Mirko Rehberg

Burosumab is effective in improving rickets in children with X-linked hypophosphatemia (XLH). Predictors of health-related quality of life (HRQoL) in pediatric XLH patients treated with burosumab are unknown. In this cross-sectional analysis of a prospective binational observational study, we investigated HRQoL in 64 pediatric XLH patients (36 female) on burosumab treatment, using the KIDSCREEN-52 questionnaire and qualitative interviews. Associations between HRQoL and clinical findings were analysed using multiple regression and receiver operating characteristics (ROC) curve analyses. Median age at investigation and duration of burosumab treatment were 13.1 (IQR 10.4; 14.8) and 2.8 (IQR 1.4; 3.8) years, respectively; 54.7% of patients received secondary burosumab treatment following prior active vitamin D and phosphate. Overall, HRQoL scores were comparable to national reference values. Caregivers rated Physical Well-Being, Moods & Emotions, and Bullying lower than the patients themselves. Burosumab dose was significantly associated with Physical Well-Being, Psychological Well-Being, and Self-Perception in self-report, and with total T-values and Physical Well-Being in proxy questionnaires. The duration of prior treatment with active vitamin D and phosphate was significantly associated with the dimension of Autonomy in self-report and proxy reports. A burosumab dosage above 0.6 mg/kg was associated with a good Physical Well-Being (above the mean of the general population) with a sensitivity and specificity of 75% and 70% in self-report, and 67% and 70% in proxy questionnaires, respectively. In this real-world study, HRQoL in burosumab-treated children with XLH was comparable to that of the general population and associated with burosumab dosage.

Burosumab is effective for treatment of rickets in children with X-linked hypophosphatemia (XLH). The effects of burosumab on markers and regulators of osteoblast and osteoclast activity are largely unknown. In this cross-sectional observational study, we investigated 7 key markers and regulators of osteoblast and osteoclast activity in 107 burosumab-treated children with XLH. We calculated z-scores for bone-specific alkaline phosphatase (BAP), procollagen-1-N-terminal propeptide (P1NP), carboxy-terminal telopeptide of type 1 collagen (CTX), tartrate-resistant acid phosphatase type 5b (TRAP5b), soluble RANKL (sRANKL), osteoprotegerin (OPG), and sclerostin. The median age at investigation and duration of burosumab treatment were 10.7 and 2.2 yr, respectively, with 18.7% of patients on primary burosumab treatment and 81.3% with prior treatment with phosphate and active vitamin D. Height and BMI improved by approximately 0.3 z-score from baseline with burosumab treatment, and serum phosphate, 1,25-dihydroxyvitamin D, and alkaline phosphatase improved by 2 z-scores (each p < .01 vs prior burosumab), but phosphate (−1.8 z-score) and calcium (−0.65 z-score) remained reduced (each p < .001 vs age and sex-specific reference values). The z-scores for osteoblast (BAP, P1NP) and osteoclast (CTX, TRAP5b) activity markers and for the osteoblast suppressor sclerostin were increased (each p < .001). Standardized sRANKL was reduced (p < .05), while the RANKL inhibitor OPG was increased resulting in a reduced sRANKL/OPG ratio (each p < .001). Multivariate analysis revealed significant associations between serum sclerostin and serum phosphate (negative), serum calcium and vitamin D sufficiency (positive), and primary burosumab treatment with BAP (negative). In this real-world setting, pediatric XLH patients receiving burosumab treatment showed persisting mild hypophosphatemia and increased markers of osteoblast and osteoclast activity despite negative counter-regulation of osteoblasts by sclerostin and osteoclasts by OPG/RANKL. Our data suggest a more pronounced normalization osteoblast activity when children are primarily treated with burosumab and underscore the need for adequate vitamin D supplementation.

While Research Electronic Data Capture (REDCap) is widely adopted in rare disease research, its unconstrained data format often lacks native interoperability with global health standards, limiting secondary use. We developed RareLink , an open-source framework implementing our published ontology-based rare disease common data model. It enables standardised data exchange between REDCap, international registries, and downstream analysis tools by linking Global Alliance for Genomics and Health Phenopackets and Health Level 7 Fast Healthcare Interoperability Resources (FHIR) instances conforming to International Patient Summary and Genomics Reporting profiles. RareLink was developed in three phases across Germany, Canada, South Africa, and Japan for registry and data analysis purposes. We defined a simulated Kabuki syndrome cohort and demonstrated data export to Phenopackets and FHIR. RareLink can enhance the clinical utility of REDCap through its global applicability, supporting equitable rare disease research. Broader adoption and coordination with international entities are thus essential to realise its full potential.

Osteogenesis imperfecta (OI) is a rare genetic disorder predominantly resulting from mutations in COL1A1 and COL1A2. Denosumab, a monoclonal antibody targeting RANKL, inhibits osteoclast differentiation and activation, thereby preventing bone resorption. Despite its efficacy as an anti-resorptive therapy, concerns of rebound hypercalcemia limit its clinical use. This investigation was part of the multicenter trial NCT02352753, which was terminated early due to calcium-related adverse events. We implemented a sub-study to investigate dynamics of bone resorption markers and calcium, and the precise timepoint of rebound during denosumab therapy in OI patients. About 40 participants between 2 and 16 yr received subcutaneous denosumab (1 mg/kgBW) every 6 mo for 3 yr. Calcium supplementation was started on the day of denosumab injection. Spot urine samples were collected at weeks 2, 8, 12, 16, 18, 20, and 22 post-injection in every treatment cycle to measure urinary bone resorption markers (n-terminal telopeptide [NTX] and deoxypyridinoline [DPD]), calcium and creatinine. Calcium supplementation was ended when urinary Ca/Creatinine ratios reached age-specific thresholds. Denosumab effectively suppressed bone resorption within the first 2 mo post-injection. However, after 8 wk, uNTX and DPD levels re-increased again, reaching baseline levels after 3 mo, followed by a mild rebound after 4 mo. Average duration of Ca supplementation was 10 wk, two patients developed mild nephrocalcinosis. In conclusion, we saw that rebound of bone resorption emerges as early as 4 mo after denosumab injection. Continuous monitoring of calcium levels and careful handling of calcium supplementation is mandatory during therapy, but Ca-related side effects can still occur.

Summary: While Research Electronic Data Capture (REDCap) has been widely adopted in rare disease research, its unconstrained data format often leads to implementations that lack native interoperability with global health data standards, limiting secondary data use. To address this, we developed and validated RareLink , an open-source framework implementing our previously-published ontology-based rare disease common data model, enabling standardised data exchange between REDCap, international registries, and downstream analysis tools. Its preconfigured pipelines interact with the local REDCap application programming interface and enable semi-automatic import or export of data to the Global Alliance for Genomics and Health (GA4GH) Phenopackets and Health Level 7 (HL7) Fast Healthcare Interoperability Resources (FHIR) instances, conforming to the HL7 International Patient Summary and Genomics Reporting profiles. The framework was developed in three iterative phases using retrospective and prospective clinical data from patients with various rare metabolic and neuromuscular disorders, as well as inborn errors of immunity. Phase one involved deployment across four German university hospitals for registry and data analysis purposes. Phase two integrated RareLink with the Canadian Inborn Errors of Immunity National Registry, enhancing extensibility. Phase three focuses on international implementation in South Africa and Japan to assess global scalability. Implementation feedback was continuously incorporated to validate outputs and improve usability. For evaluation purposes, we defined a simulated Kabuki syndrome cohort based on published cases and demonstrated data export to both Phenopackets and FHIR instances. RareLink can enhance the clinical utility of REDCap by enabling structured data analysis and interoperability. Its global applicability and open-source nature can support equitable rare disease research with the ultimate goal to improve patient care. Broader adoption and coordination with entities such as HL7 and the European Reference Networks are thus essential to realise its full potential. The framework and its documentation are freely available through GitHub and Read the Docs , respectively.

Context: Vosoritide is the first approved targeted therapy for achondroplasia (ACH) based on increased annualized growth velocity in clinical trials. The aim of our project was an assessment of the real-world setting and treatment with vosoritide. Design: This was a 12-month, retrospective observational study on an inception cohort of 34 patients with ACH treated with vosoritide. Patients and Methods: Thirty-four patients with ACH (22 males; aged 2.8 to 15.3 years at treatment initiation) who received vosoritide treatment for at least 12 months at a specialized clinic for skeletal dysplasia in childhood were included in the analysis. Auxological measurements at baseline and after 12 months of therapy were converted into disease-specific (ACH) and general population [Centers for Disease Control and Prevention (CDC)] z-scores. Physical function assessed by a 6-minute walk test was converted into z-scores and compared to an unaffected reference cohort. Results: After 12 months of treatment, both ACH and CDC height z-scores showed significant increases, with mean changes (mean ± SD) of 0.52 ± 0.35 and 0.38 ± 0.44, respectively (both P < .0001). The annualized growth velocity exceeded reference values for untreated children with ACH. No significant changes were observed in body mass index, upper to lower body segment ratio (sitting height/height), or head circumference. The 6-minute walking distance improved, with z-scores increasing from −2.00 ± 1.12 to −1.39 ± 1.23 (P = .0215). Conclusion: In a real-world setting, children with ACH showed significant improvements in growth and physical function after 12 months of treatment with vosoritide.

The formation of functional bone requires a delicate interplay between osteogenesis and osteolysis. Disturbances in this subtle balance result in an increased risk for fractures. Besides its mechanical function, bone tissue represents a key player in the regulation of calcium homeostasis. Impaired bone formation results in bone fragility, which is especially pronounced in osteogenesis imperfecta (OI). This rare genetic disorder is characterized by frequent fractures as well as extraskeletal manifestations. The current classification of OI includes 23 distinct types. In recent years, several new mutations in different genes have been identified, although the exact pathomechanisms leading to the clinical presentation of OI often remain unclear. While bisphosphonates are still the standard of care, novel therapeutic approaches are emerging. Especially, targeted antibody therapies, originally developed for osteoporosis, are increasingly being investigated in children with OI and represent a promising approach to alleviate the consequences of impaired osteogenesis and improve quality of life in OI patients. This review aims to provide insight into the pathophysiology of OI and the consequences of distinct disease-causing mutations affecting the regulation of bone homeostasis. In this context, we describe the four most recently identified OI-causing genes and provide an update on current approaches for diagnosis and treatment.

Background: X-linked hypophosphatemia (XLH) is a rare inherited phosphate-wasting disorder associated with bone and dental complications. Health-related quality of life (HRQoL) is reduced in XLH patients on conventional treatment with phosphate supplements and active vitamin D, while information on patients treated with burosumab is rare. Methods: HRQoL was assessed in 63 pediatric XLH patients participating in a prospective, observational study and patient registry in Germany using the KIDSCREEN-52 survey instrument and standardized qualitative interviews. Results: The median age of the XLH patients was 13.2 years (interquartile range 10.6 – 14.6). At the time of the survey, 55 (87%) patients received burosumab and 8 (13%) conventional treatment. Forty-six patients (84%) currently being treated with burosumab previously received conventional treatment. Overall, HRQoL was average compared to German reference values (mean ± SD: self-report, 53.36 ± 6.47; caregivers’ proxy, 51.33 ± 7.15) and even slightly above average in some dimensions, including physical, mental, and social well-being. In general, XLH patients rated their own HRQoL higher than their caregivers. In qualitative interviews, patients and caregivers reported that, compared with conventional therapy, treatment with burosumab reduced stress, bone pain, and fatigue, improved physical health, and increased social acceptance by peers and the school environment. Conclusions: In this real-world study in pediatric XLH patients, HRQoL was average or even slightly above that of the general population, likely due to the fact that the vast majority of patients had their treatment modality switched from conventional treatment to burosumab resulting in improved physical health and well-being. Graphical

Osteogenesis imperfecta (OI) is a hereditary skeletal disorder primarily affecting collagen type I structure and function, causing bone fragility and occasionally versatile extraskeletal symptoms. This study expands the spectrum of OI-causing TAPT1 mutations and links extracellular matrix changes to signaling regulation.

Context: Burosumab has been approved for the treatment of children and adults with X-linked hypophosphatemia (XLH). Real-world data and evidence for its efficacy in adolescents are lacking. Objective: To assess the effects of 12 months of burosumab treatment on mineral metabolism in children (aged <12 years) and adolescents (aged 12-18 years) with XLH. Design: Prospective national registry. Setting: Hospital clinics. Patients: A total of 93 patients with XLH (65 children, 28 adolescents). Main Outcome Measures: Z scores for serum phosphate, alkaline phosphatase (ALP), and renal tubular reabsorption of phosphate per glomerular filtration rate (TmP/GFR) at 12 months. Results: At baseline, patients showed hypophosphatemia (−4.4 SD), reduced TmP/GFR (−6.5 SD), and elevated ALP (2.7 SD, each P < .001 vs healthy children) irrespective of age, suggesting active rickets despite prior therapy with oral phosphate and active vitamin D in 88% of patients. Burosumab treatment resulted in comparable increases in serum phosphate and TmP/GFR in children and adolescents with XLH and a steady decline in serum ALP (each P < .001 vs baseline). At 12 months, serum phosphate, TmP/GFR, and ALP levels were within the age-related normal range in approximately 42%, 27%, and 80% of patients in both groups, respectively, with a lower, weight-based final burosumab dose in adolescents compared with children (0.72 vs 1.06 mg/kg, P < .01). Conclusions: In this real-world setting, 12 months of burosumab treatment was equally effective in normalizing serum ALP in adolescents and children, despite persistent mild hypophosphatemia in one-half of patients, suggesting that complete normalization of serum phosphate is not mandatory for substantial improvement of rickets in these patients. Adolescents appear to require lower weight-based burosumab dosage than children.