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Objective: The aim of this study was to evaluate the effectiveness of burosumab therapy in children with X-Linked Hypophosphatemia (XLH)., Materials and Methods: We systematically reviewed literature from PubMed, Web of Science, The Cochrane Library, and Embase up until January 2024, using EndNote Web for study organization. The Newcastle-Ottawa scale guided quality assessment, while Revman software was used for data analysis and visualization. Study selection, quality evaluation, and data aggregation were independently performed by three researchers., Results: The meta-analysis encompassed ten studies, including eight cohort studies that examined burosumab's impact pre- and post-administration, and two randomized controlled trials comparing burosumab to standard therapy. The evidence from this review suggests burosumab's superiority in managing XLH in pediatric populations, particularly in improving key biochemical markers including 1,25-dihydroxyvitamin D (1,25-(OH) 2 D), phosphorus, and alkaline phosphatase (ALP), alongside improvements in the renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmP/GFR), and significant skeletal improvements as indicated by the rickets severity score (RSS) and the 6-minute walk test (6MWT). However, the long-term safety and effects, including height and quality of life (QOL) data, remains to be elucidated., Conclusions: Burosumab has shown significant therapeutic effectiveness in treating children with XLH, highlighting its potential as a key treatment option., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Wang, Zhang, Chen, Bai and He.)

Introduction: Hereditary Vitamin D-dependent rickets type II (HVDDR-type II) is a rare autosomal recessive disorder caused by molecular variation in the gene encoding the vitamin D receptor (VDR). This study aims to evaluate phenotype and genotype characteristics and long-term follow-up of the largest group of patients with (HVDDR-type II) in Saudi Arabia., Methodology: We conducted a retrospective chart review to collect the clinical, biochemical, and genetic data for all HVDDR-type II patients currently receiving treatment at King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia., Results: A total of 42 patients, 57.1% female, and 42.9% male were included in the study. Seven patients were treated with high doses of oral calcium, while 35 patients were treated with IV calcium infusion. The median age at presentation was 15.5 months. Alopecia was found in 97.6%, 21.4% presented with bowing legs, 14.3% with delayed walking, 9.5% with seizure, and 2.4% presented with respiratory failure, while a family history of the disease was positive in 71.4% of total patients. Molecular genetic testing of the VDR gene in our cohort identified six different gene variants c.885 C>A (p.Tyr295Ter), c.88 C>T (p.Arg30Ter), c.1036G>A (p.Val346Met), c.820C>T (p.Arg274Cys), c.803 T>C (p.Ile268Thr), and c.2T>G (p.Met1?)., Conclusion: We are describing the largest cohort of patients with HVDDR-type II, their clinical biochemical findings, and the most prevalent genetic variants in our population., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Alsagheir, Al-Ashwal, Binladen, Alhuthil, Joueidi, Ramzan and Imtiaz.)

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., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Brener, Cleper, Baruch, Rothschild, Yackobovitch-Gavan, Beer, Zeitlin and Kapusta.)

X-linked hypophosphatemia (XLH) is a rare, progressive, genetic disease with multisystem impact that typically begins to manifest in early childhood. Two treatment options exist: oral phosphate in combination with active vitamin D ("conventional therapy") and a fully human monoclonal anti-FGF23 antibody, burosumab. The clinical benefit of conventional therapy in adults is limited, and poor tolerance and complications are common. Burosumab was first approved as a treatment for XLH in 2018 and its disease-modifying benefits in clinical trials in children suggest burosumab treatment could also alter the disease course in adults. Without long-term clinical data on multiple XLH-related sequelae available, the results of an elicitation exercise are reported, in which eight global experts in XLH posited how long-term treatment with burosumab is anticipated to impact the life course of clinical sequelae in adults with XLH. Based on their clinical experiences, the available evidence and their disease understanding, the experts agreed that some long-term benefits of using burosumab are likely in adults with XLH even if they have a misaligned skeleton from childhood. Burosumab treatment is anticipated to reduce the incidence of fractures and halt the progression of clinical sequelae associated with conventional therapy. While the trajectories for established dental abscesses are not expected to improve with burosumab treatment, dental abscess development may be prevented. Starting treatment with burosumab in childhood to increase the likelihood of an aligned skeleton and continuation into and throughout adulthood to maintain euphosphatemia may optimize patient outcomes, although future real-world investigation is required to support this hypothesis., Competing Interests: LS has received honoraria and institutional grant support from Kyowa Kirin. MD has received honoraria and institutional grant support from Kyowa Kirin. KB has received honoraria, institutional grant support from Kyowa Kirin and participated in clinical trials with Ultragenyx and Kyowa Kirin. PF has received institutional grant support from Ultragenyx and honoraria as a consultant from Kyowa Kirin. MJ has received honoraria and institutional grant support from Kyowa Kirin and participated in clinical trials with Ultragenyx. LW has been a consultant to, and participated in clinical trials, with Ultragenyx funds to Dr Ward’s institution. NH is an employee of Visible Analytics, the company that was compensated for the elicitation exercise by Kyowa Kirin. RE is a former employee of Visible Analytics, the company that was compensated for the elicitation exercise by Kyowa Kirin. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. This study was sponsored by Kyowa Kirin International. The authors received no specific funding for this work., (Copyright © 2023 Seefried, Duplan, Briot, Collins, Evans, Florenzano, Hawkins, Javaid, Lachmann and Ward.)

Given the relatively recent introduction of burosumab in the management of X-linked hypophosphatemia (XLH), there is limited real-world data to guide its use in clinical practice. As a group of European physicians experienced with burosumab treatment in clinical practice, we convened with the objective of sharing these practice-based insights on the use of burosumab in children and adolescents with XLH. We attended two virtual meetings, then discussed key questions via Within3, a virtual online platform. Points of discussion related to patient selection criteria, burosumab starting dose, dose titration and treatment monitoring. Our discussions revealed that criteria for selecting children with XLH varied across Europe from all children above 1 year to only children with overt rickets despite conventional treatment being eligible. We initiated burosumab dosing according to guidance in the Summary of Product Characteristics, an international consensus statement from 2019 and local country guidelines. Dose titration was primarily guided by serum phosphate levels, with some centers also using the ratio of tubular maximum reabsorption of phosphate to glomerular filtration rate (TmP/GFR). We monitored response to burosumab treatment clinically (growth, deformities, bone pain and physical functioning), radiologically (rickets and deformities) and biochemically (serum phosphate, alkaline phosphatase, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, urine calcium-creatinine ratio and TmP/GFR). Key suggestions made by our group were initiation of burosumab treatment in children as early as possible, from the age of 1 year, particularly in those with profound rickets, and a need for clinical studies on continuation of burosumab throughout adolescence and into adulthood., Competing Interests: MZM, received honoraria from Kyowa Kirin International for attending advisory boards and for educational lectures/webinars. GIB, received honoraria from Kyowa Kirin International for attending advisory boards and webinars. CdLC, received honoraria from Kyowa Kirin International for attending advisory boards and for educational lectures. AL, an investigator for clinical trials for Kyowa Kirin International and has received research grant support from Kyowa Kirin International. AM, received an honorarium from Kyowa Kirin International for participation in the Expert Practice Exchange meeting. AR, received honoraria from Kyowa Kirin International for consultancy and for lectures. FS, received honoraria from Kyowa Kirin International for teaching activities and scientific consultancy. DS, received honoraria from Kyowa Kirin Germany for scientific consultancy. NS, received an honorarium from Kyowa Kirin International for participation in the Expert Practice Exchange meeting. ON, received honoraria from Kyowa Kirin International for attending advisory boards and for educational lectures/webinars, as well as speakers’ honoraria from Abbott and Biomarin. The authors declare that this study received funding from Kyowa Kirin International. The funder had a role in organising meetings upon which this manuscript is based. The medical writing support was also funded by Kyowa Kirin International., (Copyright © 2023 Mughal, Baroncelli, de Lucas-Collantes, Linglart, Magnolato, Raimann, Santos, Schnabel, Shaw and Nilsson.)

Introduction: X-linked hypophosphatemia (XLH) is the most prevalent type of heritable fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets. Recently, anti-FGF23 antibody, burosumab, has become clinically available. We herein report a patient with adult XLH and tertiary hyperparathyroidism., Case Presentation: The serum phosphate level and tubular maximum reabsorption of phosphate per glomerular filtration rate (TmP/GFR) remained low, despite burosumab treatment. While the influence of the relationship between FGF23 and parathyroid hormone (PTH) on the phosphaturic effect is unclear, it was considered that a high level of PTH due to tertiary hyperparathyroidism remains to suppress renal phosphate reabsorption. A calcimimetic, evocalcet, increased the serum phosphate level and TmP/GFR., Discussion and Conclusion: Therefore, it is important to evaluate the presence of secondary-tertiary hyperparathyroidism in patients whose serum phosphate level does not increase with burosumab treatment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Takashi, Toyokawa, Oda, Muta, Yokomizo, Fukumoto and Kawanami.)

An inactivating PHEX gene mutation with the resultant accumulation of several mineralization-inhibiting proteins (e.g., FGF23) causes skeletal and dental morbidity in X-linked hypophosphatemia (XLH). This prospective case-control study explored the effect of burosumab, an anti-FGF23 antibody, on dental health of children with XLH. Ten children (age 4.3-15 years) with XLH underwent burosumab treatment per protocol. Assessment of their dental status at treatment initiation and after 1 and 3 years of treatment included clinical, laboratory and radiographic evaluation of rickets and dentition. Orthopantomographic examinations of ten healthy sex- and age-matched controls were selected for comparison. Coronal and pulp dimensions of a selected permanent mandibular molar were measured with Planmeca Romexis ® software. One year of treatment led to improvement of height z-score ( p =0.019) and healing of the rickets ( p <0.001) in the XLH patients, and those achievements were maintained after three years of treatment. Dental morphology of XLH patients, distinguished by increased pulp-coronal ratios compared to controls ( p =0.002), remained larger after the first year of treatment ( p <0.001) and did not attain the decrease expected with age after three years of treatment. Five patients had a history of recurrent dental abscesses, with three having undergone at least one episode during the year before burosumab initiation. One patient sustained recurrent abscesses throughout three years of treatment. The persistence of the unique dental morphology of XLH patients undergoing burosumab therapy, as evidenced by excessively larger pulp dimensions, supports the role of other PHEX gene-related local mineralization inhibitors, such as osteopontin, in the pathogenesis of dental morbidity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Brener, Zeitlin, Lebenthal and Brener.)

Background: Vitamin D-dependant rickets type 1A (VDDR1A) is a rare autosomal recessive disorder caused by pathogenic variants in the CYP27B1 gene. This gene is essential for vitamin D activation. Although VDDR1A is a rare condition worldwide, its prevalence is high in the Saguenay-Lac-Saint-Jean (SLSJ) region due to a founder effect. Daily intake of calcitriol before the onset of clinical manifestations can prevent them in affected children., Methods: A genetic screening test was developed and validated for the CYP27B1 gene c.262del pathogenic variant. Newborn screening was implemented in the SLSJ region for this variant, and the feasibility and acceptability were assessed. Sixteen medical records of children affected with VDDR1A were reviewed to document the consequences of the disease at diagnosis., Results: A total of 2000 newborns were tested for VDDR1A. Most families (96.5%) accepted the genetic test. We found a carrier rate of 1/29 for the c.262delG variant in our cohort, which is suggestive of a founder effect. We identified one child affected with VDDR1A and treatment was initiated before the onset of clinical manifestations. On average, children with VDDR1A were diagnosed at 13.8 ± 5 months of age, they had a significant failure to thrive at diagnosis, among other harmful health consequences., Conclusion: Our study showed that in our population, the newborn genetic screening program is safe and feasible, it has high acceptability, and it is efficient to identify affected children. VDDR1A health consequences can be prevented by early initiation of treatment. Therefore, screening programs should be available for populations where it is deemed as beneficial from a public health perspective., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Fortin, Girard, Bonenfant, Leblanc, Cruz-Marino, Blackburn, Desmeules and Bouchard.)

Background: Gait deviations, lower limb pain and joint stiffness represent key symptoms in patients with X-linked hypophosphatemia (XLH, OMIM 307800), a rare disorder of mineral homeostasis. While the pathomechanism for rickets is well understood, the direct role of PHEX (Phosphate-regulating neutral endopeptidase) deficiency in non-rachitic features including complex deformities, skull and dental affections remains unclear. FGF23-inhibiting antibody treatment can normalize serum phosphate levels and to improve rickets in XLH patients. However, linear growth remains impaired and effects on lower limb deformity and gait are insufficiently studied., Aims: To characterize and evaluate the course of lower limb deformity in a case series of pediatric XLH patients receiving Burosumab therapy., Methods: Comparative assessment of planar radiographs, gait analysis, biochemical and clinical features of pediatric patients before and ≥12 months after initiation of FGF23-inhibiting was performed prospectively. Lower limb maltorsion was quantified by torsional MRI and gait analysis. Standardized deformity analysis of lower limb anteroposterior radiographs was conducted., Results: Seven patients (age 9.0 +/-3.6 years) were eligible for this study. All patients received conventional treatment before onset of antibody treatment. Maltorsion of the femur was observed in 8/14 legs using torsional MRI (mean antetorsion 8.79°). Maltorsion of the tibia was observed in 9/14 legs (mean external torsion 2.8°). Gait analysis confirmed MRI findings with femoral external malrotation prior to and one year after onset of Burosumab therapy. Internal foot progression (intoeing gait) remained pathological in all cases (mean 2.2°). Knee rotation was pathologically internal 10/14 legs. Mean mechanical axis deviation (MAD) of 16.1mm prior to Burosumab changed in average by 3.9mm. Three children underwent guided growth procedures within the observation period. Mild postprocedural rebound of frontal axis deviation was observed under Burosumab treatment in one patient., Conclusions: This is the first study to investigate lower limb deformity parameters quantitatively in children with XLH receiving Burosumab. One year of Burosumab therapy was associated with persistent maltorsion and frontal axis deviation (varus/valgus) despite improved rickets in this small, prospective uncontrolled study., Competing Interests: AR and GM received non-related honoraria from Kyowa Kirin for consultancy and scientific presentations. RG and CR received non-related honoraria from Nuvasive Inc. and Smith and Nephew for consultancy. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be constructed as a potential conflict of interest., (Copyright © 2022 Mindler, Stauffer, Kranzl, Penzkofer, Ganger, Radler, Haeusler and Raimann.)

Burosumab (KRN23) is an FGF23 neutralizing antibody that has been the subject of several recent clinical trials principally focused on the treatment of hypophosphatemic rickets in patients with X-linked hypophosphatemia (XLH). Since the first publications in 2014, these trials have demonstrated efficacy with minimal safety concerns in both adult and pediatric cohorts. These studies have used dose-escalation to establish a dosing regimen that is well-tolerated in clinical use. This review summarizes the clinical trial data with respect to burosumab treatment in adults and children as well as noting several clinical trials currently underway. While burosumab appears transformative for the treatment of XLH, long term follow-up studies would be required to allay concerns over the potential for nephrocalcinosis and cardiac calcification. While these do not appear to be problematic in current trials, the effects of chronic or lifelong treatment have yet to be established., (Copyright © 2020 Schindeler, Biggin and Munns.)