Context:Cutaneous skeletal hypophosphatemia syndrome (CSHS) is an ultrarare disorder defined by epidermal and/or melanocytic nevi, mosaic skeletal dysplasia, and FGF23-mediated hypophosphatemia. As in other FGF23-mediated hypophosphatemia conditions, individuals with CSHS have renal phosphate wasting and inappropriately normal or frankly low 1,25-dihydroxyvitamin D levels with resultant hypophosphatemia leading to rickets and osteomalacia. Conventional therapy for FGF23-mediated hypophosphatemia consists of multiple daily doses of oral phosphate and active vitamin D. Objective:Burosumab is a fully human immunoglobulin G1 monoclonal antibody that binds to and inhibits the activity of FGF23, leading to an increase in serum phosphorus levels and skeletal healing. Given its efficacy in tumor-induced osteomalacia and X-linked hypophosphatemic rickets, two related disorders of FGF23-mediated hypophosphatemia, we explored treatment with burosumab in a young adult with CSHS. Methods:In this open-label, single-patient trial conducted in the clinical research unit of an academic children's hospital, burosumab was administered subcutaneously every 4 weeks for 3 years. The participant was an 18-year-old woman with CSHS and FGF23-mediated hypophosphatemia. Burosumab was administered subcutaneously every 4 weeks, starting at 0.3 mg/kg/dose and increasing up to 0.9 mg/kg/dose. Main outcome measures included change in blood phosphorus levels. Results:Burosumab therapy was well tolerated with correction of hypophosphatemia and improvement in other measures including renal phosphate loss, alkaline phosphatase, active vitamin D metabolism, skeletal imaging, pain, physical function, and overall quality of life. Adverse events were manageable, with unclear relationship to burosumab treatment. Conclusion:These findings suggest that burosumab may be an effective treatment for CSHS.

Disclosure: P.J. Tebben: Consultancy fees and research funding from Calcilytix. T. Alexander: Steering Committee Member Calcilytix Therapeutics Inc. Honoraria Ultragenyx. S. Mora: Consultancy fees from Calcilytix. R. Padidela: Consultancy fees from Calcilytix. M. Roberts: Employee of BridgeBio and own company stock. D. Li: Employee of BridgeBio and own company stock. S. Adler: Employee of BridgeBio and own company stock. R.I. Gafni: The NIDCR receives research funding from Calcilytix Therapeutics, Steering committee member (unpaid) for adult and pediatric encaleret studies, Medical advisory board (unpaid) of The Hypoparathyroidism Association. Objectives: Autosomal dominant hypocalcemia type 1 (ADH1), caused by gain-of-function variants in the calcium-sensing receptor gene, is characterized by low/inappropriately normal parathyroid hormone (PTH), hypocalcemia, and hypercalciuria. Standard-of-care (SoC) treatment (calcium and active vitamin D) worsens hypercalciuria, increasing renal morbidity. Encaleret, a negative allosteric modulator of the calcium-sensing receptor, is under investigation as a potential ADH1 treatment. In a Phase 2b study [NCT04581629] in 13 adults with ADH1, encaleret led to sustained normalization in PTH, albumin-corrected calcium (cCa), phosphorus, magnesium and 24-hr urine calcium (UCa) excretion over 24 weeks, without serious adverse events reported. A Phase 3 study [NCT05680818, CALIBRATE] in adults with ADH1 is ongoing. CALIBRATE-PEDS is a Phase 2/3 study evaluating pharmacokinetics (PK), efficacy, and safety of encaleret in children with ADH1. Methods: Approximately 28 children (birth-18y) will be enrolled in 4 age cohorts sequentially, starting with the oldest cohort (12-18y). After 3-6 months of stable SoC/PTH treatment, eligible participants will enter Period 1, an inpatient stay lasting up to 6 days, for PK sampling and individualized dose titration. Period 2 follows, during which encaleret doses will be optimized to maintain target cCa while minimizing UCa over 20 outpatient weeks. Period 3 is a 4-week dose maintenance period, when the dose is intended to be fixed. Participants may then continue into a long-term extension period for safety monitoring and continued access to encaleret. PK data from Period 1 will be used to refine population-based PK modeling and inform dosage in younger cohorts. Results: The primary endpoint is the composite endpoint of a) cCa within 8.4 to 10.4 mg/dL in participants aged ≥ 1 year, and within 8.2 to 11.4 mg/dL in participants aged < 1 year and b) UCa <4 mg/kg/d in toilet-trained participants or spot ratio of UCa/UCr within the age-specific reference range in non-toilet-trained participants. Participants meeting both criteria at the end of Period 3 will be considered responders. Key secondary endpoints include safety and tolerability, mineral homeostasis, renal ultrasound, bone density, and self-reported outcomes. The statistical analyses will be descriptive; no statistical testing is planned. Conclusions: CALIBRATE-PEDS is the first pediatric study of encaleret. It is under development and is expected to be initiated globally in 2025. Presentation: Sunday, July 13, 2025

Jansen metaphyseal chondrodysplasia (JMC) is an ultra-rare disorder caused by constitutive activation of parathyroid hormone type 1 receptor (PTH1R). We sought to characterize the craniofacial phenotype of patients with the disease. Six patients with genetically confirmed JMC underwent comprehensive craniofacial phenotyping revealing a distinct facial appearance that prompted a cephalometric analysis demonstrating a pattern of mandibular retrognathia. Oral examination was notable for flat and shallow palate, delayed eruption pattern, and impacted maxillary teeth. Subclinical and/or mild hearing loss was noted in 4 of 5 patients studied. The most common etiology was conductive, likely due to overcrowding of epitympanum which impedes the normal vibration of ossicles to sound. Paranasal sinus obliteration was noted in 5 of 6 patients. Computed tomography (CT) scan evaluation of craniofacial bones revealed bilaterally symmetric expansile lesions with predominant involvement of neural crest cell (NCC)-derived bones. Bilateral narrowing of facial nerve canals, particularly at the labyrinthine segment, was seen in 5 of 6 patients when compared to age-matched controls; 1 patient presented with progressive facial nerve palsy. Sagittal suture craniosynostosis was present in 5 of 6 patients-one of whom had a history of cranial reconstruction for pansynostosis in infancy. All patients demonstrated a significant degree of upper airway stenosis, as well as a more anterior hyoid bone displacement. Two patients had a diagnosis of obstructive sleep apnea. 18F-NaF Positron-emission tomography (PET)-CT revealed increased uptake associated with the skull base and gnathic bones in all patients. In conclusion, this first detailed systematic evaluation of the craniofacial phenotype of patients with JMC demonstrates a distinct and pronounced phenotype that predominantly affects the NCC-derived cranial bones indicating a critical role of PTH1R signaling in their development. These affects can result in significant disease-related morbidity, include hearing loss, nerve compression, craniosynostosis, dentoskeletal malocclusion, and airway compromise; all of which require close monitoring. Patients with Jansen metaphyseal chondrodysplasia (JMC) have severely shortened long bones. However, the effect on craniofacial bones has not been studied. We evaluated 6 individuals with JMC and noted a distinct facial appearance prompting a detailed analysis which revealed a pattern of premature cranial suture fusion, retrusion of the lower jaw, increased distance between the inner corners of eyelids, and low set ears. Oral examination demonstrated a flattened palate, delayed eruption pattern, impacted maxillary teeth, and structural dental abnormalities. Analysis of skull using CT revealed that the facial bones and cranial base are predominantly affected. Hearing was affected in 4 of 5 patients tested likely due to bony growth in the middle ear interfering with normal sound conduction. Comparison with age-matched controls revealed narrowing of the facial nerve canal in 5 patients-one of whom developed progressive facial nerve paralysis. All patients had significant upper airway narrowing-2 were diagnosed with obstructive sleep apnea. In summary, patients with JMC have a distinct facial appearance associated with hearing loss, facial nerve palsy, premature fusion of skull bones, delayed eruption of teeth, and airway stenosis. Patients and physicians should be aware of these issues for appropriate monitoring and treatment.

Generalized arterial calcification of infancy (GACI) and autosomal recessive hypophosphatemic rickets type 2 (ARHR2) are age-related phenotypes of the rare genetic mineralization disorder, ENPP1 Deficiency, which evolve on a phenotypic continuum. To date, our understanding of the clinical spectrum of ENPP1 Deficiency is based on small studies or case reports, across which there is significant variability in clinical presentation, and limited duration of follow-up. From a previously published large retrospective natural history study, we performed a subgroup analysis to elucidate the most prevalent signs and symptoms of ENPP1 Deficiency diagnosed as GACI or ARHR2, to illustrate the onset and incidence of these complications over the lifetime, and to characterize the associated medical burden of disease. Of the 84 individuals with ENPP1 Deficiency analyzed, 51 had a recorded diagnosis of GACI, 11 were diagnosed with ARHR2, and 22 were diagnosed with both. We confirmed that those diagnosed with GACI presented predominantly with early-onset arterial calcification, respiratory distress, heart failure, and hypertension, necessitating acute inpatient care and leading to high (44%) infant mortality. Notably, we found that the majority (60.3%) of those with a history of GACI had prenatal ultrasound anomalies, including effusions, polyhydramnios, and hydrops fetalis. We estimated that 70% of individuals with ENPP1 Deficiency who survive to age 10 will have developed musculoskeletal complications, primarily rickets and/or osteomalacia. The clinical picture of ARHR2 in this study extended beyond skeletal deformities to include hearing impairment, joint involvement, and ongoing risk of cardiovascular problems. This study sheds light on the signs and symptoms of ENPP1 Deficiency in the real world, with implications for life-long patient monitoring.

Abstract Disclosure: F. Obiezu: None. K. Pan: None. A. Ninan: None. K.L. Roszko: None. L.S. Weinstein: None. C.R. Ferreira: None. R.I. Gafni: None. T. Magone De Quadros Costa: None. M.T. Collins: None. S. Jha: None. Jansen Metaphyseal Chondrodysplasia (JMC) is an ultra-rare disorder, with only 30 patients estimated to have the disease globally. It is caused by heterozygous pathogenic variants in PTHR1 that result in constitutive activation of parathyroid hormone type 1 receptor (PTHR1) signaling. A detailed description of craniofacial manifestations of the disease is lacking. Here we characterize the ophthalmological manifestations in patients with JMC. Six patients (4 males, 67%) with genetically confirmed JMC underwent a detailed ophthalmological evaluation, spectral-domain optical coherence tomography (OCT), craniofacial CT and 18F-NaF PET/CT scans. Median age at the time of the visit was 27.5 [IQR: 29] years. On physical examination, all patients were noted to have widely spaced eyes; 5 of the 6 had down slanted palpebral fissures, proptosis, or ptosis. Two patients had incomplete or defective closure of the eyelids (lagophthalmos), of which one had a history of progressive right facial nerve palsy with profuse epiphora. The second patient had central visual field defects, bilateral moderate optic disc pallor and bilateral retinal nerve fiber layer (RNFL) atrophy on OCT exam with bilateral optic canal narrowing on CT. Notably, comparison of these findings with a prior scan performed 5 years earlier showed progressive decrease in RNFL bilaterally. This patient had a history of prolonged intravenous bisphosphonate therapy, initiated in infancy for hypercalcemia and continued for over a decade. A third patient had normal vision, subtle temporal pallor of the optic nerve heads on dilated fundus exam, normal average RNFL, but decreased retinal ganglion cell layer analysis (GCA) on OCT. GCA was decreased in 4 of the 6 patients compared to age-matched reference range indicating a chronic optic nerve atrophic process. These data represent the first comprehensive report of the ophthalmologic findings in a cohort of patients with JMC. They demonstrate that patients with JMC have significant eye findings that appear to be more prevalent and pronounced with age. This suggests age-related, progressive optic neuropathy, which can be assessed by demonstrating OCT retinal GCA and RNFL loss and, may be a feature of JMC. The benefit and effect of long-term bisphosphonate therapy in patients with JMC remains unclear. Patients with JMC should undergo regular ophthalmologic examination including optic nerve OCT, visual field testing, and craniofacial imaging. Presentation: 6/1/2024

Jansen Metaphyseal Chondrodysplasia (JMC) is an ultra-rare disorder caused by germline heterozygous PTHR1 variants resulting in constitutive activation of parathyroid hormone type 1 receptor (PTHR1) with only 30 patients identified globally. A description of ocular manifestations of the disease is lacking. Six patients with JMC underwent a detailed ophthalmic evaluation, spectral-domain optical coherence tomography (OCT), visual field testing and craniofacial CT scans. Five of six patients had good visual acuity. All patients had widely spaced eyes; 5/6 had downslanted palpebral fissures. One patient had proptosis, and another had bilateral ptosis. Two patients had incomplete closure of the eyelids (lagophthalmos), one had a history of progressive right facial nerve palsy with profuse epiphora while the second had advanced optic nerve atrophy with corresponding retinal nerve fiber layer (RNFL) thinning on OCT and significant bilateral optic canal narrowing on CT scan. Additionally, this patient also had central visual field defects, and abnormal color vision. A third patient had normal visual acuity, subtle temporal pallor of the optic nerve head, normal average RNFL, but decreased temporal RNFL and retinal ganglion cell layer analysis (GCA) on OCT. GCA was decreased in 4/6 patients indicating a subclinical optic nerve atrophic process. None of the patients had glaucoma or high myopia. These data represent the first comprehensive report of ophthalmic findings in JMC. Patients with JMC have significant eye findings associated with optic canal narrowing due to extensive skull base dysplastic bone overgrowth that appear to be more prevalent and pronounced with age. Progressive optic neuropathy from optic canal narrowing may be a feature of JMC and OCT GCA can serve as a useful biomarker for progression in the setting of optic canal narrowing. We suggest that patients with JMC should undergo regular ophthalmic examination including color vision, OCT, visual field testing, orbital and craniofacial imaging.

Abstract Disclosure: A. Grover: None. C.R. Ferreira: None. R.I. Gafni: None. S. Jumani: None. M.T. Collins: None. K.L. Roszko: None. I.R. Hartley: None. Introduction: Diaphyseal medullary stenosis with malignant fibrous histiocytoma (DMS-MFH) is a rare autosomal dominant syndrome associated with pathologic fractures, myopathy, premature hair graying, and aggressive osteosarcomas. DMS-MFH has been linked to genetic variants in the methylthioadenosine phosphorylase (MTAP) gene, which encodes an enzyme in the methionine salvage and polyamine synthesis pathway. This pathway is implicated in other skeletal fragility disorders, such as Snyder-Robinson syndrome, suggesting a still undefined role of this pathway in bone biology. We describe a kindred with DMS-MFH and identify diagnostic challenges. Case: A 53-year-old perimenopausal woman presented with four fragility fractures over one year. Relevant history included premature hair graying, esophageal strictures, and nephrolithiasis. The patient’s bone formation markers were slightly elevated; bone resorption markers were within reference range. Her only osteoporosis risk factor was perimenopausal status. Bone series showed a diffuse heterogeneous appearance of the long bones with a mixed lytic/sclerotic appearance. DEXA scan revealed osteopenia. Family history was significant for 2 sons with aggressive osteosarcomas diagnosed in their late teens; one died at age 20. The other son is currently 39-years-old with recurrent osteosarcomas in three different limbs. The family also has a multigenerational history of severe bone fragility, muscle weakness, and premature hair graying. The patient, her living son, and his father underwent genome sequencing that identified a variant in MTAP (c.885A>G; p.(R295=)) in the patient and son. This variant was previously reported in three other families with DMS-MFH and has been shown to alter splicing. Notably, commercial genetic testing did not report this as a relevant variant, and diagnosis required independent analysis of the raw sequence data. Based on these findings, the patient and her son were diagnosed with DMS-MFH. Given the bone fragility with elevated bone turnover markers we treated the patient with yearly zoledronic acid infusions with no subsequent fractures. Surveillance for osteosarcoma is also being performed with annual whole-body MRI. Conclusion: DMS-MFH has been reported in only five families to date. The sixth family described here has clinical characteristics similar to the other kindreds. Due to high risk of aggressive osteosarcoma, timely diagnosis is imperative to decrease morbidity and mortality. Commercial genome sequencing may miss this diagnosis, so targeted genetic testing should be pursued. As more cases are identified, characterization of affected families may enhance our understanding of the natural history of the disease and guide surveillance and treatment strategies. Presentation: 6/2/2024

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Abstract Disclosure: I.R. Hartley: Research Investigator; Self; Calcilytix Therapeutics, Inc. R.I. Gafni: Research Investigator; Self; Calcilytix Therapeutics, Inc. K.L. Roszko: Research Investigator; Self; Calcilytix Therapeutics, Inc. X. Li: None. E.A. Ferguson: Research Investigator; Self; Calcilytix Therapeutics, Inc. C.A. Moore: Research Investigator; Self; Calcilytix Therapeutics, Inc. K.A. Pozo: Research Investigator; Self; Calcilytix Therapeutics, Inc. K.T. Ampuero: Research Investigator; Self; Calcilytix Therapeutics, Inc. A.V. Sridhar: Employee; Self; Calcilytix Therapeutics, Inc. A.S. Mathew: Employee; Self; Calcilytix Therapeutics, Inc. M. Roberts: Employee; Self; Calcilytix Therapeutics, Inc. S.H. Adler: Employee; Self; Calcilytix Therapeutics, Inc. E.F. Nemeth: Consulting Fee; Self; Calcilytix Therapeutics, Inc. M.T. Collins: Research Investigator; Self; Calcilytix Therapeutics, Inc. Parathyroid hormone (PTH) and the calcium-sensing receptor (CaSR) are the primary regulators of blood and urinary calcium. The independent contributions of PTH and the CaSR on renal calcium handling are not well understood, largely due to their intertwined physiology. In individuals with functioning parathyroid tissue, calcilytics (negative modulators of the CaSR) increase PTH secretion and decrease urinary calcium excretion, leading to increased blood calcium levels. We hypothesized that calcilytic administration to individuals with post-surgical hypoparathyroidism (PSH) may reveal the PTH-independent effects of CaSR modulation on renal calcium handling and clarify the potential therapeutic role of calcilytics in PSH. Four women (26-69y) with PSH enrolled in an ongoing, open-label, phase 2, proof-of-principle study of encaleret, an oral investigational calcilytic (NCT05735015). Encaleret 162 mg was administered every 12 hours for up to 10 doses. Calcitriol was discontinued one day prior to the first dose of encaleret. All participants received calcium supplementation initially. To maintain eucalcemia, 1 participant discontinued calcium supplementation and 3 required re-initiation of low-dose calcitriol (0.25 mcg daily). Results are presented as mean (range) of fasting baseline pre-dose levels compared to fasting levels 12 hours after the last dose of encaleret. Fractional excretion of calcium (FECa), a measure of renal calcium handling that quantifies the relationship between blood and urinary calcium, decreased by 52% (34-78). Albumin-corrected blood calcium increased from 8.4 mg/dL (range 8.1-8.6; nl 8.4-10.2) to 9.3 (8.6-10.7). Urinary calcium excretion decreased from 348 mg/day (range 204-501; nl <250) to 169 (76-350), with normalization in 3 participants and a 30% decrease in the fourth. Baseline PTH of 7.4 pg/mL (range 4.6-10.1; nl 15-65) transiently increased 30 minutes after the first dose to 13.0 (4.5-18.1), then returned to near baseline levels. Bone turnover markers were normal and did not change on encaleret. There were no serious adverse events reported. The only treatment-related adverse events (AEs) were mild hypercalcemia causing headache in 1 participant. Her blood calcium levels continued to be mildly elevated for 60 hours after the last dose of encaleret even after calcium and calcitriol supplementation was discontinued. Despite elevated blood calcium, her 24-hour urine calcium remained <200 mg/day. Encaleret reduced FECa in the first four participants with PSH, improving the relationship between blood and urinary calcium. These preliminary results from this Phase 2 study support continued evaluation of encaleret as an orally administered therapy for the treatment of patients with PSH. Presentation: 6/1/2024

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.

This chapter provides an overview of hypocalcemic conditions and the role of vitamin D in their etiology and therapy. Clinical manifestations of hypocalcemia are presented, and the physiologic consequences of acute and chronic hypocalcemia are described. Functional mechanisms maintaining circulating calcium within its narrow normal range are discussed in the context of regulation by the calciotropic hormones, parathyroid hormone (PTH), and vitamin D. The hypocalcemic disorders are classified by their functional etiologies and discussed in relationship to primary homeostatic disturbances including inadequate PTH secretion, resistance to PTH action, or PTH independence. The PTH-independent disorders focus on those conditions in which the availability, metabolic activation, or molecular action of vitamin D is compromised, as well as other clinical scenarios in which hypocalcemia may occur. Guidelines for the acute and long-term management of the hypocalcemic conditions are provided.

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare disorder caused by deficient FGF23 signaling and resultant ectopic calcification. Here, we systematically characterized and quantified macro- and micro-calcification in a HFTC cohort using CT and 18F-sodium fluoride PET/CT (18F-NaF PET/CT). Fourier-transform infrared (FTIR) spectroscopy was performed on 4 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 (eg, total calcific burden and lesion volume) and density (Hounsfield units) were quantified and compared to PET-based measures of mineralization activity (eg, mean standardized uptake values-SUVs). Microcalcification scores were calculated for the vasculature of 6 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 abdominal aorta, carotid, and coronaries in 50%, 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 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.