Burosumab and 1-25 (OH) Vitamin D on Human Osteoclasts

Study Overview
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Brief Summary
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Fibroblast growth factor 23 (FGF23) is the cornerstone of phosphate / calcium / vitamin D metabolism: it is synthesized mainly by osteocytes and acts as a Phosphating agent, inhibitor of dihydroxyvitamin D, and inhibitor of synthesis and secretion of Parathyroid hormone (PTH) in most tissues. The specific role of FGF23 on bone has yet to be demonstrated. In some diseases such as hypophosphatemic rickets (HR), the direct role of FGF23 on bone has not yet been studied to our knowledge, whereas these genetic hypophosphatemias are secondary to overexpression of FGF23, whether an activating mutation of FGF23 or inhibitory mutations of its inhibitors (Dentin matrix acidic phosphoprotein 1 (DMP1) and Phosphate-regulating neutral endopeptidase, X-linked (PHEX)). However, patients with X-linked hypophosphatemic rickets (XLH) have higher circulating FGF23 levels than healthy controls and these levels are higher in treated patients. Management of XLH consists primarily of correcting the native vitamin D defect by prescribing active vitamin D analogs as well as phosphate supplementation to improve bone mineralization and decrease dental complications, growth, and bone deformities. Recently, a new therapeutic option has been developed for XLH, burosumab, a human monoclonal antibody that binds and inhibits FGF23 activity. The use of burosumab is currently authorized in France in some pediatric patients with severe forms of XLH. Independently of the indirect bone effects of phosphate correction and vitamin D levels, the direct role of burosumab on bone cells has never been studied. The objective of this project is to study the osteoclastic biology of patients with HR compared to control patients, and to evaluate the direct impact of the treatments used in this pathology on human osteoclasts.

Official Title
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Effect of Burosumab and 1-25 (OH) Vitamin D on Human Osteoclasts From Patients With Hypophosphatemic Rickets (HR)

Conditions
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Hypophosphatemic Rickets

Intervention / Treatment
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* Other: blood sample


Participation Criteria
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Eligibility Criteria
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hypophosphatemic rickets patients: Inclusion Criteria: children from 2 yars-old to 18 years old and adults patients with HR followed in the center of calcium and phosphorus metabolism rare diseases in Lyon- Patients and parent / holder of parental authority who have been informed of the study and do not object to participate Exclusion Criteria: Patient being treated with oral corticosteroid or having received more than 3 months of corticosteroid treatment before surgery. Patients under tutorship or curatorship Pregnant and / or breastfeeding woman Patient deprived of liberty Controls patients: Inclusion Criteria: children from 2 years-old to 18 years old and adults patients with normal renal function (Schwartz glomerular filtration rate (GFR) >90 ml/min/1.73m²) Patients and parent / holder of parental authority who have been informed of the study and do not object to participate Exclusion Criteria: Patient being treated with oral corticosteroid or having received more than 3 months of corticosteroid treatment before surgery. Patients under tutorship or curatorship Pregnant and / or breastfeeding woman Patient deprived of liberty Patient treated with immunosuppressive drugs Patient with inflammatory disease

Ages Eligible for Study
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Minimum Age: 2 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| hypophosphatemic rickets patients<br>30 hypophosphatemic rickets patients older than 2 years will be included in this study | Other: blood sample<br>* 25 mL blood sample will be collected on citrate tubes for osteoclastic analysis.<br>|
| controls patients<br>10 controls patients from pediatric nephrology unit without hypophosphatemic rickets, older than 2 years will be included in this study | Other: blood sample<br>* 25 mL blood sample will be collected on citrate tubes for osteoclastic analysis.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| number of osteoclastic cells obtained after at the end of differentiation | The analysis of osteoclastic differentiation will be obtained from the bone cells from patients with burosumab and/or 1-25 (OH) vitamin D | 1 day |