Rachel Ilana Gafni

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.

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 mCS _mean and mCS _max 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.

Introduction. Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disorder where patients present with hypophosphatemia, chronic diffuse bone pain, and occasionally fractures. Benign phosphaturic mesenchymal tumors (PMT) are responsible for the TIO and are largely soft tissue tumors. Cases. Two male patients with TIO secondary to PMT were reportedone in the bony scapula and the other in the plantar foot soft tissue. The first case describes a 63-year-old Caucasian male, who sustained an intertrochanteric proximal femur stress fracture and approximately two years of diffuse bone pain and hypophosphatemia. Wide excision of a left scapula boney lesion resulted in immediate resolution of his electrolyte abnormalities and bone pain. Case 2 describes a 58-year-old male with four years of multifocal bone pain and atraumatic fractures. A ⁶⁸Ga-DOTATATE-positron emission tomography/computed tomography (PET/CT) scan identified a soft tissue tumor in his plantar foot, which was ultimately excised. He also experienced near immediate resolution of his pain and no additional fractures. Conclusion. TIO is a rare condition presenting with chronic multifocal bone pain, stress fractures, and hypophosphatemia. These two cases highlight that the causative tumor may originate in soft tissue or bone. Furthermore, a high index of suspicion, along with fibroblast growth factor-23 testing and DOTATATE-PET/CT localization, can help with diagnosis and minimize treatment delays.

Tumor‐induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by ectopic production of fibroblast growth factor 23 (FGF23) by phosphaturic mesenchymal tumors (PMTs). Acting on renal tubule cells, excess FGF23 decreases phosphate reabsorption and 1,25‐dihydroxy‐vitamin D (1,25D) production, leading to hypophosphatemia, impaired bone mineralization, pain, and fractures. Fibronectin 1‐fibroblast growth factor receptor 1 (FN1‐FGFR1) gene fusions have been identified as possible drivers in up to 40% of resected PMTs. Based on the presumptive role of FGFR1 signaling by chimeric FN1‐FGFR1 proteins, the effectiveness of infigratinib, a FGFR1‐3 tyrosine kinase inhibitor, was studied in an open‐label, single‐center, phase 2 trial. The primary endpoint was persistent normalization of blood phosphate and FGF23 after discontinuation. Four adults with TIO (two nonlocalized, two nonresectable PMTs) were treated with daily infigratinib for up to 24 weeks. All patients had a favorable biochemical response that included reduction in intact FGF23, and normalization of blood phosphate and 1,25D. However, these effects disappeared after drug discontinuation with biochemistries returning to baseline; no patients entered biochemical remission. In the two patients with identifiable tumors, 68Gallium (68Ga)‐DOTATATE and 18Fluoride (18F)‐Fluorodeoxyglucose (FDG) PET/CT scans showed a decrease in PMT activity without change in tumor size. Patients experienced mild to moderate, treatment‐related, dose‐limiting adverse events (AEs), but no serious AEs. Three patients had dose interruptions due to AEs; one patient continued on a low dose for the entire 24 weeks and one patient stopped therapy at 17 weeks due to an AE. The study closed early due to a failure to meet the primary endpoint and a higher‐than‐expected incidence of ocular AEs. Infigratinib treatment lowered FGF23, increased blood phosphate, and suppressed PMT activity, confirming the role of FGFR signaling in PMT pathogenesis. However, treatment‐related AEs at efficacy doses and disease persistence on discontinuation support restricting the use of infigratinib to patients with life‐limiting metastatic PMTs. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism caused by gain-of-function pathogenic variants in the gene (CASR) encoding the calcium-sensing receptor (CaSR). It is characterized by variable degrees of hypocalcemia, hyperphosphatemia, and hypomagnesemia, inappropriately low levels of parathyroid hormone (PTH) and hypercalciuria. Conventional therapy includes oral calcium and activated Vitamin D, targeting blood calcium at or slightly below the low-normal level to minimize hypocalcemic symptoms. This supplementation typically causes or exacerbates hypercalciuria, which may lead to nephrolithiasis, nephrocalcinosis, and renal insufficiency. It has been demonstrated in in vitro and in vivo models of ADH1, as well as in a Phase 2b clinical study (Roberts et al, JBMR 2019) that calcilytics (negative allosteric modulators of the CaSR), have the ability to shift the concentration-response relationship between extracellular calcium and the mutant CaSR towards normal. Six adults with ADH1 due to four distinct activating variants of the CASR were studied in an ongoing, three period, Phase 2b, open-label, dose-ranging study [NCT04581629] of the calcilytic encaleret (CLTX-305). Calcium, magnesium, and calcitriol supplements were discontinued at the start of Period 1, and subjects received sequential, increasing daily doses of encaleret for 3d (30 mg, 90 mg, 180 mg) followed by 120 or 180 mg twice daily on day 4 and 5, while undergoing frequent blood and urine sampling. The mean baseline PTH was 3.4 ± 4.5 pg/mL (mean ± SD; nl 10–65); on encaleret, there was a rapid, dose-dependent increase in PTH to a mean level of 64.8 ± 49.6 pg/mL over 24 hours by day 5. Albumin-corrected blood calcium (cCa) increased from a baseline of 7.6 ± 0.6 mg/dL (nl 8.4–10.2) to a 24-hour mean on day 5 of 9.0 ± 0.5 mg/dL. Phosphorus decreased from a baseline of 4.5 ± 0.7 mg/dL (nl 2.3–4.7) to a 24-hour day 5 mean of 2.9 ± 0.5 mg/dL. Magnesium increased from a baseline of 1.6 ± 0.4 mg/dL (nl 1.6–2.6) to a 24-hour day 5 mean of 2.0 ± 0.5 mg/dL. Blood calcium, phosphorus and magnesium were mostly maintained within the normal range in ADH1 subjects by days 4 and 5. Twenty-four hour urine calcium was elevated at the screening visit while subjects were on conventional therapy (436 ± 255 mg/day, nl < 250–300) and decreased with increasing doses of encaleret to 63 ± 127 mg/day on day 5. Urinary calcium excretion became normal in 3 subjects and undetectable in 3 subjects while on encaleret. Encaleret was well-tolerated, with no serious adverse events reported. The consistent mineral responses following encaleret administration in all six ADH1 subjects with four distinct CASR genotypes represents preliminary proof-of-concept that encaleret may be an efficacious treatment for ADH1. The longer-term evaluation of encaleret in ADH1 subjects is ongoing.

Fibroblast growth factor-23 (FGF23) measurement is a critical tool in the evaluation of patients with disordered phosphate homeostasis. Available laboratory reference ranges for blood FGF23 were developed using samples from normophosphatemic individuals. Reliance on such values can lead to misdiagnosis in patients with FGF23-mediated hypophosphatemia, such as X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO), in whom pathology-driving FGF23 levels can be in the “normal range.” To determine FGF23 levels that are diagnostic for the identification of patients with FGF23-mediated hypophosphatemic disorders, we studied 149 patients with various disorders of FGF23-mediated and FGF23-independent hypophosphatemia and defined cut-off levels for both intact FGF23 (iFGF23) and C-terminal FGF23 (cFGF23) that can accurately distinguish between FGF23-mediated and FGF23-independent hypophosphatemia. In addition, to demonstrate the relationship between FGF23 and phosphate across the spectrum of human physiology, we assessed blood levels of FGF23 and phosphate in 434 patients with various forms of hypophosphatemia, hyperphosphatemia, and normophosphatemia. An intact FGF23 cut point of 27 pg/mL was 100% sensitive and specific in distinguishing FGF23-mediated from FGF23-independent hypophosphatemia, and a cFGF23 cut point of 90 RU/mL was 100% sensitive and specific in distinguishing specifically TIO from FGF23-independent hypophosphatemia. There was overlap in the cFGF23 range of 45–90 RU/mL between genetic forms of FGF23 excess and FGF23-independent hypophosphatemia, substantiating the superiority of iFGF23 over cFGF23 in making the diagnosis of FGF23-mediated hypophosphatemia. In this cohort, using the laboratory upper limit of normal for cFGF23 (180 RU/mL) would result in a misdiagnosis in more than half of patients with FGF23-mediated hypophosphatemia. In this, the largest study of FGF23 in chronic hypophosphatemia to date, we established iFGF23 and cFGF23 cut-off values to assist in the evaluation and diagnosis of hypophosphatemic conditions. © 2022 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by US Government employees and their work is in the public domain in the USA. Abstract Fibroblast growth factor-23 (FGF23) measurement is a critical tool in the evaluation of chronic hypophosphatemia. Reliance on laboratory reference ranges, developed from normophosphatemic individuals, however, can lead to misdiagnosis in patients with FGF23-mediated hypophosphatemia in whom pathology-driving FGF23 levels can be “inappropriately normal.” In this study, we establish clinically useful diagnostic cut points for both intact FGF23 (iFGF23, 27 pg/mL) and c-terminal FGF23 (cFGF23, 45–90 RU/mL) to accurately distinguish between FGF23-mediated and FGF23-independent hypophosphatemia.

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism due to activating variants of the calcium-sensing receptor gene (CASR). Inherited or de novo activating variants of the CASR alter the set point for extracellular calcium, resulting in inadequate parathyroid hormone (PTH) secretion and inappropriate renal calcium excretion leading to hypocalcemia and hypercalciuria. Conventional therapy includes calcium and activated vitamin D, which can worsen hypercalciuria, resulting in renal complications. A systematic literature review, using published reports from 1994 to 2021, was conducted to catalog CASR variants, to define the ADH1 clinical spectrum, and to determine the effect of treatment on patients with ADH1. There were 113 unique CASR variants reported, with a general lack of genotype/phenotype correlation. Clinical data were available in 191 patients; 27% lacked symptoms, 32% had mild/moderate symptoms, and 41% had severe symptoms. Seizures, the most frequent clinical presentation, occurred in 39% of patients. In patients with blood and urine chemistries available at the time of diagnosis (n = 91), hypocalcemia (99%), hyperphosphatemia (59%), low PTH levels (57%), and hypercalciuria (34%) were observed. Blood calcium levels were significantly lower in patients with severe symptoms compared with asymptomatic patients (6.8 ± 0.7 versus 7.6 ± 0.7 mg/dL [mean ± SD]; p < 0.0001), and the age of presentation was significantly lower in severely symptomatic patients (9.1 ± 15.0 versus 19.3 ± 19.4 years; p < 0.01). Assessments for complications including nephrocalcinosis, nephrolithiasis, renal impairment, and brain calcifications in 57 patients on conventional therapy showed that 75% had at least one complication. Hypercalciuria was associated with nephrocalcinosis, nephrolithiasis, renal impairment, or brain calcifications (odds ratio [OR] = 9.3; 95% confidence interval [CI] 2.4–37.2; p < 0.01). In 27 patients with urine calcium measures before and after starting conventional therapy, the incidence of hypercalciuria increased by 91% (p < 0.05) after therapy initiation. ADH1 is a condition often associated with severe symptomatology at presentation with an increase in the risk of renal complications after initiation of conventional therapy. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).