Hyperphosphatemic Tumoral Calcinosis: Pathogenesis, Clinical Presentation, and Challenges in Management

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

This systematic review was performed to understand better the myriad presentations, various therapeutic options, response to therapy, and its clinical outcomes in hyperphosphatemic tumoral calcinosis (HTC). Full texts were selected according to strict inclusion criteria. All case reports of HTC wherein baseline phosphate was measured, treatment offered was mentioned, and information on follow-up and response to therapy that were available were included. A total of 43 of 188 eligible studies (N = 63 patients) met the inclusion criteria. A list of desired data was extracted and graded for methodological quality. A total of 63 individuals (Males = 33) were included from the 43 eligible case studies. The median age of the patients was 18 (IQR 8-32) years. 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%). Three patients had conjunctival calcific deposits. The mean (SD) phosphate was 6.9 (1.1) mg/dL. Among the subjects, 36/63 (57.1%) underwent surgical excision with some form of medical therapy. Two patients underwent only surgical excision (2.1%). One patient was maintained on follow-up (1.6%) and 24/63 (38.1%) patients were treated with medical measures. The median (IQR) follow-up duration was 3 (1-9) years. 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%). We report for the first time a detailed description of the clinical and therapeutic response of HTC. A combination of medical measures aimed at lowering serum phosphate appears to be the cornerstone of treatment, although clinical responses may vary.

Spatial Atlas for Mapping Vascular Microcalcification Using 18F-NaF PET/CT: Application in Hyperphosphatemic Familial Tumoral Calcinosis

BACKGROUND

Vascular calcification causes significant morbidity and occurs frequently in diseases of calcium/phosphate imbalance. Radiolabeled sodium fluoride positron emission tomography/computed tomography has emerged as a sensitive and specific method for detecting and quantifying active microcalcifications. We developed a novel technique to quantify and map total vasculature microcalcification to a common space, allowing simultaneous assessment of global disease burden and precise tracking of site-specific microcalcifications across time and individuals.

METHODS

To develop this technique, 4 patients with hyperphosphatemic familial tumoral calcinosis, a monogenic disorder of FGF23 (fibroblast growth factor-23) deficiency with a high prevalence of vascular calcification, underwent radiolabeled sodium fluoride positron emission tomography/computed tomography imaging. One patient received serial imaging 1 year after treatment with an IL-1 (interleukin-1) antagonist. A radiolabeled sodium fluoride-based microcalcification score, as well as calcification volume, was computed at all perpendicular slices, which were then mapped onto a standardized vascular atlas. Segment-wise mCSmean and mCSmax were computed to compare microcalcification score levels at predefined vascular segments within subjects.

RESULTS

Patients with hyperphosphatemic familial tumoral calcinosis had notable peaks in microcalcification score near the aortic bifurcation and distal femoral arteries, compared with a control subject who had uniform distribution of vascular radiolabeled sodium fluoride uptake. This technique also identified microcalcification in a 17-year-old patient, who had no computed tomography-defined calcification. This technique could not only detect a decrease in microcalcification score throughout the patient treated with an IL-1 antagonist but it also identified anatomic areas that had increased responsiveness while there was no change in computed tomography-defined macrocalcification after treatment.

CONCLUSIONS

This technique affords the ability to visualize spatial patterns of the active microcalcification process in the peripheral vasculature. Further, this technique affords the ability to track microcalcifications at precise locations not only across time but also across subjects. This technique is readily adaptable to other diseases of vascular calcification and may represent a significant advance in the field of vascular biology.

A Sole Case of the FGF23 Gene Mutation c.202A>G (p.Thr68Ala) Associated with Multiple Severe Vascular Aneurysms and a Hyperphosphatemic Variant of Tumoral Calcinosis-A Case Report

Tumoral calcinosis is an extremely rare genetic disease caused by mutations in three genes, GALNT3, FGF23, and KL, which disrupt phosphorus metabolism. The hallmark of this condition is the formation of tumors in the soft tissues around the joints. Other phenotypic features of tumoral calcinosis are dental involvement and brain and vascular calcifications. The clinical case reported herein presents for the first time to the scientific community the c.202A>G (p.Thr68Ala) mutation of the FGF23 gene, associated with a hyperphosphatemic variant of tumoral calcinosis and multiple severe vascular aneurysms. A female patient underwent multiple surgeries for tumor formations in her soft tissues that first appeared at the age of 12 months. On this occurrence, the patient was found to have hyperphosphatemia, low phosphate clearance, increased tubular reabsorption with normal levels of total and ionized calcium, vitamin D3, and parathyroid hormone, and no effect of treatment with sevelamer hydrochloride and a low-phosphate diet. At the age of 39, the patient underwent imaging studies due to edema and a pulsating formation in the neck area, which revealed multiple vascular aneurysms with thrombosis, for which she received operative and interventional treatment. In this connection, and because of the established phosphorus metabolism disturbance, a genetic disease was suspected. The sequence analysis and deletion/duplication testing of the 358 genes performed on this occasion revealed that the woman was homozygous for a variant of the c.202A>G (p.Thr68Ala) mutation of the FGF23 gene. The established mutation is not present in population databases. The presented clinical case is the first and only one in the world to demonstrate the role of this type of FGF23 gene mutation in the development of a hyperphosphatemic variant of tumoral calcinosis characterized by aggressive formation of multiple vascular aneurysms.

Non-Classical Effects of FGF23: Molecular and Clinical Features

This article reviews the role of fibroblast growth factor 23 (FGF23) protein in phosphate metabolism, highlighting its regulation of vitamin D, parathyroid hormone, and bone metabolism. Although it was traditionally thought that phosphate-calcium homeostasis was controlled exclusively by parathyroid hormone (PTH) and calcitriol, pathophysiological studies revealed the influence of FGF23. This protein, expressed mainly in bone, inhibits the renal reabsorption of phosphate and calcitriol formation, mediated by the α-klotho co-receptor. In addition to its role in phosphate metabolism, FGF23 exhibits pleiotropic effects in non-renal systems such as the cardiovascular, immune, and metabolic systems, including the regulation of gene expression and cardiac fibrosis. Although it has been proposed as a biomarker and therapeutic target, the inhibition of FGF23 poses challenges due to its potential side effects. However, the approval of drugs such as burosumab represents a milestone in the treatment of FGF23-related diseases.

Intact FGF23 concentration in healthy infants, children, and adolescents, and diagnostic usefulness in patients with X-linked hypophosphatemic rickets

OBJECTIVE

FGF23 measurement may have a diagnostic role to investigate patients with phosphate disorders. However, normal values for infants, children, and adolescents have not been defined.

METHODS

In a total of 282 (males 145, females 137) healthy infants (n = 30), prepubertal (n = 147), pubertal (n = 59), and postpubertal (n = 46), and in twenty patients with X-linked hypophosphatemic rickets (XLH, age 10.2 ± 5.6 years) serum phosphate (automated analyzer), and plasma intact FGF23 (immunochemiluminescent sandwich assay, DiaSorin) concentrations were measured.

RESULTS

Intact FGF23 concentrations were higher in healthy infants than in prepubertal (P < 0.01) and postpubertal subjects (P < 0.05); pubertal subjects showed higher values (P < 0.05) than postpubertal subjects. Serum phosphate concentrations were higher (P < 0.001) in healthy infants than in prepubertal, pubertal, and postpubertal subjects. Pubertal subjects had higher (P < 0.001) serum phosphate concentrations than postpubertal subjects. Intact FGF23 and serum phosphate concentrations did not differ (P = NS) by sex, age of menarche, and time after menarche. In healthy subjects, there was no correlation between intact FGF23 and serum phosphate concentrations. Intact FGF23 concentrations were higher (P < 0.0001) in patients with XLH than in healthy subjects according to chronological age and pubertal development. In all patients, intact FGF23 concentrations were above 40 pg/mL; intact FGF23 concentrations were inversely correlated with serum phosphate concentrations (r = -0.65; P < 0.01).

CONCLUSION

In healthy subjects, chronological age and puberty were main determinants of intact FGF23 concentrations. Intact FGF23 concentrations may be a useful marker for the early diagnosis of XLH in pediatric patients.

Three Siblings With a Rare Familial Hyperphosphatemia Syndrome: A Case Series

Hyperphosphatemia familial tumoral calcinosis (HFTC) and hyperphosphatemia hyperostosis syndrome (HHS) are rare autosomal recessive disorders caused by mutations in the polypeptide N-acetylgalactosaminyltransferase 3 (GALNT3), fibroblast growth factor 23 (FGF23), or klotho (KL) genes. They are characterized by hyperphosphatemia and recurrent episodes of bone lesions with hyperostosis and/or soft tissue calcinosis. Management options include phosphate-lowering therapies, anti-inflammatory medications, and surgical excision of the calcified masses in significantly disabled cases. We describe three cases from a consanguineous family who were found to have the same genetic mutation caused by a homozygous mutation in intron eight of GALNT3 c.1524+1 G>A (IVS8+1). The first case had a presentation similar to chronic osteomyelitis, while the second one presented with a calcified mass in her gluteal area. The third case presented with left leg pain. Being a rare disease, the findings of tumoral calcinosis/ bony abnormalities, along with elevated phosphate levels, should raise the possibility of this entity. Family history and biochemical findings can help reach the diagnosis.

Effectiveness of topical sodium thiosulfate for ectopic calcifications and ossifications. Results of the CATSS-O study

INTRODUCTION

Ectopic calcifications (ECs) and heterotopic ossifications (HOs) form in non-mineralized tissues, most often in subcutaneous and muscular areas. Local and systemic complications can cause severe disability. Systemic administration of sodium thiosulfate (STS) gives promising results but is difficult to use in clinical practice.

OBJECTIVE

Evaluation of the efficacy and safety of topical STS in ECs and HOs.

METHODS

Retrospective analysis of the CATSS-O registry that included patients receiving topical STS 25 % prepared by the pharmacy of Limoges hospital during 2014-2020. The efficacy of STS was assessed by imaging (radiography or CT) after at least 6 months' treatment.

RESULTS

Among 126 patients who received STS 25 %, 35 had complete clinical and radiographic data for analysis (28 with ECs and 7 with HOs; 18 children [mean age 8.9 years, range 1.5-16], 17 adults [mean age 52.4 years, range 24-90]). Calcifications or ossifications were due to dermatomyositis (8 children, 6 adults), systemic scleroderma (6 adults) or pseudo-hypoparathyroidism 1A (7 children). They were single (37.1 %) or multiple (62.9 %). Treated regions were in the lower limbs (31.4 %), upper limbs (37.1 %) or both (28.6 %) and the axial region (2.9 %). Topical STS was clinically effective in 9/28 (32.1 %) patients with ECs and 2/7 (28.6 %) children with HOs. Three patients experienced complete disappearance of their calcifications. Response for ECs was better in children than adults (54.5% vs 17.6 %, p = 0.035). Topical STS was well tolerated.

CONCLUSION

Local STS seems effective for ossifications, particularly pediatric calcifications or ossifications. Randomized and experimental studies are needed to confirm this observation and to identify the underlying mechanisms.

Canakinumab in addition to phosphate-binding and phosphaturia-inducing therapy were effective in achieving remission in a child with a large familial calcinotic tumour

We describe the clinical evolution of a patient with tumoral calcinosis due to a pathogenic variant in the GALNT3 gene presented with a large mass overlying her left hip associated complicated by inflammatory flares. Therapy (sevelamer, acetazolamide, and probenecid) was unsuccessful in preventing tumour surgeries, therefore, interleukin-1β monoclonal antibody therapy was added; this was successful in the prevention of tumour re-growth. This case highlights the importance of assessing and treating the inflammatory aspect of calcinotic tumour.

Recurrent Bilateral Lower Motor Neuron Type of Facial Palsy with Hearing Impairment: Hyperphosphatemic Familial Tumoral Calcinosis

Hyperphosphatemic familial tumoral calcinosis (HFTC) presents with varied neurological manifestations that have been reported in the literature like facial palsy, vision and hearing impairment, stroke, and headache. In this article, we reported a 12-year-old girl child patient with recurrent facial weakness with bilateral hearing impairment and multiple ulcerative lesions on lower limbs and elbows. On examination, she had lower motor neuron (LMN) facial palsy with conductive hearing loss. The investigations showed hyperphosphatemia (9.3 mg/dL) with normal serum calcium (10.4 mg/dL), alkaline phosphatase (147.9 U/L), parathyroid hormone (23.12 pg/mL), and renal function tests. Elevated serum calcium and phosphorus product (96.72 mg 2 /mL 2 ) and elevated renal tubular reabsorption of phosphate (TMPxGFR) value (9.16) were noted. Skeletal survey showed hyperostosis in the long bone diaphysis, vertebrae, ribs, pelvic bone, skull, and facial bones with narrowing of cranial ostium, characteristically without any peri-articular soft tissue calcifications. An angiogram showed multiple intravascular calcifications. She was managed with a low-phosphate diet, sevelamer, niacinamide, acetazolamide, sucroferric oxyhydroxide to lower serum phosphate level, and topical sodium thiosulfate ectopic cutaneous calcification. Exome sequencing showed novel homozygous inframe deletion of ACG in FGF23 gene exon 3 at c.374_376 delins position (p. Asp125del) in the proband and a mutation in the heterozygous state in the mother and elder sibling, thus confirming a molecular diagnosis of HFTC. Our case had a unique neurological presentation of recurrent bilateral lower motor nerve facial palsy, hearing loss, multiple ectopic cutaneous calcifications without peri-articular deposits, multiple intravascular, intracranial, and vertebral endplate calcification, which has not been reported earlier. The proband showed a novel pathogenic variant suggesting an expanding phenotype of HFTC.

Elderly-onset calcinosis of hyperphosphataemic familial tumoural calcinosis/hyperostosis-hyperphosphataemia syndrome: the role of comorbid scleroderma

Summary

A 73-year-old woman with type 2 diabetes mellitus was referred to our department for glycaemic control. Physical examination revealed two subcutaneous hard masses around the left shoulder and the right hip joint. The patient could not fully extend her fingers because of skin sclerosis in both hands. Laboratory studies showed hyperphosphataemia and a high ratio of renal tubular maximum reabsorption of phosphate to glomerular filtration rate. There were no abnormalities in serum calcium, creatinine, alkaline phosphatase, and intact parathyroid hormone levels, whereas serum fibroblast growth factor 23 was low. Hyperphosphataemic familial tumoural calcinosis/hyperostosis-hyperphosphataemia syndrome (HFTC/HHS) was diagnosed using whole genome sequencing that revealed a novel frameshift beyond the 584th threonine located in the lectin domain of UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 3 associated with a duplication of the 1748th thymine in the coding region of the corresponding gene. Furthermore, anti-nuclear, anti-centromere, and anti-cardiolipin antibodies were positive, implying that comorbid limited type scleroderma might play a role in tumoural calcinosis (TC) development. A low phosphate diet was prescribed with phosphate-lowering medications, including aluminium hydroxide, acetazolamide, and sevelamer hydrochloride. The patient displayed a decrease in serum phosphate levels from 6.5 to 5.5 mg/dL 10 months after the initiation of treatment, but her TC had not improved during treatment for more than 1 year. This case was interesting because the patient with HFTC/HHS exhibited TC despite being over her 60s, and subsequent scleroderma might contribute to the specific clinical course. When HFTC/HHS presents with elderly-onset TC, the involvement of comorbidities in exacerbating TC should be considered.

Learning points

HFTC/HHS occurs on an autosomal recessive basis, but its clinical course and manifestations differ significantly throughout the cases. HFTC/HHS may be undiagnosed until later in life because of its rarity, unfamiliarity, and phenotype diversity; therefore, HFTC/HHS should be included in the differential diagnosis of elderly patients with unexplained hyperphosphataemia or ectopic calcinosis. Comorbidities, including rheumatologic disorders, may contribute to developing HFTC/HHS-associated calcinosis.

Alterations in SAMD9, AHSG, FRG2C, and FGFR4 Genes in a Case of Late-Onset Massive Tumoral Calcinosis

Background/Objective

Tumoral calcinosis (TC) is a rare, arcane, and debilitating disorder of phosphate metabolism manifesting as hard masses in soft tissues. Primary hyperphosphatemic TC has been shown to be caused by pathogenic variants in the genes encoding FGF23, GALNT3, and KLOTHO. We report a case of massive TC mechanistically associated with phosphatonin resistance associated with heterozygous alterations in the sterile alfa motif domain-containing protein-9 gene (SAMD9), alfa 2-Heremans-Schmid glycoprotein gene (AHSG), FSHD region gene 2-family member-C gene (FRG2C), and fibroblast growth factor receptor-4 gene (FGFR4).

Case Report

A middle-aged Malay woman with systemic sclerosis presented with painful hard lumps of her axillae, lower limbs, and external genitalia. She was eucalcemic with mild hyperphosphatemia associated with reduced urinary phosphate excretion. Magnetic resonance imaging revealed calcified soft tissue masses. Paradoxically, the serum intact FGF23 level increased to 89.6 pg/mL, corroborated by Western blots, which also showed overexpression of sFRP4 and MEPE, consistent with phosphatonin resistance.

Discussion

Whole genome sequencing identified 2 heterozygous alterations (p.A454T and p.T479M) in SAMD9, 2 heterozygous alterations (p.M248T and p.S256T) in AHSG, a frameshift alteration (p.Arg156fs) in FRG2C, and a heterozygous alteration (p.G388R) in FGFR4, all of which are associated with calcinosis. Nonsynonymous alterations of FRP4 and MEPE were also detected.

Conclusion

This highlights that the simultaneous occurrence of alterations in several genes critical in phosphate homeostasis may trigger massive TC despite their heterozygosity. These findings should prompt functional studies in cell and animal models to reveal mechanistic insights in the pathogenesis of such crippling mineralization disorders.

Tumoral calcinosis of the knee treated with open, physeal sparing iliotibial band ACL reconstruction

Tumoral calcinosis is a hereditary disease of calcium and phosphate metabolism causing peri-articular tumors of calcium deposits. We present a case of tumoral calcinosis in a 13-year-old male with a history of a 12q13.11 genetic deletion. Surgical resection of the tumor necessitated resection of the ACL in its entirety with curettage and adjuvant therapy to the lateral femoral notch, which resulted in ligamentous instability and bony structural incompetency at the femoral insertion. Given the patient's radiographically-apparent skeletal immaturity, and lack of reliable bony architecture to accommodate a femoral ACL tunnel, ACL reconstruction was performed using a physeal-sparing technique. This is a case of tumoral calcinosis treated with, to our knowledge, the first ACL reconstruction using this modified open technique.

A case of hyperphosphatemic familial tumoral calcinosis due to maternal uniparental disomy of a GALNT3 variant

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare, inherited autosomal recessive disorder caused by fibroblast growth factor-23 (FGF23), N-acetylgalactosaminyltransferase 3 (GALNT3), or Klotho (KL) gene variants. Here, we report the case of a Japanese boy who presented with a mass in his left elbow at the age of three. Laboratory test results of the patient revealed normocalcemia (10.3 mg/dL) and hyperphosphatemia (8.7 mg/dL); however, despite hyperphosphatemia, serum intact FGF23 level was low, renal tubular reabsorption of phosphate (TRP) level was inappropriately increased, and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) level was inappropriately normal. Genetic analysis revealed maternal uniparental disomy (UPD) of chromosome 2, which included a novel GALNT3 variant (c.1780-1G>C). Reverse transcription-polymerase chain reaction (RT-PCR) analysis of GALNT3 mRNA confirmed that this variant resulted in the destruction of exon 11. We resected the mass when the patient was five years old, owing to its gradual enlargement. No relapse or new pathological lesions were observed four years after tumor resection. This is the first case report of a Japanese patient with HFTC associated with a novel GALNT3 variant, as well as the first case of HFTC caused by maternal UPD of chromosome 2 that includes the GALNT3 variant.

Tumoral Calcinosis in the Larynx

Tumoral calcinosis is a rare benign disease defined as calcium salt deposits in the periarticular soft tissue region. Tumoral calcinosis is rare in the neck and larynx. In this case, we described a 58-year-old man who had numerous calcified nodules in the larynx.

The Measurement and Interpretation of Fibroblast Growth Factor 23 (FGF23) Concentrations

Two decades after the discovery of the hormone FGF23, we know more about phosphate homeostasis as it turned out that FGF23 is the central hormone that regulates this. Hereditary hypophosphatemic rickets and tumor-induced osteomalacia could by then be explained, by autonomous FGF23 production, and the nephrology field was excited by this new marker as it turned out to be independently associated with mortality in people treated by hemodialysis. This led to the development of several immunoassays to be able to measure FGF23 in blood. In the past years we learned that FGF23 is a rather stable peptide, the precision of the assays is acceptable but assays are not standardized and therefore not comparable. This means that reference values and cutoff values need to be assay specific. For several assays reference values have been established and gender and age did not seem of high importance. The phosphate content of the diet, which can be culturally dependent, however, should be taken into account when interpreting results, but to what extent is not totally clear. Currently, clinical application of the immunoassays is established in the diagnosis of hereditary hypophosphatemic rickets and diagnosis and follow-up of tumor-induced osteomalacia. Definite conclusions on the usefulness of the FGF23 measurement in people with CKD either as a marker for risk prediction or a as target for treatment remains to be determined. The latter applications would require dedicated prospective clinical trials, which may take years, before providing answers. To improve the standardization of the FGF23 assays and to shed light on the biological functions that fragments might have we might aim for an LC-MS/MS-based method to quantify both intact and fragmented FGF23. In this literature review we will summarize the current knowledge on the physiological role of FGF23, its quantification, and the clinical usefulness of its determination.

Solitary Radio-Opaque Lesion of Wrist (Tumoral Calcinosis) Disappears Spontaneously After Causing Acute Carpal Tunnel Syndrome: A Case Report

CASE

We describe the case of a 53-year-old male patient with a history of acute carpal tunnel syndrome (CTS) provoked by a radio-opaque mass on the palmar side of the wrist. Although the mass disappeared in new radiographs 6 weeks later without any intervention apart from the carpal tunnel release, excisional biopsy was conducted on the residue, revealing tumoral calcinosis.

CONCLUSION

Both acute CTS and spontaneous resolution are clinical manifestations of this rare condition on suspicion of which biopsy can be avoided by following a "wait and see" strategy.

FGF23 functions and disease

The main function of fibroblast growth factor 23 (FGF23) is the regulation of phosphate metabolism through its action on the sodium-dependent phosphate cotransporters in the proximal renal tubules. Additionally, FGF23 interacts with vitamin D and parathyroid hormone in a complex metabolic pathway whose detailed mechanisms are still not clear in human physiology and disease. More recently, research has also focused on the understanding of mechanisms of FGF23 action on organs and system other than the kidneys and bone, as well as on its interaction with other metabolic pathways. Collectively, the new evidence are successfully used for the clinical evaluation and management of FGF23-related disorders, for which new therapies with many potential applications are now available.

Disorders of phosphate homeostasis in children, part 2: hypophosphatemic and hyperphosphatemic disorders

Phosphorus, predominantly in the form of inorganic phosphate PO₄^-3, has many essential physiological functions. In the skeleton, phosphate and calcium form the mineral component and phosphate is also essential in regulating function of skeletal cells. Considerable advances have been made in our understanding of phosphate homeostasis since the recognition of fibroblast growth factor-23 (FGF23) as a bone-derived phosphaturic hormone. This second part of a two-part review of disorders of phosphate homeostasis in children covers hypophosphatemic and hyperphosphatemic disorders that are of interest to the pediatric radiologist, emphasizing, but not limited to, those related to abnormalities of FGF23 signaling.

Sedimentation sign: a classical finding on tumorous calcinosis

The authors describe the case of a man in his 60s who presented with progressive pain and swelling of the right hip. Imaging features showed a densely calcified lesion associated with 'sedimentation sign'. Laboratory tests revealed slight hyperphosphataemia. Surgical excision of the lesion was performed. Histological examination revealed chalky material surrounded by fibrosis and giant multinucleated cells, compatible with tumorous calcinosis. Patient made a full recovery. We report a rare case of tumorous calcinosis and compare this condition with its common mimics.

PTH and FGF23 Exert Interdependent Effects on Renal Phosphate Handling: Evidence From Patients With Hypoparathyroidism and Hyperphosphatemic Familial Tumoral Calcinosis Treated With Synthetic Human PTH 1-34

Parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) both influence blood phosphate levels by regulating urinary phosphate reabsorption. Clinical data suggest that adequate renal phosphate handling requires the presence of both FGF23 and PTH, but robust evidence is lacking. To investigate whether the phosphaturic effects of PTH and FGF23 are interdependent, 11 patients with hypoparathyroidism, which features high blood phosphate in spite of concomitant FGF23 elevation, and 1 patient with hyperphosphatemic familial tumoral calcinosis (HFTC), characterized by deficient intact FGF23 action and resulting hyperphosphatemia, were treated with synthetic human PTH 1-34 (hPTH 1-34). Biochemical parameters, including blood phosphate, calcium, intact FGF23 (iFGF23), nephrogenic cAMP, 1,25(OH)₂ vitamin D (1,25D), and tubular reabsorption of phosphate (TRP), were measured at baseline and after hPTH 1-34 treatment. In patients with hypoparathyroidism, administration of hPTH 1-34 increased nephrogenic cAMP, which resulted in serum phosphate normalization followed by a significant decrease in iFGF23. TRP initially decreased and returned to baseline. In the patient with HFTC, hPTH 1-34 administration also increased nephrogenic cAMP, but this did not produce changes in phosphate or TRP. No changes in calcium were observed in any of the studied patients, although prolonged hPTH 1-34 treatment did induce supraphysiologic 1,25D levels in the patient with HFTC. Our results indicate that PTH and FGF23 effects on phosphate regulation are interdependent and both are required to adequately regulate renal phosphate handling. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

The regulation of FGF23 under physiological and pathophysiological conditions

Fibroblast growth factor 23 (FGF23) is an important bone hormone that regulates phosphate homeostasis in the kidney along with active vitamin D (1,25(OH)₂D₃) and parathyroid hormone (PTH). Endocrine effects of FGF23 depend, at least in part, on αKlotho functioning as a co-receptor whereas further paracrine effects in other tissues are αKlotho-independent. Regulation of FGF23 production is complex under both, physiological and pathophysiological conditions. Physiological regulators of FGF23 include, but are not limited to, 1,25(OH)₂D₃, PTH, dietary phosphorus intake, and further intracellular and extracellular factors, kinases, cytokines, and hormones. Moreover, several acute and chronic diseases including chronic kidney disease (CKD) or further cardiovascular disorders are characterized by early rises in the plasma FGF23 level pointing to further mechanisms effective in the regulation of FGF23 under pathophysiological conditions. Therefore, FGF23 also serves as a prognostic marker in several diseases. Our review aims to comprehensively summarize the regulation of FGF23 in health and disease.

Primary hyperphosphatemic tumoral calcinosis: a case report

Tumoral calcinosis (TC) is a rare disease characterized by periarticular soft tissue calcification. Some cases were reported in Africa and the Middle East. We report an 11-year-old Chinese girl presenting with recurrent multiple subcutaneous masses around the right elbow and hip regions. Although we found abnormalities in FGF23, a protein associated with phosphate metabolism, no positive results were observed in gene sequencing and analysis. The imaging features, laboratory examination, and pathology results confirmed our diagnosis. By using oral phosphorus-lowering drugs (acetazolamide) combined with complete surgical excision, good results were achieved, and no recurrence was reported during the follow-up of 18 months. We report a case of primary hyperphosphatemic TC. The combined use of oral phosphorus-lowering drugs (acetazolamide) and complete surgical excision produced good results, and no recurrence was reported during the follow-up of 18 months.

Pathologic Fracture of Femoral Neck in a Patient with Tumoral Calcinosis

Tumoral calcinosis is a rare disease characterized by massive subcutaneous soft tissue deposits of calcium phosphate around large joints in patients with chronic kidney disease. Invasion of bone by tumoral calcinosis is rare. We experienced a case involving a femoral neck pathologic fracture due to bony invasion of tumoral calcinosis in a 46-year-old female with chronic kidney disease who had been on dialysis for 15 years. Successful outcomes were obtained by performance of total hip arthroplasty for treatment of the pathologic fracture of the femoral neck. Careful precaution is necessary to prevent pathologic fractures in patients with tumoral calcinosis around the hip joint.

Hyperphosphatemic Familial Tumoral Calcinosis Hidden in Plain Sight for 73 Years: A Case Report

While dental pulp calcifications and root anomalies may be inconsequential incidental findings in dental radiographs, they can, especially in combination, represent a clue, hidden in plain sight, for the diagnosis of hyperphosphatemic familial tumoral calcinosis (HFTC). HFTC is an autosomal recessive disease of mineral metabolism characterized by sometimes massive, painful calcification around large joints, systemic inflammation, dental pulp calcification, and thistle-shaped roots. This paper describes a woman with HFTC who endured not only the symptoms of HFTC for decades, but also the frustration of not knowing the cause. The diagnosis was finally made at the age of 73 years, when the connection between a large right shoulder calcification and hyperphosphatemia was made. The dental findings were likely present on her initial radiographs taken in childhood. Increased awareness of the association between characteristic dental findings and HFTC may allow for earlier diagnosis and interventions to improve the care of patients with this rare condition.

FGFR Inhibitors in Oncology: Insight on the Management of Toxicities in Clinical Practice

Simple Summary

FGFR inhibitors evolved as therapeutic options in cholangiocarcinoma and urothelial malignancies. Given the implications of FGFR pathway in various physiological functions, FGFR inhibitors are known to cause unique toxicities. In this review, we summarized the physiology of FGF/FGFR signaling and briefly discussed the possible mechanisms that could lead to FGFR inhibitor resistance and side effects. In addition, we proposed treatment guidelines for the management of FGFR-inhibitor-associated toxicities.

Abstract

Fibroblast Growth Factor receptor (FGFR) pathway aberrations have been implicated in approximately 7% of the malignancies. As our knowledge of FGFR aberrations in cancer continues to evolve, FGFR inhibitors emerged as potential targeted therapeutic agents. The promising results of pemigatinib and infigratinib in advanced unresectable cholangiocarcinoma harboring FGFR2 fusions or rearrangement, and erdafitinib in metastatic urothelial carcinoma with FGFR2 and FGFR3 genetic aberrations, lead to their accelerated approval by the United States (USA) FDA. Along with these agents, many phase II/III clinical trials are currently evaluating the use of derazantinib, infigratinib, and futibatinib either alone or in combination with immunotherapy. Despite the encouraging results seen with FGFR inhibitors, resistance mechanisms and side effect profile may limit their clinical utility. A better understanding of the unique FGFR-inhibitor-related toxicities would invariably help us in the prevention and effective management of FGFR-inhibitor-induced adverse events thereby enhancing their clinical benefit. Herein, we summarized the physiology of FGF/FGFR signaling and briefly discussed the possible mechanisms that could lead to FGFR inhibitor resistance and side effects. In addition, we proposed treatment guidelines for the management of FGFR-inhibitor-associated toxicities. This work would invariably help practicing oncologists to effectively manage the unique toxicities of FGFR inhibitors.

A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disorder caused by mutations in FGF23, GALNT3, KLOTHO, or FGF23 autoantibodies. Prominent features include high blood phosphate and calcific masses, usually adjacent to large joints. Dental defects have been reported, but not systematically described. Seventeen patients with HFTC followed at the National Institutes of Health underwent detailed clinical, biochemical, molecular, and dental analyses. Studies of teeth included intraoral photos and radiographs, high-resolution μCT, histology, and scanning electron microscopy (SEM). A scoring system was developed to assess the severity of tooth phenotype. Pulp calcification was found in 13 of 14 evaluable patients. Short roots and midroot bulges with apical thinning were present in 12 of 13 patients. Premolars were most severely affected. μCT analyses of five HFTC teeth revealed that pulp density increased sevenfold, whereas the pulp volume decreased sevenfold in permanent HFTC teeth compared with age- and tooth-matched control teeth. Histology revealed loss of the polarized odontoblast cell layer and an obliterated pulp cavity that was filled with calcified material. The SEM showed altered pulp and cementum structures, without differences in enamel or dentin structures, when compared with control teeth. This study defines the spectrum and confirms the high penetrance of dental features in HFTC. The phenotypes appear to be independent of genetic/molecular etiology, suggesting hyperphosphatemia or FGF23 deficiency may be the pathomechanistic driver, with prominent effects on root and pulp structures, consistent with a role of phosphate and/or FGF23 in tooth development. Given the early appearance and high penetrance, cognizance of HFTC-related features may allow for earlier diagnosis and treatment. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

The role of O-glycosylation in human disease

O-glycosylation is a highly frequent post-translation modification of proteins, with important functional implications in both physiological and disease contexts. The biosynthesis of O-glycans depends on several layers of regulation of the cellular glycosylation machinery, being organ-, tissue- and cell-specific. This review provides insights on the molecular mechanism underlying O-glycan biosynthesis and modification, and highlights illustrative examples of diseases that are triggered or modulated by aberrant cellular O-glycosylation. Particular relevance is given to genetic disorders of glycosylation, infectious diseases and cancer. Finally, we address the potential of O-glycans and their biosynthetic pathways as targets for novel therapeutic strategies.