Iron and bones: effects of iron overload, deficiency and anemia treatments on bone.

Iron is a vital trace element and exerts opposing effects on bone in both iron overload and iron deficiency situations. Remarkably, iron supplementation through intravenous infusion in patients with iron deficiency can also have detrimental effects on bone in special cases. The diverse mechanisms underlying these effects and their manifestations contribute to the complexity of this relationship. Iron overload impacts both bone resorption and formation, accelerating bone resorption while reducing bone formation. These effects primarily result from the direct action of reactive oxygen species (ROS), which influence the proliferation, differentiation, and activity of both osteoclasts and osteoblasts differently. This imbalance favors osteoclasts and inhibits the osteoblasts. Simultaneously, multiple pathways, including bone morphogenic proteins, RANK ligand, and others, contribute to these actions, leading to a reduction in bone mass and an increased susceptibility to fractures. In contrast, iron deficiency induces low bone turnover due to energy and co-factor deficiency, both of which require iron. Anemia increases the risk of fractures in both men and women. This effect occurs at various levels, reducing muscular performance and, on the bone-specific level, decreasing bone mineral density. Crucially, anemia increases the synthesis of the phosphaturic hormone iFGF23, which is subsequently inactivated by cleavage under physiological conditions. Thus, iFGF23 levels and phosphate excretion are not increased. However, in specific cases where anemia has to be managed with intravenous iron treatment, constituents-particularly maltoses-of the iron infusion suppress the cleavage of iFGF23. As a result, patients can experience severe phosphate wasting and, consequently, hypophosphatemic osteomalacia. This condition is often overlooked in clinical practice and is often caused by ferric carboxymaltose. Ending iron infusions or changing the agent, along with phosphate and vitamin D supplementation, can be effective in addressing this issue.

Fibroblast growth factor 23 inhibition attenuates steroid-induced osteonecrosis of the femoral head through pyroptosis.

Steroid-induced osteonecrosis of the femoral head (SONFH) is the predominant cause of non-traumatic osteonecrosis of the femoral head (ONFH). Impaired blood supply and reduced osteogenic activity of the femoral head are the key pathogenic mechanisms of SONFH. Fibroblast growth factor 23 (FGF23) levels are not only a biomarker for early vascular lesions caused by abnormal mineral metabolism, but can also act directly on the peripheral vascular system, leading to vascular pathology. The aim of this study was to observe the role of FGF23 on bone microarchitecture and vascular endothelium, and to investigate activation of pyroptosis in SONFH. Lipopolysaccharide (LPS) combined with methylprednisolone (MPS) was applied for SONFH mouse models, and adenovirus was used to increase or decrease the level of FGF23. Micro-CT and histopathological staining were used to observe the structure of the femoral head, and immunohistochemical staining was used to observe the vascular density. The cells were further cultured in vitro and placed in a hypoxic environment for 12 h to simulate the microenvironment of vascular injury during SONFH. The effect of FGF23 on osteogenic differentiation was evaluated using alkaline phosphatase staining, alizarin red S staining and expression of bone formation-related proteins. Matrigel tube formation assay in vitro and immunofluorescence were used to detect the ability of FGF23 to affect endothelial cell angiogenesis. Steroids activated the pyroptosis signaling pathway, promoted the secretion of inflammatory factors in SONFH models, led to vascular endothelial dysfunction and damaged the femoral head structure. In addition, FGF23 inhibited the HUVECs angiogenesis and BMSCs osteogenic differentiation. FGF23 silencing attenuated steroid-induced osteonecrosis of the femoral head by inhibiting the pyroptosis signaling pathway, and promoting osteogenic differentiation of BMSCs and angiogenesis of HUVECs in vitro.

Autosomal Recessive Hypophosphatemic Rickets Type 2 Associated with a Novel ENPP1 Variant in a Taiwanese Girl.

Autosomal recessive hypophosphatemic rickets (HR) type 2 (ARHR2) is a rare form of HR caused by variant of the gene encoding ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). Our patient presented with a history of unsteady gait and progressively bowing legs that had commenced at the age of 1 year. Laboratory tests revealed an elevated level of fibroblast growth factor 23 (FGF23), hypophosphatemia, and a high urine phosphate level. Radiography revealed the typical features of rickets. Next-generation sequencing identified a previously reported c.783C>G (p.Tyr261Ter) and a novel c.1092-42A>G variant in the ENPP1 gene. The patient was prescribed oral phosphates and active vitamin D and underwent guided growth of both distal femora and proximal tibiae commencing at the age of 3 years. No evidence of generalized arterial calcification was apparent during follow-up, and growth rate was satisfactory.

Latent metabolic bone disease, skeletal dysplasia and other conditions related to low bone formation among 38 patients with subtrochanteric femoral fractures: a retrospective observational study.

Subtrochanteric femoral fracture is rare and intractable due to the possible association with low bone formation. Retrospective analysis of 38 patients with subtrochanteric femoral fractures revealed that four patients suffered from disorders related to low bone formation and there were specific treatments for two of them. PURPOSE: The main aim of this study was to detect latent metabolic bone diseases and skeletal dysplasia associated with low bone formation among patients with morphologic atypical femoral fracture (AFF). A second aim was to evaluate the frequency of recognized risk factors, such as antiresorptive agents, glucocorticoids, and age. METHODS: Clinical information was retrospectively analyzed among 38 Japanese patients who were admitted to the Department of Orthopedic Surgery and Spinal Surgery and the Division of Emergency and Critical Care Medicine at the University of Tokyo Hospital with diagnoses of subtrochanteric fractures between February 2012 and March 2022. RESULTS: Among 38 patients (including 30 females), 21 patients were aged 75 and over. Ten patients had past oral glucocorticoid use, and 18 had past antiresorptive agent use. Two patients were diagnosed with hypophosphatemic osteomalacia after the development of fractures. One patient was suspected to be a carrier of a loss-of-function variant of alkaline phosphatase, biomineralization associated (ALPL), and one other patient had previously been genetically diagnosed with pycnodysostosis. Among four patients with a diagnosis or suspicion of these metabolic bone diseases and skeletal dysplasia, four had past clinical fractures, two had past subtrochanteric femoral fractures, and two had subtrochanteric femoral fractures on both sides. CONCLUSION: If clinicians encounter patients with morphologic AFF, latent diseases related to low bone formation should be carefully differentiated because appropriate treatment may prevent delayed union and recurrent fractures. Additionally, it may be desirable to exclude these bone diseases in advance before initiating long-term use of antiresorptive agents in osteoporotic patients by screening with serum alkaline phosphatase levels to reduce the risk of morphologic AFF.

Structural and Molecular Imaging-based Characterization of Soft Tissue and Vascular Calcification in Hyperphosphatemic Familial Tumoral Calcinosis.

Hyperphosphatemic Familial Tumoral Calcinosis (HFTC) is a rare disorder caused by deficient FGF23 signaling and resultant ectopic calcification. In this study, we systematically characterized and quantified macro- and micro-calcification in an HFTC cohort using computed tomography (CT) and 18F-sodium fluoride positron emission tomography/CT (18F-NaF PET/CT). Fourier-transform infrared (FTIR) spectroscopy was performed on four phenotypically different calcifications from a patient with HFTC, showing the dominant component to be hydroxyapatite. Eleven patients with HFTC were studied with CT and/or 18F-NaF PET/CT. Qualitative review was done to describe the spectrum of imaging findings on both modalities. CT-based measures of volume (e.g., total calcific burden and lesion volume) and density (Hounsfield units) were quantified and compared to PET-based measures of metabolic activity (e.g., mean standardized uptake values). Microcalcification scores (mCSs) were calculated for the vasculature of six patients using 18F-NaF PET/CT and visualized on a standardized vascular atlas. Ectopic calcifications were present in 82% of patients, predominantly near joints and the distal extremities. Considerable heterogeneity was observed in total calcific burden per patient (823.0 ± 670.1 cm3, n = 9) and lesion volume (282.5 ± 414.8 cm3, n = 27). The largest lesions were found at the hips and shoulders. 18F-NaF PET offered the ability to differentiate active vs. quiescent calcifications. Calcifications were also noted in multiple anatomic locations, including brain parenchyma (50%). Vascular calcification was seen in the distal aorta, carotid, and coronaries in 50%, 70%, 73%, and 50%, respectively. 18F-NaF-avid, but CT-negative calcification was seen in a 17-year-old patient, implicating early onset vascular calcification. This first systematic assessment of calcifications in a cohort of patients with HFTC has identified the early onset, prevalence, and extent of macro- and micro-calcification. It supports 18F-NaF PET/CT as a clinical tool for distinguishing between active and inactive calcification, informing disease progression, and quantification of ectopic and vascular disease burden.

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare disorder in which patients develop sometimes large debilitating calcifications of soft tissues and blood vessels. It is caused by deficient fibroblast growth factor-23 that leads to high phosphate levels, which contributes to the calcifications. The calcifications and manifestations of this disorder have not been well characterized. We determined the mineral composition of the calcifications to be hydroxyapatite. Capitalizing on the fact fluoride can be integrated into hydroxyapatite, we used radiolabeled sodium fluoride positron emission tomography/computed tomography scans (18F-NaF PET/CT) to characterize and quantify the calcifications in 11 patients. 82% of the patients had calcifications, with the largest located at the hips and shoulders. Micro-calcifications were found in the blood vessels of most patients, including children. The technique also enabled us to differentiate between active versus stable calcifications. This first systematic assessment of calcifications in patients with HFTC showed the utility of 18F-NaF PET/CT as a tool to identify and quantify calcifications, as well as distinguish between active and stable calcifications. This approach will inform disease progression and may prove useful for measuring response to treatment.

Hypophosphatemic Rickets and Short Stature.

An 18-month old male presented with gross motor delay and poor growth (weight z-score -2.21, length z-score -4.26). Radiographs showed metaphyseal irregularities suggesting metaphyseal dysplasia and sagittal craniosynostosis. Biochemical evaluation revealed evidence of hypophosphatemic rickets [serum phosphorus 2.3 mg/dL (reference range (RR) 4.3-6.8), alkaline phosphatase 754 unit/L (RR 156-369)] due to renal phosphate wasting (TmP/GFR 4.3 mg/dL, normal for age 4.3-6.8), with C-terminal FGF23 125 RU/mL (>90 during hypophosphatemia suggests FGF23-mediated hypophosphatemia). Treatment was initiated with calcitriol and phosphate. Genetic analysis showed a pathogenic variant of FGF23: c.527G > A (p.Arg176Gln) indicative of autosomal dominant hypophosphatemic rickets (ADHR). Consistent with reports linking iron deficiency with the ADHR phenotype, low ferritin was detected, 18 ng/mL (RR 24-336). Oral ferrous sulfate replacement was initiated. Following normalization of ferritin level (41 ng/mL) biochemical improvement was demonstrated (FGF23 69 RU/mL, phosphorus 5.0 mg/dL and alkaline phosphatase 228 unit/L). Calcitriol and phosphate were discontinued. Three years later, the patient demonstrated improved developmental milestones, linear growth (length Z-score -2.01), radiographic normalization of metaphyses, and stabilization of craniosynostosis. While the most common cause of hypophosphatemic rickets is X-linked hypophosphatemia, other etiologies should be considered as treatment differs. In ADHR, normalization of iron leads to biochemical and clinical improvement.

Burosumab treatment of X-linked hypophosphatemia patients: interim analysis of the SUNFLOWER longitudinal, observational cohort study.

X-linked hypophosphatemia (XLH) is a genetic disease that results in excessive FGF23, chronic hypophosphatemia, and musculoskeletal abnormalities, with affected patients experiencing symptoms such as bone pain, bone deformity, fracture, and pseudofracture. Burosumab is a fully human monoclonal antibody that binds to FGF23, improving lowered serum 1,25(OH)2D and phosphate levels in patients with XLH. There are insufficient data on the use of burosumab, its safety, and the outcomes of treated patients in a real-world setting. The SUNFLOWER (Study of longitUdinal observatioN For patients with X-Linked hypOphosphatemic rickets/osteomalacia in collaboration With Asian partnERs) study is an ongoing longitudinal, observational cohort study of patients with XLH in Japan and South Korea. Enrollment occurred between April 2018 and December 2020. This interim analysis compared the background characteristics of patients who received burosumab with those who did not, and assessed improvements in biomarkers, physical and motor function, health-related quality-of-life (HRQOL) and other patient-reported outcome (PRO) measures, as well as the safety of burosumab treatment in 143 Japanese patients from 15 institutions over 6 mo. The patients had a median [interquartile range] age of 17.5 [11.0, 38.8] yr and 98 (68.5%) were female. Among patients aged <18 and ≥18 yr, 40/73 (54.8%) and 25/70 (35.7%) received burosumab, respectively. More patients aged ≥18 who received burosumab had bone pain at baseline vs those not treated with burosumab (6/25, 24.0% vs 2/45, 4.4%, p=.021). Patients treated with burosumab had improved serum phosphate and 1,25(OH)2D levels; moreover, rickets severity and HRQOL/PRO measures, such as pain, appeared to improve over 6 mo of burosumab treatment, and no new safety concerns were identified. This study identified trends in the background characteristics of patients with XLH who receive burosumab in real-world clinical practice. Furthermore, the results support the use of burosumab therapy in real-world settings.

Impact of Elevated Fibroblast Growth Factor 23 (FGF23) on the Cardiovascular System: A Comprehensive Systematic Literature Review.

Fibroblast growth factors (FGF) are a type of cell signaling proteins that are mostly produced by macrophages. They are essential for a variety of biological activities involved in normal development. Fibroblast growth factor 23 (FGF23) is the newest and youngest member of the FGF endocrine subfamily, along with fibroblast growth factor 19 (FGF19) and fibroblast growth factor 21 (FGF21). In this study, we conduct a systematic review of all known literature to identify the risk of elevated FGF23 in the cardiovascular system. The analysis includes the risk of cardiovascular disease for both primary and secondary causes of elevated FGF23, such as chronic renal insufficiency. This systematic literature review adhered to the Preferred Reporting Items and Meta-Analysis (PRISMA) standards. A total of 4,793 records were identified across different databases. After that, 273 records were retrieved and reviewed. After carefully examining the titles and summaries of each report, 249 additional entries were eliminated. About 24 studies from the remaining records were chosen by primary and secondary authors for screening, and they performed a quality assessment using common quality check tools. Finally, this review included 11 studies. Following a thorough analysis, we came to the conclusion that FGF23 can be regarded as a novel biomarker and should be included in the group of heart biomarkers that have already been identified, such as B-type natriuretic peptide (BNP), for the early identification of a variety of highly prevalent cardiovascular disorders.

X-Linked hypophosphatemia. Data from a Spanish adult population cohort.

BACKGROUND: X-linked hypophosphatemia (XLH) represents the most prevalent cause of hereditary hypophosphatemia. X-linked hypophosphatemia causes an elevation of fibroblast growth factor 23 (FGF23), a hormone responsible for inducing hyperphosphaturia, and reduced active vitamin D synthesis. Challenges in diagnosis and the absence of well-defined clinical guidelines have resulted in higher rates of late diagnoses. While numerous reports focus on pediatric X-linked hypophosphatemia patients, studies in adults are limited. METHODS: Multicenter, cross-sectional, observational study of a cohort of adult patients diagnosed with X-linked hypophosphatemia. The study identified demographic, clinical, genetic, laboratory variables, treatments used, comorbidities, and complications. RESULTS: Twenty patients diagnosed with X-linked hypophosphatemia were collected. The median age at diagnosis was 11 (1-56) years and at data collection was 44 (21-68) years. Fifty percent of cases were diagnosed in adulthood. Main clinical manifestation was osteoarticular pain, in 75% of cases, and no relation to age at diagnosis, height, phosphorus, or parathyroid hormone (PTH) levels was observed (p > 0.05). Lower limb deformities were associated with reduced stature and earlier diagnosis (p < 0.05). Sixty percent of patients reported pain requiring chronic medication and no significant correlation was found with other variables. Anxiety and depression were found in an important number of patients. FGF23 levels were not related to any of the clinical variables studied (p > 0.05). DISCUSSION: This is the largest study on adult patients with X-linked hypophosphatemia in southern Europe. It may offer valuable insights into the natural progression and course of the condition in adults, which can aid in better clinical management.

Changes in body composition, adipokines, ghrelin, and FGF23 in growth hormone-deficient children during rhGH therapy.

INTRODUCTION: Beyond growth acceleration, growth hormone (GH) therapy improves body composition of GH-deficient (GHD) children due to the interaction of GH with lipid and carbohydrate metabolism, possibly mediated by adipokines secreted by adipose tissue and ghrelin. To promote linear growth, it is essential to have normal phosphate homeostasis. Fibroblast growth factor 23 (FGF23) is a known regulator of serum phosphorus and may be responsible for the increased renal phosphorus reabsorption observed during GH therapy. This study aimed to assess the impact of one-year GH therapy on body composition, adipokines, acylated/unacylated ghrelin (AG/UAG), and FGF23 in GHD children. MATERIAL AND METHODS: A prospective observational study of 42 prepubertal, non-obese GHD children followed up in the first year of GH replacement therapy, investigating changes in adipokine profiles, AG/UAG, FGF23, and body composition. Data before therapy onset were compared with measurements obtained after 6 and 12 months of GH therapy. RESULTS: All children with a mean age of 9.2 ± 2.6 years grew at an accelerated pace. Total body fat decreased significantly, while the lipid profile improved, and total bone mineral density (BMD) significantly increased over the 12 months of treatment. Leptin and UAG levels decreased significantly, whereas adiponectin and AG values increased. A significant increase in plasma FGF23 and insulin growth factor 1 (IGF1) was accompanied by increased serum phosphate. Changes in FGF23 concentration did not have an impact on BMD. The strong association of FGF23 with IGF1 and height standard deviation (SD) could reveal a role of FGF23 in linear growth. In regression analysis models, GH therapy influences the changes of leptin and adiponectin, but not ghrelin, independently of body composition - lean or fat mass. CONCLUSIONS: GH replacement therapy improves body composition and adipokine profile in GHD children and directly impacts leptin and adiponectin concentrations independently of body composition. Also, GHD children have increased serum phosphate, correlated with upregulation rather than with suppression of FGF23, an unexpected observation given the phosphaturic role of FGF23. Further research is needed to identify the molecular mechanisms by which the GH/IGF1 axis influences adipokines secretion and plasma changes of FGF23.

Preoperative inflammatory biomarkers reveal renal involvement in postsurgical mortality in hip fracture patients: an exploratory study.

Background: Hip fractures in frail patients result in excess mortality not accounted for by age or comorbidities. The mechanisms behind the high risk of mortality remain undetermined but are hypothesized to be related to the inflammatory status of frail patients. Methods: In a prospective observational exploratory cohort study of hospitalized frail hip fracture patients, 92 inflammatory markers were tested in pre-operative serum samples and markers were tested against 6-month survival post-hip fracture surgery and incidence of acute kidney injury (AKI). After correcting for multiple testing, adjustments for comorbidities and demographics were performed on the statistically significant markers. Results: Of the 92 markers tested, circulating levels of fibroblast growth factor 23 (FGF-23) and interleukin-15 receptor alpha (IL15RA), both involved in renal disease, were significantly correlated with 6-month mortality (27.5% overall) after correcting for multiple testing. The incidence of postoperative AKI (25.4%) was strongly associated with 6-month mortality, odds ratio = 10.57; 95% CI [2.76-40.51], and with both markers plus estimated glomerular filtration rate (eGFR)- cystatin C (CYSC) but not eGFR-CRE. The effect of these markers on mortality was significantly mediated by their effect on postoperative AKI. Conclusion: High postoperative mortality in frail hip fracture patients is highly correlated with preoperative biomarkers of renal function in this pilot study. The effect of preoperative circulating levels of FGF-23, IL15RA, and eGFR-CYSC on 6-month mortality is in part mediated by their effect on postoperative AKI. Creatinine-derived preoperative renal function measures were very poorly correlated with postoperative outcomes in this group.

Both enantiomers of ß-aminoisobutyric acid BAIBA regulate Fgf23 via MRGPRD receptor by activating distinct signaling pathways in osteocytes.

With exercise, muscle and bone produce factors with beneficial effects on brain, fat, and other organs. Exercise in mice increased fibroblast growth factor 23 (FGF23), urine phosphate, and the muscle metabolite L-ß-aminoisobutyric acid (L-BAIBA), suggesting that L-BAIBA may play a role in phosphate metabolism. Here, we show that L-BAIBA increases in serum with exercise and elevates Fgf23 in osteocytes. The D enantiomer, described to be elevated with exercise in humans, can also induce Fgf23 but through a delayed, indirect process via sclerostin. The two enantiomers both signal through the same receptor, Mas-related G-protein-coupled receptor type D, but activate distinct signaling pathways; L-BAIBA increases Fgf23 through Gαs/cAMP/PKA/CBP/ß-catenin and Gαq/PKC/CREB, whereas D-BAIBA increases Fgf23 indirectly through sclerostin via Gαi/NF-κB. In vivo, both enantiomers increased Fgf23 in bone in parallel with elevated urinary phosphate excretion. Thus, exercise-induced increases in BAIBA and FGF23 work together to maintain phosphate homeostasis.

N1F(Improved-Nephropathy 1 Formula) Ameliorates Renal Interstitial Fibrosis via Inhibiting Extracellular Matrix Deposition and Regulating the FGF23/P38MAPK/Wnt Pathway.

BACKGROUND: Renal fibrosis is the primary pathway in the progression of chronic kidney disease (CKD) towards end-stage renal failure. The currently used drugs currently are ineffective, and their mechanisms of action remain unclear. This study aims to investigate the nephroprotective effect of Improved-Nephropathy 1 Formula (N1F) in a rat model of unilateral ureteral obstruction (UUO) and explore the potential mechanisms of N1F-containing serum in treating TGF-ß1-induced human renal tubular epithelial cells (HK-2). METHODS: SD rats received 2-week continuous N1F gavage starting on day 2 after UUO. HK-2 cells were pretreated with a P38MAPK inhibitor for 1 h in vitro, followed by induction of the cells with TGF-ß1 and treatment with N1F 48 h later. The chemical composition of N1F was analyzed using high-performance liquid chromatography-Q-Orbitrap high-resolution liquid mass spectrometry. Renal function was assessed by measuring serum creatinine (Scr), blood urea nitrogen (BUN) and urine protein (Upro) levels. Hematoxylin and eosin (HE) and Masson's trichrome (Masson) staining were used to evaluate the extent of renal tissue damage and fibrosis. Western blotting, immunohistochemistry, and immunofluorescence were used to detect the protein levels of relevant indices. The RNA levels of the relevant indices were detected using real-time fluorescence quantitative PCR (RT-qPCR). RESULTS: We identified 361 chemical components in the water extract of N1F. These chemical components of N1F significantly reduced the area associated with interstitial fibrosis in the kidneys of UUO rats and the levels of serum creatinine, urea nitrogen, and urinary protein. Additionally, N1F decreased the protein levels of FGF23, Wnt1, ß-catenin and p-P38MAPK/P38MAPK, along with the expression of renalfibrosis-associated proteins, α-SMA, FN, Collagen III, and Vimentin in the renal tissues of the UUO rats, while enhancing klotho and DKK1 protein levels. In vitro experiments revealed that inhibition of P38MAPK signaling significantly suppressed the expression of proteins related to the Wnt signaling pathway, with a concomitant decrease in the expression of FGF23 and an increase in the expression of Klotho. Notably, the P38MAPK inhibitor (SB203580) had similar effects to N1F in altering the above-mentioned indices in vitro. CONCLUSIONS: N1F may exhibit potential therapeutic efficacy against renal fibrosis by inhibiting the FGF23/P38MAPK/Wnt signaling pathway, consequently inhibiting extracellular matrix deposition due to renal injury.

A Rare Association Between Osteomalacia, Phosphaturic Mesenchymal Tumor, and Ovarian Cancer: A Case Report and Literature Review.

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by hypophosphatemia, bone mineralization disorders with increased risk of fragility fractures, muscle pain, and progressive weakness. TIO has been associated with increased production of the phosphaturic hormone Fibroblast Growth Factor 23 (FGF23) usually by mesenchymal tumors of soft tissue or bone (Phosphaturic Mesenchymal Tumors-PMTs). In rare cases TIO may be observed in association with other malignancies. We report the case of a 66-year-old woman with an occasional diagnosis of both a PMT and an ovarian cancer during the evaluation of TIO. We also systematically review the literature to discover possible correlations between osteomalacia, FGF23 production, and ovarian cancer. Four studies were eligible for the analysis. Two case reports described an association between TIO development and ovarian cancer, whereas the two case-control studies hypothesized a possible correlation between FGF/FGF receptor axis and cancer development. Although it does not provide conclusive evidence regarding the association between TIO and ovarian cancer, this case report highlights the possibility that in the diagnostic workup of suspected TIO, both FGF23-secreting tumors distinct from PMT and tumors unrelated to the clinical presentation of TIO could be identified. This information is important for guiding successful tumor staging and determining the necessity for surgical intervention and/or eventual adjuvant therapy.

Cardiovascular health in pediatric patients with X-linked hypophosphatemia under two years of burosumab therapy.

Introduction: X-linked hypophosphatemia (XLH) is caused by an inactivating mutation in the phosphate-regulating endopeptidase X-linked (PHEX) gene whose defective product fails to control phosphatonin fibroblast growth factor 23 (FGF23) serum levels. Although elevated FGF23 levels have been linked with detrimental cardiac effects, the cardiologic outcomes in XLH patients have been subject to debate. Our study aimed to evaluate the prevalence and severity of cardiovascular morbidity in pediatric XLH patients before, during, and after a 2-year treatment period with burosumab, a recombinant anti-FGF23 antibody. Methods: This prospective observational study was conducted in a tertiary medical center, and included 13 individuals with XLH (age range 0.6-16.2 years) who received burosumab every 2 weeks. Clinical assessment at treatment initiation and after .5, 1, and 2 years of uninterrupted treatment included anthropometric measurements and cardiologic evaluations (blood pressure [BP], electrocardiogram, conventional echocardiography, and myocardial strain imaging). Results: The linear growth of all patients improved significantly (mean height z-score: from -1.70 ± 0.80 to -0.96 ± 1.08, P=0.03). Other favorable effects were decline in overweight/obesity rates (from 46.2% to 23.1%) and decreased rates of elevated BP (systolic BP from 38.5% to 15.4%; diastolic BP from 38.5% to 23.1%). Electrocardiograms revealed no significant abnormality throughout the study period. Cardiac dimensions and myocardial strain parameters were within the normative range for age at baseline and remained unchanged during the study period. Conclusion: Cardiologic evaluations provided reassurance that 2 years of burosumab therapy did not cause cardiac morbidity. The beneficial effect of this treatment was a reduction in cardiovascular risk factors, as evidenced by the lower prevalence of both overweight/obesity and elevated BP.

Activin A: a marker of mineral bone disorder in children with chronic kidney disease?

BACKGROUND: Activin A has been shown to enhance osteoclast activity and its inhibition results in bone growth. The potential role of activin A as a marker of chronic kidney disease-mineral bone disease (CKD-MBD) and its relationship with other markers has not been studied in children with CKD. METHODS: A cross sectional study was conducted among 40 children aged 2 to 18 years with CKD (Stage 2 to 5; 10 in each stage) and 40 matched controls. Activin A, cathepsin K, FGF-23, PTH, serum calcium, phosphorous and alkaline phosphatase in both groups were measured and compared. The correlation of activin A and markers of CKD-MBD was studied. A p value of < 0.05 was considered significant. RESULTS: The mean age of children with CKD was 9.30 ± 3.64 years. Mean levels of activin A in cases were 485.55 pg/ml compared to 76.19 pg/ml in controls (p < 0.001). FGF-23 levels in cases were 133.18 pg/ml while in controls it was 6.93 pg/ml (p < 0.001). Mean levels of cathepsin K were also significantly higher in cases as compared to controls. There was a progressive increase in activin A and cathepsin K levels with increasing stage of CKD. Activin A had a significant positive correlation with serum creatinine (r = 0.51; p < 0.001). CONCLUSIONS: Activin A levels progressively rise with advancing CKD stage. These findings suggest that activin A can be a potential early marker of CKD-MBD in children.

Quantitative correlation of ENPP1 pathogenic variants with disease phenotype.

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) codes for a type 2 transmembrane glycoprotein which hydrolyzes extracellular phosphoanhydrides into bio-active molecules that regulate, inter alia, ectopic mineralization, bone formation, vascular endothelial proliferation, and the innate immune response. The clinical phenotypes produced by ENPP1 deficiency are disparate, ranging from life-threatening arterial calcifications to cutaneous hypopigmentation. To investigate associations between disease phenotype and enzyme activity we quantified the enzyme velocities of 29 unique ENPP1 pathogenic variants in 41 patients enrolled in an NIH study along with 33 other variants reported in literature. We correlated the relative enzyme velocities with the presenting clinical diagnoses, performing the catalytic velocity measurements simultaneously in triplicate using a high-throughput assay to reduce experimental variation. We found that ENPP1 variants associated with autosomal dominant phenotypes reduced enzyme velocities by 50 % or more, whereas variants associated with insulin resistance had non-significant effects on enzyme velocity. In Cole disease the catalytic velocities of ENPP1 variants associated with AD forms trended to lower values than those associated with autosomal recessive forms - 8-32 % vs. 33 % of WT, respectively. Additionally, ENPP1 variants leading to life-threatening vascular calcifications in GACI patients had widely variable enzyme activities, ranging from no significant differences compared to WT to the complete abolishment of enzyme velocity. Finally, disease severity in GACI did not correlate with the mean enzyme velocity of the variants present in affected compound heterozygotes but did correlate with the more severely damaging variant. In summary, correlation of ENPP1 enzyme velocity with disease phenotypes demonstrate that enzyme velocities below 50 % of WT levels are likely to occur in the context of autosomal dominant disease (due to a monoallelic variant), and that disease severity in GACI infants correlates with the more severely damaging ENPP1 variant in compound heterozygotes, not the mean velocity of the pathogenic variants present.

Tumor-induced osteomalacia: A systematic literature review.

Introduction: Tumor-induced osteomalacia (TIO), is a rare acquired paraneoplastic syndrome characterized by defective bone mineralization, caused by the overproduction of fibroblast growth factor 23 (FGF23) by a tumor. Material and methods: We conducted a systematic review to identify all case reports of TIO, focusing on those associated with mesenchymal tumors. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) consensus, and we included patients with a diagnosis of TIO and histological confirmation of phosphaturic mesenchymal tumors or resolution of the condition after treatment of the tumor. Bibliographical searches were carried out until December 2023 in the Cochrane Library, Medline and Embase, as well as congress abstracts online. Results: We identified 769 articles with 1979 cases reported. Most patients were adults, with a higher incidence on men. Disease duration before diagnosis is a mean of 4.8 years. Most tumors were histologically classified as PMT. Lower limbs were the predominant location. Hypophosphatemia was present in 99.8 % of patients. The FGF23 was elevated at diagnosis in 95.5 %. Resection of the tumor was the treatment of choice in most of patients. After resection, there was a clinical improvement in 97.6 % of cases, and serum phosphorus and FGF23 levels returned to normal ranges in 91.5 % and 81.4 % of the patients, respectively. Conclusion: TIO is usually misdiagnosed with rheumatological or musculoskeletal disorders. The diagnosis should be suspected in patients with hypophosphatemic osteomalacia, and the measurement of serum FGF23 can be useful for diagnosis and management.

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.

Preclinical development of EXT608, an investigational parathyroid hormone derivative with extended half-life for the treatment of hypoparathyroidism.

Hypoparathyroidism, a deficiency of parathyroid hormone (PTH), results in hypocalcemia, hyperphosphatemia, and hypercalciuria. The disease is poorly controlled by calcium and vitamin D supplements or native PTH(1-84) replacement therapy. A version of PTH is being developed using D-VITylation technology, whereby vitamin D is conjugated to a therapeutic peptide, which confers a long plasma half-life by virtue of binding to the abundant vitamin D binding protein (DBP). D-VITylation of PTH caused no reduction in activity at the PTHR1 receptor, and resulted in a plasma elimination half-life of 7-15 h in rats and 24-32 h in cynomolgus monkeys. Analysis of steady-state pharmacokinetics as a function of dose showed flat profiles with smaller peak:trough ratios at low doses, indicative of slower subcutaneous absorption. In thyroparathyroidectomized (TPTx) rats, PTH(1-34)-vitamin D conjugates restored serum calcium and phosphate levels into the normal range over the 24 h dosing period, and increased bone turnover markers and reduced bone mineral density. Urinary calcium was initially elevated, but normalized by the end of treatment on day 27. In healthy monkeys, a single dose of PTH(1-34)-vitamin D conjugates elevated serum calcium levels above the normal range for a period of 24-48 h while simultaneously reducing urinary calcium. Therefore, the lead compound, EXT608, is a promising candidate as a therapeutic that can truly mimic the endogenous activity of PTH and warrants further study in patients with hypoparathyroidism.