Linear growth in patients with hypophosphatemic vitamin D-resistant rickets: influence of treatment regimen and parental height

Dental health of patients with X-linked hypophosphatemia: A controlled study

Objective

The present study compared the dental health of patients with X-linked hypophosphatemia (XLH) with healthy age- and gender-matched controls to increase our knowledge of the impact of XLH on oral health.

Materials and methods

Twenty-two adult patients with XLH in the Stockholm region of Sweden were referred to the Department of Orofacial Medicine at Karolinska Institutet for an extended clinical and radiological examination. Pre-existing radiologic examinations of 44 healthy age- and gender-matched controls were retrieved from the Department of Oral Radiology, at Karolinska Institutet.

Results

The 22 patients with XLH (15 females, median age 38 years, range 20-71; 7 males, median age 49 years, range 24-67) had a significantly higher number of root-filled teeth compared to healthy controls (p = .001). In the XLH group, females had significantly better oral health than males, especially concerning endodontic and cariological status (p's = .01 and .02, respectively). Periodontal status differed non-significantly between the XLH and control groups.

Conclusion

Patients with XLH had a significantly lower oral health status compared to a healthy population especially concerning endodontic conditions. Male patients with XLH had a higher risk of poor oral health compared to female patients with XLH.

Growth hormone treatment improves final height in children with X-linked hypophosphatemia

BACKGROUND/AIM

Despite 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.

METHODS

Two 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.

RESULTS

In 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.

CONCLUSION

Treatment 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.

Growth pattern in children with X-linked hypophosphatemia treated with burosumab and growth hormone

BACKGROUND

X-linked hypophosphatemia (XLH) is characterized by increased serum concentrations of fibroblast growth factor 23 (FGF23), hypophosphatemia and insufficient endogenous synthesis of calcitriol. Beside rickets, odonto- and osteomalacia, disproportionate short stature is seen in most affected individuals. Vitamin D analogs and phosphate supplements, i.e., conventional therapy, can improve growth especially when started early in life. Recombinant human growth hormone (rhGH) therapy in XLH children with short stature has positive effects, although few reports are available. Newly available treatment (burosumab) targeting increased FGF23 signaling leads to minimal improvement of growth in XLH children. So far, we lack data on the growth of XLH children treated with concomitant rhGH and burosumab therapies.

RESULTS

Thirty-six patients received burosumab for at least 1 year after switching from conventional therapy. Of these, 23 received burosumab alone, while the others continued rhGH therapy after switching to burosumab. Children treated with burosumab alone showed a minimal change in height SDS after 1 year (mean ± SD 0.0 ± 0.3 prepubertal vs. 0.1 ± 0.3 pubertal participants). In contrast, rhGH clearly improved height during the first year of treatment before initiating burosumab (mean ± SD of height gain 1.0 ± 0.4); patients continued to gain height during the year of combined burosumab and rhGH therapies (mean ± SD height gain 0.2 ± 0.1). As expected, phosphate serum levels normalized upon burosumab therapy. No change in serum calcium levels, urinary calcium excretion, or 25-OHD levels was seen, though 1,25-(OH)₂D increased dramatically under burosumab therapy.

CONCLUSION

To our knowledge, this is the first study on growth under concomitant rhGH and burosumab treatments. We did not observe any safety issue in this cohort of patients which is one of the largest in Europe. Our data suggest that continuing treatment with rhGH after switching from conventional therapy to burosumab, if the height prognosis is compromised, might be beneficial for the final height.

Skeletal and extraskeletal disorders of biomineralization

The physiological process of biomineralization is complex and deviation from it leads to a variety of diseases. Progress in the past 10 years has enhanced understanding of the genetic, molecular and cellular pathophysiology underlying these disorders; sometimes, this knowledge has both facilitated restoration of health and clarified the very nature of biomineralization as it occurs in humans. In this Review, we consider the principal regulators of mineralization and crystallization, and how dysregulation of these processes can lead to human disease. The knowledge acquired to date and gaps still to be filled are highlighted. The disorders of mineralization discussed comprise a broad spectrum of conditions that encompass bone disorders associated with alterations of mineral quantity and quality, as well as disorders of extraskeletal mineralization (hyperphosphataemic familial tumoural calcinosis). Included are disorders of alkaline phosphatase (hypophosphatasia) and phosphate homeostasis (X-linked hypophosphataemic rickets, fluorosis, rickets and osteomalacia). Furthermore, crystallopathies are covered as well as arterial and renal calcification. This Review discusses the current knowledge of biomineralization derived from basic and clinical research and points to future studies that will lead to new therapeutic approaches for biomineralization disorders.

The efficacy and safety of different doses of calcitriol combined with neutral phosphate in X-linked hypophosphatemia: a prospective study

The present study was the first prospective cohort evaluated the efficacy and safety of different doses of calcitriol in XLH children. The results suggested that a dose of 40 ng/kg/day calcitriol, compared with 20 ng/kg/day, was more effective in relieving the rickets, with similar safety outcomes. Further investigations were expected to set more dose groups.

INTRODUCTION

Dose recommended for calcitriol in X-linked hypophosphatemia (XLH) varies in different studies. Therefore, we aimed to compare the efficacy as well as the safety of 20 ng/kg/d and 40 ng/kg/d calcitriol in Chinese XLH pediatrics population.

METHODS

A 2-year, randomized, open-label, prospective study recruited 68 XLH children, which were randomized to receive either 40 ng/kg/day or 20 ng/kg/day calcitriol. Efficacy endpoints were the total Thacher ricket severity score (RSS) change from baseline to month 12 and 24, the difference in serum TALP level, fasting serum phosphate level, body height Z-score, and frequency of dental abscess. Safety assessments were done using renal ultrasound nephrocalcinosis grades (0-4), fasting serum and 24 h urine calcium level, and the occurrence of hyperparathyroidism.

RESULTS

The decrease in the total RSS from baseline was more significant in the high-dose group at 12 (difference 0.87, p = 0.049) and 24 month (difference 1.23, p = 0.011). The serum TALP level was significantly lower in the high-dose group at 6 months. Pi level, height Z-score change, frequency of dental abscess and ratio of de novo nephrocalcinosis were comparable. A lower incidence of secondary hyperparathyroidism was seen in the high-dose group (p < 0.0001).

CONCLUSION

For the first time in this prospective cohort, 40 ng/kg/d calcitriol was shown to be the more effective therapy in XLH children than the 20 ng/kg/d. Moreover, 40 ng/kg/d calcitriol was not associated with increasing adverse events.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT 03,820,518.

Interdisciplinary management of FGF23-related phosphate wasting syndromes: a Consensus Statement on the evaluation, diagnosis and care of patients with X-linked hypophosphataemia

X-linked hypophosphataemia (XLH) is the most frequent cause of hypophosphataemia-associated rickets of genetic origin and is associated with high levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23). In addition to rickets and osteomalacia, patients with XLH have a heavy disease burden with enthesopathies, osteoarthritis, pseudofractures and dental complications, all of which contribute to reduced quality of life. This Consensus Statement presents the outcomes of a working group of the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases, and provides robust clinical evidence on management in XLH, with an emphasis on patients' experiences and needs. During growth, conventional treatment with phosphate supplements and active vitamin D metabolites (such as calcitriol) improves growth, ameliorates leg deformities and dental manifestations, and reduces pain. The continuation of conventional treatment in symptom-free adults is still debated. A novel therapeutic approach is the monoclonal anti-FGF23 antibody burosumab. Although promising, further studies are required to clarify its long-term efficacy, particularly in adults. Given the diversity of symptoms and complications, an interdisciplinary approach to management is of paramount importance. The focus of treatment should be not only on the physical manifestations and challenges associated with XLH and other FGF23-mediated hypophosphataemia syndromes, but also on the major psychological and social impact of the disease.

Health assessment of patients with achondroplasia, pseudoachondroplasia, and rickets based on 3D non-linear diagnostics

The goal of this study was to analyze diminishment of the functional status of the skeleton, parts of organs, regions of the brain, connective tissues, and chondrocytes in patients with achondroplasia (ACH), pseudoachondroplasia (PSACH), and rickets. Three-dimensional non-linear scanning (3D-NLS) was used to analyze the functional status of patients with genetic bone disorders, including 7 patients with ACH, 3 patients with PSACH, and 3 patients with rickets. Results indicated that the percentage of patients with long bones in the decompensatory phase did not differ depending on whether they had ACH, PSACH, or rickets. Joints in the decompensatory phase did not differ in patients with ACH except for the right hip (16.67%). Various joints were in the decompensatory phase (16.7-33.3%) in patients with rickets. The thoracic vertebrae, lumbar vertebrae, and liver were in the decompensatory phase in all 3 groups of patients. Connective tissues were in the decompensatory phase in 33.33% of patients with ACH. None of the patients with PSACH had chondrocytes in the decompensatory phase but 66.67% of patients with ACH or rickets did. Regions of the brain in the decompensatory phase were most prevalent in patients with rickets or ACH but not in patients with PSACH. In conclusion, diagnosis based on 3D-NLS was able to identify the functional status of genetic bone disorders. Some areas of decompensation were common to the 3 diseases studied but other areas were specific to a given disease.

Diagnosis, treatment-monitoring and follow-up of children and adolescents with X-linked hypophosphatemia (XLH)

Early diagnosis, optimal therapeutic management and regular follow up of children with X-linked hypophosphatemia (XLH) determine their long term outcomes and future quality of life. Biochemical screening of potentially affected newborns in familial cases and improving physician's knowledge on clinical signs, symptoms and biochemical characteristics of XLH for de novo cases should lead to earlier diagnosis and treatment initiation. The follow-up of children with XLH includes clinical, biochemical and radiological monitoring of treatment (efficacy and complications) and screening for XLH-related dental, neurosurgical, rheumatological, cardiovascular, renal and ENT complications. In 2018, the European Union approved the use of burosumab, a humanized monoclonal anti-FGF23 antibody, as an alternative therapy to conventional therapy (active vitamin D analogues and phosphate supplements) in growing children with XLH and insufficiently controlled disease. Diagnostic criteria of XLH and the principles of disease management with conventional treatment or with burosumab are reviewed in this paper.

Clinical practice recommendations for the diagnosis and management of X-linked hypophosphataemia

X-linked hypophosphataemia (XLH) is the most common cause of inherited phosphate wasting and is associated with severe complications such as rickets, lower limb deformities, pain, poor mineralization of the teeth and disproportionate short stature in children as well as hyperparathyroidism, osteomalacia, enthesopathies, osteoarthritis and pseudofractures in adults. The characteristics and severity of XLH vary between patients. Because of its rarity, the diagnosis and specific treatment of XLH are frequently delayed, which has a detrimental effect on patient outcomes. In this Evidence-Based Guideline, we recommend that the diagnosis of XLH is based on signs of rickets and/or osteomalacia in association with hypophosphataemia and renal phosphate wasting in the absence of vitamin D or calcium deficiency. Whenever possible, the diagnosis should be confirmed by molecular genetic analysis or measurement of levels of fibroblast growth factor 23 (FGF23) before treatment. Owing to the multisystemic nature of the disease, patients should be seen regularly by multidisciplinary teams organized by a metabolic bone disease expert. In this article, we summarize the current evidence and provide recommendations on features of the disease, including new treatment modalities, to improve knowledge and provide guidance for diagnosis and multidisciplinary care.

Hypocalcaemic and hypophosphatemic rickets

Rickets refers to deficient mineralization at the growth plate and is usually associated with abnormal serum calcium and/or phosphate. There are several subtypes of rickets, including hypophosphatemic rickets (vitamin-D-resistant rickets secondary to renal phosphate wasting), vitamin D-dependent rickets (defects of vitamin D metabolism) and nutritional rickets (caused by dietary deficiency of vitamin D, and/or calcium, and/or phosphate). Most rickets manifest as bone deformities, bone pain, and impaired growth velocity. Diagnosis of rickets is established through the medical history, physical examination, biochemical tests and radiographs. It is of crucial importance to determine the cause of rickets, including the molecular characterization in case of vitamin D resistant rickets, and initiate rapidly the appropriate therapy. In this review, we describe the different causes and therapies of genetic and nutritional rickets, supported by the recent progress in genetics and development of novel molecules such as anti-FGF23 antibody.

X-linked vitamin D-resistant rickets: 12 years of follow-up

Rickets are abnormalities of mineralization that can lead to bone fractures and deformities. Vitamin-resistant rickets is defined as any rickets not prevented by regular, early and prolonged administration of vitamin D and not cured by a sufficient total dose. The aim of our work is to describe the clinical, paraclinical and therapeutic aspects of X-linked hypophosphatemic rickets (XLHR), which is the most common cause of hereditary rickets and on the other hand to highlight the interest not only of the early care but also the regular long-term monitoring of these children.

Therapeutic management of hypophosphatemic rickets from infancy to adulthood

In children, hypophosphatemic rickets (HR) is revealed by delayed walking, waddling gait, leg bowing, enlarged cartilages, bone pain, craniostenosis, spontaneous dental abscesses, and growth failure. If undiagnosed during childhood, patients with hypophosphatemia present with bone and/or joint pain, fractures, mineralization defects such as osteomalacia, entesopathy, severe dental anomalies, hearing loss, and fatigue. Healing rickets is the initial endpoint of treatment in children. Therapy aims at counteracting consequences of FGF23 excess, i.e. oral phosphorus supplementation with multiple daily intakes to compensate for renal phosphate wasting and active vitamin D analogs (alfacalcidol or calcitriol) to counter the 1,25-diOH-vitamin D deficiency. Corrective surgeries for residual leg bowing at the end of growth are occasionally performed. In absence of consensus regarding indications of the treatment in adults, it is generally accepted that medical treatment should be reinitiated (or maintained) in symptomatic patients to reduce pain, which may be due to bone microfractures and/or osteomalacia. In addition to the conventional treatment, optimal care of symptomatic patients requires pharmacological and non-pharmacological management of pain and joint stiffness, through appropriated rehabilitation. Much attention should be given to the dental and periodontal manifestations of HR. Besides vitamin D analogs and phosphate supplements that improve tooth mineralization, rigorous oral hygiene, active endodontic treatment of root abscesses and preventive protection of teeth surfaces are recommended. Current outcomes of this therapy are still not optimal, and therapies targeting the pathophysiology of the disease, i.e. FGF23 excess, are desirable. In this review, medical, dental, surgical, and contributions of various expertises to the treatment of HR are described, with an effort to highlight the importance of coordinated care.

Approach to the hypophosphatemic patient

Hypophosphatemia is commonly missed due to nonspecific signs and symptoms, but it causes considerable morbidity and in some cases contributes to mortality. Three primary mechanisms of hypophosphatemia exist: increased renal excretion, decreased intestinal absorption, and shifts from the extracellular to intracellular compartments. Renal hypophosphatemia can be further divided into fibroblast growth factor 23-mediated or non-fibroblast growth factor 23-mediated causes. Proper diagnosis requires a thorough medication history, family history, physical examination, and assessment of renal tubular phosphate handling to identify the cause. During the past decade, our understanding of phosphate metabolism has grown greatly through the study of rare disorders of phosphate homeostasis. Treatment of hypophosphatemia depends on the underlying disorder and requires close biochemical monitoring. This article illustrates an approach to the hypophosphatemic patient and discusses normal phosphate metabolism.

Vitamin D receptor genotype in hypophosphatemic rickets as a predictor of growth and response to treatment

CONTEXT

Treatment of X-linked hypophosphatemic rickets improves bone mineralization and bone deformities, but its effect on skeletal growth is highly variable.

OBJECTIVE

Genetic variants in the promoter region of the vitamin D receptor (VDR) gene may explain the response to treatment because this receptor mediates vitamin D action.

DESIGN

We studied the VDR promoter haplotype structure in a large cohort of 91 patients with hypophosphatemic rickets including 62 patients receiving 1alpha-hydroxyvitamin D3 derivatives and phosphates from early childhood on.

RESULTS

Treatment improved bone deformities and final height, but 39% of treated patients still had short stature at the end of growth (-2 sd score or below). Height was closely associated with VDR promoter Hap1 genotype. Hap1(-) patients (35% of the cohort) had severe growth defects. This disadvantageous association of Hap1(-) status with height was visible before treatment, under treatment, and on to adulthood. Gender and age at initiation of treatment could not account for the Hap1 effect. No association with growth was found with a polymorphism of the PTH receptor gene otherwise found to be associated with adult height. Compared with Hap1(+) patients, those who were Hap1(-) had a higher urinary calcium response to 1alpha-hydroxyvitamin D3 and had significantly lower circulating FGF23 levels (C-terminal assay), taking into account their phosphate and 1alpha-hydroxyvitamin D3 intakes.

CONCLUSIONS

The present work identifies the VDR promoter genotype as a key predictor of growth under treatment with 1alpha-hydroxyvitamin D3 derivatives in patients with hypophosphatemic rickets, including those with established PHEX alterations. The VDR promoter genotype appears to provide valuable information for adjusting treatment and for deciding upon the utility of early GH therapy.

Dentin structure in familial hypophosphatemic rickets: benefits of vitamin D and phosphate treatment

OBJECTIVE

To evaluate the outcome of 1-(OH) vitamin D and oral phosphate treatment on dentin structure in patients with familial hypophosphatemic rickets, and expression of SIBLINGs (a family of non-collagenous proteins involved in dentinogenesis) and osteocalcin.

PATIENTS AND METHODS

Seven patients with familial hypophosphatemic rickets (age 3-16 years) were studied before or during treatment. Deciduous and permanent teeth were prepared for scanning electron microscopy (SEM) analysis and immunohistochemistry.

RESULTS

Untreated or inadequately treated patients had necrotic teeth with impaired dentin mineralization including unmerged calcospherites and accumulation of non-collagenous proteins in wide interglobular spaces. Most of the primary incisors analyzed displayed fissures linking enamel subsurface to pulp horn. These elements may explain the bacterial penetration and dental abscesses despite the absence of carious lesions. Well-treated patients had healthy teeth with good dentin mineralization and little evidence of calcospherites.

CONCLUSION

Treatment of hypophosphatemic children with 1-(OH) vitamin D and oral phosphate insures good dentin development and mineralization, and prevents clinical anomalies such as the dental necrosis classically associated with the disease. Starting treatment during early childhood and good adherence to the therapy are mandatory to observe these beneficial effects.

Comparison of growth in primary Fanconi syndrome and proximal renal tubular acidosis

To compare the difference between primary proximal renal tubular acidosis (PRTA) and Fanconi syndrome (FS), and to find out possible risk factors for growth retardation, we studied the long-term growth, clinical, laboratory, and radiological findings associated with the treatment of six children with primary FS and 15 children with PRTA. The ages of the children with FS were much older than those with PRTA at initial diagnosis (7.03+/-3.82 vs. 1.63+/-1.56 years). The height standard deviation score (SDS) at the start of treatment was significantly lower in FS than in PRTA. Catch-up growth was noted in PRTA at the end of follow-up (initial height SDS -2.13+/-1.10 vs. last height SDS -1.33+/-1.43, P=0.023 by paired t-test), whereas apparent linear growth impairment was found in FS in terms of overall growth velocity index (82.70+/-8.37%) and height SDS (initial -3.25+/-0.95 vs. last -3.15+/-0.31, P=0.791). There was also a higher rate of rickets occurrence in FS (3/6 vs. 0/15 in PRTA). Hypophosphatemia during the follow-up period was more frequent for FS than PRTA (69.2+/-26.1% vs. 7.0+/-25.8%, P<0.001), whereas metabolic acidosis (blood HCO(3)<20 mmol/l) was less efficiently corrected in PRTA (49.1+/-20.5% vs. 25.2+/-21.6% in FS, P=0.028). Moreover, the height Delta SDS correlated well with the mean serum P level during the treatment period in these patients (R=0.528, P=0.014 for all children; R=0.917, P=0.01 for FS patients). Our data suggest that metabolic acidosis may not be the sole factor causing growth impairment in FS. Correction of metabolic acidosis may indeed improve growth in PRTA but not in FS. This study indicates that factors other than metabolic acidosis, such as phosphate depletion and delayed diagnosis/treatment, should be considered to be important causes of growth retardation in FS.

Anthropometric characteristics of X-linked hypophosphatemia

An anthropometric study was undertaken to assess head proportions of patients with X-linked hypophosphatemia (XLH). Fourteen morphometric parameters of the head were measured and 10 cephalic indices calculated in 82 affected persons (57 females and 25 males) from 55 unrelated families with XLH, and compared with the results obtained in the group of their healthy relatives (37 females and 33 males), as well as with general population control values. Normalized values (SD, z-score) were analyzed statistically. The group of healthy relatives, both males and females, differed significantly from Polish population control values in most of the normalized variables measured, making population control values useless as a control group for the analyzed XLH group. Intrafamilial values of cephalic parameters in healthy relatives of the XLH patients were finally applied for statistical analysis. Generally patients with XLH showed highly statistically significant increase in head length (males 0.95 +/- 1.07 vs. -0.37 +/- 1.02, females 0.57 +/- 1.59 vs. -0.06 +/- 1.15), significant decrease in occipital breadth (males -0.56 +/- 1.27 vs. 0.70 +/- 1.28, females -0.59 +/- 1.7 vs. 0.13 +/- 1.1) and several milder anomalies of craniofacial proportions. Mean cephalic index was significantly lower in XLH patients when compared with the healthy relatives (males -0.909 vs. 0.278 P < 0.0001, females -0.705 vs. 0.381 P = 0.007). The cephalic changes were found both in XLH children and XLH adults and were more pronounced in affected males than in females. There were no differences between offspring born by hypophosphatemic and normophosphatemic mothers.

Renal phosphate wasting disorders: clinical features and pathogenesis

Rickets and osteomalacia are associated with hypophosphatemia in several disease states, including X-linked hypophosphatemic rickets, autosomal-dominant hypophosphatemic rickets, and tumor-induced osteomalacia. Recent advances in the understanding of these diseases include discovery of mutations in the genes encoding human phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and fibroblast growth factor 23 (FGF-23) and the finding of overproduction of FGF-23 and other proteins including matrix extracellular phosphoglycoprotein (MEPE) and frizzled-related protein 4 (FRP-4) in tumor-induced osteomalacia. Research is ongoing to better define how these proteins relate to each other and to the sodium-phosphate cotransporter in both normal and abnormal phosphate metabolism. New and improved therapies for disorders of phosphate metabolism, osteomalacia, and rickets will develop as our knowledge of phosphate metabolism grows.

Early treatment improves growth and biochemical and radiographic outcome in X-linked hypophosphatemic rickets

X-Linked hypophosphatemic rickets (XLH) is characterized by hypophosphatemia, rickets, and impaired growth. Despite oral phosphate and 1,25-dihydroxyvitamin D(3) treatment, many patients have suboptimal growth and bone healing. The aim of this study was to assess whether age at treatment onset impacts the outcome. Growth data, biochemistry, and radiographs of 19 well-controlled patients with XLH were analyzed retrospectively. Patients were divided into two groups based on the age at treatment onset (group 1, <1.0 yr; group 2, >or=1.0 yr). The median height z-score was higher in group 1 (n = 8) than in group 2 (n = 11) at treatment onset [-0.4 SD score (SDS) vs. -1.7 SDS; P = 0.001], at the end of the first treatment year (-0.7 SDS vs. -1.8 SDS; P = 0.009), throughout childhood (P > 0.05) and until predicted adult height (-0.2 SDS vs. -1.2 SDS; P = 0.06). The degree of hypophosphatemia was similar in both groups, but serum alkaline phosphatase remained higher in group 2 throughout childhood. Radiographic signs of rickets were more marked in group 2, but even patients with early treatment developed significant skeletal changes of rickets. These data suggest that treatment commenced in early infancy results in improved outcome in patients with XLH, but does not completely normalize skeletal development.

Dental abnormalities in patients with familial hypophosphatemic vitamin D-resistant rickets: prevention by early treatment with 1-hydroxyvitamin D

OBJECTIVE

To evaluate the dental effects of 1-hydroxylated vitamin D3 treatment in patients with familial hypophosphatemic vitamin D-resistant rickets. Study design Forty-eight children and adult patients were included in the study; 16 had received no treatment or phosphate supplements with vitamin D/25-(OH) D3 before puberty. The 32 younger ones had received phosphate supplements with 1alpha-(OH)D3 from infancy. All patients were clinically examined, and panoramic and periapical radiographs were made. Evaluations of decayed, missing, or filled teeth and decayed or filled teeth indexes and of pulp ratios allowed comparison with healthy age-matched control patients.

RESULTS

Poor dental health and characteristic dental anomalies were found in the 16 older patients. In contrast, the 32 younger patients had a normal dental status as regards reference ranges in healthy age-matched populations, although they still showed prominent pulp horns on deciduous teeth and increased pulp area/tooth area ratios.

CONCLUSIONS

This investigation shows the beneficial effects of 1alpha-(OH)D3 treatment on the dental status of vitamin D-resistant rickets patients and emphasizes the necessity of early treatment. Remaining defects may result from early exposure of odontoblasts and surrounding osteoblasts to hypophosphatemia, before the commencement of treatment, and/or from intrinsic cell disturbances linked to the genetic alteration(s).

Effect of growth hormone treatment on final height, phosphate metabolism, and bone mineral density in children with X-linked hypophosphatemic rickets

OBJECTIVE

To evaluate the effect of growth hormone treatment on final height, phosphate metabolism, bone markers, and bone mineral density in children with X-linked hypophosphatemic rickets.

STUDY DESIGN

Six patients (aged 7.8 +/- 1.8 years; height z score, -3.4 +/- 0.5) received conventional treatment (1,25-dihydroxyvitamin D(3) plus phosphate salts) combined with growth hormone (0.6-0.9 IU/kg per week, subcutaneously) (group A); 6 patients (aged 7.9 +/- 2.5 years; height z score, -2.1 +/- 0.6, P <.01 with respect to group A) received only conventional treatment (group B).

RESULTS

Final height z score significantly improved in group A (-2.4 +/- 0.5, P <.03 with respect to the value at entry), whereas it did not change in group B (-2.8 +/- 0.5, P = NS). At final height, degree of body disproportion was similar between the groups (group A, 1.3 +/- 0.2; group B, 1.2 +/- 0.1; P = NS). Phosphate retention, bone markers, and radial bone mineral density increased only in group A. No adverse effects were observed.

CONCLUSIONS

In poorly growing patients with X-linked hypophosphatemic rickets, growth hormone therapy combined with conventional treatment improves final height, phosphate retention, and radial bone mineral density, but it does not influence degree of body disproportion.

[Growth hormone treatment of familial hypophosphatemic rickets]

X-linked hypophosphatemic rickets (XLHR) is frequently associated with growth retardation and short adult stature, even with an appropriate conventional treatment associating phosphate and calcitriol or 1 alpha-hydroxyvitamin D. Its pathogenesis is unclear; growth hormone (GH) secretion is usually normal. Six children with XLHR and growth retardation were treated with GH during 6 years. In addition, they received the conventional treatment. At the beginning of the treatment mean age was 7.8 +/- 1.8 years, and height mean Z score was -3.4 +/- 0.5. A control group was composed of six children with XLHR (age: 7.9 +/- 2.5 years) receiving the conventional treatment only. Under GH treatment statural growth was improved, with significant increase in Z score and predicted adult height; the height gain was significantly higher in the GH treated group as compared with the group receiving the conventional treatment only. In addition, radial bone mineral density increased significantly under GH treatment. GH treatment thus appears to be a useful treatment to improve statural growth in children with XLHR.

New perspectives on the biology and treatment of X-linked hypophosphatemic rickets

This article updates the practicing pediatrician's knowledge of the hypophophatemic disorders that may occur in children. The classic X-linked disorder is emphasized. Details of clinical manifestations, the wide spectrum of disease severity, and complications of the disorder in adults are reviewed. Recent research, new genetic findings, and speculations regarding pathophysiology are discussed. A strategy for approaching medical treatment of X-linked hypophosphatemic rickets is provided, together with complications of treatment and treatment after cessation of growth.

Long-term growth hormone treatment in children with renal hypophosphatemic rickets: effects on growth, mineral metabolism, and bone density

OBJECTIVE

To evaluate the effects of treatment with recombinant human growth hormone (rhGH) on growth, mineral metabolism, and bone density in children with renal hypophosphatemic rickets (RHR).

DESIGN

Long-term rhGH treatment combined with conventional therapy with 1,25-dihydroxyvitamin D3 plus inorganic phosphate salts.

SETTING

Endocrine unit, department of pediatrics, university hospital.

SUBJECTS

Twelve patients (5 boys; age range 4.6 to 12.5 years, median 7.0 years) were subdivided into two groups of six patients on the basis of the median of height z score (-2.41) and the median bone age/statural age (BA/SA) ratio (1.23). Group A included patients with a severe degree of short stature (height z score -3.4 +/- 0.5) (mean +/- SD) and altered BA/SA ratio (1.26 +/- 0.08); group B included patients with a lesser degree of short stature (height z score -2.1 +/- 0.6, p < 0.001 vs group A) and more normal BA/SA ratio (1.04 +/- 0.15, p < 0.01 vs group A).

INTERVENTION

Group A received rhGH treatment (0.6 IU/kg per week subcutaneously) combined with conventional therapy; group B received conventional therapy alone.

MEASUREMENTS

Height, growth velocity, predicted adult height, serum values of calcium, phosphate, bone alkaline phosphatase isoenzyme, osteocalcin, propeptides of type I and type III procollagen, intact parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and urinary calcium/urinary creatinine ratio and tubular maximum for phosphate reabsorption normalized to the glomerular filtration rate (TmP/GFR), as well as radial bone density, were measured at baseline and for 3 years.

RESULTS

Height z score, growth velocity z score, predicted adult height, serum values of phosphate, bone alkaline phosphatase isoenzyme, osteocalcin, propeptides of type I and type III procollagen, intact parathyroid hormone 1,25-dihydroxyvitamin D, and TmP/GFR, as well as radial bone density, improved significantly only in group A. Serum calcium and 25-hydroxyvitamin D, and urinary calcium/urinary creatinine ratio did not change in either group.

CONCLUSIONS

Long-term rhGH administration may benefit growth, phosphate retention, and bone density in patients with RHR, without evidence of side effects.

Autonomous hyperparathyroidism in X-linked hypophosphataemia

Four patients with familial hypophosphataemic rickets developed significant hypercalcaemia which persisted after discontinuation of vitamin D therapy. They had increased PTH levels and were operated for hyperparathyroidism at the ages of 18, 20, 24 and 45 years, respectively. Three of the patients had previously received phosphate treatment and one patient developed hyperparathyroidism 7 years after treatment with calcitriol. Histological evaluation revealed different degrees of parathyroid hyperplasia in all patients, with persistently increased PTH and/or calcium levels after surgery. The possibility of autonomous hyperparathyroidism should be evaluated in the follow-up of patients with X-linked hypophosphataemic rickets.

Growth hormone secretion in poorly growing children with renal hypophosphataemic rickets

We evaluated growth hormone (GH) secretion and baseline serum free insulin-like growth factor-I (IGF-I) levels in 12 poorly growing patients (5 males and 7 females; age 1.6-12.5 years, median 6.4) with renal hypophosphataemic rickets treated with 1,25-dihydroxy-vitamin D3 plus inorganic oral phosphate salts. Eleven healthy normally growing children (6 males and 5 females; age 3.1-10.8 years, median 6.6) were studied as control group. All patients had a normal GH response (GH peak > or = 10 micrograms/l) to at least one provocative pharmacological stimulus (levodopa or insulin tolerance test), as well as all the controls. Mean growth hormone concentrations (MGHC), mean pulse amplitude, number of GH peaks above 5 micrograms/l, and IGF-I values overlapped between patients and controls, even though four patients had MGHC below the lower limit of MGHC of controls. In these patients, however, height-SDS, serum calcium, phosphate, alkaline phosphatase, intact parathyroid hormone, 1,25-dihydroxyvitamin D concentrations and maximum tubular phosphate reabsorption/glomerular filtration rate ratio did not differ in respect to the patients who showed MGHC in the range of controls (n = 6). MGHC IGF-I and biochemical parameters of phospho-calcium metabolism did not differ when the patients were subdivided in two groups on the basis of the median (-2.4) of height-SDS. No relationship was found between MGHC or IGF-I and height-SDS or growth velocity-SDS. Height-SDS and years of treatment or age at which therapy was started were not related.(ABSTRACT TRUNCATED AT 250 WORDS)

X-Linked hypophosphatemic rickets: a disease often unknown to affected patients

X-Linked hypophosphatemic rickets (XLH) is an X-linked dominant disorder that is secondary to renal phosphate wasting. Affected individuals frequently present the following characteristics: short stature, lower-extremity deformity, bone pain, dental abscesses, enthesopathy, rickets, and osteomalacia. Since the disorder is characterized by evident phenotypic abnormalities, we hypothesized that there would be a high degree of knowledge about the disease in affected kindreds. Thus, we constructed a six-page, self-administered questionnaire to determine whether family members are, in fact, aware of their disease and properly diagnosed and treated. We also designed the survey to determine rates of symptoms thought to be associated with rickets/osteomalacia in a population with a lower referral bias than is usually seen in tertiary care centers. We administered the questionnaire to 234 study subjects (57 affected) who were members of one of three large kindreds. Although 62% of affected individuals knew they had some problem with their bones, only 22.6% were told by a physician that they had rickets or osteomalacia. This apparent lack of awareness occurred in spite of 61.1% of affected subjects complaining of bone or joint problems to their personal physician. Indeed, of those patients who had persistent complaints, only 34.5% were told they had rickets or osteomalacia. Only one patient was taking phosphate and vitamin D.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutics of X-linked hypophosphatemic rickets

X-linked hypophosphatemia, the most common form of familial rickets, is conventionally treated with 1,25-dihydroxyvitamin D3 (5-50 ng/kg per day) plus phosphate supplementation (70-100 mg/kg per day). However, nephrocalcinosis is noted in many children treated with this therapy. Whether to treat or not and whether such treatment should be continued into adulthood or in pregnancy are unsettled questions. This article reviews these controversies and provides current recommendations.

Growth in children with X-linked hypophosphataemic rickets

Currently, X-linked hypophosphataemic rickets (XLHR) is most commonly treated with a combination of phosphate and vitamin D, but there is conflicting evidence about the effects of this treatment on linear growth. In all, 25 patients with XLHR (current age range, 4.1-22.1 years; median, 8.2 years) were studied to determine whether there was any improvement in height SDS during treatment. The duration of therapy was 2.9-15.0 years (median, 5.7 years). Measurements before the age of 2 years or after the onset of puberty were excluded to remove the effects of measurement difficulties in small infants and of variation in pubertal timing. The growth of these patients was compared with a similar group of untreated historical controls. Patients treated with calcitriol and phosphate for at least 2 years before the onset of puberty (n = 22) had a significantly better mean height SDS than the historical controls (-1.23 compared with -2.05 for the historical controls; p = 0.02). Among patients treated with calcitriol and phosphate for at least 2 years (n = 21), the change in height SDS had a positive correlation with the duration of therapy (r = 0.51; p = 0.02). The growth of children with XLHR treated with combination therapy was thus significantly better than that of historical controls.

The pattern of growth and growth retardation of patients with hypophosphataemic vitamin D-resistant rickets: a longitudinal study

Growth in height of 16 patients (5 boys and 11 girls) with hypophosphataemic rickets (HR) was studied in a longitudinal survey. The data shortly before and during puberty were analysed on the basis of Preece Baines curves, fitted to the original data; for the analysis at the age of 5 years, the original data were used. It appeared that the overall shape of the individual and average growth pattern could be adequately described by the Preece Baines method. The results further showed that from the age of 5 years onwards, average height was approximately two standard deviations below the normal mean for Dutch children. The patients showed a normal pubertal growth spurt which was, in general, insufficient to restore the growth retardation already established before adolescence. The four children who did show catch-up growth between the age of 5 years and adulthood had minimal rachitic lesions. The greater impact of the disease on growth in early childhood than on adolescent growth could be explained by the fact that HR mainly affects the growth of the legs, the major contributor to body size in early childhood. Finally, it was found that the difference between bone age, as determined by the Tanner Whitehouse (TW2)-method, and chronological age was not significant and the adult height in all patients except two could be adequately predicted from bone age and height.

X-linked hypophosphatemic rickets: a study (with literature review) of linear growth response to calcitriol and phosphate therapy

Not all children with X-linked hypophosphatemia (XLH) have demonstrated improved linear growth with calcitriol [1,25-(OH)2D3] and inorganic phosphate (Pi) therapy. To assess which factors are associated with a favorable growth response during this treatment, we retrospectively compared demographics and biochemical parameters of bone metabolism to the linear growth patterns of 20 children with XLH who were prepubertal and had not required osteotomy. A total of 15 patients had family histories consistent with XLH; 5 appeared to be sporadic cases. During 3 years of therapy, the growth velocities of 12 patients had been at or above the mean for age (good growers) and those of 8 patients had been below the mean (poor growers). Data from the two groups were contrasted. We found no difference between the good growers and poor growers before or after the 3 year period of therapy in mean age, dietary calcium, calcitriol dose or compliance, or Pi dose or compliance. Both groups increased their mean fasting serum Pi levels with treatment. The TmP/GFR (mean +/- SEM) of the good growers improved with therapy (1.9 +/- 0.2 to 2.6 +/- 0.2 mg/dl, p = 0.01), and their posttreatment value was higher compared to that of the poor growers (2.6 +/- 0.1 versus 2.2 +/- 0.1 mg/dl, p = 0.02). However, their enhanced TmP/GFR was not associated with a reduction in serum iPTH levels (before, 693 +/- 50; after, 688 +/- 76 pg/ml; p = 0.9). The Z test for binomial proportions showed that the group that grew well contained a disproportionate number of girls (10 of 12, p = 0.04). Our findings suggest that calcitriol may exert a direct effect on the renal tubule to improve Pi reclamation in XLH. The observation that heterozygous girls appear to respond better than hemizygous boys to calcitriol and Pi therapy provides evidence for a gene dosage effect in the expression of this X-linked dominant disorder.

Effects of therapy in X-linked hypophosphatemic rickets

BACKGROUND

Patients with X-linked hypophosphatemic rickets, which is clinically manifested by growth failure and bowing of the legs, are usually treated with phosphate and a vitamin D preparation. However, the efficacy of this treatment has been disputed, and nephrocalcinosis is a recognized complication of therapy.

METHODS

We studied 24 patients with X-linked hypophosphatemic rickets (9 boys and 15 girls) ranging in age from 1 to 16 years (median, 5.3). The duration of combination therapy ranged from 0.3 to 11.8 years (median, 3.0). We measured height as a standard-deviation (SD) score (the number of SDs from the mean height for chronologic age). Measurements made before the age of two years or after the onset of puberty were excluded. We compared the results with those reported in 1971 for 16 untreated prepubertal Australian patients. We also determined the severity of nephrocalcinosis (on a scale of 0 to 4, with 0 indicating no abnormalities and 4 stone formation) with renal ultrasonography and whether it could be related to the dosage of phosphate or vitamin D or to other factors.

RESULTS

Patients treated for at least two years before the onset of puberty (n = 19) had a mean height SD score of -1.08, as compared with -2.05 in the untreated historical controls. The 13 patients who had been treated with calcitriol and phosphate for at least two years had an increase in the mean height SD score of 0.33, from -1.58 to -1.25 (95 percent confidence interval, 0 to 0.67; P = 0.05). Nineteen of the 24 patients (79 percent) had nephrocalcinosis detected on renal ultrasonography. The grade of nephrocalcinosis was significantly correlated with the mean phosphate dose (r = 0.60, P = 0.002), but not with the dose of vitamin D or the duration of therapy. All patients had normal serum creatinine concentrations.

CONCLUSIONS

Therapy with calcitriol and phosphate may increase the growth of children with X-linked hypophosphatemic rickets. Nephrocalcinosis in these children represents a complication of therapy and is associated with the dose of phosphate received.

Acute effects of calcitriol and phosphate salts on mineral metabolism in children with hypophosphatemic rickets

We investigated the acute effects of oral administration of 1,25-dihydroxyvitamin D (1,25-(OH)2D) and phosphate on the major mineral metabolism indexes in six children with vitamin D-resistant rickets treated with a long-term regimen of phosphate and calcitriol. Two acute tests were performed in which plasma calcium, phosphate, immunoreactive parathyroid hormone (iPTH) (intact molecule), 25-hydroxyvitamin D (25-OHD), and 1,25-(OH)2D levels were measured: the first after an oral phosphate load (20 mg/kg) was administered after calcitriol had been discontinued for 10 days, and the second after a calcitriol load (0.03 microgram/kg) plus the same phosphate load but with the children receiving the usual combination treatment. There were no significant differences in basal levels of calcium, phosphate, iPTH, 25-OHD, or 1,25-(OH)2D between the two tests, nor were delta percent calcium and 25-OHD values significantly different. The delta percent plasma phosphate concentration at 60 minutes was significantly higher during test 2 than during test 1 (p less than 0.01) and delta percent iPTH concentration at 60 minutes was significantly higher during test 1 than during test 2 (p less than 0.01). In test 2 the iPTH level returned to baseline at 180 minutes. Higher delta percent 1,25-(OH)2D values at 60 minutes were observed in test 2 than in test 1 (p less than 0.01). Furthermore, the delta percent 1,25-(OH)2D levels were still higher at 180 minutes in test 2 than during test 1 (p less than 0.01). Our study indicates that oral calcitriol has an inhibitory effect on iPTH secretion in the hours immediately after oral phosphate administration in children with vitamin D-resistant rickets.