship to the formation step that follows.
Disorganised Compensatory Bone Formation
Osteoblasts respond to the resorption by forming bone rapidly and without the normal lamellar organisation. The result is the mosaic of woven and lamellar bone with irregular cement lines that is the pathological signature. The osteoblast is behaving normally here - it is coupling to resorption as it should - which is why the disease is properly described as osteoclast-driven rather than as a disorder of formation.
osteoblast CL:0000062 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves osteoblast (CL:0000062). CL:0000062 is a cell type from the Cell Ontology.
ossification GO:0001503 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased ossification (GO:0001503). GO:0001503 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Expanded Structurally Weak Hypervascular Bone
Show evidence (1 reference)
PMID:30671590 SUPPORT Human Clinical
"a subsequent compensatory increase in bone formation, resulting in a disorganized mosaic of woven and lamellar bone at one or more affected skeletal sites"
Describes both the compensatory formation and the mosaic tissue architecture it produces.
Expanded Structurally Weak Hypervascular Bone
The remodelled bone is enlarged in diameter, mechanically inferior and highly vascular. That combination generates the entire clinical burden: pain, bowing deformity of weight-bearing long bones, secondary osteoarthritis at adjacent joints, pathological fracture, cranial nerve compression with hearing loss where the skull is involved, and - in extensive polyostotic disease - a high-output cardiac state from the vascularity. Rarely the same site undergoes neoplastic transformation.
bony pelvis UBERON:0001270 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in bony pelvis (UBERON:0001270). UBERON:0001270 is an anatomical location from the Uberon multi-species anatomy ontology. femur UBERON:0000981 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in femur (UBERON:0000981). UBERON:0000981 is an anatomical location from the Uberon multi-species anatomy ontology. cranium UBERON:0003128 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in cranium (UBERON:0003128). UBERON:0003128 is an anatomical location from the Uberon multi-species anatomy ontology. vertebral column UBERON:0001130 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in vertebral column (UBERON:0001130). UBERON:0001130 is an anatomical location from the Uberon multi-species anatomy ontology.
Show evidence (3 references)
PMID:30671590 SUPPORT Human Clinical
"As a result, bone pain, noticeable deformities, arthritis at adjacent joints, and fractures can occur."
Enumerates the clinical consequences that follow from the abnormal bone at this node.
PMID:37180975 SUPPORT Human Clinical
"The disorder predominantly affects the axial skeleton, with the highest incidence observed in the pelvis (70%), femur (55%), lumbar spine (53%), cranium (42%), and tibia (32%)."
Gives the skeletal distribution recorded in this node's locations.
PMID:30671590 SUPPORT Human Clinical
"In a small proportion of cases neoplastic degeneration in osteosarcoma, or, less frequently, giant cell tumor has been also described at PDB sites."
Establishes neoplastic transformation as an outcome arising at pagetic sites.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Paget Disease of Bone 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

7
Ear 1
Hearing Impairment FREQUENT HP:0000365 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hearing impairment (HP:0000365). HP:0000365 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36858336 SUPPORT Human Clinical
"hearing impairment (51.9 % vs. 61.1 %; p = 0.1000)"
The reported hearing impairment frequencies.
Limbs 1
Bone Deformity OCCASIONAL Bowing of the long bones HP:0006487 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bowing of the long bones (HP:0006487). HP:0006487 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36858336 SUPPORT Human Clinical
"lower bone deformities (13.0 % vs. 54.0 %; p < 0.0001)"
The contemporary and historical deformity frequencies this record is based on.
Musculoskeletal 2
Secondary Osteoarthritis FREQUENT HP:0002758 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Osteoarthritis (HP:0002758). HP:0002758 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36858336 SUPPORT Human Clinical
"secondary osteoarthritis (43.0 % vs. 51.6 %; p = 1.0000)"
The frequencies in both cohorts, and the absence of a significant decline.
Sarcomatous Transformation VERY_RARE Osteosarcoma HP:0002669 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Osteosarcoma (HP:0002669). HP:0002669 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:17550323 SUPPORT Human Clinical
"Most tumors were osteosarcomas (88%). All tumors were high grade."
Establishes the histology and grade of the tumours arising in pagetic bone.
PMID:17550323 SUPPORT Human Clinical
"Survival ranged from 1 month to 20 years, with a 5-year survival rate of 10%."
The survival figure quoted in this entry.
PMID:17550323 SUPPORT Human Clinical
"There is no significant correlation between the number of bones involved with Paget disease or the duration of disease and development of Paget sarcoma."
The negative result behind this entry's statement that sarcoma risk is not predictable from disease burden.
Constitutional 1
Pagetic Bone Pain FREQUENT HP:0002653 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bone pain (HP:0002653). HP:0002653 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36858336 SUPPORT Human Clinical
"There was no significant difference for pagetic bone pain (52.0 % vs. 52.6 %; p = 1.0000)"
Gives the frequency in both cohorts and, in doing so, shows pain did not decline with the rest of the phenotype.
Other 2
Elevated Serum Alkaline Phosphatase FREQUENT Elevated circulating alkaline phosphatase concentration HP:0003155 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating alkaline phosphatase concentration (HP:0003155). HP:0003155 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"In around 70% of patients, PDB is asymptomatic and is typically discovered incidentally through elevated alkaline phosphatase (ALP) values"
Establishes both the asymptomatic majority and ALP elevation as the route to detection.
Pathological Fracture OCCASIONAL Increased susceptibility to fractures HP:0002659 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Increased susceptibility to fractures (HP:0002659). HP:0002659 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36858336 SUPPORT Human Clinical
"lower pagetic bone fractures (6.7 % vs. 36.7 %; p = 0.0078)"
The fracture frequencies in the two cohorts.
🧬

Genetic Associations

4
SQSTM1
Gene: SQSTM1 hgnc:11280 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SQSTM1 (hgnc:11280). hgnc:11280 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"PDB has a complex genetic basis involving multiple genes, with SQSTM1 being the gene most frequently associated with its development."
Establishes SQSTM1 as the principal gene.
ZNF687
Gene: ZNF687 hgnc:29277 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is ZNF687 (hgnc:29277). hgnc:29277 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (1 reference)
PMID:30671590 SUPPORT Human Clinical
"It is now clear that PDB is a genetically heterogeneous disorder, with mutations in at least two different genes (SQSTM1, ZNF687) and more common predisposing variants."
Names ZNF687 alongside SQSTM1 as an established causal gene.
TNFRSF11A
Gene: TNFRSF11A hgnc:11908 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is TNFRSF11A (hgnc:11908). hgnc:11908 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: SUSCEPTIBILITY
Show evidence (1 reference)
PMID:21623375 SUPPORT Human Clinical
"We previously identified variants at the CSF1, OPTN and TNFRSF11A loci as risk factors for PDB by genome-wide association study."
The association result establishing TNFRSF11A as a susceptibility locus.
PFN1
Gene: PFN1 hgnc:8881 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PFN1 (hgnc:8881). hgnc:8881 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"Germline mutations in other genes such as TNFRSF11A, ZNF687 and PFN1, have also been associated with the development of the disease."
Names PFN1 among the germline causes.
💊

Medical Actions

3
Zoledronic Acid
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: zoledronic acid CHEBI:46557 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses zoledronic acid (CHEBI:46557). CHEBI:46557 is a therapeutic agent from Chemical Entities of Biological Interest.
A single 5 mg intravenous infusion, and the most effective bisphosphonate tested in this disease by a wide margin. Therapeutic response was 97% against 45% for pamidronate in a head-to-head randomised comparison, and over 6.5 years of follow-up without retreatment relapse occurred in 1 of 152 patients given zoledronate against 23 of 115 given risedronate.
Mechanism Target:
INHIBITS Giant Hypernucleated Hyperactive Osteoclasts — Acts on the osteoclast directly, which is why it works so well on the biochemistry - it targets the cell that drives the whole pathograph.
Show evidence (2 references)
PMID:17605632 SUPPORT Human Clinical
"At 6 mo, 97% of patients receiving zoledronate had a therapeutic response compared with 45% of patients receiving pamidronate."
The head-to-head randomised comparison behind the response figures quoted here.
PMID:21638319 SUPPORT Human Clinical
"Relapse rates were substantially greater in the risedronate group (23 of 115, 20%) than in those treated with zoledronic acid (1 of 152, 0.7%, p < .001)"
The long-term durability result quoted in this entry.
Neridronate
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
An alternative aminobisphosphonate, and the practically useful thing about it is the route: a 200 mg course given intramuscularly performed as well as the same dose intravenously - 96.5% versus 92.6% therapeutic response at 6 months - which matters for patients who cannot or will not have an infusion. Response was not durable in the way a single zoledronic acid infusion is; it held at 12 months and fell progressively at 24 and 36.
Mechanism Target:
INHIBITS Giant Hypernucleated Hyperactive Osteoclasts — Same osteoclast target as zoledronic acid, with a different administration route and a shorter duration of effect.
Show evidence (2 references)
PMID:20814970 SUPPORT Human Clinical
"At 6 months, 92.6% and 96.5% of patients receiving intravenous and intramuscular neridronate, respectively, achieved a therapeutic response"
The head-to-head route comparison behind the response figures quoted here.
PMID:20814970 SUPPORT Human Clinical
"Response rates were maintained at 12 months but decreased progressively at 24 and 36 months without significant differences between the two neridronate regimens"
The durability limitation that distinguishes neridronate from a single zoledronic acid infusion.
Symptom-Directed Rather Than Turnover-Directed Management
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
This is a treatment-strategy entry rather than an agent, because the strategy question has been answered directly and the answer is counterintuitive. The PRISM-EZ trial randomised 502 patients to intensive bisphosphonate therapy aimed at normalising bone turnover versus bisphosphonates given only for pain. Intensive treatment achieved markedly better biochemistry and produced no reduction in fracture, no fewer orthopaedic procedures, and no better quality of life - with a non-significant increase in fractures, orthopaedic events and serious adverse events. In established disease, therefore, the target is symptoms, not the ALP.
Mechanism Target:
MODULATES Expanded Structurally Weak Hypervascular Bone — Addresses the clinical consequences of the abnormal bone rather than the remodelling rate that produces it.
Show evidence (2 references)
PMID:28176386 SUPPORT Human Clinical
"There were no clinically important differences in quality of life measures or bone pain between the treatment groups."
The primary comparative result on symptoms and quality of life.
PMID:28176386 SUPPORT Human Clinical
"The results of this study suggest that in patients with established PDB, bisphosphonate therapy should focus on control of symptoms rather than suppression of bone turnover."
The trial's own conclusion, which is the strategy this entry records.
🌍

Environmental Factors

1
Unidentified declining environmental exposure
No exposure_term is bound because the exposure is not identified. ECTO cannot represent "an unknown environmental determinant", and binding a speculative term (a paramyxovirus exposure, coal smoke, livestock contact) would assert something the evidence does not support.
Something environmental is strongly implicated, and it is going away. Standardised UK incidence fell from 0.75 to 0.20 per 10,000 person-years between 1999 and 2015 - far too fast to be genetic drift - and the same decline has been reported in other countries. Together with the focality of lesions and the incomplete penetrance within families, that is the case for an environmental co-factor acting on a genetically susceptible osteoclast lineage. Its identity is unknown. This entry says "strongly implicated" rather than "required" on purpose. The P394L Sqstm1 knock-in mouse develops a PDB-like focal skeletal disorder with no additional trigger, which is direct evidence against strict necessity. The human epidemiology and the mouse disagree, and the disagreement is recorded as a HUMAN_MODEL_MISMATCH discussion rather than resolved in favour of either. The long-standing paramyxovirus hypothesis is discussed separately and is not currently supported.
Show evidence (2 references)
PMID:33742666 SUPPORT Human Clinical
"The reason for the decline in incidence remains unknown, although the rapidity of change points to an alteration in one or more environmental determinants."
The epidemiological argument for an environmental determinant, and for its being unidentified.
PMID:33742666 SUPPORT Human Clinical
"The overall standardized incidence decreased from 0.75/10 000 person-years in 1999 to 0.20/10 000 person-years in 2015."
Quantifies the decline this entry rests on.
Mechanism Target:
TRIGGERS Osteoclast Precursor Hypersensitivity to RANKL — Modelled as a co-factor that converts inherited susceptibility into focal disease. The link is inferred from epidemiology and penetrance, not from a demonstrated exposure-to-osteoclast mechanism, and the target is the pathway the genetics implicate rather than a measured one. It is not modelled as necessary: see the HUMAN_MODEL_MISMATCH discussion for the mouse evidence against that.
Show evidence (1 reference)
PMID:30671590 SUPPORT Human Clinical
"The exact nature of these triggers and how they might interact with the genetic factors are less understood"
PARTIAL by design - the source states that the interaction between trigger and genotype is not understood, which is precisely the strength this link should carry.
🔬

Diagnosis

3
Plain Radiography
The primary diagnostic modality. Radiographs show cortical thickening, coarse trabeculation, bone expansion, osteoporosis circumscripta in the skull and the flame-shaped advancing lytic front in long bones. Guidelines pair it with serum ALP for initial diagnosis and reserve the radionuclide scan for mapping extent - so the X-ray characterises the lesion and the scan counts the lesions.
X-ray imaging NCIT:C38101 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:32803929 SUPPORT Other
"Evidence-based guidelines recommend the use of plain radiography and serum alkaline phosphatase testing for initial diagnosis and radionuclide scans for delineation of the extent of disease."
States the guideline-recommended division of labour between radiography, ALP and scintigraphy that this entry follows.
PMID:31574000 SUPPORT Other
"Diagnosis is through plain film imaging, with radionuclide bone scan to determine the extent."
The second guideline review, agreeing that plain film imaging is the diagnostic modality.
Serum Total Alkaline Phosphatase
The first-line biochemical test, used both to detect disease and to follow activity. Not specific - it rises in liver disease and pregnancy, so bone-specific ALP is used where those confound - and not perfectly sensitive, since limited monostotic disease can be biochemically silent.
laboratory procedure NCIT:C25294 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"However, ALP levels can also be elevated in other conditions, such as liver disease or during pregnancy, making additional tests necessary for diagnosis confirmation"
States the specificity limitation that this entry describes.
Radionuclide Bone Scintigraphy
Technetium-99m bone scan, used after diagnosis to map the full extent of skeletal involvement. It answers a different question from the radiograph: the X-ray characterises a lesion, the scan finds the others.
radionuclide imaging NCIT:C62667 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"A set of plain X-rays and bone scintigraphy are used to evaluate PDB, but bone scintigraphy may be negative in some cases."
PARTIAL because the source establishes scintigraphy's role in evaluation while noting it can be falsely negative, rather than reporting a sensitivity figure for extent mapping.
📊

Prevalence

2
Worldwide
Point Prevalence 1500.0 per 100,000 (1500.0–8300.0) >1 in 1,000
Reported as a 1.5%-8.3% prevalence range, normalised here to 1,500-8,300 per 100,000 with the lower bound as the point estimate. The range is wide because it spans populations with very different risk - highest in the UK and in populations of British descent, low in Scandinavia, Africa and Asia - so a single worldwide figure is not really meaningful and this record should be read as an upper-bound envelope rather than an estimate.
Show evidence (1 reference)
PMID:37180975 SUPPORT Human Clinical
"Paget's disease of bone (PDB) is the second most prevalent metabolic bone disorder worldwide, with a prevalence rate of 1.5%-8.3%."
The prevalence range this record normalises.
United Kingdom
Annual Incidence 2.0 per 100,000 1–9 per 100,000
Standardised incidence of 0.20 per 10,000 person-years in 2015, normalised to 2.0 per 100,000 per year. The 1999 figure was 0.75 per 10,000, so this record captures a moving quantity - which is the point of including it.
Show evidence (1 reference)
PMID:33742666 SUPPORT Human Clinical
"The overall standardized incidence decreased from 0.75/10 000 person-years in 1999 to 0.20/10 000 person-years in 2015."
The incidence figures this record normalises.
🐁

Animal Models

1
P394L Sqstm1 knock-in mouse
The murine equivalent of the human SQSTM1 p.Pro392Leu allele, and the model that carries most of the mechanistic weight in this disease. It reproduces the focal, asymmetric, age-accumulating lesions of human PDB, the giant hypernucleated osteoclasts with nuclear inclusions, the RANKL hypersensitivity of osteoclast precursors, and the autophagy dysregulation - four of this entry's six nodes, in one model. It is also the source of this entry's most awkward evidence. Human PDB is focal and its incidence is falling, which argues for an environmental co-factor; this mouse develops the disease with no trigger at all. See the HUMAN_MODEL_MISMATCH discussion.
Species
Mouse
Genotype
Sqstm1 p.Pro394Leu knock-in, heterozygous and homozygous
Publication
PMID:21515589
Pathograph links
Osteoclast Precursor Hypersensitivity to RANKL recapitulates fidelity: high Osteoclast precursors from mutant mice are measurably more sensitive to RANKL than wild-type, and the sensitivity increases further with age - which is what makes this model an explanation for the age-dependence of human penetrance rather than only a phenocopy.
Limitations: The sensitivity is measured in vitro on precursors from the mouse, so it establishes a cell-autonomous property of the mutant lineage rather than the in vivo trigger sequence.
Readouts
Osteoclastogenesis from precursors at fixed RANKL
Direction: INCREASED
Interpretation: Increased relative to wild-type and increasing with age in both genotypes, which is the age-penetrance link.
Show evidence (1 reference)
PMID:30154079 SUPPORT Model Organism
"p62P394L+/+ osteoclast precursors had increased sensitivity to RANKL (also known as TNFSF11) compared with wild-type (WT) cells, and the sensitivity further increased in both genotypes with ageing."
The quantitative RANKL-sensitivity measurement and its age dependence.
Show evidence (1 reference)
PMID:21515589 SUPPORT Model Organism
"Osteoclast precursors from P394L mutant mice had increased sensitivity to RANKL in vitro resulting in the generation of osteoclasts that were larger and more nucleated than those generated from wild-type littermates."
Establishes the model as informative for this node, and links precursor hypersensitivity directly to the hypernucleated osteoclast phenotype downstream.
Giant Hypernucleated Hyperactive Osteoclasts recapitulates fidelity: high Osteoclasts within murine lesions are larger and more nucleated than normal and some carry the nuclear inclusion bodies seen in human pagetic osteoclasts - the cellular signature of the disease reproduced in full.
Limitations: Inclusion bodies are reported in some but not all lesional osteoclasts, as in humans; the model does not resolve what they are.
Show evidence (1 reference)
PMID:21515589 SUPPORT Model Organism
"Osteoclasts within lesions were larger and more nucleated than normal and some contained nuclear inclusions similar to those observed in human PDB."
The cellular phenotype matching the human disease, including the inclusion bodies.
Focal Accelerated Bone Resorption recapitulates fidelity: moderate Focal lesions accumulate with age - 77% of heterozygotes and 95% of homozygotes by 12 months against none in wild-type littermates - and predominantly affect the lower limbs asymmetrically, reproducing the focality and asymmetry that a germline allele does not obviously explain.
Limitations: Penetrance is far higher than in human heterozygotes, and the lesion distribution is limb-predominant rather than matching the human axial preference for pelvis, spine and skull.
Readouts
Proportion of animals with focal bone lesions at 12 months
Direction: INCREASED
Interpretation: Genotype-dependent and age-dependent lesion development against a zero wild-type baseline.
Show evidence (1 reference)
PMID:21515589 SUPPORT Model Organism
"The P394L mutant mice developed focal bone lesions with increasing age and by 12 months, 14/18 (77%) heterozygotes and 20/21 (95%) homozygotes had lesions, compared with 0/18 (0%) wild-type littermates (P< 0.001)."
The lesion counts by genotype and age.
Show evidence (1 reference)
PMID:21515589 SUPPORT Model Organism
"mice with a proline to leucine mutation at codon 394 of mouse sqstm1 (P394L), equivalent to the P392L SQSTM1 mutation in humans, develop a bone disorder with remarkable similarity to PDB"
Establishes the allele equivalence and the overall phenotypic correspondence that makes this model informative.
Show evidence (1 reference)
PMID:30154079 SUPPORT Model Organism
"ZA prevented the development of pagetic-like lesions, and increased trabecular bone volume tenfold compared with vehicle by 12 months of age (P<0.01)."
A treatment result in the model that joins the pathograph to the treatment section: zoledronic acid prevents lesion development, which is the mechanistic counterpart of its biochemical effect in humans.
{ }

Source YAML

click to show 
name: Paget Disease of Bone
creation_date: '2026-08-28T22:30:00Z'
category: Complex
description: 'Paget disease of bone is a focal disorder of remodelling. Its defining lesion is the osteoclast:
  in affected sites the osteoclasts are larger, more numerous and carry far more nuclei than normal, and they
  resorb bone at a rate the skeleton is not built to sustain. Osteoblasts then respond normally to an abnormal
  stimulus, laying down bone fast and without organisation, so the resorbed site is replaced by a mosaic of
  woven and lamellar bone that is expanded, hypervascular and mechanically inferior.

  Two features make it unlike most metabolic bone disease. It is focal - a germline SQSTM1 variant is present
  in every cell, yet lesions appear at a handful of sites and characteristically do not cross joints - and
  it is disappearing. UK standardised incidence fell by roughly two thirds between 1999 and 2015, over a period
  far too short for the gene pool to have changed. Both observations point the same way: the genetics set susceptibility
  and something environmental, still unidentified, decides where and whether disease occurs.

  The therapeutic story contains a genuine surprise, and it is the reason this entry separates the biochemical
  target from the clinical one. A single 5 mg infusion of zoledronic acid suppresses bone turnover more durably
  than any earlier bisphosphonate - one relapse in 152 patients over 6.5 years. But when normalising turnover
  was tested directly against treating symptoms in a 502-patient randomised trial, it produced no reduction
  in fracture, no fewer orthopaedic procedures, and no better quality of life. Excellent control of the biochemistry
  is achievable and is not, by itself, the point.'
disease_term:
  preferred_term: bone Paget disease
  term:
    id: MONDO:0005382
    label: bone Paget disease
synonyms:
- osteitis deformans
- Paget's disease of bone
- Paget disease of bone
- PDB
parents:
- Metabolic Bone Disease
has_subtypes:
- name: SQSTM1-related
  display_name: SQSTM1/p62-related Paget disease (PDB2)
  description: The commonest genetic form. Variants affect the ubiquitin-associated (UBA) domain of SQSTM1,
    recurrently p.Pro392Leu, and are found in both familial and sporadic disease. They are associated with
    more severe and more extensive clinical expression than sporadic disease without an identified variant.
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mutations affecting the UBA domain of SQSTM1 have been detected in both familial and sporadic
      PDB cases, and these mutations are often associated with severe clinical expression.
    explanation: Establishes the UBA-domain localisation and the severity association that define this subtype.
  subtype_term:
    preferred_term: Paget disease of bone 2, early-onset
    term:
      id: MONDO:0011183
      label: Paget disease of bone 2, early-onset
- name: ZNF687-related
  display_name: ZNF687-related Paget disease (PDB6)
  description: A rarer germline cause associated with severe, early-onset, polyostotic disease and a predisposition
    to giant cell tumour arising in pagetic bone.
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Germline mutations in other genes such as TNFRSF11A, ZNF687 and PFN1, have also been associated
      with the development of the disease.
    explanation: Names ZNF687 among the established germline causes beyond SQSTM1.
  subtype_term:
    preferred_term: Paget disease of bone 6
    term:
      id: MONDO:0014792
      label: Paget disease of bone 6
inheritance:
- name: Autosomal dominant with incomplete age-dependent penetrance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: Familial clustering is common and SQSTM1-linked families segregate the variant dominantly, but
    penetrance is incomplete and rises with age, and expressivity varies within families. That variable expressivity
    is itself part of the argument for an environmental co-factor, since relatives sharing the same allele
    do not share the same disease.
  evidence:
  - reference: PMID:30671590
    reference_title: Paget's Disease of Bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the focal nature of lesions, the decline in prevalence rates, and the incomplete penetrance of
      the disease among family members suggest that one or more environmental triggers may play a role in the
      pathophysiology of PDB
    explanation: States the incomplete penetrance among family members and the inference drawn from it.
- name: Complex polygenic susceptibility
  description: Beyond the monogenic families, common variants at seven loci - CSF1, OPTN, TNFRSF11A, TM7SF4/DCSTAMP,
    PML, RIN3 and NUP205 - contribute to risk. Most act on osteoclast differentiation or fusion, which is the
    same pathway the monogenic causes reach by a different route.
  evidence:
  - reference: PMID:21623375
    reference_title: Genome-wide association identifies three new susceptibility loci for Paget's disease of
      bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here we extended this study, identified three new loci and confirmed their association with PDB
      in 2,215 affected individuals (cases) and 4,370 controls from seven independent populations.
    explanation: The association study establishing the common-variant contribution to risk.
pathophysiology:
- name: SQSTM1 UBA-Domain Variant Impairs Selective Autophagy
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: p62/sequestosome-1 uses its UBA domain to bind ubiquitinated cargo, which is how it links that
    cargo both to autophagic degradation and to NF-kB signalling. UBA-domain variants impair ubiquitin binding,
    so damaged protein is cleared less efficiently and the NF-kB arm loses a regulator. The consequence is
    a corruption of two coupled housekeeping functions rather than the loss of a single enzyme activity, which
    is part of why the resulting disease is focal and late rather than congenital and generalised.
  genetic_context:
    gene:
      preferred_term: SQSTM1
      term:
        id: hgnc:11280
        label: SQSTM1
  biological_processes:
  - preferred_term: autophagy
    modifier: ABNORMAL
    term:
      id: GO:0006914
      label: autophagy
  - preferred_term: positive regulation of canonical NF-kappaB signal transduction
    modifier: INCREASED
    term:
      id: GO:0043123
      label: positive regulation of canonical NF-kappaB signal transduction
  cell_types:
  - preferred_term: osteoclast precursor
    term:
      id: CL:0000092
      label: osteoclast
  downstream:
  - target: Osteoclast Precursor Hypersensitivity to RANKL
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The p62 protein plays a crucial role in autophagy, a process involved in removing damaged cellular
      components. When this function is compromised, it can lead to the accumulation of damaged proteins in
      bone cells.
    explanation: States the autophagic function of p62 and the consequence of losing it in bone cells.
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mutations affecting the UBA domain of SQSTM1 have been detected in both familial and sporadic
      PDB cases
    explanation: Localises the disease-causing variants to the UBA domain this node is about.
- name: Osteoclast Precursor Hypersensitivity to RANKL
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: 'Osteoclast differentiation is governed by the RANK-RANKL-OPG triad: RANKL from osteoblasts
    and marrow stroma drives differentiation through RANK on precursors, and OPG restrains it as a decoy receptor.
    Pagetic precursors are hypersensitive to RANKL, and the susceptibility loci that emerged from association
    studies sit largely in this pathway - RANK itself, CSF1, and DCSTAMP, which mediates precursor fusion.
    The most direct evidence that this axis is the disease''s centre of gravity comes from a different disease:
    loss of OPG causes juvenile Paget disease, a generalised recessive disorder of the same remodelling machinery.'
  biological_processes:
  - preferred_term: positive regulation of osteoclast differentiation
    modifier: INCREASED
    term:
      id: GO:0045672
      label: positive regulation of osteoclast differentiation
  cell_types:
  - preferred_term: osteoclast precursor
    term:
      id: CL:0000092
      label: osteoclast
  downstream:
  - target: Giant Hypernucleated Hyperactive Osteoclasts
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: OPG, a decoy receptor, binds to RANKL to prevent RANK binding. Thereby, OPG suppresses the differentiation
      of osteoclasts.
    explanation: Describes the regulatory triad whose balance this node concerns.
  - reference: PMID:21623375
    reference_title: Genome-wide association identifies three new susceptibility loci for Paget's disease of
      bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We previously identified variants at the CSF1, OPTN and TNFRSF11A loci as risk factors for PDB
      by genome-wide association study.
    explanation: Places the susceptibility loci in the osteoclast differentiation pathway described here.
- name: Giant Hypernucleated Hyperactive Osteoclasts
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: The cellular signature of the disease, and the finding that makes a pagetic biopsy recognisable.
    Osteoclasts at affected sites are larger, more numerous and contain many more nuclei than normal, and they
    carry characteristic nuclear inclusion bodies. Everything downstream is a consequence of what these cells
    do; nothing about the osteoblast is primarily abnormal.
  cell_types:
  - preferred_term: multinuclear osteoclast
    term:
      id: CL:0000779
      label: multinuclear osteoclast
  downstream:
  - target: Focal Accelerated Bone Resorption
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This results in increased bone remodeling and mass, with the osteoclasts being larger in size,
      number, and with more nuclei compared to normal cells
    explanation: The direct description of the abnormal osteoclast morphology this node names.
- name: Focal Accelerated Bone Resorption
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: 'Intense, localised resorption produces the early lytic phase - osteoporosis circumscripta in
    the skull, and in long bones an advancing flame-shaped lytic front that begins at one end and travels along
    the shaft. The focality is the part that is still unexplained: the genetic lesion is in every cell, but
    only a few sites are affected, and lesions do not cross joint spaces.'
  biological_processes:
  - preferred_term: bone resorption
    modifier: INCREASED
    term:
      id: GO:0045453
      label: bone resorption
  cell_types:
  - preferred_term: osteoclast
    term:
      id: CL:0000092
      label: osteoclast
  locations:
  - preferred_term: bone element
    term:
      id: UBERON:0001474
      label: bone element
  downstream:
  - target: Disorganised Compensatory Bone Formation
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:30671590
    reference_title: Paget's Disease of Bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: characterized by increased osteoclast-mediated bone resorption and a subsequent compensatory increase
      in bone formation
    explanation: States the resorption step and its temporal relationship to the formation step that follows.
- name: Disorganised Compensatory Bone Formation
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: Osteoblasts respond to the resorption by forming bone rapidly and without the normal lamellar
    organisation. The result is the mosaic of woven and lamellar bone with irregular cement lines that is the
    pathological signature. The osteoblast is behaving normally here - it is coupling to resorption as it should
    - which is why the disease is properly described as osteoclast-driven rather than as a disorder of formation.
  biological_processes:
  - preferred_term: ossification
    modifier: INCREASED
    term:
      id: GO:0001503
      label: ossification
  cell_types:
  - preferred_term: osteoblast
    term:
      id: CL:0000062
      label: osteoblast
  downstream:
  - target: Expanded Structurally Weak Hypervascular Bone
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:30671590
    reference_title: Paget's Disease of Bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: a subsequent compensatory increase in bone formation, resulting in a disorganized mosaic of woven
      and lamellar bone at one or more affected skeletal sites
    explanation: Describes both the compensatory formation and the mosaic tissue architecture it produces.
- name: Expanded Structurally Weak Hypervascular Bone
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: 'The remodelled bone is enlarged in diameter, mechanically inferior and highly vascular. That
    combination generates the entire clinical burden: pain, bowing deformity of weight-bearing long bones,
    secondary osteoarthritis at adjacent joints, pathological fracture, cranial nerve compression with hearing
    loss where the skull is involved, and - in extensive polyostotic disease - a high-output cardiac state
    from the vascularity. Rarely the same site undergoes neoplastic transformation.'
  locations:
  - preferred_term: bony pelvis
    term:
      id: UBERON:0001270
      label: bony pelvis
  - preferred_term: femur
    term:
      id: UBERON:0000981
      label: femur
  - preferred_term: cranium
    term:
      id: UBERON:0003128
      label: cranium
  - preferred_term: vertebral column
    term:
      id: UBERON:0001130
      label: vertebral column
  evidence:
  - reference: PMID:30671590
    reference_title: Paget's Disease of Bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: As a result, bone pain, noticeable deformities, arthritis at adjacent joints, and fractures can
      occur.
    explanation: Enumerates the clinical consequences that follow from the abnormal bone at this node.
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The disorder predominantly affects the axial skeleton, with the highest incidence observed in
      the pelvis (70%), femur (55%), lumbar spine (53%), cranium (42%), and tibia (32%).
    explanation: Gives the skeletal distribution recorded in this node's locations.
  - reference: PMID:30671590
    reference_title: Paget's Disease of Bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In a small proportion of cases neoplastic degeneration in osteosarcoma, or, less frequently, giant
      cell tumor has been also described at PDB sites.
    explanation: Establishes neoplastic transformation as an outcome arising at pagetic sites.
phenotypes:
- category: Musculoskeletal
  name: Pagetic Bone Pain
  frequency: FREQUENT
  description: The commonest symptom when the disease is symptomatic at all, reported by about half of patients.
    Notably it is the one clinical feature that has not become less common as the disease has otherwise grown
    milder.
  phenotype_term:
    preferred_term: Bone pain
    term:
      id: HP:0002653
      label: Bone pain
  evidence:
  - reference: PMID:36858336
    reference_title: 'Decline in clinical severity of Paget''s disease of bone: Comparison between a contemporary
      cohort and a historical cohort.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: There was no significant difference for pagetic bone pain (52.0 % vs. 52.6 %; p = 1.0000)
    explanation: Gives the frequency in both cohorts and, in doing so, shows pain did not decline with the
      rest of the phenotype.
- category: Laboratory
  name: Elevated Serum Alkaline Phosphatase
  frequency: FREQUENT
  description: 'The biochemical hallmark and the usual route to diagnosis, since around 70% of patients are
    asymptomatic and come to attention through an incidental ALP elevation. Recorded as FREQUENT rather than
    VERY_FREQUENT deliberately: the cited source counts how patients are *detected*, not what fraction have
    a raised ALP, and this entry''s own diagnosis section notes that limited monostotic disease - 60.5% of
    a contemporary cohort - can be biochemically silent. No reviewed source counts the proportion with an elevated
    ALP directly.'
  phenotype_term:
    preferred_term: Elevated circulating alkaline phosphatase concentration
    term:
      id: HP:0003155
      label: Elevated circulating alkaline phosphatase concentration
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In around 70% of patients, PDB is asymptomatic and is typically discovered incidentally through
      elevated alkaline phosphatase (ALP) values
    explanation: Establishes both the asymptomatic majority and ALP elevation as the route to detection.
- category: Musculoskeletal
  name: Bone Deformity
  frequency: OCCASIONAL
  description: 'Bowing of weight-bearing long bones, skull enlargement and kyphosis. This is among the features
    that has declined most sharply: 13% of a contemporary Quebec cohort versus 54% of the historical one.'
  phenotype_term:
    preferred_term: Bowing of the long bones
    term:
      id: HP:0006487
      label: Bowing of the long bones
  evidence:
  - reference: PMID:36858336
    reference_title: 'Decline in clinical severity of Paget''s disease of bone: Comparison between a contemporary
      cohort and a historical cohort.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: lower bone deformities (13.0 % vs. 54.0 %; p < 0.0001)
    explanation: The contemporary and historical deformity frequencies this record is based on.
- category: Musculoskeletal
  name: Pathological Fracture
  frequency: OCCASIONAL
  description: Fracture through structurally inferior pagetic bone, most often in a weight-bearing long bone.
    Reported in 6.7% of a contemporary cohort against 36.7% historically.
  phenotype_term:
    preferred_term: Increased susceptibility to fractures
    term:
      id: HP:0002659
      label: Increased susceptibility to fractures
  evidence:
  - reference: PMID:36858336
    reference_title: 'Decline in clinical severity of Paget''s disease of bone: Comparison between a contemporary
      cohort and a historical cohort.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: lower pagetic bone fractures (6.7 % vs. 36.7 %; p = 0.0078)
    explanation: The fracture frequencies in the two cohorts.
- category: Musculoskeletal
  name: Secondary Osteoarthritis
  frequency: FREQUENT
  description: Degenerative change in joints adjacent to pagetic bone, from altered joint mechanics rather
    than from disease within the joint itself. Around 43-52% of patients, and unlike deformity and fracture
    it has not declined.
  phenotype_term:
    preferred_term: Osteoarthritis
    term:
      id: HP:0002758
      label: Osteoarthritis
  evidence:
  - reference: PMID:36858336
    reference_title: 'Decline in clinical severity of Paget''s disease of bone: Comparison between a contemporary
      cohort and a historical cohort.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: secondary osteoarthritis (43.0 % vs. 51.6 %; p = 1.0000)
    explanation: The frequencies in both cohorts, and the absence of a significant decline.
- category: Otologic
  name: Hearing Impairment
  frequency: FREQUENT
  description: Hearing loss when the skull is involved, from a combination of cranial nerve compression and
    changes in the otic capsule. Reported in about half to two-thirds of patients in cohorts where skull disease
    is present.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:36858336
    reference_title: 'Decline in clinical severity of Paget''s disease of bone: Comparison between a contemporary
      cohort and a historical cohort.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: hearing impairment (51.9 % vs. 61.1 %; p = 0.1000)
    explanation: The reported hearing impairment frequencies.
- category: Neoplastic
  name: Sarcomatous Transformation
  frequency: VERY_RARE
  description: Osteosarcoma arising within pagetic bone. Rare, high-grade, and with a dismal prognosis - 5-year
    survival around 10%. It arises in older men, predominantly in the axial skeleton and pelvis, and notably
    does not correlate with how much bone is involved or how long the disease has been present, so it cannot
    be predicted from disease burden.
  phenotype_term:
    preferred_term: Osteosarcoma
    term:
      id: HP:0002669
      label: Osteosarcoma
  evidence:
  - reference: PMID:17550323
    reference_title: 'Sarcomas arising in Paget disease of bone: a clinicopathologic analysis of 70 cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Most tumors were osteosarcomas (88%). All tumors were high grade.
    explanation: Establishes the histology and grade of the tumours arising in pagetic bone.
  - reference: PMID:17550323
    reference_title: 'Sarcomas arising in Paget disease of bone: a clinicopathologic analysis of 70 cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Survival ranged from 1 month to 20 years, with a 5-year survival rate of 10%.
    explanation: The survival figure quoted in this entry.
  - reference: PMID:17550323
    reference_title: 'Sarcomas arising in Paget disease of bone: a clinicopathologic analysis of 70 cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: There is no significant correlation between the number of bones involved with Paget disease or
      the duration of disease and development of Paget sarcoma.
    explanation: The negative result behind this entry's statement that sarcoma risk is not predictable from
      disease burden.
genetic:
- name: SQSTM1
  gene_term:
    preferred_term: SQSTM1
    term:
      id: hgnc:11280
      label: SQSTM1
  relationship_type: CAUSATIVE
  notes: The single most frequently implicated gene. Variants affect the UBA domain, recurrently p.Pro392Leu,
    and are germline. The mechanism is impaired ubiquitin binding rather than absence of the protein, which
    is why the variants cluster in one domain rather than being distributed as nulls.
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: PDB has a complex genetic basis involving multiple genes, with SQSTM1 being the gene most frequently
      associated with its development.
    explanation: Establishes SQSTM1 as the principal gene.
- name: ZNF687
  gene_term:
    preferred_term: ZNF687
    term:
      id: hgnc:29277
      label: ZNF687
  relationship_type: CAUSATIVE
  notes: Rare germline cause of severe, early-onset polyostotic disease with giant cell tumour predisposition.
  evidence:
  - reference: PMID:30671590
    reference_title: Paget's Disease of Bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: It is now clear that PDB is a genetically heterogeneous disorder, with mutations in at least two
      different genes (SQSTM1, ZNF687) and more common predisposing variants.
    explanation: Names ZNF687 alongside SQSTM1 as an established causal gene.
- name: TNFRSF11A
  gene_term:
    preferred_term: TNFRSF11A
    term:
      id: hgnc:11908
      label: TNFRSF11A
  relationship_type: SUSCEPTIBILITY
  notes: RANK. Carries both rare germline causal variants and a common susceptibility signal, so it appears
    in this entry twice over - as a gene and as the receptor at the centre of the mechanism.
  evidence:
  - reference: PMID:21623375
    reference_title: Genome-wide association identifies three new susceptibility loci for Paget's disease of
      bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We previously identified variants at the CSF1, OPTN and TNFRSF11A loci as risk factors for PDB
      by genome-wide association study.
    explanation: The association result establishing TNFRSF11A as a susceptibility locus.
- name: PFN1
  gene_term:
    preferred_term: PFN1
    term:
      id: hgnc:8881
      label: PFN1
  relationship_type: CAUSATIVE
  notes: A very rare cause of severe disease; essentially absent from most cohorts.
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Germline mutations in other genes such as TNFRSF11A, ZNF687 and PFN1, have also been associated
      with the development of the disease.
    explanation: Names PFN1 among the germline causes.
environmental:
- name: Unidentified declining environmental exposure
  description: 'Something environmental is strongly implicated, and it is going away. Standardised UK incidence
    fell from 0.75 to 0.20 per 10,000 person-years between 1999 and 2015 - far too fast to be genetic drift
    - and the same decline has been reported in other countries. Together with the focality of lesions and
    the incomplete penetrance within families, that is the case for an environmental co-factor acting on a
    genetically susceptible osteoclast lineage. Its identity is unknown.


    This entry says "strongly implicated" rather than "required" on purpose. The P394L Sqstm1 knock-in mouse
    develops a PDB-like focal skeletal disorder with no additional trigger, which is direct evidence against
    strict necessity. The human epidemiology and the mouse disagree, and the disagreement is recorded as a
    HUMAN_MODEL_MISMATCH discussion rather than resolved in favour of either. The long-standing paramyxovirus
    hypothesis is discussed separately and is not currently supported.'
  influences_mechanisms:
  - target: Osteoclast Precursor Hypersensitivity to RANKL
    environmental_effect: TRIGGERS
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: 'Modelled as a co-factor that converts inherited susceptibility into focal disease. The link
      is inferred from epidemiology and penetrance, not from a demonstrated exposure-to-osteoclast mechanism,
      and the target is the pathway the genetics implicate rather than a measured one. It is not modelled as
      necessary: see the HUMAN_MODEL_MISMATCH discussion for the mouse evidence against that.'
    evidence:
    - reference: PMID:30671590
      reference_title: Paget's Disease of Bone.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The exact nature of these triggers and how they might interact with the genetic factors are
        less understood
      explanation: PARTIAL by design - the source states that the interaction between trigger and genotype
        is not understood, which is precisely the strength this link should carry.
  evidence:
  - reference: PMID:33742666
    reference_title: 'Incidence of Paget''s disease of bone in the UK: evidence of a continuing decline.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The reason for the decline in incidence remains unknown, although the rapidity of change points
      to an alteration in one or more environmental determinants.
    explanation: The epidemiological argument for an environmental determinant, and for its being unidentified.
  - reference: PMID:33742666
    reference_title: 'Incidence of Paget''s disease of bone in the UK: evidence of a continuing decline.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The overall standardized incidence decreased from 0.75/10 000 person-years in 1999 to 0.20/10
      000 person-years in 2015.
    explanation: Quantifies the decline this entry rests on.
  notes: No exposure_term is bound because the exposure is not identified. ECTO cannot represent "an unknown
    environmental determinant", and binding a speculative term (a paramyxovirus exposure, coal smoke, livestock
    contact) would assert something the evidence does not support.
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 1500.0
  rate_low: 1500.0
  rate_high: 8300.0
  notes: Reported as a 1.5%-8.3% prevalence range, normalised here to 1,500-8,300 per 100,000 with the lower
    bound as the point estimate. The range is wide because it spans populations with very different risk -
    highest in the UK and in populations of British descent, low in Scandinavia, Africa and Asia - so a single
    worldwide figure is not really meaningful and this record should be read as an upper-bound envelope rather
    than an estimate.
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Paget's disease of bone (PDB) is the second most prevalent metabolic bone disorder worldwide,
      with a prevalence rate of 1.5%-8.3%.
    explanation: The prevalence range this record normalises.
- population: United Kingdom
  measure_type: ANNUAL_INCIDENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 2.0
  notes: Standardised incidence of 0.20 per 10,000 person-years in 2015, normalised to 2.0 per 100,000 per
    year. The 1999 figure was 0.75 per 10,000, so this record captures a moving quantity - which is the point
    of including it.
  evidence:
  - reference: PMID:33742666
    reference_title: 'Incidence of Paget''s disease of bone in the UK: evidence of a continuing decline.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The overall standardized incidence decreased from 0.75/10 000 person-years in 1999 to 0.20/10
      000 person-years in 2015.
    explanation: The incidence figures this record normalises.
diagnosis:
- name: Plain Radiography
  description: The primary diagnostic modality. Radiographs show cortical thickening, coarse trabeculation,
    bone expansion, osteoporosis circumscripta in the skull and the flame-shaped advancing lytic front in long
    bones. Guidelines pair it with serum ALP for initial diagnosis and reserve the radionuclide scan for mapping
    extent - so the X-ray characterises the lesion and the scan counts the lesions.
  diagnosis_term:
    preferred_term: X-ray imaging
    term:
      id: NCIT:C38101
      label: X-Ray Imaging
  evidence:
  - reference: PMID:32803929
    reference_title: Paget Disease of Bone for Primary Care.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Evidence-based guidelines recommend the use of plain radiography and serum alkaline phosphatase
      testing for initial diagnosis and radionuclide scans for delineation of the extent of disease.
    explanation: States the guideline-recommended division of labour between radiography, ALP and scintigraphy
      that this entry follows.
  - reference: PMID:31574000
    reference_title: 'Paget''s disease of bone: updates for clinicians.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Diagnosis is through plain film imaging, with radionuclide bone scan to determine the extent.
    explanation: The second guideline review, agreeing that plain film imaging is the diagnostic modality.
- name: Serum Total Alkaline Phosphatase
  description: The first-line biochemical test, used both to detect disease and to follow activity. Not specific
    - it rises in liver disease and pregnancy, so bone-specific ALP is used where those confound - and not
    perfectly sensitive, since limited monostotic disease can be biochemically silent.
  diagnosis_term:
    preferred_term: laboratory procedure
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: However, ALP levels can also be elevated in other conditions, such as liver disease or during
      pregnancy, making additional tests necessary for diagnosis confirmation
    explanation: States the specificity limitation that this entry describes.
- name: Radionuclide Bone Scintigraphy
  description: 'Technetium-99m bone scan, used after diagnosis to map the full extent of skeletal involvement.
    It answers a different question from the radiograph: the X-ray characterises a lesion, the scan finds the
    others.'
  diagnosis_term:
    preferred_term: radionuclide imaging
    term:
      id: NCIT:C62667
      label: Radionuclide Imaging
  evidence:
  - reference: PMID:37180975
    reference_title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A set of plain X-rays and bone scintigraphy are used to evaluate PDB, but bone scintigraphy may
      be negative in some cases.
    explanation: PARTIAL because the source establishes scintigraphy's role in evaluation while noting it can
      be falsely negative, rather than reporting a sensitivity figure for extent mapping.
treatments:
- name: Zoledronic Acid
  therapeutic_modality: SMALL_MOLECULE
  description: A single 5 mg intravenous infusion, and the most effective bisphosphonate tested in this disease
    by a wide margin. Therapeutic response was 97% against 45% for pamidronate in a head-to-head randomised
    comparison, and over 6.5 years of follow-up without retreatment relapse occurred in 1 of 152 patients given
    zoledronate against 23 of 115 given risedronate.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: zoledronic acid
      term:
        id: CHEBI:46557
        label: zoledronic acid
  target_mechanisms:
  - target: Giant Hypernucleated Hyperactive Osteoclasts
    treatment_effect: INHIBITS
    description: Acts on the osteoclast directly, which is why it works so well on the biochemistry - it targets
      the cell that drives the whole pathograph.
  evidence:
  - reference: PMID:17605632
    reference_title: Comparison of different intravenous bisphosphonate regimens for Paget's disease of bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At 6 mo, 97% of patients receiving zoledronate had a therapeutic response compared with 45% of
      patients receiving pamidronate.
    explanation: The head-to-head randomised comparison behind the response figures quoted here.
  - reference: PMID:21638319
    reference_title: 'A single infusion of zoledronic acid produces sustained remissions in Paget disease:
      data to 6.5 years.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Relapse rates were substantially greater in the risedronate group (23 of 115, 20%) than in those
      treated with zoledronic acid (1 of 152, 0.7%, p < .001)
    explanation: The long-term durability result quoted in this entry.
- name: Neridronate
  therapeutic_modality: SMALL_MOLECULE
  description: 'An alternative aminobisphosphonate, and the practically useful thing about it is the route:
    a 200 mg course given intramuscularly performed as well as the same dose intravenously - 96.5% versus 92.6%
    therapeutic response at 6 months - which matters for patients who cannot or will not have an infusion.
    Response was not durable in the way a single zoledronic acid infusion is; it held at 12 months and fell
    progressively at 24 and 36.'
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: Giant Hypernucleated Hyperactive Osteoclasts
    treatment_effect: INHIBITS
    description: Same osteoclast target as zoledronic acid, with a different administration route and a shorter
      duration of effect.
  evidence:
  - reference: PMID:20814970
    reference_title: Comparison of intravenous and intramuscular neridronate regimens for the treatment of
      Paget disease of bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At 6 months, 92.6% and 96.5% of patients receiving intravenous and intramuscular neridronate,
      respectively, achieved a therapeutic response
    explanation: The head-to-head route comparison behind the response figures quoted here.
  - reference: PMID:20814970
    reference_title: Comparison of intravenous and intramuscular neridronate regimens for the treatment of
      Paget disease of bone.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Response rates were maintained at 12 months but decreased progressively at 24 and 36 months without
      significant differences between the two neridronate regimens
    explanation: The durability limitation that distinguishes neridronate from a single zoledronic acid infusion.
- name: Symptom-Directed Rather Than Turnover-Directed Management
  therapeutic_modality: OTHER
  description: This is a treatment-strategy entry rather than an agent, because the strategy question has been
    answered directly and the answer is counterintuitive. The PRISM-EZ trial randomised 502 patients to intensive
    bisphosphonate therapy aimed at normalising bone turnover versus bisphosphonates given only for pain. Intensive
    treatment achieved markedly better biochemistry and produced no reduction in fracture, no fewer orthopaedic
    procedures, and no better quality of life - with a non-significant increase in fractures, orthopaedic events
    and serious adverse events. In established disease, therefore, the target is symptoms, not the ALP.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Expanded Structurally Weak Hypervascular Bone
    treatment_effect: MODULATES
    description: Addresses the clinical consequences of the abnormal bone rather than the remodelling rate
      that produces it.
  evidence:
  - reference: PMID:28176386
    reference_title: 'Long-Term Randomized Trial of Intensive Versus Symptomatic Management in Paget''s Disease
      of Bone: The PRISM-EZ Study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: There were no clinically important differences in quality of life measures or bone pain between
      the treatment groups.
    explanation: The primary comparative result on symptoms and quality of life.
  - reference: PMID:28176386
    reference_title: 'Long-Term Randomized Trial of Intensive Versus Symptomatic Management in Paget''s Disease
      of Bone: The PRISM-EZ Study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The results of this study suggest that in patients with established PDB, bisphosphonate therapy
      should focus on control of symptoms rather than suppression of bone turnover.
    explanation: The trial's own conclusion, which is the strategy this entry records.
discussions:
- discussion_id: pdb_environmental_trigger_unidentified
  kind: KNOWLEDGE_GAP
  attaches_to:
  - environmental#Unidentified declining environmental exposure
  - pathophysiology#Focal Accelerated Bone Resorption
  prompt: What is the environmental exposure whose withdrawal is making Paget disease disappear, and is the
    paramyxovirus hypothesis dead?
  rationale: 'Three observations demand an environmental co-factor and none identifies it. Incidence has fallen
    by roughly two thirds in the UK in sixteen years and similarly elsewhere; lesions are focal despite a germline
    variant in every cell; and penetrance within SQSTM1 families is incomplete. A purely genetic account explains
    none of these.

    The candidate that has absorbed most of the effort is chronic paramyxovirus infection of the osteoclast
    - measles, RSV or canine distemper virus - and it has not held up. Measles RNA was reported in pagetic
    osteoclasts by in-situ hybridisation, but PCR failed to find paramyxovirus sequence in pagetic bone, pet
    ownership was not a risk factor, and a serological study of several hundred patients found no elevation
    of measles, distemper or RSV antibodies. The weight of evidence is against it. Weaker recent candidates
    - rural residence and breeding-cattle density, historical domestic coal burning - are ecological correlations
    without a mechanism.

    This gap is unusually well posed and unusually urgent, because the exposure is disappearing on its own.
    Whatever it is, the population of people who encountered it is ageing out, and the natural experiment that
    could identify it is closing.'
  proposed_experiments:
  - experiment_id: pdb_birth_cohort_exposure_reconstruction
    name: Birth-cohort exposure reconstruction in declining-incidence populations
    description: Use the steep incidence gradient across birth cohorts in populations with good historical
      exposure records to test candidate exposures - domestic solid-fuel combustion, livestock contact, childhood
      infection history - against year and place of birth rather than against current residence, since the
      relevant exposure is likely to be decades before diagnosis.
    would_support:
    - environmental#Unidentified declining environmental exposure
    supporting_outcome:
    - A candidate exposure whose historical prevalence tracks the birth-cohort incidence gradient in more than
      one country, with a dose-response relationship.
    refuting_outcome:
    - No candidate exposure tracks the cohort gradient, which would move the explanation toward a change in
      diagnostic practice or ascertainment rather than a change in biology.
  evidence:
  - reference: PMID:3701300
    reference_title: Measles virus RNA detected in Paget's disease bone tissue by in situ hybridization.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: measles virus RNA sequences were detected not only in 80 to 90% of the multinucleated osteoclasts
      where there is morphological and immunocytological evidence of measles virus activity but also in 30
      to 40% of mononucleated bone cells
    explanation: The in-situ hybridisation result that established the paramyxovirus hypothesis, quoted here
      as the case for it rather than against.
  - reference: PMID:1805546
    reference_title: Failure to detect paramyxovirus sequences in Paget's disease of bone using the polymerase
      chain reaction.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: we found no evidence of viral products in RNA extracts of affected bone from 10 consecutive patients
      with Paget's disease
    explanation: The PCR study that failed to reproduce it, using a method the authors showed could detect
      as few as 50 infected cells.
  - reference: PMID:2376461
    reference_title: 'Paget''s disease of bone and previous pet ownership in the United States: dogs exonerated.'
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: We conclude that past dog (or cat) ownership is not a risk factor for the development of Paget's
      disease.
    explanation: The epidemiological test of the canine distemper route, in 433 cases with matched controls.
  - reference: PMID:28361207
    reference_title: Antibody Response to Paramyxoviruses in Paget's Disease of Bone.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: there was no significant difference in circulating antibody concentrations between PDB cases and
      controls for MV, CDV, RSV, rubella or VZV
    explanation: The serological test in 463 patients, which is the largest direct test of chronic paramyxovirus
      infection and is negative for every candidate virus.
- discussion_id: pdb_biochemical_remission_is_not_clinical_benefit
  kind: KNOWLEDGE_GAP
  attaches_to:
  - treatments#Zoledronic Acid
  - treatments#Symptom-Directed Rather Than Turnover-Directed Management
  prompt: Why does suppressing bone turnover so effectively fail to improve fractures, orthopaedic outcomes
    or quality of life?
  rationale: 'Zoledronic acid does what it is supposed to do: it suppresses the osteoclast, normalises ALP
    in most patients, and holds that for years. If the pagetic burden were caused by ongoing high turnover,
    that should translate into fewer fractures and better function. In PRISM-EZ it did not, and the point estimates
    for fracture and orthopaedic procedures moved the wrong way.

    The most economical explanation is that the damage is architectural and already done. Once a site has been
    remodelled into expanded mosaic bone, the mechanical deficit is a property of the tissue, not of the rate
    at which it is turning over, and stopping the turnover does not restore the architecture. If that is right,
    the interesting question is not whether to suppress turnover but whether there is an earlier window - before
    a lesion has remodelled - in which suppression would matter. That has never been tested, because trials
    enrol patients with established disease and asymptomatic early disease is not systematically identified.

    A second possibility, harder to exclude, is that suppressed turnover impairs repair of microdamage in already-abnormal
    bone, which would explain the direction of the non-significant fracture excess rather than dismissing it
    as noise.'
- discussion_id: pdb_mouse_needs_no_trigger_but_humans_seem_to
  kind: HUMAN_MODEL_MISMATCH
  attaches_to:
  - environmental#Unidentified declining environmental exposure
  - animal_models#P394L Sqstm1 knock-in mouse
  - pathophysiology#Focal Accelerated Bone Resorption
  prompt: The P394L mouse develops pagetic disease with no environmental trigger, while the human epidemiology
    says a trigger is doing most of the work. Which is right about human disease?
  rationale: 'This entry rests substantially on an environmental co-factor: incidence fell by two thirds in
    the UK in sixteen years, lesions are focal despite a germline allele in every cell, and penetrance within
    SQSTM1 families is incomplete. The mouse says the opposite. P394L knock-in animals develop focal, asymmetric,
    age-accumulating lesions with giant hypernucleated osteoclasts and no trigger of any kind, and the authors
    state the conclusion plainly - SQSTM1 mutations can cause a PDB-like disorder in the absence of an additional
    trigger.


    Both observations are solid, so the interesting question is what the disagreement is made of. Three readings
    are open.


    The first is dose. Murine penetrance is 77% in heterozygotes by 12 months; human SQSTM1 heterozygote penetrance
    is far lower and later. A laboratory mouse may simply sit above a threshold that most human carriers sit
    below, in which case the environmental factor is a modifier of penetrance rather than a necessary second
    hit - which would reconcile the two without either being wrong.


    The second is that the environmental signal is not about susceptibility at all. Incidence here means *clinically
    diagnosed* incidence, and it has fallen over exactly the period in which routine biochemistry and imaging
    changed. Some of the decline could be ascertainment. The counter is that severity fell too - deformity
    54% to 13%, fracture 36.7% to 6.7% - and ascertainment drift should make a disease look milder without
    changing what the severe end looks like.


    The third is that the mouse models the SQSTM1-driven minority and the environmental factor operates on
    the sporadic majority, who have no SQSTM1 variant at all. This entry''s own genetics section supports that
    split: SQSTM1 explains a minority of sporadic disease, and the GWAS loci together explain only about 13%
    of familial risk.


    Nothing published distinguishes these. Recorded as a mismatch rather than resolved, because the entry''s
    environmental claim has been softened from ''required'' to ''strongly implicated'' on the strength of the
    mouse, and that is as far as the evidence goes.'
  proposed_experiments:
  - experiment_id: pdb_p394l_penetrance_under_controlled_exposure
    name: Genotype-stratified penetrance against candidate exposures in the P394L model
    description: Test whether candidate human exposures modify penetrance and lesion burden in P394L heterozygotes,
      which is the genotype that matches human carriers. A trigger that raises murine heterozygote lesion burden
      would support the modifier reading; one that does nothing in a model already at 77% penetrance would
      show the model is saturated and cannot address the question.
    would_support:
    - environmental#Unidentified declining environmental exposure
    supporting_outcome:
    - Candidate exposure raises lesion burden or lowers age at onset in P394L heterozygotes relative to unexposed
      littermates, establishing the environmental factor as a penetrance modifier rather than a necessary trigger.
    refuting_outcome:
    - No exposure alters murine lesion burden, leaving the human epidemiological signal unexplained by anything
      the model can represent and pointing at ascertainment or at the SQSTM1-negative majority instead.
references:
- reference: PMID:30671590
  title: Paget's Disease of Bone.
- reference: PMID:37180975
  title: 'Paget''s disease: a review of the epidemiology, etiology, genetics, and treatment.'
- reference: PMID:36858336
  title: 'Decline in clinical severity of Paget''s disease of bone: Comparison between a contemporary cohort
    and a historical cohort.'
- reference: PMID:21623375
  title: Genome-wide association identifies three new susceptibility loci for Paget's disease of bone.
- reference: PMID:28176386
  title: 'Long-Term Randomized Trial of Intensive Versus Symptomatic Management in Paget''s Disease of Bone:
    The PRISM-EZ Study.'
- reference: PMID:17605632
  title: Comparison of different intravenous bisphosphonate regimens for Paget's disease of bone.
- reference: PMID:21638319
  title: 'A single infusion of zoledronic acid produces sustained remissions in Paget disease: data to 6.5
    years.'
- reference: PMID:33742666
  title: 'Incidence of Paget''s disease of bone in the UK: evidence of a continuing decline.'
- reference: PMID:17550323
  title: 'Sarcomas arising in Paget disease of bone: a clinicopathologic analysis of 70 cases.'
- reference: PMID:1805546
  title: Failure to detect paramyxovirus sequences in Paget's disease of bone using the polymerase chain reaction.
- reference: PMID:20814970
  title: Comparison of intravenous and intramuscular neridronate regimens for the treatment of Paget disease
    of bone.
- reference: PMID:21515589
  title: A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause a Paget's disease-like
    disorder in mice.
- reference: PMID:2376461
  title: 'Paget''s disease of bone and previous pet ownership in the United States: dogs exonerated.'
- reference: PMID:28361207
  title: Antibody Response to Paramyxoviruses in Paget's Disease of Bone.
- reference: PMID:30154079
  title: Zoledronic acid prevents pagetic-like lesions and accelerated bone loss in the p62(P394L) mouse model
    of Paget's disease.
- reference: PMID:31574000
  title: 'Paget''s disease of bone: updates for clinicians.'
- reference: PMID:32803929
  title: Paget Disease of Bone for Primary Care.
- reference: PMID:3701300
  title: Measles virus RNA detected in Paget's disease bone tissue by in situ hybridization.
notes: 'Scope. This entry covers classic adult-onset Paget disease of bone. MONDO places five descendants under
  MONDO:0005382, and they do not all belong in one entry. PDB2, PDB3, PDB4 and PDB6 are genetic loci for the
  same disease and are handled as has_subtypes here (only those with evidence in the reviewed literature are
  recorded). Juvenile Paget disease (MONDO:0009394) is excluded: it is autosomal recessive, usually from biallelic
  loss of TNFRSF11B/osteoprotegerin, presents in infancy, and is generalised rather than focal. It is a different
  disease that shares a pathway, and it keeps its own curation stub.

  Deep research. Curated with a single OpenScientist deep-research report (research/Paget_Disease_of_Bone-deep-research-openscientist.md).
  Its reference validation reported needs_review with three unsupported quotes (PMID:38963497, PMID:33768371,
  PMID:21515589); no quoted material from those three was reused here. Its term validation flagged HP:0002750,
  which the report labelled "Abnormal long bone morphology" but which HPO calls "Delayed skeletal maturation";
  the deformity phenotype in this entry is bound to HP:0006487 (Bowing of the long bones) instead. A second
  term error not caught by the report''s own validation was found during curation: the report suggested UBERON:0000033
  for skull, which is "head"; this entry uses UBERON:0003128 (cranium).'
animal_models:
- name: P394L Sqstm1 knock-in mouse
  species: Mouse
  genotype: Sqstm1 p.Pro394Leu knock-in, heterozygous and homozygous
  publication: PMID:21515589
  description: 'The murine equivalent of the human SQSTM1 p.Pro392Leu allele, and the model that carries most
    of the mechanistic weight in this disease. It reproduces the focal, asymmetric, age-accumulating lesions
    of human PDB, the giant hypernucleated osteoclasts with nuclear inclusions, the RANKL hypersensitivity
    of osteoclast precursors, and the autophagy dysregulation - four of this entry''s six nodes, in one model.


    It is also the source of this entry''s most awkward evidence. Human PDB is focal and its incidence is falling,
    which argues for an environmental co-factor; this mouse develops the disease with no trigger at all. See
    the HUMAN_MODEL_MISMATCH discussion.'
  modeled_mechanisms:
  - target: Osteoclast Precursor Hypersensitivity to RANKL
    relationship: RECAPITULATES
    fidelity: HIGH
    description: Osteoclast precursors from mutant mice are measurably more sensitive to RANKL than wild-type,
      and the sensitivity increases further with age - which is what makes this model an explanation for the
      age-dependence of human penetrance rather than only a phenocopy.
    limitations: The sensitivity is measured in vitro on precursors from the mouse, so it establishes a cell-autonomous
      property of the mutant lineage rather than the in vivo trigger sequence.
    readouts:
    - name: Osteoclastogenesis from precursors at fixed RANKL
      target: Osteoclast Precursor Hypersensitivity to RANKL
      direction: INCREASED
      interpretation: Increased relative to wild-type and increasing with age in both genotypes, which is the
        age-penetrance link.
      evidence:
      - reference: PMID:30154079
        reference_title: Zoledronic acid prevents pagetic-like lesions and accelerated bone loss in the p62(P394L)
          mouse model of Paget's disease.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: p62P394L+/+ osteoclast precursors had increased sensitivity to RANKL (also known as TNFSF11)
          compared with wild-type (WT) cells, and the sensitivity further increased in both genotypes with
          ageing.
        explanation: The quantitative RANKL-sensitivity measurement and its age dependence.
    evidence:
    - reference: PMID:21515589
      reference_title: A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause
        a Paget's disease-like disorder in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Osteoclast precursors from P394L mutant mice had increased sensitivity to RANKL in vitro resulting
        in the generation of osteoclasts that were larger and more nucleated than those generated from wild-type
        littermates.
      explanation: Establishes the model as informative for this node, and links precursor hypersensitivity
        directly to the hypernucleated osteoclast phenotype downstream.
  - target: Giant Hypernucleated Hyperactive Osteoclasts
    relationship: RECAPITULATES
    fidelity: HIGH
    description: Osteoclasts within murine lesions are larger and more nucleated than normal and some carry
      the nuclear inclusion bodies seen in human pagetic osteoclasts - the cellular signature of the disease
      reproduced in full.
    limitations: Inclusion bodies are reported in some but not all lesional osteoclasts, as in humans; the
      model does not resolve what they are.
    evidence:
    - reference: PMID:21515589
      reference_title: A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause
        a Paget's disease-like disorder in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Osteoclasts within lesions were larger and more nucleated than normal and some contained nuclear
        inclusions similar to those observed in human PDB.
      explanation: The cellular phenotype matching the human disease, including the inclusion bodies.
  - target: Focal Accelerated Bone Resorption
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: Focal lesions accumulate with age - 77% of heterozygotes and 95% of homozygotes by 12 months
      against none in wild-type littermates - and predominantly affect the lower limbs asymmetrically, reproducing
      the focality and asymmetry that a germline allele does not obviously explain.
    limitations: Penetrance is far higher than in human heterozygotes, and the lesion distribution is limb-predominant
      rather than matching the human axial preference for pelvis, spine and skull.
    readouts:
    - name: Proportion of animals with focal bone lesions at 12 months
      target: Focal Accelerated Bone Resorption
      direction: INCREASED
      interpretation: Genotype-dependent and age-dependent lesion development against a zero wild-type baseline.
      evidence:
      - reference: PMID:21515589
        reference_title: A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause
          a Paget's disease-like disorder in mice.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: The P394L mutant mice developed focal bone lesions with increasing age and by 12 months, 14/18
          (77%) heterozygotes and 20/21 (95%) homozygotes had lesions, compared with 0/18 (0%) wild-type littermates
          (P< 0.001).
        explanation: The lesion counts by genotype and age.
    evidence:
    - reference: PMID:21515589
      reference_title: A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause
        a Paget's disease-like disorder in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: mice with a proline to leucine mutation at codon 394 of mouse sqstm1 (P394L), equivalent to
        the P392L SQSTM1 mutation in humans, develop a bone disorder with remarkable similarity to PDB
      explanation: Establishes the allele equivalence and the overall phenotypic correspondence that makes
        this model informative.
  evidence:
  - reference: PMID:30154079
    reference_title: Zoledronic acid prevents pagetic-like lesions and accelerated bone loss in the p62(P394L)
      mouse model of Paget's disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: ZA prevented the development of pagetic-like lesions, and increased trabecular bone volume tenfold
      compared with vehicle by 12 months of age (P<0.01).
    explanation: 'A treatment result in the model that joins the pathograph to the treatment section: zoledronic
      acid prevents lesion development, which is the mechanistic counterpart of its biochemical effect in humans.'
📚

References & Deep Research

References

18
PMID:30671590
Paget's Disease of Bone.
No top-level findings curated for this source.
PMID:37180975
Paget's disease: a review of the epidemiology, etiology, genetics, and treatment.
No top-level findings curated for this source.
PMID:36858336
Decline in clinical severity of Paget's disease of bone: Comparison between a contemporary cohort and a historical cohort.
No top-level findings curated for this source.
PMID:21623375
Genome-wide association identifies three new susceptibility loci for Paget's disease of bone.
No top-level findings curated for this source.
PMID:28176386
Long-Term Randomized Trial of Intensive Versus Symptomatic Management in Paget's Disease of Bone: The PRISM-EZ Study.
No top-level findings curated for this source.
PMID:17605632
Comparison of different intravenous bisphosphonate regimens for Paget's disease of bone.
No top-level findings curated for this source.
PMID:21638319
A single infusion of zoledronic acid produces sustained remissions in Paget disease: data to 6.5 years.
No top-level findings curated for this source.
PMID:33742666
Incidence of Paget's disease of bone in the UK: evidence of a continuing decline.
No top-level findings curated for this source.
PMID:17550323
Sarcomas arising in Paget disease of bone: a clinicopathologic analysis of 70 cases.
No top-level findings curated for this source.
PMID:1805546
Failure to detect paramyxovirus sequences in Paget's disease of bone using the polymerase chain reaction.
No top-level findings curated for this source.
PMID:20814970
Comparison of intravenous and intramuscular neridronate regimens for the treatment of Paget disease of bone.
No top-level findings curated for this source.
PMID:21515589
A point mutation in the ubiquitin-associated domain of SQSMT1 is sufficient to cause a Paget's disease-like disorder in mice.
No top-level findings curated for this source.
PMID:2376461
Paget's disease of bone and previous pet ownership in the United States: dogs exonerated.
No top-level findings curated for this source.
PMID:28361207
Antibody Response to Paramyxoviruses in Paget's Disease of Bone.
No top-level findings curated for this source.
PMID:30154079
Zoledronic acid prevents pagetic-like lesions and accelerated bone loss in the p62(P394L) mouse model of Paget's disease.
No top-level findings curated for this source.
PMID:31574000
Paget's disease of bone: updates for clinicians.
No top-level findings curated for this source.
PMID:32803929
Paget Disease of Bone for Primary Care.
No top-level findings curated for this source.
PMID:3701300
Measles virus RNA detected in Paget's disease bone tissue by in situ hybridization.
No top-level findings curated for this source.

Deep Research

1
OpenScientist ▸
Paget Disease of Bone — Comprehensive Disease Characteristics Report
openscientist-autonomous 33 citations 2026-08-28T21:45:26.958053

Paget Disease of Bone — Comprehensive Disease Characteristics Report

Disease: Paget Disease of Bone (PDB; osteitis deformans) Category: Metabolic Bone Disorder Primary identifiers: MONDO:0005479 · OMIM #167250 (PDB2, SQSTM1) / #602080 (PDB3) / #616833 (PDB6, ZNF687) · Orphanet ORPHA:2801 · ICD-10 M88 · ICD-11 FB80.0 · MeSH D010001 (Osteitis Deformans) Evidence base: 9 confirmed findings, 39 primary papers reviewed across 5 iterations. Evidence is drawn from aggregated disease-level resources (OMIM, Orphanet, GWAS meta-analyses, guideline statements), human clinical cohorts and registries, knock-in mouse models, and in-vitro osteoclast studies.

Summary

Paget disease of bone (PDB) is a chronic, focal, adult-onset metabolic bone disorder in which giant, hyperactive, hypernucleated osteoclasts drive intense localized bone resorption. This is followed by a disorganized compensatory increase in osteoblastic bone formation, producing expanded, structurally weak, hypervascular "mosaic" bone (mixed woven and lamellar). Clinically this manifests as bone pain, deformity, secondary osteoarthritis, pathological fracture, deafness (when the skull is involved), and — rarely (~0.7–1%) — malignant transformation to osteosarcoma. Many patients are asymptomatic and are detected incidentally through an elevated serum alkaline phosphatase (ALP) or an X-ray taken for another reason.

PDB is best understood as a complex gene–environment disorder that converges on the osteoclast RANK–RANKL–OPG signaling axis and p62/autophagy machinery. Mutations affecting the ubiquitin-associated (UBA) domain of SQSTM1 (which encodes p62), especially the recurrent p.P392L variant, are the single most common genetic cause. Beyond SQSTM1, rarer causal genes (ZNF687, PFN1, VCP) and at least seven common susceptibility loci (CSF1, OPTN, TNFRSF11A/RANK, TM7SF4/DCSTAMP, PML, RIN3, NUP205) shape polygenic risk. A parallel, distinct recessive childhood disorder — juvenile Paget's disease — is caused chiefly by loss of osteoprotegerin (TNFRSF11B/OPG), directly confirming the centrality of the RANK–RANKL–OPG axis. The steadily declining incidence and severity of PDB across multiple countries strongly implicates a diminishing environmental trigger whose identity remains unresolved.

Diagnosis rests on the combination of characteristic plain radiographs, an elevated serum ALP (the standard marker of disease activity), and a technetium-99m radionuclide bone scan to map disease extent. A single 5-mg intravenous infusion of zoledronic acid is first-line therapy and produces durable biochemical remission in ~90–97% of patients — far superior to older bisphosphonates — although a large randomized trial (PRISM-EZ) showed that intensively normalizing bone turnover does not improve fractures, pain, or quality of life versus symptomatic management. This report details all requested disease characteristics with primary-literature citations.

Section 1 — Disease Information

PDB is a chronic focal disorder of bone remodeling, the second most common metabolic bone disease after osteoporosis (PMID: 28690091). It is characterized by "increased osteoclast-mediated bone resorption and a subsequent compensatory increase in bone formation, resulting in a disorganized mosaic of woven and lamellar bone at one or more affected skeletal sites" (PMID: 30671590).

Key identifiers: MONDO:0005479; OMIM #167250 (classic SQSTM1-related PDB2), with additional loci PDB3 (#602080) and PDB6/ZNF687 (#616833); Orphanet ORPHA:2801; ICD-10 M88 (with subsite codes M88.0 skull, M88.8 other bones, M88.9 unspecified); ICD-11 FB80.0; MeSH D010001 (Osteitis Deformans).

Synonyms / alternative names: Osteitis deformans; Paget's disease of bone; Paget disease, bone; osteitis deformans of Paget. (Note: distinct from Paget disease of the breast/nipple and extramammary Paget disease, which are unrelated epithelial neoplasms.)

Information source type: Predominantly aggregated disease-level resources (OMIM, Orphanet, GWAS meta-analyses, guideline statements) supplemented by clinical cohorts, health-administrative databases (e.g., Quebec, UK), and disease registries. Some findings derive from individual-patient EHR/registry data (e.g., contemporary vs historical cohort comparisons; VCP CoRDS registry).

Section 2 — Etiology

Primary causal factors. PDB is a genetically heterogeneous disorder with a strong hereditary component overlaid on one or more environmental triggers. As reviewed, "PDB is a genetically heterogeneous disorder, with mutations in at least two different genes (SQSTM1, ZNF687) and more common predisposing variants," while "the focal nature of lesions, the decline in prevalence rates, and the incomplete penetrance of the disease among family members suggest that one or more environmental triggers may play a role" (PMID: 30671590).

Genetic risk factors. - Causal: SQSTM1 UBA-domain mutations (p.P392L most common) — present in ~10–40% of familial and ~5–10% of sporadic cases (Finding F001). Rarer causal genes: ZNF687 and PFN1 (severe, early-onset, polyostotic, giant-cell-tumor–prone forms) and VCP (syndromic PDB). - Susceptibility loci: Seven common GWAS loci — CSF1 (1p13), OPTN (10p13), TNFRSF11A/RANK (18q21), TM7SF4/DCSTAMP (rs2458413), PML (rs5742915), RIN3 (rs10498635), NUP205 (rs4294134) — together explaining ~13% of familial risk (Finding F006; PMID: 21623375).

Environmental risk factors. Age (incidence rises sharply after ~55 y), male sex, and family history are the principal established risk factors. Geographic and rural clustering suggests an environmental/zoonotic contribution: a Spanish study of 2,342 new cases found a moderate positive correlation between PDB incidence and density of female breeding cattle (R²=0.236) (PMID: 40408225). A separate hypothesis links historical PDB prevalence to domestic bituminous coal burning (PMID: 38902530). The long-postulated chronic paramyxovirus (measles) infection of osteoclasts remains unconfirmed and contested (see Section 5).

Protective factors. No validated genetic protective variants or dietary/lifestyle protective factors are established. The declining incidence implies that reduced exposure to the (unidentified) environmental trigger is effectively protective at the population level (Finding F002).

Gene–environment interactions. The prevailing model holds that a genetic predisposition (e.g., SQSTM1/p62 UBA mutation or risk alleles at RANK/OPTN/CSF1/DCSTAMP) sensitizes osteoclast precursors, which then require an environmental "second hit" to produce focal lesions — explaining incomplete penetrance and the focal, localized nature of disease despite a germline mutation present in every cell (Findings F001, F009).

Section 3 — Phenotypes

Phenotype Type HPO term Characteristics / frequency
Bone pain Symptom HP:0002653 (Bone pain) Most common symptom; ~52% of symptomatic patients report pagetic bone pain in both historical and contemporary cohorts (PMID: 36858336); progressive/fluctuating
Bone deformity (bowing of long bones, skull enlargement) Physical manifestation HP:0002750 (Abnormal long bone morphology) 13% contemporary vs 54% historical cohort — declining severity (PMID: 36858336)
Pathological fracture Clinical sign HP:0002659 (Increased susceptibility to fractures) 6.7% contemporary vs 36.7% historical (PMID: 36858336)
Secondary osteoarthritis Clinical sign HP:0002758 (Osteoarthritis) ~43–52% of patients (PMID: 36858336)
Hearing impairment (skull involvement) Clinical sign HP:0000365 (Hearing impairment) ~52–61% when skull affected (PMID: 36858336)
Elevated serum alkaline phosphatase Laboratory abnormality HP:0003155 (Elevated circulating ALP) Core biochemical hallmark; reflects disease activity/extent
Skull enlargement / cranial nerve compression Physical manifestation HP:0000256 (Macrocephaly); HP:0000365 Variable
Osteosarcoma (malignant transformation) Clinical sign HP:0002669 (Osteosarcoma) Rare, ~0.7–1% (see Section 11)

Age of onset: adult/late-onset; typically diagnosed after age 55, mean age at diagnosis ~68.7 y in a contemporary cohort (PMID: 36858336). Progression: slowly progressive but focally stable; individual lesions expand over years. Severity: highly variable, ranging from asymptomatic incidental findings (~85% at diagnosis in contemporary series) to disabling deformity. Quality-of-life impact: driven mainly by chronic pain, deformity, secondary arthritis, and deafness; notably, the PRISM-EZ RCT found no QoL benefit from intensive bone-turnover suppression (PMID: 28176386).

Contemporary disease is milder: patients are older at diagnosis, more often monostotic (60.5%), with lower ALP, fewer pagetic bones, fewer fractures and deformities than historical cohorts (PMID: 36858336).

Section 4 — Genetic / Molecular Information

Causal genes. - SQSTM1 (HGNC:11280; encodes p62/sequestosome-1; OMIM 601530) — the major gene. UBA-domain mutations, recurrent p.P392L (c.1175C>T), occur in ~10–40% of familial and ~5–10% of sporadic PDB and associate with more severe/extensive disease (PMID: 37180975; Finding F001). Functional consequence: impaired ubiquitin binding → dysregulated NF-κB signaling and autophagy → osteoclast hyperactivity. - ZNF687 (HGNC:13809) — causes severe, early-onset, polyostotic PDB with giant-cell tumor predisposition; variants cluster in the nuclear localization signal (e.g., p.Pro937Arg, p.Pro937His, p.Arg939Cys) (PMID: 37728743). - PFN1 (profilin-1) — very rare cause of severe PDB; essentially absent in most cohorts (PMID: 37728743). - VCP (p97; HGNC:12666) — autosomal-dominant missense mutations cause syndromic PDB within multisystem proteinopathy (see Section 6 & Finding F005). - TNFRSF11B/OPG, TNFRSF11A/RANK, SP7/osterix* — cause the distinct recessive juvenile Paget's disease (Finding F008).

Variant classification (ACMG/AMP): SQSTM1 p.P392L and other recurrent UBA-domain variants are classified pathogenic/likely pathogenic; ZNF687 NLS variants are supported as disease-associated (PMID: 37728743). Variant types are predominantly missense, with some truncating UBA-domain variants; large deletions dominate the most severe JPD phenotypes.

Somatic vs germline: Causal variants are germline. Somatic changes are relevant to the osteosarcomas that arise in pagetic bone (COSMIC-type analysis beyond present scope).

Modifier genes: The seven GWAS loci act as susceptibility/severity modifiers on top of SQSTM1; DCSTAMP, OPTN and CSF1 modulate osteoclast fusion and differentiation.

Epigenetic / chromosomal: No recurrent large-scale chromosomal abnormality defines classic PDB (JPD can involve large TNFRSF11B deletions). Systematic disease-specific methylation/histone data were not identified in the reviewed literature — a knowledge gap.

Section 5 — Environmental Information

Environmental / occupational factors. Rural residence and proximity to livestock correlate with higher incidence (breeding-cattle density R²=0.236) (PMID: 40408225). Historical domestic coal combustion has been proposed as a candidate exposure whose decline parallels falling PDB prevalence (PMID: 38902530).

Lifestyle factors. No robust smoking/diet/alcohol association is established; age and male sex remain the dominant demographic risk factors.

Infectious agents (contested). A chronic paramyxovirus infection of osteoclasts — variously measles virus (MV), respiratory syncytial virus (RSV), or canine distemper virus (CDV) — has been hypothesized for decades. Supporting: measles virus RNA was detected by in-situ hybridization in pagetic osteoclasts and other bone cells but not controls (PMID: 3701300). Refuting: PCR failed to detect paramyxovirus sequences in pagetic bone from 10 consecutive patients (PMID: 1805546); prior dog/cat ownership was not a risk factor in 433 US cases (PMID: 2376461); and a serological study of 463 patients found no elevation of MV/CDV/RSV antibodies (only a modest increase in mumps antibody) (PMID: 28361207). Net assessment: the viral hypothesis remains unproven and is not currently supported by the weight of evidence.

Section 6 — Mechanism / Pathophysiology

Central causal chain (Finding F009). Genetic predisposition (SQSTM1/p62 UBA mutation; risk alleles at TNFRSF11A/RANK, OPTN, CSF1, TM7SF4/DCSTAMP) + a putative environmental trigger → osteoclast precursor hypersensitivity to RANKL → dysregulated NF-κB signaling and autophagy (increased SQSTM1, ATG5, LC3-II) → formation of giant, hypernucleated, hyperactive osteoclasts with nuclear inclusions → focal intense bone resorption → compensatory disorganized osteoblastic bone formation (mixed woven + lamellar "mosaic" bone) → expanded, weak, hypervascular bone → pain, deformity, fracture, deafness, and rare osteosarcoma.

The osteoclast is the central effector: "the osteoclast, a myeloid-derived cell responsible for bone resorption, contributes to the disease" (PMID: 33768371). The P394L knock-in mouse confirms autophagy dysregulation downstream of the UBA mutation, with "increased expression of sqstm1, autophagy-related gene 5 (atg5) and light chain 3 gene (lc3) in osteoclast precursors" (PMID: 21515589).

Molecular pathways. RANK–RANKL–OPG (TNFRSF11A–TNFSF11–TNFRSF11B) axis; NF-κB signaling; ubiquitin–proteasome system and autophagy/lysosomal degradation (p62, VCP). GO suggestions: GO:0045672 (positive regulation of osteoclast differentiation), GO:0006914 (autophagy), GO:0043123 (positive regulation of canonical NF-κB signal transduction), GO:0045453 (bone resorption), GO:0002446 (neutrophil/myeloid-lineage regulation).

Protein dysfunction. p62 UBA-domain mutations impair ubiquitin binding, disrupting selective autophagy and NF-κB regulation. VCP/p97 is an AAA+ ATPase; "pathogenic mutations frequently found at the interface between the NTD domain and D1 ATPase domain … cause malfunction of VCP" (PMID: 38963497). MSP genes "share disruption of RNA stress granule function and autophagic degradation" (PMID: 33145792).

Cell types (CL): osteoclast (CL:0000092), osteoblast (CL:0000062), osteocyte (CL:0000137), osteoclast precursor / myeloid monocyte lineage. Subcellular (GO CC): autophagosome (GO:0005776), lysosome (GO:0005764), nucleus/nuclear inclusion bodies, cytoplasmic ubiquitin-rich inclusions.

Immune/inflammatory involvement. Osteoimmunology is central: RANKL-driven osteoclastogenesis is regulated by immune signaling; PDB is framed as an osteoclast-centric immunoskeletal disorder in "Osteoimmunology and Osteoclast Pathology" (PMID: 33768371).

Metabolic changes. High local bone turnover markedly elevates serum ALP and collagen breakdown products; systemic metabolic derangement is uncommon except high-output cardiac states in extensive polyostotic disease.

Section 7 — Anatomical Structures Affected

Organ/skeletal-site level. PDB is focal and can be monostotic or polyostotic. Commonly affected sites (UBERON): pelvis (UBERON:0001270), spine/vertebral column especially lumbar (UBERON:0001130), femur (UBERON:0000981), skull (UBERON:0000033), tibia (UBERON:0000979). Skull involvement causes cranial nerve compression and hearing loss; spinal involvement can cause radiculopathy/myelopathy. The spine — particularly the lumbar spine — is a common site and a frequent location of malignant transformation (PMID: 42359209).

Secondary/system involvement. Cardiovascular (high-output state in extensive disease), nervous system (nerve/cord compression, deafness), joints (secondary osteoarthritis). Tissue level: bone/connective tissue; hypervascular marrow fibrosis. Cell populations (CL): osteoclasts (primary), osteoblasts, osteocytes.

Localization/laterality. Lesions are typically asymmetric and focal, may be unilateral or bilateral, and characteristically do not cross joint spaces; disease begins at one end of a long bone and advances along it (the radiographic "blade of grass"/flame-shaped front).

Section 8 — Temporal Development

Onset. Adult/late-onset, chronic, insidious; rarely diagnosed before age 40. Classic PDB is essentially never congenital (contrast juvenile Paget's disease, which presents in infancy/childhood — Section 9).

Progression. Individual lesions advance slowly and locally; overall the disease is chronic and lifelong but not systemically progressive in most patients. Stages within a lesion: an early osteolytic/resorptive phase → a mixed phase → a late sclerotic/burnt-out phase.

Patterns. Biochemical remission is treatment-induced (bisphosphonates); spontaneous remission of established lesions does not occur. The main "critical period" for intervention is symptomatic active disease with elevated ALP, where a single zoledronic acid infusion yields prolonged suppression (PMID: 31574000).

Section 9 — Inheritance and Population

Epidemiology. PDB is common in older adults of European descent but is declining. UK standardized incidence fell from 0.75/10,000 person-years (1999) to 0.20/10,000 (2015) (PMID: 33742666). In Quebec, standardized incidence fell from 0.77/1,000 (2000/01) to 0.28/1,000 (2019/20) while standardized prevalence stayed stable (~0.44% → 0.43%) (PMID: 37683713). Incidence rises steeply with age (UK crude incidence ≥85 y: 6.3/10,000 men, 3.7/10,000 women) and is higher in men.

Inheritance. Classic PDB is complex/polygenic with autosomal-dominant familial clustering in SQSTM1-linked families showing incomplete, age-dependent penetrance and variable expressivity. About 15–40% of patients have a family history. Seven common loci explain ~13% of familial risk (PMID: 21623375).

Juvenile Paget's disease (JPD; OMIM 239000) is a distinct autosomal-recessive disorder, most often from biallelic loss-of-function of TNFRSF11B/OPG — first shown as a homozygous deletion in Navajos (PMID: 32298837); the most severe phenotypes arise from "major gene deletions or mutations affecting cysteine residues in the ligand-binding domain" (PMID: 25108083). Heterozygous TNFRSF11A/RANK duplication and heterozygous SP7 mutation are rarer causes.

Population demographics. Highest prevalence historically in Britain and in populations of British descent (North America, Australia, New Zealand); largely absent in indigenous populations of those regions and low in Asia/Africa (PMID: 38902530). Male predominance (male:female ≈ 1.2–1.4:1). Founder effects operate in JPD (Navajo TNFRSF11B deletion).

Section 10 — Diagnostics

Recommended workup (Finding F007). Guidelines (Endocrine Society 2014; IOF/ASBMR/ECTS/UK Bone Research Society 2019) recommend plain radiography + serum total alkaline phosphatase for initial diagnosis and technetium-99m radionuclide bone scintigraphy to delineate extent (PMID: 32803929; PMID: 31574000).

  • Laboratory: Elevated serum total ALP (bone-specific ALP if hepatic/pregnancy confounding); markers of bone turnover (P1NP, serum/urinary CTX, NTX) to assess activity and treatment response, typically remeasured at 3–6 months. Serum calcium usually normal.
  • Imaging: X-ray shows cortical thickening, coarse trabeculation, bone expansion, osteoporosis circumscripta (skull), and the flame-shaped advancing lytic front in long bones. Bone scan identifies all active sites. CT/MRI is reserved for complications and suspected malignant transformation (PMID: 42359209).
  • Biopsy: Not routinely required; reserved for atypical lesions or to exclude sarcoma. Histology shows the pathognomonic "mosaic" pattern with giant multinucleated osteoclasts.
  • Genetic testing: SQSTM1 sequencing (single-gene / small panels including ZNF687, VCP, PFN1) is available but not routine — used mainly in early-onset, severe, or strongly familial disease and for research/cascade evaluation. WES/WGS have research utility for gene discovery.

Clinical criteria & differential diagnosis. Diagnosis is radiographic + biochemical. Differentials: osteoblastic metastases (esp. prostate/breast), primary bone tumors, sclerotic/lytic metabolic bone disease, fibrous dysplasia, and hyperparathyroidism.

Screening. No population screening is recommended. Because ALP elevation is often incidental, biochemical detection is common. Cascade genetic screening of relatives in SQSTM1 families is possible but not standard given incomplete penetrance and lack of proven benefit from early asymptomatic treatment.

Section 11 — Outcome / Prognosis

Overall prognosis is good for most patients; PDB is usually not life-limiting, and modern disease is milder. Prognosis "mainly depends on the occurrence of complications involving bones and joints, neurological, cardiovascular or metabolic systems" (PMID: 28690091).

Complications. Bone pain, deformity, secondary osteoarthritis, pathological fracture, deafness/cranial neuropathy, spinal stenosis, high-output cardiac failure (extensive disease), and — rarely — sarcomatous transformation.

Malignant transformation (Finding F004). Osteosarcoma occurs in ~0.7–1% of patients (historically up to ~5.5%). Contemporary incidence: "The incidence of malignant transformation was 0.7%, and the most frequent histologic type was osteogenic sarcoma" (PMID: 1451058). Tumors are mostly high-grade osteosarcomas (~88%), arise in older men (mean ~66 y), predominate in axial skeleton/pelvis and femur, and carry a dismal ~10% 5-year survival (PMID: 17550323). Surgery ± chemotherapy offers the only realistic survival benefit but outcomes remain poor (PMID: 20652460; PMID: 42359209).

Prognostic factors. Extent/number of bones involved and baseline ALP correlate with disease burden; notably, sarcoma risk did not significantly correlate with number of bones involved or disease duration (PMID: 17550323). New/worsening pain, a soft-tissue mass, or a lytic lesion in known pagetic bone should prompt urgent evaluation for malignancy.

Section 12 — Treatment

First-line pharmacotherapy: intravenous bisphosphonates (NCIT: Zoledronic Acid; Bisphosphonate). A single 5-mg IV zoledronic acid infusion is standard first-line therapy and produces durable biochemical remission (Finding F003). It normalizes bone-turnover markers in the majority for ≥2 years independent of prior therapy (PMID: 17032148), and in head-to-head trials achieved therapeutic response in ~90–97% of patients versus ~45% for pamidronate (PMID: 17605632). Long-term durability: over 6.5 years without retreatment, relapse occurred in only 1/152 (0.7%) zoledronate vs 23/115 (20%) risedronate patients (p<0.001) (PMID: 21638319).

Regimen Therapeutic response Durability
Zoledronic acid 5 mg IV (single) ~90–97% 1/152 relapse at 6.5 y (PMID: 21638319)
Neridronate 200 mg (IV or IM) 92.6% (IV), 96.5% (IM) at 6 mo Response declines by 24–36 mo (PMID: 20814970)
Pamidronate 30 mg IV ~45% Inferior (PMID: 17605632)
Risedronate 30 mg PO Lower 20% relapse at 6.5 y (PMID: 21638319)

Treatment goal — an important caveat. Despite superb biochemical control, the PRISM-EZ RCT (n=502) found that intensively normalizing bone turnover did not reduce fractures, orthopedic procedures, or bone pain, nor improve quality of life versus symptomatic treatment: "There were no clinically important differences in quality of life measures or bone pain between the treatment groups" (PMID: 28176386). Treatment is therefore aimed mainly at symptom (pain) relief and protection of complication-prone sites, not universal biochemical normalization.

Supportive care. Analgesics/NSAIDs for pain; calcium and vitamin D repletion before bisphosphonate dosing (response correlates with 25(OH)D — PMID: 20814970); physical therapy, hearing aids. Surgery: joint replacement for pagetic osteoarthritis, fracture fixation, osteotomy for deformity, decompression for neural compression; pre-operative bisphosphonate reduces hypervascular bleeding. Experimental/advanced: no gene, cell, or RNA therapy is approved for PDB. Adverse events of IV bisphosphonates: acute-phase reaction (~14%), hypocalcemia, and rare osteonecrosis of the jaw and atypical femoral fractures.

Section 13 — Prevention

  • Primary prevention: None established, because the environmental trigger is unidentified. The natural population-level decline in incidence suggests reduced trigger exposure is effectively preventive (PMID: 33742666; PMID: 38902530).
  • Secondary prevention: Detection via incidental ALP elevation or radiographs; no formal population screening program.
  • Tertiary prevention: Bisphosphonates and vitamin D/calcium repletion to control active disease; orthopedic surveillance; prompt imaging + biopsy for suspected sarcoma.
  • Genetic counseling: Appropriate for early-onset/familial (SQSTM1) disease and for autosomal-recessive JPD families; incomplete penetrance limits predictive value in classic PDB.
  • Immunization / prophylaxis: Not applicable.

Section 14 — Other Species / Natural Disease

  • Taxonomy: Human disease (Homo sapiens, NCBI:txid9606). Engineered mouse models exist (Mus musculus, NCBI:txid10090).
  • Orthologous genes: mouse Sqstm1, Vcp, Tnfrsf11b (Opg), Tnfrsf11a (Rank), Csf1, Optn.
  • Natural disease in other species: No well-established spontaneous PDB analog in companion animals in the reviewed literature; the epidemiologic association with cattle density (PMID: 40408225) is ecological, not evidence of a natural animal disease. Prior pet ownership (dogs/cats) was exonerated as a risk factor (PMID: 2376461).
  • Comparative biology: The RANK–RANKL–OPG axis and p62/autophagy machinery are evolutionarily conserved, underpinning the translational validity of mouse models.
  • Zoonotic potential: None demonstrated; the paramyxovirus/zoonosis hypotheses remain unproven (Section 5).

Section 15 — Model Organisms

  • P394L SQSTM1 knock-in mouse (mammalian; equivalent to human p.P392L) — the key model. Heterozygotes develop focal pagetic-like lesions in 77% and homozygotes in 95% by 12 months vs 0% in wild-type (P<0.001), with enlarged multinucleated osteoclasts containing nuclear inclusions and increased RANKL sensitivity: "mice with a proline to leucine mutation at codon 394 of mouse sqstm1 (P394L) … develop a bone disorder with remarkable similarity to PDB" (PMID: 21515589). This model also demonstrated that zoledronic acid prevents pagetic-like lesions and accelerated bone loss (PMID: 30154079).
  • Phenotype recapitulation: Excellent for the focal osteolytic/mixed lesions, giant osteoclasts, RANKL hypersensitivity, and autophagy dysregulation.
  • Limitations: Requires the germline mutation plus aging; incomplete recapitulation of the human environmental trigger and of extensive polyostotic deforming disease; does not model osteosarcoma.
  • In-vitro systems: Patient-derived and mutant osteoclast precursor cultures show increased RANKL sensitivity, giant osteoclast formation, and elevated SQSTM1/ATG5/LC3 (PMID: 21515589).
  • Resources: MGI (mouse), Alliance of Genome Resources.

Mechanistic Model / Interpretation

   GENETIC PREDISPOSITION                         ENVIRONMENTAL TRIGGER
  ┌──────────────────────────┐                   ┌──────────────────────┐
  │ SQSTM1/p62 UBA mut(P392L) │                   │ Unknown, declining    │
  │ ZNF687, PFN1, VCP         │   +               │ (?paramyxovirus, coal │
  │ Risk loci: RANK, OPTN,    │                   │  smoke, rural/cattle) │
  │ CSF1, DCSTAMP, PML, RIN3, │                   └──────────┬───────────┘
  │ NUP205                    │                              │
  └───────────┬──────────────┘                              │
      └──────────────┬───────────────────────────────┘
             ▼
Osteoclast precursor HYPERSENSITIVITY to RANKL
+ dysregulated NF-κB signaling + autophagy (↑SQSTM1/ATG5/LC3)
             ▼
GIANT, hypernucleated, hyperactive OSTEOCLASTS (nuclear inclusions)
             ▼
Focal intense BONE RESORPTION (osteolytic phase)
             ▼
Compensatory DISORGANIZED OSTEOBLASTIC bone formation
             ▼
Expanded, weak, hypervascular "MOSAIC" bone (woven + lamellar)
             ▼
   ┌─────────────┬───────────────┬────────────┬─────────────┬────────────┐
  Pain        Deformity       Fracture      Deafness     2° Osteoarthritis
                                    └── Rare: OSTEOSARCOMA (~0.7–1%)

Upstream vs downstream: SQSTM1/p62 dysfunction and RANK–RANKL–OPG imbalance are the most upstream molecular events; the osteoclast is the central effector; osteoblastic overactivity and mosaic bone are downstream consequences. Juvenile Paget's disease (OPG loss → unopposed RANKL) is a "natural experiment" that isolates the RANK–RANKL–OPG limb and confirms its centrality (Finding F008).

Evidence Base

PMID How it supports / challenges findings
21515589 P394L knock-in mouse recapitulates PDB; establishes causal role of UBA mutation and autophagy dysregulation (F001, F009)
37180975 SQSTM1 as most frequent genetic cause; UBA mutations linked to severity (F001)
33742666 Declining UK incidence → changing environmental trigger (F002)
40408225 Rural livestock (cattle) association; environmental contribution (F002)
21638319 Durable remission from single zoledronic acid infusion (F003)
28176386 PRISM-EZ: intensive therapy gives no QoL/pain/fracture benefit (F003)
17550323 Paget sarcoma histology (88% osteosarcoma) and 10% 5-yr survival (F004)
1451058 0.7% malignant transformation incidence (F004)
40037468 VCP-MSP/IBMPFD — syndromic PDB (F005)
33145792 Shared stress-granule/autophagy defect across MSP genes (F005)
21623375 Seven GWAS loci; ~13% familial risk (F006)
31574000 Diagnostic workup + zoledronic acid first-line (F007)
32803929 Radiography + ALP + bone scan algorithm (F007)
32298837 OPG (TNFRSF11B) loss causes JPD; SP7 mutation (F008)
25108083 OPG genotype–phenotype correlation in JPD (F008)
33768371 Osteoclast as central effector cell (F009)
3701300 / 1805546 / 28361207 / 2376461 Conflicting/negative evidence on the paramyxovirus hypothesis

Limitations and Knowledge Gaps

  1. The environmental trigger is unidentified. Declining incidence strongly implies one, but coal-smoke, paramyxovirus, and cattle-exposure hypotheses are unconfirmed and partly contradicted.
  2. Genotype–phenotype gaps. SQSTM1 and the seven GWAS loci explain only a minority of heritability; many familial cases are unexplained (PMID: 41024681).
  3. Epigenetics. No robust disease-specific DNA-methylation/histone dataset was identified.
  4. Treatment paradox. Excellent biochemical control does not translate into fewer fractures or better QoL (PRISM-EZ), leaving the optimal treatment goal (biochemical vs symptomatic) unresolved.
  5. Sarcoma risk stratification. No reliable biomarker predicts which patients will undergo malignant transformation; surveillance guidelines are underdeveloped (PMID: 42359209).
  6. Modern data are cohort/registry-based, subject to referral and ascertainment bias; SEER-type survival data for classic PDB are limited.

Proposed Follow-up Experiments / Actions

  1. Trigger identification: Metagenomic/16S and viral-capture sequencing of active pagetic bone vs controls, paired with geospatial exposure analysis (cattle density, historical coal use) to test environmental hypotheses definitively.
  2. Heritability completion: Large multi-ancestry GWAS + WGS/burden testing in SQSTM1-negative families to find the missing causal genes.
  3. Epigenomic profiling: ATAC-seq/WGBS/ChIP-seq of pagetic vs normal osteoclasts to map disease-specific regulatory changes.
  4. Randomized trial of a symptom-guided vs biochemical-target treatment strategy with fracture, deformity progression, deafness, and validated QoL endpoints (extending PRISM-EZ).
  5. Sarcoma biomarker discovery: Longitudinal imaging + circulating tumor DNA/somatic mutation surveillance in high-burden pagetic bone to enable early detection.
  6. Mechanistic dissection in models: Cross P394L-Sqstm1 mice onto RANK/OPG-modified backgrounds and test autophagy modulators to define the causal hierarchy and identify targeted (non-bisphosphonate) therapies.

Report compiled from 9 confirmed findings and 39 primary papers over 5 investigation iterations. Evidence source types are indicated throughout: human clinical/registry, model organism (P394L mouse), in-vitro osteoclast, and computational/GWAS.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 34
Resolved 34
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 12
Quoted claims found in source 9
Quoted claims not found in source 3
References weighed for topical relevance 34
On topic 24
Off topic 0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMID:38963497 (abstract only): "pathogenic mutations frequently found at the interface between the NTD domain and D1 ATPase domain … cause malfunction of VCP"
  • closest text in source: "Pathogenic mutations frequently found at the interface between the NTD domain and D1 ATPase domain have been shown to cause malfunction of VCP, leading to degenerative disorders including the inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD), amyotrophic lateral sclerosis (ALS), and cancers"
  • PMID:33768371 (abstract only): "Osteoimmunology and Osteoclast Pathology"
  • Text part not found as substring: 'Osteoimmunology and Osteoclast Pathology' (note: only abstract available for PMID:33768371, full text may contain this excerpt)
  • PMID:21515589 (abstract only): "mice with a proline to leucine mutation at codon 394 of mouse sqstm1 (P394L) … develop a bone disorder with remarkable similarity to PDB"
  • closest text in source: "Here we show that mice with a proline to leucine mutation at codon 394 of mouse sqstm1 (P394L), equivalent to the P392L SQSTM1 mutation in humans, develop a bone disorder with remarkable similarity to PDB"

Term Validation

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

Outcome Count
Terms checked 28
Resolved 24
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 4
Terms whose name was checked 12
Terms named correctly 8
Terms named as a different term 1
Terms whose name is worth a second look 3

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • HP:0002750 (1 mention) - the report calls it "Abnormal long bone morphology"; HP calls it Delayed skeletal maturation

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • HP:0003155 (1 mention) - the report calls it "Elevated circulating ALP"; HP calls it Elevated circulating alkaline phosphatase concentration, and lists "Elevated ALP" among its other names
  • GO:0043123 (1 mention) - the report calls it "positive regulation of canonical NF-κB signal transduction"; GO calls it positive regulation of canonical NF-kappaB signal transduction
  • GO:0002446 (1 mention) - the report calls it "neutrophil/myeloid-lineage regulation"; GO calls it neutrophil mediated immunity

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.