Hypophosphatemic Rickets

Surgical outcome of angular deformity correction of lower limbs in rickets: a cross-sectional study

PURPOSE

This study aims to compare the functional and radiological outcomes following both guided growth surgery (GGS) and acute corrective osteotomy (ACO) correction of angular deformities in children with rickets.

METHODS

A total of 8 and 7 children who had gradual GGS and ACO correction, respectively, for angular deformities due to rickets from 2002 to 2022 were recalled for follow-up. Demographic data, types of rickets, data on pharmacological treatment, biochemical parameters, recurrence of angular deformity and postoperative complications were obtained from the medical records. A radiographic evaluation of the leg was performed to determine the tibiofemoral angle. For functional evaluation, the Active Scale for Kids (ASK) and Lower Extremity Functional Scale (LEFS) instruments were used for children below and above 15 years old, respectively.

RESULTS

In terms of the tibiofemoral angle, the GGS group documented greater angle changes compared to the ACO group, but the difference was not significant. In terms of functional outcomes, the overall score percentage of both groups was comparable with the GGS group showing a trend of higher score percentage compared to the ACO group. The GGS group presented no complication while 2 neurovascular injuries and 1 implant failure were recorded in the ACO group.

CONCLUSION

Both GGS and ACO procedures resulted in similar radiographic and functional outcomes for the treatment of rickets in children. GGS may be advantageous in terms of reducing complications of surgery. Nevertheless, the choice of surgical intervention should be made based on the patient's circumstances and the surgeon's preference.

X-linked hypophosphatemia in 4 generations due to an exon 13-15 duplication in PHEX, in the absence of the c.*231A>G variant

X-linked hypophosphatemia is the most common cause of inherited rickets, due to inactivating variants of PHEX. More than 800 variants have been described to date and one which consists of a single base change in the 3' untranslated region (UTR) (c.*231A>G) is reported as prevalent in North America. Recently an exon 13-15 duplication has been found to occur in concert with the c.*231A>G variant, and thus it is unclear whether the pathogenicity is solely a function of the UTR variant. We present a family with XLH who harbors the exon 13-15 duplication but does not carry the 3'UTR variant, providing evidence that the duplication itself is the pathogenic variant when these two variants are found in cis.

Mineral Metabolism in Children: Interrelation between Vitamin D and FGF23

Fibroblast growth factor 23 (FGF23) was identified at the turn of the century as the long-sought circulating phosphatonin in human pathology. Since then, several clinical and experimental studies have investigated the metabolism of FGF23 and revealed its relevant pathogenic role in various diseases. Most of these studies have been performed in adult individuals. However, the mineral metabolism of the child is, to a large extent, different from that of the adult because, in addition to bone remodeling, the child undergoes a specific process of endochondral ossification responsible for adequate mineralization of long bones’ metaphysis and growth in height. Vitamin D metabolism is known to be deeply involved in these processes. FGF23 might have an influence on bones’ growth as well as on the high and age-dependent serum phosphate concentrations found in infancy and childhood. However, the interaction between FGF23 and vitamin D in children is largely unknown. Thus, this review focuses on the following aspects of FGF23 metabolism in the pediatric age: circulating concentrations’ reference values, as well as those of other major variables involved in mineral homeostasis, and the relationship with vitamin D metabolism in the neonatal period, in vitamin D deficiency, in chronic kidney disease (CKD) and in hypophosphatemic disorders.

Temporary hemiepiphysiodesis using eight-plates for angular deformities of the lower extremities in children with X-linked hypophosphataemic rickets

PURPOSES

Temporary hemiepiphysiodesis (TH) using eight-plates is one of the most frequently performed surgeries for correcting angular deformities of the lower extremities in adolescents. Rarely have studies examined children with X-linked hypophosphataemic rickets (X-LHPR) treated with TH using eight-plates. This study was conducted to investigate the efficacy, the endpoint, and the complications of TH using eight-plates to correct angular deformities of the lower extremities in skeletally immature children.

METHODS

We reviewed a total of 26 children (86 physes, 52 knees) with X-LHPR (mean age of 6.2 years, range from 2 to 13 years) who underwent TH using eight-plate to correct angular deformities of the lower extremities. Radiographs and clinical records of these patients were evaluated for demographic data and related clinical factors.

RESULTS

The average correction of the mechanical lateral distal femoral angle (mLDFA) was 11.7 ± 8.7° (range from 1.0 to 29.7°), and the average correction of the mechanical medial proximal tibial angle (mMPTA) was 8.4 ± 5.0° (range from 0.3 to 16.7°). The mean deformity correction time was 22.7 months (range from 7 to 60 months), and the mean follow-up after eight-plate removal was 43.9 months (range from 24 to 101 months). Overall, 76.9% (20/26 patients) of the angular deformities of the knee were completely corrected and 15.4% (4/26) of the patients received osteotomy surgery. The femoral correction velocity (0.9° per month) was significantly higher than the proximal tibial (0.6° per month) (p = 0.02). The correction velocity of the mLDFA and mMPTA with the TH procedure was faster than that in the absence of intervention (0.9° vs. 0.2°, 0.7° vs. 0.4° per month, p < 0.05). The correction velocity of the mLDFA (1.2° vs. 0.5° per month, [Formula: see text]) and mMPTA (0.7° vs. 0.5° per month, p = 0.04) of patients whose age ≤ five years old was faster than that of patients whose age > five years old. A total of 69.2% (18/26) patients experienced one TH procedure using eight-plates only. Two patients had screw loosening (2/26, 7.7%). One patient (1/26, 3.8%) had a rebound phenomenon after the removal of eight-plate and had the TH procedure again. There was no breakage, infection, physis preclosure, or limited range of movement found in the follow-up.

CONCLUSION

TH using eight-plates is a safe and effective procedure with a relatively low incidence of complication and rebound, and it could be used as part of a streamlined treatment for younger X-LHPR patients with resistant or progressive lower limb deformity despite optimal medical treatment. Early intervention can achieve better results.

Dental manifestations and treatment of hypophosphatemic rickets: A case report and review of literature

BACKGROUND

The treatment and management of patients suffering from hypophosphatemic rickets (HR) remain a major challenge for dental practitioners and affected patients.

OBJECTIVES

To report a case of HR presenting with specific dental findings and to review the dental manifestations and treatment of HR patients.

METHODS

Case: A 32-year-old male presented with multiple dental abscesses and short stature. A thorough history was taken followed by clinical oral examination, and relevant radiological investigation was done. Literature research: In 2020, electronic literature searches were carried out in PubMed and complemented by a careful assessment of the reference lists of the identified relevant papers. Articles and reports fulfilled the inclusion criteria: indexed reviews, case series and case reports in English and restricted to human studies were considered.

RESULTS

The intraoral examination revealed multiple dental abscesses and general periodontal disease; the radiographic examination showed poorly defined lamina dura, large pulp chambers and periapical lesions. Based on the contents of the 43 articles identified in the search, the current knowledge of dental manifestations, treatment and management of HR was summarized.

CONCLUSIONS

As HR is a multisystem disease, multidisciplinary care is needed. By summarizing current evidences, we proposed an evidence-based dental management and provided recommendations on diagnosis and treatment of the disease. It is of profound clinical significance to acquire knowledge of the dental manifestations and provide optimal treatment options for patients.

Rare PHEX intron variant causes complete and severe phenotype in a family with hypophosphatemic rickets: a case report

OBJECTIVES

Lower limb deformities in children need careful orthopedic evaluation to distinguish physiological forms from pathological ones. X-linked hypophosphatemia (XLH) is a rare hereditary condition caused by PHEX gene mutations where tibial varum can be the first sign.

CASE PRESENTATION

We report a family presenting with severe tibial varum, harbouring a rare PHEX intron mutation, c.1586+6T>C. This is the first clinical description available in literature for this variant. Despite the previous prediction of a mild phenotype in functional study, our patients showed important bone deformities, rickets and impaired growth since infancy followed by severe bone pain, hearing loss and reduced life quality in adulthood. Burosumab therapy improved biochemical and radiological findings in children and ameliorated quality of life in adults.

CONCLUSIONS

This case demonstrated c.1586+6T>C causes a severe XLH phenotype, responsive to Burosumab. Familial genetic screening, enlarged to intronic region analysis, when XLH is suspected, allows precocious diagnosis to start timely the appropriate treatment.

Whole exome sequencing identifies two novel variants in PHEX and DMP1 in Malaysian children with hypophosphatemic rickets

BACKGROUND

Hypophosphatemic rickets (HR) is a genetic disease of phosphate wasting that is characterized by defective bone mineralization. The most common cause of the disease is mutations in the phosphate regulating gene with homologies to endopeptidases on the X chromosome (PHEX) gene. The aims of this study were to identify the gene variants responsible for HR in three cases of Malaysian origin from three independent families and to describe their clinical, biochemical, and radiological features.

METHODS

Whole exome sequencing (WES) was performed on all patients and their parents, followed by Sanger sequencing validation. Bioinformatics tools were used to provide supporting evidence for pathogenicity of variants. To confirm that a mutation is de novo, paternity test was carried out. High resolution melting curve analysis was performed to assess the allele frequency in normal controls for mutations that were found in the patients.

RESULTS

The patients showed typical characteristics of HR including lower limb deformity, hypophosphatemia, and elevated alkaline phosphatase. WES revealed two variants in the PHEX gene and one variant in the dentin matrix protein 1 (DMP1) gene. Two of the three variants were novel, including c.1946_1954del (p.Gly649_Arg651del) in PHEX and c.54 + 1G > A in DMP1. Our data suggests that the novel p.Gly649_Arg651del variant is likely pathogenic for HR disease.

CONCLUSIONS

This study extends the variant spectrum of the PHEX and DMP1 genes. Our findings indicate that WES is an advantageous approach for diagnosis of genetic diseases which are heterogeneous.

Compounding vulnerabilities: Syndemics and the social determinants of disease in the past

OBJECTIVE

This article explores the theory and utility of a syndemic approach for the study of disease in the past. Syndemic principles are examined alongside other theoretical developments within bioarchaeology. Two case studies are provided to illustrate the efficacy of this approach: Tuberculosis and vitamin D deficiency in 18th and 19th century England, and malaria and helminth infections in Early Medieval England.

MATERIALS

Public health studies of present syndemics, in addition to published bioarchaeological, clinical and social information relating to the chosen case studies.

METHODS

The data from these two historical examples are revisited within a syndemic framework to draw deeper conclusions about disease clustering and heterogeneity in the past.

RESULTS

A syndemic framework can be applied to past contexts using clinical studies of diseases in a modern context and relevant paleopathological, archaeological, and historical data.

CONCLUSIONS

This approach provides a means for providing a deeper, contextualised understanding ancient diseases, and integrates well with extant theoretical tools in bioarchaeology SIGNIFICANCE: Syndemics provides scholars a deep-time perspective on diseases that still impact modern populations.

LIMITATIONS

Many of the variables essential for a truly syndemic approach cannot be obtained from current archaeological, bioarchaeological, or historical methods.

SUGGESTIONS FOR FURTHER RESEARCH

More detailed and in-depth analysis of specific disease clusters within the past and the present, which draws on a comprehensive analysis of the social determinants of health.

Osteomalacia Is Not a Single Disease

Among bone-material qualities, mineralization is pivotal in conferring stiffness and toughness to the bone. Osteomalacia, a disease ensuing from inadequate mineralization of the skeleton, is caused by different processes leading to decreased available mineral (calcium and/or phosphate) or enzymatic alterations. Vitamin D deficiency, which remains the major cause of altered mineralization leading to inadequate intestinal calcium and phosphate absorption, may be also associated with other conditions primarily responsible for abnormal mineralization. Given the reality of widespread vitamin D inadequacy, a full biochemical assessment of mineral metabolism is always necessary to rule out or confirm other conditions. Both too-high or too-low serum alkaline phosphatase (ALP) levels are important for diagnosis. Osteomalacic syndrome is reversible, at least in part, by specific treatment. Osteomalacia and bone mineralization themselves constitute largely unexplored fields of research. The true prevalence of the different forms of osteomalacia and the recovery after proper therapy have yet to be determined in the real world. Although non-invasive techniques to assess bone mineralization are not available in clinical practice, the systematic assessment of bone quality could help in refining the diagnosis and guiding the treatment. This review summarizes what is known of osteomalacia recent therapeutic developments and highlights the future issues of research in this field.

Disorders of phosphate homeostasis in children, part 2: hypophosphatemic and hyperphosphatemic disorders

Phosphorus, predominantly in the form of inorganic phosphate PO₄^-3, has many essential physiological functions. In the skeleton, phosphate and calcium form the mineral component and phosphate is also essential in regulating function of skeletal cells. Considerable advances have been made in our understanding of phosphate homeostasis since the recognition of fibroblast growth factor-23 (FGF23) as a bone-derived phosphaturic hormone. This second part of a two-part review of disorders of phosphate homeostasis in children covers hypophosphatemic and hyperphosphatemic disorders that are of interest to the pediatric radiologist, emphasizing, but not limited to, those related to abnormalities of FGF23 signaling.

Disorders of phosphate homeostasis in children, part 1: primer on mineral ion homeostasis and the roles of phosphate in skeletal biology

Phosphate has extensive physiological roles including energy metabolism, genetic function, signal transduction and membrane integrity. Regarding the skeleton, not only do phosphate and calcium form the mineral component of the skeleton, but phosphate is also essential in regulating function of skeletal cells. Although our understanding of phosphate homeostasis has lagged behind and remains less than that for calcium, considerable advances have been made since the recognition of fibroblast growth factor-23 (FGF23) as a bone-derived phosphaturic hormone that is a major regulator of phosphate homeostasis. In this two-part review of disorders of phosphate homeostasis in children, part 1 covers the basics of mineral ion homeostasis and the roles of phosphate in skeletal biology. Part 1 includes phosphate-related disorders of mineralization for which overall circulating mineral ion homeostasis remains normal. Part 2 covers hypophosphatemic and hyperphosphatemic disorders, emphasizing, but not limited to, those related to increased and decreased FGF23 signaling, respectively.

A Case of X-Linked Hypophosphatemic Rickets with Dentin Dysplasia in Mandibular Third Molars

X-linked hypophosphatemic rickets (XLH) is a disease characterized by impaired bone mineralization, and its dental features include gingival abscesses and large pulp spaces due to dentin dysplasia. A 20-year-old woman with XLH was referred to oral surgery for extraction of mandibular third molars. She was diagnosed with XLH at approximately 1 year of age and was treated thereafter. There was no history of gingival abscesses, and panoramic radiographic and computed tomographic examinations revealed no evidence of dentin dysplasia. However, histopathological examination of the extracted teeth showed dentin dysplasia, including interglobular dentin. In this XLH patient, dentin dysplasia was revealed histologically even though no obvious abnormality was found on visual and radiographic examinations. These findings suggest that in patients with XLH, oral management must take dentin dysplasia of the permanent teeth into consideration even if the patient’s general condition is well controlled with conventional therapy.

X‐linked hypophosphatemic rickets: Case report of late diagnosis and bone pain improvement with targeted treatment

X‐linked hypophosphatemia (XLH) is a rare disexase in which patients present with severe bowing of the legs, joint pain, and mobility problems. XLH has major adverse repercussions on the quality of life.

Effects of Routine Health Care Combined with Oral Vitamin D on Linear Growth in 5-Year-Old Children

Objective

The aim is to evaluate the effects of routine health care combined with oral vitamin D on linear growth in 5-year-old children.

Materials and Methods

The 5-year-old children who received routine health care in Shiyan Maternal and Child Health Care Hospital from January 2019 to January 2021 were retrospectively analyzed. They were divided into the supplement group and the non-supplement group according to whether or not they received oral vitamin D, and reasons for not taking oral vitamin D and its influence on children's linear growth were analyzed.

Results

A total of 368 children were enrolled, including 228 children in the supplement group, accounting for 61.96%. The analysis of the influencing factors of vitamin D supplementation showed that the proportion of children with well-educated parents and living in cities and towns was higher (all P < 0.05). Comparing the general situation of children in the two groups, it was found that the height, weight, and head circumference of children in the supplement group were notably higher than those in the non-supplement group (all P < 0.05). At age 4 and 5, the height of the supplement group was significantly higher than that of the non-supplement group (all P < 0.001). Linear analysis showed that the relationship between height and age in the supplement group was Y (height, cm) = 10.07 × X (age, years) + 61.18, while that in the non-supplement group was Y (height, cm) = 8.296 × X (age, years) + 62.81, with significant difference (all P < 0.05). Serum 25-hydroxyvitamin D concentration in the supplement group was significantly higher than that in the non-supplement group, and the proportion of children ≥75 nmol/L was evidently higher than that in the supplement group (all P < 0.05). In addition, the incidence of vitamin D-related hypercalcemia in the supplement group was significantly higher than that in the non-supplement group (all P < 0.05).

Conclusion

There are still more children without vitamin D supplement, which is closely related to their parents' education background and place of residence. Additionally, vitamin D supplementation can promote growth and improve 25-hydroxyvitamin D levels in children, but with the risk of related complications.

Decreased Trabecular Bone Mass in Col22a1-Deficient Mice

The bone matrix is constantly remodeled by the coordinated activities of bone-forming osteoblasts and bone-resorbing osteoclasts. Whereas type I collagen is the most abundant bone matrix protein, there are several other proteins present, some of them specifically produced by osteoblasts. In a genome-wide expression screening for osteoblast differentiation markers we have previously identified two collagen-encoding genes with unknown function in bone remodeling. Here we show that one of them, Col22a1, is predominantly expressed in bone, cultured osteoblasts, but not in osteoclasts. Based on this specific expression pattern we generated a Col22a1-deficient mouse model, which was analyzed for skeletal defects by µCT, undecalcified histology and bone-specific histomorphometry. We observed that Col22a1-deficient mice display trabecular osteopenia, accompanied by significantly increased osteoclast numbers per bone surface. In contrast, cortical bone parameters, osteoblastogenesis or bone formation were unaffected by the absence of Col22a1. Likewise, primary osteoblasts from Col22a1-deficient mice did not display a cell-autonomous defect, and they did not show altered expression of Rankl or Opg, two key regulators of osteoclastogenesis. Taken together, we provide the first evidence for a physiological function of Col22a1 in bone remodeling, although the molecular mechanisms explaining the indirect influence of Col22a1 deficiency on osteoclasts remain to be identified.

Hearing loss in inherited metabolic disorders: A systematic review

Inherited metabolic disorders (IMDs) have been observed in individuals with hearing loss (HL), but IMDs are rarely the cause of syndromic HL. With early diagnosis, management of HL is more effective and cortical reorganization is possible with hearing aids or cochlear implants. This review describes relationships between IMDs and HL in terms of incidence, etiology of HL, pathophysiology, and treatment. Forty types of IMDs are described in the literature, mainly in case reports. Management and prognosis are noted where existing. We also describe IMDs with HL given age of occurrence of HL. Reviewing the main IMDs that are associated with HL may provide an additional clinical tool with which to better diagnose syndromic HL.

Autosomal Dominant Hypophosphatemic Rickets: A Case Report and Review of the Literature

Autosomal dominant hypophosphatemic rickets (ADHR) is an extremely rare form of genetic rickets caused by mutations in the fibroblast growth factor 23 gene. ADHR is characterized by hypophosphatemia secondary to isolated renal phosphate wasting. Only a few cases of ADHR have been reported in the literature to date. We describe the case of a 17-month-old girl who presented with severe failure to thrive (length: −4.08 standard deviation (SD), weight: −2.2 SD) and hypotonia. Hypophosphatemia, decreased tubular phosphate reabsorption (69%), and rachitic lesions were found. Genetic analysis showed the heterozygous variant c.536G>A (NM_020638.3:c.536G>A) in exon 3 of the FGF23 gene, leading to the diagnosis of ADHR. She was treated with phosphate salts and oral alfacalcidol. After 4 years of treatment, at 5 years of age, the patient’s ADHR resolved spontaneously. Considering the lack of knowledge regarding ADHR, we reviewed the literature to describe the features of this rare and poorly understood disease. Eleven ADHR pediatric cases have been described thus far, with cases tending to be more common in females than males. Similar to the general population, two groups of patients with ADHR can be described depending on the mutations present: patients with an R179 and R176 mutation have early-onset of disease and higher frequency of rickets, and a milder and late-onset of disease, respectively. Symptoms and disease severity may fluctuate. Spontaneous remission may occur during the pediatric age.

Rickets in Children: An Update

Rickets refers to a deficient mineralization of the growth plate cartilage, predominantly affecting longer bones. Despite the fact that preventive measures are available, it is still a common disease worldwide; nutritional rickets, due to vitamin D deficiency or dietary calcium inadequate intake, remains the most common form. Medical history, physical examination, radiologic features and biochemical tests are essential for diagnosis. Although recent studies suggest hypophosphatemia as the leading alteration, rickets is classically divided into two categories: calcipenic rickets and phosphopenic rickets. Knowledge of this categorization and of respective clinical and laboratory features is essential for rapid diagnosis and correct management. The aim of this review is to analyze the epidemiological, pathogenetic, clinical, and therapeutic aspects of the different forms of rickets, describing the novelties on this “long-lived” disease.

Demographics, in-hospital analysis, and prevalence of 33 rare diseases with effective treatment in Shanghai

BACKGROUND

Rare diseases are ailments which impose a heavy burden on individual patients and global society as a whole. The rare disease management landscape is not a smooth one-a rare disease is quite often hard to diagnose, treat, and investigate. In China, the country's rapid economic rise and development has brought an increased focus on rare diseases. At present, there is a growing focus placed on the importance and public health priority of rare diseases and on improving awareness, definitions, and treatments.

METHODS

In this work we utilized clinical data from the Shanghai HIE System to characterize the status of 33 rare diseases with effective treatment in Shanghai for the time period of 2013-2016.

RESULTS AND CONCLUSION

First, we describe the total number of patients, year-to-year change in new patients with diagnosis in one of the target diseases and the distribution of gender and age for the top six (by patient number) diseases of the set of 33 rare diseases. Second, we describe the hospitalization burden in terms of in-hospital ratio, length of stay, and medical expenses during hospitalization. Finally, rare disease period prevalence is calculated for the rare diseases set.

[A complex case of renal phosphate wasting…]

We describe here the case report of a young man of 34-years old suffering from a haemorrhagic rectocolitis and presenting with marked hypophosphatemia secondary to an infusion of ferric-carboxymaltose. The renal phosphate wasting was asserted by a very low renal maximal reabsorption rate of phosphate associated with a high plasma FGF-23 level. Three months later we explored the patient and his father since we learnt that both of them had suffered from kidney stones for years with marked hypercalciuria. Kidney stones were composed of weddellite and carbapatite. We suspected a familial phosphate renal wasting syndrome but however no mutation of the renal phosphate carriers could be identified.

Effect of high phosphate diet on the formation of dentin in Fam20c-deficient mice

FAM20C (family with sequence similarity 20-member C), a kinase that phosphorylates secretory proteins, plays essential roles in various biological processes. In humans, mutations in FAM20C gene cause Raine syndrome, an autosomal recessive hereditary disease manifesting a broad spectrum of developmental defects including skeletal and craniofacial deformities. Our previous studies revealed that inactivation of Fam20c in mice led to hypophosphatemic rickets and that high phosphate (hPi) diet significantly improved the development of the skeleton in Fam20c-deficient mice. In this study, we evaluated the effects of hPi diet on the formation of dentin in Fam20c-deficient mice, using plain x-ray radiography, micro-computed tomography (µCT), histology, and immunohistochemistry. Plain x-ray radiography and µCT analyses showed that the hPi diet improved the dentin volume fraction and dentin mineral density of the Fam20c-deficient mice. Histology analyses further demonstrated that the hPi diet dramatically improved the integrity of the mandibular first molars and prevented pulp infection and dental abscesses in Fam20c-deficient mice. Our results support that the hPi diet significantly increased the formation and mineralization of dentin in Fam20c-deficient mice, implying that hypophosphatemia is a significant contributor to the dentin defects in Fam20c-deficient subjects.

Phenotypic characterization of X-linked hypophosphatemia in pediatric Spanish population

Background

X-linked hypophosphatemia (XLH) is a hereditary rare disease caused by loss-of-function mutations in PHEX gene leading tohypophosphatemia and high renal loss of phosphate. Rickets and growth retardation are the major manifestations of XLH in children, but there is a broad phenotypic variability. Few publications have reported large series of patients. Current data on the clinical spectrum of the disease, the correlation with the underlying gene mutations, and the long-term outcome of patients on conventional treatment are needed, particularly because of the recent availability of new specific medications to treat XLH.

Results

The RenalTube database was used to retrospectively analyze 48 Spanish patients (15 men) from 39 different families, ranging from 3 months to 8 years and 2 months of age at the time of diagnosis (median age of 2.0 years), and with XLH confirmed by genetic analysis. Bone deformities, radiological signs of active rickets and growth retardation were the most common findings at diagnosis. Mean (± SEM) height was − 1.89 ± 0.19 SDS and 55% (22/40) of patients had height SDS below—2. All cases had hypophosphatemia, serum phosphate being − 2.81 ± 0.11 SDS. Clinical manifestations and severity of the disease were similar in both genders. No genotype—phenotype correlation was found. Conventional treatment did not attenuate growth retardation after a median follow up of 7.42 years (IQR = 11.26; n = 26 patients) and failed to normalize serum concentrations of phosphate. Eleven patients had mild hyperparathyroidism and 8 patients nephrocalcinosis.

Conclusions

This study shows that growth retardation and rickets were the most prevalent clinical manifestations at diagnosis in a large series of Spanish pediatric patients with XLH confirmed by mutations in the PHEX gene. Traditional treatment with phosphate and vitamin D supplements did not improve height or corrected hypophosphatemia and was associated with a risk of hyperparathyroidism and nephrocalcinosis. The severity of the disease was similar in males and females.

Black phosphorus-based 2D materials for bone therapy

Since their discovery, Black Phosphorus (BP)-based nanomaterials have received extensive attentions in the fields of electromechanics, optics and biomedicine, due to their remarkable properties and excellent biocompatibility. The most essential feature of BP is that it is composed of a single phosphorus element, which has a high degree of homology with the inorganic components of natural bone, therefore it has a full advantage in the treatment of bone defects. This review will first introduce the source, physicochemical properties, and degradation products of BP, then introduce the remodeling process of bone, and comprehensively summarize the progress of BP-based materials for bone therapy in the form of hydrogels, polymer membranes, microspheres, and three-dimensional (3D) printed scaffolds. Finally, we discuss the challenges and prospects of BP-based implant materials in bone immune regulation and outlook the future clinical application.

Mineralized tissues in hypophosphatemic rickets

Hypophosphatemic rickets is caused by renal phosphate wasting that is most commonly due to X-linked dominant mutations in PHEX. PHEX mutations cause hypophosphatemia indirectly, through the increased expression of fibroblast growth factor 23 (FGF23) by osteocytes. FGF23 decreases renal phosphate reabsorption and thereby increases phosphate excretion. The lack of phosphate leads to a mineralization defect at the level of growth plates (rickets), bone tissue (osteomalacia), and teeth, where the defect facilitates the formation of abscesses. The bone tissue immediately adjacent to osteocytes often remains unmineralized ("periosteocytic lesions"), highlighting the osteocyte defect in this disorder. Common clinical features of XLH include deformities of the lower extremities, short stature, enthesopathies, dental abscesses, as well as skull abnormalities such as craniosynostosis and Chiari I malformation. For the past four decades, XLH has been treated by oral phosphate supplementation and calcitriol, which improves rickets and osteomalacia and the dental manifestations, but often does not resolve all aspects of the mineralization defects. A newer treatment approach using inactivating FGF23 antibodies leads to more stable control of serum inorganic phosphorus levels and seems to heal rickets more reliably. However, the long-term benefits of FGF23 antibody treatment remain to be elucidated.

Rickets in association with skin diseases and conditions: A review with emphasis on screening and prevention

BACKGROUND

Rickets is a common disease worldwide. In the developed world, its prevalence dramatically decreased but still diagnosed in at-risk populations. The skin plays a critical role in vitamin D synthesis. Therefore, several skin diseases, especially keratinization disorders, could lead to impaired vitamin D metabolism and vitamin D deficient rickets.

OBJECTIVE

The article aimed to summarize the current knowledge of skin diseases and conditions associated with rickets.

METHODS

To examine the association between rickets and skin diseases, we performed a systematic review of the literature using PubMed database. The search included studies published from the database inception to August 2019.

RESULTS

A total number of 75 articles were included. Identified conditions associated with rickets were ichthyosis being a more common skin diseases, alopecia, epidermal and melanocytic nevi, xeroderma pigmentosum, mastocytosis, psoriasis, and atopic dermatitis. Three types of rickets were identified: vitamin D-dependent rickets, hypocalcemic vitamin D-dependent rickets type 2, and hypophosphatemic rickets. Cutaneous skeletal hypophosphatemia syndrome is a newly described and under-recognized condition. It is defined by the association of epidermal or melanocytic nevi, hypophosphatemic rickets, and elevated levels of fibroblast growth factor 23. Rickets in patients with ichthyosis was mainly due to impaired ability of ichthyotic skin to synthesize vitamin D, poor UV penetration of the skin caused by keratinocyte proliferation, and dark phototype. The latter may be considered a risk factor for rickets in patients with ichthyosis.

CONCLUSION

Despite its rarity, these associations should be properly recognized by dermatologists. Early diagnosis of rickets is important to prevent growth retardation and skeletal deformities.

Long-term outcomes for Asian patients with X-linked hypophosphataemia: rationale and design of the SUNFLOWER longitudinal, observational cohort study

INTRODUCTION

X-linked hypophosphataemic rickets/osteomalacia (XLH) is a chronic, debilitating genetic disease characterised by skeletal abnormalities and growth disorder. The burden of XLH begins in childhood and continues throughout life. Conventional medical therapy with phosphate, active vitamin D and surgery do not address the underlying pathophysiology of the disease. While treatment during childhood may improve bone deformity and growth retardation, a large proportion of adult patients still fail to reach normal stature. Furthermore, adult patients with XLH report comorbidities associated with unresolved childhood disease, as well as newly developed disease-related complications and significantly impaired quality of life (QOL). Despite the multiple negative aspects of XLH, Asian consensus statements for diagnosis and management are lacking.

METHODS AND ANALYSIS

The Study of longitUdinal observatioN For patients with X-Linked hypOphosphataemic rickets/osteomalacia in collaboration With Asian partnERs study is a longitudinal observational cohort study of patients with XLH, designed to determine the medical characteristics and burdens (physical, emotional and financial) of this progressive disease and to evaluate the impact of treatment (including the use of burosumab) on clinical outcomes. The study was initiated in April 2018, and registration will remain open until 30 April 2022. The sample size planned for analyses is 160 patients, consisting of 100 patients in Japan and 60 patients in Korea. Up to 5 years of observation are planned per patient, from enrolment through to April 2023. Prospective and retrospective data will be collected to evaluate variables, including height/growth, rickets severity score, QOL, motor function and biomarkers for phosphate metabolism and bone turnover.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the Ethics Committee of Osaka University, the Ethics Committee of Kyowa Kirin Co and by the Ethics Committee of each participating medical institution. Two interim analyses and associated publications are planned using retrospective and enrolment data at year 1 and results at year 3.

TRIAL REGISTRATION NUMBERS

NCT03745521; UMIN000031605.

Nationwide Turkish Cohort Study of Hypophosphatemic Rickets

OBJECTIVE

Hypophosphatemic rickets (HR) is a rare renal phosphate-wasting disorder, which is usually X-linked and is commonly caused by PHEX mutations. The treatment and follow-up of HR is challenging due to imperfect treatment options.

METHODS

Here we present nationwide initial and follow-up data on HR.

RESULTS

From 24 centers, 166 patients were included in the study. Genetic analysis (n=75) showed PHEX mutation in 80% of patients. The mean follow-up period was 6.7±2.4 years. During the first 3-years of treatment (n=91), mild increase in phosphate, decrease in alkaline phosphatase and elevation in parathyroid hormone (PTH) levels were detected. The height standard deviation scores were -2.38, -2.77, -2.72, -2.47 at initial, 1^st, 2^nd and 3^rd year of treatment, respectively (p>0.05). On follow-up 36% of the patients showed complete or significant improvement in leg deformities and these patients had similar phosphate levels at presentation with better levels in 1^st and 2^nd years of treatment; even the treatment doses of phosphate were similar. Furthermore, 27 patients developed nephrocalcinosis (NC), the patients showed no difference in biochemical differences at presentation and follow-up, but 3^rd year PTH was higher. However, higher treatment doses of phosphate and calcitriol were found in the NC group.

CONCLUSION

HR treatment and follow-up is challenging and our results showed higher treatment doses were associated with NC without any change in serum phosphate levels, suggesting that giving higher doses led to increased phosphaturia, probably through stimulation of fibroblast growth factor 23. However, higher calcitriol doses could improve bone deformities. Safer and more efficacious therapies are needed.

Surgical Indications in Hypophosphataemic Rickets

Low levels of phosphate in blood secondary to a lack of phosphorous reabsorption in the renal tubule cause hypophosphataemic rickets. To increase blood calcium levels, bone calcium is released into the bloodstream by increasing the activity of osteoclasts in the bones. These alterations in bone metabolism lead to delayed growth and small height, diffuse bone pain, bone fragility with microfractures, and frequent fractures and bone deformities. Although management of some of these conditions is mainly conservative, in cases of bone deformities or severe osteomalacia surgery should be considered: from minimally invasive surgical techniques of guided growth in patients with less deformity and open physeal cartilage to correction osteotomies in three-dimensional deformities. This article briefly reviews the indications for surgery procedures to be performed in these patients, highlighting when to use aggressive and non-aggressive approaches.

Hypophosphataemic Rickets: Similar Phenotype of Different Diseases

Hypophosphataemic rickets (HR) is a group of rare disorders caused by excessive renal phosphate wasting in which the participation of fibroblast growth factor 23 (FGF23) can be prominent. These diseases pose therapeutic challenges with important consequences for growth and bone development in childhood, with higher risk of fractures and poorer bone healing, dental problems, and nephrolithiasis or nephrocalcinosis. In some cases, the diagnostic delay can be very long; laboratory findings and an exhaustive anamnesis could help distinguish between various pathologies, and FGF23 values-although currently not routinely measured-have implications for the differential diagnosis. Genetic testing is encouraged, especially in sporadic or insidious cases. In this review we discuss the clinical features of HR, with a particular emphasis on the differential diagnosis and the therapeutic implications.

New aspects of vitamin D metabolism and action - addressing the skin as source and target

Vitamin D has a key role in stimulating calcium absorption from the gut and promoting skeletal health, as well as many other important physiological functions. Vitamin D is produced in the skin. It is subsequently metabolized to its hormonally active form, 1,25-dihydroxyvitamin D (1,25(OH)₂D), by the 1-hydroxylase and catabolized by the 24-hydroxylase. In this Review, we pay special attention to the effect of mutations in these enzymes and their clinical manifestations. We then discuss the role of vitamin D binding protein in transporting vitamin D and its metabolites from their source to their targets, the free hormone hypothesis for cell entry and HSP70 for intracellular transport. This is followed by discussion of the vitamin D receptor (VDR) that mediates the cellular actions of 1,25(OH)₂D. Cell-specific recruitment of co-regulatory complexes by liganded VDR leads to changes in gene expression that result in distinct physiological actions by 1,25(OH)₂D, which are disrupted by mutations in the VDR. We then discuss the epidermis and hair follicle, to provide a non-skeletal example of a tissue that expresses VDR that not only makes vitamin D but also can metabolize it to its hormonally active form. This enables vitamin D to regulate epidermal differentiation and hair follicle cycling and, in so doing, to promote barrier function, wound healing and hair growth, while limiting cancer development.

High-Phosphate Diet Improved the Skeletal Development of Fam20c-Deficient Mice

FAM20C (family with sequence similarity 20 - member C) is a protein kinase that phosphorylates secretory proteins, including the proteins that are essential to the formation and mineralization of calcified tissues. Previously, we reported that inactivation of Fam20c in mice led to hypophosphatemic rickets/osteomalacia along with increased circulating fibroblast growth factor 23 (FGF23) levels and dental defects. In this study, we examined whether a high-phosphate (hPi) diet could rescue the skeletal defects in Fam20c-deficient mice. Fam20c conditional knockout (cKO) mice were generated by crossing female Fam20c-floxed mice (Fam20cfl/fl) with male Sox2-Cre;Fam20cfl/+ mice. The pregnant female Fam20cfi/fl mice were fed either a normal or hPi diet until the litters were weaned. The cKO and control offspring were continuously given a normal or hPi diet for 4 weeks after weaning. Plain X-ray radiography, micro-CT, histology, immunohistochemistry (FGF23, DMP1, OPN, and SOX9), and in situ hybridization (type II and type X collagen) analyses were performed to evaluate the effects of an hPi diet on the mouse skeleton. Plain X-ray radiography and micro-CT radiography analyses showed that the hPi diet improved the shape and mineral density of the Fam20c-deficient femurs/tibiae, and rescued the growth plate defects in the long bone. Histology analyses further demonstrated that an hPi diet nearly completely rescued the growth plate-widening defects in the long bone and restored the expanded hypertrophic zone to nearly normal width. These results suggested that the hPi diet significantly improved the skeletal development of the Fam20c-deficient mice, implying that hypophosphatemia partially contributed to the skeletal defects in Fam20c-deficient subjects.

Familial hypophosphatemic rickets caused by a PHEX gene mutation accompanied by a NPR2 missense mutation

Background Familial hypophosphatemic rickets, which is usually acknowledged as X-linked hypophosphatemic rickets (XLH), is a rare hereditary disease. XLH caused by mutations in the PHEX gene often manifests as growth retardation, skeletal deformities, osteodynia and dental dysplasia. NPR2 mutations are reported to cause disproportionate short stature. Our study was designed to identify the gene mutations of three patients in one family. Case description A 40-year-old Chinese male visited the hospital for continuous osteodynia and presented with bilateral leg bowing, absent teeth and a progressive limp. The age of onset was approximately 2 years old. His 63-year-old mother and 42-year-old brother both shared identical symptoms with him. The laboratory tests were consistent with XLH, which showed decreased levels of blood phosphorus and 1,25-dihydroxyvitamin D3 as well as increased urinary phosphorus excretion. Mutation analysis revealed that the proband as well as his mother and his brother all had a PHEX mutation in exon 14 (c.1543C > T), and the proband also had a NPR2 mutation in exon 21 (c.3058C > T). Conclusions We report the familial hypophosphatemic rickets of three patients in a Chinese family caused by a PHEX gene mutation in exon 14 (c.1543C > T), which had never been reported in Chinese patients. We first report an XLH case together with a NPR2 mutation that had never been reported before.

Developmental Changes in Phosphate Homeostasis

Phosphate is a multivalent ion critical for a variety of physiological functions including bone formation, which occurs rapidly in the developing infant. In order to ensure maximal bone mineralization, young animals must maintain a positive phosphate balance. To accomplish this, intestinal absorption and renal phosphate reabsorption are greater in suckling and young animals relative to adults. This review discusses the known intestinal and renal adaptations that occur in young animals in order to achieve a positive phosphate balance. Additionally, we discuss the ontogenic changes in phosphotropic endocrine signalling as it pertains to intestinal and renal phosphate handling, including several endocrine factors not always considered in the traditional dogma of phosphotropic endocrine signalling, such as growth hormone, triiodothyronine, and glucocorticoids. Finally, a proposed model of how these factors may contribute to achieving a positive phosphate balance during development is proposed.

Positive Response to One-Year Treatment With Burosumab in Pediatric Patients With X-Linked Hypophosphatemia

X-linked hypophosphatemia (XLH) causes significant burden in pediatric patients in spite of maintained treatment with phosphate supplements and vitamin D derivatives. Administration of burosumab has shown promising results in clinical trial but studies assessing its effect in the everyday practice are missing. With this aim, we analyzed the response to one-year treatment with burosumab, injected subcutaneously at 0.8 mg/kg every 2 weeks, in five children (three females) aged from 6 to 16 years, with genetically confirmed XLH. Patients were being treated with phosphate and vitamin D analogs until the beginning of burosumab treatment. In all children, burosumab administration led to normalization of serum phosphate in association with marked increase of tubular reabsorption of phosphate and reduction of elevated serum alkaline phosphatase levels. Baseline height of patients, from -3.56 to -0.46 SD, increased in the three prepubertal children (+0.84, +0.89, and +0.16 SD) during burosumab treatment. Growth improvement was associated with reduction in body mass index (-1.75, -1.47, and -0.17 SD, respectively), suggesting a salutary effect of burosumab on physical activity and body composition. Burosumab was well-tolerated, mild local pain at the injection site and transient and mild headache following the initial doses of burosumab being the only reported undesirable side effects. No patient exhibited hyperphosphatemia, progression of nephrocalcinosis, worsening of metabolic control or developed hyperparathyroidism. Mild elevation of serum PTH present at the beginning of treatment in one patient 4 was not modified by burosumab administration. These results indicate that in the clinical setting, beyond the strict conditions and follow-up of clinical trials, burosumab treatment for 1 year exerts positive effects in pediatric patients with XLH without major adverse events.