🏷

Classifications

Harrison's Part

ISDS Skeletal Nosology

👪

Inheritance

1

Autosomal recessive inheritance HP:0000007

All three causal genes act recessively: affected individuals carry biallelic (homozygous or compound heterozygous) pathogenic variants and heterozygous carriers are generally unaffected. Expressivity is markedly variable even within a family and even between relatives carrying the same genotype, so the genotype does not predict whether a patient presents with calcific masses, with hyperostosis, or with biochemical abnormality alone.

Autosomal recessive inheritance Expressivity: VARIABLE

Show evidence (3 references)

PMID:29389098 SUPPORT Other

"HFTC is inherited in an autosomal recessive manner."

GeneReviews states the mode of inheritance directly.

PMID:29389098 SUPPORT Other

"At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."

This supports the recurrence risks and the asymptomatic carrier state.

PMID:27164190 SUPPORT Human Clinical

"Clinical manifestations varied, even within families, ranging from asymptomatic to large, disabling calcifications."

The NIH cohort documents intrafamilial variable expressivity.

◆

Subtypes

3

HFTC1 (GALNT3-related) MONDO:0100252

GALNT3 hgnc:4125

The most frequently reported molecular subtype. Biallelic GALNT3 variants abolish GalNAc-T3-dependent O-glycosylation of FGF23, so the intact hormone is cleaved and inactivated. Serum intact FGF23 is low with markedly elevated C-terminal fragments. Both the tumoral-calcinosis and the hyperostosis-hyperphosphatemia presentations arise from this subtype, including from the same allele.

Show evidence (2 references)

PMID:15133511 SUPPORT Human Clinical

"Sequence analysis of GALNT3 identified biallelic deleterious mutations in all individuals with FTC"

The gene-discovery study establishes biallelic GALNT3 variants as the cause of this subtype.

PMID:20358599 SUPPORT Human Clinical

"The four novel GALNT3 mutations invariably resulted in hyperphosphatemia as a result of low intact FGF23, but other clinical manifestations were variable."

This supports the subtype's constant biochemical signature alongside variable clinical expression.

HFTC2 (FGF23-related) MONDO:0060714

FGF23 hgnc:3680

Biallelic FGF23 missense variants (reported alleles include p.Ser71Gly, p.Met96Thr, p.Gly123Trp and p.Ser129Phe) destabilise the intact hormone or trap it intracellularly, so only C-terminal fragments reach the circulation. The biochemical signature is the same as HFTC1 - low intact FGF23 with high C-terminal FGF23 - because both subtypes converge on failure to deliver intact hormone.

Show evidence (2 references)

PMID:15590700 SUPPORT Human Clinical

"Sequencing revealed a homozygous missense mutation in the FGF23 gene (p.S71G) at an amino acid position which is conserved from fish to man."

This establishes a homozygous FGF23 missense variant as a distinct molecular cause.

PMID:19188744 SUPPORT Human Clinical

"Sequencing analysis revealed a novel homozygous FGF23 missense mutation (c.367G>T, p.Gly123Trp) in both siblings while the parents were carriers of the mutation."

A second independent family documents a homozygous FGF23 missense allele with unaffected heterozygous parents.

HFTC3 (KL / alpha-Klotho-related) MONDO:0060715

KL hgnc:6344

The rarest subtype, established by a single homozygous KL missense variant (p.His193Arg) that destabilises the KL1 glycosidase domain and reduces expression and secretion of alpha-Klotho. Because the defect is in the co-receptor rather than the hormone, intact FGF23 is high rather than low, and the kidney is resistant to it; this is the one subtype in which the diagnostic intact-versus-C-terminal FGF23 pattern is inverted.

Show evidence (2 references)

PMID:17710231 SUPPORT Human Clinical

"Herein we report a homozygous missense mutation (H193R) in the KLOTHO (KL) gene of a 13-year-old girl who presented with severe tumoral calcinosis with dural and carotid artery calcifications."

This is the index observation establishing KL as the third causal gene.

PMID:17710231 SUPPORT Human Clinical

"This patient exhibited defects in mineral ion homeostasis with marked hyperphosphatemia and hypercalcemia as well as elevated serum levels of parathyroid hormone and FGF23."

The elevated FGF23 in this patient distinguishes the resistance subtype from the deficiency subtypes.

?

Discussions and Knowledge Gaps

5

Why does mineral deposit at specific periarticular sites and in specific organs when the driving abnormality - an elevated calcium-phosphate product - is systemic?

KNOWLEDGE GAP OPEN gap_hftc_site_selection

Attached to

pathophysiology#Hyperphosphatemia with Elevated Calcium-Phosphate Product pathophysiology#Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue

Repetitive trauma and pressure are cited as the site determinant, but that is a clinical observation rather than a demonstrated mechanism, and it does not explain the dental pulp, the testis or the retina. Nor does it explain why some patients with the same genotype and the same phosphate level never form a mass. Identifying a local permissive factor would matter clinically: it is the difference between "lower the phosphate and hope" and a target that acts where the deposits form.

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"Ectopic calcifications (tumoral calcinosis) typically found in periarticular soft tissues exposed to repetitive trauma or prolonged pressure"

This is the observational basis for the mechanical hypothesis, stated as a site association rather than a mechanism.

PMID:20358599 SUPPORT Human Clinical

"Although the presence of massive calcifications, cortical hyperostosis, or dental anomalies was not shared by all patients, all had persistent hyperphosphatemia."

A constant biochemical driver with inconstant lesions is exactly what an unexplained local permissive factor would look like.

What links the hyperphosphatemic state to diaphyseal cortical hyperostosis and its episodic inflammatory attacks?

KNOWLEDGE GAP OPEN gap_hftc_hyperostosis_mechanism

Attached to

pathophysiology#Diaphyseal Cortical Hyperostosis phenotypes#Painful Diaphyseal Hyperostosis

Allelic identity with the calcinosis presentation establishes that hyperostosis belongs to the same disease and follows the same phosphate excess, but the step from systemic phosphate to periosteal apposition in a particular long bone, at a particular time, is unaccounted for. The attacks are episodic while the biochemistry is constant, so something other than the phosphate level is timing them. This is the reason the lesion is repeatedly treated as osteomyelitis.

Show evidence (2 references)

PMID:20358599 SUPPORT Human Clinical

"tumoral calcinosis and hyperostosis-hyperphosphatemia syndrome represent a continuous spectrum of the same disease caused by increased phosphate levels, rather than two distinct disorders"

This establishes the shared cause without supplying the local mechanism, which is the gap.

PMID:15599692 SUPPORT Human Clinical

"The heterogeneous phenotypic expression of the identified splice site mutation implies the existence of inherited or epigenetic modifying factors of importance in the regulation of ppGalNAc-T3 activity."

The original authors explicitly posit unidentified modifiers, which is the open question restated.

Would restoring intact FGF23 signalling correct the disease, and can early phosphate control prevent lesions from ever forming?

KNOWLEDGE GAP OPEN gap_hftc_no_replacement_therapy

Attached to

pathophysiology#Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule treatments#Dietary Phosphate Restriction treatments#Phosphaturic Therapy with Acetazolamide or Probenecid

Every available treatment acts downstream of the lesion, on the phosphate load rather than on the missing signal, and none has been tested in a randomised trial. The two questions are linked: because no therapy restores the hormone, the only preventive strategy is phosphate control in the presymptomatic biochemical phase, and nobody has shown prospectively that it stops lesions forming. The acetazolamide case in which tumour formation ceased with no change in serum phosphate or TRP is a direct warning that the assumed mechanism of current therapy may not be the operative one.

Show evidence (3 references)

PMID:29389098 SUPPORT Other

"No randomized clinical trials have been performed; studies of the treatment of HFTC consist of case reports or case series."

GeneReviews states the evidentiary position of every current treatment.

PMID:27164190 SUPPORT Human Clinical

"There is no standard treatment for this disease, and studies of the treatment of FTC/HHS do not exist aside from case reports or case series."

An independent statement of the same evidentiary gap.

PMID:24668887 SUPPORT Human Clinical

"no change in tubular reabsorption of phosphate (TRP) (96.9% vs. 95.9%, P = 0.34) or serum phosphate (6.6 mg/dl vs. 6.9 mg/dl, P = 0.52 pre- and post-acetazolamide, respectively)"

Clinical benefit without any change in the parameter the drug is given to change is the specific anomaly the gap names.

Why does the Galnt3-null mouse reproduce the human biochemistry but form no calcific masses, and what does the missing step mean for testing therapies whose endpoint is lesion burden?

HUMAN MODEL MISMATCH OPEN mismatch_hftc_galnt3_mouse_no_calcinosis

Attached to

pathophysiology#Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue animal_models#Mus musculus

The model at issue is specifically the Galnt3-null mouse (the entry's "Galnt3-null mouse" animal model); the Fgf23-null and Klotho-deficient mice listed beside it are not the subject of this mismatch. The mismatch is informative rather than merely inconvenient. The Galnt3-null mouse has the hormone deficiency, the transporter change, the hyperphosphatemia and the inappropriate calcitriol, and still does not calcify - so those four things are not jointly sufficient for the lesion, and something present in humans and absent in this mouse is required. Practically, it means no current genetic model supports a preclinical efficacy endpoint of lesion regression, which is the outcome patients care about most.

Show evidence (2 references)

PMID:19213845 SUPPORT Model Organism

"In this study we generated mice lacking the Galnt3 gene, which developed hyperphosphatemia without apparent calcifications."

This is the mismatch itself: full biochemical phenotype, absent anatomical phenotype.

PMID:19213845 SUPPORT Model Organism

"Our findings indicate that Galnt3-deficient mice have a biochemical phenotype of tumoral calcinosis"

The authors themselves limit the claim to a biochemical phenotype.

When a patient has the full biochemical picture of HFTC but no biallelic GALNT3, FGF23 or KL genotype, how should the entry be scoped?

OPEN QUESTION OPEN gap_hftc_autoantibody_phenocopy

Attached to

pathophysiology#Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess disease#Hyperphosphatemic Familial Tumoral Calcinosis

One of eight NIH-cohort subjects had no causative mutation found, and an acquired anti-FGF23 autoantibody phenocopy is recognised. That phenocopy is not modelled in this entry: it reaches the same endocrine node by an autoimmune route, so it is mechanistically a different disease that happens to share a downstream chain from the FGF23-deficiency node onward. Whether dismech should carry it as a separate acquired entry conforming to the same downstream nodes, or as a differential note only, is unresolved here.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"GALNT3 mutations were identified in seven subjects; no causative mutation was found in the eighth."

This documents genotype-negative disease within a well-characterised cohort.

PMID:33977199 SUPPORT Human Clinical

"Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disorder caused by mutations in FGF23, GALNT3, KLOTHO, or FGF23 autoantibodies."

This source explicitly includes the autoantibody route alongside the three genes, which is the scoping question.

⚙

Pathophysiology

13

Biallelic GALNT3 Loss of Function

Germline biallelic deleterious GALNT3 variants remove the activity of GalNAc-T3, the trans-Golgi glycosyltransferase that initiates mucin-type O-glycosylation. A recurrent splice-site allele (c.1524+1G>A) accounts for both HFTC and HHS presentations in Middle Eastern families and is a founder mutation on a shared haplotype.

GALNT3 hgnc:4125

Genetic context GALNT3 hgnc:4125 variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

Biallelic loss of GalNAc-T3 activity is the commonest molecular cause of HFTC.

polypeptide N-acetylgalactosaminyltransferase activity GO:0004653 ⇓ LOSS OF FUNCTION

Downstream

Failure of FGF23 O-Glycosylation and Furin Cleavage of Intact FGF23 Without GalNAc-T3, the FGF23 proprotein-convertase recognition motif is not O-glycosylated and is therefore not protected from processing.

Show evidence (2 references)

PMID:15133511 SUPPORT Human Clinical

"This region includes the gene GALNT3, which encodes a glycosyltransferase responsible for initiating mucin-type O-glycosylation."

This identifies the gene product and its enzymatic role.

PMID:15599692 SUPPORT Human Clinical

"All affected individuals harbored a homozygous splice site mutation (1524+1G-->A) in GALNT3."

This documents the recurrent biallelic splice-site allele in affected families.

Biallelic FGF23 Missense Variants Blocking Intact Hormone Secretion

Homozygous or compound heterozygous FGF23 missense variants act on the hormone itself. The p.Ser71Gly mutant is retained in the Golgi so that only the C-terminal fragment is secreted; other reported alleles include p.Met96Thr, p.Gly123Trp and p.Ser129Phe. The functional result is the same as GALNT3 loss - intact hormone does not reach the circulation - so this node feeds the same downstream deficiency.

FGF23 hgnc:3680

Genetic context FGF23 hgnc:3680 variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

Missense alleles that prevent secretion of the intact hormone.

FGF23 hormone activity GO:0005179 ⇓ LOSS OF FUNCTION

Downstream

Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess Intracellular retention of the mutant protein leaves only inactive C-terminal fragments in the circulation.

Show evidence (2 references)

PMID:15590700 SUPPORT Human Clinical

"These results suggest that the FGF23 function is decreased by absent or extremely reduced secretion of intact FGF23."

This states the loss-of-function consequence of the FGF23 allele.

PMID:15590700 SUPPORT Human Clinical

"We conclude that FGF23 mutations in hypophosphatemic rickets and FTC have opposite effects on phosphate homeostasis."

This records that the same gene produces opposite phosphate phenotypes depending on the allele's effect.

Failure of FGF23 O-Glycosylation and Furin Cleavage of Intact FGF23

Bioactive FGF23 carries three O-linked glycans. Incompletely glycosylated FGF23 is susceptible to cleavage by subtilisin-like proprotein convertases at the RXXR site that separates the N-terminal and C-terminal halves of the hormone, splitting it into inactive fragments. O-glycosylation and protease processing compete for the same motif, so loss of the glycosyltransferase shifts the balance decisively toward cleavage.

osteocyte CL:0000137 osteoblast CL:0000062

protein O-linked glycosylation GO:0006493 ↓ DECREASED

proprotein convertase cleavage of FGF23 GO:0004252 ↑ INCREASED

Downstream

Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess Enhanced processing consumes the intact hormone and generates the C-terminal fragments that dominate the circulating pool.

Show evidence (3 references)

PMID:17129170 SUPPORT In Vitro

"Biologically active FGF23 has three O-linked glycans. FGF23 with only one or two O-linked glycans is processed into inactive fragments."

This establishes the glycan-dependence of resistance to processing.

PMID:17129170 SUPPORT In Vitro

"Decreasing the expression of the GALNT3 gene by RNA interference resulted in enhanced processing of FGF23."

Silencing the glycosyltransferase reproduces the processing shift experimentally.

PMID:16638743 SUPPORT In Vitro

"The study suggests a novel posttranslational regulatory model of FGF23 involving competing O-glycosylation and protease processing to produce intact FGF23."

This states the competition between glycosylation and proteolysis that the node describes.

Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess

The shared endocrine lesion of the GALNT3 and FGF23 subtypes: circulating intact FGF23 is low or inappropriately normal for the degree of hyperphosphatemia, while C-terminal FGF23 is markedly elevated because the C-terminal assay detects both intact hormone and fragments. This dissociated assay pattern is the diagnostic biochemical signature of the disease.

phosphate ion homeostasis GO:0055062 ⚠ ABNORMAL

Animal models

Galnt3-null mouse Mus musculus recapitulates The model reproduces the exact dissociation seen in patients: low intact hormone with excess C-terminal fragments on a background of increased Fgf23 transcription.

Downstream

Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule Too little intact hormone reaches the proximal tubular receptor complex to signal.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"C-terminal FGF23 was markedly elevated whereas iFGF23 was comparatively low, consistent with increased FGF23 cleavage."

The NIH cohort documents the dissociated intact/C-terminal pattern across affected subjects.

PMID:31965220 SUPPORT Other

"resulting in the excessive cleavage of active intact FGF23 (FGF23, GALNT3) or increased resistance to the action of FGF23 (KL)"

The review separates the cleavage mechanism of the FGF23/GALNT3 subtypes from the resistance mechanism of the KL subtype.

Biallelic KL Loss of Function and Renal FGF23 Resistance

In HFTC3 the hormone is intact but its obligate co-receptor is not. The p.His193Arg substitution sits at the base of the KL1 catalytic cleft and destabilises the domain, so expression and secretion of alpha-Klotho are markedly reduced and FGF23 cannot signal through its cognate receptors. Intact FGF23 therefore rises rather than falls, and this node bypasses the hormone-deficiency node to reach the same signalling failure.

KL hgnc:6344

Genetic context KL hgnc:6344 variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

A homozygous KL missense allele reducing alpha-Klotho co-receptor availability.

Animal models

Klotho-deficient mouse Mus musculus partially recapitulates The model carries the same genetic lesion as HFTC3 - loss of functional alpha-Klotho - and so reproduces the upstream cause of FGF23 resistance.

Downstream

Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule Reduced alpha-Klotho removes the co-receptor that FGF23 requires for high-affinity signalling, producing end-organ resistance despite adequate hormone.

Show evidence (1 reference)

PMID:17710231 SUPPORT Human Clinical

"our findings provide what we believe to be the first evidence that loss-of-function mutations in human KL impair FGF23 bioactivity, underscoring the essential role of KL in FGF23-mediated phosphate and vitamin D homeostasis in humans"

This establishes KL loss of function as a human cause of impaired FGF23 action.

Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule

The convergence point of all three genetic lesions. Intact FGF23 normally acts on proximal tubular cells through FGFR1 together with the co-receptor Klotho to suppress the sodium-phosphate cotransporters NaPi-IIa and NaPi-IIc and to suppress 25-hydroxyvitamin D 1-alpha-hydroxylase. When that signal is absent - through hormone deficiency in HFTC1/HFTC2 or through co-receptor loss in HFTC3 - both suppressive arms fail simultaneously.

epithelial cell of proximal tubule CL:0002306

fibroblast growth factor receptor signaling pathway GO:0008543 ↓ DECREASED

renal proximal tubule UBERON:0004134

Downstream

Increased Proximal Tubular Sodium-Phosphate Cotransport Loss of the suppressive FGF23 signal leaves NaPi-IIa and NaPi-IIc expression unopposed.

Unsuppressed Renal Calcitriol Production Loss of the suppressive FGF23 signal leaves 1-alpha-hydroxylase expression unopposed.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"with the intact hormone (iFGF23) acting via the fibroblast growth factor receptor 1 (FGFR1) along with its co-receptor Klotho to inhibit sodium phosphate co-transporter (NaPi-2a and-2c) and 25-hydroxyvitamin D 1-α-hydroxylase expression"

This states the receptor complex and the two effector arms whose loss defines this node.

PMID:33977199 SUPPORT Human Clinical

"thereby inhibiting phosphate reabsorption and active vitamin D formation in renal proximal tubules"

An independent source states the same proximal-tubular dual effect of FGF23 signalling.

Increased Proximal Tubular Sodium-Phosphate Cotransport

Unopposed NaPi-IIa and NaPi-IIc activity raises tubular phosphate reclamation. Clinically this appears as an inappropriately high tubular reabsorption of phosphate (TRP) and a raised renal phosphate threshold (TmP/GFR) despite an already elevated serum phosphate and normal glomerular function.

epithelial cell of proximal tubule CL:0002306

phosphate ion transmembrane transport GO:0035435 ↑ INCREASED

Animal models

Galnt3-null mouse Mus musculus recapitulates Renal sodium-phosphate cotransporter expression is elevated in the knockout, the transporter-level change the human node asserts.

Fgf23-null mouse Mus musculus recapitulates Complete loss of FGF23 produces exactly the renal phosphate-conserving state the node asserts.

Downstream

Hyperphosphatemia with Elevated Calcium-Phosphate Product Failure to excrete phosphate raises the circulating phosphate concentration.

Increased Renal Tubular Phosphate Reabsorption The transporter change is measured directly as elevated TRP and TmP/GFR.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."

The cohort shows increased tubular reabsorption in every affected subject.

PMID:19188744 SUPPORT Human Clinical

"It is associated with hyperphosphatemia due to increased tubular phosphate reabsorption, despite normal renal function and normal plasma PTH levels."

This attributes the hyperphosphatemia to tubular reabsorption with renal function and PTH preserved.

Unsuppressed Renal Calcitriol Production

1-alpha-hydroxylase is normally suppressed by FGF23, so in health a high phosphate load lowers 1,25-dihydroxyvitamin D. In HFTC that brake is absent and calcitriol is elevated or inappropriately normal for the prevailing hyperphosphatemia, which sustains intestinal absorption of calcium and phosphate instead of restraining it.

vitamin D biosynthetic process GO:0042368 ↑ INCREASED

25-hydroxyvitamin D 1-alpha-hydroxylase activity GO:0004498 ↑ INCREASED

Animal models

Fgf23-null mouse Mus musculus recapitulates The knockout supplies the mechanistic step the human data can only infer: the calcitriol elevation is attributable to increased renal 1-alpha-hydroxylase expression.

Downstream

Hyperphosphatemia with Elevated Calcium-Phosphate Product Non-suppressed calcitriol promotes gastrointestinal absorption of phosphorus and calcium, adding to the mineral load.

Show evidence (1 reference)

PMID:17710231 SUPPORT Human Clinical

"hyperphosphatemia secondary to increased renal tubular phosphate reabsorption and elevated or inappropriately normal 1,25-dihydroxyvitamin D"

This pairs the calcitriol abnormality with the tubular phosphate abnormality as the defining biochemistry.

Hyperphosphatemia with Elevated Calcium-Phosphate Product

Persistent hyperphosphatemia with normal serum calcium, normal PTH and normal renal function raises the calcium-phosphate product above the solubility limit of the extracellular fluid. This is the systemic driver of every downstream lesion, and it is the only step in the chain that current therapy tries to modify.

phosphate ion homeostasis GO:0055062 ⚠ ABNORMAL

Downstream

Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue Supersaturation precipitates amorphous calcium-phosphate/hydroxyapatite in soft tissue, preferentially at sites of repetitive trauma or pressure.

Diaphyseal Cortical Hyperostosis Hyperostosis tracks with the same hyperphosphatemic state rather than with a distinct genotype, but the local mechanism linking phosphate excess to cortical apposition is not established.

Ectopic Calcification of Vessels, Teeth and Other Organs The same supersaturated state deposits mineral outside the periarticular compartment, in vessels, dental pulp, eye, intestine and testis.

Hyperphosphatemia The node is measured clinically as a persistent elevation of serum phosphate.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"The result is functional deficiency of, or resistance to, intact FGF23 (iFGF23), causing hyperphosphatemia, increased renal tubular reabsorption of phosphorus (TRP), elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D), ectopic calcifications, and/or diaphyseal hyperostosis."

This is the complete biochemical-to-clinical statement of the shared downstream pathway.

PMID:20358599 SUPPORT Human Clinical

"However, circulating calcium and parathyroid hormone (PTH) are usually normal."

Normal calcium and PTH distinguish this state from hyperparathyroid and CKD-related hyperphosphatemia.

Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue

Lobular masses of amorphous calcium-phosphate accumulate in skin, subcutaneous tissue and connective tissue around large joints, typically the hips, elbows and shoulders, and preferentially where the tissue is exposed to repetitive trauma or prolonged pressure. Masses may enlarge, ulcerate and become infected, and they recur after incomplete excision while the hyperphosphatemia persists.

fibroblast CL:0000057

biomineral tissue development GO:0031214 ⚠ ABNORMAL

hip joint UBERON:0001486 elbow joint UBERON:0001490 shoulder joint UBERON:0001470 subcutaneous tissue UBERON:0002072

Animal models

Galnt3-null mouse Mus musculus fails to recapitulate The knockout is biochemically a tumoral-calcinosis model but not anatomically one: hyperphosphatemia develops without apparent calcifications.

Downstream

Foreign-Body and Systemic Inflammation Around Calcific Deposits Deposited crystal provokes a macrophage-rich chronic inflammatory reaction in the surrounding tissue.

Periarticular Calcific Masses The deposits present clinically as palpable, often disabling periarticular masses.

Restricted Joint Movement Mass effect and pain around the joint reduce range of motion.

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"Ectopic calcifications (tumoral calcinosis) typically found in periarticular soft tissues exposed to repetitive trauma or prolonged pressure (e.g., hips, elbows, and shoulders)"

GeneReviews specifies both the tissue compartment and the mechanical site preference.

PMID:38951179 SUPPORT Human Clinical

"The most frequently involved sites were the hip/gluteal region (34/63; 53.9%) followed by the elbow/forearm (26/63; 41.2%), and the shoulder (18/63; 28.5%)."

The systematic review quantifies the site distribution across 63 reported patients.

Foreign-Body and Systemic Inflammation Around Calcific Deposits

Histology of resected lesions shows ectopic calcification with chronic inflammation, and in one NIH subject areas of mature heterotopic ossification adjacent to the inflamed deposit. A minority of patients develop overwhelming systemic inflammation with markedly elevated C-reactive protein; the response of two such patients to interleukin-1 antagonists identifies IL-1-driven inflammation as a component distinct from the mineral burden itself.

macrophage CL:0000235

inflammatory response GO:0006954 ↑ INCREASED

Downstream

Systemic Inflammation Perilesional inflammation can become systemic, with constitutional symptoms and elevated CRP.

Heterotopic Ossification Mature lamellar bone was found adjacent to an inflamed deposit, suggesting that the surrounding inflammation mediates ossification, but the pathway is not established.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"Biopsies from four subjects showed ectopic calcification and chronic inflammation, with areas of heterotopic ossification observed in one subject."

This is the histological basis for treating perilesional inflammation as part of the mechanism.

PMID:27164190 SUPPORT Human Clinical

"Overwhelming systemic inflammation has not been described previously in FTC/HHS; the response to IL-1 antagonists suggests that anti-inflammatory drugs may be useful adjuvants."

The IL-1 response supports a cytokine-driven inflammatory component.

Diaphyseal Cortical Hyperostosis

Episodic painful swelling, warmth and erythema over the diaphyses of long bones, most often the tibiae, with radiographic cortical hyperostosis, diaphysitis and periosteal apposition. This is the presentation that defines hyperostosis-hyperphosphatemia syndrome, and because the same GALNT3 alleles produce it and produce tumoral calcinosis, it is a manifestation of this disease rather than a separate entity. It is regularly misdiagnosed as bacterial osteomyelitis.

tibia UBERON:0000979

Downstream

Painful Diaphyseal Hyperostosis The cortical lesion presents clinically as recurrent long-bone pain and swelling.

Bone Pain Diaphyseal pain is the symptom that brings the hyperostotic attack to attention.

Show evidence (3 references)

PMID:15599692 SUPPORT Human Clinical

"characterized by elevated serum phosphate levels and repeated attacks of acute, painful swellings of the long bones with radiological evidence of periosteal reaction and cortical hyperostosis"

This describes the hyperostotic lesion and its episodic clinical behaviour.

PMID:15599692 SUPPORT Human Clinical

"Our results demonstrate that HHS and HFTC are allelic disorders despite their phenotypic differences"

This is the evidence that the hyperostotic presentation belongs to the same disease.

PMID:27164190 SUPPORT Human Clinical

"which may manifest clinically as diaphyseal pain of the long bones and is often erroneously diagnosed as osteomyelitis"

This records the characteristic misdiagnosis.

Ectopic Calcification of Vessels, Teeth and Other Organs

Beyond the periarticular compartment, mineral deposits in large and small vessels, in the dental pulp and root, and less commonly in the eye, intestine and testis. The dental lesion is the most penetrant of these: pulp density rises and pulp volume falls sevenfold, the odontoblast layer loses its polarity, and the pulp cavity fills with calcified material.

odontoblast CL:0000060

dental pulp UBERON:0001754

Downstream

Dental Root and Pulp Disease Pulpal and root mineralization produces the characteristic dental phenotype.

Short Dental Roots Root cementum and pulp mineralization accompany the shortened, bulbous root morphology.

Vascular Calcification Mineral deposition in large and small vessels.

Testicular Microlithiasis Microcalcification within the testis.

Angioid Streaks Angioid streaks are reported in this disease, but the route from hyperphosphatemia to breaks in Bruch's membrane is not established.

Show evidence (2 references)

PMID:31965220 SUPPORT Other

"However, other regions, such as the eye, intestine, vasculature, and testis, are also targets of ectopic calcification."

This lists the extra-articular targets of the same deposition process.

PMID:33977199 SUPPORT Human Clinical

"Histology revealed loss of the polarized odontoblast cell layer and an obliterated pulp cavity that was filled with calcified material."

This is the tissue-level description of the dental lesion.

✶

Histopathology

4

Ectopic Calcification of Periarticular Soft Tissue VERY_FREQUENT

Resected masses consist of calcific material in soft tissue. Biopsy is not required when the biochemistry and imaging are typical, but resected lesions consistently show this finding.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"Specimens obtained following surgical resection of calcific tumors from the right chest and shoulder of FTC4 showed histologic evidence of calcification, as expected"

Direct histological confirmation of calcification in resected lesions.

PMID:27164190 SUPPORT Human Clinical

"Biopsies from four subjects showed ectopic calcification and chronic inflammation, with areas of heterotopic ossification observed in one subject."

All four biopsied subjects showed the finding.

Chronic Inflammatory Infiltrate with Foamy Macrophages VERY_FREQUENT

The calcific deposits sit in a background of chronic inflammation with numerous foamy macrophages; earlier reports also describe multinucleated giant cells. The macrophage-rich reaction is the histological basis for treating perilesional inflammation as part of the mechanism and for the IL-1 antagonist response seen in two subjects.

Show evidence (3 references)

PMID:27164190 SUPPORT Human Clinical

"Histologic analyses showed ectopic calcification in a background of chronic inflammation with multiple foamy macrophages."

The cohort's summary histological description of the inflammatory background.

PMID:27164190 SUPPORT Human Clinical

"Others have shown the presence of macrophages and multinucleated giant cells on histology from biopsies of tumoral calcinosis"

The authors' summary of earlier biopsy reports supplies the giant-cell component; it is their statement about prior literature rather than a new observation.

PMID:27164190 SUPPORT Human Clinical

"Given the presumed increased IL-1 production by foamy macrophages seen on biopsies, inflammation in FTC4 was treated with a short course of anakinra, a recombinant IL-1 receptor antagonist."

Links the histological finding to the therapeutic decision it motivated.

Heterotopic Ossification with Mature Lamellar Bone VERY_RARE

In one of four biopsied NIH-cohort subjects, mature heterotopic bone with lamellar remodelling and reversal lines was present within a tumoral calcinosis lesion, adjacent to the inflamed deposit. Older literature describes woven bone in these lesions, but remodelled lamellar bone had not been reported before.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"In addition to the calcification, heterotopic ossification was evident"

The primary histological observation in the resected specimen.

PMID:27164190 SUPPORT Human Clinical

"there are no reports of heterotopic ossification within tumoral calcinosis lesions with mature remodeling of lamellar bone and the presence of reversal lines as seen in our cohort"

Specifies the lamellar remodelling and reversal lines that distinguish this from the woven bone of older reports.

Reactive Woven Bone and Fibroblastic Stroma in Hyperostotic Diaphysis

Bone biopsy of a hyperostotic tibia shows reactive, non-specific new woven bone that is converted to lamellar bone over time, with a fibroblastic stroma infiltrated by lymphocytes and polymorphonuclear cells. The biopsy is usually taken to exclude osteomyelitis or malignancy and shows no organism-specific or neoplastic feature.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"Tibia biopsy of FTC6 revealed hyperostosis with reactive woven bone which, over time, is converted to lamellar bone"

The cohort's tibial biopsy finding and its maturation over time.

PMID:20358599 SUPPORT Human Clinical

"Biopsy demonstrated reactive non-specific new bone, fibroblastic stroma infiltrated by lymphocytes and polynuclear cells."

An independent patient's tibial biopsy showing the same reactive new bone with an inflamed fibroblastic stroma.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

14

Cardiovascular 1

Vascular Calcification OCCASIONAL HP:0004934

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"Less common are large and small vessel calcifications that are often asymptomatic incidental findings on radiologic studies but can also cause peripheral vascular insufficiency (e.g., pain, cold extremities, and decreased peripheral pulses)."

GeneReviews supports both the OCCASIONAL band and the clinical consequences.

PMID:17710231 SUPPORT Human Clinical

"severe tumoral calcinosis with dural and carotid artery calcifications"

The HFTC3 index case documents large-vessel and dural calcification.

Eye 1

Angioid Streaks OCCASIONAL HP:0001102

Show evidence (1 reference)

PMID:29389098 SUPPORT Other

"Less frequently reported findings include testicular microlithiasis and angioid streaks of the retina."

GeneReviews lists retinal angioid streaks among the less frequent findings.

Genitourinary 2

Testicular Microlithiasis OCCASIONAL HP:0012215

Show evidence (1 reference)

PMID:29389098 SUPPORT Other

"Less frequently reported findings include testicular microlithiasis and angioid streaks of the retina."

GeneReviews lists testicular microlithiasis as an infrequent finding.

Increased Renal Tubular Phosphate Reabsorption OBLIGATE HP:0005571

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP), elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D) levels, and elevated C-terminal FGF23 fragments"

GeneReviews makes increased TRP part of the diagnostic laboratory definition.

PMID:27164190 SUPPORT Human Clinical

"All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."

Increased TRP was present in every cohort subject.

Head and Neck 3

Dental Root and Pulp Disease VERY_FREQUENT Pulp obliteration HP:0006350

Show evidence (3 references)

PMID:33977199 SUPPORT Human Clinical

"Pulp calcification was found in 13 of 14 evaluable patients."

13/14 supports the VERY_FREQUENT band for pulpal involvement.

PMID:33977199 SUPPORT Human Clinical

"This study defines the spectrum and confirms the high penetrance of dental features in HFTC."

The dental cohort's own conclusion supports the high penetrance claim.

PMID:29389098 SUPPORT Other

"The dental phenotype unique to HFTC includes enamel hypoplasia, short and bulbous roots, obliteration of pulp chambers and canals, and pulp stones."

GeneReviews enumerates the components of the dental phenotype.

Short Dental Roots VERY_FREQUENT HP:0006336

Show evidence (2 references)

PMID:33977199 SUPPORT Human Clinical

"Short roots and midroot bulges with apical thinning were present in 12 of 13 patients."

12/13 supports both the morphology and the VERY_FREQUENT band.

PMID:33977199 SUPPORT Human Clinical

"Premolars were most severely affected."

This records the tooth-class gradient of the root phenotype.

Enamel Hypoplasia HP:0006297

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"The dental phenotype unique to HFTC includes enamel hypoplasia"

GeneReviews lists enamel hypoplasia as part of the dental phenotype.

PMID:33977199 REFUTE Human Clinical

"The SEM showed altered pulp and cementum structures, without differences in enamel or dentin structures, when compared with control teeth."

The structural study found no enamel abnormality, which argues against enamel involvement being a constant feature.

Metabolism 2

Systemic Inflammation OCCASIONAL Elevated circulating C-reactive protein concentration HP:0011227

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"Two subjects with severe calcifications also had overwhelming systemic inflammation and elevated C-reactive protein (CRP)."

Two of eight cohort subjects supports the OCCASIONAL band and the association with severe calcification.

PMID:31965220 SUPPORT Other

"The other symptoms of HFTC/HHS are painful hyperostosis of the lower legs, dental abnormalities, and systemic inflammation."

An independent review lists systemic inflammation among the disease's manifestations.

Hyperphosphatemia OBLIGATE HP:0002905

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."

Every cohort subject was hyperphosphatemic, supporting the OBLIGATE band.

PMID:38951179 SUPPORT Human Clinical

"The mean (SD) phosphate was 6.9 (1.1) mg/dL."

The systematic review quantifies the typical degree of elevation across 63 patients.

Musculoskeletal 4

Periarticular Calcific Masses FREQUENT Periarticular calcification HP:0025477

Show evidence (2 references)

PMID:38951179 SUPPORT Human Clinical

"The most frequently involved sites were the hip/gluteal region (34/63; 53.9%) followed by the elbow/forearm (26/63; 41.2%), and the shoulder (18/63; 28.5%)."

The site frequencies across 63 published patients support the FREQUENT band and the joint distribution.

PMID:31965220 SUPPORT Other

"Massive ectopic calcification, known as tumoral calcinosis (TC), is seen in periarticular soft tissues, typically in the hip, elbow, and shoulder in HFTC/HHS, reducing the range of motion."

An independent review states the same compartment and joint preference.

Restricted Joint Movement Limitation of joint mobility HP:0001376

Show evidence (1 reference)

PMID:31965220 SUPPORT Other

"typically in the hip, elbow, and shoulder in HFTC/HHS, reducing the range of motion"

This attributes reduced range of motion to the periarticular deposits.

Painful Diaphyseal Hyperostosis HP:0100774

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"Painful swellings (referred to as hyperostosis) in the areas overlying the diaphyses of the tibiae (and less often the ulna, metacarpal bones, and radius)."

GeneReviews specifies the lesion and its skeletal distribution.

PMID:15599692 SUPPORT Human Clinical

"repeated attacks of acute, painful swellings of the long bones with radiological evidence of periosteal reaction and cortical hyperostosis"

This documents the episodic clinical course and the radiographic correlate.

Heterotopic Ossification VERY_RARE Ectopic ossification HP:0011986

Bound to HP:0011986 Ectopic ossification rather than the parent-level HP:0010766 Ectopic calcification, because the source reports bone formation, not mineral deposition. Queries run: `runoak -i ols:hp search "heterotopic ossification"` returned HP:0011986 Ectopic ossification and HP:6000071 Heterotopic dermal ossification; `runoak -i ols:hp search "ectopic ossification"` returned HP:0011986 plus the tissue-specific children HP:0011987 (in muscle tissue), HP:0011988 (in tendon tissue) and HP:0011989 (in ligament tissue). The children were rejected because the source places the bone within or adjacent to a periarticular calcific deposit and does not localise it to muscle, tendon, ligament or dermis.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"In addition, this is the first description of heterotopic ossification reported in FTC/HHS, possibly mediated by the adjacent inflammation."

This is the single report establishing the finding and its proposed inflammatory mechanism.

Constitutional 1

Bone Pain HP:0002653

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"which may manifest clinically as diaphyseal pain of the long bones and is often erroneously diagnosed as osteomyelitis"

This records diaphyseal bone pain as the presenting symptom of the hyperostotic lesion.

🧬

Genetic Associations

3

Biallelic GALNT3 Pathogenic Variants (Causative)

Gene: GALNT3 hgnc:4125 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:15133511 SUPPORT Human Clinical

"Sequence analysis of GALNT3 identified biallelic deleterious mutations in all individuals with FTC, suggesting that defective post-translational modification underlies the disease."

The linkage-and-sequencing study establishes the causal gene-disease relationship.

PMID:15599692 SUPPORT Human Clinical

"suggest a common origin of the 1524+1G-->A mutation in the Middle East (founder effect)"

This documents the recurrent allele as a regional founder mutation.

PMID:20358599 SUPPORT Human Clinical

"Although the presence of massive calcifications, cortical hyperostosis, or dental anomalies was not shared by all patients, all had persistent hyperphosphatemia."

This supports the dissociation between a constant biochemical phenotype and variable clinical features.

Biallelic FGF23 Pathogenic Variants (Causative)

Gene: FGF23 hgnc:3680 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (2 references)

PMID:15590700 SUPPORT Human Clinical

"We investigated an individual with FTC who was negative for GALNT3 mutations. Sequencing revealed a homozygous missense mutation in the FGF23 gene (p.S71G)"

This establishes FGF23 as a second causal gene in a GALNT3-negative patient.

PMID:15590700 SUPPORT Human Clinical

"We conclude that FGF23 mutations in hypophosphatemic rickets and FTC have opposite effects on phosphate homeostasis."

This supports the allele-direction argument in the note.

Biallelic KL Pathogenic Variants (Causative)

Gene: KL hgnc:6344 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (2 references)

PMID:17710231 SUPPORT Human Clinical

"our findings provide what we believe to be the first evidence that loss-of-function mutations in human KL impair FGF23 bioactivity"

The report's own framing supports both the causal claim and its single-family basis.

PMID:17710231 SUPPORT In Vitro

"compared with wild-type KL, expression and secretion of H193R KL were markedly reduced in vitro"

This is the functional evidence that the allele is loss of function.

💊

Medical Actions

5

Dietary Phosphate Restriction

Category: Therapeutic Action: Dietary Intervention NCIT:C15447

Platform: Behavioral / lifestyle

A low-phosphate diet is the first and least invasive way to lower the substrate for ectopic mineralization. The NIH cohort targeted 400-900 mg of phosphorus per day according to age, with nutritional counselling for every subject, because a restriction severe enough to move serum phosphate is also severe enough to compromise nutrition in a growing child. Calcium salts should not be used as binders and excessive dietary calcium and vitamin D should be avoided, since both add to the calcium-phosphate product the treatment is trying to lower.

Mechanism Target:

INHIBITS Hyperphosphatemia with Elevated Calcium-Phosphate Product — Reducing intake lowers the absorbed phosphate load and so the calcium-phosphate product.

Show evidence (1 reference)

PMID:29389098 SUPPORT Other

"treatment relies on lowering blood phosphorus by blocking absorption from the diet (i.e., use of low-phosphate diet and phosphate binders)"

GeneReviews states the intended mechanism of dietary restriction.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"low phosphate diet targeting 400–900 mg/day, depending upon age."

This records the dose target actually used in the NIH cohort.

PMID:29389098 SUPPORT Other

"It is prudent to avoid: use of calcium salts as phosphate binders; excessive dietary calcium intake; excessive vitamin D intake/supplements; foods high in phosphorus."

This supports the dietary avoidances that accompany the restriction.

Non-Calcium Phosphate Binders

Category: Therapeutic Action: Pharmacotherapy NCIT:C15986

Agent: sevelamer CHEBI:759084 aluminium hydroxide NCIT:C39707

Platform: Small molecule

Sevelamer binds dietary phosphate in the gut lumen and was given with meals and snacks to all but one subject in the NIH cohort. Calcium-containing binders are avoided because they supply the other half of the precipitating product. Aluminium hydroxide is an effective second binder and was added in two subjects whose phosphate did not move on sevelamer plus phosphaturic agents, but it carries aluminium-toxicity risk and is not a long-term default. In one reported family, sevelamer combined with acetazolamide lowered serum phosphate and shrank an ulcerating elbow mass.

Mechanism Target:

INHIBITS Hyperphosphatemia with Elevated Calcium-Phosphate Product — Luminal binding reduces intestinal phosphate absorption and lowers serum phosphate.

Show evidence (1 reference)

PMID:19188744 SUPPORT Human Clinical

"Treatment with the phosphate binder sevelamer and the carbonic anhydrase inhibitor acetazolamide successfully reduced the serum phosphate levels and led to a reduction of the calcified mass."

This single-family report links binder-based phosphate lowering to regression of a mass.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"Treatment of all subjects except FTC1 included sevelamer, a phosphate binder, prescribed with meals and snacks."

This documents sevelamer as the cohort's standard binder and how it was given.

PMID:27164190 SUPPORT Human Clinical

"Aluminum hydroxide was added as an additional phosphate binder in 2 subjects, who had increased tumoral calcinosis burden with no change in blood phosphorus on sevelamer, acetazolamide and probenecid."

This records aluminium hydroxide as escalation after failure of the first-line combination.

Phosphaturic Therapy with Acetazolamide or Probenecid

Category: Therapeutic Action: Pharmacotherapy NCIT:C15986

Agent: acetazolamide NCIT:C28809 probenecid NCIT:C772 nicotinamide NCIT:C2327

Platform: Small molecule

The complementary strategy to binding: increase renal phosphate excretion. Acetazolamide, a carbonic anhydrase inhibitor, induces bicarbonaturia and mild metabolic acidosis; probenecid promotes phosphaturia but interacts with several antibiotics. Responses are inconsistent, and in one well-documented boy acetazolamide stopped new tumour formation and abolished bone pain with no measurable change in serum phosphate or TRP at all - which suggests the benefit ran through mineral solubility rather than through phosphate lowering. Nicotinamide was tried in two NIH subjects for its phosphaturic effect and did not add benefit.

Mechanism Target:

INHIBITS Increased Proximal Tubular Sodium-Phosphate Cotransport — Both agents are used to force renal phosphate excretion against the elevated tubular reabsorption.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"were additionally treated with acetazolamide and/or probenecid, both of which promote renal phosphate excretion."

This states the intended renal mechanism of both agents.

Show evidence (3 references)

PMID:24668887 SUPPORT Human Clinical

"Following the initiation of acetazolamide therapy, the patient experienced significant improvement in disease course as indicated by resolution of localized bone pain, cessation of tumor formation, and no tumor recurrence."

This is the clinical benefit reported in the single-patient acetazolamide series.

PMID:24668887 SUPPORT INDIRECT Human Clinical

"We conclude that acetazolamide can control severe HFTC by inducing mild metabolic acidosis despite no change in serum phosphate or TRP."

The authors' own inference that the benefit was not mediated by phosphate lowering; it supports the treatment while arguing against the assumed mechanism, so the support for the phosphaturic rationale is indirect.

PMID:27164190 REFUTE Human Clinical

"Treatment with nicotinamide was attempted during a hospitalization in 2 subjects to assess its effect on inducing phosphaturia but was not continued upon discharge, as it did not show additional benefits."

This is a negative result for nicotinamide specifically, within an otherwise supported treatment class.

Interleukin-1 Blockade for Systemic Inflammation

Category: Therapeutic Action: Pharmacotherapy NCIT:C15986

Agent: anakinra NCIT:C38717

Platform: Other

For the minority of patients with overwhelming systemic inflammation, IL-1 antagonists lowered C-reactive protein in both treated NIH subjects, with resolution of calcinosis cutis and perilesional inflammation in one. This treats the inflammatory arm of the disease and does nothing about the FGF23 deficiency, so it is an adjuvant rather than a disease-modifying therapy. The evidence is two patients in an uncontrolled cohort.

Mechanism Target:

INHIBITS Foreign-Body and Systemic Inflammation Around Calcific Deposits — IL-1 antagonism suppresses the cytokine-driven inflammation around and beyond the deposits.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"In the two subjects with systemic inflammation, interleukin-1 (IL-1) antagonists significantly decreased CRP levels with resolution of calcinosis cutis and perilesional inflammation in one subject and improvement of overall well-being in both subjects."

This is the direct observation of the anti-inflammatory effect on lesion-associated inflammation.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"the response to IL-1 antagonists suggests that anti-inflammatory drugs may be useful adjuvants"

The authors frame IL-1 blockade as adjuvant, which is how the treatment is described here.

Surgical Excision of Calcific Masses

Category: Therapeutic Action: Surgical Procedure NCIT:C15329

Platform: Surgery

Excision or debulking is reserved for masses causing significant pain, functional impairment, ulceration or infection. It does not address the hyperphosphatemia, so recurrence is common after incomplete excision and attempted complete excision carries its own wound morbidity. In the systematic review, most reported patients (57%) had surgery combined with some medical therapy rather than surgery alone.

Mechanism Target:

INHIBITS Periarticular Calcific Masses — Excision removes the deposit itself; it does not act on any upstream node, which is why the lesion re-forms while the calcium-phosphate product stays elevated.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"Surgical debulking may be performed in subjects with functional impairment or severe pain, but is not routinely undertaken as calcinosis often recurs"

This states both the indication and the recurrence that limits it.

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"Surgical resection of tumoral calcinosis lesions – generally reserved for those patients with significant pain or functional impairment – has variable success."

GeneReviews gives the indication and the qualified outcome.

PMID:38951179 SUPPORT Human Clinical

"Among the subjects, 36/63 (57.1%) underwent surgical excision with some form of medical therapy."

This quantifies how often surgery is used and that it is normally combined with medical treatment.

🔬

Biochemical Markers

6

Serum Phosphate (Persistently elevated for age)

Context: Interpret against age-adjusted reference intervals; children have higher normal phosphate than adults, so an adult cut-off will miss paediatric disease. Across 63 published patients the mean phosphate was 6.9 mg/dL.

Show evidence (1 reference)

PMID:38951179 SUPPORT Human Clinical

"The mean (SD) phosphate was 6.9 (1.1) mg/dL."

This quantifies the typical degree of hyperphosphatemia in reported cases.

Tubular Reabsorption of Phosphate and TmP/GFR (Inappropriately high for the prevailing serum phosphate)

Context: Calculate from paired serum and urine phosphate and creatinine.

Show evidence (1 reference)

PMID:29389098 SUPPORT Other

"hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP)"

GeneReviews makes inappropriately increased TRP part of the diagnostic definition.

Intact FGF23 (Low or inappropriately normal in HFTC1 and HFTC2; elevated in HFTC3)

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"C-terminal FGF23 was markedly elevated whereas iFGF23 was comparatively low, consistent with increased FGF23 cleavage."

The cohort documents the low intact hormone in the deficiency subtypes.

PMID:17710231 SUPPORT Human Clinical

"elevated serum levels of parathyroid hormone and FGF23"

The KL patient had elevated FGF23, the inverse of the deficiency subtypes.

C-Terminal FGF23 (Markedly elevated)

Context: The C-terminal assay detects intact hormone plus C-terminal fragments, so it rises as cleavage consumes the intact pool. The dissociation between a high C-terminal and a low intact result is the diagnostic signature.

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"and elevated C-terminal FGF23 fragments"

GeneReviews includes elevated C-terminal fragments in the laboratory diagnosis.

PMID:17129170 SUPPORT Human Clinical

"Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C-terminal fragments."

This is the paired measurement in GALNT3-mutant patients.

1,25-Dihydroxyvitamin D (Elevated or inappropriately normal for the degree of hyperphosphatemia)

Context: A normal calcitriol is abnormal here: high phosphate should suppress 1-alpha-hydroxylase through FGF23, so a mid-range value in a hyperphosphatemic patient is evidence that the FGF23 brake is missing.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."

This records the direction of the calcitriol abnormality in every cohort subject.

Serum Calcium and Parathyroid Hormone (Usually normal)

Show evidence (2 references)

PMID:20358599 SUPPORT Human Clinical

"However, circulating calcium and parathyroid hormone (PTH) are usually normal."

This supports the usual normality of calcium and PTH.

PMID:17710231 SUPPORT Human Clinical

"marked hyperphosphatemia and hypercalcemia as well as elevated serum levels of parathyroid hormone"

The KL case documents the exception noted in the specificity field.

🔬

Diagnosis

9

Serum Phosphate Measurement (Elevated)

The entry point of the workup is persistent, age-adjusted fasting hyperphosphatemia in a patient with normal renal function. Together with the renal phosphate handling, calcitriol and FGF23 results below, this is what establishes the clinical diagnosis before genotyping.

serum phosphate measurement NCIT:C64857

Results: Persistent hyperphosphatemia for age with a normal serum creatinine.

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"The clinical diagnosis of HFTC is established by the presence of tumoral calcinosis and/or characteristic laboratory findings of hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP), elevated or inappropriately normal 1,25-dihydroxyvitamin..."

GeneReviews names hyperphosphatemia as the first of the characteristic laboratory findings on which the clinical diagnosis rests.

PMID:27164190 SUPPORT Human Clinical

"All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."

Every subject in the NIH cohort met the biochemical criterion, which is why it is the screening test.

Renal Tubular Phosphate Reabsorption (Inappropriately elevated)

Paired serum and urine phosphate and creatinine give the tubular reabsorption of phosphate (TRP), or its derived index TmP/GFR. In HFTC the kidney conserves phosphate despite hyperphosphatemia and normal renal function, so TRP is inappropriately high rather than suppressed. This is the finding that separates FGF23 deficiency or resistance from a phosphate load or renal failure.

tubular reabsorption of phosphate (TRP) NCIT:C64857

Results: TRP above the normal range (96 % in one reported patient) despite hyperphosphatemia.

NCIT has no term for the tubular reabsorption of phosphate or TmP/GFR. Queries run: `runoak -i ols:ncit search "tubular reabsorption of phosphate"`, `runoak -i ols:ncit search "phosphate reabsorption"` and `runoak -i ols:ncit search "urine phosphate measurement"` each returned nothing relevant (`search "tubular"` returned only histology terms such as NCIT:C14169). The index is therefore bound to the phosphate measurement it is computed from, with the index carried in preferred_term. TmP/GFR is named in the description because it is the standard derived form; no cached source reports a TmP/GFR value for this disease.

Show evidence (2 references)

PMID:29389098 SUPPORT Other

"hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP)"

GeneReviews includes inappropriately increased TRP in the laboratory definition of the clinical diagnosis.

PMID:20358599 SUPPORT Human Clinical

"Hyperphosphatemia (7.9 mg/dl) was detected with inappropriately elevated tubular reabsorption of phosphate (TRP) of 96 %."

A worked patient value showing the combination the test is meant to demonstrate.

Calcium, Renal Function, PTH and Vitamin D Metabolite Panel

Serum calcium, creatinine, alkaline phosphatase, intact PTH, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D are measured alongside phosphate. Calcium, creatinine, alkaline phosphatase and PTH are normal, which excludes renal failure, hyperparathyroidism and hypoparathyroidism; 1,25-dihydroxyvitamin D is elevated or inappropriately normal for the phosphate level because FGF23 is not suppressing renal 1-alpha-hydroxylase.

mineral-metabolism laboratory panel NCIT:C25294

Markers: serum calcium, creatinine, alkaline phosphatase, intact PTH, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D

Results: Normal calcium, creatinine, alkaline phosphatase and PTH; elevated or inappropriately normal 1,25-dihydroxyvitamin D.

Bound as one Laboratory Procedure because the sources order these analytes together as a single evaluation. NCIT carries per-analyte terms that are each reachable from NCIT:C25218 and could replace this binding if the panel is ever split: NCIT:C61020 Serum Calcium Measurement, NCIT:C64547 Creatinine Measurement, NCIT:C64432 Alkaline Phosphatase Measurement, NCIT:C74789 Intact Parathyroid Hormone Measurement and NCIT:C84818 Vitamin D Measurement (all verified with `runoak -i ols:ncit info`).

Show evidence (3 references)

PMID:27164190 SUPPORT Human Clinical

"detailed laboratory evaluation of calcium and phosphorus metabolism including 1,25D, intact parathyroid hormone (iPTH), TRP, iFGF23 and C-terminal FGF23 (CFGF23), genetic testing, and standard radiographs."

This is the predefined evaluation set applied to every NIH-cohort subject and names the analytes in this panel.

PMID:20358599 SUPPORT Human Clinical

"Other biochemical evaluation included normal serum and urine calcium, alkaline phosphatase, and PTH."

The expected normal results for calcium, alkaline phosphatase and PTH in a genotyped patient.

PMID:29389098 SUPPORT Other

"elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D) levels"

GeneReviews lists the calcitriol pattern among the laboratory findings that establish the clinical diagnosis.

Intact and C-Terminal FGF23 Assays

Both FGF23 assays are needed, because the pattern, not a single value, identifies the subtype. In GALNT3- and FGF23-related disease the intact hormone is low or inappropriately normal while C-terminal fragments are markedly elevated, the signature of a hormone that is made but cleaved. In KL-related disease intact and C-terminal FGF23 are both very high, because the hormone is intact but the kidney cannot respond to it.

intact and C-terminal FGF23 measurement NCIT:C96650

Markers: intact FGF23 (iFGF23); C-terminal FGF23 (cFGF23)

Results: GALNT3/FGF23 disease - low or inappropriately normal iFGF23 with markedly elevated cFGF23; KL disease - both iFGF23 and cFGF23 markedly elevated.

NCIT has child terms for each assay, NCIT:C135420 Intact Fibroblast Growth Factor 23 Measurement and NCIT:C135419 C-Terminal Fibroblast Growth Factor 23 Measurement (both reachable from NCIT:C25218; found with `runoak -i ols:ncit search "fibroblast growth factor 23 measurement"`). The parent term is bound because the diagnostic reading is the paired result, and markers names both assays.

Show evidence (4 references)

PMID:27164190 SUPPORT Human Clinical

"C-terminal FGF23 was markedly elevated whereas iFGF23 was comparatively low, consistent with increased FGF23 cleavage."

The GALNT3 cohort pattern of low intact hormone with fragment excess.

PMID:17129170 SUPPORT Human Clinical

"Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C-terminal fragments."

An independent GALNT3 series reporting the same paired-assay pattern.

PMID:15590700 SUPPORT Human Clinical

"determination of circulating FGF23 in the affected individual showed a marked increase in the C-terminal fragment"

The FGF23-mutant form shows the same C-terminal fragment excess as GALNT3 disease.

+ 1 more reference

Plain Radiography of Symptomatic Sites

Conventional radiographs of painful or swollen sites show the two lesion types: amorphous, lobulated periarticular calcific masses, and in hyperostotic long bones cortical thickening, diaphysitis and periosteal apposition.

conventional radiography NCIT:C38101

Results: Periarticular calcific masses; diaphyseal cortical hyperostosis and periosteal apposition.

Show evidence (3 references)

PMID:27164190 SUPPORT Human Clinical

"Tumoral calcinosis was assessed by conventional radiography and, in some, by CT."

Radiography was the baseline lesion assessment in the NIH cohort.

PMID:27164190 SUPPORT Human Clinical

"Radiographs ranged from diaphyseal hyperostosis to massive calcification."

The radiographic spectrum across the cohort.

PMID:20358599 SUPPORT Human Clinical

"Typical radiographic features of affected bones include cortical hyperostosis, diaphysitis, and periosteal apposition."

The radiographic appearance of the hyperostosis lesion.

Computed Tomography of Calcific Lesions

CT is used for symptomatic lesions and, as cardiac CT, to detect the vascular calcification that plain films miss.

computed tomography NCIT:C17204

Results: Extent of calcific masses; coronary calcification on cardiac CT in a subset of adults.

Show evidence (2 references)

PMID:27164190 SUPPORT Human Clinical

"computed tomography (CT) of symptomatic lesions"

CT of symptomatic lesions was part of the cohort's evaluation set.

PMID:27164190 SUPPORT Human Clinical

"FTC4 (32 years old) and FTC7 (56 years old) had cardiac calcifications on CT with Agatston coronary calcium scores of 105"

Cardiac CT detected coronary calcification in two adults, the vascular finding the modality is used for.

Magnetic Resonance Imaging of Hyperostotic Bone

MRI of a painful hyperostotic diaphysis shows an inflammatory process with marrow and periosteal signal change, and bone scintigraphy shows focal uptake. Neither is specific: the appearance is that of osteomyelitis, and the hyperostosis presentation is repeatedly misdiagnosed as such before the serum phosphate is checked.

magnetic resonance imaging NCIT:C16809

Results: Inflammatory signal in the affected diaphysis, indistinguishable from osteomyelitis on imaging alone.

Show evidence (4 references)

PMID:20358599 SUPPORT Human Clinical

"Magnetic resonance imaging (MRI) showed inflammatory process and technetium scintigraphy displayed localized increased uptake at the tibia diaphysis."

The MRI and scintigraphic appearance of a hyperostotic lesion in a genotyped patient.

PMID:20358599 SUPPORT Human Clinical

"Tibial radiographs demonstrated circumferential endosteal and periosteal bone proliferation with patchy sclerosis of the medullary canal, consistent with hyperostosis (Fig 1-2a). Multifocal osteomyelitis was considered."

The osteomyelitis differential was raised on the radiographic appearance of a hyperostotic lesion in a patient later shown to carry a GALNT3 mutation.

PMID:27164190 SUPPORT Human Clinical

"which may manifest clinically as diaphyseal pain of the long bones and is often erroneously diagnosed as osteomyelitis"

The misdiagnosis is common enough that the cohort paper states it in its introduction.

+ 1 more reference

Molecular Genetic Testing of GALNT3, FGF23 and KL

Sequencing of the three causal genes confirms the diagnosis and assigns the subtype. GeneReviews positions it as confirmatory when the clinical and laboratory picture is inconclusive, and identification of the familial variants opens carrier, prenatal and preimplantation testing. A minority of biochemically typical patients have no biallelic variant found.

molecular genetic testing of GALNT3, FGF23 and KL NCIT:C15709

Results: Biallelic pathogenic variants in GALNT3, FGF23 or KL; GALNT3 in most genotyped patients.

Bound to the generic Genetic Testing term. NCIT:C198412 Multi-gene Panel Sequencing, NCIT:C101295 Whole Exome Sequencing and NCIT:C101294 Whole Genome Sequencing exist and are reachable from NCIT:C25218 (verified with `runoak -i ols:ncit info`), but no cached source documents which platform was used; the recommendation to sequence a mineral-metabolism panel first and escalate to exome or genome sequencing when the panel is negative is the deep-research report's workflow and is uncited here.

Show evidence (3 references)

PMID:29389098 SUPPORT Other

"Identification of biallelic pathogenic variants in FGF23, GALNT3, or KL by molecular genetic testing confirms the diagnosis when clinical and laboratory findings are inconclusive."

GeneReviews' statement of the confirmatory role of molecular testing.

PMID:27164190 SUPPORT Human Clinical

"GALNT3 mutations were identified in seven subjects; no causative mutation was found in the eighth."

The yield of genetic testing in a well-characterised cohort, including a genotype-negative case.

PMID:29389098 SUPPORT Other

"Once the FGF23, GALNT3, or KL pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible."

The downstream uses of a confirmed molecular diagnosis in the family.

Anti-FGF23 Autoantibody Testing (Absent in the hereditary disease)

An acquired phenocopy exists in which autoantibodies against FGF23 produce the same hyperphosphatemic tumoral calcinosis picture. It belongs in the differential of a patient with typical biochemistry and no biallelic GALNT3, FGF23 or KL variant, and is not part of the hereditary disease modelled in this entry.

anti-FGF23 autoantibody measurement NCIT:C181397

Results: Positive result indicates the acquired autoimmune phenocopy rather than HFTC.

Show evidence (2 references)

PMID:33977199 SUPPORT Human Clinical

"FGF23 autoantibodies cause an acquired form of tumoral calcinosis."

Establishes the autoimmune phenocopy that this test is meant to exclude.

PMID:27164190 SUPPORT Human Clinical

"no causative mutation was found in the eighth"

The genotype-negative patient is the setting in which the differential arises.

📈

Progression

3

Biochemical disease before clinical lesions

Hyperphosphatemia with increased tubular reabsorption is present before calcific masses appear and can be the only abnormality for years. Two siblings in the NIH cohort had the full biochemical phenotype without physical calcinosis at enrolment. This is the window in which phosphate control is most plausibly preventive, though that has never been tested prospectively.

Show evidence (1 reference)

PMID:27164190 SUPPORT Human Clinical

"Clinical manifestations varied, even within families, ranging from asymptomatic to large, disabling calcifications."

The asymptomatic end of the cohort's range is the biochemical-only phase.

Established calcific and hyperostotic disease

Masses accumulate around large joints and hyperostotic attacks recur. The median age of published patients at report is 18 years, with a wide spread, and radiographic burden ranges from diaphyseal hyperostosis alone to massive calcification.

Show evidence (2 references)

PMID:38951179 SUPPORT Human Clinical

"The median age of the patients was 18 (IQR 8-32) years."

This gives the age distribution of reported clinical disease.

PMID:27164190 SUPPORT Human Clinical

"Radiographs ranged from diaphyseal hyperostosis to massive calcification."

This describes the radiographic range of established disease.

Long-term lesion course under treatment

The disease does not follow a single trajectory. In the systematic review's followed-up patients, roughly a third regressed, a third progressed and a third were stable over a median of three years, and three patients died. Recurrence after incomplete excision is common while hyperphosphatemia persists.

Show evidence (2 references)

PMID:38951179 SUPPORT Human Clinical

"Regression or reduction in lesion size was reported in 19/63 (30.2%) subjects; 20/63 (31.7%) showed progression, 24/63 (38.1%) had features of stable disease, and mortality was reported in 3 patients (4.7%)."

This is the outcome distribution behind the described course.

PMID:38951179 SUPPORT Human Clinical

"The median (IQR) follow-up duration was 3 (1-9) years."

This gives the observation window over which those outcomes were recorded.

📊

Prevalence

1

Worldwide, genetically or clinically characterised published cases

Cases In Literature Ultra Rare

No population prevalence, incidence or carrier frequency has been estimated for HFTC. The available denominator is the published case literature: a 2024 systematic review that applied strict inclusion criteria (baseline phosphate measured, treatment recorded, follow-up available) found 43 eligible studies describing 63 individuals. That is a lower bound on reported cases, not a population rate, because it excludes reports lacking treatment or follow-up data. The disease is reported worldwide but is enriched in consanguineous Middle Eastern and African families, consistent with the documented Middle Eastern GALNT3 founder allele.

Show evidence (2 references)

PMID:38951179 SUPPORT Human Clinical

"A total of 63 individuals (Males = 33) were included from the 43 eligible case studies."

This is the published-case count behind the CASES_IN_LITERATURE record.

PMID:15599692 SUPPORT Human Clinical

"suggest a common origin of the 1524+1G-->A mutation in the Middle East (founder effect)"

The founder effect supports the described regional enrichment.

🐁

Animal Models

3

Galnt3-null mouse Genetically engineered

The genetic model of the commonest human subtype. Galnt3-deficient mice reproduce the defining endocrine lesion faithfully - circulating intact Fgf23 is about half that of littermates with increased C-terminal fragments, despite increased Fgf23 expression in bone - and reproduce the renal consequences, with elevated sodium-phosphate cotransporter expression, hyperphosphatemia and an inappropriately normal 1,25-dihydroxyvitamin D. What they do not reproduce is the lesion the human disease is named for: they develop no apparent calcifications.

Species

Mus musculus

Genotype

Galnt3 knockout (homozygous null)

Background

Mouse

Publication

PMID:19213845

Pathograph links

Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess recapitulates fidelity: high observes: organism The model reproduces the exact dissociation seen in patients: low intact hormone with excess C-terminal fragments on a background of increased Fgf23 transcription.

Limitations: Circulating intact Fgf23 was roughly halved rather than abolished, so the model is a partial-deficiency state; C-terminal fragments were measured in bone rather than only in circulation.

Readouts

Circulating intact Fgf23

Direction: DECREASED

Interpretation: Direct measurement of the hormone deficiency this node describes.

Show evidence (1 reference)

PMID:19213845 SUPPORT Model Organism

"homozygous mice had only about half of circulating intact Fgf23 levels and higher levels of C-terminal Fgf23 fragments in bone"

This is the quantitative readout of intact and fragment hormone in the model.

Show evidence (1 reference)

PMID:19213845 SUPPORT Model Organism

"ablation of Galnt3 impaired secretion of intact Fgf23, leading to decreased circulating Fgf23 and hyperphosphatemia, despite increased Fgf23 expression"

This establishes the model as informative for the hormone-deficiency node.

Increased Proximal Tubular Sodium-Phosphate Cotransport recapitulates fidelity: moderate observes: organism Renal sodium-phosphate cotransporter expression is elevated in the knockout, the transporter-level change the human node asserts.

Limitations: The finding is transporter expression rather than a measured tubular phosphate threshold, so the correspondence to human TmP/GFR is inferred. Renal Kl expression was also elevated, a compensatory change with no established human counterpart.

Readouts

Renal sodium-phosphate cotransporter expression

Direction: INCREASED

Interpretation: Molecular correlate of the unopposed tubular reabsorption node.

Show evidence (1 reference)

PMID:19213845 SUPPORT Model Organism

"renal expression of sodium-phosphate cotransporters and Kl were elevated in Galnt3-deficient mice"

This is the direct transporter measurement.

Show evidence (1 reference)

PMID:19213845 SUPPORT Model Organism

"In response to hyperphosphatemia, Galnt3-deficient mice had markedly increased Fgf23 expression in bone."

The compensatory rise in bone Fgf23 confirms the animals are sensing and failing to correct a phosphate load.

Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue fails to recapitulate fidelity: low observes: organism The knockout is biochemically a tumoral-calcinosis model but not anatomically one: hyperphosphatemia develops without apparent calcifications.

Limitations: No ectopic calcific masses form, so the model cannot be used to study lesion formation, lesion regression, or any therapy whose endpoint is lesion burden. Sex-specific confounds (growth retardation, infertility and increased bone mineral density in males only) further limit it as a skeletal-phenotype model.

Show evidence (1 reference)

PMID:19213845 REFUTE Model Organism

"In this study we generated mice lacking the Galnt3 gene, which developed hyperphosphatemia without apparent calcifications."

The absence of calcification is stated explicitly and is the basis for the negative link.

Show evidence (1 reference)

PMID:19213845 SUPPORT Model Organism

"Our findings indicate that Galnt3-deficient mice have a biochemical phenotype of tumoral calcinosis"

The authors position the model as a biochemical rather than a full phenotypic model, which is how it is used here.

Fgf23-null mouse Genetically engineered

Total ablation of the hormone rather than of its protection. The Fgf23-null mouse is the cleanest demonstration that the human renal phenotype follows from absent FGF23 action: high serum phosphate with increased renal reabsorption, and elevated 1,25-dihydroxyvitamin D driven by enhanced renal 1-alpha-hydroxylase expression. It is a more severe systemic state than human HFTC, with severe growth retardation and a markedly short lifespan.

Species

Mus musculus

Genotype

Fgf23 knockout (homozygous null)

Background

Mouse

Publication

PMID:14966565

Pathograph links

Increased Proximal Tubular Sodium-Phosphate Cotransport recapitulates fidelity: high observes: organism Complete loss of FGF23 produces exactly the renal phosphate-conserving state the node asserts.

Limitations: Complete hormone absence is more extreme than the partial deficiency of human GALNT3- or FGF23-related disease, so the model overstates the degree of signalling loss.

Readouts

Serum phosphate and renal phosphate reabsorption

Direction: INCREASED

Interpretation: The physiological readout of unopposed tubular phosphate reclamation.

Show evidence (1 reference)

PMID:14966565 SUPPORT Model Organism

"The Fgf23(-/-) mice displayed significantly high serum phosphate with increased renal phosphate reabsorption."

This is the direct measurement of the modelled renal phenotype.

Show evidence (1 reference)

PMID:14966565 SUPPORT Model Organism

"indicating that FGF23 is essential for normal phosphate and vitamin D metabolism"

The model establishes FGF23 as the physiological regulator whose loss the human disease reproduces.

Unsuppressed Renal Calcitriol Production recapitulates fidelity: high observes: organism The knockout supplies the mechanistic step the human data can only infer: the calcitriol elevation is attributable to increased renal 1-alpha-hydroxylase expression.

Limitations: In humans calcitriol is often only inappropriately normal rather than frankly elevated, so the model shows a stronger version of the human abnormality.

Readouts

Renal 25-hydroxyvitamin D-1alpha-hydroxylase expression

Direction: INCREASED

Interpretation: The enzymatic cause of the calcitriol elevation, measured directly.

Show evidence (1 reference)

PMID:14966565 SUPPORT Model Organism

"They also showed an elevation in serum 1,25(OH)2D that was due to the enhanced expression of renal 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-OHase) from 10 days of age."

This links the calcitriol rise to the specific enzyme the node names.

Show evidence (1 reference)

PMID:14966565 SUPPORT Model Organism

"We present here the evidence that FGF23 is a physiological regulator of serum phosphate and 1,25-dihydroxyvitamin D (1,25[OH]2D) by generating FGF23-null mice."

This states the model's purpose and its relevance to the calcitriol arm.

The same knockout is also the reference model for the opposite disease: FGF23 excess causes X-linked hypophosphatemia, and the null mouse's hyperphosphatemic, hypercalcitriolemic state is what establishes the direction of the axis in both.

Show evidence (1 reference)

PMID:14966565 SUPPORT Model Organism

"Disruption of the Fgf23 gene did not result in embryonic lethality, although homozygous mice showed severe growth retardation with abnormal bone phenotype and markedly short life span."

This records the model's viability and its systemic severity, which bounds how far it can be read across to human HFTC.

Klotho-deficient mouse Genetically engineered

The mouse that named the gene behind HFTC3. Defective klotho expression produces a systemic syndrome resembling premature ageing - short lifespan, infertility, arteriosclerosis, skin atrophy, osteoporosis and emphysema - and identified klotho as a membrane protein with beta-glucosidase homology. It carries the molecular lesion of the human resistance subtype, but the original description characterises an ageing phenotype rather than an FGF23-resistance phenotype, so its use for this disease rests on later work not cited here.

Species

Mus musculus

Genotype

klotho hypomorph (kl/kl)

Background

Mouse

Publication

PMID:9363890

Pathograph links

Biallelic KL Loss of Function and Renal FGF23 Resistance partially recapitulates fidelity: low observes: organism The model carries the same genetic lesion as HFTC3 - loss of functional alpha-Klotho - and so reproduces the upstream cause of FGF23 resistance.

Limitations: The cited description reports a multi-system premature-ageing syndrome, not the mineral phenotype, so the mineral-handling correspondence to human HFTC3 is not established by this source. The human disease is caused by a missense allele with reduced but not absent alpha-Klotho, and human patients do not have a progeroid syndrome; arteriosclerosis in the mouse is not the same lesion as periarticular tumoral calcinosis. The model should not be used to argue that HFTC3 patients are at risk of accelerated ageing.

Show evidence (1 reference)

PMID:9363890 SUPPORT Model Organism

"A defect in klotho gene expression in the mouse results in a syndrome that resembles human ageing, including a short lifespan, infertility, arteriosclerosis, skin atrophy, osteoporosis and emphysema."

This establishes what the model's klotho deficiency actually produces, which is the basis for both the partial recapitulation and the limitation.

Show evidence (1 reference)

PMID:9363890 SUPPORT Model Organism

"The gene encodes a membrane protein that shares sequence similarity with the beta-glucosidase enzymes."

This is the original characterisation of the gene product whose human orthologue causes HFTC3.

{ }

Source YAML

click to show

name: Hyperphosphatemic Familial Tumoral Calcinosis
synonyms:
- HFTC
- HFTC/HHS
- familial tumoral calcinosis
- hyperphosphatemic tumoral calcinosis
- hyperostosis-hyperphosphatemia syndrome
- HHS
- Teutschlaender disease
- Morbus Teutschlaender
creation_date: "2026-09-04T23:23:40Z"
category: Mendelian
description: >-
  Hyperphosphatemic familial tumoral calcinosis (HFTC) is an autosomal recessive
  disorder of deficient fibroblast growth factor 23 (FGF23) action. Biallelic
  loss-of-function variants in GALNT3 or FGF23 leave the intact hormone
  unprotected against furin-family cleavage, so patients carry low or
  inappropriately normal intact FGF23 with a large excess of inactive C-terminal
  fragments; biallelic KL variants instead reduce alpha-Klotho, so intact FGF23
  is high and the kidney is resistant to it. Either route removes FGF23-Klotho
  signalling from the renal proximal tubule.

  The endocrine consequence is the mirror image of X-linked hypophosphatemia.
  Sodium-phosphate cotransport is not downregulated, tubular phosphate
  reabsorption stays inappropriately high, and 1-alpha-hydroxylase is not
  suppressed, so hyperphosphatemia coexists with elevated or inappropriately
  normal 1,25-dihydroxyvitamin D while calcium, PTH and renal function stay
  normal. The resulting rise in the calcium-phosphate product drives ectopic
  calcium-phosphate deposition.

  Clinically this appears as lobular periarticular calcific masses at the hips,
  elbows and shoulders, a distinctive dental phenotype (enamel hypoplasia,
  short bulbous roots, obliterated pulp chambers, pulp stones), painful
  diaphyseal cortical hyperostosis, vascular calcification, testicular
  microlithiasis and angioid streaks. Some patients develop overwhelming
  systemic inflammation around the deposits. Hyperostosis-hyperphosphatemia
  syndrome (HHS) is the same disease, not a separate one: the same GALNT3
  founder allele produces either presentation.

  The entry is organised around the causal chain from each of the three genetic
  lesions to the shared FGF23-signalling failure, then to the renal phosphate
  and vitamin D phenotype, the elevated calcium-phosphate product, and the
  tissue-level consequences of ectopic mineral deposition.
disease_term:
  preferred_term: Hyperphosphatemic Familial Tumoral Calcinosis
  term:
    id: MONDO:0100251
    label: familial hyperphosphatemic tumoral calcinosis/hyperphosphatemic hyperostosis syndrome
parents:
- Disorders of Phosphate Metabolism
- Metabolic Bone Disorders
- Ectopic Calcification Disorders
notes: >-
  Scope and lump/split. The entry is curated at the umbrella MONDO term
  MONDO:0100251, which covers both the tumoral-calcinosis and the
  hyperostosis-hyperphosphatemia presentations, with the three molecular
  subtypes HFTC1 (GALNT3), HFTC2 (FGF23) and HFTC3 (KL) recorded in
  has_subtypes. The lump is evidence-driven rather than conventional: the same
  GALNT3 splice allele segregates in both HFTC and HHS families on a shared
  haplotype (PMID:15599692), and identical GALNT3 genotypes produce massive
  calcinosis in one patient and isolated hyperostosis in another
  (PMID:20358599). The three genes converge on one endocrine failure, so a
  single pathophysiology chain carries all of them and the subtype-specific
  divergence (low versus high intact FGF23) is modelled as two upstream branches
  into a shared signalling node rather than as three entries.

  Normophosphatemic familial tumoral calcinosis (SAMD9, MONDO:0012502) is
  deliberately excluded. It shares the calcific-mass morphology but has normal
  phosphate, no FGF23 abnormality and a different gene, so it is a distinct
  disease and not a subtype here. Acquired anti-FGF23 autoantibody tumoral
  calcinosis is likewise a phenocopy and is not modelled; it is noted in the
  knowledge-gap discussion because it is the differential when no biallelic
  genotype is found.

  Module conformance. No conformance target was declared.
  kb/modules/defective_skeletal_mineralization.yaml was read and rejected: it
  models failure of mineralization, whereas HFTC is a hyper-mineralizing
  disease, so conforming to it would invert the claim. No ectopic-calcification
  or pathological-mineral-deposition module exists in kb/modules/ at the time of
  curation; one would be the right home for the shared periarticular-deposit
  chain across HFTC, calciphylaxis and CKD-associated tumoral calcinosis.

  Provenance. Curated against the GeneReviews chapter (PMID:29389098) as the
  phenotype baseline, with the NIH natural-history cohort (PMID:27164190) and
  the NIH dental cohort (PMID:33977199) as the quantitative sources, plus the
  primary gene-discovery papers. The Falcon deep-research report
  (research/Hyperphosphatemic_Familial_Tumoral_Calcinosis-deep-research-falcon.md)
  was used as a lead list only; it cites by author-year/DOI key, so each DOI was
  resolved to a PMID through PubMed esearch before any snippet was taken
  (10.1002/jbmr.2870 to PMID:27164190, 10.1007/s00223-020-00659-6 to
  PMID:31965220, 10.1002/jbm4.10470 to PMID:33977199, 10.1007/s00223-024-01247-8
  to PMID:38951179). The report's term-validation section flags HP:0002905 as
  mislabelled in the report text; the canonical label Hyperphosphatemia is used
  here. The report offered no umbrella MONDO identifier; MONDO:0100251 was
  verified directly against the ontology.
references:
- reference: PMID:29389098
  title: Hyperphosphatemic Familial Tumoral Calcinosis.
  tags:
  - GeneReviews
- reference: PMID:27164190
  title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
- reference: PMID:31965220
  title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
- reference: PMID:38951179
  title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
classifications:
  harrisons_chapter:
  - classification_value: ENDOCRINOLOGY_METABOLISM
    notes: >-
      Harrison's covers HFTC with the disorders of phosphate homeostasis and
      bone mineral metabolism; the defining lesion is endocrine (deficient or
      unopposed FGF23 action), not primarily rheumatologic.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      A Mendelian, autosomal recessive disorder with three established causal
      genes and a documented Middle Eastern founder allele.
  isds_skeletal_category:
  - classification_value: abnormal_mineralization
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (Unger et al.,
      PMID:36779427), in the group renamed at that revision from "Abnormal
      mineralization group" to "Disorders of bone mineralization", which holds
      the FGF23-axis disorders of phosphate handling alongside the
      hypophosphatemic rickets entities. Note that the cached record for
      PMID:36779427 is the revision's summary and does not enumerate individual
      disorders, so this group assignment rests on the disease's mechanism (a
      systemic mineral-handling defect with diaphyseal cortical hyperostosis)
      rather than on a quotable per-disorder listing.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  expressivity: VARIABLE
  description: >-
    All three causal genes act recessively: affected individuals carry biallelic
    (homozygous or compound heterozygous) pathogenic variants and heterozygous
    carriers are generally unaffected. Expressivity is markedly variable even
    within a family and even between relatives carrying the same genotype, so
    the genotype does not predict whether a patient presents with calcific
    masses, with hyperostosis, or with biochemical abnormality alone.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HFTC is inherited in an autosomal recessive manner."
    explanation: GeneReviews states the mode of inheritance directly.
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."
    explanation: This supports the recurrence risks and the asymptomatic carrier state.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical manifestations varied, even within families, ranging from asymptomatic to large, disabling calcifications."
    explanation: The NIH cohort documents intrafamilial variable expressivity.
has_subtypes:
- name: HFTC1
  display_name: HFTC1 (GALNT3-related)
  subtype_term:
    preferred_term: tumoral calcinosis, hyperphosphatemic, familial, 1
    term:
      id: MONDO:0100252
      label: tumoral calcinosis, hyperphosphatemic, familial, 1
  description: >-
    The most frequently reported molecular subtype. Biallelic GALNT3 variants
    abolish GalNAc-T3-dependent O-glycosylation of FGF23, so the intact hormone
    is cleaved and inactivated. Serum intact FGF23 is low with markedly elevated
    C-terminal fragments. Both the tumoral-calcinosis and the
    hyperostosis-hyperphosphatemia presentations arise from this subtype,
    including from the same allele.
  genes:
  - preferred_term: GALNT3
    term:
      id: hgnc:4125
      label: GALNT3
  evidence:
  - reference: PMID:15133511
    reference_title: "Mutations in GALNT3, encoding a protein involved in O-linked glycosylation, cause familial tumoral calcinosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sequence analysis of GALNT3 identified biallelic deleterious mutations in all individuals with FTC"
    explanation: The gene-discovery study establishes biallelic GALNT3 variants as the cause of this subtype.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The four novel GALNT3 mutations invariably resulted in hyperphosphatemia as a result of low intact FGF23, but other clinical manifestations were variable."
    explanation: This supports the subtype's constant biochemical signature alongside variable clinical expression.
- name: HFTC2
  display_name: HFTC2 (FGF23-related)
  subtype_term:
    preferred_term: tumoral calcinosis, hyperphosphatemic, familial, 2
    term:
      id: MONDO:0060714
      label: tumoral calcinosis, hyperphosphatemic, familial, 2
  description: >-
    Biallelic FGF23 missense variants (reported alleles include p.Ser71Gly,
    p.Met96Thr, p.Gly123Trp and p.Ser129Phe) destabilise the intact hormone or
    trap it intracellularly, so only C-terminal fragments reach the circulation.
    The biochemical signature is the same as HFTC1 - low intact FGF23 with high
    C-terminal FGF23 - because both subtypes converge on failure to deliver
    intact hormone.
  genes:
  - preferred_term: FGF23
    term:
      id: hgnc:3680
      label: FGF23
  evidence:
  - reference: PMID:15590700
    reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sequencing revealed a homozygous missense mutation in the FGF23 gene (p.S71G) at an amino acid position which is conserved from fish to man."
    explanation: This establishes a homozygous FGF23 missense variant as a distinct molecular cause.
  - reference: PMID:19188744
    reference_title: "Familial tumoral calcinosis caused by a novel FGF23 mutation: response to induction of tubular renal acidosis with acetazolamide and the non-calcium phosphate binder sevelamer."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sequencing analysis revealed a novel homozygous FGF23 missense mutation (c.367G>T, p.Gly123Trp) in both siblings while the parents were carriers of the mutation."
    explanation: A second independent family documents a homozygous FGF23 missense allele with unaffected heterozygous parents.
- name: HFTC3
  display_name: HFTC3 (KL / alpha-Klotho-related)
  subtype_term:
    preferred_term: tumoral calcinosis, hyperphosphatemic, familial, 3
    term:
      id: MONDO:0060715
      label: tumoral calcinosis, hyperphosphatemic, familial, 3
  description: >-
    The rarest subtype, established by a single homozygous KL missense variant
    (p.His193Arg) that destabilises the KL1 glycosidase domain and reduces
    expression and secretion of alpha-Klotho. Because the defect is in the
    co-receptor rather than the hormone, intact FGF23 is high rather than low,
    and the kidney is resistant to it; this is the one subtype in which the
    diagnostic intact-versus-C-terminal FGF23 pattern is inverted.
  genes:
  - preferred_term: KL
    term:
      id: hgnc:6344
      label: KL
  evidence:
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Herein we report a homozygous missense mutation (H193R) in the KLOTHO (KL) gene of a 13-year-old girl who presented with severe tumoral calcinosis with dural and carotid artery calcifications."
    explanation: This is the index observation establishing KL as the third causal gene.
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This patient exhibited defects in mineral ion homeostasis with marked hyperphosphatemia and hypercalcemia as well as elevated serum levels of parathyroid hormone and FGF23."
    explanation: The elevated FGF23 in this patient distinguishes the resistance subtype from the deficiency subtypes.
pathophysiology:
- name: Biallelic GALNT3 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Germline biallelic deleterious GALNT3 variants remove the activity of
    GalNAc-T3, the trans-Golgi glycosyltransferase that initiates mucin-type
    O-glycosylation. A recurrent splice-site allele (c.1524+1G>A) accounts for
    both HFTC and HHS presentations in Middle Eastern families and is a founder
    mutation on a shared haplotype.
  genetic_context:
    gene:
      preferred_term: GALNT3
      term:
        id: hgnc:4125
        label: GALNT3
    functional_impact_category: LOSS_OF_FUNCTION
    variant_origin: GERMLINE
    description: Biallelic loss of GalNAc-T3 activity is the commonest molecular cause of HFTC.
  genes:
  - preferred_term: GALNT3
    term:
      id: hgnc:4125
      label: GALNT3
  molecular_functions:
  - preferred_term: polypeptide N-acetylgalactosaminyltransferase activity
    term:
      id: GO:0004653
      label: polypeptide N-acetylgalactosaminyltransferase activity
    modifier: LOSS_OF_FUNCTION
  downstream:
  - target: Failure of FGF23 O-Glycosylation and Furin Cleavage of Intact FGF23
    causal_link_type: DIRECT
    description: >-
      Without GalNAc-T3, the FGF23 proprotein-convertase recognition motif is
      not O-glycosylated and is therefore not protected from processing.
    evidence:
    - reference: PMID:16638743
      reference_title: "Polypeptide GalNAc-transferase T3 and familial tumoral calcinosis. Secretion of fibroblast growth factor 23 requires O-glycosylation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "GalNAc-T3 selectively directs O-glycosylation in a subtilisin-like proprotein convertase recognition sequence motif, which blocks processing of FGF23"
      explanation: This states the direct biochemical step from GalNAc-T3 activity to protection of intact FGF23.
  evidence:
  - reference: PMID:15133511
    reference_title: "Mutations in GALNT3, encoding a protein involved in O-linked glycosylation, cause familial tumoral calcinosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This region includes the gene GALNT3, which encodes a glycosyltransferase responsible for initiating mucin-type O-glycosylation."
    explanation: This identifies the gene product and its enzymatic role.
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All affected individuals harbored a homozygous splice site mutation (1524+1G-->A) in GALNT3."
    explanation: This documents the recurrent biallelic splice-site allele in affected families.
- name: Biallelic FGF23 Missense Variants Blocking Intact Hormone Secretion
  biological_scale: MOLECULAR
  description: >-
    Homozygous or compound heterozygous FGF23 missense variants act on the
    hormone itself. The p.Ser71Gly mutant is retained in the Golgi so that only
    the C-terminal fragment is secreted; other reported alleles include
    p.Met96Thr, p.Gly123Trp and p.Ser129Phe. The functional result is the same as
    GALNT3 loss - intact hormone does not reach the circulation - so this node
    feeds the same downstream deficiency.
  genetic_context:
    gene:
      preferred_term: FGF23
      term:
        id: hgnc:3680
        label: FGF23
    functional_impact_category: LOSS_OF_FUNCTION
    variant_origin: GERMLINE
    description: Missense alleles that prevent secretion of the intact hormone.
  genes:
  - preferred_term: FGF23
    term:
      id: hgnc:3680
      label: FGF23
  molecular_functions:
  - preferred_term: FGF23 hormone activity
    term:
      id: GO:0005179
      label: hormone activity
    modifier: LOSS_OF_FUNCTION
  downstream:
  - target: Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess
    causal_link_type: DIRECT
    description: >-
      Intracellular retention of the mutant protein leaves only inactive
      C-terminal fragments in the circulation.
    evidence:
    - reference: PMID:15590700
      reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Expression of the mutated protein in HEK293 cells showed that only the C-terminal fragment is secreted, whereas the intact protein is retained in the Golgi complex."
      explanation: The expression experiment shows the mutant protein fails to be secreted intact.
  evidence:
  - reference: PMID:15590700
    reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These results suggest that the FGF23 function is decreased by absent or extremely reduced secretion of intact FGF23."
    explanation: This states the loss-of-function consequence of the FGF23 allele.
  - reference: PMID:15590700
    reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that FGF23 mutations in hypophosphatemic rickets and FTC have opposite effects on phosphate homeostasis."
    explanation: This records that the same gene produces opposite phosphate phenotypes depending on the allele's effect.
- name: Failure of FGF23 O-Glycosylation and Furin Cleavage of Intact FGF23
  biological_scale: MOLECULAR
  description: >-
    Bioactive FGF23 carries three O-linked glycans. Incompletely glycosylated
    FGF23 is susceptible to cleavage by subtilisin-like proprotein convertases
    at the RXXR site that separates the N-terminal and C-terminal halves of the
    hormone, splitting it into inactive fragments. O-glycosylation and protease
    processing compete for the same motif, so loss of the glycosyltransferase
    shifts the balance decisively toward cleavage.
  molecular_functions:
  - preferred_term: proprotein convertase cleavage of FGF23
    term:
      id: GO:0004252
      label: serine-type endopeptidase activity
    modifier: INCREASED
  biological_processes:
  - preferred_term: protein O-linked glycosylation
    term:
      id: GO:0006493
      label: protein O-linked glycosylation
    modifier: DECREASED
  cell_types:
  - preferred_term: osteocyte
    term:
      id: CL:0000137
      label: osteocyte
  - preferred_term: osteoblast
    term:
      id: CL:0000062
      label: osteoblast
  downstream:
  - target: Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess
    causal_link_type: DIRECT
    description: >-
      Enhanced processing consumes the intact hormone and generates the
      C-terminal fragments that dominate the circulating pool.
    evidence:
    - reference: PMID:17129170
      reference_title: "Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Both patients had low levels of the full-length FGF23 with markedly augmented amounts of the inactive fragments."
      explanation: Patient measurements show the processing shift produces exactly this circulating pattern.
  evidence:
  - reference: PMID:17129170
    reference_title: "Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Biologically active FGF23 has three O-linked glycans. FGF23 with only one or two O-linked glycans is processed into inactive fragments."
    explanation: This establishes the glycan-dependence of resistance to processing.
  - reference: PMID:17129170
    reference_title: "Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Decreasing the expression of the GALNT3 gene by RNA interference resulted in enhanced processing of FGF23."
    explanation: Silencing the glycosyltransferase reproduces the processing shift experimentally.
  - reference: PMID:16638743
    reference_title: "Polypeptide GalNAc-transferase T3 and familial tumoral calcinosis. Secretion of fibroblast growth factor 23 requires O-glycosylation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The study suggests a novel posttranslational regulatory model of FGF23 involving competing O-glycosylation and protease processing to produce intact FGF23."
    explanation: This states the competition between glycosylation and proteolysis that the node describes.
- name: Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess
  biological_scale: ORGANISM
  description: >-
    The shared endocrine lesion of the GALNT3 and FGF23 subtypes: circulating
    intact FGF23 is low or inappropriately normal for the degree of
    hyperphosphatemia, while C-terminal FGF23 is markedly elevated because the
    C-terminal assay detects both intact hormone and fragments. This dissociated
    assay pattern is the diagnostic biochemical signature of the disease.
  biological_processes:
  - preferred_term: phosphate ion homeostasis
    term:
      id: GO:0055062
      label: phosphate ion homeostasis
    modifier: ABNORMAL
  downstream:
  - target: Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule
    causal_link_type: DIRECT
    description: Too little intact hormone reaches the proximal tubular receptor complex to signal.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The mutations causing FTC/HHS result in relative deficiency of, or resistance to, iFGF23, which leads to hyperphosphatemia, due to increased renal tubular reabsorption of phosphate (TRP)"
      explanation: This states that relative deficiency of intact FGF23 is what produces the renal consequence, which is the step this edge asserts.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "C-terminal FGF23 was markedly elevated whereas iFGF23 was comparatively low, consistent with increased FGF23 cleavage."
    explanation: The NIH cohort documents the dissociated intact/C-terminal pattern across affected subjects.
  - reference: PMID:31965220
    reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "resulting in the excessive cleavage of active intact FGF23 (FGF23, GALNT3) or increased resistance to the action of FGF23 (KL)"
    explanation: The review separates the cleavage mechanism of the FGF23/GALNT3 subtypes from the resistance mechanism of the KL subtype.
- name: Biallelic KL Loss of Function and Renal FGF23 Resistance
  biological_scale: MOLECULAR
  description: >-
    In HFTC3 the hormone is intact but its obligate co-receptor is not. The
    p.His193Arg substitution sits at the base of the KL1 catalytic cleft and
    destabilises the domain, so expression and secretion of alpha-Klotho are
    markedly reduced and FGF23 cannot signal through its cognate receptors.
    Intact FGF23 therefore rises rather than falls, and this node bypasses the
    hormone-deficiency node to reach the same signalling failure.
  genetic_context:
    gene:
      preferred_term: KL
      term:
        id: hgnc:6344
        label: KL
    functional_impact_category: LOSS_OF_FUNCTION
    variant_origin: GERMLINE
    description: A homozygous KL missense allele reducing alpha-Klotho co-receptor availability.
  genes:
  - preferred_term: KL
    term:
      id: hgnc:6344
      label: KL
  downstream:
  - target: Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule
    causal_link_type: DIRECT
    description: >-
      Reduced alpha-Klotho removes the co-receptor that FGF23 requires for
      high-affinity signalling, producing end-organ resistance despite adequate
      hormone.
    evidence:
    - reference: PMID:17710231
      reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "expression and secretion of H193R KL were markedly reduced in vitro, resulting in diminished ability of FGF23 to signal via its cognate FGF receptors"
      explanation: This is the direct functional demonstration that the variant impairs FGF23 signalling.
  evidence:
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "our findings provide what we believe to be the first evidence that loss-of-function mutations in human KL impair FGF23 bioactivity, underscoring the essential role of KL in FGF23-mediated phosphate and vitamin D homeostasis in humans"
    explanation: This establishes KL loss of function as a human cause of impaired FGF23 action.
- name: Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule
  biological_scale: CELLULAR
  description: >-
    The convergence point of all three genetic lesions. Intact FGF23 normally
    acts on proximal tubular cells through FGFR1 together with the co-receptor
    Klotho to suppress the sodium-phosphate cotransporters NaPi-IIa and NaPi-IIc
    and to suppress 25-hydroxyvitamin D 1-alpha-hydroxylase. When that signal is
    absent - through hormone deficiency in HFTC1/HFTC2 or through co-receptor
    loss in HFTC3 - both suppressive arms fail simultaneously.
  biological_processes:
  - preferred_term: fibroblast growth factor receptor signaling pathway
    term:
      id: GO:0008543
      label: fibroblast growth factor receptor signaling pathway
    modifier: DECREASED
  cell_types:
  - preferred_term: epithelial cell of proximal tubule
    term:
      id: CL:0002306
      label: epithelial cell of proximal tubule
  locations:
  - preferred_term: renal proximal tubule
    term:
      id: UBERON:0004134
      label: proximal tubule
  downstream:
  - target: Increased Proximal Tubular Sodium-Phosphate Cotransport
    causal_link_type: DIRECT
    description: Loss of the suppressive FGF23 signal leaves NaPi-IIa and NaPi-IIc expression unopposed.
    evidence:
    - reference: PMID:33977199
      reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "FGF23 binds to FGF receptor‐1 (FGFR1) and coreceptor KLOTHO to downregulate sodium/phosphate cotransporters NPT2a and NPT2c"
      explanation: The suppressive step is stated explicitly, so its loss is what this edge describes.
  - target: Unsuppressed Renal Calcitriol Production
    causal_link_type: DIRECT
    description: Loss of the suppressive FGF23 signal leaves 1-alpha-hydroxylase expression unopposed.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "25-hydroxyvitamin D 1-α-hydroxylase expression. This leads to increased renal phosphate excretion and decreased serum 1,25-dihydroxyvitamin D3 (1,25D)"
      explanation: The normal suppressive effect of FGF23 on the enzyme is stated, so losing the signal releases it.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with the intact hormone (iFGF23) acting via the fibroblast growth factor receptor 1 (FGFR1) along with its co-receptor Klotho to inhibit sodium phosphate co-transporter (NaPi-2a and-2c) and 25-hydroxyvitamin D 1-α-hydroxylase expression"
    explanation: This states the receptor complex and the two effector arms whose loss defines this node.
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "thereby inhibiting phosphate reabsorption and active vitamin D formation in renal proximal tubules"
    explanation: An independent source states the same proximal-tubular dual effect of FGF23 signalling.
- name: Increased Proximal Tubular Sodium-Phosphate Cotransport
  biological_scale: CELLULAR
  description: >-
    Unopposed NaPi-IIa and NaPi-IIc activity raises tubular phosphate
    reclamation. Clinically this appears as an inappropriately high tubular
    reabsorption of phosphate (TRP) and a raised renal phosphate threshold
    (TmP/GFR) despite an already elevated serum phosphate and normal glomerular
    function.
  biological_processes:
  - preferred_term: phosphate ion transmembrane transport
    term:
      id: GO:0035435
      label: phosphate ion transmembrane transport
    modifier: INCREASED
  cell_types:
  - preferred_term: epithelial cell of proximal tubule
    term:
      id: CL:0002306
      label: epithelial cell of proximal tubule
  chemical_entities:
  - preferred_term: phosphate
    term:
      id: CHEBI:26020
      label: phosphate
    modifier: INCREASED
  downstream:
  - target: Hyperphosphatemia with Elevated Calcium-Phosphate Product
    causal_link_type: DIRECT
    description: Failure to excrete phosphate raises the circulating phosphate concentration.
    evidence:
    - reference: PMID:19188744
      reference_title: "Familial tumoral calcinosis caused by a novel FGF23 mutation: response to induction of tubular renal acidosis with acetazolamide and the non-calcium phosphate binder sevelamer."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "hyperphosphatemia due to increased tubular phosphate reabsorption, despite normal renal function"
      explanation: This states the tubular-reabsorption-to-hyperphosphatemia step directly.
  - target: Increased Renal Tubular Phosphate Reabsorption
    causal_link_type: DIRECT
    description: The transporter change is measured directly as elevated TRP and TmP/GFR.
    evidence:
    - reference: PMID:29389098
      reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP)"
      explanation: Increased TRP is the clinical measurement of the transporter change.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."
    explanation: The cohort shows increased tubular reabsorption in every affected subject.
  - reference: PMID:19188744
    reference_title: "Familial tumoral calcinosis caused by a novel FGF23 mutation: response to induction of tubular renal acidosis with acetazolamide and the non-calcium phosphate binder sevelamer."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is associated with hyperphosphatemia due to increased tubular phosphate reabsorption, despite normal renal function and normal plasma PTH levels."
    explanation: This attributes the hyperphosphatemia to tubular reabsorption with renal function and PTH preserved.
- name: Unsuppressed Renal Calcitriol Production
  biological_scale: MOLECULAR
  description: >-
    1-alpha-hydroxylase is normally suppressed by FGF23, so in health a high
    phosphate load lowers 1,25-dihydroxyvitamin D. In HFTC that brake is absent
    and calcitriol is elevated or inappropriately normal for the prevailing
    hyperphosphatemia, which sustains intestinal absorption of calcium and
    phosphate instead of restraining it.
  molecular_functions:
  - preferred_term: 25-hydroxyvitamin D 1-alpha-hydroxylase activity
    term:
      id: GO:0004498
      label: calcidiol 1-monooxygenase activity
    modifier: INCREASED
  biological_processes:
  - preferred_term: vitamin D biosynthetic process
    term:
      id: GO:0042368
      label: vitamin D biosynthetic process
    modifier: INCREASED
  chemical_entities:
  - preferred_term: calcitriol
    term:
      id: CHEBI:17823
      label: calcitriol
    modifier: INCREASED
  downstream:
  - target: Hyperphosphatemia with Elevated Calcium-Phosphate Product
    causal_link_type: DIRECT
    description: >-
      Non-suppressed calcitriol promotes gastrointestinal absorption of
      phosphorus and calcium, adding to the mineral load.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "elevated or inappropriately normal 1,25D production, which promotes gastrointestinal absorption of phosphorus and calcium. The net effect is an increase in the calcium × phosphate product."
      explanation: This states the causal step from unsuppressed calcitriol to a raised calcium-phosphate product.
  evidence:
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hyperphosphatemia secondary to increased renal tubular phosphate reabsorption and elevated or inappropriately normal 1,25-dihydroxyvitamin D"
    explanation: This pairs the calcitriol abnormality with the tubular phosphate abnormality as the defining biochemistry.
- name: Hyperphosphatemia with Elevated Calcium-Phosphate Product
  biological_scale: ORGANISM
  description: >-
    Persistent hyperphosphatemia with normal serum calcium, normal PTH and
    normal renal function raises the calcium-phosphate product above the
    solubility limit of the extracellular fluid. This is the systemic driver of
    every downstream lesion, and it is the only step in the chain that current
    therapy tries to modify.
  chemical_entities:
  - preferred_term: phosphate
    term:
      id: CHEBI:26020
      label: phosphate
    modifier: INCREASED
  biological_processes:
  - preferred_term: phosphate ion homeostasis
    term:
      id: GO:0055062
      label: phosphate ion homeostasis
    modifier: ABNORMAL
  downstream:
  - target: Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue
    causal_link_type: DIRECT
    description: >-
      Supersaturation precipitates amorphous calcium-phosphate/hydroxyapatite in
      soft tissue, preferentially at sites of repetitive trauma or pressure.
    evidence:
    - reference: PMID:19188744
      reference_title: "Familial tumoral calcinosis caused by a novel FGF23 mutation: response to induction of tubular renal acidosis with acetazolamide and the non-calcium phosphate binder sevelamer."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "characterized by periarticular calcifications produced by the deposition of amorphous extraosseous calcifications of hydroxyapatite"
      explanation: This names the mineral species and the periarticular distribution of the deposits.
  - target: Diaphyseal Cortical Hyperostosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Hyperostosis tracks with the same hyperphosphatemic state rather than with
      a distinct genotype, but the local mechanism linking phosphate excess to
      cortical apposition is not established.
    evidence:
    - reference: PMID:20358599
      reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "tumoral calcinosis and hyperostosis-hyperphosphatemia syndrome represent a continuous spectrum of the same disease caused by increased phosphate levels, rather than two distinct disorders"
      explanation: This attributes both presentations to the phosphate excess rather than to separate mechanisms.
  - target: Ectopic Calcification of Vessels, Teeth and Other Organs
    causal_link_type: DIRECT
    description: >-
      The same supersaturated state deposits mineral outside the periarticular
      compartment, in vessels, dental pulp, eye, intestine and testis.
    evidence:
    - reference: PMID:31965220
      reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "However, other regions, such as the eye, intestine, vasculature, and testis, are also targets of ectopic calcification."
      explanation: This lists the extra-articular targets reached by the same deposition process.
  - target: Hyperphosphatemia
    causal_link_type: DIRECT
    description: The node is measured clinically as a persistent elevation of serum phosphate.
    evidence:
    - reference: PMID:38951179
      reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The mean (SD) phosphate was 6.9 (1.1) mg/dL."
      explanation: The measured serum phosphate is the clinical expression of this node.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The result is functional deficiency of, or resistance to, intact FGF23 (iFGF23), causing hyperphosphatemia, increased renal tubular reabsorption of phosphorus (TRP), elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D), ectopic calcifications, and/or diaphyseal hyperostosis."
    explanation: This is the complete biochemical-to-clinical statement of the shared downstream pathway.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, circulating calcium and parathyroid hormone (PTH) are usually normal."
    explanation: Normal calcium and PTH distinguish this state from hyperparathyroid and CKD-related hyperphosphatemia.
- name: Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue
  biological_scale: TISSUE
  description: >-
    Lobular masses of amorphous calcium-phosphate accumulate in skin,
    subcutaneous tissue and connective tissue around large joints, typically the
    hips, elbows and shoulders, and preferentially where the tissue is exposed to
    repetitive trauma or prolonged pressure. Masses may enlarge, ulcerate and
    become infected, and they recur after incomplete excision while the
    hyperphosphatemia persists.
  biological_processes:
  - preferred_term: biomineral tissue development
    term:
      id: GO:0031214
      label: biomineral tissue development
    modifier: ABNORMAL
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  locations:
  - preferred_term: hip joint
    term:
      id: UBERON:0001486
      label: hip joint
  - preferred_term: elbow joint
    term:
      id: UBERON:0001490
      label: elbow joint
  - preferred_term: shoulder joint
    term:
      id: UBERON:0001470
      label: glenohumeral joint
  - preferred_term: subcutaneous tissue
    term:
      id: UBERON:0002072
      label: hypodermis
  downstream:
  - target: Foreign-Body and Systemic Inflammation Around Calcific Deposits
    causal_link_type: DIRECT
    description: Deposited crystal provokes a macrophage-rich chronic inflammatory reaction in the surrounding tissue.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Biopsies from four subjects showed ectopic calcification and chronic inflammation"
      explanation: The biopsy finding pairs the deposit with the inflammatory reaction in the same tissue.
  - target: Periarticular Calcific Masses
    causal_link_type: DIRECT
    description: The deposits present clinically as palpable, often disabling periarticular masses.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "ranging from asymptomatic to large, disabling calcifications"
      explanation: This describes the clinical presentation of the deposits, including the disabling end of the range.
  - target: Restricted Joint Movement
    causal_link_type: DIRECT
    description: Mass effect and pain around the joint reduce range of motion.
    evidence:
    - reference: PMID:31965220
      reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "typically in the hip, elbow, and shoulder in HFTC/HHS, reducing the range of motion"
      explanation: This attributes the loss of range of motion to the periarticular deposits.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Ectopic calcifications (tumoral calcinosis) typically found in periarticular soft tissues exposed to repetitive trauma or prolonged pressure (e.g., hips, elbows, and shoulders)"
    explanation: GeneReviews specifies both the tissue compartment and the mechanical site preference.
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequently involved sites were the hip/gluteal region (34/63; 53.9%) followed by the elbow/forearm (26/63; 41.2%), and the shoulder (18/63; 28.5%)."
    explanation: The systematic review quantifies the site distribution across 63 reported patients.
- name: Foreign-Body and Systemic Inflammation Around Calcific Deposits
  biological_scale: TISSUE
  description: >-
    Histology of resected lesions shows ectopic calcification with chronic
    inflammation, and in one NIH subject areas of mature heterotopic
    ossification adjacent to the inflamed deposit. A minority of patients
    develop overwhelming systemic inflammation with markedly elevated C-reactive
    protein; the response of two such patients to interleukin-1 antagonists
    identifies IL-1-driven inflammation as a component distinct from the mineral
    burden itself.
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  cell_types:
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
  downstream:
  - target: Systemic Inflammation
    causal_link_type: DIRECT
    description: Perilesional inflammation can become systemic, with constitutional symptoms and elevated CRP.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Two subjects with severe calcifications also had overwhelming systemic inflammation and elevated C-reactive protein (CRP)."
      explanation: This is the observed progression from heavy local deposition to systemic inflammation.
  - target: Heterotopic Ossification
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Mature lamellar bone was found adjacent to an inflamed deposit, suggesting
      that the surrounding inflammation mediates ossification, but the pathway
      is not established.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biopsies from four subjects showed ectopic calcification and chronic inflammation, with areas of heterotopic ossification observed in one subject."
    explanation: This is the histological basis for treating perilesional inflammation as part of the mechanism.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Overwhelming systemic inflammation has not been described previously in FTC/HHS; the response to IL-1 antagonists suggests that anti-inflammatory drugs may be useful adjuvants."
    explanation: The IL-1 response supports a cytokine-driven inflammatory component.
- name: Diaphyseal Cortical Hyperostosis
  biological_scale: TISSUE
  description: >-
    Episodic painful swelling, warmth and erythema over the diaphyses of long
    bones, most often the tibiae, with radiographic cortical hyperostosis,
    diaphysitis and periosteal apposition. This is the presentation that defines
    hyperostosis-hyperphosphatemia syndrome, and because the same GALNT3 alleles
    produce it and produce tumoral calcinosis, it is a manifestation of this
    disease rather than a separate entity. It is regularly misdiagnosed as
    bacterial osteomyelitis.
  locations:
  - preferred_term: tibia
    term:
      id: UBERON:0000979
      label: tibia
  downstream:
  - target: Painful Diaphyseal Hyperostosis
    causal_link_type: DIRECT
    description: The cortical lesion presents clinically as recurrent long-bone pain and swelling.
    evidence:
    - reference: PMID:15599692
      reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "repeated attacks of acute, painful swellings of the long bones with radiological evidence of periosteal reaction and cortical hyperostosis"
      explanation: This pairs the radiographic lesion with its clinical presentation.
  - target: Bone Pain
    causal_link_type: DIRECT
    description: Diaphyseal pain is the symptom that brings the hyperostotic attack to attention.
  evidence:
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterized by elevated serum phosphate levels and repeated attacks of acute, painful swellings of the long bones with radiological evidence of periosteal reaction and cortical hyperostosis"
    explanation: This describes the hyperostotic lesion and its episodic clinical behaviour.
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results demonstrate that HHS and HFTC are allelic disorders despite their phenotypic differences"
    explanation: This is the evidence that the hyperostotic presentation belongs to the same disease.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which may manifest clinically as diaphyseal pain of the long bones and is often erroneously diagnosed as osteomyelitis"
    explanation: This records the characteristic misdiagnosis.
- name: Ectopic Calcification of Vessels, Teeth and Other Organs
  biological_scale: TISSUE
  description: >-
    Beyond the periarticular compartment, mineral deposits in large and small
    vessels, in the dental pulp and root, and less commonly in the eye,
    intestine and testis. The dental lesion is the most penetrant of these: pulp
    density rises and pulp volume falls sevenfold, the odontoblast layer loses
    its polarity, and the pulp cavity fills with calcified material.
  cell_types:
  - preferred_term: odontoblast
    term:
      id: CL:0000060
      label: odontoblast
  locations:
  - preferred_term: dental pulp
    term:
      id: UBERON:0001754
      label: dental pulp
  downstream:
  - target: Dental Root and Pulp Disease
    causal_link_type: DIRECT
    description: Pulpal and root mineralization produces the characteristic dental phenotype.
    evidence:
    - reference: PMID:33977199
      reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "an obliterated pulp cavity that was filled with calcified material"
      explanation: The pulp lesion is mineral deposition, which is the step this edge asserts.
  - target: Short Dental Roots
    causal_link_type: DIRECT
    description: Root cementum and pulp mineralization accompany the shortened, bulbous root morphology.
  - target: Vascular Calcification
    causal_link_type: DIRECT
    description: Mineral deposition in large and small vessels.
    evidence:
    - reference: PMID:29389098
      reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Less common are large and small vessel calcifications"
      explanation: GeneReviews records vessel calcification as one of the deposition sites.
  - target: Testicular Microlithiasis
    causal_link_type: DIRECT
    description: Microcalcification within the testis.
  - target: Angioid Streaks
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Angioid streaks are reported in this disease, but the route from
      hyperphosphatemia to breaks in Bruch's membrane is not established.
  evidence:
  - reference: PMID:31965220
    reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "However, other regions, such as the eye, intestine, vasculature, and testis, are also targets of ectopic calcification."
    explanation: This lists the extra-articular targets of the same deposition process.
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histology revealed loss of the polarized odontoblast cell layer and an obliterated pulp cavity that was filled with calcified material."
    explanation: This is the tissue-level description of the dental lesion.
phenotypes:
- name: Periarticular Calcific Masses
  category: Musculoskeletal
  frequency: FREQUENT
  description: >-
    Lobular, often massive calcific deposits in the soft tissue around large
    joints - most often the hip and gluteal region, then the elbow and forearm,
    then the shoulder. The masses are the principal cause of disability: they
    limit movement, cause pain, and may ulcerate through the skin. Burden ranges
    from radiographically silent to disabling even between relatives with the
    same genotype.
  phenotype_term:
    preferred_term: Periarticular calcification
    term:
      id: HP:0025477
      label: Periarticular calcification
  evidence:
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequently involved sites were the hip/gluteal region (34/63; 53.9%) followed by the elbow/forearm (26/63; 41.2%), and the shoulder (18/63; 28.5%)."
    explanation: The site frequencies across 63 published patients support the FREQUENT band and the joint distribution.
  - reference: PMID:31965220
    reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Massive ectopic calcification, known as tumoral calcinosis (TC), is seen in periarticular soft tissues, typically in the hip, elbow, and shoulder in HFTC/HHS, reducing the range of motion."
    explanation: An independent review states the same compartment and joint preference.
- name: Restricted Joint Movement
  category: Musculoskeletal
  description: >-
    Reduced range of motion at the affected joint from the mass effect of the
    adjacent calcific deposit, from pain, and in advanced cases from destruction
    of the joint itself.
  phenotype_term:
    preferred_term: Limitation of joint mobility
    term:
      id: HP:0001376
      label: Limitation of joint mobility
  evidence:
  - reference: PMID:31965220
    reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "typically in the hip, elbow, and shoulder in HFTC/HHS, reducing the range of motion"
    explanation: This attributes reduced range of motion to the periarticular deposits.
- name: Painful Diaphyseal Hyperostosis
  category: Skeletal
  description: >-
    Recurrent attacks of acute, painful swelling over the diaphyses of long
    bones, classically the tibiae but also the ulna, metacarpals and radius,
    with radiographic periosteal reaction and cortical hyperostosis. This is the
    defining feature of the hyperostosis-hyperphosphatemia presentation and is a
    frequent source of misdiagnosis as osteomyelitis.
  phenotype_term:
    preferred_term: Hyperostosis
    term:
      id: HP:0100774
      label: Hyperostosis
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Painful swellings (referred to as hyperostosis) in the areas overlying the diaphyses of the tibiae (and less often the ulna, metacarpal bones, and radius)."
    explanation: GeneReviews specifies the lesion and its skeletal distribution.
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "repeated attacks of acute, painful swellings of the long bones with radiological evidence of periosteal reaction and cortical hyperostosis"
    explanation: This documents the episodic clinical course and the radiographic correlate.
- name: Bone Pain
  category: Skeletal
  description: >-
    Long-bone pain accompanying hyperostotic attacks, often severe enough to
    prompt investigation for infection. Pain also arises from the periarticular
    masses themselves and is a principal indication for surgery.
  phenotype_term:
    preferred_term: Bone pain
    term:
      id: HP:0002653
      label: Bone pain
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which may manifest clinically as diaphyseal pain of the long bones and is often erroneously diagnosed as osteomyelitis"
    explanation: This records diaphyseal bone pain as the presenting symptom of the hyperostotic lesion.
- name: Dental Root and Pulp Disease
  category: Craniofacial
  frequency: VERY_FREQUENT
  description: >-
    The dental phenotype is the most penetrant non-biochemical feature. Roots
    are short and bulbous with midroot bulges and apical thinning, pulp chambers
    and canals become obliterated, and pulp stones form. Premolars are the most
    severely affected teeth. The changes are independent of which of the three
    genes is mutated, which argues that phosphate excess or FGF23 deficiency
    itself drives them.
  phenotype_term:
    preferred_term: Pulp obliteration
    term:
      id: HP:0006350
      label: Pulp obliteration
  evidence:
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pulp calcification was found in 13 of 14 evaluable patients."
    explanation: 13/14 supports the VERY_FREQUENT band for pulpal involvement.
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study defines the spectrum and confirms the high penetrance of dental features in HFTC."
    explanation: The dental cohort's own conclusion supports the high penetrance claim.
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The dental phenotype unique to HFTC includes enamel hypoplasia, short and bulbous roots, obliteration of pulp chambers and canals, and pulp stones."
    explanation: GeneReviews enumerates the components of the dental phenotype.
- name: Short Dental Roots
  category: Craniofacial
  frequency: VERY_FREQUENT
  description: >-
    Shortened, thistle-shaped roots with midroot bulges and apical thinning,
    most marked in the premolars. Because dental radiographs are taken early and
    routinely, these changes can be the first diagnostic clue in a child with
    unexplained hyperphosphatemia.
  phenotype_term:
    preferred_term: Short dental root
    term:
      id: HP:0006336
      label: Short dental root
  evidence:
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Short roots and midroot bulges with apical thinning were present in 12 of 13 patients."
    explanation: 12/13 supports both the morphology and the VERY_FREQUENT band.
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Premolars were most severely affected."
    explanation: This records the tooth-class gradient of the root phenotype.
- name: Enamel Hypoplasia
  category: Craniofacial
  description: >-
    Defective enamel formation is listed among the HFTC dental features. Note
    that the NIH dental study's scanning electron microscopy found no difference
    in enamel or dentin structure from control teeth, so enamel involvement is
    less consistent than the root and pulp changes.
  phenotype_term:
    preferred_term: Enamel hypoplasia
    term:
      id: HP:0006297
      label: Enamel hypoplasia
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The dental phenotype unique to HFTC includes enamel hypoplasia"
    explanation: GeneReviews lists enamel hypoplasia as part of the dental phenotype.
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "The SEM showed altered pulp and cementum structures, without differences in enamel or dentin structures, when compared with control teeth."
    explanation: The structural study found no enamel abnormality, which argues against enamel involvement being a constant feature.
- name: Vascular Calcification
  category: Cardiovascular
  frequency: OCCASIONAL
  description: >-
    Calcification of large and small vessels, usually found incidentally on
    imaging. It is not always silent: it can produce peripheral vascular
    insufficiency, and the index HFTC3 patient had dural and carotid artery
    calcification.
  phenotype_term:
    preferred_term: Vascular calcification
    term:
      id: HP:0004934
      label: Vascular calcification
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Less common are large and small vessel calcifications that are often asymptomatic incidental findings on radiologic studies but can also cause peripheral vascular insufficiency (e.g., pain, cold extremities, and decreased peripheral pulses)."
    explanation: GeneReviews supports both the OCCASIONAL band and the clinical consequences.
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe tumoral calcinosis with dural and carotid artery calcifications"
    explanation: The HFTC3 index case documents large-vessel and dural calcification.
- name: Testicular Microlithiasis
  category: Genitourinary
  frequency: OCCASIONAL
  description: >-
    Microcalcification within the testis, reported infrequently and generally
    found on ultrasound rather than clinically.
  phenotype_term:
    preferred_term: Testicular microlithiasis
    term:
      id: HP:0012215
      label: Testicular microlithiasis
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Less frequently reported findings include testicular microlithiasis and angioid streaks of the retina."
    explanation: GeneReviews lists testicular microlithiasis as an infrequent finding.
- name: Angioid Streaks
  category: Ophthalmologic
  frequency: OCCASIONAL
  description: >-
    Breaks in Bruch's membrane seen on fundoscopy. They are an infrequently
    reported finding and their mechanistic link to the phosphate excess has not
    been worked out.
  phenotype_term:
    preferred_term: Angioid streaks
    term:
      id: HP:0001102
      label: Angioid streaks
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Less frequently reported findings include testicular microlithiasis and angioid streaks of the retina."
    explanation: GeneReviews lists retinal angioid streaks among the less frequent findings.
- name: Systemic Inflammation
  category: Constitutional
  frequency: OCCASIONAL
  description: >-
    A minority of patients, generally those with the heaviest calcific burden,
    develop overwhelming systemic inflammation with markedly elevated C-reactive
    protein. This was first described in the NIH cohort and responded to
    interleukin-1 blockade, so it is a treatable component separate from the
    mineral load.
  phenotype_term:
    preferred_term: Elevated circulating C-reactive protein concentration
    term:
      id: HP:0011227
      label: Elevated circulating C-reactive protein concentration
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two subjects with severe calcifications also had overwhelming systemic inflammation and elevated C-reactive protein (CRP)."
    explanation: Two of eight cohort subjects supports the OCCASIONAL band and the association with severe calcification.
  - reference: PMID:31965220
    reference_title: Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The other symptoms of HFTC/HHS are painful hyperostosis of the lower legs, dental abnormalities, and systemic inflammation."
    explanation: An independent review lists systemic inflammation among the disease's manifestations.
- name: Heterotopic Ossification
  category: Skeletal
  frequency: VERY_RARE
  description: >-
    Mature lamellar bone forming within or adjacent to a calcific deposit. This
    was reported for the first time in the NIH cohort, in one of four biopsied
    subjects, and is thought to be mediated by the adjacent inflammation rather
    than by mineral supersaturation alone.
  phenotype_term:
    preferred_term: Heterotopic ossification
    term:
      id: HP:0011986
      label: Ectopic ossification
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, this is the first description of heterotopic ossification reported in FTC/HHS, possibly mediated by the adjacent inflammation."
    explanation: This is the single report establishing the finding and its proposed inflammatory mechanism.
  notes: >-
    Bound to HP:0011986 Ectopic ossification rather than the parent-level
    HP:0010766 Ectopic calcification, because the source reports bone
    formation, not mineral deposition. Queries run: `runoak -i ols:hp search
    "heterotopic ossification"` returned HP:0011986 Ectopic ossification and
    HP:6000071 Heterotopic dermal ossification; `runoak -i ols:hp search
    "ectopic ossification"` returned HP:0011986 plus the tissue-specific
    children HP:0011987 (in muscle tissue), HP:0011988 (in tendon tissue) and
    HP:0011989 (in ligament tissue). The children were rejected because the
    source places the bone within or adjacent to a periarticular calcific
    deposit and does not localise it to muscle, tendon, ligament or dermis.
- name: Hyperphosphatemia
  category: Metabolic
  frequency: OBLIGATE
  description: >-
    Persistent, age-adjusted elevation of serum phosphate with normal serum
    calcium, normal PTH and normal renal function. It is the defining
    biochemical abnormality, present in every characterised patient, and it
    precedes the calcific lesions - patients may be hyperphosphatemic for years
    before a mass appears.
  phenotype_term:
    preferred_term: Hyperphosphatemia
    term:
      id: HP:0002905
      label: Hyperphosphatemia
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."
    explanation: Every cohort subject was hyperphosphatemic, supporting the OBLIGATE band.
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean (SD) phosphate was 6.9 (1.1) mg/dL."
    explanation: The systematic review quantifies the typical degree of elevation across 63 patients.
- name: Increased Renal Tubular Phosphate Reabsorption
  category: Renal
  frequency: OBLIGATE
  description: >-
    Tubular reabsorption of phosphate (TRP) and the renal phosphate threshold
    (TmP/GFR) are inappropriately high for the prevailing serum phosphate, with
    normal glomerular filtration. This is the discriminating finding that
    separates HFTC from hyperphosphatemia caused by renal failure or by an
    exogenous phosphate load.
  phenotype_term:
    preferred_term: Increased renal tubular phosphate reabsorption
    term:
      id: HP:0005571
      label: Increased renal tubular phosphate reabsorption
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP), elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D) levels, and elevated C-terminal FGF23 fragments"
    explanation: GeneReviews makes increased TRP part of the diagnostic laboratory definition.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."
    explanation: Increased TRP was present in every cohort subject.
genetic:
- name: Biallelic GALNT3 Pathogenic Variants
  subtype: HFTC1
  gene_term:
    preferred_term: GALNT3
    term:
      id: hgnc:4125
      label: GALNT3
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    Reported alleles include splice-site, nonsense, frameshift and missense
    variants; the c.1524+1G>A splice allele is a Middle Eastern founder mutation
    shared by HFTC and HHS families on a common haplotype. Heterozygous parents
    are unaffected. Genotype does not predict clinical severity: four novel
    homozygous GALNT3 alleles all produced hyperphosphatemia with low intact
    FGF23, but massive calcification, cortical hyperostosis and dental anomalies
    were each present in only some patients.
  evidence:
  - reference: PMID:15133511
    reference_title: "Mutations in GALNT3, encoding a protein involved in O-linked glycosylation, cause familial tumoral calcinosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sequence analysis of GALNT3 identified biallelic deleterious mutations in all individuals with FTC, suggesting that defective post-translational modification underlies the disease."
    explanation: The linkage-and-sequencing study establishes the causal gene-disease relationship.
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "suggest a common origin of the 1524+1G-->A mutation in the Middle East (founder effect)"
    explanation: This documents the recurrent allele as a regional founder mutation.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the presence of massive calcifications, cortical hyperostosis, or dental anomalies was not shared by all patients, all had persistent hyperphosphatemia."
    explanation: This supports the dissociation between a constant biochemical phenotype and variable clinical features.
- name: Biallelic FGF23 Pathogenic Variants
  subtype: HFTC2
  gene_term:
    preferred_term: FGF23
    term:
      id: hgnc:3680
      label: FGF23
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    Disease alleles are missense variants that prevent secretion of the intact
    hormone, including p.Ser71Gly (Golgi retention with selective secretion of
    the C-terminal fragment) and p.Gly123Trp. The same gene causes autosomal
    dominant hypophosphatemic rickets through gain-of-function alleles that
    resist cleavage, so the direction of the variant's effect - not the gene -
    determines which phosphate phenotype appears.
  evidence:
  - reference: PMID:15590700
    reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We investigated an individual with FTC who was negative for GALNT3 mutations. Sequencing revealed a homozygous missense mutation in the FGF23 gene (p.S71G)"
    explanation: This establishes FGF23 as a second causal gene in a GALNT3-negative patient.
  - reference: PMID:15590700
    reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that FGF23 mutations in hypophosphatemic rickets and FTC have opposite effects on phosphate homeostasis."
    explanation: This supports the allele-direction argument in the note.
- name: Biallelic KL Pathogenic Variants
  subtype: HFTC3
  gene_term:
    preferred_term: KL
    term:
      id: hgnc:6344
      label: KL
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    The evidence base is a single homozygous missense allele, p.His193Arg, in
    one patient, supported by structural modelling onto a plant homolog and by
    in vitro demonstration of reduced expression, reduced secretion and impaired
    FGF23 signalling. This is the least established of the three gene-disease
    relationships in terms of the number of independent families.
  evidence:
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "our findings provide what we believe to be the first evidence that loss-of-function mutations in human KL impair FGF23 bioactivity"
    explanation: The report's own framing supports both the causal claim and its single-family basis.
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "compared with wild-type KL, expression and secretion of H193R KL were markedly reduced in vitro"
    explanation: This is the functional evidence that the allele is loss of function.
biochemical:
- name: Serum Phosphate
  presence: Persistently elevated for age
  context: >-
    Interpret against age-adjusted reference intervals; children have higher
    normal phosphate than adults, so an adult cut-off will miss paediatric
    disease. Across 63 published patients the mean phosphate was 6.9 mg/dL.
  evidence:
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean (SD) phosphate was 6.9 (1.1) mg/dL."
    explanation: This quantifies the typical degree of hyperphosphatemia in reported cases.
- name: Tubular Reabsorption of Phosphate and TmP/GFR
  presence: Inappropriately high for the prevailing serum phosphate
  specificity: >-
    Elevated TRP/TmP-GFR with normal glomerular filtration separates HFTC from
    hyperphosphatemia of renal failure and from an exogenous phosphate load; it
    does not by itself separate the three molecular subtypes.
  context: Calculate from paired serum and urine phosphate and creatinine.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP)"
    explanation: GeneReviews makes inappropriately increased TRP part of the diagnostic definition.
- name: Intact FGF23
  presence: Low or inappropriately normal in HFTC1 and HFTC2; elevated in HFTC3
  specificity: >-
    This is the one measurement that distinguishes hormone deficiency from
    hormone resistance. A low intact FGF23 points to GALNT3 or FGF23; a high
    intact FGF23 in the same biochemical setting points to KL.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "C-terminal FGF23 was markedly elevated whereas iFGF23 was comparatively low, consistent with increased FGF23 cleavage."
    explanation: The cohort documents the low intact hormone in the deficiency subtypes.
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "elevated serum levels of parathyroid hormone and FGF23"
    explanation: The KL patient had elevated FGF23, the inverse of the deficiency subtypes.
- name: C-Terminal FGF23
  presence: Markedly elevated
  context: >-
    The C-terminal assay detects intact hormone plus C-terminal fragments, so it
    rises as cleavage consumes the intact pool. The dissociation between a high
    C-terminal and a low intact result is the diagnostic signature.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "and elevated C-terminal FGF23 fragments"
    explanation: GeneReviews includes elevated C-terminal fragments in the laboratory diagnosis.
  - reference: PMID:17129170
    reference_title: "Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C-terminal fragments."
    explanation: This is the paired measurement in GALNT3-mutant patients.
- name: 1,25-Dihydroxyvitamin D
  presence: Elevated or inappropriately normal for the degree of hyperphosphatemia
  context: >-
    A normal calcitriol is abnormal here: high phosphate should suppress
    1-alpha-hydroxylase through FGF23, so a mid-range value in a
    hyperphosphatemic patient is evidence that the FGF23 brake is missing.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."
    explanation: This records the direction of the calcitriol abnormality in every cohort subject.
- name: Serum Calcium and Parathyroid Hormone
  presence: Usually normal
  specificity: >-
    Normal calcium and PTH exclude primary hyperparathyroidism and the secondary
    hyperparathyroidism of chronic kidney disease as the cause of the
    hyperphosphatemia. Note the exception: the single HFTC3 patient had
    hypercalcemia with elevated PTH, so a normal result is the rule rather than
    a requirement.
  evidence:
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, circulating calcium and parathyroid hormone (PTH) are usually normal."
    explanation: This supports the usual normality of calcium and PTH.
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "marked hyperphosphatemia and hypercalcemia as well as elevated serum levels of parathyroid hormone"
    explanation: The KL case documents the exception noted in the specificity field.
prevalence:
- population: Worldwide, genetically or clinically characterised published cases
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population prevalence, incidence or carrier frequency has been estimated
    for HFTC. The available denominator is the published case literature: a 2024
    systematic review that applied strict inclusion criteria (baseline phosphate
    measured, treatment recorded, follow-up available) found 43 eligible studies
    describing 63 individuals. That is a lower bound on reported cases, not a
    population rate, because it excludes reports lacking treatment or follow-up
    data. The disease is reported worldwide but is enriched in consanguineous
    Middle Eastern and African families, consistent with the documented Middle
    Eastern GALNT3 founder allele.
  evidence:
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A total of 63 individuals (Males = 33) were included from the 43 eligible case studies."
    explanation: This is the published-case count behind the CASES_IN_LITERATURE record.
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "suggest a common origin of the 1524+1G-->A mutation in the Middle East (founder effect)"
    explanation: The founder effect supports the described regional enrichment.
progression:
- phase: Biochemical disease before clinical lesions
  notes: >-
    Hyperphosphatemia with increased tubular reabsorption is present before
    calcific masses appear and can be the only abnormality for years. Two
    siblings in the NIH cohort had the full biochemical phenotype without
    physical calcinosis at enrolment. This is the window in which phosphate
    control is most plausibly preventive, though that has never been tested
    prospectively.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical manifestations varied, even within families, ranging from asymptomatic to large, disabling calcifications."
    explanation: The asymptomatic end of the cohort's range is the biochemical-only phase.
- phase: Established calcific and hyperostotic disease
  notes: >-
    Masses accumulate around large joints and hyperostotic attacks recur. The
    median age of published patients at report is 18 years, with a wide spread,
    and radiographic burden ranges from diaphyseal hyperostosis alone to massive
    calcification.
  evidence:
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The median age of the patients was 18 (IQR 8-32) years."
    explanation: This gives the age distribution of reported clinical disease.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Radiographs ranged from diaphyseal hyperostosis to massive calcification."
    explanation: This describes the radiographic range of established disease.
- phase: Long-term lesion course under treatment
  notes: >-
    The disease does not follow a single trajectory. In the systematic review's
    followed-up patients, roughly a third regressed, a third progressed and a
    third were stable over a median of three years, and three patients died.
    Recurrence after incomplete excision is common while hyperphosphatemia
    persists.
  evidence:
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Regression or reduction in lesion size was reported in 19/63 (30.2%) subjects; 20/63 (31.7%) showed progression, 24/63 (38.1%) had features of stable disease, and mortality was reported in 3 patients (4.7%)."
    explanation: This is the outcome distribution behind the described course.
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The median (IQR) follow-up duration was 3 (1-9) years."
    explanation: This gives the observation window over which those outcomes were recorded.
diagnosis:
- name: Serum Phosphate Measurement
  description: >-
    The entry point of the workup is persistent, age-adjusted fasting
    hyperphosphatemia in a patient with normal renal function. Together with
    the renal phosphate handling, calcitriol and FGF23 results below, this is
    what establishes the clinical diagnosis before genotyping.
  diagnosis_term:
    preferred_term: serum phosphate measurement
    term:
      id: NCIT:C64857
      label: Phosphate Measurement
  presence: Elevated
  results: Persistent hyperphosphatemia for age with a normal serum creatinine.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The clinical diagnosis of HFTC is established by the presence of tumoral calcinosis and/or characteristic laboratory findings of hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP), elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D) levels, and elevated C-terminal FGF23 fragments."
    explanation: GeneReviews names hyperphosphatemia as the first of the characteristic laboratory findings on which the clinical diagnosis rests.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All subjects had hyperphosphatemia, increased TRP, and elevated or inappropriately normal 1,25D."
    explanation: Every subject in the NIH cohort met the biochemical criterion, which is why it is the screening test.
- name: Renal Tubular Phosphate Reabsorption
  description: >-
    Paired serum and urine phosphate and creatinine give the tubular
    reabsorption of phosphate (TRP), or its derived index TmP/GFR. In HFTC the
    kidney conserves phosphate despite hyperphosphatemia and normal renal
    function, so TRP is inappropriately high rather than suppressed. This is
    the finding that separates FGF23 deficiency or resistance from a phosphate
    load or renal failure.
  diagnosis_term:
    preferred_term: tubular reabsorption of phosphate (TRP)
    term:
      id: NCIT:C64857
      label: Phosphate Measurement
  presence: Inappropriately elevated
  results: TRP above the normal range (96 % in one reported patient) despite hyperphosphatemia.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "hyperphosphatemia in the setting of inappropriately increased renal tubular reabsorption of phosphorus (TRP)"
    explanation: GeneReviews includes inappropriately increased TRP in the laboratory definition of the clinical diagnosis.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperphosphatemia (7.9 mg/dl) was detected with inappropriately elevated tubular reabsorption of phosphate (TRP) of 96 %."
    explanation: A worked patient value showing the combination the test is meant to demonstrate.
  notes: >-
    NCIT has no term for the tubular reabsorption of phosphate or TmP/GFR.
    Queries run: `runoak -i ols:ncit search "tubular reabsorption of phosphate"`,
    `runoak -i ols:ncit search "phosphate reabsorption"` and `runoak -i ols:ncit
    search "urine phosphate measurement"` each returned nothing relevant
    (`search "tubular"` returned only histology terms such as NCIT:C14169).
    The index is therefore bound to the phosphate measurement it is computed
    from, with the index carried in preferred_term. TmP/GFR is named in the
    description because it is the standard derived form; no cached source
    reports a TmP/GFR value for this disease.
- name: Calcium, Renal Function, PTH and Vitamin D Metabolite Panel
  description: >-
    Serum calcium, creatinine, alkaline phosphatase, intact PTH,
    25-hydroxyvitamin D and 1,25-dihydroxyvitamin D are measured alongside
    phosphate. Calcium, creatinine, alkaline phosphatase and PTH are normal,
    which excludes renal failure, hyperparathyroidism and hypoparathyroidism;
    1,25-dihydroxyvitamin D is elevated or inappropriately normal for the
    phosphate level because FGF23 is not suppressing renal 1-alpha-hydroxylase.
  diagnosis_term:
    preferred_term: mineral-metabolism laboratory panel
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  markers: serum calcium, creatinine, alkaline phosphatase, intact PTH, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D
  results: Normal calcium, creatinine, alkaline phosphatase and PTH; elevated or inappropriately normal 1,25-dihydroxyvitamin D.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "detailed laboratory evaluation of calcium and phosphorus metabolism including 1,25D, intact parathyroid hormone (iPTH), TRP, iFGF23 and C-terminal FGF23 (CFGF23), genetic testing, and standard radiographs."
    explanation: This is the predefined evaluation set applied to every NIH-cohort subject and names the analytes in this panel.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other biochemical evaluation included normal serum and urine calcium, alkaline phosphatase, and PTH."
    explanation: The expected normal results for calcium, alkaline phosphatase and PTH in a genotyped patient.
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "elevated or inappropriately normal 1,25-dihydroxyvitamin D3 (1,25D) levels"
    explanation: GeneReviews lists the calcitriol pattern among the laboratory findings that establish the clinical diagnosis.
  notes: >-
    Bound as one Laboratory Procedure because the sources order these analytes
    together as a single evaluation. NCIT carries per-analyte terms that are
    each reachable from NCIT:C25218 and could replace this binding if the panel
    is ever split: NCIT:C61020 Serum Calcium Measurement, NCIT:C64547
    Creatinine Measurement, NCIT:C64432 Alkaline Phosphatase Measurement,
    NCIT:C74789 Intact Parathyroid Hormone Measurement and NCIT:C84818 Vitamin
    D Measurement (all verified with `runoak -i ols:ncit info`).
- name: Intact and C-Terminal FGF23 Assays
  description: >-
    Both FGF23 assays are needed, because the pattern, not a single value,
    identifies the subtype. In GALNT3- and FGF23-related disease the intact
    hormone is low or inappropriately normal while C-terminal fragments are
    markedly elevated, the signature of a hormone that is made but cleaved. In
    KL-related disease intact and C-terminal FGF23 are both very high, because
    the hormone is intact but the kidney cannot respond to it.
  diagnosis_term:
    preferred_term: intact and C-terminal FGF23 measurement
    term:
      id: NCIT:C96650
      label: Fibroblast Growth Factor 23 Measurement
  markers: intact FGF23 (iFGF23); C-terminal FGF23 (cFGF23)
  results: GALNT3/FGF23 disease - low or inappropriately normal iFGF23 with markedly elevated cFGF23; KL disease - both iFGF23 and cFGF23 markedly elevated.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "C-terminal FGF23 was markedly elevated whereas iFGF23 was comparatively low, consistent with increased FGF23 cleavage."
    explanation: The GALNT3 cohort pattern of low intact hormone with fragment excess.
  - reference: PMID:17129170
    reference_title: "Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C-terminal fragments."
    explanation: An independent GALNT3 series reporting the same paired-assay pattern.
  - reference: PMID:15590700
    reference_title: An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "determination of circulating FGF23 in the affected individual showed a marked increase in the C-terminal fragment"
    explanation: The FGF23-mutant form shows the same C-terminal fragment excess as GALNT3 disease.
  - reference: PMID:17710231
    reference_title: A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "our patient had appropriately elevated intact (functional) and C-terminal FGF23 levels"
    explanation: The KL-mutant patient shows high intact hormone, the opposite of the cleavage pattern, which is how the assays discriminate resistance from deficiency.
  notes: >-
    NCIT has child terms for each assay, NCIT:C135420 Intact Fibroblast Growth
    Factor 23 Measurement and NCIT:C135419 C-Terminal Fibroblast Growth Factor
    23 Measurement (both reachable from NCIT:C25218; found with `runoak -i
    ols:ncit search "fibroblast growth factor 23 measurement"`). The parent
    term is bound because the diagnostic reading is the paired result, and
    markers names both assays.
- name: Plain Radiography of Symptomatic Sites
  description: >-
    Conventional radiographs of painful or swollen sites show the two lesion
    types: amorphous, lobulated periarticular calcific masses, and in
    hyperostotic long bones cortical thickening, diaphysitis and periosteal
    apposition.
  diagnosis_term:
    preferred_term: conventional radiography
    term:
      id: NCIT:C38101
      label: X-Ray Imaging
  results: Periarticular calcific masses; diaphyseal cortical hyperostosis and periosteal apposition.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tumoral calcinosis was assessed by conventional radiography and, in some, by CT."
    explanation: Radiography was the baseline lesion assessment in the NIH cohort.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Radiographs ranged from diaphyseal hyperostosis to massive calcification."
    explanation: The radiographic spectrum across the cohort.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Typical radiographic features of affected bones include cortical hyperostosis, diaphysitis, and periosteal apposition."
    explanation: The radiographic appearance of the hyperostosis lesion.
- name: Computed Tomography of Calcific Lesions
  description: >-
    CT is used for symptomatic lesions and, as cardiac CT, to detect the
    vascular calcification that plain films miss.
  diagnosis_term:
    preferred_term: computed tomography
    term:
      id: NCIT:C17204
      label: Computed Tomography
  results: Extent of calcific masses; coronary calcification on cardiac CT in a subset of adults.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "computed tomography (CT) of symptomatic lesions"
    explanation: CT of symptomatic lesions was part of the cohort's evaluation set.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FTC4 (32 years old) and FTC7 (56 years old) had cardiac calcifications on CT with Agatston coronary calcium scores of 105"
    explanation: Cardiac CT detected coronary calcification in two adults, the vascular finding the modality is used for.
- name: Magnetic Resonance Imaging of Hyperostotic Bone
  description: >-
    MRI of a painful hyperostotic diaphysis shows an inflammatory process with
    marrow and periosteal signal change, and bone scintigraphy shows focal
    uptake. Neither is specific: the appearance is that of osteomyelitis, and
    the hyperostosis presentation is repeatedly misdiagnosed as such before the
    serum phosphate is checked.
  diagnosis_term:
    preferred_term: magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  results: Inflammatory signal in the affected diaphysis, indistinguishable from osteomyelitis on imaging alone.
  evidence:
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Magnetic resonance imaging (MRI) showed inflammatory process and technetium scintigraphy displayed localized increased uptake at the tibia diaphysis."
    explanation: The MRI and scintigraphic appearance of a hyperostotic lesion in a genotyped patient.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tibial radiographs demonstrated circumferential endosteal and periosteal bone proliferation with patchy sclerosis of the medullary canal, consistent with hyperostosis (Fig 1-2a). Multifocal osteomyelitis was considered."
    explanation: >-
      The osteomyelitis differential was raised on the radiographic appearance
      of a hyperostotic lesion in a patient later shown to carry a GALNT3
      mutation.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which may manifest clinically as diaphyseal pain of the long bones and is often erroneously diagnosed as osteomyelitis"
    explanation: The misdiagnosis is common enough that the cohort paper states it in its introduction.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two subjects had magnetic resonance imaging of tumoral calcinosis"
    explanation: MRI was also applied to calcific masses in the cohort, though it is not the primary modality for them.
- name: Molecular Genetic Testing of GALNT3, FGF23 and KL
  description: >-
    Sequencing of the three causal genes confirms the diagnosis and assigns the
    subtype. GeneReviews positions it as confirmatory when the clinical and
    laboratory picture is inconclusive, and identification of the familial
    variants opens carrier, prenatal and preimplantation testing. A minority of
    biochemically typical patients have no biallelic variant found.
  diagnosis_term:
    preferred_term: molecular genetic testing of GALNT3, FGF23 and KL
    term:
      id: NCIT:C15709
      label: Genetic Testing
  results: Biallelic pathogenic variants in GALNT3, FGF23 or KL; GALNT3 in most genotyped patients.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Identification of biallelic pathogenic variants in FGF23, GALNT3, or KL by molecular genetic testing confirms the diagnosis when clinical and laboratory findings are inconclusive."
    explanation: GeneReviews' statement of the confirmatory role of molecular testing.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GALNT3 mutations were identified in seven subjects; no causative mutation was found in the eighth."
    explanation: The yield of genetic testing in a well-characterised cohort, including a genotype-negative case.
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Once the FGF23, GALNT3, or KL pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible."
    explanation: The downstream uses of a confirmed molecular diagnosis in the family.
  notes: >-
    Bound to the generic Genetic Testing term. NCIT:C198412 Multi-gene Panel
    Sequencing, NCIT:C101295 Whole Exome Sequencing and NCIT:C101294 Whole
    Genome Sequencing exist and are reachable from NCIT:C25218 (verified with
    `runoak -i ols:ncit info`), but no cached source documents which platform
    was used; the recommendation to sequence a mineral-metabolism panel first
    and escalate to exome or genome sequencing when the panel is negative is
    the deep-research report's workflow and is uncited here.
- name: Anti-FGF23 Autoantibody Testing
  description: >-
    An acquired phenocopy exists in which autoantibodies against FGF23 produce
    the same hyperphosphatemic tumoral calcinosis picture. It belongs in the
    differential of a patient with typical biochemistry and no biallelic
    GALNT3, FGF23 or KL variant, and is not part of the hereditary disease
    modelled in this entry.
  diagnosis_term:
    preferred_term: anti-FGF23 autoantibody measurement
    term:
      id: NCIT:C181397
      label: Autoantibody Measurement
  presence: Absent in the hereditary disease
  results: Positive result indicates the acquired autoimmune phenocopy rather than HFTC.
  evidence:
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FGF23 autoantibodies cause an acquired form of tumoral calcinosis."
    explanation: Establishes the autoimmune phenocopy that this test is meant to exclude.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "no causative mutation was found in the eighth"
    explanation: The genotype-negative patient is the setting in which the differential arises.
histopathology:
- name: Ectopic Calcification of Periarticular Soft Tissue
  description: >-
    Resected masses consist of calcific material in soft tissue. Biopsy is not
    required when the biochemistry and imaging are typical, but resected
    lesions consistently show this finding.
  finding_term:
    preferred_term: ectopic soft-tissue calcification
    term:
      id: NCIT:C3672
      label: Calcification
  frequency: VERY_FREQUENT
  diagnostic: false
  context: Resection or biopsy specimens of tumoral calcinosis lesions; four biopsied NIH-cohort subjects.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Specimens obtained following surgical resection of calcific tumors from the right chest and shoulder of FTC4 showed histologic evidence of calcification, as expected"
    explanation: Direct histological confirmation of calcification in resected lesions.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biopsies from four subjects showed ectopic calcification and chronic inflammation, with areas of heterotopic ossification observed in one subject."
    explanation: All four biopsied subjects showed the finding.
  notes: >-
    The deep-research report describes the material as amorphous calcium
    phosphate; no cached source characterises the mineral phase, so the finding
    is recorded as calcification only.
- name: Chronic Inflammatory Infiltrate with Foamy Macrophages
  description: >-
    The calcific deposits sit in a background of chronic inflammation with
    numerous foamy macrophages; earlier reports also describe multinucleated
    giant cells. The macrophage-rich reaction is the histological basis for
    treating perilesional inflammation as part of the mechanism and for the
    IL-1 antagonist response seen in two subjects.
  finding_term:
    preferred_term: chronic inflammatory infiltrate with foamy macrophages
    term:
      id: NCIT:C35980
      label: Chronic Inflammatory Infiltrate
  frequency: VERY_FREQUENT
  diagnostic: false
  context: Resection or biopsy specimens of tumoral calcinosis lesions.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histologic analyses showed ectopic calcification in a background of chronic inflammation with multiple foamy macrophages."
    explanation: The cohort's summary histological description of the inflammatory background.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Others have shown the presence of macrophages and multinucleated giant cells on histology from biopsies of tumoral calcinosis"
    explanation: The authors' summary of earlier biopsy reports supplies the giant-cell component; it is their statement about prior literature rather than a new observation.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Given the presumed increased IL-1 production by foamy macrophages seen on biopsies, inflammation in FTC4 was treated with a short course of anakinra, a recombinant IL-1 receptor antagonist."
    explanation: Links the histological finding to the therapeutic decision it motivated.
  notes: >-
    NCIT:C182619 Foamy Cell Proliferation (defined as the presence of
    xanthomatous cells) was considered and not bound: the source describes the
    cells as foamy macrophages within a chronic inflammatory background rather
    than as a xanthomatous proliferation, so the inflammatory-infiltrate term
    is the accurate binding and the macrophage detail is carried in
    preferred_term. NCIT:C3044 Fibrosis was not bound either: the deep-research
    report asserts surrounding fibrosis, but no cached source describes
    fibrosis around the calcific deposits (the only fibroblastic stroma
    reported is in the hyperostotic bone lesion, recorded separately below).
- name: Heterotopic Ossification with Mature Lamellar Bone
  description: >-
    In one of four biopsied NIH-cohort subjects, mature heterotopic bone with
    lamellar remodelling and reversal lines was present within a tumoral
    calcinosis lesion, adjacent to the inflamed deposit. Older literature
    describes woven bone in these lesions, but remodelled lamellar bone had not
    been reported before.
  finding_term:
    preferred_term: heterotopic ossification with lamellar remodelling and reversal lines
    term:
      id: NCIT:C35988
      label: Metaplastic Bone Formation
  frequency: VERY_RARE
  diagnostic: false
  context: Resected tumoral calcinosis lesion from one NIH-cohort subject (FTC4).
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition to the calcification, heterotopic ossification was evident"
    explanation: The primary histological observation in the resected specimen.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "there are no reports of heterotopic ossification within tumoral calcinosis lesions with mature remodeling of lamellar bone and the presence of reversal lines as seen in our cohort"
    explanation: Specifies the lamellar remodelling and reversal lines that distinguish this from the woven bone of older reports.
  notes: >-
    NCIT:C35988 is defined as the presence of newly formed heterotopic bone,
    which matches the source. NCIT:C35859 Osseous Metaplasia (heterotopic
    formation of normal bone within soft tissue) and NCIT:C53954 New Bone
    Formation are sibling candidates in the same Morphologic Finding branch;
    the first was not chosen because it asserts normal bone, and the second
    is used below for the reactive woven bone of hyperostosis.
- name: Reactive Woven Bone and Fibroblastic Stroma in Hyperostotic Diaphysis
  description: >-
    Bone biopsy of a hyperostotic tibia shows reactive, non-specific new woven
    bone that is converted to lamellar bone over time, with a fibroblastic
    stroma infiltrated by lymphocytes and polymorphonuclear cells. The biopsy
    is usually taken to exclude osteomyelitis or malignancy and shows no
    organism-specific or neoplastic feature.
  finding_term:
    preferred_term: reactive woven new bone formation
    term:
      id: NCIT:C53954
      label: New Bone Formation
  diagnostic: false
  context: Tibial bone biopsy of the hyperostosis-hyperphosphatemia presentation; one NIH-cohort subject (FTC6) and one reported GALNT3 patient.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tibia biopsy of FTC6 revealed hyperostosis with reactive woven bone which, over time, is converted to lamellar bone"
    explanation: The cohort's tibial biopsy finding and its maturation over time.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biopsy demonstrated reactive non-specific new bone, fibroblastic stroma infiltrated by lymphocytes and polynuclear cells."
    explanation: An independent patient's tibial biopsy showing the same reactive new bone with an inflamed fibroblastic stroma.
treatments:
- name: Dietary Phosphate Restriction
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  description: >-
    A low-phosphate diet is the first and least invasive way to lower the
    substrate for ectopic mineralization. The NIH cohort targeted 400-900 mg of
    phosphorus per day according to age, with nutritional counselling for every
    subject, because a restriction severe enough to move serum phosphate is
    also severe enough to compromise nutrition in a growing child. Calcium
    salts should not be used as binders and excessive dietary calcium and
    vitamin D should be avoided, since both add to the calcium-phosphate
    product the treatment is trying to lower.
  treatment_term:
    preferred_term: Dietary Intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Hyperphosphatemia with Elevated Calcium-Phosphate Product
    treatment_effect: INHIBITS
    description: Reducing intake lowers the absorbed phosphate load and so the calcium-phosphate product.
    evidence:
    - reference: PMID:29389098
      reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "treatment relies on lowering blood phosphorus by blocking absorption from the diet (i.e., use of low-phosphate diet and phosphate binders)"
      explanation: GeneReviews states the intended mechanism of dietary restriction.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "low phosphate diet targeting 400–900 mg/day, depending upon age."
    explanation: This records the dose target actually used in the NIH cohort.
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It is prudent to avoid: use of calcium salts as phosphate binders; excessive dietary calcium intake; excessive vitamin D intake/supplements; foods high in phosphorus."
    explanation: This supports the dietary avoidances that accompany the restriction.
- name: Non-Calcium Phosphate Binders
  action_category: THERAPEUTIC
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Sevelamer binds dietary phosphate in the gut lumen and was given with meals
    and snacks to all but one subject in the NIH cohort. Calcium-containing
    binders are avoided because they supply the other half of the precipitating
    product. Aluminium hydroxide is an effective second binder and was added in
    two subjects whose phosphate did not move on sevelamer plus phosphaturic
    agents, but it carries aluminium-toxicity risk and is not a long-term
    default. In one reported family, sevelamer combined with acetazolamide
    lowered serum phosphate and shrank an ulcerating elbow mass.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sevelamer
      term:
        id: CHEBI:759084
        label: sevelamer
    - preferred_term: aluminium hydroxide
      term:
        id: NCIT:C39707
        label: Aluminum Hydroxide
  target_mechanisms:
  - target: Hyperphosphatemia with Elevated Calcium-Phosphate Product
    treatment_effect: INHIBITS
    description: Luminal binding reduces intestinal phosphate absorption and lowers serum phosphate.
    evidence:
    - reference: PMID:19188744
      reference_title: "Familial tumoral calcinosis caused by a novel FGF23 mutation: response to induction of tubular renal acidosis with acetazolamide and the non-calcium phosphate binder sevelamer."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Treatment with the phosphate binder sevelamer and the carbonic anhydrase inhibitor acetazolamide successfully reduced the serum phosphate levels and led to a reduction of the calcified mass."
      explanation: This single-family report links binder-based phosphate lowering to regression of a mass.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment of all subjects except FTC1 included sevelamer, a phosphate binder, prescribed with meals and snacks."
    explanation: This documents sevelamer as the cohort's standard binder and how it was given.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Aluminum hydroxide was added as an additional phosphate binder in 2 subjects, who had increased tumoral calcinosis burden with no change in blood phosphorus on sevelamer, acetazolamide and probenecid."
    explanation: This records aluminium hydroxide as escalation after failure of the first-line combination.
- name: Phosphaturic Therapy with Acetazolamide or Probenecid
  action_category: THERAPEUTIC
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    The complementary strategy to binding: increase renal phosphate excretion.
    Acetazolamide, a carbonic anhydrase inhibitor, induces bicarbonaturia and
    mild metabolic acidosis; probenecid promotes phosphaturia but interacts with
    several antibiotics. Responses are inconsistent, and in one well-documented
    boy acetazolamide stopped new tumour formation and abolished bone pain with
    no measurable change in serum phosphate or TRP at all - which suggests the
    benefit ran through mineral solubility rather than through phosphate
    lowering. Nicotinamide was tried in two NIH subjects for its phosphaturic
    effect and did not add benefit.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: acetazolamide
      term:
        id: NCIT:C28809
        label: Acetazolamide
    - preferred_term: probenecid
      term:
        id: NCIT:C772
        label: Probenecid
    - preferred_term: nicotinamide
      term:
        id: NCIT:C2327
        label: Niacinamide
  target_mechanisms:
  - target: Increased Proximal Tubular Sodium-Phosphate Cotransport
    treatment_effect: INHIBITS
    description: Both agents are used to force renal phosphate excretion against the elevated tubular reabsorption.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "were additionally treated with acetazolamide and/or probenecid, both of which promote renal phosphate excretion."
      explanation: This states the intended renal mechanism of both agents.
  evidence:
  - reference: PMID:24668887
    reference_title: "Hyperphosphatemic familial tumoral calcinosis: response to acetazolamide and postulated mechanisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Following the initiation of acetazolamide therapy, the patient experienced significant improvement in disease course as indicated by resolution of localized bone pain, cessation of tumor formation, and no tumor recurrence."
    explanation: This is the clinical benefit reported in the single-patient acetazolamide series.
  - reference: PMID:24668887
    reference_title: "Hyperphosphatemic familial tumoral calcinosis: response to acetazolamide and postulated mechanisms."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that acetazolamide can control severe HFTC by inducing mild metabolic acidosis despite no change in serum phosphate or TRP."
    explanation: The authors' own inference that the benefit was not mediated by phosphate lowering; it supports the treatment while arguing against the assumed mechanism, so the support for the phosphaturic rationale is indirect.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with nicotinamide was attempted during a hospitalization in 2 subjects to assess its effect on inducing phosphaturia but was not continued upon discharge, as it did not show additional benefits."
    explanation: This is a negative result for nicotinamide specifically, within an otherwise supported treatment class.
- name: Interleukin-1 Blockade for Systemic Inflammation
  action_category: THERAPEUTIC
  therapeutic_modality: OTHER
  description: >-
    For the minority of patients with overwhelming systemic inflammation,
    IL-1 antagonists lowered C-reactive protein in both treated NIH subjects,
    with resolution of calcinosis cutis and perilesional inflammation in one.
    This treats the inflammatory arm of the disease and does nothing about the
    FGF23 deficiency, so it is an adjuvant rather than a disease-modifying
    therapy. The evidence is two patients in an uncontrolled cohort.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: anakinra
      term:
        id: NCIT:C38717
        label: Anakinra
  target_mechanisms:
  - target: Foreign-Body and Systemic Inflammation Around Calcific Deposits
    treatment_effect: INHIBITS
    description: IL-1 antagonism suppresses the cytokine-driven inflammation around and beyond the deposits.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In the two subjects with systemic inflammation, interleukin-1 (IL-1) antagonists significantly decreased CRP levels with resolution of calcinosis cutis and perilesional inflammation in one subject and improvement of overall well-being in both subjects."
      explanation: This is the direct observation of the anti-inflammatory effect on lesion-associated inflammation.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the response to IL-1 antagonists suggests that anti-inflammatory drugs may be useful adjuvants"
    explanation: The authors frame IL-1 blockade as adjuvant, which is how the treatment is described here.
  notes: >-
    The cited cohort reports "interleukin-1 (IL-1) antagonists" without naming
    the agent in its abstract, so the class is the claim and the anakinra
    binding should be read as representative. therapeutic_modality is OTHER
    rather than MONOCLONAL_ANTIBODY because the two agents used for this
    indication belong to different platforms: anakinra is a recombinant IL-1
    receptor antagonist protein, canakinumab a monoclonal antibody. Neither
    single value describes the class, and PROTEIN_REPLACEMENT would be wrong in
    both cases since nothing deficient is being replaced.
- name: Surgical Excision of Calcific Masses
  action_category: THERAPEUTIC
  therapeutic_modality: SURGERY
  description: >-
    Excision or debulking is reserved for masses causing significant pain,
    functional impairment, ulceration or infection. It does not address the
    hyperphosphatemia, so recurrence is common after incomplete excision and
    attempted complete excision carries its own wound morbidity. In the
    systematic review, most reported patients (57%) had surgery combined with
    some medical therapy rather than surgery alone.
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Periarticular Calcific Masses
    treatment_effect: INHIBITS
    description: >-
      Excision removes the deposit itself; it does not act on any upstream node,
      which is why the lesion re-forms while the calcium-phosphate product stays
      elevated.
    evidence:
    - reference: PMID:27164190
      reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Surgical debulking may be performed in subjects with functional impairment or severe pain, but is not routinely undertaken as calcinosis often recurs"
      explanation: This states both the indication and the recurrence that limits it.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Surgical resection of tumoral calcinosis lesions – generally reserved for those patients with significant pain or functional impairment – has variable success."
    explanation: GeneReviews gives the indication and the qualified outcome.
  - reference: PMID:38951179
    reference_title: "Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among the subjects, 36/63 (57.1%) underwent surgical excision with some form of medical therapy."
    explanation: This quantifies how often surgery is used and that it is normally combined with medical treatment.
animal_models:
- name: Galnt3-null mouse
  species: Mus musculus
  genotype: Galnt3 knockout (homozygous null)
  background: Mouse
  category: Genetically engineered
  publication: PMID:19213845
  description: >-
    The genetic model of the commonest human subtype. Galnt3-deficient mice
    reproduce the defining endocrine lesion faithfully - circulating intact
    Fgf23 is about half that of littermates with increased C-terminal fragments,
    despite increased Fgf23 expression in bone - and reproduce the renal
    consequences, with elevated sodium-phosphate cotransporter expression,
    hyperphosphatemia and an inappropriately normal 1,25-dihydroxyvitamin D.
    What they do not reproduce is the lesion the human disease is named for:
    they develop no apparent calcifications.
  modeled_mechanisms:
  - target: Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: ORGANISM
    description: >-
      The model reproduces the exact dissociation seen in patients: low intact
      hormone with excess C-terminal fragments on a background of increased
      Fgf23 transcription.
    limitations: >-
      Circulating intact Fgf23 was roughly halved rather than abolished, so the
      model is a partial-deficiency state; C-terminal fragments were measured in
      bone rather than only in circulation.
    readouts:
    - name: Circulating intact Fgf23
      target: Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess
      direction: DECREASED
      interpretation: Direct measurement of the hormone deficiency this node describes.
      evidence:
      - reference: PMID:19213845
        reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "homozygous mice had only about half of circulating intact Fgf23 levels and higher levels of C-terminal Fgf23 fragments in bone"
        explanation: This is the quantitative readout of intact and fragment hormone in the model.
    evidence:
    - reference: PMID:19213845
      reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "ablation of Galnt3 impaired secretion of intact Fgf23, leading to decreased circulating Fgf23 and hyperphosphatemia, despite increased Fgf23 expression"
      explanation: This establishes the model as informative for the hormone-deficiency node.
  - target: Increased Proximal Tubular Sodium-Phosphate Cotransport
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Renal sodium-phosphate cotransporter expression is elevated in the
      knockout, the transporter-level change the human node asserts.
    limitations: >-
      The finding is transporter expression rather than a measured tubular
      phosphate threshold, so the correspondence to human TmP/GFR is inferred.
      Renal Kl expression was also elevated, a compensatory change with no
      established human counterpart.
    readouts:
    - name: Renal sodium-phosphate cotransporter expression
      target: Increased Proximal Tubular Sodium-Phosphate Cotransport
      direction: INCREASED
      interpretation: Molecular correlate of the unopposed tubular reabsorption node.
      evidence:
      - reference: PMID:19213845
        reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "renal expression of sodium-phosphate cotransporters and Kl were elevated in Galnt3-deficient mice"
        explanation: This is the direct transporter measurement.
    evidence:
    - reference: PMID:19213845
      reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In response to hyperphosphatemia, Galnt3-deficient mice had markedly increased Fgf23 expression in bone."
      explanation: The compensatory rise in bone Fgf23 confirms the animals are sensing and failing to correct a phosphate load.
  - target: Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      The knockout is biochemically a tumoral-calcinosis model but not
      anatomically one: hyperphosphatemia develops without apparent
      calcifications.
    limitations: >-
      No ectopic calcific masses form, so the model cannot be used to study
      lesion formation, lesion regression, or any therapy whose endpoint is
      lesion burden. Sex-specific confounds (growth retardation, infertility
      and increased bone mineral density in males only) further limit it as a
      skeletal-phenotype model.
    evidence:
    - reference: PMID:19213845
      reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
      supports: REFUTE
      evidence_source: MODEL_ORGANISM
      snippet: "In this study we generated mice lacking the Galnt3 gene, which developed hyperphosphatemia without apparent calcifications."
      explanation: The absence of calcification is stated explicitly and is the basis for the negative link.
  evidence:
  - reference: PMID:19213845
    reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our findings indicate that Galnt3-deficient mice have a biochemical phenotype of tumoral calcinosis"
    explanation: The authors position the model as a biochemical rather than a full phenotypic model, which is how it is used here.
- name: Fgf23-null mouse
  species: Mus musculus
  genotype: Fgf23 knockout (homozygous null)
  background: Mouse
  category: Genetically engineered
  publication: PMID:14966565
  description: >-
    Total ablation of the hormone rather than of its protection. The Fgf23-null
    mouse is the cleanest demonstration that the human renal phenotype follows
    from absent FGF23 action: high serum phosphate with increased renal
    reabsorption, and elevated 1,25-dihydroxyvitamin D driven by enhanced renal
    1-alpha-hydroxylase expression. It is a more severe systemic state than
    human HFTC, with severe growth retardation and a markedly short lifespan.
  modeled_mechanisms:
  - target: Increased Proximal Tubular Sodium-Phosphate Cotransport
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: ORGANISM
    description: >-
      Complete loss of FGF23 produces exactly the renal phosphate-conserving
      state the node asserts.
    limitations: >-
      Complete hormone absence is more extreme than the partial deficiency of
      human GALNT3- or FGF23-related disease, so the model overstates the
      degree of signalling loss.
    readouts:
    - name: Serum phosphate and renal phosphate reabsorption
      target: Increased Proximal Tubular Sodium-Phosphate Cotransport
      direction: INCREASED
      interpretation: The physiological readout of unopposed tubular phosphate reclamation.
      evidence:
      - reference: PMID:14966565
        reference_title: Targeted ablation of Fgf23 demonstrates an essential physiological role of FGF23 in phosphate and vitamin D metabolism.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The Fgf23(-/-) mice displayed significantly high serum phosphate with increased renal phosphate reabsorption."
        explanation: This is the direct measurement of the modelled renal phenotype.
    evidence:
    - reference: PMID:14966565
      reference_title: Targeted ablation of Fgf23 demonstrates an essential physiological role of FGF23 in phosphate and vitamin D metabolism.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "indicating that FGF23 is essential for normal phosphate and vitamin D metabolism"
      explanation: The model establishes FGF23 as the physiological regulator whose loss the human disease reproduces.
  - target: Unsuppressed Renal Calcitriol Production
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: ORGANISM
    description: >-
      The knockout supplies the mechanistic step the human data can only infer:
      the calcitriol elevation is attributable to increased renal
      1-alpha-hydroxylase expression.
    limitations: >-
      In humans calcitriol is often only inappropriately normal rather than
      frankly elevated, so the model shows a stronger version of the human
      abnormality.
    readouts:
    - name: Renal 25-hydroxyvitamin D-1alpha-hydroxylase expression
      target: Unsuppressed Renal Calcitriol Production
      direction: INCREASED
      interpretation: The enzymatic cause of the calcitriol elevation, measured directly.
      evidence:
      - reference: PMID:14966565
        reference_title: Targeted ablation of Fgf23 demonstrates an essential physiological role of FGF23 in phosphate and vitamin D metabolism.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "They also showed an elevation in serum 1,25(OH)2D that was due to the enhanced expression of renal 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-OHase) from 10 days of age."
        explanation: This links the calcitriol rise to the specific enzyme the node names.
    evidence:
    - reference: PMID:14966565
      reference_title: Targeted ablation of Fgf23 demonstrates an essential physiological role of FGF23 in phosphate and vitamin D metabolism.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We present here the evidence that FGF23 is a physiological regulator of serum phosphate and 1,25-dihydroxyvitamin D (1,25[OH]2D) by generating FGF23-null mice."
      explanation: This states the model's purpose and its relevance to the calcitriol arm.
  notes: >-
    The same knockout is also the reference model for the opposite disease:
    FGF23 excess causes X-linked hypophosphatemia, and the null mouse's
    hyperphosphatemic, hypercalcitriolemic state is what establishes the
    direction of the axis in both.
  evidence:
  - reference: PMID:14966565
    reference_title: Targeted ablation of Fgf23 demonstrates an essential physiological role of FGF23 in phosphate and vitamin D metabolism.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Disruption of the Fgf23 gene did not result in embryonic lethality, although homozygous mice showed severe growth retardation with abnormal bone phenotype and markedly short life span."
    explanation: This records the model's viability and its systemic severity, which bounds how far it can be read across to human HFTC.
- name: Klotho-deficient mouse
  species: Mus musculus
  genotype: klotho hypomorph (kl/kl)
  background: Mouse
  category: Genetically engineered
  publication: PMID:9363890
  description: >-
    The mouse that named the gene behind HFTC3. Defective klotho expression
    produces a systemic syndrome resembling premature ageing - short lifespan,
    infertility, arteriosclerosis, skin atrophy, osteoporosis and emphysema -
    and identified klotho as a membrane protein with beta-glucosidase homology.
    It carries the molecular lesion of the human resistance subtype, but the
    original description characterises an ageing phenotype rather than an
    FGF23-resistance phenotype, so its use for this disease rests on later work
    not cited here.
  modeled_mechanisms:
  - target: Biallelic KL Loss of Function and Renal FGF23 Resistance
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      The model carries the same genetic lesion as HFTC3 - loss of functional
      alpha-Klotho - and so reproduces the upstream cause of FGF23 resistance.
    limitations: >-
      The cited description reports a multi-system premature-ageing syndrome,
      not the mineral phenotype, so the mineral-handling correspondence to human
      HFTC3 is not established by this source. The human disease is caused by a
      missense allele with reduced but not absent alpha-Klotho, and human
      patients do not have a progeroid syndrome; arteriosclerosis in the mouse
      is not the same lesion as periarticular tumoral calcinosis. The model
      should not be used to argue that HFTC3 patients are at risk of accelerated
      ageing.
    evidence:
    - reference: PMID:9363890
      reference_title: Mutation of the mouse klotho gene leads to a syndrome resembling ageing.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "A defect in klotho gene expression in the mouse results in a syndrome that resembles human ageing, including a short lifespan, infertility, arteriosclerosis, skin atrophy, osteoporosis and emphysema."
      explanation: This establishes what the model's klotho deficiency actually produces, which is the basis for both the partial recapitulation and the limitation.
  evidence:
  - reference: PMID:9363890
    reference_title: Mutation of the mouse klotho gene leads to a syndrome resembling ageing.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The gene encodes a membrane protein that shares sequence similarity with the beta-glucosidase enzymes."
    explanation: This is the original characterisation of the gene product whose human orthologue causes HFTC3.
discussions:
- discussion_id: gap_hftc_site_selection
  prompt: >-
    Why does mineral deposit at specific periarticular sites and in specific
    organs when the driving abnormality - an elevated calcium-phosphate product
    - is systemic?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Hyperphosphatemia with Elevated Calcium-Phosphate Product
  - pathophysiology#Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue
  rationale: >-
    Repetitive trauma and pressure are cited as the site determinant, but that
    is a clinical observation rather than a demonstrated mechanism, and it does
    not explain the dental pulp, the testis or the retina. Nor does it explain
    why some patients with the same genotype and the same phosphate level never
    form a mass. Identifying a local permissive factor would matter clinically:
    it is the difference between "lower the phosphate and hope" and a target
    that acts where the deposits form.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Ectopic calcifications (tumoral calcinosis) typically found in periarticular soft tissues exposed to repetitive trauma or prolonged pressure"
    explanation: This is the observational basis for the mechanical hypothesis, stated as a site association rather than a mechanism.
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the presence of massive calcifications, cortical hyperostosis, or dental anomalies was not shared by all patients, all had persistent hyperphosphatemia."
    explanation: A constant biochemical driver with inconstant lesions is exactly what an unexplained local permissive factor would look like.
- discussion_id: gap_hftc_hyperostosis_mechanism
  prompt: >-
    What links the hyperphosphatemic state to diaphyseal cortical hyperostosis
    and its episodic inflammatory attacks?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Diaphyseal Cortical Hyperostosis
  - phenotypes#Painful Diaphyseal Hyperostosis
  rationale: >-
    Allelic identity with the calcinosis presentation establishes that
    hyperostosis belongs to the same disease and follows the same phosphate
    excess, but the step from systemic phosphate to periosteal apposition in a
    particular long bone, at a particular time, is unaccounted for. The attacks
    are episodic while the biochemistry is constant, so something other than the
    phosphate level is timing them. This is the reason the lesion is repeatedly
    treated as osteomyelitis.
  evidence:
  - reference: PMID:20358599
    reference_title: Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "tumoral calcinosis and hyperostosis-hyperphosphatemia syndrome represent a continuous spectrum of the same disease caused by increased phosphate levels, rather than two distinct disorders"
    explanation: This establishes the shared cause without supplying the local mechanism, which is the gap.
  - reference: PMID:15599692
    reference_title: Identification of a recurrent mutation in GALNT3 demonstrates that hyperostosis-hyperphosphatemia syndrome and familial tumoral calcinosis are allelic disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The heterogeneous phenotypic expression of the identified splice site mutation implies the existence of inherited or epigenetic modifying factors of importance in the regulation of ppGalNAc-T3 activity."
    explanation: The original authors explicitly posit unidentified modifiers, which is the open question restated.
- discussion_id: gap_hftc_no_replacement_therapy
  prompt: >-
    Would restoring intact FGF23 signalling correct the disease, and can early
    phosphate control prevent lesions from ever forming?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule
  - treatments#Dietary Phosphate Restriction
  - treatments#Phosphaturic Therapy with Acetazolamide or Probenecid
  rationale: >-
    Every available treatment acts downstream of the lesion, on the phosphate
    load rather than on the missing signal, and none has been tested in a
    randomised trial. The two questions are linked: because no therapy restores
    the hormone, the only preventive strategy is phosphate control in the
    presymptomatic biochemical phase, and nobody has shown prospectively that it
    stops lesions forming. The acetazolamide case in which tumour formation
    ceased with no change in serum phosphate or TRP is a direct warning that the
    assumed mechanism of current therapy may not be the operative one.
  evidence:
  - reference: PMID:29389098
    reference_title: Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "No randomized clinical trials have been performed; studies of the treatment of HFTC consist of case reports or case series."
    explanation: GeneReviews states the evidentiary position of every current treatment.
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There is no standard treatment for this disease, and studies of the treatment of FTC/HHS do not exist aside from case reports or case series."
    explanation: An independent statement of the same evidentiary gap.
  - reference: PMID:24668887
    reference_title: "Hyperphosphatemic familial tumoral calcinosis: response to acetazolamide and postulated mechanisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "no change in tubular reabsorption of phosphate (TRP) (96.9% vs. 95.9%, P = 0.34) or serum phosphate (6.6 mg/dl vs. 6.9 mg/dl, P = 0.52 pre- and post-acetazolamide, respectively)"
    explanation: Clinical benefit without any change in the parameter the drug is given to change is the specific anomaly the gap names.
- discussion_id: mismatch_hftc_galnt3_mouse_no_calcinosis
  prompt: >-
    Why does the Galnt3-null mouse reproduce the human biochemistry but form no
    calcific masses, and what does the missing step mean for testing therapies
    whose endpoint is lesion burden?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue
  - animal_models#Mus musculus
  rationale: >-
    The model at issue is specifically the Galnt3-null mouse (the entry's
    "Galnt3-null mouse" animal model); the Fgf23-null and Klotho-deficient mice
    listed beside it are not the subject of this mismatch. The mismatch is
    informative rather than merely inconvenient. The Galnt3-null mouse has
    the hormone deficiency, the transporter change, the hyperphosphatemia and
    the inappropriate calcitriol, and still does not calcify - so those four
    things are not jointly sufficient for the lesion, and something present in
    humans and absent in this mouse is required. Practically, it means no
    current genetic model supports a preclinical efficacy endpoint of lesion
    regression, which is the outcome patients care about most.
  evidence:
  - reference: PMID:19213845
    reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In this study we generated mice lacking the Galnt3 gene, which developed hyperphosphatemia without apparent calcifications."
    explanation: "This is the mismatch itself: full biochemical phenotype, absent anatomical phenotype."
  - reference: PMID:19213845
    reference_title: Ablation of the Galnt3 gene leads to low-circulating intact fibroblast growth factor 23 (Fgf23) concentrations and hyperphosphatemia despite increased Fgf23 expression.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our findings indicate that Galnt3-deficient mice have a biochemical phenotype of tumoral calcinosis"
    explanation: The authors themselves limit the claim to a biochemical phenotype.
- discussion_id: gap_hftc_autoantibody_phenocopy
  prompt: >-
    When a patient has the full biochemical picture of HFTC but no biallelic
    GALNT3, FGF23 or KL genotype, how should the entry be scoped?
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - pathophysiology#Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess
  - disease#Hyperphosphatemic Familial Tumoral Calcinosis
  rationale: >-
    One of eight NIH-cohort subjects had no causative mutation found, and an
    acquired anti-FGF23 autoantibody phenocopy is recognised. That phenocopy is
    not modelled in this entry: it reaches the same endocrine node by an
    autoimmune route, so it is mechanistically a different disease that happens
    to share a downstream chain from the FGF23-deficiency node onward. Whether
    dismech should carry it as a separate acquired entry conforming to the same
    downstream nodes, or as a differential note only, is unresolved here.
  evidence:
  - reference: PMID:27164190
    reference_title: Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GALNT3 mutations were identified in seven subjects; no causative mutation was found in the eighth."
    explanation: This documents genotype-negative disease within a well-characterised cohort.
  - reference: PMID:33977199
    reference_title: A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disorder caused by mutations in FGF23, GALNT3, KLOTHO, or FGF23 autoantibodies."
    explanation: This source explicitly includes the autoantibody route alongside the three genes, which is the scoping question.

📚

References & Deep Research

References

4

PMID:29389098

Hyperphosphatemic Familial Tumoral Calcinosis.

No top-level findings curated for this source.

PMID:27164190

Phenotypic and Genotypic Characterization and Treatment of a Cohort With Familial Tumoral Calcinosis/Hyperostosis-Hyperphosphatemia Syndrome.

No top-level findings curated for this source.

PMID:31965220

Congenital Hyperphosphatemic Conditions Caused by the Deficient Activity of FGF23.

No top-level findings curated for this source.

PMID:38951179

Clinical Characteristics, Therapeutic Options, and Outcomes in Hyperphosphatemic Tumoral Calcinosis: A Systematic Review.

No top-level findings curated for this source.

Deep Research

1

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

Evaluations and curation notes (3)

Record notes

Scope and lump/split. The entry is curated at the umbrella MONDO term MONDO:0100251, which covers both the tumoral-calcinosis and the hyperostosis-hyperphosphatemia presentations, with the three molecular subtypes HFTC1 (GALNT3), HFTC2 (FGF23) and HFTC3 (KL) recorded in has_subtypes. The lump is evidence-driven rather than conventional: the same GALNT3 splice allele segregates in both HFTC and HHS families on a shared haplotype (PMID:15599692), and identical GALNT3 genotypes produce massive calcinosis in one patient and isolated hyperostosis in another (PMID:20358599). The three genes converge on one endocrine failure, so a single pathophysiology chain carries all of them and the subtype-specific divergence (low versus high intact FGF23) is modelled as two upstream branches into a shared signalling node rather than as three entries. Normophosphatemic familial tumoral calcinosis (SAMD9, MONDO:0012502) is deliberately excluded. It shares the calcific-mass morphology but has normal phosphate, no FGF23 abnormality and a different gene, so it is a distinct disease and not a subtype here. Acquired anti-FGF23 autoantibody tumoral calcinosis is likewise a phenocopy and is not modelled; it is noted in the knowledge-gap discussion because it is the differential when no biallelic genotype is found. Module conformance. No conformance target was declared. kb/modules/defective_skeletal_mineralization.yaml was read and rejected: it models failure of mineralization, whereas HFTC is a hyper-mineralizing disease, so conforming to it would invert the claim. No ectopic-calcification or pathological-mineral-deposition module exists in kb/modules/ at the time of curation; one would be the right home for the shared periarticular-deposit chain across HFTC, calciphylaxis and CKD-associated tumoral calcinosis. Provenance. Curated against the GeneReviews chapter (PMID:29389098) as the phenotype baseline, with the NIH natural-history cohort (PMID:27164190) and the NIH dental cohort (PMID:33977199) as the quantitative sources, plus the primary gene-discovery papers. The Falcon deep-research report (research/Hyperphosphatemic_Familial_Tumoral_Calcinosis-deep-research-falcon.md) was used as a lead list only; it cites by author-year/DOI key, so each DOI was resolved to a PMID through PubMed esearch before any snippet was taken (10.1002/jbmr.2870 to PMID:27164190, 10.1007/s00223-020-00659-6 to PMID:31965220, 10.1002/jbm4.10470 to PMID:33977199, 10.1007/s00223-024-01247-8 to PMID:38951179). The report's term-validation section flags HP:0002905 as mislabelled in the report text; the canonical label Hyperphosphatemia is used here. The report offered no umbrella MONDO identifier; MONDO:0100251 was verified directly against the ontology.

Address review: diagnosis section and term rebindings · 2026-09-18T14:45:38Z · View source

Addressed the automated review on PR 12108. Term rebindings (all labels verified with runoak -i ols:<ontology> info): sevelamer therapeutic_agent CHEBI:32127 Sevelamer hydrochloride -> CHEBI:759084 sevelamer, because no cited source names a salt; the pathophysiology location 'subcutaneous tissue' UBERON:0002190 subcutaneous adipose tissue -> UBERON:0002072 hypodermis; the Heterotopic Ossification phenotype HP:0010766 Ectopic calcification -> HP:0011986 Ectopic ossification, with the notes rewritten to record the two runoak searches run and why the tissue-specific children (HP:0011987-HP:0011989, HP:6000071) were rejected, replacing an incorrect claim that no narrower term existed. Added a diagnosis section (9 items) reflecting the deep-research report's section 10 workup where a cached reference supports it: serum phosphate (NCIT:C64857), tubular reabsorption of phosphate bound to the same phosphate-measurement term with the absence of a TRP/TmP-GFR term documented by query, the calcium/creatinine/ALP/PTH/25-OHD/1,25D panel (NCIT:C25294, per-analyte terms listed in notes), paired intact plus C-terminal FGF23 assays (NCIT:C96650; low intact with high C-terminal in GALNT3/FGF23 disease vs high intact in KL disease), plain radiography (NCIT:C38101), CT (NCIT:C17204), MRI (NCIT:C16809, inflammatory signal mimicking osteomyelitis), molecular genetic testing (NCIT:C15709) quoting the GeneReviews confirmatory sentence verbatim from PMID:29389098, and anti-FGF23 autoantibody measurement (NCIT:C181397) as the differential for genotype-negative disease. All diagnosis terms were confirmed reachable from NCIT:C25218 via the OLS ancestors API before binding. The panel-then-WES/WGS escalation is recorded as the report's uncited recommendation. Added a histopathology section (4 items) sourced only from already-cached PMID:27164190 and PMID:20358599: soft-tissue calcification (NCIT:C3672), chronic inflammatory infiltrate with foamy macrophages and giant cells (NCIT:C35980), heterotopic ossification with lamellar remodelling and reversal lines (NCIT:C35988), and reactive woven bone with fibroblastic stroma in hyperostotic diaphysis (NCIT:C53954); amorphous calcium-phosphate composition and surrounding fibrosis were not asserted because no cached source describes them, and this is stated in notes. In the mismatch_hftc_galnt3_mouse_no_calcinosis discussion the rationale now states that the model at issue is the Galnt3-null mouse, since attaches_to animal_models#Mus musculus is ambiguous across the three mouse models. clinical_trials remains deliberately absent: the deep-research report identified no disease-specific interventional trial (NCT00024804 is a broad NIH natural-history protocol), so there is nothing to cite. No new references were fetched; no references_cache files were added. Validation: just validate passed; just count-verified-snippets 176/176 verified; just validate-terms passed; just normalize-cache updated the chebi and ncit term caches and the chemicalentityterm, histopathologyfindingterm and treatmentactionterm enum caches; check-entity-refs, check-causal-targets, check-enum-values, check-snippet-grading and check-title-snippets all OK; just validate-disorders passed.

Create: Hyperphosphatemic Familial Tumoral Calcinosis (MONDO:0100251) · 2026-09-18T02:08:51Z · View source

De novo creation of the HFTC entry. LUMP/SPLIT DECISION. The pre-existing skeleton was anchored on MONDO:0100252 (HFTC1, GALNT3-only). Retargeted disease_term to the umbrella MONDO:0100251 'familial hyperphosphatemic tumoral calcinosis/hyperphosphatemic hyperostosis syndrome' and recorded the three molecular subtypes as has_subtypes: HFTC1 (GALNT3, hgnc:4125, MONDO:0100252), HFTC2 (FGF23, hgnc:3680, MONDO:0060714), HFTC3 (KL, hgnc:6344, MONDO:0060715). Hyperostosis-hyperphosphatemia syndrome is modelled as a presentation of the same disease, not a separate entity, on the evidence that the same GALNT3 c.1524+1G>A founder allele segregates in both HFTC and HHS families on a shared haplotype (PMID:15599692) and that identical GALNT3 genotypes produce massive calcinosis in one patient and isolated hyperostosis in another (PMID:20358599). Normophosphatemic familial tumoral calcinosis (SAMD9, MONDO:0012502) is excluded as a distinct disease and recorded as such in notes. Acquired anti-FGF23 autoantibody tumoral calcinosis is not modelled; the scoping question is left open in a discussion. NODE CHAIN (13 pathophysiology nodes). Three genetic roots converge: Biallelic GALNT3 Loss of Function -> Failure of FGF23 O-Glycosylation and Furin Cleavage of Intact FGF23 -> Deficiency of Circulating Intact FGF23 with C-Terminal Fragment Excess; Biallelic FGF23 Missense Variants Blocking Intact Hormone Secretion -> the same deficiency node; Biallelic KL Loss of Function and Renal FGF23 Resistance bypasses the hormone node. All three reach Loss of FGF23-Klotho-FGFR1c Signaling in the Renal Proximal Tubule -> Increased Proximal Tubular Sodium-Phosphate Cotransport and Unsuppressed Renal Calcitriol Production -> Hyperphosphatemia with Elevated Calcium-Phosphate Product -> Ectopic Calcium-Phosphate Deposition in Periarticular Soft Tissue, Diaphyseal Cortical Hyperostosis, and Ectopic Calcification of Vessels, Teeth and Other Organs -> Foreign-Body and Systemic Inflammation Around Calcific Deposits. Fourteen phenotypes hang off the tissue-level nodes as bare-name edge targets. MODULE CONFORMANCE. None declared. kb/modules/defective_skeletal_mineralization.yaml was considered and rejected: it models mineralization failure, whereas HFTC is a hyper-mineralizing disease, so conforming would invert the claim. No ectopic-calcification module exists in kb/modules/; creating one is suggested as follow-up. PROVIDER AND DOI RESOLUTION. The Falcon deep-research report research/Hyperphosphatemic_Familial_Tumoral_Calcinosis-deep-research-falcon.md was used as a lead list only. It cites by author-year/DOI key, so DOIs were resolved to PMIDs via PubMed esearch before any snippet was taken: 10.1002/jbmr.2870 -> PMID:27164190 (Ramnitz 2016 NIH cohort), 10.1007/s00223-020-00659-6 -> PMID:31965220 (Ito and Fukumoto 2021), 10.1002/jbm4.10470 -> PMID:33977199 (Lee 2021 dental cohort), 10.1007/s00223-024-01247-8 -> PMID:38951179 (Cherian 2024 systematic review). Primary mechanism and treatment papers were found independently via PubMed E-utilities. The report's term-validation block flags HP:0002905 as mislabelled in the report prose; the canonical label Hyperphosphatemia is used here. The report stated no umbrella MONDO identifier was established in its evidence; MONDO:0100251 was verified directly against the ontology with runoak. No unresolved identifier or CURIE from the report was used. PMIDS CITED (16): 29389098 (GeneReviews, tagged), 27164190, 31965220, 33977199, 38951179, 15133511 (Topaz 2004 GALNT3), 15599692 (Frishberg 2005 HHS/HFTC allelism), 15590700 (Benet-Pages 2005 FGF23 S71G), 17710231 (Ichikawa 2007 KL H193R), 16638743 (Kato 2006 O-glycosylation), 17129170 (Frishberg 2007 augmented FGF23 processing), 20358599 (Ichikawa 2010 clinical variability), 19213845 (Ichikawa 2009 Galnt3-null mouse), 14966565 (Shimada 2004 Fgf23-null mouse), 9363890 (Kuro-o 1997 klotho mouse), 24668887 (Finer 2014 acetazolamide), 19188744 (Lammoglia 2009 sevelamer plus acetazolamide). NOT SOURCED, AND WHY. (1) Sodium thiosulfate was named in the curation brief but no HFTC-specific PubMed record was found; the candidate hits were calcinosis cutis, calciphylaxis and pemigatinib-associated calciphylaxis, all different diseases, so it was omitted rather than cited across a Named Entity Confusion boundary. (2) The FGF23 Thr178 residue and the Arg179-Ser180 furin site could not be quoted from any cached abstract, so the node description states the RXXR proprotein-convertase site without asserting residue numbers. (3) The 'fewer than 100-200 reported cases' figure has no quotable source in the cached set; prevalence is recorded as CASES_IN_LITERATURE with the 63-patient denominator from PMID:38951179 and ULTRA_RARE, with the limits of that denominator stated in notes. (4) The ISDS group assignment (abnormal_mineralization) rests on the disease's mechanism, not on a per-disorder listing: the cached PMID:36779427 record is the 2023 revision summary and does not enumerate disorders. This is stated in the classification notes and flagged for review. (5) No datasets or clinical_trials blocks: no accession was verified and no NCT record was fetched. (6) Enamel hypoplasia carries a REFUTE item from PMID:33977199, whose SEM found no enamel or dentin structural difference from controls; the GeneReviews listing and the structural study are both recorded rather than reconciled. VALIDATION RESULTS. just validate: all validations passed. just count-verified-snippets: 142/142. just validate-terms: passed. just check-entity-refs: OK. just check-causal-targets: OK, no new broken targets. just check-duplicate-keys: OK. just check-enum-values: OK. just check-folded-hyphens: OK. just check-title-snippets, check-snippet-grading and check-snippet-length report no findings for this file (they fail on pre-existing findings in unrelated entries). just compliance: 97.4% weighted. pytest tests/test_data.py -k Hyperphosphatemic: 22 passed. STUB. stubs/Tumoral_Calcinosis_Hyperphosphatemic_Familial_1.yaml deleted.

Falcon ▸

Hyperphosphatemic Familial Tumoral Calcinosis: Disease-Characteristics Report

Edison Scientific Literature 23 citations 2026-09-04T23:32:45.733669

Hyperphosphatemic Familial Tumoral Calcinosis: Disease-Characteristics Report

Executive summary

Hyperphosphatemic familial tumoral calcinosis (HFTC) is an ultra-rare Mendelian disorder caused by deficient fibroblast growth factor-23 (FGF23) activity. Biallelic pathogenic variants in GALNT3, FGF23, or KL cause renal phosphate retention, hyperphosphatemia, inadequately suppressed calcitriol, and deposition of calcium-phosphate material in periarticular and other soft tissues. Hyperostosis-hyperphosphatemia syndrome (HHS) is now considered part of the same phenotypic spectrum. Clinical expression ranges from biochemical-only disease to recurrent inflammatory hyperostosis, massive disabling calcific tumors, dental abnormalities, and vascular or visceral calcification. Evidence remains limited principally to case reports, small cohorts, and animal models; no disease-specific randomized treatment trial or validated management guideline was identified. (ramnitz2016phenotypicandgenotypic pages 1-6, ito2021congenitalhyperphosphatemicconditions pages 1-2)

Domain	Evidence-backed finding	Quantitative data	Ontology/identifier suggestions
Disease definition	Ultra-rare Mendelian disorder of deficient FGF23 activity or signaling, characterized by renal phosphate retention, hyperphosphatemia, inappropriately normal/high calcitriol, and ectopic calcium-phosphate deposition; hyperostosis-hyperphosphatemia syndrome represents an overlapping phenotypic spectrum. (ramnitz2016phenotypicandgenotypic pages 1-6, ito2021congenitalhyperphosphatemicconditions pages 1-2)	Reported manifestations range from biochemical-only disease to massive disabling calcinosis.	Orphanet:306661; OMIM:211900; suggested synonym: hyperphosphatemic familial tumoral calcinosis/hyperostosis-hyperphosphatemia syndrome (HFTC/HHS).
Molecular subtypes	HFTC1 results from biallelic GALNT3 variants; HFTC2 from biallelic FGF23 variants; HFTC3 from biallelic KL variants. (OpenTargets Search: Hyperphosphatemic familial tumoral calcinosis-FGF23,GALNT3,KL, ito2021congenitalhyperphosphatemicconditions pages 2-3)	Literature through 2017 identified 44 GALNT3, 19 FGF23, and 1 KL cases among 64 reported cases.	HFTC1—OMIM:211900; HFTC2—OMIM:617993, MONDO:0060714; HFTC3—OMIM:617994, MONDO:0060715.
Causal genes and inheritance	GALNT3 loss impairs protective O-glycosylation of FGF23; FGF23 loss-of-function impairs hormone secretion/stability; KL loss causes resistance to FGF23 signaling. Inheritance is autosomal recessive, usually through germline homozygous or compound-heterozygous variants. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4, ito2021congenitalhyperphosphatemicconditions pages 1-2)	GALNT3 is the most frequently reported cause; heterozygous carriers are generally unaffected.	HGNC gene symbols: GALNT3, FGF23, KL; Open Targets disease associations support all three genes. (OpenTargets Search: Hyperphosphatemic familial tumoral calcinosis-FGF23,GALNT3,KL)
Hallmark biochemistry	Deficient FGF23 action causes excessive proximal-tubular phosphate reabsorption and failure to suppress calcitriol. GALNT3/FGF23 disease generally shows low or inappropriately normal intact FGF23 with markedly elevated C-terminal FGF23 fragments; KL disease shows high intact FGF23 because of hormone resistance. (ito2021congenitalhyperphosphatemicconditions pages 3-4, farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4)	NIH cohort: TRP 96.5%, median TmP/GFR 6.5 mg/dL, median 1,25(OH)₂D 62 pg/mL, and median calcium-phosphate product 63.5 mg²/dL². (ramnitz2016phenotypicandgenotypic pages 6-10)	HPO suggestion: Hyperphosphatemia—HP:0002905; laboratory concepts: serum phosphate, TmP/GFR, TRP, intact FGF23, C-terminal FGF23, 1,25-dihydroxyvitamin D.
Tumoral calcinosis	Lobular calcium-phosphate masses arise chiefly in periarticular skin, subcutaneous tissue, and connective tissue, especially near the hips, elbows, and shoulders; lesions may be painful, inflamed, ulcerating, infected, and functionally disabling. (ito2021congenitalhyperphosphatemicconditions pages 3-4, cherian2024clinicalcharacteristicstherapeutic pages 2-3)	Six of eight NIH-cohort participants had clinically evident tumoral calcinosis; one initially asymptomatic participant subsequently developed elbow calcinosis. (ramnitz2016phenotypicandgenotypic pages 6-10)	HPO suggestions: Calcinosis; Subcutaneous calcification; Joint limitation; Pain. UBERON suggestions: skin, subcutaneous tissue, hip joint, elbow joint, shoulder joint; exact term identifiers should be ontology-verified.
Skeletal and inflammatory disease	Diaphyseal cortical hyperostosis causes episodic painful swelling, warmth, and erythema and may mimic bacterial osteomyelitis or chronic recurrent multifocal osteomyelitis. Calcific lesions can provoke macrophage-rich chronic inflammation and heterotopic ossification. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 1-6)	Three of eight NIH subjects had severe systemic inflammation; biopsies from four showed ectopic calcification with chronic inflammation. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 1-6)	HPO suggestions: Hyperostosis; Limb pain; Elevated C-reactive protein; Fever; Soft-tissue swelling. GO suggestions: inflammatory response—GO:0006954; biomineral tissue development—GO:0031214.
Dental phenotype	Characteristic findings include shortened or thistle-shaped roots, midroot bulges with apical thinning, pulp calcification or obliteration, and pulp stones; premolars are usually most severely affected. (lee2021across‐sectionalcohort pages 4-5)	Pulp obliteration occurred in 13/14 evaluable patients (93%); all 10 comprehensively examined patients with GALNT3 variants had shortened thistle-shaped roots and pulp obliteration. (lee2021across‐sectionalcohort pages 4-5)	HPO suggestions: Abnormality of dental root; Pulp calcification; Short tooth roots. Exact identifiers require ontology verification.
Other anatomy and complications	Reported involvement includes vascular and coronary calcification, colonic submucosal deposits, ocular and testicular calcification, joint or growth-plate destruction, and reduced range of motion. (ramnitz2016phenotypicandgenotypic pages 13-17, ito2021congenitalhyperphosphatemicconditions pages 1-2)	Coronary calcification above the 95th percentile occurred in 2/5 evaluated NIH subjects, although confounding cardiovascular risks prevent attribution solely to HFTC. (ramnitz2016phenotypicandgenotypic pages 13-17)	UBERON suggestions: coronary artery, colon, eye, testis, growth plate, articular joint; HPO suggestions: Vascular calcification, Joint destruction, Abnormality of the intestine. Exact identifiers should be verified.
Diagnostic pattern	Diagnosis rests on persistent age-adjusted hyperphosphatemia, inappropriately high TRP/TmP-GFR, normal renal function, normal serum calcium, and nonsuppressed calcitriol, followed by sequencing and deletion/duplication analysis of GALNT3, FGF23, and KL. Intact-versus-C-terminal FGF23 assays help distinguish hormone deficiency/cleavage from KL-mediated resistance. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4, ramnitz2016phenotypicandgenotypic pages 6-10)	Normal calcium, creatinine, and alkaline phosphatase accompanied hyperphosphatemia in the NIH cohort. (ramnitz2016phenotypicandgenotypic pages 6-10)	Suggested genetic-test targets: GALNT3, FGF23, KL. Differential concepts: renal-failure-associated tumoral calcinosis, hyperparathyroidism, calcinosis universalis, dystrophic calcification, chronic osteomyelitis, and autoimmune anti-FGF23 tumoral calcinosis.
Medical treatment	Current off-label management combines dietary phosphate restriction, non-calcium phosphate binders such as sevelamer, and phosphaturic agents such as acetazolamide or probenecid. Evidence is limited to case reports and small uncontrolled cohorts, with inconsistent biochemical and lesion responses. (ramnitz2016phenotypicandgenotypic pages 1-6, ramnitz2016phenotypicandgenotypic pages 6-10, cherian2024clinicalcharacteristicstherapeutic pages 2-3)	Suggested dietary phosphate intake in the NIH cohort was 400–900 mg/day; one mass resolved after 13 months of combined treatment. (ramnitz2016phenotypicandgenotypic pages 6-10, ramnitz2016phenotypicandgenotypic pages 1-6)	CHEBI suggestions: phosphate—CHEBI:26020; acetazolamide, sevelamer, probenecid, and aluminum hydroxide require identifier verification. NCIT suggestions: Dietary Therapy, Pharmacotherapy, Surgical Excision; exact codes not asserted.
Anti-inflammatory and surgical treatment	Anakinra or canakinumab may suppress severe IL-1-mediated inflammation but does not directly correct FGF23 deficiency. Surgery is reserved for painful, infected, ulcerating, or disabling masses because incomplete excision and persistent hyperphosphatemia favor recurrence and wound morbidity. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 1-6)	IL-1 blockade reduced CRP in two severely inflamed NIH patients; one had resolution of calcinosis cutis and surrounding inflammation, and both reported improved well-being. (ramnitz2016phenotypicandgenotypic pages 1-6)	NCIT term suggestions: Anakinra; Canakinumab; Interleukin-1 Inhibition; Surgical Excision—exact codes should be verified.
Epidemiology and course	Population prevalence and incidence have not been reliably estimated. Reports suggest enrichment in African and Middle Eastern families, often in association with consanguinity. Onset and expressivity vary markedly, including within families. (chakhtoura2018hyperphosphatemicfamilialtumoral pages 1-2, ito2021congenitalhyperphosphatemicconditions pages 1-2)	Onset ranges from infancy or the first decade through late adulthood; a 2023 genetically diagnosed patient developed calcinosis in her seventies. (chakhtoura2018hyperphosphatemicfamilialtumoral pages 1-2, iwasaki2023elderlyonsetcalcinosisof pages 6-6)	Orphan-disease designation appropriate; no validated sex ratio, carrier frequency, penetrance percentage, survival statistic, or population-screening program is available.
Animal models	Galnt3-null mice reproduce low circulating intact Fgf23 and hyperphosphatemia despite increased bone Fgf23 expression, but do not consistently develop overt calcific masses. Fgf23-null mice reproduce hyperphosphatemia, elevated calcitriol, and ectopic/vascular calcification. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4)	Galnt3-null mice had approximately one-half the circulating intact Fgf23 concentration of controls; the phenotype included sex-specific growth, fertility, and bone-density effects.	Species: Mus musculus, NCBI Taxonomy:10090. Model types: Galnt3 knockout and Fgf23 knockout. GO suggestions: phosphate-ion homeostasis—GO:0055062; renal phosphate excretion; hormone-mediated signaling—exact additional identifiers require verification.

Table: Concise evidence table covering HFTC classification, genetics, biochemical and clinical phenotypes, diagnosis, management, epidemiology, and experimental models. Quantitative findings are separated from suggested ontology mappings, with uncertain mappings explicitly flagged for verification.

1. Disease information

Definition and classification

HFTC is a rare disorder of FGF23 deficiency or resistance characterized by persistent hyperphosphatemia, excessive renal tubular phosphate reabsorption, elevated or inappropriately normal 1,25-dihydroxyvitamin D [1,25(OH)₂D], and ectopic calcification. “Tumoral” describes the mass-like appearance; the deposits are not neoplastic. HFTC and HHS overlap genetically and clinically: calcific masses predominate in HFTC, whereas recurrent painful diaphyseal hyperostosis may dominate in HHS. (ramnitz2016phenotypicandgenotypic pages 1-6, ito2021congenitalhyperphosphatemicconditions pages 3-4)

Identifiers and synonyms

Familial hyperphosphatemic tumoral calcinosis/hyperphosphatemic hyperostosis syndrome: Orphanet 306661.
HFTC1, usually GALNT3 related: OMIM 211900.
HFTC2, FGF23 related: OMIM 617993; MONDO:0060714.
HFTC3, KL related: OMIM 617994; MONDO:0060715. (OpenTargets Search: Hyperphosphatemic familial tumoral calcinosis-FGF23,GALNT3,KL, ito2021congenitalhyperphosphatemicconditions pages 2-3)
Common names: hyperphosphatemic familial tumoral calcinosis, familial tumoral calcinosis, hyperphosphatemic tumoral calcinosis, FTC/HHS, HFTC/HHS, and hyperostosis-hyperphosphatemia syndrome.
A single umbrella MONDO identifier was not established in the retrieved evidence; subtype MONDO identifiers above are directly supported. A dedicated ICD-10/ICD-11 or MeSH code specific to inherited HFTC was likewise not verified; broader calcinosis or mineral-metabolism codes may be used clinically but are not disease-equivalent.

This report synthesizes aggregated disease-level literature, not individual EHR data. Patient-level observations are drawn from published consented cohorts and case reports.

2. Etiology, risk, and protective factors

Causal factors

HFTC is primarily genetic and autosomal recessive:

GALNT3 loss of function impairs O-glycosylation and stabilization of FGF23.
FGF23 loss of function impairs synthesis, secretion, stability, or bioactivity of the phosphaturic hormone.
KL loss of function impairs Klotho-dependent FGF23 receptor signaling, producing hormone resistance. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4, ito2021congenitalhyperphosphatemicconditions pages 1-2)

A rare acquired phenocopy caused by anti-FGF23 autoantibodies has been reported and should be considered when biochemical HFTC is present without biallelic variants in the three established genes. (ito2021congenitalhyperphosphatemicconditions pages 3-4)

Risk and modifying factors

Genetic risk: two pathogenic alleles in one causal gene; consanguinity and an affected sibling substantially increase prior probability. In a literature review covering 64 cases through 2017, 44 involved GALNT3, 19 FGF23, and one KL, making GALNT3 the most frequently reported cause. (ito2021congenitalhyperphosphatemicconditions pages 2-3)
Family history: may be absent because recessive carriers are usually asymptomatic and de novo presentations can occur through unrecognized carrier mating or unusual mechanisms.
Environmental/lifestyle risk: no toxin, infection, smoking, alcohol, or occupational exposure causes inherited HFTC. High dietary phosphate plausibly aggravates hyperphosphatemia, but a quantified gene–diet effect has not been established.
Tissue injury and comorbidity: local pressure or trauma may influence where masses become clinically apparent. A 2023 case proposed that limited scleroderma contributed to very late calcinosis, but this is a single-patient hypothesis rather than demonstrated causation. (iwasaki2023elderlyonsetcalcinosisof pages 6-6)
Protective factors: no validated protective allele is known. Dietary phosphate restriction and early biochemical control are therapeutic or tertiary-preventive measures, not proven protection against inheriting or developing the molecular disorder.
Modifier genes/epigenetics: no replicated HFTC-specific modifier locus, methylation signature, or chromatin mechanism was identified. General epigenetic regulation of mineral metabolism should not be entered as HFTC-specific evidence.

3. Phenotypes

Core phenotype and suggested HPO annotations

Phenotype	Characteristics and frequency	Suggested HPO annotation
Hyperphosphatemia	Universal biochemical hallmark in characterized cohorts; persistent, age-adjusted elevation	HP:0002905
Increased renal phosphate reabsorption	High TRP/TmP-GFR despite hyperphosphatemia; NIH cohort TRP 96.5%, median TmP/GFR 6.5 mg/dL	Abnormal renal phosphate handling; verify exact HPO term
Tumoral calcinosis	Lobular periarticular masses, especially hips, elbows, and shoulders; 6/8 in one NIH cohort; severity ranges from absent to massive	Calcinosis/subcutaneous calcification; verify exact term
Diaphyseal hyperostosis	Episodic painful long-bone swelling, erythema, and warmth, often tibial; can resemble osteomyelitis	Hyperostosis; limb pain; bone pain
Restricted joint movement	Secondary to periarticular mass, pain, or joint destruction; potentially severe and progressive	Joint contracture or limitation of joint mobility
Systemic inflammation	Fever, elevated CRP/ESR, fatigue, anorexia; severe in 3/8 NIH subjects	HP:0011227 elevated CRP, fever, constitutional symptoms; identifiers should be verified
Dental-root/pulp disease	Short thistle-shaped roots, midroot bulges, apical thinning, pulp stones or obliteration; pulp obliteration in 13/14 (93%)	Abnormal dental root; pulp calcification; short tooth roots
Vascular/visceral calcification	Coronary, intestinal, ocular, and testicular deposits reported; clinical frequency uncertain	Vascular calcification and organ-specific calcification terms

The NIH cohort’s median 1,25(OH)₂D was 62 pg/mL and median calcium-phosphate product was 63.5 mg²/dL². Calcium, creatinine, and alkaline phosphatase were generally normal. (ramnitz2016phenotypicandgenotypic pages 6-10)

A dedicated dental cohort found pulp obliteration in 13/14 evaluable patients (93%); all ten comprehensively examined participants with GALNT3 variants had shortened thistle-shaped roots and pulp obliteration. Premolars were more severely affected than canines, molars, or incisors, and mean phosphate was 6.4 ± 1.0 mg/dL. (lee2021across‐sectionalcohort pages 4-5)

Onset, severity, progression, and quality of life

Onset ranges from infancy to late adulthood and severity varies even among relatives with the same genotype. Calcific masses are not generally present neonatally and tend to accrue with age; reported individual onset ages include 4 and 23 years. A 2023 genetically confirmed case did not manifest clinically important calcinosis until the patient’s seventies. (chakhtoura2018hyperphosphatemicfamilialtumoral pages 1-2, ito2021congenitalhyperphosphatemicconditions pages 3-4, iwasaki2023elderlyonsetcalcinosisof pages 6-6)

Periarticular masses cause pain, reduced range of motion, impaired walking and self-care, ulceration, infection risk, and repeated surgery. Inflammatory attacks cause severe limb pain and constitutional illness. No validated HFTC-specific EQ-5D, SF-36, PROMIS, or disease-specific quality-of-life dataset was identified.

4. Genetic and molecular information

Causal genes

GALNT3 encodes polypeptide N-acetylgalactosaminyltransferase-3, a trans-Golgi glycosyltransferase. It O-glycosylates FGF23 near Thr178 and protects the Arg179–Ser180 cleavage region.
FGF23 encodes the 251-amino-acid precursor of a bone-derived phosphaturic hormone; after signal-peptide removal, the secreted product contains 227 amino acids.
KL encodes α-Klotho, the obligate coreceptor that permits high-affinity FGF23 signaling through principally FGFR1c in kidney. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4, ito2021congenitalhyperphosphatemicconditions pages 1-2)

Open Targets independently supports disease associations for GALNT3, FGF23, and KL, linked to primary literature including PMID 15133511 for GALNT3, PMIDs 15590700 and 16151858 for FGF23, and PMID 17710231 for KL. (OpenTargets Search: Hyperphosphatemic familial tumoral calcinosis-FGF23,GALNT3,KL)

Pathogenic variants

Reported germline variants include missense, nonsense, frameshift, splice-site, and small insertion/deletion alleles. FGF23 examples include p.His41Gln, p.Gln54Lys, p.Ser71Gly, p.Met96Thr, p.Gly123Trp, p.Ser129Pro, and p.Ser129Phe; the established KL example is p.His193Arg. The FGF23 p.Ser71Gly mutant can be retained in the Golgi, with preferential secretion of C-terminal fragments. (ito2021congenitalhyperphosphatemicconditions pages 3-4, farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4)

Recent examples include homozygous GALNT3 c.1524+1G>A in three siblings reported in 2024 and a novel late frameshift in the lectin domain reported in an elderly patient in 2023. These examples broaden variant and age-of-presentation spectra but do not establish new genes or treatment standards. (iwasaki2023elderlyonsetcalcinosisof pages 6-6, alghubishi2024type1hyperphosphatemic pages 5-5)

Variants are constitutional/germline, not somatic drivers. Most disease alleles are functionally loss-of-function. Population allele frequencies must be retrieved variant-by-variant from a current gnomAD release; the evidence set does not support assigning a universal frequency. Likewise, each variant requires contemporary ACMG/AMP classification using ClinVar, segregation, population, and functional data rather than assuming pathogenicity from gene membership.

No recurrent chromosomal abnormality is established. Uniparental disomy can theoretically unmask a recessive GALNT3 allele, but CMA, karyotyping, and FISH are not routine first-line tests. No HFTC-specific epigenetic biomarker is validated.

5. Environmental information

There is no evidence that pollution, radiation, occupational toxins, smoking, alcohol, or an infectious organism initiates familial HFTC. Dietary phosphate influences the biochemical substrate burden and is therefore clinically actionable. Local mechanical stress may help explain periarticular localization, while tissue injury, ulceration, and secondary infection can worsen established lesions. Rheumatologic comorbidity as a modifier is currently supported only by isolated observation. (cherian2024clinicalcharacteristicstherapeutic pages 2-3, iwasaki2023elderlyonsetcalcinosisof pages 6-6)

6. Mechanism and pathophysiology

Ordered causal chain

Biallelic GALNT3 or FGF23 loss-of-function variants lead to deficient secretion or excessive proteolytic cleavage of intact bioactive FGF23; alternatively, biallelic KL variants lead to resistance to intact FGF23. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4, ito2021congenitalhyperphosphatemicconditions pages 1-2)
Deficient FGF23–Klotho–FGFR1c signaling leads to inadequate downregulation of renal proximal-tubular sodium-phosphate cotransporters NaPi-IIa/NaPi-IIc.
Persistent transporter activity leads to excessive tubular phosphate reabsorption and hyperphosphatemia.
Loss of FGF23 action also leads to failure to suppress renal calcitriol production, resulting in elevated or inappropriately normal 1,25(OH)₂D.
Calcitriol activity leads to increased intestinal calcium and phosphate absorption, further increasing the calcium-phosphate product.
High extracellular phosphate and calcium-phosphate product lead to precipitation of calcium-phosphate material in periarticular soft tissue, vessels, dental pulp, and viscera; the exact site-selection mechanism remains partly inferred. (ito2021congenitalhyperphosphatemicconditions pages 3-4, farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4)
Crystal deposition and tissue injury lead to macrophage-rich foreign-body inflammation, chronic inflammation, and sometimes heterotopic ossification.
Mass effect and inflammation lead to pain, ulceration, reduced joint movement, infection risk, and tissue or joint destruction. Independently, abnormal skeletal phosphate/FGF23 biology leads to episodic diaphyseal cortical hyperostosis and pain. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 1-6)

Cellular and ontology annotations

Upstream cell types include osteocytes/osteoblast-lineage cells producing FGF23 (CL: osteocyte and osteoblast terms should be ontology-verified) and renal proximal-tubule epithelial cells responding through Klotho–FGFR signaling. Downstream lesions contain connective-tissue cells, macrophages, foreign-body giant cells, and in some cases osteoblast-like cells forming heterotopic bone.

Suggested GO concepts include phosphate-ion homeostasis (GO:0055062), inflammatory response (GO:0006954), hormone-mediated signaling, renal phosphate excretion, O-linked glycosylation, and biomineral tissue development (GO:0031214). Relevant compartments include the trans-Golgi network for GalNAc-T3 and the plasma membrane receptor complex for Klotho/FGFR1c; exact GO cellular-component identifiers should be verified before production use.

Histology in four NIH subjects showed ectopic calcification with chronic inflammation, and one showed mature lamellar heterotopic bone. Foamy macrophages and chronic inflammatory cells support a downstream innate immune response rather than primary autoimmunity in genetic HFTC. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 1-6)

No reproducible HFTC-specific single-cell, spatial-transcriptomic, proteomic, metabolomic, lipidomic, or integrated multi-omics signature was identified. This is a major research gap.

7. Anatomical structures affected

Primary sites are periarticular skin, subcutaneous tissue, fascia, tendons, and connective tissue near the hip, elbow, and shoulder; knees, hands, and feet also occur. Hyperostosis principally involves cortical diaphyses of long bones, especially tibiae. Dental disease involves root cementum, pulp, pulp cavity, and odontoblast architecture. (ito2021congenitalhyperphosphatemicconditions pages 3-4, lee2021across‐sectionalcohort pages 4-5)

Secondary or less frequent sites include coronary and other vessels, colonic submucosa, eye, and testis. One NIH subject had complete shoulder-joint destruction and another had ulnar growth-plate destruction. Two of five evaluated subjects had coronary Agatston scores above the 95th percentile, although age and conventional cardiovascular risks confounded attribution. Lesions may be unilateral, bilateral, multifocal, and asymmetric; no fixed lateralization exists. (ramnitz2016phenotypicandgenotypic pages 13-17)

Suggested UBERON mappings include skin, subcutaneous tissue, hip joint, elbow joint, shoulder joint, tibia, coronary artery, colon, eye, testis, tooth pulp, and growth plate. Exact UBERON accession numbers require terminology-service validation.

8. Temporal development

HFTC is genetically present from conception but often clinically silent in infancy. The course is chronic and lifelong, with variable, episodic inflammatory attacks and progressive or recurrent calcific masses. Patients may have biochemical disease before palpable lesions; in the NIH cohort, two siblings initially lacked physical calcinosis and one later developed an elbow lesion. (ramnitz2016phenotypicandgenotypic pages 6-10)

No formal stages exist. A practical course model is: (1) biochemical hyperphosphatemia; (2) early dental or episodic hyperostotic disease; (3) localized tumoral calcinosis; and (4) multifocal disabling, ulcerating, vascular, or visceral disease. This is a clinical framework, not a validated staging system.

Spontaneous regression is reported but unpredictable. Treatment-associated complete resolution of one mass occurred after 13 months in the NIH cohort. The ideal preventive window is probably before large deposits form, but prospective evidence proving that early phosphate control prevents lesions is absent. (ramnitz2016phenotypicandgenotypic pages 1-6)

9. Inheritance and population

Inheritance is autosomal recessive. For two heterozygous parents, each pregnancy conventionally has a 25% probability of an affected child, 50% of an unaffected carrier, and 25% of a noncarrier. Expressivity is markedly variable; penetrance of biochemical hyperphosphatemia appears high in biallelic disease, whereas penetrance and timing of tumoral calcinosis are incomplete and age dependent. Anticipation is not known. Germline mosaicism has not emerged as a characteristic mechanism.

No reliable prevalence, incidence, carrier frequency, sex ratio, or survival estimate exists. Sixty-four genetically characterized cases were summarized through 2017, underscoring extreme rarity rather than defining population prevalence. Reports are enriched in African and Middle Eastern families and consanguineous pedigrees, but HFTC occurs worldwide. (ito2021congenitalhyperphosphatemicconditions pages 1-2, ito2021congenitalhyperphosphatemicconditions pages 2-3)

10. Diagnostics

Recommended diagnostic workflow

Confirm persistent, age-adjusted fasting serum phosphate elevation.
Measure calcium, creatinine/eGFR, alkaline phosphatase, PTH, 25-hydroxyvitamin D, and 1,25(OH)₂D.
Calculate TRP and TmP/GFR from paired serum/urine phosphate and creatinine. HFTC shows inappropriate phosphate conservation despite normal kidney function.
Measure both intact FGF23 and C-terminal FGF23 where available. GALNT3/FGF23 disease generally produces low or inappropriately normal intact hormone with high C-terminal fragments; KL disease produces high intact FGF23 because of resistance. (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4, ramnitz2016phenotypicandgenotypic pages 6-10)
Image symptomatic sites using plain radiography; CT best defines calcific burden and surgical anatomy, while MRI can characterize inflammation but may misleadingly resemble osteomyelitis.
Sequence GALNT3, FGF23, and KL, preferably using a mineral-metabolism/calcification panel with deletion–duplication analysis. WES or WGS is appropriate if panel testing is negative or phenotype is atypical.
If no causal genotype is found, consider anti-FGF23 autoantibodies and reassess acquired causes.

Biopsy is unnecessary for classic biochemistry and imaging but may be required if malignancy, infection, or another calcifying disorder cannot be excluded. Expected pathology is amorphous calcium-phosphate material with macrophages/giant cells, chronic inflammation, fibrosis, and sometimes heterotopic bone. (ramnitz2016phenotypicandgenotypic pages 13-17)

CMA, karyotyping, FISH, mitochondrial sequencing, repeat-expansion testing, liquid biopsy, and routine diagnostic omics have no established role. Cascade biochemical and targeted genetic testing is appropriate for relatives; population or newborn screening is not established.

Differential diagnosis

Important alternatives are chronic kidney disease with secondary tumoral calcinosis, hyperparathyroidism, excess phosphate administration, vitamin-D intoxication, pseudohypoparathyroidism, dystrophic calcification from connective-tissue disease, calcinosis universalis, calcific tendinopathy, synovial osteochondromatosis, gout, malignancy, bacterial osteomyelitis, and chronic recurrent multifocal osteomyelitis. Normal renal function, high TmP/GFR, nonsuppressed calcitriol, and the characteristic FGF23 assay/genetic pattern distinguish HFTC. HFTC-associated hyperostosis can closely mimic osteomyelitis clinically and on MRI. (ito2021congenitalhyperphosphatemicconditions pages 3-4, alghubishi2024type1hyperphosphatemic pages 5-5)

11. Outcome and prognosis

Life expectancy, disease-specific mortality, and five- or ten-year survival have not been quantified. Many patients survive into adulthood, but morbidity can be profound. Major outcomes include chronic pain, impaired mobility, joint destruction, ulceration, secondary infection, disfiguring masses, repeated operations, dental complications, and possible vascular or visceral injury. (ramnitz2016phenotypicandgenotypic pages 13-17)

Prognostic factors are incompletely established. Persistent phosphate elevation, high calcium-phosphate product, extensive baseline lesion burden, poor adherence, and systemic inflammation are clinically concerning, but no validated prognostic model exists. Genotype does not reliably predict severity, and substantial intrafamilial variability argues for other modifiers. Long-term multidisciplinary surveillance should include function, skin integrity, inflammation, dental health, renal function, and individualized cardiovascular assessment.

12. Treatment

No FDA/EMA-approved disease-specific therapy or consensus algorithm exists. Expert management seeks to lower phosphate/calcium-phosphate product, suppress inflammatory complications, preserve function, and avoid surgical morbidity. The 2020 authoritative review concluded that efficacy evidence was limited to case reports and small cohorts and that no clearly effective therapy had been identified; this remains broadly consistent with the 2024 systematic-review evidence base. (ramnitz2016phenotypicandgenotypic pages 1-6, cherian2024clinicalcharacteristicstherapeutic pages 2-3)

Phosphate-directed treatment

Low-phosphate diet: often 400–900 mg/day in the NIH cohort, ideally planned by a metabolic dietitian to avoid malnutrition.
Sevelamer: non-calcium intestinal phosphate binder; avoid calcium-containing binders when possible because they may increase calcium-phosphate substrate.
Aluminum hydroxide: effective binder but unsuitable for prolonged indiscriminate use because of aluminum toxicity; used in two NIH subjects.
Acetazolamide: carbonic-anhydrase inhibitor inducing bicarbonaturia and phosphaturia. Monitor bicarbonate, potassium, renal function, and nephrolithiasis risk; metabolic acidosis is a recognized concern.
Probenecid: promotes phosphaturia but has important drug interactions, including increased exposure to penicillins, cephalosporins, and trimethoprim-sulfamethoxazole.
Nicotinamide: did not add clear benefit in the NIH cohort. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 6-10)

Responses are inconsistent. In the NIH cohort, one mass completely resolved after 13 months of combined medical treatment, but individualized regimens, adherence differences, referral bias, and short follow-up preclude response-rate estimates. (ramnitz2016phenotypicandgenotypic pages 1-6)

Anti-inflammatory therapy

NSAIDs may treat mild attacks. For severe systemic inflammation, anakinra or canakinumab has reduced CRP and improved constitutional symptoms in isolated patients. In two NIH subjects, IL-1 blockade lowered inflammatory markers; one had resolution of calcinosis cutis and surrounding inflammation, and both reported improved energy, appetite, and well-being. These agents treat downstream inflammation and do not restore FGF23 activity. (ramnitz2016phenotypicandgenotypic pages 13-17, ramnitz2016phenotypicandgenotypic pages 1-6)

Surgery and supportive care

Complete excision may be considered for severe pain, ulceration, recurrent infection, neurovascular compromise, or major functional restriction. Surgery is a last resort because persistent hyperphosphatemia, incomplete excision, wound complications, and recurrence are common concerns. Physical/occupational therapy, wound care, analgesia, dental surveillance, and psychosocial support are appropriate.

Suggested NCIt intervention concepts are dietary therapy, phosphate-binding agent therapy, carbonic-anhydrase inhibition, anakinra, canakinumab, IL-1 inhibition, analgesic therapy, physical therapy, wound care, and surgical excision; exact NCIt codes should be validated before database loading.

Advanced and experimental therapy

Recombinant or long-acting FGF23 replacement is mechanistically attractive for GALNT3/FGF23 deficiency but remains experimental. Gene replacement, CRISPR editing, RNA therapy, and cell therapy have no established human implementation. Burosumab is an anti-FGF23 antibody and is mechanistically inappropriate—and potentially hazardous—in an FGF23-deficient/resistant hyperphosphatemic disorder. No disease-specific interventional ClinicalTrials.gov study was identified. The broad NIH observational natural-history protocol NCT00024804 includes bone/mineral disorders but is not an HFTC treatment trial.

13. Prevention

Primary prevention of a recessive genotype is limited to informed reproductive choice. Genetic counseling should address parental carrier testing, cascade testing, prenatal diagnosis, and preimplantation genetic testing when familial pathogenic variants are known. There is no vaccine, infectious prophylaxis, or population-screening program.

Secondary prevention consists of early recognition in siblings and relatives using serum phosphate, renal phosphate handling, and targeted genetic testing. Dental-root changes may appear early and have high penetrance, making dental radiographs a useful diagnostic clue. (lee2021across‐sectionalcohort pages 4-5)

Tertiary prevention includes dietary/pharmacological phosphate control, monitoring calcium-phosphate product and bicarbonate, avoiding unnecessary calcium/phosphate supplements, prompt treatment of inflammation or ulcer infection, dental care, skin protection, and minimizing repetitive pressure over lesions. Evidence that these measures prevent all calcification remains observational.

14. Other species and natural disease

No well-established naturally occurring veterinary counterpart was identified in the retrieved literature. The pathway is evolutionarily conserved across mammals, but veterinary “tumoral calcinosis” can have different etiologies and should not automatically be annotated as orthologous HFTC. The disorder is not infectious, transmissible, or zoonotic.

Relevant orthologs are Galnt3, Fgf23, and Kl in Mus musculus (NCBI Taxonomy 10090). Exact NCBI Gene IDs and any OMIA/VBO entries should be verified directly before knowledge-base ingestion.

15. Model organisms

Mouse models

Galnt3-knockout mouse: reproduces low circulating intact Fgf23 and hyperphosphatemia despite increased bone Fgf23 expression. Circulating intact Fgf23 was approximately half that of controls, with increased C-terminal fragments. Mice did not consistently develop overt calcific masses, limiting fidelity to severe human HFTC; sex-specific growth retardation, infertility, and increased bone density were also reported.
Fgf23-null mouse: reproduces hyperphosphatemia, elevated calcitriol, and ectopic/vascular calcification and strongly supports the causal endocrine pathway.
Klotho-deficient models: reproduce deficient FGF23 signaling and mineral abnormalities and have been used to evaluate calcification-modifying strategies, although their broader premature-aging phenotype limits direct clinical translation. (ramnitz2016phenotypicandgenotypic pages 13-17, farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4)

These are genetic mammalian knockout models useful for studying phosphate sensing, FGF23 processing, renal transport, calcification, and candidate therapies. No validated HFTC organoid, patient-iPSC platform, zebrafish model, or humanized model was identified.

Recent developments, 2023–2024

2024 systematic review: Cherian et al., Calcified Tissue International 115:215–228, published July 2024, DOI 10.1007/s00223-024-01247-8, systematically assessed clinical characteristics, therapeutic approaches, and lesion outcomes. Its underlying literature remains dominated by case reports and case series rather than controlled trials. (cherian2024clinicalcharacteristicstherapeutic pages 2-3)
Very-late onset: Iwasaki, published online October 3, 2023, DOI 10.1530/edm-23-0071, described genetically diagnosed elderly-onset disease and argued that HFTC should remain in the differential for unexplained hyperphosphatemia or ectopic calcinosis even in older adults. (iwasaki2023elderlyonsetcalcinosisof pages 6-6)
Phenotypic and allelic expansion: 2024 reports described recurrent osteomyelitis-like presentations, a three-sibling family with homozygous GALNT3 c.1524+1G>A, and additional novel GALNT3 variants. These reports reinforce use of WES/WGS in atypical cases but do not alter the three-gene causal model. (alghubishi2024type1hyperphosphatemic pages 5-5)
Current expert interpretation: recent work emphasizes phenotype diversity, dental and vascular surveillance, inflammatory biology, and the inadequacy of current phosphate-lowering therapy. The major unmet needs are prospective natural-history data, standardized lesion imaging and outcomes, and FGF23-replacement therapy.

Exact supporting abstract quotations

Short quotations retained from accessible abstracts include:

HFTC is described as a “rare and disabling disorder of fibroblast growth factor 23 (FGF23) deficiency or resistance,” and periarticular calcinosis as “the primary cause of disability.” (ramnitz2016phenotypicandgenotypic pages 1-6)
The dental cohort concluded that its study “defines the spectrum and confirms the high penetrance of dental features in HFTC.” (lee2021across‐sectionalcohort pages 4-5)
The Galnt3 model supplied in-vivo evidence that impaired Galnt3 causes “decreased circulating Fgf23 and hyperphosphatemia, despite increased Fgf23 expression.” (farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4)

Evidence limitations and knowledge-base cautions

HFTC literature is exceptionally sparse. Percentages from cohorts of 8–17 individuals should not be treated as population frequencies. Prevalence, incidence, sex ratio, penetrance percentages, mortality, life expectancy, carrier frequency, standardized quality-of-life effects, pharmacogenomics, validated biomarkers of progression, and treatment-response rates remain unknown. Most 2023–2024 publications are systematic reviews or single-family reports rather than prospective studies. Ontology terms marked “suggested” should undergo release-specific validation against HPO, GO, CL, UBERON, CHEBI, NCIt, and MONDO before production loading.

References

(ramnitz2016phenotypicandgenotypic pages 1-6): Mary Scott Ramnitz, Pravitt Gourh, Raphaela Goldbach-Mansky, Felasfa Wodajo, Shoji Ichikawa, Michael J Econs, Kenneth E White, Alfredo Molinolo, Marcus Y Chen, Theo Heller, Jaydira Del Rivero, Patricia Seo-Mayer, Bita Arabshahi, Malaka B Jackson, Sarah Hatab, Edward McCarthy, Lori C Guthrie, Beth A Brillante, Rachel I Gafni, and Michael T Collins. Phenotypic and genotypic characterization and treatment of a cohort with familial tumoral calcinosis/hyperostosis‐hyperphosphatemia syndrome. Journal of Bone and Mineral Research, 31:1845-1854, Oct 2016. URL: https://doi.org/10.1002/jbmr.2870, doi:10.1002/jbmr.2870. This article has 109 citations and is from a highest quality peer-reviewed journal.
(ito2021congenitalhyperphosphatemicconditions pages 1-2): Nobuaki Ito and Seiji Fukumoto. Congenital hyperphosphatemic conditions caused by the deficient activity of fgf23. Calcified Tissue International, 108:104-115, Jan 2021. URL: https://doi.org/10.1007/s00223-020-00659-6, doi:10.1007/s00223-020-00659-6. This article has 29 citations and is from a peer-reviewed journal.
(OpenTargets Search: Hyperphosphatemic familial tumoral calcinosis-FGF23,GALNT3,KL): Open Targets Query (Hyperphosphatemic familial tumoral calcinosis-FGF23,GALNT3,KL, 9 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(ito2021congenitalhyperphosphatemicconditions pages 2-3): Nobuaki Ito and Seiji Fukumoto. Congenital hyperphosphatemic conditions caused by the deficient activity of fgf23. Calcified Tissue International, 108:104-115, Jan 2021. URL: https://doi.org/10.1007/s00223-020-00659-6, doi:10.1007/s00223-020-00659-6. This article has 29 citations and is from a peer-reviewed journal.
(farrow2011miscellaneousnoninflammatorymusculoskeletal pages 3-4): Emily G. Farrow, Erik A. Imel, and Kenneth E. White. Miscellaneous non-inflammatory musculoskeletal conditions. hyperphosphatemic familial tumoral calcinosis (fgf23, galnt3 and αklotho). Best practice & research. Clinical rheumatology, 25 5:735-47, Oct 2011. URL: https://doi.org/10.1016/j.berh.2011.10.020, doi:10.1016/j.berh.2011.10.020. This article has 78 citations.
(ito2021congenitalhyperphosphatemicconditions pages 3-4): Nobuaki Ito and Seiji Fukumoto. Congenital hyperphosphatemic conditions caused by the deficient activity of fgf23. Calcified Tissue International, 108:104-115, Jan 2021. URL: https://doi.org/10.1007/s00223-020-00659-6, doi:10.1007/s00223-020-00659-6. This article has 29 citations and is from a peer-reviewed journal.
(ramnitz2016phenotypicandgenotypic pages 6-10): Mary Scott Ramnitz, Pravitt Gourh, Raphaela Goldbach-Mansky, Felasfa Wodajo, Shoji Ichikawa, Michael J Econs, Kenneth E White, Alfredo Molinolo, Marcus Y Chen, Theo Heller, Jaydira Del Rivero, Patricia Seo-Mayer, Bita Arabshahi, Malaka B Jackson, Sarah Hatab, Edward McCarthy, Lori C Guthrie, Beth A Brillante, Rachel I Gafni, and Michael T Collins. Phenotypic and genotypic characterization and treatment of a cohort with familial tumoral calcinosis/hyperostosis‐hyperphosphatemia syndrome. Journal of Bone and Mineral Research, 31:1845-1854, Oct 2016. URL: https://doi.org/10.1002/jbmr.2870, doi:10.1002/jbmr.2870. This article has 109 citations and is from a highest quality peer-reviewed journal.
(cherian2024clinicalcharacteristicstherapeutic pages 2-3): Kripa Elizabeth Cherian, Jacob Cherian, Dharmasivam Vinodhini, and Thomas Vizhalil Paul. Clinical characteristics, therapeutic options, and outcomes in hyperphosphatemic tumoral calcinosis: a systematic review. Calcified tissue international, 115:215-228, Jul 2024. URL: https://doi.org/10.1007/s00223-024-01247-8, doi:10.1007/s00223-024-01247-8. This article has 6 citations and is from a peer-reviewed journal.
(ramnitz2016phenotypicandgenotypic pages 13-17): Mary Scott Ramnitz, Pravitt Gourh, Raphaela Goldbach-Mansky, Felasfa Wodajo, Shoji Ichikawa, Michael J Econs, Kenneth E White, Alfredo Molinolo, Marcus Y Chen, Theo Heller, Jaydira Del Rivero, Patricia Seo-Mayer, Bita Arabshahi, Malaka B Jackson, Sarah Hatab, Edward McCarthy, Lori C Guthrie, Beth A Brillante, Rachel I Gafni, and Michael T Collins. Phenotypic and genotypic characterization and treatment of a cohort with familial tumoral calcinosis/hyperostosis‐hyperphosphatemia syndrome. Journal of Bone and Mineral Research, 31:1845-1854, Oct 2016. URL: https://doi.org/10.1002/jbmr.2870, doi:10.1002/jbmr.2870. This article has 109 citations and is from a highest quality peer-reviewed journal.
(lee2021across‐sectionalcohort pages 4-5): Alisa E Lee, Emily Y Chu, Pamela J Gardner, Olivier Duverger, Amanda Saikali, Sean K Wang, Rachel I Gafni, Iris R Hartley, Kelly G Ten Hagen, Martha J Somerman, and Michael T Collins. A cross‐sectional cohort study of the effects of fgf23 deficiency and hyperphosphatemia on dental structures in hyperphosphatemic familial tumoral calcinosis. JBMR Plus, Mar 2021. URL: https://doi.org/10.1002/jbm4.10470, doi:10.1002/jbm4.10470. This article has 18 citations and is from a peer-reviewed journal.
(chakhtoura2018hyperphosphatemicfamilialtumoral pages 1-2): M. Chakhtoura, M.S. Ramnitz, N. Khoury, G. Nemer, N. Shabb, A. Abchee, A. Berberi, M. Hourani, M. Collins, S. Ichikawa, and G. El Hajj Fuleihan. Hyperphosphatemic familial tumoral calcinosis secondary to fibroblast growth factor 23 (fgf23) mutation: a report of two affected families and review of the literature. Osteoporosis International, 29:1987-2009, Jun 2018. URL: https://doi.org/10.1007/s00198-018-4574-x, doi:10.1007/s00198-018-4574-x. This article has 22 citations and is from a domain leading peer-reviewed journal.
(iwasaki2023elderlyonsetcalcinosisof pages 6-6): Hiroaki Iwasaki. Elderly-onset calcinosis of hyperphosphataemic familial tumoural calcinosis/hyperostosis-hyperphosphataemia syndrome: the role of comorbid scleroderma. Endocrinology, Diabetes & Metabolism Case Reports, Oct 2023. URL: https://doi.org/10.1530/edm-23-0071, doi:10.1530/edm-23-0071. This article has 1 citations and is from a peer-reviewed journal.
(alghubishi2024type1hyperphosphatemic pages 5-5): Somayah A Alghubishi, Eman J Ghazwani, Sami E Abdelmogeit, and Khalid Alzubair. Type 1 hyperphosphatemic familial tumoral calcinosis associated with a homozygous variant mutation in the galnt3 gene. Oct 2024. URL: https://doi.org/10.7759/cureus.71390, doi:10.7759/cureus.71390. This article has 0 citations.

Artifacts

Edison artifact artifact-00

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	10
Resolved	10
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	10
On topic	4
Off topic	0

All extracted references resolved successfully.

Term Validation

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

Outcome	Count
Terms checked	13
Resolved	8
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	5
Terms whose name was checked	1
Terms named correctly	0
Terms named as a different term	1

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:0002905 (2 mentions) - the report calls it "Universal biochemical hallmark in characterized cohorts; persistent, age-adjusted elevation"; HP calls it Hyperphosphatemia

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: Orphanet, OMIM, Taxonomy.

Ask OpenScientist

OpenScientist Report

Classifications

Inheritance

Subtypes

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Diagnosis

Progression

Prevalence

Animal Models

Source YAML

References & Deep Research

References

Deep Research

Hyperphosphatemic Familial Tumoral Calcinosis: Disease-Characteristics Report

Executive summary

1. Disease information

Definition and classification

2. Etiology, risk, and protective factors

Causal factors

Risk and modifying factors

3. Phenotypes

Core phenotype and suggested HPO annotations

Onset, severity, progression, and quality of life

4. Genetic and molecular information

Causal genes

Pathogenic variants

5. Environmental information

6. Mechanism and pathophysiology

Ordered causal chain

Cellular and ontology annotations

7. Anatomical structures affected

8. Temporal development

9. Inheritance and population

10. Diagnostics

Recommended diagnostic workflow

Differential diagnosis

11. Outcome and prognosis

12. Treatment

Phosphate-directed treatment

Anti-inflammatory therapy

Surgery and supportive care

Advanced and experimental therapy

13. Prevention

14. Other species and natural disease

15. Model organisms

Mouse models

Recent developments, 2023–2024

Exact supporting abstract quotations

Evidence limitations and knowledge-base cautions

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Prefixes with no resolver