Project description:Although relatively uncommon individually, the various causes of hypophosphataemic rickets have provided an impetus for unravelling the mechanisms of phosphate homeostasis and bone mineralisation. Over the past 10 years, considerable advances have been made in establishing the gene mutations responsible for a number of the inherited causes and in understanding the mechanisms responsible for tumour-induced osteomalacia/rickets. The most exciting aspects of these discoveries have been the discovery of a whole new class of hormones or phosphatonins which are thought to control phosphate homoeostasis and 1 alpha-hydroxylase activity in the kidney, through a bone-kidney-intestinal tract axis. Although our understanding of the interrelationships is far from complete, it raises the possibilities of improved therapeutic agents in the long-term, and has resulted in improved diagnostic abilities in the short-term.
Project description:Three siblings, aged 12, 4 and 2 years, presented at a Gambian clinic with bone deformities. Radiographs of knees and wrists confirmed the presence of florid rickets. The family (including 2 unaffected siblings and the mother) were investigated for hereditary rickets. The three affected siblings had biochemical features of hereditary hypophosphataemic rickets with hypercalciuria (HHRH) with normal plasma calcium and 25-hydroxyvitamin D concentrations, elevated 1,25-dihydroxyvitamin D, hypophosphataemia, hyperphosphaturia and hypercalciuria. At presentation, two of the three affected siblings had an elevated fibroblast growth factor-23 (FGF23) concentration. The mother and clinically unaffected siblings had largely normal biochemistry. Genetic analysis of the SLC34A3 gene, encoding the type IIc sodium-phosphate cotransporter, in DNA samples from the siblings and their mother was conducted. Three single nucleotide polymorphisms (SNPs) S168F, E513V and L599L were identified. E513V and L599L had been previously identified as benign polymorphisms. S168F however, is a previously unreported variant. In silico mutation evaluation predicted that the S168F mutation causes changes in the protein product which are damaging to its function. In addition, the three clinically affected siblings were homozygous in the S168F variant whereas the unaffected family members were carriers. This study describes a biochemical profile and complementary gene data consistent with a rare genetic hypophosphataemic rickets disease in a family from rural Gambia. To our knowledge, this study reports the first cases of HHRH in Africa and describes a novel causal mutation within the SLC34A3 gene.
Project description:Pathogenic variants in the PHEX gene cause rare and severe X-linked dominant hypophosphataemia (XLH), a form of heritable hypophosphatemic rickets (HR) characterized by renal phosphate wasting and elevated fibroblast growth factor 23 (FGF23) levels. Burosumab, the approved human monoclonal anti-FGF23 antibody, is the treatment of choice for XLH. The genetic and phenotypic heterogeneity of HR often delays XLH diagnoses, with critical effects on disease course and therapy. We herein report the clinical and genetic features of two Italian female infants with sporadic HR who successfully responded to burosumab. Their diagnoses were based on clinical and laboratory findings and physical examinations. Next-generation sequencing (NGS) of the genes associated with inherited HR and multiple ligation probe amplification (MLPA) analysis of the PHEX and FGF23 genes were performed. While a conventional analysis of the NGS data did not reveal pathogenic or likely pathogenic small nucleotide variants (SNVs) in the known HR-related genes, a quantitative analysis identified two different heterozygous de novo large intragenic deletions in PHEX, and this was confirmed by MLPA. Our molecular data indicated that deletions in the PHEX gene can be the cause of a significant fraction of XLH; hence, their presence should be evaluated in SNV-negative female patients. Our patients successfully responded to burosumab, demonstrating the efficacy of this drug in the treatment of XLH. In conclusion, the execution of a phenotype-oriented genetic test, guided by known types of variants, including the rarest ones, was crucial to reach the definitive diagnoses and ensure our patients of long-term therapy administration.
Project description:ObjectivesX-linked hypophosphataemic rickets (XLHR) is a disease of impaired bone mineralization characterized by hypophosphataemia caused by renal phosphate wasting. The main clinical manifestations of the disorder are O-shaped legs, X-shaped legs, delayed growth, and bone pain. XLHR is the most common inheritable form of rickets, with an incidence of 1/20 000 in humans. It accounts for approximately 80% of familial cases of hypophosphataemia and serves as the prototype of defective tubular phosphate (PO43+) transport, due to extra renal defects resulting in unregulated FGF23 activity. XLHR is caused by loss-of-function mutations in the PHEX gene. The aim of this research was to identify the genetic defect responsible for familial hypophosphataemic rickets in a four-generation Chinese Han pedigree and to analyze the function of this mutation.MethodsThe genome DNA samples of all members in the pedigree were extracted from whole blood. We sequenced all exons of the PHEX and FGF23 genes, as well as the adjacent splice site sequence with Sanger sequencing. Next, we analyzed the de novo mutation c.1692 del A of the PHEX gene with an online digital service and investigated the mutant PHEX with SWISS-MODEL, immunofluorescence, and protein stability detection.ResultsThrough Sanger sequencing, we found a de novo mutation, c.1692 del A, in exon 16 of the PHEX gene in this pedigree. This mutation can make the PHEX protein become unstable and decay rapidly, which results in familial XLHR.ConclusionWe have found a de novo loss-of-function mutation, c.1692 del A, in exon 16 of the PHEX gene that can cause XLHR.Cite this article: J. Huang, X. Bao, W. Xia, L. Zhu, J. Zhang, J. Ma, N. Jiang, J. Yang, Q. Chen, T. Jing, J. Liu, D. Ma, G. Xu. Functional analysis of a de novo mutation c.1692 del A of the PHEX gene in a Chinese family with X-linked hypophosphataemic rickets. Bone Joint Res 2019;8:405-413. DOI: 10.1302/2046-3758.88.BJR-2018-0276.R1.
Project description:Background/aimDespite optimal conventional treatment (oral phosphate supplements and active vitamin D analogs), about 40-50% of children with well-controlled X-linked hypophosphatemia (XLH) show linear growth failure, making them less likely to achieve an acceptable final height. Here, we studied the hypothesis that rhGH treatment improves final height in children with XLH and growth failure.MethodsTwo cohorts of children with XLH were included in this retrospective longitudinal analysis: (1) a cohort treated with rhGH for short stature (n = 34) and (2) a cohort not treated with rhGH (n = 29). The mean duration of rhGH treatment was 4.4 ± 2.9 years. We collected the auxological parameters at various time points during follow-up until final height.ResultsIn rhGH-treated children, 2 years of rhGH therapy was associated with a significant increase in height from - 2.4 ± 0.9 to - 1.5 ± 0.7 SDS (p < 0.001). Their mean height at rhGH discontinuation was - 1.2 ± 0.9 SDS and at final height was - 1.3 ± 0.9 SDS corresponding to 165.5 ± 6.4 cm in boys and 155.5 ± 6.3 cm in girls. Notably, the two groups had similar final heights; i.e., the final height in children not treated with rhGH being - 1.2 ± 1.1 SDS (165.4 ± 6.8 cm in boys and 153.7 ± 7.8 cm in girls), p = 0.7.ConclusionTreatment with rhGH permits to improve final height in children with XLH and growth failure, despite optimal conventional treatment. We propose therefore that rhGH therapy could be considered as an option for short stature in the context of XLH.
Project description:PurposeThe aim was to evaluate the measurement properties of the Growth Hormone Deficiency-Child Treatment Burden Measure-Child (GHD-CTB-Child), a patient-reported outcome (PRO) for children aged 9 to < 13 years; the Growth Hormone Deficiency-Child Treatment Burden Measure-Observer (GHD-CTB-Observer), an observer-reported outcome (ObsRO) version completed by parents/guardians of children with growth hormone deficiency (GHD) aged 4 to < 9 years; and the Growth Hormone Deficiency-Parent Treatment Burden Measure (GHD-PTB), a PRO that assesses the treatment burden of parents/guardians living with children with GHD aged 4 to < 13 years.MethodsA non-interventional, multi-center, clinic-based study across 30 private practice and large institutional sites in the United States and the United Kingdom was conducted. The sample consisted of 145 pre-pubertal children aged 9 to < 13 years at enrollment with a physician confirmed GHD diagnosis as well as 98 parents/guardians of pre-pubertal younger children aged 4 to < 9 years at enrollment with a physician confirmed GHD diagnosis. The child sample consisted of 59 treatment-naïve children (no prior exposure to growth hormone [GH] therapy; were starting GH treatment at study start per standard of care) and 184 children already maintained on treatment for at least 6 months. At baseline, all study participants completed a paper validation battery including all measures needed to conduct the validation analyses. Follow-up assessments with children in the maintenance group and their caregiver/parent were conducted approximately 2 weeks post-baseline to evaluate test-retest reproducibility. To evaluate sensitivity to change and meaningful change thresholds, treatment-naïve participants in both child and parent/guardian populations were assessed within 1 week of report of minimal improvement between week 3 and week 11 and at week 12. Psychometric analyses were implemented following an a priori statistical analysis plan.ResultsFactor analyses confirmed the a priori conceptual domains and Overall score for each measure (GHD-CTB-Child and GHD-CTB-Observer domains: Physical, Emotional Well-being, and Interference; GHD-PTB domains: Emotional Well-being and Interference). Internal consistency was acceptable for all measures (Cronbach's alpha > 0.70). Test-retest reliability was acceptable for the Physical, Emotional, and Overall domains of the GHD-CTB versions, and the Emotional and Overall domains of the GHD-PTB (intraclass correlation coefficient above 0.70). All but one of the convergent validity hypotheses for the GHD-CTB versions and all hypotheses for the GHD-PTB were proven (r > 0.40). Known-groups validity hypotheses were significant for length of time to administer the injections in the GHD-CTB versions (p < 0.001 for Physical, Emotional, and Overall, and p < 0.01 for Interference) and whether parents/guardians versus child gave the injections more often for the Emotional domain of the GHD-PTB (p < 0.05). Associated effect sizes ranged from -0.27 to -0.57 for GHD-CTB versions and from -0.74 to -0.69 for the GHD-PTB, indicating that the measures are sensitive to change. Anchor-based patient and parent/guardian ratings of severity suggest preliminary meaningful change thresholds (GHD-CTB: 6 points for Physical score, 9 for Emotional, and 6 for Interference; GHD-PTB: 10 points for Emotional and 6 for Interference scores).ConclusionsThe psychometric properties of the GHD-CTB-Child, GHD-CTB-Observer, and GHD-PTB support the validity of their use as PRO and ObsRO measures to capture the experiences associated with treatment burden for children with GHD and their parents/guardians in both clinical and research settings. The Clinicaltrials.gov registration number NCT02580032 was first posted October 20, 2015.
Project description:Raine Syndrome (RS) also referred to as lethal osteosclerotic bone dysplasia describes an exceptionally rare autosomal recessive disorder with an estimated prevalence of <1 in 1,000,000. Endocrinological manifestations such as hypophosphataemic rickets depict a recent finding within the phenotypic spectrum of nonlethal RS. The dental sequelae of hypophosphataemic rickets are significant. Spontaneous recurrent abscesses on noncarious teeth result in significant odontogenic pain and multiple dental interventions. The dental presentations of nonlethal RS are less widely described within the literature. Amelogenesis Imperfecta (AI), however, was recently postulated as a key characteristic. This article presents the dental manifestations and extensive restorative and oral surgical intervention of three siblings with hypophosphataemic rickets secondary to Raine Syndrome treated at Great Ormond Street Hospital for Children, a tertiary referral hospital.
Project description:X-linked hypophosphatemia (XLH), the most common cause of hypophosphatemic rickets, affects one in every 20,000 people. Although conventional therapy for XLH was introduced approximately 4 decades ago, the temporary replacement of oral phosphate salts and activated vitamin D cannot completely control chronic hypophosphatemia, leaving patients with incomplete healing and residual skeletal deformity as well as at risk of endocrine abnormalities and adverse drug reactions. However, understanding the pathophysiology has led to the development of a targeted therapy, burosumab, a fibroblast growth factor-23 inhibitor that was recently approved in Korea for the treatment of XLH. This review provides insight into the diagnosis, evaluation, treatment, and recommended follow-up for a typical case of XLH and reviews its pathophysiology.
Project description:Neurofibromatosis-Noonan syndrome (NFNS) is a distinct entity which shows the features of both NF1 (neurofibromatosis 1) and Noonan syndrome (NS). While growth hormone deficiency (GHD) has been relatively frequently identified in NF1 and NS patients, there is limited experience in NFNS cases. The literature includes only one case report of a NFNS patient having GHD and that report primarily focuses on the dermatological lesions that accompany the syndrome and not on growth hormone (GH) treatment. Here, we present a 13-year-old girl who had clinical features of NFNS with a mutation in the NF1 gene. The case is the first NFNS patient reported in the literature who was diagnosed to have GHD and who received GH treatment until reaching final height. The findings in this patient show that short stature is a feature of NFNS and can be caused by GHD. Patients with NFNS who show poor growth should be evaluated for GHD.
Project description:BackgroundX-linked hypophosphatemic rickets (XLH) is the first cause of inherited hypophosphatemia and is caused by mutation in the PHEX gene, resulting in excessive expression of the phosphaturic factor FGF23. Symptoms are mainly related to rickets in children and osteomalacia in adults and cause several complications that can be highly invalidating. Due to its rarity, XLH is poorly known and diagnosis is frequently delayed. Conventional treatment is based on oral phosphate salts supplementation and activated vitamin D analogs, which however, cannot cure the disease in most cases.ObjectiveDue to the low prevalence of XLH, an experts' opinion survey was conducted across Italian centers to collect data on XLH and on its management.MethodsA questionnaire was developed by a group of experts to collect data on XLH epidemiology, diagnosis and treatment in Italy.ResultsData from 10 Italian centers (nine of which pediatric) on 175 patients, followed between 1998 and 2017, were included in the survey. Most patients were followed since childhood and 63 children became adults during the investigated period. The diagnosis was made before the age of 1 and between 1 and 5 years in 11 and 50% of cases, respectively. Clinically apparent bone deformities were present in 95% of patients. These were ranked moderate/severe in 75% of subjects and caused growth stunting in 67% of patients. Other frequent complications included bone pain (40%), dental abscesses (33%), and dental malpositions (53%). Treatment protocols varied substantially among centers. Nephrocalcinosis was observed in 34% of patients. Tertiary hyperparathyroidism developed in 6% of patients.ConclusionsXLH remains a severe condition with significant morbidities.